Patent Publication Number: US-2013229953-A1

Title: Apparatus and method for indicating synchronization signals in a wireless network

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
     The present application is related to U.S. Provisional Patent Application No. 61/524,144, filed Aug. 16, 2011, entitled “SYNCHRONIZATION SIGNALS FOR WIRELESS COMMUNICATION SYSTEMS”, U.S. Provisional Patent Application No. 61/565,874, filed Dec. 1, 2011, entitled “SYNCHRONIZATION SIGNALS FOR WIRELESS COMMUNICATION SYSTEMS”, U.S. Provisional Patent Application No. 61/600,414, filed Feb. 17, 2012, entitled “SYNCHRONIZATION SIGNALS FOR WIRELESS COMMUNICATION SYSTEMS” and U.S. Provisional Patent Application No. 61/646,084, filed May 11, 2012, entitled SYNCHRONIZATION SIGNALS FOR WIRELESS COMMUNICATION SYSTEMS″. Provisional Patent Application Nos. 61/524,144, 61/565,874, 61/600,414 and 61/646,084 are assigned to the assignee of the present application and is hereby incorporated by reference into the present application as if fully set forth herein. The present application hereby claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Nos. 61/524,144, 61/565,874, 61/600,414 and 61/646,084. 
    
    
     TECHNICAL FIELD 
     The present application relates generally to wireless communications and, more specifically, to a system and method for indicating primary and secondary synchronization signals in a wireless communications system. 
     BACKGROUND 
     In 3GPP Long Term Evolution (LTE) and Long Term Evolution-Advanced (LTE-A) systems, there are two downlink synchronization signals which are used by the UE to obtain the cell identity and frame timing: Primary synchronization signal and Secondary synchronization signal. The mapping of the sequence to resource elements depends on the frame structure. There are 504 unique physical-layer cell identities. The physical-layer cell identities are grouped into 168 unique physical-layer cell-identity groups, each group containing three unique identities. The grouping is such that each physical-layer cell identity is part of one and only one physical-layer cell-identity group. A physical-layer cell identity N ID   cell =3N ID   (1) +N ID   (2)  is thus uniquely defined by a number N ID   (1)  in the range of 0 to 167, representing the physical-layer cell-identity group, and a number N ID   (2)  in the range of 0 to 2, representing the physical-layer identity within the physical-layer cell-identity group. The sequence d(n) used for the primary synchronization signal is generated from a frequency-domain Zadoff-Chu sequence. The sequence d(0) . . . , d(61) used for the second synchronization signal is an interleaved concatenation of two length-31 binary sequences. The concatenated sequence is scrambled with a scrambling sequence given by the primary synchronization signal. 
     SUMMARY 
     A base station configured to communicate with a plurality of base stations via a backhaul link and configured to communicate with a plurality of subscriber stations is provided. The base station includes a transmit path configured to transmit data, reference signals, synchronization signals and control elements to at least one of the plurality of subscriber stations. The base station also includes processing circuitry configured to map primary synchronization signals (PSS) and secondary synchronization signals (SSS) onto each of a carrier of a first carrier type and a carrier of a second carrier type. The PSS and SSS (PSS/SSS) on the second carrier type are mapped onto different time locations than in the first carrier type. In addition, the PSS/SSS are mapped onto consecutive resource elements (REs) on each of the carrier of the first type and the carrier of the second type, wherein subcarrier indices k for the REs are represented by the following: 
     
       
         
           
             
               k 
               = 
               
                 n 
                 - 
                 31 
                 + 
                 
                   
                     
                       N 
                       RB 
                       DL 
                     
                      
                     
                       N 
                       sc 
                       RB 
                     
                   
                   2 
                 
               
             
             , 
             
               n 
               = 
               0 
             
             , 
             … 
              
             
                 
             
             , 
             61 
           
         
       
     
     where N RB   DL  represents a total number of physical resource blocks (PRBs) in a respective carrier, and N sc   RB  is a number of subcarriers per PRB. 
     A method for mapping synchronization signals is provided. The method includes transmitting data, reference signals, synchronization signals and control elements to at least one of the plurality of subscriber stations. The method also includes mapping primary synchronization signals (PSS) and secondary synchronization signals (SSS) onto each of a carrier of a first carrier type and a carrier of a second carrier type. The PSS and SSS (PSS/SSS) on the second carrier type are mapped onto different time locations than in the first carrier type. In addition, the PSS/SSS are mapped onto consecutive resource elements (REs) on each of the carrier of the first type and the carrier of the second type, wherein subcarrier indices k for the REs are represented by the following: 
     
       
         
           
             
               k 
               = 
               
                 n 
                 - 
                 31 
                 + 
                 
                   
                     
                       N 
                       RB 
                       DL 
                     
                      
                     
                       N 
                       sc 
                       RB 
                     
                   
                   2 
                 
               
             
             , 
             
               n 
               = 
               0 
             
             , 
             … 
              
             
                 
             
             , 
             61 
           
         
       
     
     where N RB   DL  represents a total number of physical resource blocks (PRBs) in a respective carrier, and N sc   RB  is a number of subcarriers per PRB. 
     A subscriber station configured to communicate with at least one base station, which is configured to communicate with a plurality of base stations via a backhaul link, is provided. The subscriber station includes receiver configured to receive data, reference signals, synchronization signals and control elements from the base station. The subscriber station also includes processing circuitry configured to read primary synchronization signals (PSS) and secondary synchronization signals (SSS) mapped onto each of a carrier of a first carrier type and a carrier of a second carrier type. The PSS and SSS (PSS/SSS) on the second carrier type are mapped onto different time locations than in the first carrier type. In addition, the PSS/SSS are mapped onto consecutive resource elements (REs) on each of the carrier of the first type and the carrier of the second type, wherein subcarrier indices k for the REs are represented by the following: 
     
       
         
           
             
               k 
               = 
               
                 n 
                 - 
                 31 
                 + 
                 
                   
                     
                       N 
                       RB 
                       DL 
                     
                      
                     
                       N 
                       sc 
                       RB 
                     
                   
                   2 
                 
               
             
             , 
             
               n 
               = 
               0 
             
             , 
             … 
              
             
                 
             
             , 
             61 
           
         
       
     
     where N RB   DL  represents a total number of physical resource blocks (PRBs) in a respective carrier, and N sc   RB  is a number of subcarriers per PRB. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  illustrates a wireless network according to an embodiment of the present disclosure; 
         FIG. 2A  illustrates a high-level diagram of a wireless transmit path according to an embodiment of this disclosure; 
         FIG. 2B  illustrates a high-level diagram of a wireless receive path according to an embodiment of this disclosure; 
         FIG. 3  illustrates a subscriber station according to an exemplary embodiment of the disclosure; 
         FIG. 4  illustrates a Cell Range Expansion (CRE) region according to embodiments of the present disclosure; 
         FIG. 5  illustrates a synchronization operation in carrier aggregation according to embodiments of the present disclosure; 
         FIG. 6  illustrates placement and configuration of new sync signals according to embodiments of the present disclosure; 
         FIG. 7  illustrates a process for radio resource control signalling according to embodiments of the present disclosure; 
         FIG. 8  illustrates RRC signaling of the new sync channel resources in measurement in measurement configuration message according to embodiments of the present disclosure; 
         FIGS. 9A through 9F  illustrate synchronization signal mapping according to embodiments of the present disclosure; 
         FIGS. 10A and 10B  illustrate synchronization signal mapping according to embodiments of the present disclosure; 
         FIGS. 11A through 11D  illustrate synchronization signal mapping according to embodiments of the present disclosure; 
         FIG. 12  illustrates new PSS/SSS mapping alternatives according to embodiments of the present disclosure; 
         FIG. 13  illustrates placement of new sync signals according to embodiments of the present disclosure; 
         FIG. 14  illustrates a Coordinated Multipoint (CoMP) with Remote Radio Head having the same cell ID as the macro cell according to embodiments of the present disclosure; and 
         FIG. 15  illustrates a process for mapping synchronization according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 15 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communication system. 
     The following documents and standards descriptions are hereby incorporated into the present disclosure as if fully set forth herein: (i) 3GPP Technical Specification No. 36.211, version 10.1.0, “E-UTRA, Physical Channels and Modulation” (hereinafter “REF1”); (ii) 3GPP Technical Specification No. 36.212, version 10.1.0, “E-UTRA, Multiplexing and Channel Coding” (hereinafter “REF2”); (iii) 3GPP Technical Specification No. 36.213, version 10.1.0, “E-UTRA, Physical Layer Procedures” (hereinafter “REF3”); and (iv) 3GPP Technical Specification No. 36.300, version 10.4.0 (hereinafter “REF4”). 
       FIG. 1  illustrates a wireless network  100  according to one embodiment of the present disclosure. The embodiment of wireless network  100  illustrated in  FIG. 1  is for illustration only. Other embodiments of wireless network  100  could be used without departing from the scope of this disclosure. 
     The wireless network  100  includes eNodeB (eNB)  101 , eNB  102 , and eNB  103 . The eNB  101  communicates with eNB  102  and eNB  103 . The eNB  101  also communicates with Internet protocol (IP) network  130 , such as the Internet, a proprietary IP network, or other data network. 
     Depending on the network type, other well-known terms may be used instead of “eNodeB,” such as “base station” or “access point”. For the sake of convenience, the term “eNodeB” shall be used herein to refer to the network infrastructure components that provide wireless access to remote terminals. In addition, the term user equipment (UE) is used herein to refer to remote terminals that can be used by a consumer to access services via the wireless communications network. Other well know terms for the remote terminals include “mobile stations” and “subscriber stations.” 
     The eNB  102  provides wireless broadband access to network  130  to a first plurality of user equipments (UEs) within coverage area  120  of eNB  102 . The first plurality of UEs includes UE  111 , which may be located in a small business; UE  112 , which may be located in an enterprise; UE  113 , which may be located in a WiFi hotspot; UE  114 , which may be located in a first residence; UE  115 , which may be located in a second residence; and UE  116 , which may be a mobile device, such as a cell phone, a wireless laptop, a wireless PDA, or the like. UEs  111 - 116  may be any wireless communication device, such as, but not limited to, a mobile phone, mobile PDA and any mobile station (MS). 
     For the sake of convenience, the term “user equipment” or “UE” is used herein to designate any remote wireless equipment that wirelessly accesses an eNB, whether the UE is a mobile device (e.g., cell phone) or is normally considered a stationary device (e.g., desktop personal computer, vending machine, etc.). In other systems, other well-known terms may be used instead of “user equipment”, such as “mobile station” (MS), “subscriber station” (SS), “remote terminal” (RT), “wireless terminal” (WT), and the like. 
     The eNB  103  provides wireless broadband access to a second plurality of UEs within coverage area  125  of eNB  103 . The second plurality of UEs includes UE  115  and UE  116 . In some embodiment, eNBs  101 - 103  may communicate with each other and with UEs  111 - 116  using LTE or LTE-A techniques. 
     Dotted lines show the approximate extents of coverage areas  120  and  125 , which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with base stations, for example, coverage areas  120  and  125 , may have other shapes, including irregular shapes, depending upon the configuration of the base stations and variations in the radio environment associated with natural and man-made obstructions. 
     Although  FIG. 1  depicts one example of a wireless network  100 , various changes may be made to  FIG. 1 . For example, another type of data network, such as a wired network, may be substituted for wireless network  100 . In a wired network, network terminals may replace eNBs  101 - 103  and UEs  111 - 116 . Wired connections may replace the wireless connections depicted in  FIG. 1 . 
       FIG. 2A  is a high-level diagram of a wireless transmit path.  FIG. 2B  is a high-level diagram of a wireless receive path. In  FIGS. 2A and 2B , the transmit path  200  may be implemented, e.g., in eNB  102  and the receive path  250  may be implemented, e.g., in a UE, such as UE  116  of  FIG. 1 . It will be understood, however, that the receive path  250  could be implemented in an eNB (e.g. eNB  102  of  FIG. 1 ) and the transmit path  200  could be implemented in a UE. 
     Transmit path  200  comprises channel coding and modulation block  205 , serial-to-parallel (S-to-P) block  210 , Size N Inverse Fast Fourier Transform (IFFT) block  215 , parallel-to-serial (P-to-S) block  220 , add cyclic prefix block  225 , up-converter (UC)  230 . Receive path  250  comprises down-converter (DC)  255 , remove cyclic prefix block  260 , serial-to-parallel (S-to-P) block  265 , Size N Fast Fourier Transform (FFT) block  270 , parallel-to-serial (P-to-S) block  275 , channel decoding and demodulation block  280 . 
     At least some of the components in  FIGS. 2A and 2B  may be implemented in software while other components may be implemented by configurable hardware (e.g., a processor) or a mixture of software and configurable hardware. In particular, it is noted that the FFT blocks and the IFFT blocks described in this disclosure document may be implemented as configurable software algorithms, where the value of Size N may be modified according to the implementation. 
     Furthermore, although this disclosure is directed to an embodiment that implements the Fast Fourier Transform and the Inverse Fast Fourier Transform, this is by way of illustration only and should not be construed to limit the scope of the disclosure. It will be appreciated that in an alternate embodiment of the disclosure, the Fast Fourier Transform functions and the Inverse Fast Fourier Transform functions may easily be replaced by Discrete Fourier Transform (DFT) functions and Inverse Discrete Fourier Transform (IDFT) functions, respectively. It will be appreciated that for DFT and IDFT functions, the value of the N variable may be any integer number (i.e., 1, 2, 3, 4, etc.), while for FFT and IFFT functions, the value of the N variable may be any integer number that is a power of two (i.e., 1, 2, 4, 8, 16, etc.). 
     In transmit path  200 , channel coding and modulation block  205  receives a set of information bits, applies coding (e.g., LDPC coding) and modulates (e.g., Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM)) the input bits to produce a sequence of frequency-domain modulation symbols. Serial-to-parallel block  210  converts (i.e., de-multiplexes) the serial modulated symbols to parallel data to produce N parallel symbol streams where N is the IFFT/FFT size used in eNB  102  and UE  116 . Size N IFFT block  215  then performs an IFFT operation on the N parallel symbol streams to produce time-domain output signals. Parallel-to-serial block  220  converts (i.e., multiplexes) the parallel time-domain output symbols from Size N IFFT block  215  to produce a serial time-domain signal. Add cyclic prefix block  225  then inserts a cyclic prefix to the time-domain signal. Finally, up-converter  230  modulates (i.e., up-converts) the output of add cyclic prefix block  225  to RF frequency for transmission via a wireless channel. The signal may also be filtered at baseband before conversion to RF frequency. 
     The transmitted RF signal arrives at UE  116  after passing through the wireless channel and reverse operations to those at eNB  102  are performed. Down-converter  255  down-converts the received signal to baseband frequency and remove cyclic prefix block  260  removes the cyclic prefix to produce the serial time-domain baseband signal. Serial-to-parallel block  265  converts the time-domain baseband signal to parallel time domain signals. Size N FFT block  270  then performs an FFT algorithm to produce N parallel frequency-domain signals. Parallel-to-serial block  275  converts the parallel frequency-domain signals to a sequence of modulated data symbols. Channel decoding and demodulation block  280  demodulates and then decodes the modulated symbols to recover the original input data stream. 
     Each of eNBs  101 - 103  may implement a transmit path that is analogous to transmitting in the downlink to UEs  111 - 116  and may implement a receive path that is analogous to receiving in the uplink from UEs  111 - 116 . Similarly, each one of UEs  111 - 116  may implement a transmit path corresponding to the architecture for transmitting in the uplink to eNBs  101 - 103  and may implement a receive path corresponding to the architecture for receiving in the downlink from eNBs  101 - 103 . 
       FIG. 3  illustrates a subscriber station according to embodiments of the present disclosure. The embodiment of subscriber station (UE  116 ) illustrated in  FIG. 3  is for illustration only. Other embodiments of the wireless subscriber station could be used without departing from the scope of this disclosure. 
     UE  116  comprises antenna  305 , radio frequency (RF) transceiver  310 , transmit (TX) processing circuitry  315 , microphone  320 , and receive (RX) processing circuitry  325 . SS  116  also comprises speaker  330 , main processor  340 , input/output (I/O) interface (IF)  345 , keypad  350 , display  355 , and memory  360 . Memory  360  further comprises basic operating system (OS) program  361  and a plurality of applications  362 . The plurality of applications can include one or more of resource mapping tables (Tables 1-10 described in further detail herein below). 
     Radio frequency (RF) transceiver  310  receives from antenna  305  an incoming RF signal transmitted by a base station of wireless network  100 . Radio frequency (RF) transceiver  310  down-converts the incoming RF signal to produce an intermediate frequency (IF) or a baseband signal. The IF or baseband signal is sent to receiver (RX) processing circuitry  325  that produces a processed baseband signal by filtering, decoding, and/or digitizing the baseband or IF signal. Receiver (RX) processing circuitry  325  transmits the processed baseband signal to speaker  330  (i.e., voice data) or to main processor  340  for further processing (e.g., web browsing). 
     Transmitter (TX) processing circuitry  315  receives analog or digital voice data from microphone  320  or other outgoing baseband data (e.g., web data, e-mail, interactive video game data) from main processor  340 . Transmitter (TX) processing circuitry  315  encodes, multiplexes, and/or digitizes the outgoing baseband data to produce a processed baseband or IF signal. Radio frequency (RF) transceiver  310  receives the outgoing processed baseband or IF signal from transmitter (TX) processing circuitry  315 . Radio frequency (RF) transceiver  310  up-converts the baseband or IF signal to a radio frequency (RF) signal that is transmitted via antenna  305 . 
     In certain embodiments, main processor  340  is a microprocessor or microcontroller. Memory  360  is coupled to main processor  340 . According to some embodiments of the present disclosure, part of memory  360  comprises a random access memory (RAM) and another part of memory  360  comprises a Flash memory, which acts as a read-only memory (ROM). 
     Main processor  340  executes basic operating system (OS) program  361  stored in memory  360  in order to control the overall operation of wireless subscriber station  116 . In one such operation, main processor  340  controls the reception of forward channel signals and the transmission of reverse channel signals by radio frequency (RF) transceiver  310 , receiver (RX) processing circuitry  325 , and transmitter (TX) processing circuitry  315 , in accordance with well-known principles. 
     Main processor  340  is capable of executing other processes and programs resident in memory  360 , such as operations for CoMP communications and determining sync signals. Main processor  340  can move data into or out of memory  360 , as required by an executing process. In some embodiments, the main processor  340  is configured to execute a plurality of applications  362 , such as applications for CoMP communications and MU-MIMO communications. The main processor  340  can operate the plurality of applications  362  based on OS program  361  or in response to a signal received from BS  102 . Main processor  340  is also coupled to I/O interface  345 . I/O interface  345  provides subscriber station  116  with the ability to connect to other devices such as laptop computers and handheld computers. I/O interface  345  is the communication path between these accessories and main controller  340 . 
     Main processor  340  is also coupled to keypad  350  and display unit  355 . The operator of subscriber station  116  uses keypad  350  to enter data into subscriber station  116 . Display  355  may be a liquid crystal display capable of rendering text and/or at least limited graphics from web sites. Alternate embodiments may use other types of displays. 
     In LTE and LTE-A systems, there are two downlink synchronization signals which are used by the UE to obtain the cell identity and frame timing: Primary synchronization signal (PSS) and Secondary synchronization signal (SSS). The sequence d(n) used for the primary synchronization signal is generated from a frequency-domain Zadoff-Chu sequence according to: 
     
       
         
           
             
               
                 
                   
                     
                       d 
                       u 
                     
                      
                     
                       ( 
                       n 
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                              
                             
                               
                                 - 
                                 j 
                               
                                
                               
                                   
                               
                                
                               
                                 
                                   π 
                                    
                                   
                                       
                                   
                                    
                                   un 
                                    
                                   
                                     ( 
                                     
                                       n 
                                       + 
                                       1 
                                     
                                     ) 
                                   
                                 
                                 63 
                               
                             
                           
                         
                         
                           
                             
                               n 
                               = 
                               0 
                             
                             , 
                             1 
                             , 
                             … 
                              
                             
                                 
                             
                             , 
                             30 
                           
                         
                       
                       
                         
                           
                              
                             
                               
                                 - 
                                 j 
                               
                                
                               
                                   
                               
                                
                               
                                 
                                   π 
                                    
                                   
                                       
                                   
                                    
                                   
                                     un 
                                      
                                     
                                       ( 
                                       
                                         n 
                                         + 
                                         2 
                                       
                                       ) 
                                     
                                   
                                 
                                 63 
                               
                             
                           
                         
                         
                           
                             
                               n 
                               = 
                               31 
                             
                             , 
                             31 
                             , 
                             
                               … 
                                
                               
                                   
                               
                                
                               61 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     where the Zadoff-Chu root sequence index u is given by Table 1. 
     
       
         
           
               
             
               
                 TABLE 6.11.1.1-1 
               
             
            
               
                   
               
               
                 Root indices for the primary synchronization signal. 
               
            
           
           
               
               
               
            
               
                   
                 N ID   (2)   
                 Root index u 
               
               
                   
                   
               
               
                   
                 0 
                 25 
               
               
                   
                 1 
                 29 
               
               
                   
                 2 
                 34 
               
               
                   
                   
               
            
           
         
       
     
     The mapping of the sequence to resource elements depends on the frame structure. The UE shall not assume that the primary synchronization signal is transmitted on the same antenna port as any of the downlink reference signals. The UE shall not assume that any transmission instance of the primary synchronization signal is transmitted on the same antenna port, or ports, used for any other transmission instance of the primary synchronization signal. 
     The sequence d(n) shall be mapped to the resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           j 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           n 
                           ) 
                         
                       
                     
                     , 
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     k 
                     = 
                     
                       n 
                       - 
                       31 
                       + 
                       
                         
                           
                             N 
                             RB 
                             DL 
                           
                            
                           
                             N 
                             sc 
                             RB 
                           
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     For frame structure type 1, the primary synchronization signal is mapped to the last OFDM symbol in slots 0 and 10. 
     For frame structure type 2, the primary synchronization signal is mapped to the third OFDM symbol in subframes 1 and 6. Resource elements (k,l) in the OFDM symbols used for transmission of the primary synchronization signal where 
     
       
         
           
             k 
             = 
             
               n 
               - 
               31 
               + 
               
                 
                   
                     N 
                     RB 
                     DL 
                   
                    
                   
                     N 
                     sc 
                     RB 
                   
                 
                 2 
               
             
           
         
       
       
         
           
             
               n 
               = 
               
                 - 
                 5 
               
             
             , 
             
               - 
               5 
             
             , 
             
               … 
               - 
               1 
             
             , 
             62 
             , 
             63 
             , 
             
               … 
                
               
                   
               
                
               66 
             
           
         
       
     
     are reserved and not used for transmission of the primary synchronization signal. 
     The sequence d(0) . . . , d(61) used for the second synchronization signal is an interleaved concatenation of two length-31 binary sequences. The concatenated sequence is scrambled with a scrambling sequence given by the primary synchronization signal. 
     The combination of two length-31 sequences defining the secondary synchronization signal differs between subframe 0 and subframe 5 according to: 
     
       
         
           
             
               
                 
                   
                     d 
                      
                     
                       ( 
                       
                         2 
                          
                         n 
                       
                       ) 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 
                                   
                                     s 
                                     0 
                                     
                                       m 
                                       0 
                                     
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                                  
                                 
                                   
                                     c 
                                     0 
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 in 
                                  
                                 
                                     
                                 
                                  
                                 subframe 
                                  
                                 
                                     
                                 
                                  
                                 0 
                               
                             
                           
                           
                             
                               
                                 
                                   
                                     s 
                                     1 
                                     
                                       m 
                                       1 
                                     
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                                  
                                 
                                   
                                     c 
                                     0 
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 in 
                                  
                                 
                                     
                                 
                                  
                                 subframe 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                             
                           
                         
                          
                         
                           
 
                         
                          
                         
                           
                             d 
                             u 
                           
                            
                           
                             ( 
                             n 
                             ) 
                           
                         
                       
                       = 
                       
                         { 
                         
                           
                             
                               
                                 
                                   
                                     s 
                                     1 
                                     
                                       m 
                                       1 
                                     
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                                  
                                 
                                   
                                     c 
                                     1 
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                                  
                                 
                                   
                                     z 
                                     1 
                                     
                                       ( 
                                       
                                         m 
                                         0 
                                       
                                       ) 
                                     
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 in 
                                  
                                 
                                     
                                 
                                  
                                 subframe 
                                  
                                 
                                     
                                 
                                  
                                 0 
                               
                             
                           
                           
                             
                               
                                 
                                   
                                     s 
                                     0 
                                     
                                       m 
                                       0 
                                     
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                                  
                                 
                                   
                                     c 
                                     1 
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                                  
                                 
                                   
                                     z 
                                     1 
                                     
                                       ( 
                                       
                                         m 
                                         1 
                                       
                                       ) 
                                     
                                   
                                    
                                   
                                     ( 
                                     n 
                                     ) 
                                   
                                 
                               
                             
                             
                               
                                 in 
                                  
                                 
                                     
                                 
                                  
                                 subframe 
                                  
                                 
                                     
                                 
                                  
                                 5 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     where 0≦n≦30. The indices m 0  and m 1  are derived from the physical-layer cell-identity group N ID   (1)  according to: 
     
       
         
           
             
               
                 
                   
                     
                       m 
                       0 
                     
                     = 
                     
                       
                         m 
                         ′ 
                       
                        
                       mod 
                        
                       
                           
                       
                        
                       31 
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       m 
                       1 
                     
                     = 
                     
                       
                         ( 
                         
                           
                             m 
                             0 
                           
                           + 
                           
                             ⌊ 
                             
                               
                                 m 
                                 ′ 
                               
                               / 
                               31 
                             
                             ⌋ 
                           
                           + 
                           1 
                         
                         ) 
                       
                        
                       mod 
                        
                       
                           
                       
                        
                       31 
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         m 
                         ′ 
                       
                       = 
                       
                         
                           N 
                           ID 
                           
                             ( 
                             1 
                             ) 
                           
                         
                         + 
                         
                           
                             q 
                              
                             
                               ( 
                               
                                 q 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                           / 
                           2 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       q 
                       = 
                       
                         ⌊ 
                         
                           
                             
                               N 
                               ID 
                               
                                 ( 
                                 1 
                                 ) 
                               
                             
                             + 
                             
                               
                                 
                                   q 
                                   ′ 
                                 
                                  
                                 
                                   ( 
                                   
                                     
                                       q 
                                       ′ 
                                     
                                     + 
                                     1 
                                   
                                   ) 
                                 
                               
                               / 
                               2 
                             
                           
                           30 
                         
                         ⌋ 
                       
                     
                     , 
                     
                       
                         q 
                         ′ 
                       
                       = 
                       
                         ⌊ 
                         
                           
                             N 
                             ID 
                             
                               ( 
                               1 
                               ) 
                             
                           
                           / 
                           30 
                         
                         ⌋ 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     where the output of the above expression is listed in Table 2. 
     The two sequences s 0   (m     0     ) (n) and s 1   (m     1     ) (n) are defined as two different cyclic shifts of the m-sequence {tilde over (s)}(n) according to: 
         s   0   (m     0     ) ( n )= {tilde over (s)} (( n+m   0 )mod 31) 
         s   1   (m     1     ) ( n )= {tilde over (s)} (( n+m   1 )mod 31)[Eqn. 5] 
     where {tilde over (s)}(i)=1−2x(i), 0≦i≦30, is defined by: 
         x (    i   +5)=( x (    i   +2)+ x (    i   ))mod 2, 0≦    i   ≦25  [Eqn. 6]
 
     with initial conditions x(0)=0, x(1)=0, x(2)=0, x(3)=0, x(4)=1. 
     The two scrambling sequences c 0 (n) and c 1 (n) depend on the primary synchronization signal and are defined by two different cyclic shifts of the m-sequence {tilde over (c)}(n) according to: 
         c   0 ( n )= {tilde over (c)} (( n+N   ID   (2) )mod 31) 
         c   1 ( n )= {tilde over (c)} (( n+N   ID   (2) +3)mod 31)  [Eqn. 7]
 
     where N ID   (2) ε{0,1,2} is the physical-layer identity within the physical-layer cell identity group N ID   (1)  and {tilde over (c)}(1)=1−2x(i), 0≦i≦30, is defined by: 
         x ( ī+ 5)=( x ( ī+ 3)+ x ( ī ))mod 2, 0 ≦ī≦ 25  [Eqn. 8]
 
     with initial conditions x(0)=0, x(1)=0, x(2)=0, x(3)=0, x(4)=1. 
     The scrambling sequences z 1   (m     0     ) (n) and z 1   (m     1     ) (n) are defined by a cyclic shift of the m-sequence {tilde over (z)}(n) according to: 
         z   1   (m     0     ) ( n )= {tilde over (z)} (( n +( m   0  mod 8))mod 31)  [Eqn. 9]
 
         z   1   (m     1     ) ( n )= {tilde over (z)} (( n +( m   1  mod 8))mod 31)  [Eqn. 10]
 
     where m 0  and m 1  are obtained from Table 2 and {tilde over (z)}(i)=1−2x(i), 0≦i≦30, is defined by: 
         x ( ī+ 5)=( x ( ī +4)+ x ( ī+ 2)+ x ( ī+ 1)+ x ( ī ))mod 2, 0≦ī≦25  [Eqn. 11]
 
     with initial conditions x(0)=0, x(1)=0, x(2)=0, x(3)=0, x(4)=1. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Mapping between physical-layer cell-identity 
               
               
                 group N ID   (1)  and the indices m 0  and m 1 . 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 N ID   (1)   
                 m 0   
                 m 1   
                 N ID   (1)   
                 m 0   
                 m 1   
                 N ID   (1)   
                 m 0   
                 m 1   
                 N ID   (1)   
                 m 0   
                 m 1   
                 N ID   (1)   
                 m 0   
                 m 1   
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 0 
                 1 
                 34 
                 4 
                 6 
                 68 
                 9 
                 12 
                 102 
                 15 
                 19 
                 136 
                 22 
                 27 
               
               
                 1 
                 1 
                 2 
                 35 
                 5 
                 7 
                 69 
                 10 
                 13 
                 103 
                 16 
                 20 
                 137 
                 23 
                 28 
               
               
                 2 
                 2 
                 3 
                 36 
                 6 
                 8 
                 70 
                 11 
                 14 
                 104 
                 17 
                 21 
                 138 
                 24 
                 29 
               
               
                 3 
                 3 
                 4 
                 37 
                 7 
                 9 
                 71 
                 12 
                 15 
                 105 
                 18 
                 22 
                 139 
                 25 
                 30 
               
               
                 4 
                 4 
                 5 
                 38 
                 8 
                 10 
                 72 
                 13 
                 16 
                 106 
                 19 
                 23 
                 140 
                 0 
                 6 
               
               
                 5 
                 5 
                 6 
                 39 
                 9 
                 11 
                 73 
                 14 
                 17 
                 107 
                 20 
                 24 
                 141 
                 1 
                 7 
               
               
                 6 
                 6 
                 7 
                 40 
                 10 
                 12 
                 74 
                 15 
                 18 
                 108 
                 21 
                 25 
                 142 
                 2 
                 8 
               
               
                 7 
                 7 
                 8 
                 41 
                 11 
                 13 
                 75 
                 16 
                 19 
                 109 
                 22 
                 26 
                 143 
                 3 
                 9 
               
               
                 8 
                 8 
                 9 
                 42 
                 12 
                 14 
                 76 
                 17 
                 20 
                 110 
                 23 
                 27 
                 144 
                 4 
                 10 
               
               
                 9 
                 9 
                 10 
                 43 
                 13 
                 15 
                 77 
                 18 
                 21 
                 111 
                 24 
                 28 
                 145 
                 5 
                 11 
               
               
                 10 
                 10 
                 11 
                 44 
                 14 
                 16 
                 78 
                 19 
                 22 
                 112 
                 25 
                 29 
                 146 
                 6 
                 12 
               
               
                 11 
                 11 
                 12 
                 45 
                 15 
                 17 
                 79 
                 20 
                 23 
                 113 
                 26 
                 30 
                 147 
                 7 
                 13 
               
               
                 12 
                 12 
                 13 
                 46 
                 16 
                 18 
                 80 
                 21 
                 24 
                 114 
                 0 
                 5 
                 148 
                 8 
                 14 
               
               
                 13 
                 13 
                 14 
                 47 
                 17 
                 19 
                 81 
                 22 
                 25 
                 115 
                 1 
                 6 
                 149 
                 9 
                 15 
               
               
                 14 
                 14 
                 15 
                 48 
                 18 
                 20 
                 82 
                 23 
                 26 
                 116 
                 2 
                 7 
                 150 
                 10 
                 16 
               
               
                 15 
                 15 
                 16 
                 49 
                 19 
                 21 
                 83 
                 24 
                 27 
                 117 
                 3 
                 8 
                 151 
                 11 
                 17 
               
               
                 16 
                 16 
                 17 
                 50 
                 20 
                 22 
                 84 
                 25 
                 28 
                 118 
                 4 
                 9 
                 152 
                 12 
                 18 
               
               
                 17 
                 17 
                 18 
                 51 
                 21 
                 23 
                 85 
                 26 
                 29 
                 119 
                 5 
                 10 
                 153 
                 13 
                 19 
               
               
                 18 
                 18 
                 19 
                 52 
                 22 
                 24 
                 86 
                 27 
                 30 
                 120 
                 6 
                 11 
                 154  
                 14 
                 20 
               
               
                 19 
                 19 
                 20 
                 53 
                 23 
                 25 
                 87 
                 0 
                 4 
                 121 
                 7 
                 12 
                 155 
                 15 
                 21 
               
               
                 20 
                 20 
                 21 
                 54 
                 24 
                 26 
                 88 
                 1 
                 5 
                 122 
                 8 
                 13 
                 156 
                 16 
                 22 
               
               
                 21 
                 21 
                 22 
                 55 
                 25 
                 27 
                 89 
                 2 
                 6 
                 123 
                 9 
                 14 
                 157 
                 17 
                 23 
               
               
                 22 
                 22 
                 23 
                 56 
                 26 
                 28 
                 90 
                 3 
                 7 
                 124 
                 10 
                 15 
                 158 
                 18 
                 24 
               
               
                 23 
                 23 
                 24 
                 57 
                 27 
                 29 
                 91 
                 4 
                 8 
                 125 
                 11 
                 16 
                 159 
                 19 
                 25 
               
               
                 24 
                 24 
                 25 
                 58 
                 28 
                 30 
                 92 
                 5 
                 9 
                 126 
                 12 
                 17 
                 160 
                 20 
                 26 
               
               
                 25 
                 25 
                 26 
                 59 
                 0 
                 3 
                 93 
                 6 
                 10 
                 127 
                 13 
                 18 
                 161 
                 21 
                 27 
               
               
                 26 
                 26 
                 27 
                 60 
                 1 
                 4 
                 94 
                 7 
                 11 
                 128 
                 14 
                 19 
                 162 
                 22 
                 28 
               
               
                 27 
                 27 
                 28 
                 61 
                 2 
                 5 
                 95 
                 8 
                 12 
                 129 
                 15 
                 20 
                 163 
                 23 
                 29 
               
               
                 28 
                 28 
                 29 
                 62 
                 3 
                 6 
                 96 
                 9 
                 13 
                 130 
                 16 
                 21 
                 164 
                 24 
                 30 
               
               
                 29 
                 29 
                 30 
                 63 
                 4 
                 7 
                 97 
                 10 
                 14 
                 131 
                 17 
                 22 
                 165 
                 0 
                 7 
               
               
                 30 
                 0 
                 2 
                 64 
                 5 
                 8 
                 98 
                 11 
                 15 
                 132 
                 18 
                 23 
                 166 
                 1 
                 8 
               
               
                 31 
                 1 
                 3 
                 65 
                 6 
                 9 
                 99 
                 12 
                 16 
                 133 
                 19 
                 24 
                 167 
                 2 
                 9 
               
               
                 32 
                 2 
                 4 
                 66 
                 7 
                 10 
                 100 
                 13 
                 17 
                 134 
                 20 
                 25 
                 — 
                 — 
                 — 
               
               
                 33 
                 3 
                 5 
                 67 
                 8 
                 11 
                 101 
                 14 
                 18 
                 135 
                 21 
                 26 
                 — 
                 — 
                 — 
               
               
                   
               
            
           
         
       
     
     The mapping of the sequence to resource elements depends on the frame structure. In a sub-frame for frame structure type 1 and in a half-frame for frame structure type 2, the same antenna port as for the primary synchronization signal shall be used for the secondary synchronization signal. 
     The sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                       
                   
                    
                   
                     
                       
                         
                           
                             a 
                             
                               k 
                               , 
                               1 
                             
                           
                           = 
                           
                             d 
                              
                             
                               ( 
                               n 
                               ) 
                             
                           
                         
                         , 
                         
                           n 
                           = 
                           0 
                         
                         , 
                         … 
                          
                         
                             
                         
                         , 
                         61 
                       
                        
                       
                         
 
                       
                        
                       
                           
                       
                        
                       
                         k 
                         = 
                         
                           n 
                           - 
                           31 
                           + 
                           
                             
                               
                                 N 
                                 RB 
                                 DL 
                               
                                
                               
                                 N 
                                 sc 
                                 RB 
                               
                             
                             2 
                           
                         
                       
                     
                      
                     
                       
 
                     
                      
                     
                       l 
                       = 
                       
                         { 
                         
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 2 
                               
                             
                             
                               
                                 in 
                                  
                                 
                                     
                                 
                                  
                                 slots 
                                  
                                 
                                     
                                 
                                  
                                 0 
                                  
                                 
                                     
                                 
                                  
                                 and 
                                  
                                 
                                     
                                 
                                  
                                 10 
                               
                             
                             
                               
                                 for 
                                  
                                 
                                     
                                 
                                  
                                 frame 
                                  
                                 
                                     
                                 
                                  
                                 structure 
                                  
                                 
                                     
                                 
                                  
                                 type 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                             
                           
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 1 
                               
                             
                             
                               
                                 in 
                                  
                                 
                                     
                                 
                                  
                                 slots 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                  
                                 
                                     
                                 
                                  
                                 and 
                                  
                                 
                                     
                                 
                                  
                                 11 
                               
                             
                             
                               
                                 for 
                                  
                                 
                                     
                                 
                                  
                                 frame 
                                  
                                 
                                     
                                 
                                  
                                 structure 
                                  
                                 
                                     
                                 
                                  
                                 type 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     12 
                   
                   ] 
                 
               
             
           
         
       
     
     Resource elements (k,l) where: 
     are reserved and not used for transmission of the secondary synchronization signal. 
     The extension carrier is characterized by the following: 
     a) No PBCH/SIB/Paging; 
     b) No PSS/SSS; 
     c) No Rel.10 DL CCHs; 
     d) No CRS; 
     e) Associated with a Rel.10 carrier;
 
f) Measurements are performed on Rel.10 carriers;
 
g) Benefits including:
         a. The inefficiencies (large overhead and challenging performance) associated with transmissions of CCHs in small BWs can be avoided (by cross-scheduling an extension carrier with small BW);
           i. With Rel.10 cross-scheduling, 1 OFDM symbol still needs to be reserved for DL CCHs (7.1% unnecessary overhead when nothing is transmitted);   ii. For CA-based ICIC, CRS existence and/or interference can also be avoided for additional savings;   
           b. Desensitization issues when a DL frequency is close to an UL frequency can be avoided (reduced power, proper MCS selection, and Hybrid Automatic Repeat Request (HARQ) can be utilized for PDSCH near the band edge; this is inefficient or not possible to do for transmissions of DL CCHs which, due to interleaving, occupy substantially the entire BW);   c. Simple Coordinated Multipoint (CoMP) operation as PDCCH discrepancy among cells and CRS interference (if CRS does not exist) can be avoided;   d. Some small overhead reductions can be achieved due to the absence of transmissions for synchronization channels and broadcast control channels; and
 
h) Only possible for CA-capable UEs.
       

       FIG. 4  illustrates a Cell Range Expansion (CRE) region according to embodiments of the present disclosure. The CRE region  500  shown in  FIG. 4  is for illustration only. Other embodiments could be used without departing from the scope of this disclosure. 
     In one heterogeneous network deployment scenario, a number of pico base stations (“picos”, also referenced as remote radio heads (RRH))  405  are deployed within the coverage of a macro base station (“macro”)  410 . Cell-range expansion (CRE) is a well-known technique that lets the network offload some traffic from the macro  410  to one or more of the picos  405 , especially when the macro  410  is overloaded. When CRE  400  is implemented, one or more UEs receiving the strongest DL signal from the macro  410  are instructed to connect to a pico  405  and receive DL control/data signals from (and transmit UL signals to) the pico  405 . CRE is implemented for those UEs receiving the strongest signal from the macro  410 , while at the same time the difference of the received signal powers from the macro  410  and a pico  405  is within a max CRE bias. In certain embodiments, UEs falling in the CRE region  415  can be instructed to receive from the pico  405 , even though UE receives the strongest DL signals from the macro  410 . One well-known problem of CRE is that when the max CRE bias is too large, the UE instructed to receive DL signals from pico  405  cannot acquire a sync from pico  405 . This issue occurs as a result of the sync signals from the macro  410  and the pico  405  being transmitted in the same time-frequency resources. Therefore, the UE cannot obtain sync from pico  405  when the signal strength difference is too high, such as more than 6 dB  420 . 
       FIG. 5  illustrates a synchronization operation in carrier aggregation according to embodiments of the present disclosure. The embodiment of the synchronization operation shown in  FIG. 5  is for illustration only. Other embodiments could be used without departing from the scope of this disclosure. 
     In one carrier aggregation (CA) scenario (denoted by CA scenario 4 in REF4), a number of picos  405  are deployed within the coverage  505  of a macro  410 , in which the macro  410  transmits (and receives) signals from a carrier F 1  (or CC 1 ) and a pico  405  transmits (and receives) signals from F 2  (or CC 2 ). When CC 1  and CC 2  are backward compatible carriers, the UE is able to sync to respective carriers according to the legacy sync mechanism. Alternatively, when CC 1  is a backward compatible carrier but CC 2  is non-backward compatible carrier (e.g., extension carrier which does not transmit sync signals), the UE may not be able to obtain sync to CC 2 . 
     Embodiments of the present disclosure provide new designs of sync signals in order to resolve these example issues arising in the advanced wireless telecommunication systems. 
     In certain embodiments, new sync signals, as well as Rel-sync signals (Rel-8 PSS/SSS), are transmitted in a backward compatible component carrier (CC), i.e., a 3GPP E-UTRA (LTE) Rel-8 or Rel-9 or Rel-10 compatible carrier. The new sync signal helps CRE UEs to obtain sync to a pico  405  in the heterogeneous network illustrated in  FIG. 4 , for example. 
     In certain embodiments, new sync signals are transmitted in a non-backward compatible component carrier (CC), e.g., in an extension carrier or in a new carrier type (NCT). The new sync signal helps UEs to obtain sync to a pico  405  operating in CC 2  in carrier aggregation scenario 4 illustrated in  FIG. 5 , for example. 
       FIG. 6  illustrates placement and configuration of new sync signals according to embodiments of the present disclosure. The embodiment of the sync signals  600  shown in  FIG. 6  is for illustration only. Other embodiments could be used without departing from the scope of this disclosure. 
     In legacy wireless systems, such as LTE Rel-8, 9, 10, sync signals  605  are periodically transmitted in pre-assigned sub-frames  610  and frequency  615  resources. No configuration signals are conveyed to UEs for indicating the time-frequency resources assigned for the sync signals  605 . UEs purely rely on blind detection to detect a sync signal  605 . Although the periodic (and continuous) transmission of sync signal could be essential for supporting UEs&#39; initial access, because the UEs cannot obtain any configuration from the network  500  (or eNodeB  410 ) before the initial access, the periodic transmission may not be essential for UEs&#39; handover and sync acquisition of an extension carrier, in which case the UE is able to obtain configurations from the network  500 . Furthermore, the periodic sync transmission prevents the network  500  from flexibly consuming energy and utilizing time-frequency resources. Owing to these drawbacks of the periodic transmission, aperiodic transmission of sync signals configured by the network  500  (transmission of sync signals on demand basis) seem to be useful for better energy efficiency and flexible resource utilization. Furthermore, the aperiodic sync signal transmission is suitable even when the network  500  has only occasional access of a bandwidth (BW), of which scenario arises in cognitive access scenarios. With aperiodic sync signal transmission, the network  500  does not need to always transmit sync signals, and hence the network  500  can make sure that the network&#39;s sync signals do not interfere to another network. 
     In certain embodiments, the network  500  supports two component carriers (or two cells), a primary component carrier (PCC, or PCell) and a secondary component carrier (SCC, or SCell), of which the PCC is E-UTRA Rel-8 compatible, while the SCC is non-backward compatible, i.e., E-UTRA Rel-10 or below UEs cannot access the SCC. An example network is illustrated in  FIG. 5 . An advanced UE, such as UE  116 , performs initial access and connects to the PCC first. In certain embodiments, when connected to the PCC, the network  500  decides to configure the SCC to the advanced UE  116 , and configures to receive sync signals from the SCC in a designated time-frequency sync resources in the SCC by a Radio Resource Control (RRC) signaling. The RRC configuration may include at least one of the following information for the sync signal resources: 
     Slot numbers (ε{0, 1, . . . , 19} in a radio frame) and OFDM symbol numbers; 
     Bandwidth (e.g., in terms of PRBs); 
     Periodicity of sync signals (e.g., in terms of sub-frames or slots); and 
     Physical cell ID (PCI) of the SCC. In some cases, at least one of the following can be configured instead of PCI. 
     (a) PSS sequence number; 
     (b) SSS sequence number 
       FIG. 7  illustrates a process for radio resource control signalling according to embodiments of the present disclosure. The embodiment of the RRC signalling  700  shown in  FIG. 7  is for illustration only. Other embodiments could be used without departing from the scope of this disclosure. 
     In certain embodiments, a heterogeneous network is composed of a macro  410  and at least one pico  410 , such as illustrated in  FIG. 4 . UE  116  performs initial access and is initially connected to the macro  410 , according to E-UTRA Rel-8/9/10 initial access mechanism. That is, the macro  410  transmits a measurement configuration message  705 . UE  116  responds with a measurement report  710 . When the network (or eNodeB  410 ) desires to do CRE for UE  116  (in block  715 ), the network configures UE  116  to hand over from the macro  410  to a pico  405 . The macro  410  communicates the hand over request with the pico  405  in steps  720  and  725 . During the handover process, the macro  410  transmits an RRC signaling  730  to UE  116  informing the new sync signal resources of the pico  405 . For example, the RRC message about the new sync signal resources can be included in the RRC connection reconfiguration message including the mobility control information. Thereafter, UE  116  and the pico  405  complete the hand over procedure  740 . 
       FIG. 8  illustrates RRC signaling of the new sync channel resources in measurement in measurement configuration message according to embodiments of the present disclosure. The embodiment of the RRC signaling shown in  FIG. 8  is for illustrations only. Other embodiments could be used without departing from the scope of this disclosure. 
     In certain embodiments, the information about the designated time-frequency sync resources for the non-backward compatible carrier (can correspond to an SCell for carrier aggregation or a pico cell with CRE in a heterogeneous network) is signaled in measurement configuration message  805  (e.g., in broadcast message such as in SIB or in unicast message; e.g., in measObjectEUTRA REF4). That is, the new sync information is included in the measurement configuration for RRC connected mode. UE  116  synchronizes to the neighboring cell (e.g., pico  405  or another macro  410 ) using the new sync channel in block  810 . In block  815 , UE  116  performs measurements on the neighboring cell. Therefore, UE  116  responds with the measurement report  820 , which contains PCI detected from the new sync channel of the neighboring cells. 
       FIGS. 9A through 9F  illustrate synchronization signal mapping according to embodiments of the present disclosure. The embodiments of the synchronization mapping shown in  FIGS. 9A through 9F  are for illustration only. Other embodiments could be used without departing from the scope of the present disclosure. 
     In certain embodiments, the PSS and SSS (PSS/SSS) are mapped onto each of a carrier of a first type and a carrier of a second type, on different time locations. For example, the new synchronization signals (e.g., on carrier of a new carrier type) are transmitted in the same sub-frames as those for Rel-8 PSS/SSS, and are mapped to the same subcarriers as those of the Rel-8 PSS/SSS, but in different OFDM symbols from those of Rel-8 PSS/SSS, as illustrated in  FIG. 6 . In one example, the new sync signals include PSS and SSS, and a UE configured to read the new PSS/SSS obtains physical cell ID (PCID) from the new PSS/SSS. 
       FIGS. 9A through 9F  illustrate a few examples to map PSS/SSS  905  according to the method presented in the current embodiment. The PSS/SSS  905  includes a PSS  907  and a SSS  909 .  FIG. 9A  shows a PRB pair  900  without PSS/SSS  905 , where UE-specific RS (UE-RS)  910  RE locations and CRS port 0 (or timing RS (TRS))  915  RE locations are also indicated.  FIG. 9B  shows a PRB pair  900  that contains legacy PSS/SSS  902  according to the 3GPP LTE Rel-8/9/10 specifications. That is, the legacy PSS/SSS  902  are located in the fifth and sixth symbols. 
     In one method, the OFDM symbol numbers to map the new PSS/SSS  905  are adjacent, and some examples are: 
     Ex1) As in  FIG. 6 , the new PSS  907  and SSS  909  are located in the OFDM symbols l=N symb   DL −3 and l=N symb   DL −4 in the first slot, respectively; 
     Ex2) The new PSS  907  and SSS  909  are located in the OFDM symbols l=N symb   DL −4 and l=N symb   DL −5 in the first slot, respectively as shown in  FIG. 9C ; 
     Ex3) The new PSS  907  and SSS  909  are located in the OFDM symbols l=2 and l=1 in second slot, respectively ( FIG. 9D ); 
     Ex4) The new PSS  907  and SSS  909  are located in the OFDM symbols l=3 and l=2 in second slot, respectively. 
       FIGS. 10A and 10B  illustrate synchronization signal mapping according to embodiments of the present disclosure. The embodiments of the synchronization mapping shown in  FIGS. 10A and 10B  are for illustration only. Other embodiments could be used without departing from the scope of the present disclosure. 
     Ex5)  FIGS. 10A and 10B  show another example PSS/SSS mapping according to the present disclosure. It has additional benefit of having the same location for both normal and extended CPs. In this case, the new PSS  907  and SSS  909  are located in the OFDM symbols l=2 and l=1 in the first slot of sub-frame numbers 0 and 5, respectively, regardless of whether sub-frame type is normal-CP or extended-CP. This PSS/SSS mapping can be applied to both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) systems, in case a common mapping is desired for FDD and TDD system in the extension carrier. 
     When the new PSS/SSS  905  are mapped according to the any of the examples above, the benefits are: 
     No collision occurs between the legacy PSS/SSS  902  and the new PSS/SSS  905 ; 
     The new PSS/SSS  905  do not collide with UE-RS ports  7 - 14 , and hence the PRBs with the new PSS/SSS  905  can be used for PDSCH transmissions with UE-RS  910 , which has not been possible in Rel-10 LTE. 
     When the new PSS/SSS  905  are mapped according to Ex2, Ex3, Ex4 and Ex7, there is an additional benefit, i.e.,: the new PSS/SSS  905  do not collide with CRS ports  0   910 , regardless of extended CP or normal CP. Note that CRS port 0  910  can be used for timing synchronization in extension carriers, and hence no collision between CRS and PSS/SSS is desired. 
     In another method, the two OFDM symbols carrying the new PSS  907  and the new SSS  909  are not adjacent, which is different from the legacy mapping where two OFDM symbols carrying the legacy PSS and the legacy SSS are adjacent. Furthermore, the number of OFDM symbols between the new PSS  907  and the new SSS  909  is different from the number of OFDM symbols between the legacy TDD PSS and the legacy FDD SSS which is 3. This way, the new PSS/SSS  905  is not confused with neither TDD PSS/SSS nor FDD PSS/SSS. Some examples for the OFDM symbol numbers to map the new PSS/SSS according to this method are: 
     Ex5) The new PSS and SSS are located in the OFDM symbols l=1 in the second slot and l=1 in the first slot, respectively, as shown in  FIG. 9E  wherein a PRB  900  in which the new PSS  907  and SSS  909  are distributed; 
     Ex6) The new PSS and SSS are located in the OFDM symbols l=3 and l=1 in the first slot, respectively as shown in  FIG. 9F  wherein a PRB  900  in which the new PSS  907  and SSS  909  are distributed. 
       FIGS. 11A through 11D  illustrate synchronization signal mapping according to embodiments of the present disclosure. The embodiments of the synchronization mapping shown in  FIGS. 11A through 11D  are for illustration only. Other embodiments could be used without departing from the scope of the present disclosure. 
     In another method, the two OFDM symbols carrying the new PSS  907  and the new SSS  909  are spaced apart with the same number of OFDM symbols as the PSS and the SSS in the legacy (Rel-8) TDD system are spaced apart, while still ensuring that the new PSS/SSS  905  locations do not collide with the locations for Rel-10 UE-RS and Rel-8 CRS port 0  910 . 
     Ex8)  FIGS. 11A through 11D  show one example PSS/SSS mapping according to the current method. It has a benefit of having the same PSS-SSS OFDM symbol spacing for Rel-8 legacy TDD and the NCT, and the implementation of PSS/SSS  905  reception at UE  116  may be reused for the legacy carrier and the NCT. In this case, the new PSS  907  is located in the OFDM symbol l=N symb   DL −3 in the first slot of sub-frames 1 and 6; whereas the new SSS  909  is located in the OFDM symbol l=N symb   DL −6 in the first slot of sub-frames 1 and 6. The same mapping rule is applied regardless of whether sub-frame type is normal-CP or extended-CP. This PSS/SSS  905  mapping can be applied to TDD system in the extension carrier. Note that the DM RS mapping for the special sub-frame shown in  FIGS. 11A-11D  is for certain TDD UL-DL configurations; the PSS/SSS mapping disclosed here applies to the other TDD UL-DL configurations as well. 
     In certain embodiments, Ex 7 and Ex 8 are used for FDD and TDD PSS/SSS mapping for the NCT. The mapping of the PSS/SSS sequence to resource elements depends on the frame structure and the carrier type. 
     In the case of Primary Synchronization Signals: 
     For frame structure type 1 (FDD) configured for the legacy carrier type (implying Rel-8/9/10 compatible carrier), the primary synchronization signal shall be mapped to the last OFDM symbol in slots 0 and 10. 
     For frame structure type 1 (FDD) configured for the new carrier type, the primary synchronization signal shall be mapped to OFDM symbol number l=2 in slots 0 and 10. 
     For frame structure type 2 (TDD) configured for the legacy carrier type (implying Rel-8/9/10 compatible carrier), the primary synchronization signal shall be mapped to the third OFDM symbol in sub-frames 1 and 6. That is, for time division duplex (TDD), and for frame structure type 2, the PSS is mapped to a third OFDM symbol in sub-frames 1 and 6. 
     For frame structure type 2 (TDD) configured for the new carrier type, the primary synchronization signal shall be mapped to OFDM symbol number l=N symb   DL −3 in slots 2 and 12. 
     In the case of Secondary Synchronization Signals: 
     In a sub-frame for frame structure type 1 and in a half-frame for frame structure type 2, the same antenna port as for the primary synchronization signal shall be used for the secondary synchronization signal. 
     For the legacy carrier type, the sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                       
                   
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     are reserved and not used for transmission of the secondary synchronization signal. 
     For the new carrier type, the sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                       
                   
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     are reserved and not used for transmission of the secondary synchronization signal. 
     In certain embodiments, the new sync signals are placed in the same sub-frames and in the same frequency (or subcarrier or PRB) resources as the legacy sync signals to accommodate legacy UEs. Placing the new sync signals in the same sub-frames and in the same frequency (or subcarrier or PRB) resources as the legacy sync signals for the legacy UEs can be a better choice than placing them in any other places. If the new sync signals were placed in other places than those proposed in this embodiment, more scheduling restriction is imposed on the legacy UEs. This is because the legacy UEs do not know the existence of the new sync signals, and legacy UEs are not likely scheduled in those resources with new sync signals for fear of reliability (or throughput) impacts. Furthermore, in certain embodiments, placing the new sync signals in the same BW as the legacy sync signals is beneficial since the advanced UE  116  is allowed to rely on the legacy mechanism to determine the center of the bandwidth. 
     Alternatively, when the new PSS  907  and/or SSS  909  are transmitted according to this embodiment, the new PSS/SSS  905  is distinguishable from the legacy PSS/SSS. Otherwise, a legacy UE may be able to read the new PSS/SSS  905  as well, and the legacy UE may get confused not knowing which sync signals to obtain sync. 
     To resolve this issue, we consider the following alternatives illustrated in  FIG. 12 .  FIG. 12  illustrates new PSS/SSS mapping alternatives according to embodiments of the present disclosure. The embodiment of the PSS/SSS mapping alternatives shown in  FIG. 12  is for illustration only. Other embodiments could be used without departing from the scope of this disclosure. 
     In certain embodiments, the sequences for new PSS  907  and new SSS  909  are generated as a function of the sequences used for the legacy PSS and the legacy SSS. 
     The function should make sure that the legacy sync signals and the new sync signals are sufficiently distinguishable so that legacy UEs are not confused with the newly defined sync signals. At the same time, by reusing the legacy sequences, the new UEs will not have much burden to implement new sequences for the new PSS/SSS  905 . 
     Some alternative methods for the generation and mapping of the new PSS  907  and the SSS  909  according to this embodiment are listed below and illustrated in  FIG. 12 . Note that the below alternatives are described according to the new PSS/SSS  905  mapping option of the OFDM symbols l=N symb   DL −3 and l=N symb   DL −4 in the first slot for ease of description. The description of the below alternatives can be easily modified by replacing the OFDM symbols numbers of the new PSS/SSS  905  when the new PSS/SSS mapping option is any two OFDM symbol numbers, some of which is illustrated in  FIGS. 9A-9F  and the associated embodiment. 
     Alt 1 (Ex1  1205 ): Each of the new PSS and the new SSS is mapped to the subcarriers in the reverse direction of the legacy PSS and the legacy SSS. 
     In one example, the new PSS is mapped onto the subcarriers on OFDM symbol l=N symb   DL −3, while the new SSS is mapped onto the subcarriers on OFDM symbol N symb   DL −4 in slots 0 and 10 or frame structure type 1 (i.e., FDD). 
     In one example, the new PSS is identical to the legacy PSS defined in Section 6.11.1 in REF1 and the new PSS mapping is done as in the following. That is, the PSS/SSS are mapped onto consecutive resource elements (REs) on each of the carrier of the first type and the carrier of the second type. The sequence d(n) shall be mapped to the resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
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                       = 
                       
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                   [ 
                   
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                     17 
                   
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     The new SSS is identical to the legacy SSS defined in Section 6.11.2 in REF1 and the new SSS mapping is done as the following: 
     The sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           n 
                           ) 
                         
                       
                     
                     , 
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     k 
                     = 
                     
                       31 
                       - 
                       n 
                       + 
                       
                         
                           
                             N 
                             RB 
                             DL 
                           
                            
                           
                             N 
                             sc 
                             RB 
                           
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     18 
                   
                   ] 
                 
               
             
           
         
       
     
     Alt 2 (Ex2  1210 ): A cyclic shift is applied to each of the new PSS and the new SSS, and the cyclically shifted sync signal is mapped to the subcarriers for the PSS and the SSS. In the below examples, shift is the shift used for the cyclic shifting operation. δ shift  can be a constant, e.g., δ shift =31, which is the half of the sequence length. 
     In one example, the new PSS is mapped onto the subcarriers on OFDM symbol l=N symb   DL −3, while the new SSS is mapped onto the subcarriers on OFDM symbol N symb   DL −4 in slots 0 and 10 or frame structure type 1 (i.e., FDD). 
     In one example, the new PSS is generated by cyclically shifting the legacy PSS defined in Section 6.11.1 in REF1 and mapped to the resource elements as in the following: 
     The sequence d(n) shall be mapped to the resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 
                                   δ 
                                   shift 
                                 
                               
                               ) 
                             
                              
                             mod 
                              
                             
                                 
                             
                              
                             62 
                           
                           ) 
                         
                       
                     
                     , 
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     k 
                     = 
                     
                       n 
                       - 
                       31 
                       + 
                       
                         
                           
                             N 
                             RB 
                             DL 
                           
                            
                           
                             N 
                             sc 
                             RB 
                           
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     19 
                   
                   ] 
                 
               
             
           
         
       
     
     The new SSS is generated by cyclically shifting the legacy SSS defined in Section 6.11.2 in REF1 and mapped to the resource elements as the following: 
     The sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 
                                   δ 
                                   shift 
                                 
                               
                               ) 
                             
                              
                             mod 
                              
                             
                                 
                             
                              
                             62 
                           
                           ) 
                         
                       
                     
                     , 
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     k 
                     = 
                     
                       n 
                       - 
                       31 
                       + 
                       
                         
                           
                             N 
                             RB 
                             DL 
                           
                            
                           
                             N 
                             sc 
                             RB 
                           
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     20 
                   
                   ] 
                 
               
             
           
         
       
     
     In another example, the new PSS is generated by cyclically shifting the legacy PSS defined in Section 6.11.1 in REF1 and reversely mapped to the resource elements as in the following: 
     The sequence d(n) shall be mapped to the resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 
                                   δ 
                                   shift 
                                 
                               
                               ) 
                             
                              
                             mod 
                              
                             
                                 
                             
                              
                             62 
                           
                           ) 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     k 
                     = 
                     
                       31 
                       - 
                       n 
                       + 
                       
                         
                           
                             N 
                             RB 
                             DL 
                           
                            
                           
                             N 
                             sc 
                             RB 
                           
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     21 
                   
                   ] 
                 
               
             
           
         
       
     
     The new SSS is generated by cyclically shifting the legacy SSS defined in Section 6.11.2 in REF1 and reversely mapped to the resource elements as the following: 
     The sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           
                             
                               ( 
                               
                                 n 
                                 - 
                                 
                                   δ 
                                   shift 
                                 
                               
                               ) 
                             
                              
                             mod 
                              
                             
                                 
                             
                              
                             62 
                           
                           ) 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     k 
                     = 
                     
                       31 
                       - 
                       n 
                       + 
                       
                         
                           
                             N 
                             RB 
                             DL 
                           
                            
                           
                             N 
                             sc 
                             RB 
                           
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     22 
                   
                   ] 
                 
               
             
           
         
       
     
     Alt 3(Ex3  1215 ): Each of the new PSS and the new SSS is sequentially mapped to the subcarriers, but is interleaved in multiple OFDM symbols. In the below examples, n offset  is the offset used for the interleaving operation. The n offset  can be a constant, e.g., n offset =31, which is the half of the sequence length. 
     In one example, the new PSS is identical to the legacy PSS defined in Section 6.11.1 in REF1 and the new PSS mapping is done as in the following: 
     The sequence d(n) shall be mapped to the resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           n 
                           ) 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     
                       k 
                       = 
                       
                         n 
                         - 
                         31 
                         + 
                         
                           
                             
                               N 
                               RB 
                               DL 
                             
                              
                             
                               N 
                               sc 
                               RB 
                             
                           
                           2 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       1 
                       = 
                       
                         { 
                         
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 3 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   0 
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 
                                   n 
                                   offset 
                                 
                               
                             
                           
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 4 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   
                                     
                                       n 
                                       offset 
                                     
                                     + 
                                     1 
                                   
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 61 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     23 
                   
                   ] 
                 
               
             
           
         
       
     
     in slots 0 and 10 or frame structure type 1 (i.e., FDD). That is, for frequency division duplex (FDD), and for frame structure type 1, the PSS is mapped to a last OFDM symbol in slots 0 and 10. 
     The new SSS is generated by cyclically shifting the legacy SSS defined in Section 6.11.2 in REF1 and mapped to the resource elements as the following: 
     The sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           n 
                           ) 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     
                       k 
                       = 
                       
                         n 
                         - 
                         31 
                         + 
                         
                           
                             
                               N 
                               RB 
                               DL 
                             
                              
                             
                               N 
                               sc 
                               RB 
                             
                           
                           2 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       1 
                       = 
                       
                         { 
                         
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 4 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   0 
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 
                                   n 
                                   offset 
                                 
                               
                             
                           
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 3 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   
                                     
                                       n 
                                       offset 
                                     
                                     + 
                                     1 
                                   
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 61 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     24 
                   
                   ] 
                 
               
             
           
         
       
     
     in slots 0 and 10 or frame structure type 1 (i.e. FDD). 
     In another example, the new PSS is identical to the legacy PSS defined in Section 6.11.1 in REF1 and the new PSS mapping is done as in the following (reverse mapping): 
     The sequence d(n) shall be mapped to the resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           n 
                           ) 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     
                       k 
                       = 
                       
                         31 
                         - 
                         n 
                         + 
                         
                           
                             
                               N 
                               RB 
                               DL 
                             
                              
                             
                               N 
                               sc 
                               RB 
                             
                           
                           2 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       1 
                       = 
                       
                         { 
                         
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 3 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   0 
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 
                                   n 
                                   offset 
                                 
                               
                             
                           
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 4 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   
                                     
                                       n 
                                       offset 
                                     
                                     + 
                                     1 
                                   
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 61 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     25 
                   
                   ] 
                 
               
             
           
         
       
     
     in slots 0 and 10 or frame structure type 1 (i.e. FDD). 
     The new SSS is generated by cyclically shifting the legacy SSS defined in Section 6.11.2 in REF1 and mapped to the resource elements as the following (reverse mapping): 
     The sequence d(n) shall be mapped to resource elements according to: 
     
       
         
           
             
               
                 
                   
                     
                       
                         a 
                         
                           k 
                           , 
                           1 
                         
                       
                       = 
                       
                         d 
                          
                         
                           ( 
                           n 
                           ) 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       n 
                       = 
                       0 
                     
                     , 
                     … 
                      
                     
                         
                     
                     , 
                     61 
                   
                    
                   
                     
 
                   
                    
                   
                     
                       k 
                       = 
                       
                         31 
                         - 
                         n 
                         + 
                         
                           
                             
                               N 
                               RB 
                               DL 
                             
                              
                             
                               N 
                               sc 
                               RB 
                             
                           
                           2 
                         
                       
                     
                     , 
                     
                       
 
                     
                      
                     
                       1 
                       = 
                       
                         { 
                         
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 4 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   0 
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 
                                   n 
                                   offset 
                                 
                               
                             
                           
                           
                             
                               
                                 
                                   N 
                                   symb 
                                   DL 
                                 
                                 - 
                                 3 
                               
                             
                             
                               
                                 
                                   n 
                                   = 
                                   
                                     
                                       n 
                                       offset 
                                     
                                     + 
                                     1 
                                   
                                 
                                 , 
                                 … 
                                  
                                 
                                     
                                 
                                 , 
                                 61 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Eqn 
                     . 
                     
                         
                     
                      
                     26 
                   
                   ] 
                 
               
             
           
         
       
     
     in slots 0 and 10 or frame structure type 1 (i.e. FDD). 
     Alt 4 (Ex4 in  1220 ): Each of the new PSS  907  and the new  909  SSS is sequentially mapped to the subcarriers just like the legacy PSS/SSS. However, the new PSS comes earlier in time than the new SSS, which is different from the mapping where the legacy PSS comes later in time than the legacy SSS. This way, legacy UEs are not confused by the new sync signals. In one example, the new PSS is mapped onto the subcarriers on OFDM symbol l=N symb   DL −4 while the new SSS is mapped onto the subcarriers on OFDM symbol N symb   DL −3, in slots 0 and 10 or frame structure type 1 (i.e., FDD). 
     In certain embodiments, only the SSS  909  without PSS  907  can be configured to be transmitted on an extension carrier. This method can prevent legacy UEs from camping on the extension carrier, because in the legacy UEs&#39; implementation PSS are detected first before the SSS. Note that in this case SSS can be used for UEs&#39; time and frequency synchronization. 
     For the time-frequency location of the SSS, we consider the following: 
     In one example, time-frequency location of the SSS can be configured by RRC, where the RRC configuration may include at least one of the following: 
     Periodicity P in terms of sub-frame, SSS are transmitted in every P sub-frames; 
     Sub-frame offset P 0 . SSS are transmitted in sub-frames P 0 , P 0 +P, and so on in each (radio) frame; 
     OFDM symbol number, which contains SSS in the SSS sub-frame; and 
     PRB numbers (or subcarrier numbers), which contains SSS in the SSS sub-frame. 
       FIG. 13  illustrates placement of new sync signals according to embodiments of the present disclosure. The embodiment of the new signals shown in  FIG. 13  is for illustration only. Other embodiments could be used without departing from the scope of the disclosure. 
     In another example, time-frequency location of the SSS is fixed in the standard and not signaled to UEs: (See  FIG. 13 ). 
     The sub-frames  1305  that contain SSS are identical to those in the backward compatible carriers, i.e., sub-frames #0 and #5 in case of FDD; 
     Frequency location of the SSS is also identical to that of the backward compatible carriers, i.e., the SSS are transmitted in the center 6 PRBs; and 
     An OFDM symbol in the first slot (or slot 0) is selected for the transmission of SSS in the SSS sub-frames: 
     Alt 1: The OFDM symbol to transmit the SSS is identical to the one in the backward compatible carriers, i.e., the second to the last OFDM symbol  1310  in the first slot (or slot 0); and 
     Alt 2: The OFDM symbol to transmit the SSS is the same as the one for the PSS in the backward compatible carriers, i.e., the last OFDM symbol  1315  in the first slot (or slot 0). 
     In certain embodiments, whether UE  116  can use PSS or not in an extension carrier is configured by an RRC signaling transmitted in the primary component carrier. In other words, UE  116  is informed by an RRC signaling transmitted in the primary component carrier of whether PSS is configured in the extension carrier or not. In still other words, UE  116  is informed by an RRC signaling transmitted in the primary component carrier of whether the PSS power is non-zero or zero. 
     When UE  116  is configured to access PSS, or when UE  116  is informed that (non-zero power) PSS is configured in the extension carrier, UE  116  can use both PSS and SSS to get synchronization to the extension carrier. 
     When UE  116  is not configured to access PSS, or when the UE is informed that PSS is not configured in the extension carrier, the UE uses SSS to get synchronization to the extension carrier. 
     When the PSS is not configured, or when zero-power PSS is configured, two options can be considered for UEs&#39;  116  assumption on the PSS REs. 
     In a first option, when UE  116  is scheduled in the DL PRBs containing the PSS REs, UE  116  rate matches around the PSS REs. This provides UE implementation simplicity in that UE  116  does not need to implement two different types of rate matching blocks depending on whether the PSS is configured or not. 
     In a second option, when UE  116  is scheduled in the DL PRBs containing the PSS REs, UE  116  expects valid data symbols are transmitted in the PSS REs. This provides increased DL throughput as compared to the first option, as the PSS REs are not wasted. 
     Here, the underlying assumption is that UE  116  knows the time frequency location of PSS REs, e.g., as specified in the standard specification, or by an RRC signaling. 
     Soft-cell partitioning 
     In 36.331 v10.1.0, the following configuration is defined for CSI-RS: 
     CSI-RS-Config 
     The IE CSI-RS-Config is used to specify the CSI (Channel-State Information) reference signal configuration. 
     
       
         
           
               
             
               
                   
               
               
                 CSI-RS-Config information elements 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 -- ASN1 START 
                   
               
            
           
           
               
               
            
               
                 CSI-RS-Config-r10 ::= 
                 SEQUENCE { 
               
            
           
           
               
               
            
               
                  csi-RS-r10 
                 CHOICE { 
               
            
           
           
               
               
            
               
                   release 
                 NULL, 
               
               
                   setup 
                 SEQUENCE { 
               
            
           
           
               
               
            
               
                    antennaPortsCount-r10 
                 ENUMERATED {an1, an2, an4, an8}, 
               
               
                    resourceConfig-r10 
                 INTEGER (0..31), 
               
            
           
           
               
               
            
               
                    subframeConfig-r10 
                 INTEGER (0..154), 
               
            
           
           
               
               
            
               
                    p-C-r10 
                 INTEGER (−8..15) 
               
            
           
           
               
               
               
            
               
                   } 
                   
                   
               
            
           
           
               
               
               
            
               
                  } 
                 OPTIONAL, 
                 -- Need ON 
               
            
           
           
               
               
            
               
                  zeroTxPowerCSI-RS-r10 
                 CHOICE { 
               
               
                   release 
                 NULL, 
               
               
                   setup 
                 SEQUENCE { 
               
            
           
           
               
               
            
               
                    zeroTxPowerResourceConfigList-r10 
                 BIT STRING (SIZE (16)), 
               
               
                    zeroTxPowerSubframeConfig-r10 
                 INTEGER (0..154) 
               
            
           
           
               
               
               
            
               
                   } 
                   
                   
               
            
           
           
               
               
               
            
               
                  } 
                   
                 OPTIONAL -- 
               
            
           
           
               
               
               
            
               
                 Need ON 
                   
                   
               
               
                 } 
                   
                   
               
               
                 -- ASN1STOP 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 CSI-RS-Config field descriptions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 antennaPortsCount 
               
               
                 Parameter represents the number of antenna ports used for transmission of 
               
               
                 CSI reference signals where an1 corresponds to 1, an2 to 2 antenna ports 
               
               
                 etc. see TS 36.211 [21, 6.10.5]. 
               
               
                 p-C 
               
               
                 Parameter: P c , see TS 36.213 [23, 7.2.5]. 
               
               
                 resourceConfig 
               
               
                 Parameter: CSI reference signal configuration, see TS 36.211 [21, table 
               
               
                 6.10.5.2-1 and 6.10.5.2-2]. 
               
               
                 subframeConfig 
               
               
                 Parameter: I CSI-RS , see TS 36.211 [21, table 6.10.5.3-1]. 
               
               
                 zeroTxPowerResourceConfigList 
               
               
                 Parameter: ZeroPowerCSI-RS, see TS 36.211 [21, 6.10.5.2]. 
               
               
                 zeroTxPowerSubframeConfig 
               
               
                 Parameter: I CSI-RS , see TS 36.211 [21, table 6.10.5.3-1]. 
               
               
                   
               
            
           
         
       
     
       FIG. 14  illustrates a Coordinated Multipoint (CoMP) with Remote Radio Head having the same cell ID as the macro cell according to embodiments of the present disclosure. The embodiment of the CoMP  1400  shown in  FIG. 14  is for illustration only. Other embodiments could be used without departing from the scope of the disclosure. 
     In the example shown in  FIG. 14 , where macro 0 transmits CSI-RS according to CSI-RS configuration 1, RRH1  1405  transmits CSI-RS according to CSI-RS configuration 2, and RRH2  1410  transmits CSI-RS according to CSI-RS configuration 3, where the three CSI-RS configurations are defined below. 
     CSI-RS configuration 1 comprises at least the following fields: 
     resourceConfig=RC1 
     subframeConfig=SC1 
     antennaPortCount=APC1 
     CSI-RS configuration 2 comprises at least the following fields: 
     resourceConfig=RC2 
     subframeConfig=SC2 
     antennaPortCount=APC2 
     CSI-RS configuration 3 comprises at least the following fields: 
     resourceConfig=RC3 
     subframeConfig=SC3 
     antennaPortCount=APC3. 
     UE  116 , UE  115  and UE  113  are advanced UEs, implementing not only Rel-10 features but also new features introduced in Rel-11. 
     In certain embodiments, for CoMP operation, UE  115  configured to do soft-cell partitioning and is configured with two CSI-RS configurations, i.e., CSI-RS configuration 1 and CSI-RS configuration 2. In this case, UE  115  needs to identify one CSI-RS configuration out of the two configurations to determine n SCID2 . Once the one CSI-RS configuration is determined, UE  115  calculates n SCID2  based on the field values of the one CSI-RS configuration, and receives UE-RS scrambled with an initialization c init =(└n s /2┘+1)·(2N ID   cell +1)·2 16 +n SCID2 ·2+n SCID . Example methods for a UE to determine the one CSI-RS configuration (i.e., resourceConfig, subframeConfig, antennaPortCount) to be used for determining n SCID2  out of the two configurations are listed below: 
     The one CSI-RS configuration to determine n SCID2  is explicitly identified by a PHY signaling. In one example, one bit information field is introduced in UL DCI format(s), e.g., DCI format 0/0A and DCI format-4 to indicate one of the two CSI-RS configurations. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Explicit PHY signaling example 
               
            
           
           
               
               
            
               
                 The one bit information field in the UL 
                   
               
               
                 DCI format(s) 
                 Meaning 
               
               
                   
               
               
                 0 
                 A first CSI-RS configuration 
               
               
                 1 
                 A second CSI-RS configuration 
               
               
                   
               
            
           
         
       
     
     Some examples of determining n SCID2  are listed below, where X is a parameter providing means to TPs to control the UE-RS scrambling behavior. For example, Xε{0, 1, . . . , 2 N     x   −1} is an N x  bit parameter. For singaling of X, two alternatives are listed below. 
     Alt 0: The parameter X is fixed to be 0, and not signaled; 
     Alt 1: The parameter X is semi-statically signaled in the RRC layer; 
     Alt 2: The parameter X is dynamically signaled in a DCI format; 
     Some examples of determining n SCID2  are listed below, where ñ SCID2  is a function of RC=RC1, SC=SC1, APC=APC1: 
         n   SCID2   =ñ   SCID2 ·(1 +X )  [Eqn. 27]
 
     Here, the multiplication of (1+X) expands the possible values for the UE-RS scrambling initialization c init . 
         n   SCID2 =ñ SCID2   ·X   [Eqn. 28]
 
     Here, the multiplication of X expands the possible values for the UE-RS scrambling initialization c init , and at the same time gives flexibility of turning off the soft-cell partitioning. 
         n   SCID2   =ñ   SCID2   +X   [Eqn. 29]
 
     Here, the addition of X lets eNodeB have flexibility to choose the UE-RS scrambling initialization c init , e.g., to intentionally configure a different UE-RS scrambling to a UE than the one configured by the CSI-RS configuration. 
     Some examples of determining ñ SCID2  include: 
     ñ SCID2 =g(RC). In this case, n SCID2  only depends on the CSI-RS pattern; 
     ñ SCID2 =g(RC)·(I CSI-RS  mod 5). Here, (I CSI-RS  mod 5) is applied to ensure that at most 5 different scrambling initializations are generated with possible values of I CSI-RS , where 5 corresponds to the minimum configurable period for CSI-RS sub-frames. In this case, n SCID2  is an 8-bit quantity; 
     ñ SCID2 =g(RC)·(I CSI-RS  mod 80). Here, (I CSI-RS  mod 80) is applied to ensure that at most 80 different scrambling initializations are generated with possible values of I CSI-RS , where 80 corresponds to the maximum configurable period for CSI-RS sub-frames. In this case, n SCID2  is a 12-bit quantity; 
     ñ SCID2 =g(RC)·Δ CSI-RS . Here, A CSI-RS is applied to ensure that at most T CSI-RS  different scrambling initializations are generated with possible values of I CRI-RS . 
     In these examples, Δ CSI-RS  is CSI-RS subframe offset derived from I CSI-RS =SC1 using Table 4. 
     Furthermore, some alternatives of determining the function g(RC) are: 
     g(RC)=RC; and 
     g(RC)=RC mod 10. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 CSI reference signal sub-frame configuration 
               
            
           
           
               
               
               
            
               
                   
                 CSI-RS periodicity 
                 CSI-RS subframe offset 
               
               
                 CSI-RS-SubframeConfig 
                 T CSI-RS   
                 Δ CSI-RS   
               
               
                 I CSI-RS   
                 (subframes) 
                 (subframes) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 0-4 
                 5 
                 I CSI-RS   
               
               
                  5-14 
                 10 
                 I CSI-RS -5 
               
               
                 15-34 
                 20 
                 I CSI-RS -15 
               
               
                 35-74 
                 40 
                 I CSI-RS -35 
               
               
                  75-154 
                 80 
                 I CSI-RS -75 
               
               
                   
               
            
           
         
       
     
       FIG. 15  illustrates a process for mapping synchronization according to embodiments of the present disclosure. In block  1505 , a base station transmits data, reference signals, synchronization signals and control elements to at least one of the plurality of subscriber stations. In block  1510 , the base station maps primary synchronization signals (PSS) and secondary synchronization signals (SSS) each of a carrier of a first carrier type, such as a Rel-10 compatible carrier, and a carrier of a second carrier type, such as a NCT. The base station maps the PSS and SSS (PSS/SSS) on the second carrier type onto different time locations than in the first carrier type. In addition, the base station maps the PSS and SSS (PSS/SSS) on the second carrier type are mapped onto different time locations than in the first carrier type. The time locations difference comprises at least one of: different OFDM symbols; and different sub-frames. The PSS/SSS are mapped onto consecutive resource elements (REs) on each of the carrier of the first type and the carrier of the second type, wherein subcarrier indices k for the REs are represented by the following: 
     
       
         
           
             
               k 
               = 
               
                 n 
                 - 
                 31 
                 + 
                 
                   
                     
                       N 
                       RB 
                       DL 
                     
                      
                     
                       N 
                       sc 
                       RB 
                     
                   
                   2 
                 
               
             
             , 
             
               n 
               = 
               0 
             
             , 
             … 
              
             
                 
             
             , 
             61 
           
         
       
     
     where N RB   DL  represents a total number of physical resource blocks (PRBs) in a respective carrier, and N sc   RB  is a number of subcarriers per PRB. 
     In certain embodiments, in block  1510 , the PSS on the carrier of the first carrier type is mapped according to: 
     for frequency division duplex (FDD), and for frame structure type 1, the PSS is mapped to a last OFDM symbol in slots 0 and 10; 
     for time division duplex (TDD), and for frame structure type 2, the PSS is mapped to a third OFDM symbol in sub-frames 1 and 6; 
     wherein an SSS sequence is mapped to OFDM symbols 1 represented by the following: 
     
       
         
           
             1 
             = 
             
               { 
               
                 
                   
                     
                       
                         N 
                         symb 
                         DL 
                       
                       - 
                       2 
                     
                   
                   
                     
                       in 
                        
                       
                           
                       
                        
                       slots 
                        
                       
                           
                       
                        
                       0 
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       10 
                     
                   
                   
                     
                       for 
                        
                       
                           
                       
                        
                       FDD 
                     
                   
                 
                 
                   
                     
                       
                         N 
                         symb 
                         DL 
                       
                       - 
                       1 
                     
                   
                   
                     
                       in 
                        
                       
                           
                       
                        
                       slots 
                        
                       
                           
                       
                        
                       1 
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       11 
                     
                   
                   
                     
                       for 
                        
                       
                           
                       
                        
                       TDD 
                     
                   
                 
               
             
           
         
       
     
     wherein N symb   DL  is the total number of OFDM symbols in a corresponding time slot. 
     In certain embodiments, in block  1510 , the base station maps an SSS sequence d(n) is mapped to resource elements according to: 
     
       
         
           
             
               
                 a 
                 
                   k 
                   , 
                   1 
                 
               
               = 
               
                 d 
                  
                 
                   ( 
                   n 
                   ) 
                 
               
             
             , 
             
               
 
             
              
             
               n 
               = 
               0 
             
             , 
             … 
              
             
                 
             
             , 
             61 
           
         
       
       
         
           
             k 
             = 
             
               n 
               - 
               31 
               + 
               
                 
                   
                     N 
                     RB 
                     DL 
                   
                    
                   
                     N 
                     sc 
                     RB 
                   
                 
                 2 
               
             
           
         
       
       
         
           
             1 
             = 
             
               { 
               
                 
                   
                     
                       
                         N 
                         symb 
                         DL 
                       
                       - 
                       2 
                     
                   
                   
                     
                       in 
                        
                       
                           
                       
                        
                       slots 
                        
                       
                           
                       
                        
                       0 
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       10 
                     
                   
                   
                     
                       for 
                        
                       
                           
                       
                        
                       FDD 
                     
                   
                 
                 
                   
                     
                       
                         N 
                         symb 
                         DL 
                       
                       - 
                       1 
                     
                   
                   
                     
                       in 
                        
                       
                           
                       
                        
                       slots 
                        
                       
                           
                       
                        
                       1 
                        
                       
                           
                       
                        
                       and 
                        
                       
                           
                       
                        
                       11 
                     
                   
                   
                     
                       for 
                        
                       
                           
                       
                        
                       TDD 
                     
                   
                 
               
             
           
         
       
     
     wherein N RB   DL  is the total number of PRBs in the carrier, and N sc   RB  is the number of subcarriers per PRB. 
     In certain embodiments, the base station maps the PSS and SSS on the carrier of the second carrier type according to: 
     for FDD, PSS and SSS are located on the OFDM symbols l=2 and l=1 of slots 0 and 10, respectively; and 
     for TDD, PSS and SSS are located on the OFDM symbols 
     l=N symb   DL −3 and l=N symb   DL −6 in slots 2 and 12, respectively. 
     In certain embodiments, the base station maps the PSS and SSS on the carrier of the second carrier type according to: for FDD and TDD, PSS and SSS are located on the OFDM symbols l=2 and l=1 of slots 0 and 10, respectively. 
     Although  FIG. 15  illustrates examples of methods for mapping synchronization signals, various changes may be made to  FIG. 15 . For example, while shown as a series of steps, the steps in each figure could overlap, occur in parallel, occur in a different order, or occur any number of times. 
     Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.