Patent Publication Number: US-2015079987-A1

Title: Tone detection scheduling

Description:
BACKGROUND 
     1. Field 
     Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to frequency correction channel (FCCH) tone detection scheduling. 
     2. Background 
     Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). For example, China is pursuing TD-SCDMA as the underlying air interface in the UTRAN architecture with its existing GSM infrastructure as the core network. The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. HSPA is a collection of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA) that extends and improves the performance of existing wideband protocols. 
     As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. 
     SUMMARY 
     According to one aspect of the present disclosure, a method for wireless communication includes starting a system acquisition for a first Global System for Mobile Communications (GSM) cell. The method further includes suspending the system acquisition of the first GSM cell when a condition occurs. The method also includes storing information acquired prior to suspending. The method also includes starting a system acquisition for a second GSM cell. The method further includes resuming the system acquisition of the first GSM cell using the stored information. 
     According to another aspect of the present disclosure, an apparatus for wireless communication includes means for means for starting a system acquisition for a first Global System for Mobile Communications (GSM) cell. The apparatus may also include means for suspending the system acquisition of the first GSM cell when a condition occurs. The apparatus may also include means for storing information acquired prior to suspending. The apparatus may also include means for starting a system acquisition for a second GSM cell. The apparatus may further includes means for resuming the system acquisition of the first GSM cell using the stored information. 
     According to one aspect of the present disclosure, a computer program product for wireless communication in a wireless network includes a computer readable medium having non-transitory program code recorded thereon. The program code includes program code to start a system acquisition for a first Global System for Mobile Communications (GSM) cell. The program code may also include program code to suspend the system acquisition of the first GSM cell when a condition occurs. The program code may also include program code to store information acquired prior to suspending. The program code may further includes program code to start a system acquisition for a second GSM cell. The program code may further includes program code to resume the system acquisition of the first GSM cell using the stored information. 
     According to one aspect of the present disclosure, an apparatus for wireless communication includes a memory and a processor(s) coupled to the memory. The processor(s) is configured to start a system acquisition for a first Global System for Mobile Communications (GSM) cell. The processor(s) is also configured to suspend the system acquisition of the first GSM cell when a condition occurs. The processor(s) is also configured to store information acquired prior to suspending. The processor(s) is also configured to start a system acquisition for a second GSM cell. The processor(s) is further configured to resume the system acquisition of the first GSM cell using the stored information. 
     This has outlined, rather broadly, the features and technical advantages of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described below. It should be appreciated by those skilled in the art that this disclosure may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the teachings of the disclosure as set forth in the appended claims. The novel features, which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages, will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout. 
         FIG. 1  is a block diagram conceptually illustrating an example of a telecommunications system. 
         FIG. 2  is a block diagram conceptually illustrating an example of a frame structure in a telecommunications system. 
         FIG. 3  is a block diagram conceptually illustrating an example of a node B in communication with a UE in a telecommunications system. 
         FIG. 4  illustrates network coverage areas according to aspects of the present disclosure. 
         FIG. 5  is a block diagram illustrating the timing of channel carriers according to aspects of the present disclosure. 
         FIG. 6  is a process flow diagram illustrating a tone detection scheduling method according to one aspect of the present disclosure. 
         FIG. 7  is a diagram illustrating an example of a hardware implementation for an apparatus employing a tone detecting system according to one aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
     Turning now to  FIG. 1 , a block diagram is shown illustrating an example of a telecommunications system  100 . The various concepts presented throughout this disclosure may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. By way of example and without limitation, the aspects of the present disclosure illustrated in  FIG. 1  are presented with reference to a UMTS system employing a TD-SCDMA standard. In this example, the UMTS system includes a (radio access network) RAN  102  (e.g., UTRAN) that provides various wireless services including telephony, video, data, messaging, broadcasts, and/or other services. The RAN  102  may be divided into a number of Radio Network Subsystems (RNSs) such as an RNS  107 , each controlled by a Radio Network Controller (RNC) such as an RNC  106 . For clarity, only the RNC  106  and the RNS  107  are shown; however, the RAN  102  may include any number of RNCs and RNSs in addition to the RNC  106  and RNS  107 . The RNC  106  is an apparatus responsible for, among other things, assigning, reconfiguring and releasing radio resources within the RNS  107 . The RNC  106  may be interconnected to other RNCs (not shown) in the RAN  102  through various types of interfaces such as a direct physical connection, a virtual network, or the like, using any suitable transport network. 
     The geographic region covered by the RNS  107  may be divided into a number of cells, with a radio transceiver apparatus serving each cell. A radio transceiver apparatus is commonly referred to as a node B in UMTS applications, but may also be referred to by those skilled in the art as a base station (BS), a base transceiver station (BTS), a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an access point (AP), or some other suitable terminology. For clarity, two node Bs  108  are shown; however, the RNS  107  may include any number of wireless node Bs. The node Bs  108  provide wireless access points to a core network  104  for any number of mobile apparatuses. Examples of a mobile apparatus include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a notebook, a netbook, a smartbook, a personal digital assistant (PDA), a satellite radio, a global positioning system (GPS) device, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, or any other similar functioning device. The mobile apparatus is commonly referred to as user equipment (UE) in UMTS applications, but may also be referred to by those skilled in the art as a mobile station (MS), a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal (AT), a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. For illustrative purposes, three UEs  110  are shown in communication with the node Bs  108 . The downlink (DL), also called the forward link, refers to the communication link from a node B to a UE, and the uplink (UL), also called the reverse link, refers to the communication link from a UE to a node B. 
     The core network  104 , as shown, includes a GSM core network. However, as those skilled in the art will recognize, the various concepts presented throughout this disclosure may be implemented in a RAN, or other suitable access network, to provide UEs with access to types of core networks other than GSM networks. 
     In this example, the core network  104  supports circuit-switched services with a mobile switching center (MSC)  112  and a gateway MSC (GMSC)  114 . One or more RNCs, such as the RNC  106 , may be connected to the MSC  112 . The MSC  112  is an apparatus that controls call setup, call routing, and UE mobility functions. The MSC  112  also includes a visitor location register (VLR) (not shown) that contains subscriber-related information for the duration that a UE is in the coverage area of the MSC  112 . The GMSC  114  provides a gateway through the MSC  112  for the UE to access a circuit-switched network  116 . The GMSC  114  includes a home location register (HLR) (not shown) containing subscriber data, such as the data reflecting the details of the services to which a particular user has subscribed. The HLR is also associated with an authentication center (AuC) that contains subscriber-specific authentication data. When a call is received for a particular UE, the GMSC  114  queries the HLR to determine the UE&#39;s location and forwards the call to the particular MSC serving that location. 
     The core network  104  also supports packet-data services with a serving GPRS support node (SGSN)  118  and a gateway GPRS support node (GGSN)  120 . GPRS, which stands for General Packet Radio Service, is designed to provide packet-data services at speeds higher than those available with standard GSM circuit-switched data services. The GGSN  120  provides a connection for the RAN  102  to a packet-based network  122 . The packet-based network  122  may be the Internet, a private data network, or some other suitable packet-based network. The primary function of the GGSN  120  is to provide the UEs  110  with packet-based network connectivity. Data packets are transferred between the GGSN  120  and the UEs  110  through the SGSN  118 , which performs primarily the same functions in the packet-based domain as the MSC  112  performs in the circuit-switched domain. 
     The UMTS air interface is a spread spectrum Direct-Sequence Code Division Multiple Access (DS-CDMA) system. The spread spectrum DS-CDMA spreads user data over a much wider bandwidth through multiplication by a sequence of pseudorandom bits called chips. The TD-SCDMA standard is based on such direct sequence spread spectrum technology and additionally calls for a time division duplexing (TDD), rather than a frequency division duplexing (FDD) as used in many FDD mode UMTS/W-CDMA systems. TDD uses the same carrier frequency for both the uplink (UL) and downlink (DL) between a node B  108  and a UE  110 , but divides uplink and downlink transmissions into different time slots in the carrier. 
       FIG. 2  shows a frame structure  200  for a TD-SCDMA carrier. The TD-SCDMA carrier, as illustrated, has a frame  202  that is 10 ms in length. The chip rate in TD-SCDMA is 1.28 Mcps. The frame  202  has two 5 ms subframes  204 , and each of the subframes  204  includes seven time slots, TS0 through TS6. The first time slot, TS0, is usually allocated for downlink communication, while the second time slot, TS  1 , is usually allocated for uplink communication. The remaining time slots, TS2 through TS6, may be used for either uplink or downlink, which allows for greater flexibility during times of higher data transmission times in either the uplink or downlink directions. A downlink pilot time slot (DwPTS)  206 , a guard period (GP)  208 , and an uplink pilot time slot (UpPTS)  210  (also known as the uplink pilot channel (UpPCH)) are located between TS0 and TS1. Each time slot, TS0-TS6, may allow data transmission multiplexed on a maximum of 16 code channels. Data transmission on a code channel includes two data portions  212  (each with a length of 352 chips) separated by a midamble  214  (with a length of 144 chips) and followed by a guard period (GP)  216  (with a length of 16 chips). The midamble  214  may be used for features, such as channel estimation, while the guard period  216  may be used to avoid inter-burst interference. Also transmitted in the data portion is some Layer 1 control information, including Synchronization Shift (SS) bits  218 . SS bits  218  only appear in the second part of the data portion. The SS bits  218  immediately following the midamble can indicate three cases: decrease shift, increase shift, or do nothing in the upload transmit timing. The positions of the SS bits  218  are not generally used during uplink communications. 
       FIG. 3  is a block diagram of a node B  310  in communication with a UE  350  in a RAN  300 , where the RAN  300  may be the RAN  102  in  FIG. 1 , the node B  310  may be the node B  108  in  FIG. 1 , and the UE  350  may be the UE  110  in  FIG. 1 . In the downlink communication, a transmit processor  320  may receive data from a data source  312  and control signals from a controller/processor  340 . The transmit processor  320  provides various signal processing functions for the data and control signals, as well as reference signals (e.g., pilot signals). For example, the transmit processor  320  may provide cyclic redundancy check (CRC) codes for error detection, coding and interleaving to facilitate forward error correction (FEC), mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM), and the like), spreading with orthogonal variable spreading factors (OVSF), and multiplying with scrambling codes to produce a series of symbols. Channel estimates from a channel processor  344  may be used by a controller/processor  340  to determine the coding, modulation, spreading, and/or scrambling schemes for the transmit processor  320 . These channel estimates may be derived from a reference signal transmitted by the UE  350  or from feedback contained in the midamble  214  ( FIG. 2 ) from the UE  350 . The symbols generated by the transmit processor  320  are provided to a transmit frame processor  330  to create a frame structure. The transmit frame processor  330  creates this frame structure by multiplexing the symbols with a midamble  214  ( FIG. 2 ) from the controller/processor  340 , resulting in a series of frames. The frames are then provided to a transmitter  332 , which provides various signal conditioning functions including amplifying, filtering, and modulating the frames onto a carrier for downlink transmission over the wireless medium through smart antennas  334 . The smart antennas  334  may be implemented with beam steering bidirectional adaptive antenna arrays or other similar beam technologies. 
     At the UE  350 , a receiver  354  receives the downlink transmission through an antenna  352  and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver  354  is provided to a receive frame processor  360 , which parses each frame, and provides the midamble  214  ( FIG. 2 ) to a channel processor  394  and the data, control, and reference signals to a receive processor  370 . The receive processor  370  then performs the inverse of the processing performed by the transmit processor  320  in the node B  310 . More specifically, the receive processor  370  descrambles and despreads the symbols, and then determines the most likely signal constellation points transmitted by the node B  310  based on the modulation scheme. These soft decisions may be based on channel estimates computed by the channel processor  394 . The soft decisions are then decoded and deinterleaved to recover the data, control, and reference signals. The CRC codes are then checked to determine whether the frames were successfully decoded. The data carried by the successfully decoded frames will then be provided to a data sink  372 , which represents applications running in the UE  350  and/or various user interfaces (e.g., display). Control signals carried by successfully decoded frames will be provided to a controller/processor  390 . When frames are unsuccessfully decoded by the receive processor  370 , the controller/processor  390  may also use an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support retransmission requests for those frames. 
     In the uplink, data from a data source  378  and control signals from the controller/processor  390  are provided to a transmit processor  380 . The data source  378  may represent applications running in the UE  350  and various user interfaces (e.g., keyboard). Similar to the functionality described in connection with the downlink transmission by the node B  310 , the transmit processor  380  provides various signal processing functions including CRC codes, coding and interleaving to facilitate FEC, mapping to signal constellations, spreading with OVSFs, and scrambling to produce a series of symbols. Channel estimates, derived by the channel processor  394  from a reference signal transmitted by the node B  310  or from feedback contained in the midamble transmitted by the node B  310 , may be used to select the appropriate coding, modulation, spreading, and/or scrambling schemes. The symbols produced by the transmit processor  380  will be provided to a transmit frame processor  382  to create a frame structure. The transmit frame processor  382  creates this frame structure by multiplexing the symbols with a midamble  214  ( FIG. 2 ) from the controller/processor  390 , resulting in a series of frames. The frames are then provided to a transmitter  356 , which provides various signal conditioning functions including amplification, filtering, and modulating the frames onto a carrier for uplink transmission over the wireless medium through the antenna  352 . 
     The uplink transmission is processed at the node B  310  in a manner similar to that described in connection with the receiver function at the UE  350 . A receiver  335  receives the uplink transmission through the antenna  334  and processes the transmission to recover the information modulated onto the carrier. The information recovered by the receiver  335  is provided to a receive frame processor  336 , which parses each frame, and provides the midamble  214  ( FIG. 2 ) to the channel processor  344  and the data, control, and reference signals to a receive processor  338 . The receive processor  338  performs the inverse of the processing performed by the transmit processor  380  in the UE  350 . The data and control signals carried by the successfully decoded frames may then be provided to a data sink  339  and the controller/processor, respectively. If some of the frames were unsuccessfully decoded by the receive processor, the controller/processor  340  may also use an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support retransmission requests for those frames. 
     The controller/processors  340  and  390  may be used to direct the operation at the node B  310  and the UE  350 , respectively. For example, the controller/processors  340  and  390  may provide various functions including timing, peripheral interfaces, voltage regulation, power management, and other control functions. The computer readable media of memories  342  and  392  may store data and software for the node B  310  and the UE  350 , respectively. For example, the memory  392  of the UE  350  may store tone detection module  391  which, when executed by the controller/processor  390 , configures the UE  350  to wait an adjustable period of time before aborting a system acquisition. A scheduler/processor  346  at the node B  310  may be used to allocate resources to the UEs and schedule downlink and/or uplink transmissions for the UEs. 
       FIG. 4  illustrates coverage of a newly deployed network, such as a TD-SCDMA network and also coverage of a more established network, such as a GSM network. A geographical area  400  may include GSM cells  402  and TD-SCDMA cells  404 . A user equipment (UE)  406  may move from one cell, such as a TD-SCDMA cell  404 , to another cell, such as a GSM cell  402 . The movement of the UE  406  may specify a handover or a cell reselection. 
     The handover or cell reselection may be performed when the UE moves from a coverage area of a TD-SCDMA cell to the coverage area of a GSM cell, or vice versa. A handover or cell reselection may also be performed when there is a coverage hole or lack of coverage in the TD-SCDMA network or when there is traffic balancing between the TD-SCDMA and GSM networks. As part of that handover or cell reselection process, while in a connected mode with a first system (e.g., TD-SCDMA) a UE may be specified to perform a measurement of a neighboring cell (such as GSM cell). For example, the UE may measure the neighbor cells of a second network for signal strength, frequency channel, and base station identity code (BSIC). The UE may then connect to the strongest cell of the second network. Such measurement may be referred to as inter radio access technology (IRAT) measurement. 
     The UE may send a serving cell a measurement report indicating results of the IRAT measurement performed by the UE. The serving cell may then trigger a handover of the UE to a new cell in the other RAT based on the measurement report. The triggering may be based on a comparison between measurements of the different RATs. The measurement may include a TD-SCDMA serving cell signal strength, such as a received signal code power (RSCP) for a pilot channel (e.g., primary common control physical channel (P-CCPCH)). The signal strength is compared to a serving system threshold. The serving system threshold can be indicated to the UE through dedicated radio resource control (RRC) signaling from the network. The measurement may also include a GSM neighbor cell received signal strength indicator (RSSI). The neighbor cell signal strength can be compared with a neighbor system threshold. Before handover or cell reselection, in addition to the measurement processes, the base station IDs (e.g., BSICs) are confirmed and re-confirmed. 
     Other radio access technologies, such as a wireless local area network (WLAN) or WiFi may also be accessed by a user equipment (UE) in addition to cellular networks such as TD-SCDMA or GSM. For the UE to determine nearby WiFi access points (APs), the UE scans available WiFi channels to detect if any WiFi networks exist in the vicinity of the UE. In one configuration, the UE may use TD-SCDMA reception/transmission gaps to switch to the WiFi network to scan the WiFi channels. 
     Tone Detection Scheduling 
     Handover from a first radio access technology (RAT) to a second RAT may occur for several reasons. First, the network may prefer to have a user equipment (UE) primarily use the first RAT but use the second RAT simply for voice service(s). Second, there may be coverage holes in the network of one RAT, such as the first RAT. 
     Handover from the first RAT to the second RAT may be based on event  3 A measurement reporting. In one configuration, the event  3 A measurement reporting may be triggered based on filtered measurements of the first RAT and the second RAT, a base station identity code (BSIC) confirm procedure of the second RAT and also a BSIC re-confirm procedure of the second RAT. For example, a filtered measurement may be a Primary Common Control Physical Channel (P-CCPCH) or a Primary Common Control Physical Shared Channel (P-CCPSCH) received signal code power (RSCP) measurement of a serving cell. Other filtered measurements can be of a received signal strength indication (RSSI) of a cell of the second RAT. 
     The initial BSIC identification procedure occurs because there is no knowledge about the relative timing between a cell of the first RAT and a cell of the second RAT. The initial BSIC identification procedure includes searching for the BSIC and decoding the BSIC for the first time. The UE may trigger the initial BSIC identification within available idle time slot(s) when the UE is in a dedicated channel (DCH) mode configured for the first RAT. 
     The BSIC of a cell in the second RAT is “verified” when the UE decodes the synchronization channel (SCH) of a broadcast control channel (BCCH) carrier, identifies the BSIC, at least one time, with an initial BSIC identification and reconfirms. The initial BSIC identification is performed within a predefined time period (for example, T identify     —     abort =5 seconds). The BSIC is re-confirmed at least once every T re-confirm     —     abort  seconds (e.g., T re-confirmabort =5 seconds). Otherwise, the BSIC of a cell in the second RAT is considered “non-verified.” 
     The UE maintains timing information of some neighbor cells, e.g., at least eight identified GSM cells in one configuration. The timing information may be useful for IRAT handover to one of the neighbor cells (e.g., target neighbor cell) and may be obtained from the BSIC. For example, initial timing information of the neighbor cells may be obtained from an initial BSIC identification. The timing information may be updated every time the BSIC is decoded. 
     The initial BSIC identification procedure may take a longer amount of time to perform (e.g., up to 5 seconds or more) because there is no knowledge about the relative timing between the serving cell of the first RAT and the neighbor cells of the second RAT. This BSIC identification procedure may be part of a system acquisition of the neighbor cells. For example, the system acquisition may include a blind frequency correction channel (FCCH) burst or tone detection based on a fixed bit sequence carried on the FCCH to find the relative timing between the first RAT and the second RAT. The procedure may be considered fully blind due to a lack of knowledge about the relative timing between the first RAT and the second RAT. Exemplary timing of channel carriers are illustrated by the block diagram of  FIG. 5   
       FIG. 5  is a block diagram  500  illustrating the timing of channels according to aspects of the present disclosure. The block diagram  500  shows a broadcast control channel (BCCH)  502 , a common control channel (CCCH)  504 , a frequency correction channel (FCCH)  506 , a synchronization channel (SCH)  508  and an idle time slot  510 . The numbers at the bottom of the block diagram  500  indicate various moments in time. In one configuration, the numbers at the bottom of the block diagram  500  are in seconds. In one configuration, each block of a FCCH  506  may include eight time slots, with only the first timeslot (or TS0) used for FCCH tone detection. 
     The timing of the channels shown in the block diagram  500  may be determined in a BSIC identification procedure. The BSIC identification procedure may include detection of the FCCH carrier  506 , based on a fixed bit sequence that is carried on the FCCH  506 . FCCH tone detection is performed to find the relative timing between multiple RATs. The FCCH tone detection may be based on the SCH  508  being either a first number of frames or a second number of frames later in time than the FCCH  506 . The first number of frames may be equal to 11+n·10 frames and the second number of frames may be equal to 12+n·10 frames. The dot operator represents multiplication and n can be any positive number. These equations are used to schedule idle time slots to decode the SCH. The first number of frames and the second number of frames may be used to schedule idle time slots in order to decode the SCH  508 , in case the SCH  508  falls into a measurement gap or an idle time slot  510 . 
     For FCCH tone detection in an inter RAT measurement, the FCCH may fully or partially fall within the idle time slots of the first RAT (not shown). The UE attempts to detect FCCH tones (for example, such as the FCCH  506 ) on the BCCH carrier of the n strongest BCCH carriers of the cells in the second RAT. The strongest cells in the second RAT may be indicated by a measurement control message. In one configuration, n is eight and the n BCCH carriers are ranked in order of the signal strength. For example, a BCCH carrier may be ranked higher than other BCCH carriers when the signal strength of the BCCH carrier is stronger than the signal strength of the other BCCH carriers. The top ranked BCCH carrier may be prioritized for FCCH tone detection. 
     Each BCCH carrier may be associated with a neighbor cell in the second RAT. In some instances, the UE receives a neighbor cell list including n ranked neighbor cells from a base station of the first RAT, for example, in a measurement control message. The neighbor cells in the neighbor cell list may be ranked according to signal strength. In some configurations, the n ranked neighbor cells may correspond to the n strongest BCCH carriers, such that system acquisition of the neighbor cells includes FCCH tone detection of these BCCH carriers. 
     FCCH tone detection attempts are prioritized by the UE based on decreasing signal strength. The strongest BCCH carrier is defined as the BCCH carrier having the highest measured RSSI value after layer 3 (or network layer) filtering. The signal strength levels used in BSIC identification for arranging cells of the second RAT in decreasing signal strength order may be based on the latest carrier signal strength measurement results available for the second RAT. When the FCCH tone of a BCCH carrier of the second RAT is successfully detected, the UE immediately continues with the next BCCH carrier, in decreasing signal strength order. As a result, an unknown FCCH tone sometime in the future becomes the next detected FCCH tone. 
     In current implementations, the UE performs FCCH tone detection attempts for a next BCCH carrier in signal strength order only when the UE successfully detects an FCCH tone, or aborts the FCCH tone detection attempt after a fixed time duration. In one configuration, if the UE has not successfully detected the FCCH tone of the BCCH carrier within the fixed time (e.g., equal to 1.5 seconds), the UE aborts the FCCH tone detection attempt. The UE may then attempt to perform FCCH tone detection for the next BCCH carrier in signal strength order. Thus, tone detection is performed on a first frequency or first cell for a fixed amount of time before moving on to perform tone detection for the second frequency or second cell, the third frequency or third cell and so on. The BCCH carrier of the second RAT for which the FCCH tone detection attempts failed may be reconsidered after the FCCH tone detection attempts for the rest of the n strongest BCCH carriers of the second RAT. 
     In one configuration, the first RAT may be Time Division-Code Division Multiple Access (TD-SCDMA) and the second RAT may be Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE) or GSM EDGE Radio Access Network (GERAN). 
     During detection of an FCCH tone for the top ranked BCCH carrier, the signal strength of the top ranked BCCH carrier and/or the rest of the n BCCH carriers may change. For example, the signal strength of one or more of the n BCCH carriers may be increased or decreased due to mobility of the UE or changes in the radio frequency of the neighbor cells. The change in the signal strength of one or more of the n BCCH carriers may cause a change in the signal strength order of the n BCCH carriers. For example, the signal strength of the current top ranked BCCH carrier may be reduced below the signal strength of one or more of the other BCCH carriers. As a result, the signal strength order of the n BCCH carriers is changed. 
     In current implementations, the UE continues to attempt to detect FCCH tones for the current top ranked BCCH carrier, even though the signal strength of the current top ranked BCCH carrier is reduced below the signal strength of one or more of the other BCCH carriers. The UE stops attempting to detect FCCH tones for the current top ranked BCCH carrier only when the fixed time expires. Performing tone detection on the current top ranked BCCH carrier until the fixed time expires, results in a delay in FCCH tone detection for stronger BCCH carriers, which may result in IRAT handover failure. 
     Aspects of the present disclosure mitigate delays during system acquisition of neighbor cells, including FCCH tone detection of BCCH carriers, when an IRAT measurement condition changes. For example, a change in the IRAT measurement condition includes a change in the signal strength of one or more of the n BCCH carriers. The change in the IRAT measurement condition may cause an adjustment in the signal strength order of the n BCCH carriers. For example, a top ranked BCCH carrier may be replaced with a different BCCH carrier with a stronger signal strength. 
     In some aspects of the disclosure, during ongoing FCCH tone detection of the top ranked BCCH carrier, the FCCH tone detection may be suspended when an IRAT measurement conditions changes. For example, the FCCH tone detection of the top ranked BCCH carrier is suspended when the signal strength of the top ranked BCCH carrier falls below a signal strength of one or more other BCCH carriers. 
     In some aspects of the disclosure, the suspension of the FCCH tone detection of the top ranked BCCH carrier may be based on the change in the IRAT measurement condition and/or on a threshold operation. For example, the FCCH tone detection is suspended when the IRAT measurement condition changes and when the signal strength of the one or more BCCH carriers is above a network indicated threshold for sending a measurement report, and/or a UE internal predefined threshold. Further, the FCCH tone detection is suspended when the IRAT measurement condition changes and when a difference in signal strength between the top ranked BCCH carrier and another BCCH carrier is above a predefined threshold and maintained for a predefined time period. After the suspension, the UE may start FCCH tone detection for another BCCH carrier that is elevated to a top ranked status based on the signal strength. For example, the BCCH carrier with the strongest signal strength may be elevated to the top ranked status. 
     In some aspects of the disclosure, measurement information acquired prior to the suspension may be stored by the UE. The stored measurement information may include automatic gain control (AGC) information, coarse frequency information, coarse timing information, elapsed time and other system acquisition information. The UE may resume FCCH tone detection of the previous top ranked BCCH carrier using the stored measurement information. In this case, the FCCH tone detection for the previous top ranked BCCH carrier resumes from a time of the suspension, instead of starting a new FCCH tone detection. In one aspect of the disclosure, resuming the FCCH tone detection of the previous top ranked BCCH carrier may occur after successfully completing, suspending or aborting the FCCH detection of the elevated BCCH carrier. 
     Aspects of the present disclosure efficiently uses idle time slots for FCCH tone detection, thereby speeding up IRAT measurement procedures. The efficient use results in better IRAT handover performance as well. 
       FIG. 6  illustrates a wireless communication method  600  according to one aspect of the present disclosure. A UE starts a system acquisition for a first Global System for Mobile Communications (GSM) cell, as shown in block  602 . For example, the system acquisition for the first GSM cell may include FCCH tone detection for a BCCH carrier of the first GSM cell. The UE suspends the system acquisition of the first GSM cell when an IRAT measurement condition occurs, as shown in block  604 . The UE then stores the information that had been acquired for the FCCH tone, prior to suspending, as shown in block  606 . For example, a change in the IRAT measurement condition includes a change in the signal strength of one or more of the n BCCH carriers. As noted, the change in the IRAT measurement condition may cause a change in the signal strength order of the n BCCH carriers. The UE starts a system acquisition for a second GSM cell, as shown in block  608 . After completing the attempt to acquire the second GSM cell, the UE resumes the system acquisition of the first GSM cell using the stored information, as shown in block  610 . 
       FIG. 7  is a diagram illustrating an example of a hardware implementation for an apparatus  700  employing a tone detection system  714 . The tone detection system  714  may be implemented with a bus architecture, represented generally by the bus  724 . The bus  724  may include any number of interconnecting buses and bridges depending on the specific application of the tone detection system  714  and the overall design constraints. The bus  724  links together various circuits including one or more processors and/or hardware modules, represented by the processor  722 , a starting module  702 , a suspending module  704 , a storing module  708 , a resuming module  706 , and the computer-readable medium  726 . The bus  724  may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. 
     The apparatus includes a tone detection system  714  coupled to a transceiver  730 . The transceiver  730  is coupled to one or more antennas  720 . The transceiver  730  enables communicating with various other devices over a transmission medium. The tone detection system  714  includes a processor  722  coupled to a computer-readable medium  726 . The processor  722  is responsible for general processing, including the execution of software stored on the computer-readable medium  726 . The software, when executed by the processor  722 , causes the tone detection system  714  to perform the various functions described for any particular apparatus. The computer-readable medium  726  may also be used for storing data that is manipulated by the processor  722  when executing software. 
     The tone detection system  714  includes a starting module  702  for starting a system acquisition for a first and second GSM cells. The tone detection system  714  also includes a suspending module  704  for suspending the system acquisition of the first GSM cell when a condition occurs. The tone detection system  714  also includes a storing module  708  for storing the information acquired during the suspended attempt. The tone detection system  714  also includes a resuming module  706  for resuming the system acquisition of the first GSM cell using the stored information. The modules may be software modules running in the processor  722 , resident/stored in the computer-readable medium  726 , one or more hardware modules coupled to the processor  722 , or some combination thereof. The tone detection system  714  may be a component of the UE  350  and may include the memory  392 , and/or the controller/processor  390 . 
     In one configuration, an apparatus such as a UE is configured for wireless communication including means for starting. In one aspect, the above means may be the antenna  352 / 720 , the transceiver  730 , the receiver  354 , the channel processor  394 , the receive processor  370 , the controller/processor  390 , the memory  392 , the tone detection module  391 , the starting module  702 , the processor  722 , and/or the tone detection system  714  configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions recited by the aforementioned means. 
     In one configuration, an apparatus such as a UE is configured for wireless communication including means for suspending. In one aspect, the above means may be the controller/processor  390 , the memory  392 , the tone detection module  391 , the suspending module  704 , the processor  722 , and/or the tone detection system  714  configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions recited by the aforementioned means. 
     In one configuration, an apparatus such as a UE is configured for wireless communication including means for storing. In one aspect, the above means may be the controller/processor  390 , the memory  392 , storing module  708 , the computer readable medium  726 , the processor  722 , and/or the tone detection system  714  configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions recited by the aforementioned means. 
     In one configuration, an apparatus such as a UE is configured for wireless communication including means for resuming. In one aspect, the above means may be the antenna  352 / 720 , the transceiver  730 , the receiver  354 , the channel processor  394 , the receive processor  370 , the controller/processor  390 , the memory  392 , the tone detection module  391 , the resuming module  706 , the processor  722 , and/or the tone detection system  714  configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions recited by the aforementioned means. 
     Several aspects of a telecommunications system has been presented with reference to TD-SCDMA and GSM systems. As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other telecommunication systems, network architectures and communication standards. By way of example, various aspects may be extended to other UMTS systems such as W-CDMA, High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), High Speed Packet Access Plus (HSPA+) and TD-CDMA. Various aspects may also be extended to systems employing Long Term Evolution (LTE) (in FDD, TDD, or both modes), LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000, Evolution-Data Optimized (EV-DO), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra-Wideband (UWB), Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system. 
     Several processors have been described in connection with various apparatuses and methods. These processors may be implemented using electronic hardware, computer software, or any combination thereof. Whether such processors are implemented as hardware or software will depend upon the particular application and overall design constraints imposed on the system. By way of example, a processor, any portion of a processor, or any combination of processors presented in this disclosure may be implemented with a microprocessor, microcontroller, digital signal processor (DSP), a field-programmable gate array (FPGA), a programmable logic device (PLD), a state machine, gated logic, discrete hardware circuits, and other suitable processing components configured to perform the various functions described throughout this disclosure. The functionality of a processor, any portion of a processor, or any combination of processors presented in this disclosure may be implemented with software being executed by a microprocessor, microcontroller, DSP, or other suitable platform. 
     Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a computer-readable medium. A computer-readable medium may include, by way of example, memory such as a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., compact disc (CD), digital versatile disc (DVD)), a smart card, a flash memory device (e.g., card, stick, key drive), random access memory (RAM), read only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), a register, or a removable disk. Although memory is shown separate from the processors in the various aspects presented throughout this disclosure, the memory may be internal to the processors (e.g., cache or register). 
     Computer-readable media may be embodied in a computer-program product. By way of example, a computer-program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system. 
     It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”