Patent Publication Number: US-9907092-B2

Title: Uplink synchronization without preamble in SC-FDMA

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application Ser. No. 62/062,106, entitled “UPLINK SYNCHRONIZATION WITHOUT PREAMBLE IN SC-FDMA,” and filed on Oct. 9, 2014, which is expressly incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates generally to communication systems, and more particularly, to performing uplink synchronization without a preamble in single-carrier (SC) frequency division multiple access (FDMA) (SC-FDMA). 
     Background 
     Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems. 
     These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). LTE is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies. 
     SUMMARY 
     In an aspect of the disclosure, a method, a computer program product, and an apparatus are provided. The apparatus may be a UE. The apparatus determines an allocated set of resources within a physical random access channel (PRACH) period. The apparatus transmits pilot signals in the determined allocated set of resources. 
     Another aspect of the disclosure provides an apparatus for wireless communication that includes means for determining an allocated set of resources within a PRACH period. The apparatus includes means for transmitting pilot signals in the determined allocated set of resources. The PRACH period has a set of slots, in which each slot in the set of slots includes a set symbols, and each symbol in each set of symbols includes a set of tones. The means for determining the allocated set of resources is configured to determine a subset of slots within the set of slots in the PRACH period for transmitting the pilot signals, in which the subset of slots includes a set of even number indexed slots and a set of odd number indexed slots, to determine a first set of tone indices in the set of even number indexed slots for transmitting a first set of pilot signals, and to determine a second set of tone indices in the set of odd number indexed slots for transmitting a second set of pilot signals, in which the second set of tone indices is based on the first set of tone indices and an offset value. The means for determining the allocated set of resources is configured to determine a subset of symbols within each slot in the subset of slots in the PRACH period for transmitting the pilot signals, in which the subset of symbols within each slot is greater than or equal to 2. The first set of pilot signals has at least two pilot signals, and the second set of pilot signals has at least two pilot signals. The apparatus further includes means for transmitting information in the determined allocated set of resources, in which the information includes at least one of an identifier, control information, or a pathloss report. 
     Another aspect of the disclosure provides a computer program product stored on a computer-readable medium and the computer program product includes code that when executed on at least one processor causes the at least one processor to determine an allocated set of resources within a PRACH period and to transmit pilot signals in the determined allocated set of resources. The PRACH period has a set of slots, in which each slot in the set of slots includes a set symbols, and each symbol in each set of symbols includes a set of tones. The determining the allocated set of resources includes determining a subset of slots within the set of slots in the PRACH period for transmitting the pilot signals, in which the subset of slots includes a set of even number indexed slots and a set of odd number indexed slots, determining a first set of tone indices in the set of even number indexed slots for transmitting a first set of pilot signals, and determining a second set of tone indices in the set of odd number indexed slots for transmitting a second set of pilot signals, in which the second set of tone indices is based on the first set of tone indices and an offset value. The determining the allocated set of resources further includes determining a subset of symbols within each slot in the subset of slots in the PRACH period for transmitting the pilot signals, in which the subset of symbols within each slot is greater than or equal to 2. The first set of pilot signals has at least two pilot signals, and the second set of pilot signals has at least two pilot signals. The computer program product further includes code that when executed on the at least one processor causes the at least one processor to transmit information in the determined allocated set of resources. The information includes at least one of an identifier, control information, or a pathloss report. 
     In another aspect of the disclosure, a method, a computer program product, and an apparatus are provided. The apparatus may be a wireless device (e.g., a base station). The apparatus receives a data transmission from a user equipment (UE). The apparatus determines a channel phase offset based on the received data transmission. The apparatus determines a timing offset based on the determined channel phase offset. The apparatus transmits an acknowledgment message to the UE. The acknowledgment message includes the determined timing offset. 
     Another aspect of the disclosure provides an apparatus for wireless communication that includes means for receiving a data transmission from a UE, means for determining a channel phase offset based on the received data transmission, means for determining a timing offset based on the determined channel phase offset, and means for transmitting an acknowledgment message to the UE. The acknowledgment message includes the determined timing offset. The data transmission is received in an allocated set of resources within a PRACH period. The data transmission includes pilot signals, and the pilot signals are received in a first set of tone indices and a second set of tone indices, the first set of tone indices being associated with a set of even number indexed slots of the PRACH period and the second set of tone indices being associated with a set of odd number indexed slots of the PRACH period. The second set of tone indices is based on the first set of tone indices and an offset value. The data transmission further includes at least one of an identifier, control information, or a pathloss report. The means for determining the channel phase offset is configured to determine a first channel phase offset based on the received data transmission and to determine a second channel phase offset based on the received data transmission, and the means for determining the timing offset is configured to determine the timing offset based on the first channel phase offset and the second channel phase offset. 
     Another aspect of the disclosure provides a computer program product stored on a computer-readable medium. The computer program product includes code that when executed on at least one processor causes the at least one processor to receive a data transmission from a UE, to determine a channel phase offset based on the received data transmission, to determine a timing offset based on the determined channel phase offset, and to transmit an acknowledgment message to the UE. The acknowledgment message includes the determined timing offset. The data transmission is received in an allocated set of resources within a PRACH period. The data transmission includes pilot signals, and the pilot signals are received in a first set of tone indices and a second set of tone indices, in which the first set of tone indices is associated with a set of even number indexed slots of the PRACH period and the second set of tone indices is associated with a set of odd number indexed slots of the PRACH period. The second set of tone indices is based on the first set of tone indices and an offset value. The data transmission further includes at least one of an identifier, control information, or a pathloss report. The determining the channel phase offset includes determining a first channel phase offset based on the received data transmission and determining a second channel phase offset based on the received data transmission. The determining the timing offset includes determining the timing offset based on the first channel phase offset and the second channel phase offset. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a wireless communications system. 
         FIG. 2  illustrates a diagram of a PRACH period and a diagram of a method for utilizing a PRACH period for uplink synchronization in SC-FDMA. 
         FIG. 3  is a diagram of a physical PRACH channel mapping. 
         FIG. 4  is a flow chart of a method of wireless communication for uplink synchronization without using a preamble. 
         FIG. 5  is a flow chart of a method of wireless communication for determining a timing advance in uplink synchronization without using a preamble. 
         FIG. 6  is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus. 
         FIG. 7  is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system. 
         FIG. 8  is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus. 
         FIG. 9  is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system. 
     
    
    
     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 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 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. 
     Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. 
     By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. 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. 
     Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), compact disk ROM (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Combinations of the above should also be included within the scope of computer-readable media. 
       FIG. 1  is a diagram of a wireless communications system  100 . The wireless communications system  100  includes a number of wireless devices. The wireless communications system  100  may overlap with a cellular communications system, such as for example, a wireless wide area network (WWAN). In  FIG. 1 , a UE  104  may transmit a first information  106  in an uplink (UL) transmission to a base station  102  (e.g., an eNodeB (eNB)). The base station  102  may transmit a second information  108  to the UE  104  in a downlink (DL) transmission. Although  FIG. 1  illustrates three UEs (e.g., the UEs  104 ,  110 ,  112 ), more or less UEs may be present. 
     In wireless communications systems with single-carrier frequency division multiple access (SC-FDMA) uplink (UL), a cyclic prefix (CP) may be added before an SC-FDMA symbol to ensure orthogonality among signals. For minimal overhead, the CP length is typically set to be the maximum time dispersion of the channels without considering the difference in roundtrip delay, which may be significant in cellular systems. As such, a UE may need to know its roundtrip delay and adjust its transmission time accordingly before the UE may start normal uplink data transmission. The process of timing acquisition and adjustment for UL transmission is known as UL synchronization. In LTE, initial UL synchronization may be done by using a preamble signal specifically designed for timing estimation. Before any other uplink transmission, a UE may send a preamble signal to a base station, which the base station uses to estimate the roundtrip delay of the UE and to send the corresponding time advance command to the UE. UL synchronization using preambles, however, increases the air time of a UE, which may be undesirable for applications where the power consumption of UEs is critical, such as in Cellular Internet of Things (CIOT). Additionally, preamble signals often interfere with other signals due to asynchronous transmission. To avoid large interference, guard bands in frequency may be required. As such, a need exists to perform uplink synchronization without using a preamble in SC-FDMA. 
     Instead of specifically transmitting a preamble signal, a UE may start an UL connection directly with an initial signal, which may include pilot signals, data signals, and any other useful signals, in a designated time-frequency resource. Pilot signals may be known reference signals used by a receiver device (e.g., a base station) to perform channel estimation. Data signals may include UE identification information, control information, resource allocation request, a pathloss report, and other information that may be used for subsequent communications. To reduce overhead, the initial signaling may carry a small amount of data (e.g., 48 bits or less than 100 bits). UL synchronization may be achieved by using specially arranged pilot signals inserted into the initial signal. The initial signal may be known as a physical random access channel (PRACH) signal, in which the PRACH may be used by a UE to request dedicated resources for uplink/downlink data transfer. The time period for transmitting a PRACH signal by a UE may be known as a PRACH period. A PRACH period may be a designated time period and may include a number of symbols used for transmitting data and pilot signals. The symbols used for transmission during the PRACH period may have an extended CP (e.g., 16.7 μs or 33.3 μs), whose duration is long enough to account for channel dispersion and roundtrip delay. For every kilometer of the cell radius, for example, a roundtrip delay may be 6.7 μs. If the PRACH period allowed for transmitting PRACH signals is small, then the overall overhead due to using extended CP may be small. 
     For purposes of timing estimation, a PRACH period may be divided into a number of L slots (e.g., 20 slots), and each slot may have S symbols (e.g. 10 symbols). As such, each PRACH period may have L×S SC-FDMA symbols. The numbers L and S may be selected based upon values that would support successful timing estimation and PRACH data communication for the largest channel path loss. Within a slot, the number of pilot signals, P, may be greater than or equal to 2. For example, assuming a slot has a minimum of 2 symbols, and one tone is allocated for pilot signal transmission in the slot, then the slot will have 2 pilot signals, 1 pilot signal for each symbol on the same allocated tone. In another example, a slot may have 10 symbols total, 2 symbols may be used for pilot signal transmission and 8 symbols for data signal transmission. If a slot has more than 1 tone allocated for pilot signal transmission, then the tones may be evenly distributed within the symbol. Within the L slots, numbered with indices 0, 1, . . . L−1, a logical (or virtual) tone index is introduced that maps to a physical tone index depending on whether the slot is an even number indexed slot or an odd number indexed slot. Logical tone index m may refer to a physical tone index m at even number indexed slots (e.g., 0, 2, 4, . . . ) and (m+g) (mod N) or mod(m+g,N) at odd number indexed slots (e.g., 1, 3, 5, . . . ), in which N is a total number of tones available in a symbol (or available in a symbol not including guard tones and DC tones) and g is a predetermined offset or hop. In an aspect, a pilot signal may hop from tone index to tone index depending whether the pilot signal is being transmitted on an even or odd number indexed slot. In one aspect, if N is the total number of tones available in a symbol, all signals (data signals and pilot signals) transmitted in the PRACH period may hop from one tone index to another tone index. In another aspect, N may represent the total number of tones available to transmit PRACH signals. 
     A PRACH channel or a data channel may be assigned a number of logical tones within each PRACH period. That is, all signal transmissions hop g tones at the beginning of each odd number indexed slot. At slot 0, and any other even number indexed slots, logical tone indices may be the same as the physical tone indices. The value of g may be chosen to be the largest number such that the PRACH channel is constant (or nearly constant) within a frequency range of g tones and is also smaller than the ratio of symbol duration over the maximum roundtrip delay to avoid phase ambiguity. For example, g may be equal to 4, 6, or 8. 
     Within each PRACH period, the total resources allocated for PRACH may be further divided in a number of PRACH resource blocks, and the PRACH resource blocks may be of different sizes. Each PRACH resource block may consist of an even number of contiguous slots and start from an even-numbered slot (e.g., slot 0, slot 2, slot 4). A UE may randomly choose a PRACH resource block of appropriate size for PRACH transmission. A PRACH resource block may be assigned a number of tones (e.g., logical tones) for pilot and data signal transmission and include at least two slots. 
       FIG. 2  illustrates a diagram  200  of a PRACH period and a diagram  250  of a method for utilizing a PRACH period for uplink synchronization in SC-FDMA. As shown in  FIG. 2 , a PRACH period  210  may have 8 slots with slot indices 0-7. Each slot may have 4 symbols  212  (or some other number of symbols greater than or equal to 2). In one configuration, two or more contiguous slots (e.g., slot 0, slot 1) may be grouped into a PRACH resource block  220 . In an aspect, a symbol may have 80 tones with tone indices 0 to 79 (or another number of tones such as 128 or 256). In another configuration, the PRACH period  210  may have at least 2 slots, and each slot may have at least 2 symbols. The PRACH period  210  may be preconfigured within a base station  202  and/or one or more UEs  204 ,  230 . The base station  202  and/or one or more UEs  204 ,  230  may receive configuration information indicating when the PRACH period  210  will occur. For example, the UE  204  may receive configuration information from the base station  202 , which may receive the configuration information from another network entity. 
     In one example, the UE  204  may select the PRACH resource block  220  with two slots, each slot having 4 symbols. Assuming the total number of available tones in each symbol is 80 (e.g., i=0, . . . , 79) and a offset value/hopping distance is equal to 4 (g=4) and the PRACH resource block  220  is allocated 1 tone, such as logical tone index 3, and 2 slots, each assigned one tone index for pilot signal transmission, the UE may transmit a pilot signal at physical tone index 3 at slot 0, and transmit a pilot signal at physical tone index 7 at slot 1. In another example, if the PRACH resource block  220  has 4 allocated slots and 1 tone index such as logical tone index 3 allocated for transmission of pilot signals, then the pilot signals maybe transmitted at physical tone index 3 at slot 0, physical tone index 7 at slot 1, physical tone index 3 at slot 2, and physical tone index 7 at slot 3. Similarly, in another example, assuming g=4, if the PRACH resource block  220  has 2 logical tone indices 18 and 19 and slots 4 to 7, then pilot signals may be transmitted on physical tone indices 18 and 19 at slot 4, physical tone indices 22 and 23 at slot 5, physical tone indices 18 and 19 at slot 6, and physical tone indices 22 and 23 at slot 7. In an aspect, when more than one tone index per slot is allocated for the transmitting pilot signals, a UE may transmit pilot signals on a subset of allocated tone indices. For example, if 6 tone indices are allocated per slot, a UE may transmit pilot signals on one or more of the 6 allocated tone indices. 
     In another example, if PRACH resource blocks  220  within a PRACH period  210  have different sizes, the UE  204 , closer to the base station  202  compared to the UE  230 , may select a smaller PRACH resource block (e.g., 2 slots) and transmit data signals with a higher-order modulation (e.g., pilot signals may be known BPSK signals and data signals may use different modulation schemes depending on a channel condition). A UE  230  further away from the base station  202  may select a larger PRACH resource block (4 or more slots) and transmit data signals with a lower-order modulation. In an aspect, the UE  230  may listen to a broadcast channel of the base station  202 , which may include PRACH resource allocation information. In this aspect, the UE  230  may measure channel conditions while performing downlink synchronization with the base station  202 . The UE  230  may select a PRACH resource block based on the received PRACH resource allocation information and the measured channel conditions. 
     Referring to diagram  250  in  FIG. 2 , the UE  204  may determine an allocated set of resources within the PRACH period  210 . The allocated set of resources may be a set of slots, and each slot may include a set of symbols, and each symbol may include a set of tones. In another configuration, the allocated set of resources may be a PRACH resource block  220  that includes a set of slots. In an aspect, the UE  204  may randomly select an allocated set of resources for PRACH transmission. In another aspect, the UE  204  may select an allocated set of resources whose size is appropriate for PRACH transmission based on a measured channel condition. In another aspect, the UE  204  may determine the allocated set of resources based on a preconfigured setting (e.g., based on a UE identifier). The allocated set of resources may be (or have) a subset of slots, and the subset of slots may include a set of even number indexed slots and a set of odd number indexed slots. For example, an allocated set of resources may have 2 slots with slot index 0 and slot index 1. The UE  204  may determine that a set of logical tone indices has been allocated for slots. For example, if logical tone indices 3 and 6 have been allocated, then for the even number indexed slots (e.g., slot 0), the UE  204  may determine a first set of physical tone indices (e.g., tone indices 3 and 6) for transmitting a first set of pilot signals. For the odd number indexed slots, the UE  204  may determine a second set of physical tone indices for transmitting a second set of pilot signals. The second set of physical tone indices may be determined based on the first set of tone indices plus the offset value, g. In an example, if the first set of physical (or logical) tone indices is 3 and 6, assuming g=4, the second set of physical tone indices is 7 and 10. Although an example with 2 tone indices per set of tone indices is provided, there may be 1 or more than 1 tone index per set of tone indices. Having determined the tone indices and the symbols within the slots on which to transmit the pilot signals, the UE  204  may transmit 206 the pilot signals in the determined allocated set of tone indices in the respective symbols to the base station  202 . The base station  202  may receive the data transmission from the UE  204 . Based on the data transmission from the UE  204 , the base station  202  may determine a channel phase offset. In one configuration, the base station  202  may determine a channel phase offset between channels seen at the same frequency/tone but at different chosen times. In this configuration, the base station  202  may determine a timing offset based on the determined phase offset. 
     In another configuration, the base station  202  may determine a first channel phase offset between channels seen at the same frequency/tone but at different chosen times and determine a second channel phase offset between channels seen at two tones with a chosen offset but close in time. In this configuration, the base station  202  may determine the timing configuration based on the first determined channel phase offset and the second determined channel phase offset. For example, the UE  204  may transmit pilot signals on slots 0 and 1. In slot 0, pilot signals may be transmitted on physical tone index 3 of symbols 0 and 2. Assuming an offset value, g=4, at slot 1, the UE  204  may transmit pilot signals at slot 1 on physical tone indices 7 of symbols 0 and 2. Upon receiving these pilot signals, the base station  202  may determine a first channel phase offset between the pilot signals at physical tone index 3 of symbol 0 in slot 0 and at physical tone index 3 of symbol 2 in slot 0, and between the pilot signals at physical tone index 7 of symbol 0 in slot 1 and at physical tone index 7 of symbol 2 in slot 1. The base station  202  may determine a second channel phase offset between the pilot signals at physical tone index 3 of symbol 0 in slot 0 and at physical tone index 7 of symbol 0 in slot 1 and also between the pilot signals at physical tone index 3 of symbol 2 in slot 0 and at physical tone index 7 of symbol 2 in slot 1. The base station  202  may then determine a timing offset based on the first and the second channel phase offsets. 
     Having determined the timing offset, the base station  202  may transmit an acknowledgment message  208  to the UE  204 . The acknowledgment message  208  may include the determined timing offset (or timing advance), and may also include resource allocation information. 
     For example, with respect to the base station  202 , consider a PRACH block with K tones and 2T (T&gt;0) slots. The base station  202 , upon receiving a transmission  206  from the UE  204  that includes pilot signals, may perform a Fast Fourier Transform (FFT) followed by a K-point Inverse Discrete Fourier Transform (IDFT) at the corresponding tone locations to obtain signal y(t,k) for symbol t=0, 1, . . . , 2TS-1 and tone k (k=0, 1, . . . , K−1), where S corresponds to the number of symbols in a slot. For pilot signals, the corresponding outputs of the IDFT signals y(t,k) may be further multiplied by the complex conjugates of the pilot signals to obtain r(t,k). In r(t,k), t may correspond to symbols with pilot signals. 
     The base station  202  may first estimate the channel phase offset between two neighboring pilots in time due to any residual frequency offset. When the pilot signals within a slot are equally spaced in time, the base station  202  may collect the received signals, r(t,k), corresponding to P symbols with pilot signals, 0, 1, . . . P−2 within each slot and then each tone location sequentially into a column vector x and similarly, collect signals corresponding to pilot symbols 1, 2, . . . , P−1 into another column vector y, both x and y have 2(P−1)TK entries. Accordingly, the phase offset may be estimated as β=angle(x h y), where the superscript h stands for the Hermitian transpose. For example, in slot 0, assume there are 3 pilot signals (e.g., P 0 , P 1 , P 2 ). All three pilot signals should go through the same channel (assuming the channel stays constant during a slot). Any differences in the corresponding channel estimates on each of the pilot signals (e.g., between P 0  and P 1 , or between P 1  and P 2 ) may be frequency offset, which may be used to determine a phase offset. 
     Once the phase offset due to frequency offset is estimated, the timing may be estimated from the channel phase offset between two pilot signals that are different in physical tone location by g, but close in time (e.g., slot 0 and slot 1). In this case, the channel may be assumed to be nearly constant with the duration of 2 slots. All the pilot signals in the even-number indexed slots may be collected into a column vector w and all the pilot signals in the odd-number indexed slots may be collected into a column vector v in the same order. Both vectors w and v may have KPT entries. The timing offset (or timing of arrival) may be estimated with the following equation: 
     
       
         
           
             t 
             = 
             
               
                 - 
                 1 
               
               × 
               
                 angle 
                 ⁡ 
                 
                   [ 
                   
                     
                       w 
                       h 
                     
                     ⁢ 
                     
                       ve 
                       
                         - 
                         
                           
                             j 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             β 
                             ⁢ 
                             
                                 
                             
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                             S 
                           
                           D 
                         
                       
                     
                   
                   ] 
                 
               
               ⁢ 
               
                 
                   N 
                   fft 
                 
                 / 
                 
                   ( 
                   
                     2 
                     ⁢ 
                     π 
                     ⁢ 
                     
                         
                     
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                     g 
                   
                   ) 
                 
               
             
           
         
       
     
     In the equation above, N fft  is the FFT size, D may be the spacing between two pilot signals, and S may be the number of symbols per slot. 
       FIG. 3  is a diagram  300  of a physical PRACH channel mapping. As shown in  FIG. 3 , a PRACH may be next to the physical uplink shared channel (PUSCH) and the physical uplink control channel (PUCCH). A PRACH may occur in every frame or may occur periodically in certain designated frames. In this example, a PRACH has 24 contiguous slots. Each symbol in a slot is assigned K tones for purposes of PRACH signaling, and 80 (or some other value) may be the total number of usable tones or tone indices in a symbol (not including DC tones, guard tones, etc.) In another aspect, the number of tones, K, assigned for purposes of PRACH signaling may be equal to the total number of usable tones in a symbol. 
       FIG. 4  is a flow chart  400  of a method of wireless communication for uplink synchronization without using a preamble. The method may be performed by a UE (e.g., the UEs  104 ,  204 ). At step  402 , the UE may determine an allocated set of resources within a PRACH period. The PRACH period may have a set of slots, and each slot in the set of slots may include a set symbols, and each symbol in each set of symbols may include a set of tones. In an aspect, the UE may determine the allocated set of resources within the PRACH period by performing steps  404 - 408 . At step  404 , the UE may determine a subset of slots within the set of slots in the PRACH period for transmitting the pilot signals. The subset of slots may include a set of even number indexed slots and a set of odd number indexed slots. At step  406 , the UE may determine a first set of tone indices in the set of even number indexed slots for transmitting a first set of pilot signals. At step  408 , the UE may determine a second set of tone indices in the set of odd number indexed slots for transmitting a second set of pilot signals. The second set of tone indices may be based on the first set of tone indices and an offset value. In an aspect, the first set of pilot signals may have at least two pilot signals, and the second set of pilot signals may have at least two pilot signals. For example, referring to  FIG. 2 , the UE  204  may select PRACH resource block  220  or a subset of 2 slots. In this example, the PRACH resource block  220  may have 2 slots, an even number indexed slot (slot 0) and an odd number indexed slot (slot 1). In slot 0 of the PRACH resource block  220 , tone indices 3 and 7 may be allocated for transmitting a pilot signal. Assuming an offset value of 4, in slot 1, tone indices 7 and 11 may be allocated for transmitting a pilot signal. As such, the first set of pilot signals may be transmitted on tone indices 3 and 7, and the second set of pilot signals may be transmitted on tone indices 7 and 11. 
     At step  410 , having determined the allocated set of resources with the PRACH period, the UE may transmit pilot signals in the determined allocated set of resources. For example, referring to  FIG. 2 , the UE  204  may transmit pilot signals in slot 0 on tone indices 3 and 7, and in slot 1 on tone indices 7 and 11. 
     At step  412 , the UE may transmit information in the determined allocated set of resources. The information may include at least one of an identifier, control information, or a pathloss report. For example, referring to  FIG. 2 , the UE  204  may transmit an identifier associated with the UE  204 , a resource allocation request, and a pathloss report to the base station  202  in slots 0 and 1. 
       FIG. 5  is a flow chart  500  of a method of wireless communication for determining a timing advance in uplink synchronization without using a preamble. The method may be performed by an eNB (e.g., the base stations  102 ,  202 ). At step  502 , the eNB may receive a data transmission from a UE. In an aspect, the data transmission may be received on an allocated set of resources within a PRACH period. In an aspect, the data transmission includes pilot signals. The pilot signals may be received in a first set of tone indices and a second set of tone indices. The first set of tone indices may be associated with a set of even number indexed slots of the PRACH period, and the second set of tone indices may be associated with a set of odd number indexed slots of the PRACH period. The second set of tone indices may be based on the first set of tone indices and an offset value. For example, referring to  FIG. 2 , the base station  202  may receive a transmission  206  from the UE  204  within the PRACH period  210 . The transmission  206  may be received on an allocated set of resources (e.g., slots 0, 1, and 2 of the PRACH resource block  220 ) within the PRACH period  210 . Each slot may have 10 symbols of which 2 (e.g., symbol 3, symbol 7) may allocated for pilot signal transmission. Assuming logical tone index 0 has been allocated for pilot signal transmission, and the offset value is 6, the transmission  206  may include pilot signals received at slot 0, symbols 3 and 7 at tone index 0. Pilot signals may be received at slot 1, symbols 3 and 7 at tone index 6, and pilot signals may be received at slot 2, symbols 3 and 7, at tone index 0. The transmission  206  may include an identifier associated with the UE  204 , control information (e.g., resource allocation request), and a pathloss report. 
     At step  504 , the eNB may determine a channel phase offset based on the received data transmission. In one configuration, the eNB may determine a channel phase offset by performing the steps  506  and  508 . At step  506 , the eNB may determine a first channel phase offset based on the received data transmission. At step  508 , the eNB may determine a second channel phase offset based on the received data transmission. For example, the base station  202  may determine one or more first channel phase offsets. The base station  202  may determine a first channel phase offset based on the pilot signal received at slot 0, symbol 3, tone index 0 and the pilot signal received at slot 0, symbol 7, tone index 0. In another example, the base station  202  may determine a different first channel phase offset based on the pilot signal received at slot 1, symbol 3, tone index 6 and the pilot signal received at slot 1, symbol 7, tone index 6. In another example, the base station  202  may determine yet another first channel phase offset based on the pilot signal received at slot 2, symbol 3, tone index 0 and the pilot signal received at slot 0, symbol 7, tone index 0. 
     Similarly, the base station  202  may determine one or more second channel phase offsets. The base station  202  may determine a second channel phase offset based on the first channel phase offset, the pilot signal received at slot 0, symbol 3, tone index 0, and the pilot signal received at slot 1, symbol 3, tone index 6. The base station  202  may determine a different second channel phase offset based on the different first channel phase offset, the pilot signal received at slot 0, symbol 7, tone index 0, and the pilot signal received at slot 1, symbol 7, tone index 6. 
     At step  510 , the eNB may determine a timing offset based on the determined channel phase offset. In an aspect, the eNB may determine the timing offset by determining the timing offset based on the first channel phase offset and the second channel phase offset. For example, the base station  202  may determine the timing offset based on the first and second channel phase offset. 
     Finally, at step  512 , the eNB may transmit an acknowledgment message to the UE, wherein the acknowledgment message includes the determined timing offset. In an aspect, the acknowledgement message may include a resource allocation. For example, the base station  202  may transmit an acknowledgment message  208  to the UE  204 . The acknowledgment message  208  may include acknowledgement indicating that the transmission  206  (including the data and pilot signals) was successfully received from the UE  204 , the timing offset (or timing advance) determined based on the transmission  206  from the UE  204 , and a resource allocation for the UE  204 . 
       FIG. 6  is a conceptual data flow diagram  600  illustrating the data flow between different modules/means/components in an exemplary apparatus  602 . The apparatus may be a UE. The apparatus includes a reception module  604 , a synchronization module  606 , and a transmission module  608 . The reception module  604  may be configured to receive configuration information from a base station  650 , and the configuration information may indicate when a PRACH period occurs. The synchronization module  606  may be configured to determine an allocated set of resources within a PRACH period. In one configuration, the synchronization module  606  may determine the allocated set of resources based on configuration information received from the reception module  604 . The configuration information may include UE identification information and PRACH selection information. In an aspect, the PRACH period may have a set of slots, and each slot in the set of slots may include a set symbols, and each symbol in each set of symbols may include a set of tones. In this aspect, the synchronization module  606  may be configured to determine an allocated set of resources by determining a subset of slots within the set of slots in the PRACH period for transmitting the pilot signals. The subset of slots may include a set of even number indexed slots and a set of odd number indexed slots. The synchronization module  606  may be configured to determine a first set of tone indices in the set of even number indexed slots for transmitting a first set of pilot signals and determine a second set of tone indices in the set of odd number indexed slots for transmitting a second set of pilot signals. The second set of tone indices may be based on the first set of tone indices and an offset value. In another aspect, the first set of pilot signals may have at least two pilot signals, and the second set of pilot signals may have at least two pilot signals. The transmission module  608  may be configured to transmit pilot signals in the determined allocated set of resources to the base station  650 . In another configuration, the transmission module  608  may be configured to transmit information in the determined allocated set of resources to the base station  650 . The information may include at least one of an identifier, control information, or a pathloss report. 
     The apparatus may include additional modules that perform each of the blocks of the algorithm in the aforementioned flow charts of  FIG. 5 . As such, each block in the aforementioned flow charts of  FIG. 5  may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof. 
       FIG. 7  is a diagram  700  illustrating an example of a hardware implementation for an apparatus  602 ′ employing a processing system  714 . The processing 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 processing 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  704 , the modules  604 ,  606 ,  608 , and the computer-readable medium/memory  706 . 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 processing system  714  may be coupled to a transceiver  710 . The transceiver  710  is coupled to one or more antennas  720 . The transceiver  710  provides a means for communicating with various other apparatus over a transmission medium. The transceiver  710  receives a signal from the one or more antennas  720 , extracts information from the received signal, and provides the extracted information to the processing system  714 , specifically the reception module  604 . In addition, the transceiver  710  receives information from the processing system  714 , specifically the transmission module  608 , and based on the received information, generates a signal to be applied to the one or more antennas  720 . The processing system  714  includes a processor  704  coupled to a computer-readable medium/memory  706 . The processor  704  is responsible for general processing, including the execution of software stored on the computer-readable medium/memory  706 . The software, when executed by the processor  704 , causes the processing system  714  to perform the various functions described supra for any particular apparatus. The computer-readable medium/memory  706  may also be used for storing data that is manipulated by the processor  704  when executing software. The processing system further includes at least one of the modules  604 ,  606 , and  608 . The modules may be software modules running in the processor  704 , resident/stored in the computer readable medium/memory  706 , one or more hardware modules coupled to the processor  704 , or some combination thereof. 
     In one configuration, the apparatus  602 / 602 ′ for wireless communication includes means for determining an allocated set of resources within a PRACH period. The apparatus further includes means for transmitting pilot signals in the determined allocated set of resources. In an aspect, the PRACH period may have a set of slots, and each slot in the set of slots may include a set symbols, and each symbol in each set of symbols may include a set of tones. In one configuration, the means for determining an allocated set of resources may be configured to determine the allocated set of resources by determining a subset of slots within the set of slots in the PRACH period for transmitting the pilot signals, in which the subset of slots includes a set of even number indexed slots and a set of odd number indexed slots, determining a first set of tone indices in the set of even number indexed slots for transmitting a first set of pilot signals, and determining a second set of tone indices in the set of odd number indexed slots for transmitting a second set of pilot signals, in which the second set of tone indices may be based on the first set of tone indices and an offset value. In an aspect, the first set of pilot signals may have at least two pilot signals, and the second set of pilot signals may have at least two pilot signals. The apparatus may further include means for transmitting information in the determined allocated set of resources. The information may include at least one of an identifier, control information, or a pathloss report. The aforementioned means may be one or more of the aforementioned modules of the apparatus  602  and/or the processing system  714  of the apparatus  602 ′ configured to perform the functions recited by the aforementioned means. 
       FIG. 8  is a conceptual data flow diagram  800  illustrating the data flow between different modules/means/components in an exemplary apparatus  802 . The apparatus may be an eNB. The apparatus includes a reception module  804 , a phase module  806 , a timing module  808 , and a transmission module  810 . The reception module  804  may be configured to receive a data transmission from a UE  850 . The phase module  806  may be configured to determine a channel phase offset based on the received data transmission. The timing module  808  may be configured to determine a timing offset based on the determined channel phase offset. The transmission module  810  may be configured to transmit an acknowledgment message to the UE  850 . The acknowledgment message may include the determined timing offset. In an aspect, the data transmission may be received in an allocated set of resources within a PRACH period. In this aspect, the data transmission may include pilot signals, and the pilot signals may be received in a first set of tone indices and a second set of tone indices. The first set of tone indices may be associated with a set of even number indexed slots of the PRACH period, and the second set of tone indices may be associated with a set of odd number indexed slots of the PRACH period. The second set of tone indices may be based on the first set of tone indices and an offset value. In another aspect, the data transmission may include at least one of an identifier, control information, or a pathloss report. In one configuration, the phase module  806  may be configured to determine the channel phase offset by determining a first channel phase offset based on the received data transmission and determining a second channel phase offset based on the received data transmission. In this configuration, the timing module  808  may be configured to determine the timing offset by determining the timing offset based on the first channel phase offset and the second channel phase offset. 
     The apparatus may include additional modules that perform each of the blocks of the algorithm in the aforementioned flow charts of  FIG. 5 . As such, each block in the aforementioned flow charts of  FIG. 5  may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof. 
       FIG. 9  is a diagram  900  illustrating an example of a hardware implementation for an apparatus  802 ′ employing a processing system  914 . The processing system  914  may be implemented with a bus architecture, represented generally by the bus  924 . The bus  924  may include any number of interconnecting buses and bridges depending on the specific application of the processing system  914  and the overall design constraints. The bus  924  links together various circuits including one or more processors and/or hardware modules, represented by the processor  904 , the modules  804 ,  806 ,  808 ,  810 , and the computer-readable medium/memory  906 . The bus  924  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 processing system  914  may be coupled to a transceiver  910 . The transceiver  910  is coupled to one or more antennas  920 . The transceiver  910  provides a means for communicating with various other apparatus over a transmission medium. The transceiver  910  receives a signal from the one or more antennas  920 , extracts information from the received signal, and provides the extracted information to the processing system  914 , specifically the reception module  804 . In addition, the transceiver  910  receives information from the processing system  914 , specifically the transmission module  810 , and based on the received information, generates a signal to be applied to the one or more antennas  920 . The processing system  914  includes a processor  904  coupled to a computer-readable medium/memory  906 . The processor  904  is responsible for general processing, including the execution of software stored on the computer-readable medium/memory  906 . The software, when executed by the processor  904 , causes the processing system  914  to perform the various functions described supra for any particular apparatus. The computer-readable medium/memory  906  may also be used for storing data that is manipulated by the processor  904  when executing software. The processing system further includes at least one of the modules  804 ,  806 ,  808 ,  810 . The modules may be software modules running in the processor  904 , resident/stored in the computer readable medium/memory  906 , one or more hardware modules coupled to the processor  904 , or some combination thereof. 
     In one configuration, the apparatus  802 / 802 ′ for wireless communication includes means for receiving a data transmission from a UE. The apparatus may include means for determining a channel phase offset based on the received data transmission. The apparatus may include means for determining a timing offset based on the determined channel phase offset. The apparatus may include means for transmitting an acknowledgment message to the UE. The acknowledgment message may include the determined timing offset. In an aspect, the data transmission is received in an allocated set of resources within a PRACH period. In another aspect, the data transmission may include pilot signals, and the pilot signals may be received in a first set of tone indices and a second set of tone indices. The first set of tone indices may be associated with a set of even number indexed slots of the PRACH period, and the second set of tone indices may be associated with a set of odd number indexed slots of the PRACH period. The second set of tone indices may be based on the first set of tone indices and an offset value. In another aspect, the data transmission may include at least one of an identifier, control information, or a pathloss report. In one configuration, the means for determining the channel phase offset may be configured to determine a first channel phase offset based on the received data transmission and determine a second channel phase offset based on the received data transmission. In this configuration, the means for determining the timing offset may be configured to determine the timing offset based on the first channel phase offset and the second channel phase offset. The aforementioned means may be one or more of the aforementioned modules of the apparatus  802  and/or the processing system  914  of the apparatus  802 ′ configured to perform the functions recited by the aforementioned means. 
     It is understood that the specific order or hierarchy of blocks in the processes/flow charts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes/flow charts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
     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 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.” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “at least one of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C,” “at least one of A, B, and C,” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or 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 as a means plus function unless the element is expressly recited using the phrase “means for.”