Patent Publication Number: US-8537931-B2

Title: Methods and apparatus for synchronization and detection in wireless communication systems

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to wireless communication systems. More specifically, the present disclosure relates to methods and apparatus for synchronization and detection in wireless communication systems. 
     BACKGROUND 
     Wireless communication devices have become smaller and more powerful in order to meet consumer needs and to improve portability and convenience. Consumers have become dependent upon wireless communication devices such as cellular telephones, personal digital assistants (PDAs), laptop computers, and the like. Consumers have come to expect reliable service, expanded areas of coverage, and increased functionality. Wireless communication devices may be referred to as mobile stations, stations, access terminals, user terminals, terminals, subscriber units, user equipment, etc. 
     A wireless communication system may simultaneously support communication for multiple wireless communication devices. A wireless communication device may communicate with one or more base stations (which may alternatively be referred to as access points, Node Bs, etc.) via transmissions on the uplink and the downlink. The uplink (or reverse link) refers to the communication link from the wireless communication devices to the base stations, and the downlink (or forward link) refers to the communication link from the base stations to the wireless communication devices. 
     Wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems. 
     As indicated above, the present disclosure relates generally to wireless communication systems. More specifically, the present disclosure relates to methods and apparatus for synchronization and detection in wireless communication systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of a wireless communication system; 
         FIG. 2  illustrates an example of a transmitter and an example of a receiver that may be used within a wireless communication system that utilizes orthogonal frequency division multiplexing (OFDM) and orthogonal frequency divisional multiple access (OFDMA); 
         FIGS. 3A through 3D  illustrate an example of a frame structure for a wireless communication system that utilizes OFDM/OFDMA; 
         FIG. 4  illustrates an example of an OFDMA frame in time division duplex mode; 
         FIGS. 5A and 5B  illustrate examples of preamble sequences that may be defined for a wireless communication system that utilizes OFDM/OFDMA; 
         FIG. 6  shows an example of a frequency domain downlink preamble structure for a wireless communication system that utilizes OFDM/OFDMA; 
         FIG. 7  illustrates an example of a downlink frame prefix; 
         FIG. 8  illustrates an example of a synchronization and detection method that may be performed by a wireless device in a wireless communication system that utilizes OFDM/OFDMA; 
         FIG. 8A  illustrates means-plus-function blocks corresponding to the method shown in  FIG. 8 ; 
         FIGS. 9 and 9A  illustrate another example of a synchronization and detection method that may be performed by a wireless device in a wireless communication system that utilizes OFDM/OFDMA; 
         FIGS. 10 and 10A  illustrate means-plus-function blocks corresponding to the method shown in  FIGS. 9 and 9A ; 
         FIG. 11  illustrates an example of a synchronization and detection architecture for a wireless device in a wireless communication system that utilizes OFDM/OFDMA; and 
         FIG. 12  illustrates various components that may be utilized in a wireless device. 
     
    
    
     SUMMARY 
     A synchronization and detection method in a wireless device is disclosed. The method may include performing coarse detection and synchronization with respect to a received signal. The method may also include performing fine detection and synchronization for acquisition of the received signal. Results of the coarse detection and synchronization may be used for the fine detection and synchronization. The method may also include performing tracking mode processing when the acquisition of the received signal has been achieved. 
     A wireless device that performs synchronization and detection with respect to a received signal is also disclosed. The wireless device may include a coarse detection and synchronization component that performs coarse detection and synchronization with respect to a received signal. The wireless device may also include a fine detection and synchronization component that performs fine detection and synchronization for acquisition of the received signal. Results of the coarse detection and synchronization may be used for the fine detection and synchronization. The wireless device may also include a tracking mode processing component that performs tracking mode processing when the acquisition of the received signal has been achieved. 
     An apparatus that performs synchronization and detection with respect to a received signal is also disclosed. The apparatus may include means for performing coarse detection and synchronization with respect to a received signal. The apparatus may also include means for performing fine detection and synchronization for acquisition of the received signal. Results of the coarse detection and synchronization may be used for the fine detection and synchronization. The apparatus may also include means for performing tracking mode processing when the acquisition of the received signal has been achieved. 
     A computer-program product for performing synchronization and detection with respect to a received signal is also disclosed. The computer-program product may include a computer readable medium having instructions thereon. The instructions may include code for performing coarse detection and synchronization with respect to a received signal. The instructions may also include code for performing fine detection and synchronization for acquisition of the received signal. Results of the coarse detection and synchronization may be used for the fine detection and synchronization. The instructions may also include code for performing tracking mode processing when the acquisition of the received signal has been achieved. 
     DETAILED DESCRIPTION 
     The methods and apparatus of the present disclosure may be utilized in a broadband wireless communication system. The term “broadband wireless” refers to technology that provides wireless, voice, Internet, and/or data network access over a given area. 
     WiMAX, which stands for the Worldwide Interoperability for Microwave Access, is a standards-based broadband wireless technology that provides high-throughput broadband connections over long distances. There are two main applications of WiMAX today: fixed WiMAX and mobile WiMAX. Fixed WiMAX applications are point-to-multipoint, enabling broadband access to homes and businesses. Mobile WiMAX offers the full mobility of cellular networks at broadband speeds. 
     Mobile WiMAX is based on OFDM (orthogonal frequency division multiplexing) and OFDMA (orthogonal frequency division multiple access) technology. OFDM is a digital multi-carrier modulation technique that has recently found wide adoption in a variety of high-data-rate communication systems. With OFDM, a transmit bit stream is divided into multiple lower-rate sub-streams. Each sub-stream is modulated with one of multiple orthogonal sub-carriers and sent over one of a plurality of parallel sub-channels. OFDMA is a multiple access technique in which users are assigned sub-carriers in different time slots. OFDMA is a flexible multiple-access technique that can accommodate many users with widely varying applications, data rates, and quality of service requirements. 
     The rapid growth in wireless internets and communications has led to an increasing demand for high data rate in the field of wireless communications services. OFDM/OFDMA systems are today regarded as one of the most promising research areas and as a key technology for the next generation of wireless communications. This is due to the fact that OFDM/OFDMA modulation schemes can provide many advantages like modulation efficiency, spectrum efficiency, flexibility, and strong multipath immunity over conventional single carrier modulation schemes. 
     IEEE 802.16x is an emerging standard organization to define an air interface for fixed and mobile broadband wireless access (BWA) systems. IEEE 802.16x approved “IEEE P802.16-REVd/D5-2004” in May 2004 for fixed BWA systems and published “IEEE P802.16e/D12 October 2005” in October 2005 for mobile BWA systems. Those two standards defined four different physical layers (PHYs) and one medium access control (MAC) layer. The OFDM and OFDMA physical layer of the four physical layers are the most popular in the fixed and mobile BWA areas respectively. 
       FIG. 1  illustrates an example of a wireless communication system  100 . The wireless communication system  100  may be a broadband wireless communication system  100 . The wireless communication system  100  provides communication for a number of cells  102 , each of which is serviced by a base station  104 . A base station  104  may be a fixed station that communicates with user terminals  106 . The base station  104  may alternatively be referred to as an access point, a Node B, or some other terminology. 
       FIG. 1  shows various user terminals  106  dispersed throughout the system  100 . The user terminals  106  may be fixed (i.e., stationary) or mobile. The user terminals  106  may alternatively be referred to as remote stations, access terminals, terminals, subscriber units, mobile stations, stations, user equipment, etc. The user terminals  106  may be wireless devices, such as cellular phones, personal digital assistants (PDAs), handheld devices, wireless modems, laptop computers, personal computers, etc. 
     A variety of algorithms and methods may be used for transmissions in the wireless communication system  100  between the base stations  104  and the user terminals  106 . For example, signals may be sent and received between the base stations  104  and the user terminals  106  in accordance with OFDM/OFDMA techniques. If this is the case, the wireless communication system  100  may be referred to as an OFDM/OFDMA system  100 . 
     A communication link that facilitates transmission from a base station  104  to a user terminal  106  may be referred to as a downlink  108 , and a communication link that facilitates transmission from a user terminal  106  to a base station  104  may be referred to as an uplink  110 . Alternatively, a downlink  108  may be referred to as a forward link or a forward channel, and an uplink  110  may be referred to as a reverse link or a reverse channel. 
     A cell  102  may be divided into multiple sectors  112 . A sector  112  is a physical coverage area within a cell  102 . Base stations  104  within an OFDM/OFDMA system  100  may utilize antennas that concentrate the flow of power within a particular sector  112  of the cell  102 . Such antennas may be referred to as directional antennas. 
       FIG. 2  illustrates an example of a transmitter  202  that may be used within a wireless communication system  100  that utilizes OFDM/OFDMA. The transmitter  202  may be implemented in a base station  104  for transmitting data  206  to a user terminal  106  on a downlink  108 . The transmitter  202  may also be implemented in a user terminal  106  for transmitting data  206  to a base station  104  on an uplink  110 . 
     Data  206  to be transmitted is shown being provided as input to a serial-to-parallel (S/P) converter  208 . The S/P converter  208  splits the transmission data into N parallel data streams  210 . 
     The N parallel data streams  210  may then be provided as input to a mapper  212 . The mapper  212  maps the N parallel data streams  210  onto N constellation points. The mapping may be done using some modulation constellation, such as binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), 8 phase-shift keying (8PSK), quadrature amplitude modulation (QAM), etc. Thus, the mapper  212  outputs N parallel symbol streams  216 , each symbol stream  216  corresponding to one of the N orthogonal sub-carriers of the inverse fast Fourier transform (IFFT)  220 . These N parallel symbol streams  216  are represented in the frequency domain, and may be converted into N parallel time domain sample streams  218  by an IFFT component  220 . 
     A brief note about terminology will now be provided. N parallel modulations in the frequency domain are equal to N modulation symbols in the frequency domain, which are equal to N mapping plus N-point IFFT in the frequency domain, which is equal to one (useful) OFDM symbol in the time domain, which is equal to N samples in the time domain. One OFDM symbol in the time domain, Ns, is equal to N cp  (the number of guard samples per OFDM symbol)+N (the number of useful samples per OFDM symbol). 
     The N parallel time domain sample streams  218  may be converted into an OFDM/OFDMA symbol stream  222  by a parallel-to-serial (P/S) converter  224 . A guard insertion component  226  may insert a guard interval between successive OFDM/OFDMA symbols in the OFDM/OFDMA symbol stream  222 . The output of the guard insertion component  226  may then be upconverted to a desired transmit frequency band by a radio frequency (RF) front end  228 . An antenna  230  may then transmit the resulting signal  232 . 
       FIG. 2  also illustrates an example of a receiver  204  that may be used within a wireless communication system  100  that utilizes OFDM/OFDMA. The receiver  204  may be implemented in a user terminal  106  for receiving data  232 ′ from a base station  104  on a downlink  108 . The receiver  204  may also be implemented in a base station  104  for receiving data  232 ′ from a user terminal  106  on an uplink  110 . 
     The transmitted signal  232  is shown traveling over a wireless channel  234 . When a signal  232 ′ is received by an antenna  230 ′, the received signal  232 ′ may be downconverted to a baseband signal by an RF front end  228 ′. A guard removal component  226 ′ may then remove the guard interval that was inserted between OFDM/OFDMA symbols by the guard insertion component  226 . 
     The output of the guard removal component  226 ′ may be provided to an S/P converter  224 ′. The S/P converter  224 ′ may divide the OFDM/OFDMA symbol stream  222 ′ into the N parallel time-domain symbol streams  218 ′, each of which corresponds to one of the N orthogonal sub-carriers. A fast Fourier transform (FFT) component  220 ′ converts the N parallel time-domain symbol streams  218 ′ into the frequency domain, and outputs N parallel frequency-domain symbol streams  216 ′. 
     A demapper  212 ′ performs the inverse of the symbol mapping operation that was performed by the mapper  212 , thereby outputting N parallel data streams  210 ′. A P/S converter  208 ′ combines the N parallel data streams  210 ′ into a single data stream  206 ′. Ideally, this data stream  206 ′ corresponds to the data  206  that was provided as input to the transmitter  202 . 
       FIG. 3A  illustrates an example of a frame  306  that may be transmitted from a base station  104  to a user terminal  106  on a downlink  108  within a wireless communication system  100  that utilizes OFDM/OFDMA. The OFDM/OFDMA frame  306  is shown with respect to a time axis  308 . The OFDM/OFDMA frame  306  is shown with one preamble symbol  310  and multiple data symbols  312 . Although just one preamble symbol  310  is shown in  FIG. 3A , an OFDM/OFDMA frame  306  may include multiple preamble symbols  310 . 
       FIGS. 3B and 3C  illustrate examples of frequency domain representations of a preamble symbol  310 . These frequency domain representations are shown with respect to a sub-carrier axis  316 . A used sub-carrier region  318  is shown. Two guard regions  320  are also shown. 
     In  FIG. 3B , the used sub-carrier region  318  includes pilot sub-carriers  314   a  alternated with unmodulated sub-carriers  314   b . In  FIG. 3C , each sub-carrier  314  in the used sub-carrier region  318  is a pilot sub-carrier  314   a.    
       FIG. 3D  illustrates an example of a frequency domain representation of a data symbol  312 . The data symbol  312  includes both data sub-carriers  314   c  and pilot sub-carriers  314   a . A receiver  204  may perform channel estimation using pilot sub-carriers  314   a  of a preamble symbol  310  and/or pilot sub-carriers  314   a  of a data symbol  312 . 
     The number of sub-carriers  314  within an OFDM/OFDMA system  100  may be equal to the number of FFT points. Within a wireless communication system  100  that utilizes OFDM/OFDMA, all available sub-carriers  314  may not be used. In particular, guard sub-carriers  314   d  in guard regions  320  may be excluded. In  FIGS. 3B through 3D , guard sub-carriers  314 d are shown around the lower and higher frequency bands. These guard sub-carriers  314   d  may not be allocated for data sub-carriers  314   c  or pilot sub-carriers  314   a.    
       FIG. 4  illustrates an example of an OFDMA frame  402  (with only the mandatory zone) in time division duplex (TDD) mode. The x-axis  404  denotes the time axis or the OFDMA symbol axis, and the y-axis  406  denotes the frequency axis or the sub-channel axis. The first symbol of the frame  402  is the downlink preamble  408 , and most of the timing reference is based on this preamble  408 . The first channel of the downlink sub-frame is called the frame control header (FCH)  410 , and the contents of the FCH  410  are called the downlink frame prefix (DLFP). The following bursts  412  of the FCH  410  may include mobile application part (MAP) messages, control messages, user bursts, etc. 
     The downlink radio signals from base stations  104  to user terminals  106  may include voice or data traffic signals or both. In addition, the base stations  104  generally transmit preambles  408  in their downlink radio signals to identify to the user terminals  106  the corresponding cells  102  and corresponding segments in the cells  102  to which the downlink radio signals are directed. Such a preamble  408  from a base station  104  allows a user terminal  106  to synchronize its receiver  204  in both time and frequency with the observed downlink signal and to acquire the identity of the base station  104  that transmits the downlink signal. 
     In a wireless communication system  100  that is configured in accordance with IEEE802.16e, there are three types of preamble carrier sets that may be defined. The preamble carrier sets may be defined by allocation of different sub-carriers  314 , which may be modulated using a boosted BPSK modulation with a specific pseudo-noise (PN) code. The preamble carrier sets may be defined using the following formula:
 
 PA   cset   =s +3 z    (1)
 
     In equation (1), the term PA cset  represents all sub-carriers  314  allocated to the specific preamble  408  based on the useful sub-carrier index (i.e., an index that is assigned to the sub-carriers  314  in the used sub-carrier region  318 ). The term s represents the number of the preamble carrier set indexed 0 . . . 2 which corresponds to the segment of the sector  112 . The term z represents a running index starting from 0 to M−1, where M is the length of the PN code. For example, M=284 at N=1024 FFT mode. 
     Each segment uses a preamble  408  corresponding to a carrier set out of the three available carrier sets in the following manner: segment  0  uses preamble carrier set  0 , segment  1  uses preamble carrier set  1 , and segment  2  uses preamble carrier set  2 . (In the case of segment  0 , the DC carrier is not modulated at all and the appropriate PN is discarded. Therefore, the DC carrier is zeroed. For the preamble symbol  408  there are 86 sub-carriers  314  in the guard regions  320  on the left side and the right side of the spectrum.) For a 1024 FFT size the PN series modulating the preamble carrier set is defined in the standard specification for an IEEE802.16e OFDM/OFDMA system. 
       FIGS. 5A and 5B  illustrate examples of preamble sequences  506   a ,  506   b  that may be defined for a wireless communication system  100  that is configured in accordance with IEEE 802.16e. These preamble sequences  506   a ,  506   b  are defined in the standard specification for an IEEE 802.16e OFDM/OFDMA system. 
     The preamble sequences  506   a  shown in  FIG. 5A  correspond to an IEEE 802.16e OFDM/OFDMA system that uses 1024 sub-carriers. In the case of segment  0 , the DC carrier may not be modulated at all and the appropriate PN may be discarded; therefore, the DC carrier may always be zeroed. For the preamble symbol  408  there may be 86 sub-carriers  314  in the guard regions  320  on the left side and the right side of the spectrum. 
     The preamble sequences  506   b  shown in  FIG. 5B  correspond to an IEEE 802.16e OFDM/OFDMA system that uses 512 sub-carriers. In the case of segment  1 , the DC carrier may not be modulated at all and the appropriate PN may be discarded; therefore, the DC carrier may always be zeroed. For the preamble symbol  408  there may be 42 sub-carriers  314  in the guard regions  320  on the left side and the right side of the spectrum. 
     Each preamble sequence  506   a ,  506   b  is associated with a segment  510   a ,  510   b . Each preamble sequence  506   a ,  506   b  is also associated with a cell  102 , which is identified by a cell identifier (IDcell)  512   a ,  512   b . Each preamble sequence  506   a ,  506   b  is also associated with an index  516   a ,  516   b , which may be referred to as a preamble index  516   a ,  516   b.    
     The preamble sequence (PN series)  506  modulating the preamble carrier sets are defined in the standard specification for an IEEE 802.16e OFDM/OFDMA system. The preamble sequence  506  that is modulated depends on the segment  510  that is used and the IDcell parameter  512 . The defined preamble sequence  506  may be mapped onto the preamble sub-carriers  314  in ascending order. The tables shown in  FIGS. 5A  and  5 B include the preamble sequences  506  in a hexadecimal format. The value of the PN may be obtained by converting the series to a binary series (Wk) and mapping the PN from the most significant bit (MSB) of each symbol to the least significant bit (LSB). A “0” may be mapped to “+1,” and a “1” may be mapped to “−1.” For example, for index=0, segment=0, Wk=110000010010 . . . , and the mapping maybe: −1 −1 +1 +1 +1 +1 +1 −1 +1 +1 −1 +1 . . . A total of 114 PN series (N pn =114) are defined in the standard specification, or 38 PN series for each segment (N pnseg =38, N seg =3). 
       FIG. 6  shows a frequency domain representation of a downlink preamble  608  for an IEEE802.16e OFDM/OFDMA system with an FFT size of 1024. In  FIG. 6 , N stands for a null sub-carrier  314 , S 0  stands for a sub-carrier  314  which belongs to segment  0 , S 1  stands for a sub-carrier  314  which belongs to segment  1 , S 2  stands for a sub-carrier  314  which belongs to segment  2 , and dc stands for a DC sub-carrier  314 . Because the FFT size is 1024, there are 1024 sub-carriers  314 , and these sub-carriers  314  are numbered from SC 1  to SC 1024 . 
       FIG. 7  illustrates a 24-bit downlink frame prefix (DLFP)  702 . The frame control header (FCH)  410 , which was discussed above, is an important channel (or burst) of an IEEE802.16d/e system. The contents of the FCH  410  are called the downlink frame prefix (DLFP)  702 . The DLFP  702  is a data structure that is transmitted at the beginning of each frame  402 . The DLFP  702  contains information regarding the current frame  402  and is mapped to the FCH  410 . Successful decoding of the FCH/DLFP  410 ,  702  may be important to process the entire frame  402 . 
     To decode downlink messages or bursts  412  sent by the base station  104 , the user terminal  106  may perform the following functions before FCH decoding: automatic gain control (AGC), downlink signal detection, downlink preamble detection, frequency synchronization (fractional and integer), OFDM symbol timing detection, segment detection, and preamble sequence detection. 
     The present disclosure relates generally to a synchronization and detection architecture for a wireless communication system  100  that utilizes OFDM/OFDMA. The proposed scheme may include three major steps. The first step may include coarse detection and synchronization processes, which may include coarse signal detection, coarse preamble detection, coarse symbol timing detection, and fractional frequency offset estimation. The second step may include fine detection and synchronization processes, which may include verification of signal detection, verification of preamble detection, and fine symbol timing detection. The third step may include preamble sequence identification and integer frequency offset estimation processes, which may include preamble sequence identification, integer frequency offset estimation, segment extraction, and sampling frequency offset estimation. An automatic gain control (AGC) process may also be included as one of the synchronization processes, and a physical layer (PHY) synchronization process may also be included for acquiring the downlink PHY synchronization that is the final stage of PHY level synchronization. In addition, the present disclosure also includes a scheme for searching neighbor cells for purposes of handover. 
       FIG. 8  illustrates an example of a synchronization and detection method  800  that may be performed by a wireless device (e.g., a user terminal  106 ) in a wireless communication system  100  that utilizes OFDM/OFDMA. 
     The method  800  may include performing  802  coarse signal detection with respect to a received signal, performing  804  coarse preamble detection with respect to the received signal, performing  806  coarse symbol boundary detection with respect to the received signal, and performing  808  fractional carrier frequency offset (CFO) estimation with respect to the received signal. Collectively, these steps  802 ,  804 ,  806 ,  808  may be referred to as performing  810  coarse detection and synchronization with respect to a received signal. 
     The method  800  may also include performing  812  fine signal detection with respect to the received signal, performing  814  fine preamble detection with respect to the received signal, and performing  816  fine symbol boundary detection with respect to the received signal. Collectively, these steps  812 ,  814 ,  816  may be referred to as performing  818  fine detection and synchronization for acquisition of the received signal. 
     The results that are determined from performing  810  the coarse detection and synchronization may be used for performing  818  the fine detection and synchronization. For example, performing  812  fine signal detection may include verifying the result that was obtained by performing  802  coarse signal detection. Similarly, performing  814  fine preamble detection may include verifying the result that was obtained by performing  804  coarse preamble detection. 
     When the acquisition of the received signal has been completed, tracking mode may be entered. In particular, the method  800  may then include performing  820  preamble sequence identification, performing  822  integer carrier frequency offset (CFO) estimation, performing  824  segment estimation, performing  826  sampling frequency offset (SFO) estimation, and performing  828  physical layer synchronization. Collectively, these steps  820 ,  822 ,  824 ,  826 ,  828  may be referred to as performing  830  tracking mode processing. 
     The method  800  of  FIG. 8  described above may be performed by various hardware and/or software component(s) and/or module(s) corresponding to the means-plus-function blocks  800 A illustrated in  FIG. 8A . In other words, blocks  802  through  828  illustrated in  FIG. 8  correspond to means-plus-function blocks  802 A through  828 A illustrated in  FIG. 8A . 
       FIGS. 9 and 9A  illustrate an example of a synchronization and detection method  900  that may be performed by a wireless device (e.g., a user terminal  106 ) in a wireless communication system  100  that utilizes OFDM/OFDMA. This method  900  is an example of a possible implementation of the synchronization and detection method  800  that is shown in  FIG. 8 . 
     The method  900  includes performing  902  parameter setting and adjustment. This may include setting bandwidth, setting frame duration, setting fast Fourier transform (FFT) size, setting Gr, setting automatic gain control (AGC), setting and starting timers, setting acquisition mode parameters, setting tracking mode parameters, setting physical layer synchronized mode parameters, etc. The term Gr refers to guard ratio, which is one of 1/32, 1/16, 1/8, and 1/4 of a useful OFDMA symbol. 
     The method  900  also includes entering  904  acquisition mode  906  or tracking mode  908 . In acquisition mode  906 , timing information and base station information may not be available. Some parameters like threshold(s), timing, preamble sequence  506 , and frequency offset may be set based on acquisition mode parameter control. In acquisition mode  906 , detectors and synchronizers may continue the same processes as previous operations for all possible timing hypotheses until acquisition is verified. 
     In tracking mode  908 , some timing and frequency information may be available, so that information may be used in subsequent processes. Some parameters like threshold(s), timing, preamble sequence  506 , and frequency offset may be set based on tracking mode parameter control. Those parameters may be fine tuned over time. In tracking mode  908 , detectors and synchronizers may continue the same processes by updating synchronization and detection parameters to the values obtained during fine synchronization and detection. The timing hypotheses may be narrowed more and more to a given range over time. 
     The method  900  also includes performing  910  coarse detection and synchronization. As indicated above, coarse detection and synchronization may include coarse signal detection, coarse preamble detection, coarse symbol boundary detection, and fractional CFO estimation. 
     Once an incoming signal is recognized  912  as a candidate, then the candidate may be delivered  914  to the appropriate component(s) for fine detection and synchronization with related information like timing and frequency offset. For purposes of performing  910  coarse detection and synchronization, the incoming signal may be processed on a symbol-by-symbol basis, thereby providing real-time processing capability. In one implementation, every incoming OFDMA symbol may be considered  912  to be a candidate, and all the candidates may be delivered  914  to the appropriate component(s) for fine detection and synchronization. 
     Certain information may be determined as part of performing  910  coarse detection and synchronization. For example, the average power of the received signal may be determined. This may be referred to herein as AP. As another example, the auto-correlation of the received signal using the cyclic prefix (CP) property of the preamble may be determined. This may be referred to herein as CORRcp. Both AP and CORRcp may be determined on a continuous basis. CORRcp may be determined in the time domain. 
     As indicated above, performing  910  coarse detection and synchronization may include performing coarse signal detection. Both AP and CORRcp may be used as part of a threshold detection scheme for purposes of coarse signal detection. For example, the measured AP and CORRcp values may be compared to predetermined thresholds for purposes of coarse signal detection. 
     As indicated above, performing  910  coarse detection and synchronization may include performing coarse preamble detection. Both AP and CORRcp may be used as part of a threshold detection scheme for purposes of coarse preamble detection. For example, the measured AP and CORRcp values may be compared to predetermined thresholds for purposes of coarse preamble detection. Also, because the power may be increased (e.g., by about 4.26 dB) for transmission of the preamble  408 , this may also be taken into consideration for purposes of coarse preamble detection. 
     All possible preamble candidates may be delivered  914  to the appropriate component(s) for purposes of fine detection and synchronization. This may be done on a continuous basis. 
     As indicated above, performing  910  coarse detection and synchronization may include performing coarse symbol boundary detection. Both AP and CORRcp may be used as part of a threshold detection scheme for purposes of coarse symbol boundary detection. For example, the measured AP and CORRcp values may be compared to predetermined thresholds for purposes of coarse symbol boundary detection. Coarse symbol boundary detection may include determining a possible range for an initial timing hypothesis. This initial timing hypothesis may be referred to herein as n 0 . This range may be delivered  914  to the appropriate component(s) for purposes of fine detection and synchronization. 
     A brief explanation will now be provided about how the thresholds for coarse signal detection, coarse preamble detection, and coarse symbol boundary detection are determined. The cyclic prefix correlation metric may be expressed as: 
     
       
         
           
             
               
                 
                   
                     
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     The average power metric may be expressed as: 
     
       
         
           
             
               
                 
                   
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                   3 
                   ) 
                 
               
             
           
         
       
     
     For coarse signal detection, the following tests may be used with some state machine: 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             Hit 
                             = 
                             1 
                           
                         
                         
                           
                             
                               if 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   CORR 
                                   cp 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   m 
                                   ) 
                                 
                               
                             
                             &gt;= 
                             
                               
                                 F 
                                 
                                   sig 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   det 
                                 
                               
                               × 
                               
                                 AP 
                                 ⁡ 
                                 
                                   ( 
                                   m 
                                   ) 
                                 
                               
                             
                           
                         
                       
                       
                         
                           
                             Hit 
                             = 
                             0 
                           
                         
                         
                           otherwise 
                         
                       
                     
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     and 
                     ⁢ 
                     
                       / 
                     
                     ⁢ 
                     or 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   { 
                   
                     
                       
                         
                           Hit 
                           = 
                           1 
                         
                       
                       
                         
                           
                             if 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               AP 
                               ⁡ 
                               
                                 ( 
                                 m 
                                 ) 
                               
                             
                           
                           &gt;= 
                           
                             
                               F 
                               
                                 sig 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 det 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 bgn 
                               
                             
                             × 
                             
                               AP 
                               bgn 
                             
                           
                         
                       
                     
                     
                       
                         
                           Hit 
                           = 
                           0 
                         
                       
                       
                         otherwise 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     For coarse preamble detection, the following tests may be used with some stat machine: 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           Hit 
                           = 
                           1 
                         
                       
                       
                         
                           
                             if 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               
                                 CORR 
                                 cp 
                               
                               ⁡ 
                               
                                 ( 
                                 m 
                                 ) 
                               
                             
                           
                           &gt;= 
                           
                             
                               F 
                               
                                 pa 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 det 
                               
                             
                             × 
                             
                               AP 
                               ⁡ 
                               
                                 ( 
                                 m 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           Hit 
                           = 
                           0 
                         
                       
                       
                         otherwise 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     For coarse symbol boundary detection, the following maximum likelihood test may be used: 
     
       
         
           
             
               
                 
                   
                     n 
                     0 
                   
                   = 
                   
                     
                       
                         arg 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         max 
                       
                       m 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           CORR 
                           cp 
                         
                         ⁡ 
                         
                           ( 
                           m 
                           ) 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     F sig det  and F pa det  are factors for signal detection, preamble detection and coarse symbol boundary detection, respectively. F sig det bgn  and AP bgn  are factors for signal detection and average background noise level, respectively. 
     As indicated above, performing  910  coarse detection and synchronization may include performing fractional carrier frequency offset (CFO) estimation. CORRcp may be used for purposes of fractional CFO estimation. An example of an estimation range that may be used is −0.5 to +0.5. The fractional CFO estimate that is determined may be delivered  914  to the appropriate component(s) for purposes of fractional CFO compensation if tracking mode  908  is activated. 
     The method  900  also includes performing  916  fine detection and synchronization. In general terms, fine detection and synchronization may be thought of as verifying some or all of the results of coarse detection and synchronization. As indicated above, fine detection and synchronization may include fine signal detection, fine preamble detection, and fine symbol boundary detection. 
     One goal of fine detection and synchronization may be to recognize  918  an incoming candidate desired signal. Once this occurs, then it may be determined that acquisition is complete, and tracking mode  908  may be entered  920 . 
     When fine synchronization is performed  916 , all candidates that are determined as a result of performing  910  coarse synchronization may be processed. Incoming candidates may be processed on a symbol-by-symbol basis. All fine detection and synchronization may be done within one symbol to provide a real-time processing capability. 
     Fine detection and synchronization may be performed regardless of whether the preamble  408  is known or unknown. The following discussion of fine detection and synchronization may be applicable during acquisition mode  906 , during tracking mode  908 , or during normal operation. 
     Certain information may be determined as part of performing  916  fine detection and synchronization. For example, the average power of the received signal may be determined. As indicated above, the average power may be referred to herein as AP. As another example, the auto-correlation of delivered candidate preamble signal(s) using the conjugate symmetric (CS) property of the preamble  408  may be determined. This may be referred to herein as CORRcs. AP and CORRcs may be determined continuously for all delivered candidates. 
     A brief description will now be provided regarding how the CORRcs may be determined. A candidate preamble signal and the timing hypothesis n 0  may be received. The FFT may be applied for each half of the preamble  408 . The symbol boundary may be referenced by the timing hypothesis n 0 . The convolution function may be provided by dot-multiplying each corresponding sub-carrier  314  in the frequency domain. The IFFT may then be applied to the result. CORRcs may be determined in the time domain or in the frequency domain. 
     As indicated above, performing  916  fine detection and synchronization may include performing fine signal detection. Both AP and CORRcs may be used as part of a threshold detection scheme for purposes of fine signal detection. For example, the measured AP and CORRcp values may be compared to predetermined thresholds for purposes of fine signal detection. 
     As indicated above, performing  916  fine detection and synchronization may include performing fine preamble detection. Both AP and CORRcs may be used as part of a peak detection and/or a threshold detection scheme for purposes of fine preamble detection. For example, the measured AP and CORRcs values may be compared to predetermined thresholds for purposes of fine preamble detection. 
     The result of the fine preamble detection may be used for purposes of performing fine signal detection. For fine symbol boundary detection, peak detection may be used. This may be expressed as: 
     
       
         
           
             
               
                 
                   
                     FineSymBoundry 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       z 
                       fsb 
                     
                   
                   = 
                   
                     
                       
                         arg 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         max 
                       
                       n 
                     
                     ⁢ 
                     
                       ( 
                       
                         
                           CORR 
                           cs 
                         
                         ⁡ 
                         
                           ( 
                           n 
                           ) 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     The term z fsb  is the position of the fine symbol boundary. For fine signal detection, threshold detection may be used. In particular, CORR cs  (z fsb ) and AP may be compared. This may be expressed as: 
     
       
         
           
             
               
                 
                   FineSigDet 
                   = 
                   
                     { 
                     
                       
                         
                           1 
                         
                         
                           
                             
                               if 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 
                                   CORR 
                                   cs 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     z 
                                     fsb 
                                   
                                   ) 
                                 
                               
                             
                             ≥ 
                             
                               
                                 F 
                                 
                                   fsig 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   det 
                                 
                               
                               × 
                               AP 
                             
                           
                         
                       
                       
                         
                           0 
                         
                         
                           otherwise 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     The term F fsig det  is a factor for fine signal detection. If the fine signal detection passes the criteria, it may be determined that the coarse signal detection has been verified, the signal has been detected, and that the fine symbol boundary z fsb  is valid and final. The method  900  may then proceed to the next stage (i.e., processing the preamble sequence identification). If the fine signal detection fails the criteria, it may be determined that the coarse signal detection was wrong and that the signal has not been detected yet. Then, the coarse synchronization processes may be redone. 
     As indicated above, performing  916  fine detection and synchronization may include performing fine symbol boundary detection. Both AP and CORRcs may be used as part of a peak detection scheme for purposes of fine symbol boundary detection. The fine symbol boundary (timing) may be determined using the result of the peak detection and the initial timing hypothesis n 0  that was determined as part of coarse detection and synchronization. 
     As discussed above, fractional CFO estimation may be performed as part of coarse detection and synchronization. Fractional CFO estimation may also be performed as part of fine detection and synchronization. As discussed above, CORRcp may be used for purposes of fractional CFO estimation, depending on and based on the results of fine signal detection, fine preamble detection, and fine symbol boundary detection. An example of an estimation range that may be used is −0.5 to +0.5. 
     Next, fine detection and synchronization will be discussed assuming that the preamble  408  is known. This may be the case after acquisition has been completed (i.e., after tracking mode  908  has been entered), or during normal operation. This case may be applicable for searching neighbor cells. 
     If the preamble  408  is known, performing  916  fine detection and synchronization may also include determining the cross-correlation of the preamble  408  with respect to a reference preamble. This may be referred to herein as CORRref. CORRref may be determined only once per frame. 
     If the preamble  408  is known and CORRref is determined, CORRref may be used for purposes of fine preamble detection and fine symbol boundary detection. The results of the fine preamble detection and the fine symbol boundary detection may be listed on candidate neighbor lists. 
     The method  900  may also include performing  922  fractional carrier frequency offset (CFO) compensation. This may be done after entering tracking mode  908 , i.e., fractional CFO compensation may not be available in acquisition mode  906 . Fractional CFO compensation may be applied for all incoming signals. Fractional CFO compensation may be realized only in the baseband signal, only in the RF signal, or in both the baseband signal and the RF signal. Fractional CFO compensation may be performed in the time domain. 
     The method  900  may also include performing  924  a fast Fourier transform (FFT) for all incoming signals that are processed in the frequency domain. If the FFT is performed before acquiring physical layer synchronization, it may be sufficient to apply the FFT to only the candidate preamble signal. Different FFT modes may be supported (e.g., 1024 mode, 512 mode). The resulting signal (after the FFT is performed  924 ) may be saved in a signal buffer. 
     Referring now to  FIG. 9A , the method  900  may also include performing  926  preamble sequence identification and integer carrier frequency offset (CFO) estimation. A two-step approach may be used to reduce the search time during preamble sequence identification and integer CFO estimation. The first step may include reducing possible integer CFO candidates. The second step may include searching for all possible candidates of preamble sequences  506 , for the reduced set of integer CFO candidates. All searching operations for preamble sequence identification and integer CFO estimation may be done within one frame in order to provide real-time processing. 
     As part of performing  926  preamble sequence identification and integer CFO estimation, certain information may be determined. For example, the power of each sub-carrier  314  may be determined. In addition, the cross-correlation between the received signal and possible preamble sequences  506  may also be determined. This may be referred to herein as CORRps. 
     Performing  926  preamble sequence identification and integer CFO estimation may also include making a decision about a virtual segment. This decision may be made using the measured power of each sub-carrier  314 . The power sum of each virtual segment (Pv 0 , Pv 1 , Pv 2 ) may be computed. Peak detection may be used to decide on the virtual segment. The candidates of the integer CFO may be reduced based on the virtual segment. The candidates may be reduced by one-third, for example. 
     As indicated above, CORRps may be determined as part of performing  926  preamble sequence identification and integer CFO estimation. This may be done before acquiring physical layer synchronization. In this case, CORRps may be computed for all possible preamble sequences (e.g., 114 sequences where the FFT mode is 1024). Alternatively, CORRps may be determined after acquiring physical layer synchronization or during a cell search process. 
     CORRps may be determined for all integer CFO candidates within the reduced set of integer CFO candidates. This may be done either before or after acquiring physical layer synchronization. There may be Zi/3 integer CFO candidates per preamble sequence  506 , where Zi is the maximum allowable integer CFO value. 
     Performing  926  preamble sequence identification and integer CFO estimation may be done using peak detection for all the results of CORRps. The PAindex  516  and the cell ID  512  may be determined. In addition, the segment  510  may be determined. In addition, the integer CFO may be determined. 
     The method  900  may also include performing  928  overall CFO estimation and compensation. The overall CFO estimate may include both the fractional CFO estimate and the integer CFO estimate. Overall CFO compensation may be performed based on the estimated overall CFO. Overall CFO compensation may be realized only in the baseband signal, only in the RF signal, or both in the baseband signal and the RF signal. Overall CFO compensation may be performed in the time domain. 
     The method  900  may also include performing  930  sampling frequency offset (SFO) estimation and compensation. The SFO may be extracted from the estimated CFO. As an example, in mobile WiMAX a locked clock scheme may be used for SFO estimation. SFO compensation may be performed using the estimated SFO. SFO compensation may be realized only in the baseband signal, only in the RF signal, or both in the baseband signal and the RF signal. SFO compensation may be performed in the time domain. 
     The method  900  may also include acquiring  932  physical layer synchronization. This may include determining whether all hypotheses are correct or not. An attempt may be made to receive downlink messages including FCH/DLFP, MAP messages, Device Capability Discovery (DCD) messages, Uniform Call Distribution (UCD) messages, and so forth. It may be determined  934  that physical layer synchronization has been established if received messages look like downlink messages by checking the cyclic redundancy check (CRC) or the message rules of the downlink  108 . 
     If after investigating downlink messages (which may be done for several frames repeatedly) it is determined  934  that physical layer synchronization is not established, then the method  900  may include going back to acquisition mode  906  and retrying the entire synchronization process again. In particular, the wireless device may be set to acquisition mode  906 , parameters may be set  902  for acquisition mode  906 , and the method  900  may continue in the manner described above. 
     If after investigating downlink messages it is determined  934  that physical layer synchronization is established (e.g., if downlink messages are received successfully), then the method  900  may include entering  936  normal operation. In particular, the wireless device may be set to physical layer synchronization mode, and parameters may be set for physical layer synchronization. 
     Normal operation  936  may include estimating and compensating for CFO/SFO continuously. Normal operation  936  may also include performing channel estimation and equalization from the preamble  408  to the end of the downlink sub-frame. 
     Normal operation  936  may also include FCH/DLFP processing. This may include estimating the sub-channel bitmap before decoding the FCH/DLFP. This may also include extracting the zone boosting factor and available pilots from the estimated sub-channel bitmap. The FCH/DLFP may be decoded, and the sub-channel bitmap may be extracted from the decoded DLFP. The zone boosting factor and available pilots may be extracted from the sub-channel bitmap. Normal operation may also include downlink  108 /uplink  110  map processing, burst processing, acquiring all necessary downlink parameters from the base station  104 , entering a ranging process, and so forth. 
     Coarse detection and synchronization and fine detection and synchronization may be performed serially. In other words, the coarse detection and synchronization may be performed first, and then the fine detection and synchronization may be performed when the results of the coarse detection and synchronization are available. 
     Alternatively, coarse detection and synchronization and fine detection and synchronization may be performed concurrently. In other words, the coarse detection and synchronization and the fine detection and synchronization may begin at about the same time. Initially, the fine detection and synchronization may be performed without any results from the coarse detection and synchronization. When results from the coarse detection and synchronization are available, these results may be used for purposes of the fine detection and synchronization. 
     The method  900  of  FIGS. 9 and 9A  described above may be performed by various hardware and/or software component(s) and/or module(s) corresponding to the means-plus-function blocks  1000  illustrated in  FIGS. 10 and 10A . In other words, blocks  902  through  936  illustrated in  FIGS. 9 and 9A  correspond to means-plus-function blocks  1002  through  1036  illustrated in  FIGS. 10 and 10A . 
       FIG. 11  illustrates an example of a synchronization and detection architecture  1100  for a wireless device (e.g., a user terminal  106 ), which may be part of a wireless communication system  100  that utilizes OFDM/OFDMA. The synchronization and detection architecture  1100  may be used to implement the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  includes a component  1106  that performs coarse signal detection. This component  1106  may be referred to as a coarse signal detection component  1106 . Coarse signal detection may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes components  1108   a ,  1108   b  that perform coarse preamble detection. These components  1108   a ,  1108   b  may be referred to collectively as a coarse preamble detection component  1108 . Coarse preamble detection may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1110  that performs coarse symbol boundary detection. This component  1110  may be referred to as a coarse symbol boundary detection component  1110 . Coarse symbol boundary detection may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1112  that performs fractional CFO estimation. This component  1112  may be referred to as a fractional CFO estimation component  1112 . Fractional CFO estimation may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The coarse signal detection component  1106 , coarse preamble detection component  1108 , coarse symbol boundary detection component  1110 , and fractional CFO estimation component  1112  may be referred to collectively as a coarse detection and synchronization component  1102 . Coarse detection and synchronization may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1128  that determines CORRcp (i.e., the auto-correlation of the received signal  1104  using the cyclic prefix (CP) property of the preamble  408 , as described above). This component  1128  may be referred to herein as a cyclic prefix-based auto-correlation component  1128 . CORRcp may be determined in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1144  that determines AP (i.e., the average power of the received signal  1104 , as described above). This component  1144  may be referred to herein as an average power determination component  1144 . AP may be determined in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1118  that performs fine signal detection. This component  1118  may be referred to herein as a fine signal detection component  1118 . Fine signal detection may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1120  that performs fine preamble detection. This component  1120  may be referred to herein as a fine preamble detection component  1120 . Fine preamble detection may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1122  that performs fine symbol boundary detection. This component  1122  may be referred to herein as a fine symbol boundary detection component  1122 . Fine symbol boundary detection may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The fine signal detection component  1118 , fine preamble detection component  1120 , and fine symbol boundary detection component  1122  may be referred to collectively as a fine detection and synchronization component  1114 . Fine detection and synchronization may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     As indicated above, results  1116  of the coarse detection and synchronization may be used for the fine detection and synchronization. For example, once an incoming signal is recognized as a candidate, then the candidate may be delivered to the fine detection and synchronization component  1114  with related information like timing and frequency offset. Thus, the results  1116  of the coarse detection and synchronization that are used for the fine detection and synchronization may include one or more candidate signals, and related information like timing information and frequency offset information corresponding to the candidate signal(s). 
     The synchronization and detection architecture  1100  also includes a component  1124  that determines CORRcs (i.e., the auto-correlation of delivered candidate preamble signal(s) using the conjugate symmetric (CS) property of the preamble  408 , as described above). This component  1124  may be referred to herein as a conjugate symmetric-based auto-correlation component  1124 . CORRcs may be determined in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     As indicated above, CORRcs may be determined in the time domain or in the frequency domain.  FIG. 11  shows CORRcs being determined in the frequency domain. 
     The synchronization and detection architecture  1100  also includes a component  1126  that determines CORRref (i.e., the cross-correlation of the preamble  408  with respect to a reference preamble, as described above). This component  1126  may be referred to herein as a reference cross-correlation component  1126 . CORRref may be determined in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes various components that may be utilized when the acquisition of the received signal  1104  has been achieved (i.e., when tracking mode  908  has been entered). Collectively, these components may be referred to as a tracking mode processing component  1130 . 
     The tracking mode processing component  1130  includes a component  1146  that performs the fast Fourier transform (FFT). This component  1146  may be referred to as an FFT component  1146 . 
     The tracking mode processing component  1130  also includes a signal buffer  1148 . The signal buffer  1148  may be used to store the output of the FFT component  1146 . 
     The tracking mode processing component  1130  also includes a component  1150  that determines the power of each sub-carrier  314 . This component  1150  may be referred to as a sub-carrier power calculation component  1150 . 
     The tracking mode processing component  1130  also includes a component  1152  that determines a virtual segment for purposes of identifying a reduced set of integer CFO candidates. This component  1152  may be referred to as a virtual segment decision component  1152 . The virtual segment may be determined in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1154  that identifies a reduced set of integer CFO candidates based on the virtual segment that is identified. This component  1154  may be referred to as a candidate reduction component  1154 . The reduced set of integer CFO candidates may be determined in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1156  that determines CORRps (i.e., the cross-correlation between the received signal  1104  and possible preamble sequences  506 , as discussed above). This component  1156  may be referred to as a preamble sequence cross-correlation component  1156 . CORRps may be determined in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1132  that performs preamble sequence identification, i.e., that identifies the preamble sequence  506  within the signal  1104  that is received from the base station  104 . This component  1132  may be referred to herein as a preamble sequence identification component  1132 . Preamble sequence identification may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1134  that performs segment estimation, i.e., that determines the segment to which the transmitting base station  104  corresponds. This component  1134  may be referred to herein as a segment estimation component  1134 . Segment estimation may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1136  that performs integer CFO estimation, i.e., that determines the integer CFO of the received signal  1104 . This component  1136  may be referred to herein as an integer CFO estimation component  1136 . Integer CFO estimation may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1138  that performs overall CFO estimation, i.e., that determines the overall CFO (both integer CFO and fractional CFO) of the received signal  1104 . This component  1138  may be referred to herein as an overall CFO estimation component  1138 . Overall CFO estimation may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1140  that performs sampling frequency offset (SFO) estimation. This component  1140  may be referred to as an SFO estimation component  1140 . SFO estimation may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The tracking mode processing component  1130  also includes a component  1142  that performs physical layer (PHY) synchronization. This component  1142  may be referred to as a physical layer synchronization component  1142 . Physical layer synchronization may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     The synchronization and detection architecture  1100  also includes a component  1178  that performs CFO/SFO compensation. This component  1178  may be referred to as a CFO/SFO compensation component  1178 . CFO/SFO compensation may be performed in the manner described above in relation to the methods  800 ,  900  shown in FIGS.  8  and  9 - 9 A. 
     A neighbor cell search capability may be provided during normal operation  936 . The neighbor cell search capability will now be described briefly. 
     During normal operation after acquiring all needed synchronization for the serving cell, the neighbor cell&#39;s information (especially focused on preamble sequences for synchronization purposes or cell search purposes) may or may not be known from the serving base station  104 . One of two approaches may be used for a neighbor cell search. One approach is to use CORRref (cross-correlation using the reference preamble pattern) using time domain processing, and the other is to use CORRcs (conjugate symmetric based correlation) and preamble sequence identification using frequency/time domain processing. 
     The first scheme (CORRref based) may be used when the user terminal  106  knows the neighbor cell&#39;s information so the user terminal  106  knows the neighbor cell&#39;s preamble sequences that are used in the corresponding base stations  104 . Based on the known preamble sequences, the user terminal  106  may search the neighbor cell&#39;s timing (symbol boundary) using a CORRref correlator. 
     The second scheme may be used whether the user terminal  106  knows the neighbor cell&#39;s information or not. If the neighbor cell&#39;s information is not available, the user terminal  106  may search the neighbor cell using the similar scheme used in initial synchronization described above; however, searching efforts may be reduced using already known information (i.e., the coarse synchronization may be omitted because it may be assumed that the neighbor cell shall use almost the same timing as the serving base station  104 ). It may be assumed that there is no integer frequency offset, because all base stations  104  may use an oscillator as defined in the standard specification, and after synchronization with the serving cell this integer frequency offset will likely be zero. Thus, the preamble sequence identification may be done using reduced candidates corresponding to no integer frequency offset. In addition, power calculation and virtual segment detection may be omitted for the same reason. The serving cell&#39;s symbol boundary position may be excluded from the neighbor cell&#39;s symbol boundary detection process. 
     If the neighbor cell&#39;s information is available, the searching and synchronization processes for neighbor cells may be simplified by using the known information. For example, the coarse synchronization may be omitted. Also, it may be assumed that there is zero integer frequency offset. The preamble sequence identification may be done using the only one known preamble sequence per corresponding base station  104 . 
     The synchronization and detection architecture  1100  also includes a radio frequency (RF) front end  1170 , an analog-to-digital converter (ADC)  1172 , a signal buffer  1174 , and an automatic gain control unit  1   176 . The output of the ADC  1172  and the output of the CFO/SFO compensation component  1178  are provided to a multiplexer  1180 , which multiplexes these outputs to the average power determination component  1144 , the cyclic prefix-based auto-correlation component  1128 , the conjugate symmetric-based auto-correlation component  1124 , and the reference cross-correlation component  1126 . 
     The synchronization and detection methods described herein may provide fast signal detection, fast preamble detection, fast searching for the preamble sequence  506  and the segment  510 , and fast integer CFO estimation. For example, with the synchronization and detection methods described herein, it may be possible to achieve symbol boundary detection within two symbols (one for coarse symbol boundary detection, and one for fine symbol boundary detection). Similarly, using the synchronization and detection methods described herein it may be possible to detect a preamble sequence within one frame. This allows real-time processing capability. 
     These results may be achieved with relatively low complexity. For example, as discussed above, CORRcs (i.e., the auto-correlation of delivered candidate preamble signal(s) using the conjugate symmetric (CS) property of the preamble  408 ) may be used for purposes of signal and/or preamble detection. Auto-correlation operations based on the CS property of the preamble  408  may be less complex than other types of auto-correlation operations that may be used for signal and/or preamble detection. As another example, preamble sequence identification may be performed with respect to a reduced set of integer CFO candidates. This also may contribute to the reduced complexity of the methods and apparatus described herein. 
     The methods and apparatus described herein may provide real-time processing capability by reducing computation complexity. For example, processing may occur within one symbol for coarse synchronization and fine synchronization, respectively. Processing may occur within one frame for preamble sequence identification and integer carrier frequency offset estimation. 
     IEEE C802.16e-04/327r1 describes several synchronization and detection schemes, including a scheme that may be referred to as a “brute force” search scheme. A comparison will now be made between the method  900  shown in  FIGS. 9 and 9A  and the brute force search scheme described in IEEE C802.16e-04/327r1. Information regarding the complexity of the brute force search scheme may be found in IEEE C802.16e-04/327r1. 
     Table 1 includes certain information that compares the method  900  shown in  FIGS. 9 and 9A  with the brute force search scheme that is described in IEEE C802.16e-04/327r1. It is assumed that N SEQ =284, N FFT =1024, M=42, N CP =128, and N INT =24. The number of required computations are for a duration of one frame. The “worst case” refers to the situation where there is a false detection at the coarse synchronization stage. Except for the “worst case,” it is assumed that there are no false detections. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Comparison of the method shown in FIGS. 9 and 9A with the brute force 
               
               
                 search scheme that is described in IEEE C802.16e−04/327r1. 
               
            
           
           
               
               
               
            
               
                   
                   
                 Method of 
               
               
                   
                   
                 FIGS. 9 and 
               
               
                   
                 Brute force search 
                 9A (Coarse + Fine) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Number of FFTs 
                 48,384 FFTs 
                 3 FFTs or 
               
               
                   
                   
                 85 FFTs in the 
               
               
                   
                   
                 worst case 
               
               
                 Number of complex 
                 777,024 
                 265,038 or 
               
               
                 multipliers 
                 (This number of 
                 286,030 in the 
               
               
                   
                 multiplications is 
                 worst case 
               
               
                   
                 required per FFT) 
               
               
                 Comments on real time 
                 Real time processing is 
                 All coarse and fine 
               
               
                 processing. (Real time 
                 almost impossible to 
                 synchronization 
               
               
                 means that processing 
                 implement this scheme 
                 processing can be 
               
               
                 capability of incoming 
                 considering the 
                 processed in real 
               
               
                 signal) 
                 computation complexity 
                 time so this scheme 
               
               
                   
                   
                 can provide fast 
               
               
                   
                   
                 searching capability. 
               
               
                   
               
            
           
         
       
     
       FIG. 12  illustrates various components that may be utilized in a wireless device  1202 . The wireless device  1202  is an example of a device that may be configured to implement the various methods described herein. The wireless device  1202  may be a base station  104  or a user terminal  106 . 
     The wireless device  1202  may include a processor  1204  which controls operation of the wireless device  1202 . The processor  1204  may also be referred to as a central processing unit (CPU). Memory  1206 , which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor  1204 . A portion of the memory  1206  may also include non-volatile random access memory (NVRAM). The processor  1204  typically performs logical and arithmetic operations based on program instructions stored within the memory  1206 . The instructions in the memory  1206  may be executable to implement the methods described herein. 
     The wireless device  1202  may also include a housing  1208  that may include a transmitter  1210  and a receiver  1212  to allow transmission and reception of data between the wireless device  1202  and a remote location. The transmitter  1210  and receiver  1212  may be combined into a transceiver  1214 . An antenna  1216  may be attached to the housing  1208  and electrically coupled to the transceiver  1214 . The wireless device  1202  may also include (not shown) multiple transmitters, multiple receivers, multiple transceivers and/or multiple antenna. 
     The wireless device  1202  may also include a signal detector  1218  that may be used to detect and quantify the level of signals received by the transceiver  1214 . The signal detector  1218  may detect such signals as total energy, pilot energy per pseudonoise (PN) chips, power spectral density, and other signals. The wireless device  1202  may also include a digital signal processor (DSP)  1220  for use in processing signals. 
     The various components of the wireless device  1202  may be coupled together by a bus system  1222  which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus. However, for the sake of clarity, the various busses are illustrated in  FIG. 12  as the bus system  1222 . 
     As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like. 
     Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals and the like that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles or any combination thereof. 
     The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core or any other such configuration. 
     The steps of a method or algorithm described in connection with the present disclosure may be embodied directly in hardware, in a software module executed by a processor or in a combination of the two. A software module may reside in any form of storage medium that is known in the art. Some examples of storage media that may be used include RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM and so forth. A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs and across multiple storage media. A storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. 
     The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     The functions described may be implemented in hardware, software, firmware, or any combination thereof If implemented in software, the functions may be stored as one or more instructions on a computer-readable medium. A 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 RAM, ROM, EEPROM, 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. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. 
     Software or instructions may also be transmitted over a transmission medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of transmission medium. 
     Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein, such as those illustrated by  FIGS. 9-10 , can be downloaded and/or otherwise obtained by a mobile device and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via a storage means (e.g., random access memory (RAM), read only memory (ROM), a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a mobile device and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.