TWI482445B - Methods and systems for choosing cyclic delays in multiple antenna ofdm systems - Google Patents

Description

Method and system for selecting cyclic delay in a multi-antenna OFDM system Priority claim

The request in this case is entitled "Method and apparatus for transmitting pilots from multiple antennas" and filed on March 14, 2008, US Provisional Patent Application S/N. The benefit of priority to 61/036,895, which is hereby incorporated by reference in its entirety.

Certain embodiments of the present disclosure generally relate to wireless communications, and more particularly to a method of selecting an appropriate cyclic delay value for multi-antenna transmission to accurately estimate channel gain.

There seems to be a lack of prior art.

Certain embodiments provide a method of transmitting pilots in a wireless communication system. The method generally includes generating a first pilot frequency to a first transmit antenna based on a first cyclic delay and generating a second pilot to a second transmit antenna based on a second cyclic delay greater than a first cyclic delay by at least one cyclic prefix length frequency.

Certain embodiments provide a method of performing channel estimation in a wireless communication system. The method generally includes obtaining a first input sample comprising first and second pilot frequencies, wherein the first pilot frequency is generated based on a first cyclic delay and transmitted from a first transmit antenna, and the second pilot frequency is based on a second cyclic delay Generating and transmitting from the second transmit antenna, the second cyclic delay is greater than the first cyclic delay by at least a cyclic prefix length, and the first input samples are from the first receive antenna; and processing the first input samples to obtain A first channel estimate of a transmit antenna and a second channel estimate for a second transmit antenna.

Certain embodiments provide an apparatus for transmitting a pilot frequency in a wireless communication system. The apparatus generally includes logic for generating a first pilot frequency for the first transmit antenna based on the first cyclic delay, and for generating a second transmit delay based on a second cyclic delay greater than the first cyclic delay by at least a cyclic prefix length The logic of the second pilot frequency of the antenna.

Certain embodiments provide an apparatus for performing channel estimation in a wireless communication system. The apparatus generally includes logic for obtaining a first input sample comprising first and second pilot frequencies, wherein the first pilot frequency is generated based on a first cyclic delay and transmitted from a first transmit antenna, the second pilot frequency being based on a second cyclic delay generated and transmitted from the second transmit antenna, the second cyclic delay being greater than the first cyclic delay by at least a cyclic prefix length, and the first input samples are from the first receive antenna; and for processing the first The samples are input to obtain logic for a first channel estimate for the first transmit antenna and a second channel estimate for the second transmit antenna.

Certain embodiments provide an apparatus for transmitting a pilot frequency in a wireless communication system. The apparatus generally includes means for generating a first pilot frequency for a first transmit antenna based on a first cyclic delay, and for generating a second transmit delay based on a second cyclic delay greater than a first cyclic delay by at least a cyclic prefix length A device for the second pilot frequency of the antenna.

Certain embodiments provide an apparatus for performing channel estimation in a wireless communication system. The apparatus generally includes means for obtaining a first input sample comprising first and second pilot frequencies, wherein the first pilot frequency is generated based on a first cyclic delay and transmitted from a first transmit antenna, the second pilot frequency being based on a second cyclic delay generated and transmitted from the second transmit antenna, the second cyclic delay being greater than the first cyclic delay by at least a cyclic prefix length, and the first input samples are from the first receive antenna; and for processing the first The input samples are obtained to obtain a first channel estimate for the first transmit antenna and a second channel estimate for the second transmit antenna.

Some embodiments provide a computer program product for transmitting a pilot frequency in a wireless communication system, including computer readable media having instructions stored thereon, the instructions being executable by one or more processors. The instructions generally include instructions for generating a first pilot frequency for the first transmit antenna based on the first cyclic delay, and for generating a second transmit delay based on a second cyclic delay greater than the first cyclic delay by at least a cyclic prefix length The second pilot frequency command of the antenna.

Certain embodiments provide a computer program product for performing channel estimation in a wireless communication system, including computer readable media having instructions stored thereon, the instructions being executable by one or more processors. The instructions generally include instructions for obtaining a first input sample comprising first and second pilot frequencies, wherein the first pilot frequency is generated based on a first cyclic delay and transmitted from a first transmit antenna, the second pilot frequency being based on a second cyclic delay generated and transmitted from the second transmit antenna, the second cyclic delay being greater than the first cyclic delay by at least a cyclic prefix length, and the first input samples are from the first receive antenna; and for processing the first The samples are input to obtain an instruction for a first channel estimate for the first transmit antenna and a second channel estimate for the second transmit antenna.

The word "exemplary" is used herein to mean "serving an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous.

A cyclic delay diversity (CDD) scheme can be applied to multi-antenna orthogonal frequency division multiplexing (OFDM) transmission to provide higher frequency diversity and improved error rate performance. Multiple artificial channel paths can be generated by transmitting cyclically delayed data from multiple antennas. Estimation of the channel gain associated with the plurality of transmit antennas can be performed at the receiver side using known pilot or training sequences. However, in some cases, if the cyclically delayed pilot sequences match the path delays in the channel profile, the time domain channel paths cannot be completely separated at the receiver.

Exemplary wireless communication system

The techniques described herein can be used in a variety of broadband wireless communication systems, including communication systems based on orthogonal multiplexing schemes. Examples of such communication systems include Orthogonal Frequency Division Multiple Access (OFDMA) systems, Single-Carrier Frequency Division Multiple Access (SC-FDMA) systems, and the like. The OFDMA system utilizes orthogonal frequency division multiplexing (OFDM), which is a method of dividing the entire system bandwidth into multiple orthogonal subcarriers. Modulation technology. These subcarriers may also be referred to as tones, bins, and the like. With OFDM, each subcarrier can be independently modulated with data. The SC-FDMA system can be transmitted on subcarriers distributed across system bandwidth using interleaved FDMA (IFDMA), transmitted on blocks consisting of adjacent subcarriers using localized FDMA (LFDMA), or using enhanced FDMA (EFDMA) Transmitted on a plurality of blocks consisting of adjacent subcarriers. In general, modulation symbols are transmitted in the frequency domain under OFDM and in the time domain under SC-FDMA.

A specific example of a communication system based on an orthogonal multiplexing scheme is a WiMAX system. WiMAX, which stands for 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 WiMAX applications today: fixed WiMAX and mobile WiMAX. Fixed WiMAX applications are point-to-multipoint, enabling broadband access to, for example, households and businesses. Mobile WiMAX provides full mobility of the cellular network at broadband speeds.

IEEE 802.16 is an emerging standards organization that defines empty intermediaries for fixed and mobile broadband wireless access (BWA) systems. These standards define at least four different physical layers (PHYs) and one media access control (MAC) layer. The OFDM and OFDMA physical layers in these four physical layers are the most popular in the fixed and mobile BWA fields, respectively.

FIG. 1 illustrates an example of a wireless communication system 100 in which embodiments of the present disclosure may be employed. The wireless communication system 100 can be a broadband wireless communication system. The wireless communication system 100 can provide communication for a number of cellular cell service areas 102 served by each of the free radical stations 104. Base station 104 can be a fixed station that communicates with user terminal 106. Base station 104 may alternatively be referred to by an access point, Node B, or some other terminology.

FIG. 1 depicts various user terminals 106 throughout system 100. User terminal 106 can be fixed (i.e., stationary) or mobile. User terminal 106 can alternatively be referred to as a remote station, an access terminal, a terminal, a subscriber unit, a mobile station, a station, a user equipment, a subscriber station, and the like. User terminal 106 may be a wireless device such as a cellular telephone, a personal digital assistant (PDA), a palm-sized device, a wireless data modem, a laptop, a personal computer, and the like.

Various algorithms and methods can be used for transmissions between the base station 104 and the user terminal 106 in the wireless communication system 100. For example, signals can be transmitted and received between base station 104 and user terminal 106 in accordance with OFDM/OFDMA techniques. If this is the case, the wireless communication system 100 can be referred to as an OFDM/OFDMA system.

The communication link that facilitates the transmission from base station 104 to user terminal 106 may be referred to as downlink (DL) 108, while the communication link that facilitates transmission from user terminal 106 to base station 104 may be referred to as uplink. Link (UL) 110. Alternatively, downlink 108 may be referred to as a forward link or a forward channel, and uplink 110 may be referred to as a reverse link or a reverse channel.

The honeycomb cell service area 102 can be divided into a plurality of sectors 112. Sector 112 is the physical coverage area within cellular cell service area 102. The base station 104 within the wireless communication system 100 can utilize an antenna that concentrates power flow within a particular sector 112 of the cellular service area 102. Such an antenna may be referred to as a directional antenna.

2 illustrates an example frame structure 200 for time division duplex (TDD) mode in IEEE 802.16. The transmission isochronous line can be divided into frames. Each frame may span a predetermined duration, such as 5 milliseconds (ms), and may be partitioned into a downlink subframe and an uplink subframe. In general, the downlink and uplink subframes can cover any segment of the frame. The downlink and uplink subframes may be separated by a transmit transmission gap (TTG) and a receive transmission gap (RTG).

Several physical subchannels can be defined. Each physical subchannel may include a set of subcarriers that may be contiguous or distributed across system bandwidth. It is also possible to define several logical subchannels and map them to physical subchannels based on known mappings. Logical subchannels simplify the allocation of resources.

As shown in FIG. 2, the downlink subframe may include a preamble, a frame control header (FCH), a downlink map (DL-MAP), an uplink map (UL-MAP), And downlink (DL) bursts. The preamble can carry known transmissions that can be used by the subscriber station for frame detection and synchronization. The FCH may carry parameters for receiving DL-MAP, UL-MAP, and downlink bursts. The DL-MAP may carry a DL-MAP message, which may include information elements (IEs) for various types of control information (eg, resource allocation or assignment) for downlink access. The UL-MAP may carry a UL-MAP message, which may include IEs for various types of control information for uplink access. The downlink burst can carry data to the subscriber station being served. The uplink subframe may include uplink bursts, which may carry data transmitted by subscriber stations scheduled for uplink transmission.

The piloted transmission techniques described herein can be used for both multiple input multiple output (MIMO) transmissions and multiple input single output (MISO) transmissions. These techniques can also be used for piloted transmissions on the downlink as well as on the uplink. For clarity, certain aspects of these techniques are described below for pilot frequency transmissions on the downlink in a MIMO scenario.

3 shows a block diagram of the design of base station 104 and subscriber station 106 as one of the base stations and subscriber stations in FIG. The base station 104 is equipped with a plurality of ( M ) antennas 334a to 334m. The subscriber station 106 is equipped with a plurality of ( R ) antennas 352a through 352r.

At base station 104, transmit (TX) data processor 320 can receive data from data source 312, process (e.g., encode and symbol map) the data based on one or more modulation and coding schemes, and provide data symbols. As used herein, a data symbol is a symbol corresponding to a material, a pilot symbol is a symbol corresponding to a pilot frequency, and a symbol can be a real or complex value. The data symbols and pilot symbols may be modulation symbols derived from a modulation scheme such as PSK or QAM. The pilot frequency may include a priori known data for both the base station and the subscriber station. TX MIMO processor 330 can process these data and pilot symbols and provide M output symbol streams to M modulators (MOD) 332a through 332m. Each modulator 332 can process its output symbol stream (eg, to implement OFDM) to obtain an output sample stream. Each modulator 332 can further condition (e.g., convert to analog, filter, amplify, and upconvert) its output sample stream and generate a downlink signal. The M downlink signals from modulators 332a through 332m may be transmitted via antennas 334a through 334m, respectively.

At subscriber station 106, R antennas 352a through 352r can receive the M downlink signals from base station 104, and each antenna 352 can provide the received signal to an associated demodulator (DEMOD) 354. . Each demodulator 354 can condition (e.g., filter, amplify, downconvert, and digitize) its received signals to obtain input samples and can further process the input samples (e.g., for implementing OFDM) to obtain To the symbol. Each demodulator 354 can provide the received data symbols to the MIMO detector 360 and provide the received pilot symbols to the channel processor 394. Channel processor 394 can estimate the response of the MIMO channel from base station 104 to user station 120 based on the received pilot symbols and provide MIMO channel estimates to MIMO detector 360. MIMO detector 360 may perform MIMO detection of the received symbols based on this MIMO channel estimate and provide the detected symbols, which are estimates of the transmitted data symbols. Receive (RX) data processor 370 can process (e.g., symbol demap and decode) the detected symbols and provide the decoded data to data slot 372.

Subscriber station 106 can evaluate channel conditions and generate feedback information that can include various types of information. Feedback information and data from data source 378 may be processed (e.g., encoded and symbol mapped) by TX data processor 380, spatially processed by TX MIMO processor 382, and further processed by modulators 354a through 354r to generate R uplinks. Road signals, which can be transmitted via antennas 352a through 352r. At base station 104, the R uplink signals from subscriber station 106 can be received by antennas 334a through 334m, processed by demodulators 332a through 332m, spatially processed by MIMO detector 336, and processed by RX data processor 338. Further processing (e.g., symbol de-mapping and decoding) is performed to recover feedback information and material transmitted by the subscriber station 106. The controller/processor 340 can control the transfer of data to the subscriber station 106 based on the feedback information.

Controllers/processors 340 and 390 can direct operations at base station 104 and subscriber station 106, respectively. Memory 342 and 392 can store data and code for use by base station 104 and subscriber station 106, respectively. Scheduler 344 can schedule subscriber stations 106 and/or other subscriber stations to perform data transmission on the downlink and/or uplink based on feedback information received from all subscriber stations.

IEEE 802.16 utilizes orthogonal frequency division multiplexing (OFDM) for the downlink and uplink. OFDM partitions the system bandwidth into multiple ( N _FFT ) orthogonal subcarriers, which may also be referred to as tones, bins, and the like. Each subcarrier can be modulated with data or pilot frequency. The number of subcarriers may depend on the system bandwidth and the frequency spacing between adjacent subcarriers. For example, the N _FFT can be equal to 128, 256, 512, 1024, or 2048. This total of N _FFT subcarriers may only be used for data and pilot transmissions, while the remaining subcarriers may be used as protection subcarriers that allow the system to meet the spectral mask requirements. In the following description, the data subcarrier is a subcarrier for data, and the pilot subcarrier is a subcarrier for pilot frequency. The OFDM symbols may be transmitted in each OFDM symbol period (or simply symbol period). Each OFDM symbol may include a data subcarrier to transmit data, a pilot frequency subcarrier to transmit a pilot frequency, and/or a guard subcarrier not used for data or pilot.

4 shows a block diagram of a design of an OFDM modulator 400 that can be included in each of modulators 332a through 332m and modulators 354a through 354r in FIG. Within OFDM modulator 400, symbol-subcarrier mapper 410 receives the output symbols and maps them to the total of N _FFT subcarriers. In each OFDM symbol period, unit 412 discrete points of N _FFT inverse Fourier transform (IDFT) corresponding to these N _FFT output symbols into N _FFT total subcarriers to the time domain and provides time-domain comprising N _FFT A useful part of the sample. Each sample is a complex value to be transmitted in one chip period. A parallel-to-serial (P/S) converter 414 serializes the N _FFT samples in the useful portion. The cyclic prefix generator 416 copies the last N _CP samples of the useful portion and appends the N _CP samples to the front of the useful portion to form an OFDM symbol comprising N _FFT + N _CP samples. Each OFDM symbol thus contains a useful portion of N _FFT samples and a cyclic prefix with N _CP samples. The cyclic prefix is used to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) due to delay spread in the wireless channel.

Returning to Figure 3, on the downlink, the MIMO channels are formed by the M transmit antennas at base station 104 and the R receive antennas at subscriber station 106. The MIMO channel is composed M‧R a single input single output (SISO) channels or i.e., each possible pair of transmit and receive antennas composed of a SISO channel. The channel response of each SISO channel can be characterized by either a time domain channel impulse response or a corresponding frequency domain channel frequency response. The channel frequency response is the discrete Fourier transform (DFT) of the channel impulse response.

The channel impulse response for each SISO channel can be characterized by L time-domain channel taps, where L is typically much smaller than the N _FFT . That is, if a pulse is applied at the transmit antenna, the L time domain samples at the sample rate with respect to the pulse excitation at the receive antenna will be sufficient to characterize the response of the SISO channel. The number of channel taps ( L) required for channel impulse response depends on the delay spread of the system, which is the time difference between the earliest and latest signal instances with sufficient energy arriving at the receive antenna.

Each SISO channel may include one or more propagation paths between the transmit and receive antennas corresponding to the SISO channel, wherein the propagation paths are determined by the wireless environment. Each path can be associated with a particular complex gain and a particular delay. For each SISO channel, the complex gain of the L channel taps is determined by the complex gain of the paths of the SISO channel. Each SISO channel therefore has a channel perspective with paths d ₀ to d _{L -1} , where the complex gain of each path d _l can be zero or a non-zero value.

Cyclic Delay Diversity (CDD) can be used to establish frequency diversity in MIMO transmissions, which can improve error rate performance. With cyclic delay diversity, the OFDM symbols for each transmit antenna can be cyclically delayed by different amounts as described below. M different cyclically delayed signals can be transmitted from the M transmit antennas. However, cyclic delay diversity may adversely affect MIMO channel estimation in some situations. In particular, if the cyclically delayed signal matches the path delay in the channel perspective, it may not be possible to separate the paths. For example, for a given receive antenna, it may not be possible to determine that the complex gain corresponding to the 2 sample delay is due to (i) a downlink signal received from a transmit antenna 0 without cyclic delay and via a path with 2 sample delay. Or (ii) the downlink signal from the transmit antenna 1 with 1 sample cyclic delay and via the path with 1 sample delay, or (iii) from the transmit antenna 2 with 2 sample cyclic delay and via no delay The downlink signal received by the path.

If the channel perspective has paths d ₀ to d _{L -1} and if the M downlink signals from the M transmit antennas have a cyclic delay of t ₀ to t _{M -1} , then at ( d _l + t _m ) mod T _{When S} has different values for indexes l and m , the L channel taps of each SISO channel can be determined unambiguously, where l =0,..., L -1, m =0, ..., M -1, T _S is the duration of the useful portion and is equal to N _FFT samples, and "mod" indicates the modulo operation. This condition also applies to full frequency reuse.

For some embodiments, each loop transmit antenna (except for one transmit antenna that has a cyclic delay of 0) delay t _m may be selected to be equal to or greater than the system maximum expected delay spread. The cyclic prefix length N _CP can be selected such that it is equal to or greater than the maximum expected delay spread in the system, thereby . Thus, for some embodiments, the cyclic delay for each transmit antenna can be selected as follows:

Figure 5 shows cyclic delay diversity in an exemplary case where equation (1) has a value of N _{C , 0} =0 and for i =1, ..., M -1 has N _{C , i} = N _CP , where M = 4 transmit antennas. Transmit antenna 0 has a cyclic delay of zero, and for this transmit antenna, the useful portion is cyclically shifted by 0/delayed by 0 samples. The transmit antenna 1 has a cyclic delay of N _CP , and for this transmit antenna, the useful portion is cyclically shifted by the number of N _CP samples. The transmitting antenna 2 has a cyclic delay of 2 ‧ N _CP , and for this transmitting antenna, the useful portion is cyclically shifted by 2 ‧ N _CP samples The transmitting antenna 3 has a cyclic delay of 3 ‧ N _CP , and for this transmitting antenna, the useful portion is cyclically shifted by 3 ‧ N _CP samples

According to equation (1), the cyclic delay for the M transmit antennas can be selected as:

Formula (2) This design ensures d _l + t _m each are not the same for all values of l and m. Thus an unambiguous channel estimate (referred to as full channel estimation) for all L paths from all M transmit antennas will become possible. If the cyclic delays for the M transmit antennas are normalized or known a priori, there is no need to explicitly send a command for these cyclic delays.

The base station 104 can transmit pilot symbols from the M transmit antennas in a manner that assists the subscriber station 106 in performing full channel estimation. The pilot symbols can be transmitted on S subcarriers k ₀ to k _{S -1} , where . These S pilot frequency subcarriers can be determined as described below.

Can be defined The set of coefficients is as follows:

Where m =0 , ... , M -1, l =0 , ... , N _C,m -1, and , q = l ‧ M + m =0 , ... , Q -1 ' and b _q is the qth coefficient in the set. due to There may be less than N _CP channel taps. Thresholding can be used to zero out the non-existing channel taps.

Pilot subcarriers can be defined for the S × Q matrix B that guide the S, as follows:

among them Is the element in the i-th row and the q- th column of the matrix B, where i =0 , ... , S -1 and q =0 , ... , Q -1.

Sufficient Conditions complete channel estimation is the rank of matrix B is equal to L ‧ M. This derives the necessary conditions for each b _q to be different, which means that d _l + t _m should be different in the case of modulo T _s .

The system can operate with full frequency reuse and each honeycomb cell service area can be transmitted on all of the total N _FFT subcarriers (except for the protection subcarriers). For full frequency reuse, the pilot symbols can be transmitted on each subcarrier that can be used for transmission, or S = N _FFT , and matrix B can be an S x S Vandermonde matrix V of the form:

For full frequency reuse, the necessary conditions for b _q to be different are sufficient to allow full channel estimation. Even though some subcarriers are reserved for protection, all other subcarriers are used and there are more than Q such subcarriers, whereby the matrix V will be full rank.

The system can operate with partial frequency reuse and each honeycomb cell service area can be transmitted on a subset of a total of N _FFT subcarriers. For example, where the partial frequency reuse factor is three, each cellular cell service area can be transmitted over approximately one third of a total of N _FFT subcarriers. For partial frequency reuse, the pilot symbols can be transmitted on a subset of a total of N _FFT subcarriers, which can be a submatrix of the Vandermonde matrix, and the necessary conditions for b _q to be different may be insufficient. However, the S pilot frequency subcarriers k ₀ to k _{S -1} may be selected such that the necessary conditions are sufficient for achieving full channel estimation.

For some embodiments, the S pilot frequency subcarriers may be separated by p subcarriers, where p is a prime number that cannot divide the N _FFT . These pilot frequency subcarriers can be selected as follows:

k _i = i . p , i =0 , ... , S -1, (6)

Where k _i is the index of the ith pilot frequency subcarrier, and Mark the floor.

FIG. 6 shows an example pilot frequency subcarrier structure for one OFDM symbol corresponding to the design shown in equation (6). In this example, p = 3 and each pilot subcarrier is separated by three subcarriers. The pilot symbols can be transmitted on subcarriers 0, 3, 6, and the like. The same set of pilot frequency subcarriers can be used for each of the M transmit antennas, as shown in FIG. An OFDM symbol having these pilot frequency subcarriers can be used for the preamble or some other OFDM symbol shown in FIG. 2.

For the design shown in equation (6), matrix B is an element of the first Q column with q =0 , ... , Q -1 among the S × S van der matrix The elements of the Q column and the S column are all different from these Any element of each of the elements is constructed the same. This complete channel estimation becomes possible under the following conditions:

1. p . ( d _l + t _m ) mod N _FFT should have different values for l and m , and

2. The number of rows S in matrix B should be equal to or greater than the number of columns Q in matrix B, or .

If p is a prime number that cannot divide N _FFT and , the above two conditions can be met, regardless of the loop prefix length L. However limitation, N _CP maximum value (N _{CP, max)} may be sub Total (N _FFT) carriers, the number of transmit (M) antennas, and the guide pilot subcarrier spacing (p) as follows:

For example, for the case of M = 2, N _FFT = 1024, and p = 3, N _{CP , max} = 170. For this example, you can choose a loop prefix length of 128. As another example, for the case of M = 2, N _FFT = 1024, and p = 3, N _{CP , max} = 85. For this example, you can choose a loop prefix length of 64. As a further example, for the case of M = 2, N _FFT = 1024, and p = 5, N _{CP , max} = 102. For this example, you can choose a loop prefix length of 64.

The pilot frequency subcarrier spacing can be selected based on the cyclic delay length applied on the M transmit antennas and the total number of subcarriers N _FFT :

Figure 7 shows a block diagram of the design of modulators 332a through 332m at base station 104 of Figure 3. For the sake of simplicity, FIG. 7 only shows the process of generating pilot frequencies for the M transmit antennas. Within modulator 332a for transmit antenna 0, symbol-subcarrier mapper 710a maps pilot symbols to pilot frequency subcarriers (eg, as determined in equation (6)) and maps the zero symbols to The remaining subcarriers. IDFT unit 712a performs N _FFT point IDFT on the N _FFT pilot and zero symbols and provides N _FFT time domain samples. The P/S converter 714a serializes the N _FFT samples. For some embodiments, cyclic delay unit 716a cyclically shifts the N _FFT samples into transmit antenna 0 by N _{C, 0} samples. The cyclic prefix generator 718a appends the cyclic prefix and provides an OFDM symbol including the first pilot frequency for the transmit antenna 0.

Modulator 332b can similarly generate an OFDM symbol that includes a second pilot frequency for transmit antenna 1. However, the cyclic delay unit 716b takes the N _FFT samples as the transmit antenna 1 cyclic shift element N _{C , 0} + N _{C , 1} N _CP samples. Each of the remaining modulators 332 can similarly generate an OFDM symbol including a pilot frequency for its transmit antenna, but the N _FFT samples can be a transmit antenna m cyclic shift element Samples, where m =0 , 1 , ... , M -1.

FIG. 8 illustrates a design of a process 800 for generating pilot frequencies for a MISO or MIMO system. Process 800 may be performed by base station 104 for piloted transmission on the downlink, by user station 106 for piloted transmission on the uplink, or by some other entity.

At 810, a first pilot frequency to the first transmit antenna can be generated based on a first cyclic delay, such as a cyclic delay of zero samples. At 820, based on the length of the delay than the (m-1) is at least the length of the cycle of the cyclic prefix length N _CP m loop delay to produce the m-th to m-th transmit antenna guide pilot sequence, wherein m> 1. For some embodiments, the cyclic delay for each transmit antenna is given as shown by equation (1), where N _{C , 0} =0 and for m =1,..., M -1, with N _C,m = m . N _CP . More pilot frequencies for more transmit antennas can be generated based on appropriate cyclic delays.

At 810, a first sequence of samples including a first pilot frequency can be generated and cyclically delayed by a first cyclic delay. The first OFDM symbol including the first pilot frequency and having the first cyclic delay may be generated based on the cyclically delayed first sample sequence. At 820, an mth sample sequence including the mth pilot frequency can be generated and cyclically delayed by an mth cyclic delay, where m > 1. The mth OFDM symbol including the mth pilot frequency and having the mth cyclic delay may be generated based on the cyclically delayed mth sample sequence, where m >1. For the first OFDM symbol, the pilot symbols can be mapped to subcarriers separated by p , where p can be a prime number that cannot divide N _FFT . For the mth OFDM symbol, the pilot symbols can be mapped to subcarriers separated by p , where m >1. The same set of pilot frequency subcarriers can be used for all OFDM symbols. The number of pilot frequency subcarriers ( S ) may be equal to or greater than M‧N _CP . The pilot frequency subcarrier spacing (p) can be selected as shown in equation (8).

The subscriber station 106 can derive a channel estimate for each of the M‧R SISO channels in the MIMO channel between the base station 104 and the subscriber station 106. For each receive antenna, subscriber station 106 may obtain the S received from the S pilot subcarriers guide steered pilot symbols, and the guide may be removed to obtain the frequency modulation of these guide the S pilot subcarriers S observations. The S observations of each receive antenna j can be expressed as:

y _j = Bh _j + n' (9)

Where y _j is the receive antenna j on this guide the S pilot subcarriers S × 1 vector of observations, S × Q matrix B is formula (4) as defined, h _j is on the M transmit antennas Q × 1 channel gain vector, and n is an S × 1 noise vector.

The vector h _j includes elements h _{j, 0} to h _{j, Q -1} . before Elements h _{j, 0} to Is about the channel gain of transmit antenna 0, then Elements To Is about the channel gain of the transmit antenna 1, and so on, and finally Elements To h _{j , Q-1} is the channel gain with respect to the transmitting antenna M -1. The estimate of h _j can be obtained from y _j based on various techniques. In one design, the estimate of h _j can be obtained from y _j based on techniques such as minimum mean square error (MMSE), as follows:

among them And Is an estimate of h _j .

The same process may be performed for each receive antenna to obtain these M channels of M SISO channels between the M transmit antennas to the receive antenna is estimated.

FIG. 9 shows a block diagram of the design of the channel estimator 900. Within channel estimator 900, R units 910a through 910r obtain S received pilot symbols corresponding to the S pilot subcarriers from R receive antennas 0 through R -1, respectively. Each unit 910 removes pilot frequency modulation on the S received pilot symbols from its receiving antenna and provides S observations. The pilot frequency modulation removal can be achieved by multiplying each received pilot frequency symbol by the complex conjugate of the transmitted pilot frequency symbols. The R channel estimators 912a through 912r receive S observations from units 910a through 910r, respectively. Each channel estimator 912 as in the example shown class derived estimate regarding receiving antenna j H _j as formula (10), and providing . R demultiplexers (Demux) 914a through 914r receive from channel estimators 912a through 912r, respectively. . Each demultiplexer 914 solves multiplex Channel gain in and provides M channel estimates for these M transmit antennas.

FIG. 10 shows a design of a process 1000 for performing channel estimation for a MISO or MIMO system. Process 1000 may be performed by subscriber station 106 for downlink channel estimation, performed by base station 104 for uplink channel estimation, or by some other entity. At 1010, M cyclically delayed pilot frequency sequences may be transmitted from M transmit antennas, wherein the mth pilot frequency sequence is based on a length ratio ( m -1) cyclic delay length that is at least greater than a cyclic prefix length N _CP The m cycle delay ( m =1 , ... , M ) is cyclically delayed.

At 1020, the received samples can be processed for a total of R receive antennas to obtain an estimated channel gain for the M utilized transmit antennas. In general, received samples can be obtained from any number of receive antennas and processed to obtain channel estimates for any number of transmit antennas for each receive antenna. At 1020, the received samples can be processed to obtain observations of the pilot frequency subcarriers, such as by (1) performing OFDM demodulation on the received samples to obtain received pilot symbols corresponding to the pilot frequency subcarriers and (ii) The pilot frequency modulation is removed from these received pilot symbols to obtain observations of these pilot frequency subcarriers for this processing. These observations can be processed (e.g., based on the MMSE technique as shown in equation (10)) to obtain channel estimates for all utilized transmit antennas.

The various operations of the methods described above may be performed by various hardware and/or software components and/or modules corresponding to the device-plus-function blocks illustrated in the Figures. For example, blocks 810-820 illustrated in Figure 8 correspond to device plus function blocks 810A-820A shown in Figure 8A. Similarly, blocks 1010-1020 illustrated in Figure 10 correspond to the device plus function blocks 1010A-1020A illustrated in Figure 10A. More generally, where the method illustrated in the figures has corresponding counterparts and functional figures, the operational blocks correspond to the device plus functional blocks having similar numbers.

The various illustrative logic blocks, modules, and circuits described in connection with the present disclosure may be implemented by general purpose processors, digital signal processors (DSPs), dedicated integrated circuits (ASICs), field programmable gate arrays (FPGAs), or others. Program logic devices (PLDs), individual gate or transistor logic, individual hardware components, or any combination thereof designed to perform the functions described herein are implemented or executed. 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. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in cooperation with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the present disclosure can be implemented directly in the hardware, in a software module executed by a processor, or in a combination of the two. The software modules can reside in any form of storage medium known in the art. Some examples of storage media that may be used include random access memory (RAM), read only memory (ROM), flash memory, EPROM memory, EEPROM memory, scratchpad, hard disk, removable disk , CD-ROM, etc. A software module can include a single instruction, or a plurality of instructions, and can be distributed over several different code segments, distributed among different programs, and distributed across multiple storage media. A storage medium can be coupled to the processor to enable the processor to read and write information from/to the storage medium. In the alternative, the storage medium can be integrated into the processor.

The methods disclosed herein comprise one or more steps or actions for achieving the methods described. These method steps and/or actions may be interchanged without departing from the scope of the claims. In other words, 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 can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, each function can be stored as one or more instructions on a computer readable medium. The storage medium can be any available media that can be accessed by the computer. By way of example and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other disk storage device, or can be used to carry or store instructions or data. Any other medium in the form of a structured code that can be accessed by a computer. Disks and discs as used herein include compact discs (CDs), laser discs, compact discs, digital versatile discs (DVDs), floppy disks, and Blu-rays. Optical discs, in which disks are often magnetically reproduced, and optical discs are optically reproduced by laser.

Software or instructions can also be transferred on the transmission medium. For example, if the software is transmitted from a web site, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave. The coaxial cable, fiber optic cable, twisted pair cable, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of the transmission medium.

In addition, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user and/or a base station, where applicable. For example, such a device can be coupled to a server to facilitate forwarding of means for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage device (eg, RAM, ROM, physical storage media such as a compact disc (CD) or floppy disk, etc.) such that once the storage device is coupled to Or provided to the user terminal and/or the base station, the device can obtain various methods. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

It should be understood that the claims are not limited to the precise configurations and elements illustrated above. Various modifications, changes and variations can be made in the arrangement, operation and details of the method and apparatus described above without departing from the scope of the claims.

100. . . Wireless communication system

102. . . Honeycomb cell service area

104. . . Base station

106. . . User terminal

108. . . Downlink

110. . . Uplink

112. . . Sector

312. . . Data source

320. . . TX data processor

330. . . TX MIMO processor

340. . . Controller/processor

342. . . Memory

344. . . Scheduler

339. . . Data slot

338. . . RX data processor

336. . . MIMO detector

360. . . MIMO detector

370. . . RX data processor

372. . . Data slot

378. . . Data source

380. . . TX data processor

382. . . TX MIMO processor

390. . . Controller/processor

392. . . Memory

394. . . Channel processor

410. . . Symbol-subcarrier mapper

412. . . NFFT-point IDFT

414. . . Parallel-string (P/S) converter

416. . . Cyclic prefix generator

710a. . . Symbol-subcarrier mapper

712a. . . NFFT-point IDFT

714a. . . P/S converter

716a. . . Cyclic delay N _{C, 0} samples

718a. . . Cyclic prefix generator

718a. . . RF unit

710b. . . Symbol-subcarrier mapper

714b. . . NFFT-Point IDFT712b P/S Converter

716b. . . Cycle delay N _C,0 +N _{C, 1} sample

718b. . . Cyclic prefix generator

718b. . . RF unit

710m. . . Symbol-subcarrier mapper

712m. . . NFFT-point IDFT

714m. . . P/S converter

716m. . . Cyclic delay Sample

718m. . . Cyclic prefix generator

718m. . . RF unit

910a. . . Remove pilot frequency modulation

912a. . . Channel estimator (for example, MMSE)

914a. . . Demultiplexer

910b. . . Remove pilot frequency modulation

912b. . . Channel estimator (for example, MMSE)

914b. . . Demultiplexer

910r. . . Remove pilot frequency modulation

912r. . . Channel estimator (for example, MMSE)

914r. . . Demultiplexer

The above summary is more particularly described with reference to the embodiments of the invention, It should be noted, however, that the drawings are only illustrative of certain exemplary embodiments of the present invention, and are not to be construed as limiting.

FIG. 1 illustrates an example wireless communication system in accordance with certain embodiments of the present disclosure.

2 illustrates an example orthogonal frequency division multiplexing/orthogonal frequency division multiplexing access (OFDM/OFDMA) frame for time division duplexing (TDD), in accordance with certain embodiments of the present disclosure.

FIG. 3 illustrates an example transmitter and an example receiver that may be used within a wireless communication system, in accordance with certain embodiments of the present disclosure.

4 illustrates a block diagram of a design of an OFDM modulator, in accordance with certain embodiments of the present disclosure.

FIG. 5 illustrates an example of cyclic delay diversity, in accordance with certain embodiments of the present disclosure.

6 illustrates an example pilot frequency subcarrier structure for one OFDM symbol, in accordance with certain embodiments of the present disclosure.

7 illustrates a block diagram of a design of a modulator at the base station of FIG. 3, in accordance with certain embodiments of the present disclosure.

8 illustrates a process for generating pilot frequencies for a multiple input single output (MISO) or multiple input multiple output (MIMO) system, in accordance with certain embodiments of the present disclosure.

FIG. 8A illustrates example elements that are capable of performing the operations illustrated in FIG.

9 illustrates a block diagram of a design of a channel estimator in accordance with certain embodiments of the present disclosure.

FIG. 10 illustrates a process for performing channel estimation in a MISO or MIMO system, in accordance with certain embodiments of the present disclosure.

FIG. 10A illustrates example elements that are capable of performing the operations illustrated in FIG.

Claims (74)

A method of transmitting a pilot frequency in a wireless communication system, comprising the steps of: generating a first pilot frequency for a first transmit antenna based on a first cyclic delay; and based on being at least one greater than the first cyclic delay a second cyclic delay of the length of the cyclic prefix to generate a second pilot frequency for a second transmit antenna, wherein the step of generating the first pilot frequency and the second pilot frequency comprises the steps of: generating a plurality of The OFDM symbols are piloted, and the plurality of pilot frequencies are mapped to subcarriers separated by p , where p is a prime number that cannot divide N _FFT , and N _FFT is an FFT size for the first OFDM symbol. The method of claim 1, further comprising the step of generating a third pilot frequency for a third transmit antenna based on a third cyclic delay that is greater than the second cyclic delay by at least the length of the cyclic prefix. The method of claim 1, wherein the cyclic delay for each transmit antenna is , m =0 , 1 , ... , M -1, where N _{C ,0} 0, N _C,i N _CP , i 1, N _CP is the length of the cyclic prefix, m is a transmit antenna index, and t _m is the cyclic delay for the transmit antenna m , m =0 , 1 , ... , M -1. The method of claim 1, wherein the first loop delay is zero and the second loop delay is equal to or greater than the loop prefix length. The method of claim 1, wherein the first and second cycles are delayed and Not sent by order. The method of claim 1, wherein the step of generating the first pilot frequency further comprises the steps of: generating a first sample sequence including the first pilot frequency, and delaying the first sample sequence by the first Cycling delay; and the step of generating the second pilot frequency further comprises the steps of: generating a second sequence of samples comprising the second pilot frequency, and cyclically delaying the second sequence of samples by the second cyclic delay. The method of claim 1, wherein the generated OFDM symbols comprise: a first OFDM symbol, the first OFDM symbol includes the first pilot frequency and has the first cyclic delay, and a second OFDM symbol, The second OFDM symbol includes a second pilot frequency and has the second cyclic delay. The method of claim 7, wherein the pilot symbols are mapped to the same set of subcarriers for both the first and second OFDM symbols. The method of claim 7, wherein: Where S is the number of subcarriers with pilot symbols, M is the number of transmit antennas, and For transmit antenna m is the length of cyclic delay, m = 0, ..., M -1. The method of claim 7, wherein: Where M is the number of transmit antennas, and Is the length of the cyclic delay used to transmit the antenna m , m =0 , ... , M -1. The method of claim 1, further comprising the step of delaying the OFDM pilot symbols transmitted from each antenna by different amounts to establish frequency diversity. The method of claim 11, further comprising the step of performing channel estimation in a multiple input multiple output (MIMO) system based on the delayed OFDM pilot frequency symbols. A method of performing channel estimation in a wireless communication system, comprising the steps of: obtaining a first input sample comprising first and second pilot frequencies, the first pilot frequency being generated based on a first cyclic delay and Transmitted by a transmit antenna, the second pilot frequency is generated based on a second cyclic delay and transmitted from a second transmit antenna, the second cyclic delay being greater than the first cyclic delay by at least one cyclic prefix Length, and the first input samples are from a first receive antenna; and processing the first input samples based on pilot frequency subcarriers separated by p to obtain a first channel estimate for the first transmit antenna and A second channel estimate of the second transmit antenna, where p is a prime number that cannot divide N _FFT , and N _FFT is an FFT size for an OFDM symbol. The method of claim 13, further comprising the steps of: obtaining a second input sample comprising the first and second pilot frequencies, the second input samples being from a second receive antenna; and processing the second input A sample is obtained to obtain a third channel estimate for the first transmit antenna and a fourth channel estimate for the second transmit antenna. The method of processing the first input samples as in the method of claim 13 The method includes the steps of processing the first input samples to obtain observations of the pilot frequency subcarriers, and processing the observations to obtain the first and second channel estimates. The method of claim 15, wherein the step of processing the first input samples to obtain an observation comprises the step of performing OFDM demodulation on the first input samples to obtain received guidance of the pilot frequency subcarriers Frequency symbols; and removing pilot frequency modulation from the received pilot symbols to obtain such observations of the pilot frequency subcarriers. The method of claim 15, wherein the step of processing the observations comprises the step of processing the observations based on a minimum mean square error (MMSE) technique to obtain the first and second channel estimates. The method of claim 14, wherein the processing the second input samples comprises: processing the second input samples to obtain observations of the pilot frequency subcarriers; and processing the observations to obtain the Third and fourth channel estimates. The method of claim 18, wherein the step of processing the second input samples to obtain an observation comprises performing OFDM demodulation on the second input samples to obtain received pilot symbols of the pilot subcarriers And removing pilot frequency modulation from the received pilot symbols to obtain such observations of the pilot frequency subcarriers. The method of claim 18, wherein the step of processing the observations comprises the step of processing the observations based on a minimum mean square error (MMSE) technique to obtain the third and fourth channel estimates. An apparatus for transmitting a pilot frequency in a wireless communication system, comprising: logic for generating a first pilot frequency for a first transmit antenna based on a first cyclic delay; and for ratio based on the first loop Delaying a second cyclic delay of at least one cyclic prefix length to generate logic for a second pilot frequency of a second transmit antenna, wherein logic for generating the first pilot frequency is used to generate the first The logic of the two pilot frequencies includes logic for generating OFDM symbols comprising a plurality of pilot frequencies, and the plurality of pilot frequencies are mapped to subcarriers separated by p , where p is a prime number that cannot divide N _FFT , and The N _FFT is an FFT size for the first OFDM symbol. The apparatus of claim 21, further comprising: logic for generating a third pilot frequency for a third transmit antenna based on a third cyclic delay greater than the second cyclic delay by at least the cyclic prefix length . The device of claim 21, wherein the cyclic delay for each transmit antenna is , m =0 , 1 , ... , M -1, where N _{C ,0} 0, N _C,i N _CP , i 1, N _CP is the length of the cyclic prefix, m is a transmit antenna index, and t _m is the cyclic delay for the transmit antenna m , m =0 , 1 , ... , M -1. The apparatus of claim 21, wherein the first loop delay is zero and the second loop delay is equal to or greater than the loop prefix length. The device of claim 21, wherein the first and second cyclic delays are not transmitted by the command. The apparatus of claim 21, wherein: the logic for generating the first pilot frequency further comprises: generating a first sample sequence including the first pilot frequency, and delaying the first sample sequence by the cycle The logic of the first cyclic delay; and the logic for generating the second pilot frequency further comprises: generating a second sample sequence including the second pilot frequency, and delaying the second sample sequence by the second The logic of the cyclic delay. The apparatus of claim 21, wherein the generated OFDM symbol comprises: a first OFDM symbol including the first pilot frequency and having the first cyclic delay, and including the second pilot frequency and having the second cyclic delay a second OFDM symbol. The apparatus of claim 27, wherein for both the first and second OFDM symbols, the pilot symbols are mapped to the same set of subcarriers. The device of claim 27, wherein: Where S is the number of subcarriers with pilot symbols, M is the number of transmit antennas, and Is the length of the cyclic delay used to transmit the antenna m , m =0 , ... , M -1. The device of claim 27: Where M is the number of transmit antennas, and Is the length of the cyclic delay used to transmit the antenna m , m =0 , ... , M -1. An apparatus for performing channel estimation in a wireless communication system, comprising: logic for obtaining a first input sample comprising first and second pilot frequencies, the first pilot frequency being generated based on a first cyclic delay And transmitting, by a first transmit antenna, the second pilot frequency is generated based on a second cyclic delay and transmitted from a second transmit antenna, the second cyclic delay being greater than the first cyclic delay. a cyclic prefix length, and the first input samples are from a first receive antenna; and for processing the first input samples based on the pilot frequency subcarriers separated by p to obtain one for the first transmit antenna The first channel estimates and logic for a second channel estimate for the second transmit antenna, where p is a prime number that cannot divide N _FFT , and N _FFT is an FFT size for an OFDM symbol. The apparatus of claim 31, further comprising: logic for obtaining a second input sample comprising the first and second pilot frequencies, the second input samples being from a second receive antenna; and for processing the Waiting for a second input sample to obtain a third channel estimate for the first transmit antenna and a fourth channel for the second transmit antenna Estimated logic. The apparatus of claim 31, wherein the logic for processing the first input samples comprises: logic for processing the first input samples to obtain observations of the pilot frequency subcarriers; and for processing These observations are used to obtain the logic of the first and second channel estimates. The apparatus of claim 33, wherein the logic for processing the first input samples to obtain an observation comprises: performing OFDM demodulation on the first input samples to obtain reception of the pilot subcarriers Logic of pilot symbols; and logic for removing pilot frequency modulation from the received pilot symbols to obtain such observations of the pilot subcarriers. The apparatus of claim 33, wherein the logic for processing the observations comprises: processing the observations based on a minimum mean square error (MMSE) technique to obtain logic for the first and second channel estimates . The apparatus of claim 32, wherein the logic for processing the second input samples comprises: logic for processing the second input samples to obtain observations of the pilot frequency subcarriers; and for processing These observations are used to obtain the logic of the third and fourth channel estimates. The apparatus of claim 36, wherein the logic for processing the second input samples to obtain an observation comprises: Logic for performing OFDM demodulation on the second input samples to obtain received pilot symbols of the pilot frequency subcarriers; and for removing pilot frequency modulation from the received pilot symbols The logic to obtain such observations of the pilot frequency subcarriers. The apparatus of claim 36, wherein the logic for processing the observations comprises: processing the observations based on a minimum mean square error (MMSE) technique to obtain logic for the third and fourth channel estimates . An apparatus for transmitting a pilot frequency in a wireless communication system, comprising: means for generating a first pilot frequency for a first transmit antenna based on a first cyclic delay; and for ratio based on the first loop Delaying a second cyclic delay of at least one cyclic prefix length to generate a second pilot frequency component for a second transmit antenna, wherein the means for generating the first pilot frequency and for generating the The two pilot frequency components include: means for generating an OFDM symbol comprising a plurality of pilot frequencies, and the plurality of pilot frequencies are mapped to subcarriers separated by p , where p is a prime number that cannot divide N _FFT , and The N _FFT is an FFT size for the first OFDM symbol. The apparatus of claim 39, further comprising: means for generating a third pilot frequency for a third transmit antenna based on a third cyclic delay that is greater than the second cyclic delay by at least the length of the cyclic prefix . The apparatus of claim 39, wherein the cyclic delay for each transmit antenna is , m =0 , 1 , ... , M -1, where N _{C ,0} 0, N _C,i N _CP , i 1, N _CP is the length of the cyclic prefix, m is a transmit antenna index, and t _m is the cyclic delay for the transmit antenna m , m =0 , 1 , ... , M -1. The apparatus of claim 39, wherein the first loop delay is zero and the second loop delay is equal to or greater than the loop prefix length. The apparatus of claim 39, wherein the first and second cyclic delays are not transmitted by the command. The apparatus of claim 39, wherein: the means for generating the first pilot frequency further comprises: generating a first sample sequence including the first pilot frequency, and delaying the first sample sequence by the cycle a first cyclically delayed component; and wherein the means for generating the second pilot frequency further comprises: generating a second sample sequence comprising the second pilot frequency, and delaying the second sample sequence by the first A component of a two-cycle delay. The apparatus of claim 39, wherein the generated OFDM symbol comprises: a first OFDM symbol including the first pilot frequency and having the first cyclic delay, and including the second pilot frequency and having the second cyclic delay a second OFDM symbol. The apparatus of claim 45, wherein for both the first and second OFDM symbols, the pilot symbols are mapped to the same set of subcarriers. The device of claim 45, wherein: Where S is the number of subcarriers with pilot symbols, M is the number of transmit antennas, and Is the length of the cyclic delay used to transmit the antenna m , m =0 , ... , M -1. The device of claim 45, wherein: Where M is the number of transmit antennas, and Is the length of the cyclic delay used to transmit the antenna m , m =0 , ... , M -1. An apparatus for performing channel estimation in a wireless communication system, comprising: means for obtaining a first input sample comprising first and second pilot frequencies, the first pilot frequency being generated based on a first cyclic delay And transmitting, by a first transmit antenna, the second pilot frequency is generated based on a second cyclic delay and transmitted from a second transmit antenna, the second cyclic delay being greater than the first cyclic delay. a cyclic prefix length, and the first input samples are from a first receive antenna; and for processing the first input samples based on the pilot frequency subcarriers separated by p to obtain one for the first transmit antenna A first channel estimate and a component for a second channel estimate for the second transmit antenna, where p is a prime number that cannot divide N _FFT , and N _FFT is an FFT size for an OFDM symbol. The apparatus of claim 49, further comprising: for obtaining a second input sample comprising the first and second pilot frequencies a second input sample from a second receive antenna; and for processing the second input samples to obtain a third channel estimate for the first transmit antenna and one for the second transmit antenna The fourth channel estimated component. The apparatus of claim 49, wherein the means for processing the first input samples comprises: means for processing the first input samples to obtain observations of the pilot subcarriers; and for processing The observations are made to obtain the components of the first and second channel estimates. The apparatus of claim 51, wherein the means for processing the first input samples to obtain an observation comprises: performing OFDM demodulation on the first input samples to obtain reception of the pilot subcarriers Means of a pilot symbol; and means for removing pilot frequency modulation from the received pilot symbols to obtain such observations of the pilot subcarriers. The apparatus of claim 51, wherein the means for processing the observations comprises: means for processing the observations based on a minimum mean square error (MMSE) technique to obtain the first and second channel estimates . The apparatus of claim 50, wherein the means for processing the second input samples comprises: means for processing the second input samples to obtain observations of the pilot frequency subcarriers; and for processing The observations to obtain the estimates of the third and fourth channels member. The apparatus of claim 54, wherein the means for processing the second input samples to obtain an observation comprises: performing OFDM demodulation on the second input samples to obtain reception of the pilot subcarriers Means of a pilot symbol; and means for removing pilot frequency modulation from the received pilot symbols to obtain such observations of the pilot subcarriers. The apparatus of claim 54, wherein the means for processing the observations comprises: processing the observations based on a minimum mean square error (MMSE) technique to obtain the third and fourth channel estimates member. A computer program product for transmitting a pilot frequency in a wireless communication system, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and including: Generating an instruction for a first pilot frequency of a first transmit antenna based on the first cyclic delay; and for using a second cyclic delay that is greater than the first cyclic delay by at least one cyclic prefix length Generating a second pilot frequency instruction for a second transmit antenna, wherein the instructions for generating the first pilot frequency and the instructions for generating the second pilot frequency comprise: generating a plurality of pilot frequencies An instruction of an OFDM symbol, and the plurality of pilot frequencies are mapped to subcarriers separated by p , where p is a prime number that cannot divide N _FFT , and N _FFT is an FFT size for the first OFDM symbol. The computer program product of claim 57, the instructions further comprising: An instruction to generate a third pilot frequency for a third transmit antenna based on a third cyclic delay that is greater than the second cyclic delay by at least the length of the cyclic prefix. The computer program product of claim 57, wherein the cyclic delay for each transmit antenna is , m =0 , 1 , ... , M -1, where N _{C ,0} 0, N _C,i N _CP , i 1, N _CP is the length of the cyclic prefix, m is a transmit antenna index, and t _m is the cyclic delay for the transmit antenna m , m =0 , 1 , ... , M -1. The computer program product of claim 57, wherein the first loop delay is zero and the second loop delay is equal to or greater than the loop prefix length. The computer program product of claim 57, wherein the first and second cyclic delays are not sent by the command. The computer program product of claim 57, wherein: the instruction for generating the first pilot frequency further comprises: generating a first sample sequence including the first pilot frequency, and cycling the first sample sequence An instruction to delay the first cyclic delay; and the instruction to generate the second pilot frequency further includes: generating a second sample sequence including the second pilot frequency, and delaying the second sample sequence by the first Two-cycle delayed instruction. The computer program product of claim 57, wherein the generated OFDM symbol comprises: a first OFDM symbol including the first pilot frequency and having the first cyclic delay, and including the second pilot frequency and having the A second OFDM symbol of the second cyclic delay. The computer program product of claim 63, wherein for both the first and second OFDM symbols, the pilot symbols are mapped to the same set of subcarriers. The computer program product of claim 63, wherein: Where S is the number of subcarriers with pilot symbols, M is the number of transmit antennas, and Is the length of the cyclic delay used to transmit the antenna m , m =0 , ... , M -1. The computer program product of claim 63, wherein: Where M is the number of transmit antennas, and Is the length of the cyclic delay used to transmit the antenna m , m =0 , ... , M -1. A computer program product for performing channel estimation in a wireless communication system, comprising a computer readable medium having instructions stored thereon, the instructions being executable by one or more processors and including: Obtaining an instruction for the first input sample including the first and second pilot frequencies, the first pilot frequency is generated based on a first cyclic delay and transmitted from a first transmit antenna, the second pilot frequency is based on a second cyclic delay is generated and transmitted from a second transmit antenna, the second cyclic delay is greater than the first cyclic delay by at least one cyclic prefix length, and the first input samples are from a first Receiving antennas; and for processing the first input samples based on pilot frequency subcarriers separated by p to obtain a first channel estimate for the first transmit antenna and a second channel estimate for the second transmit antenna An instruction, where p is a prime number that cannot divide N _FFT , and N _FFT is an FFT size for an OFDM symbol. The computer program product of claim 67, the instructions further comprising: instructions for obtaining a second input sample comprising the first and second pilot frequencies, the second input samples being from a second receiving antenna; And for processing the second input samples to obtain a third channel estimate for the first transmit antenna and a fourth channel estimate for the second transmit antenna. The computer program product of claim 67, wherein the instructions for processing the first input samples comprise: instructions for processing the first input samples to obtain observations of the pilot frequency subcarriers; The observations are processed to obtain instructions for the first and second channel estimates. The computer program product of claim 69, wherein the instructions for processing the first input samples to obtain an observation comprise: performing OFDM demodulation on the first input samples to obtain the pilot frequency subcarriers An instruction to receive the pilot symbol; and an instruction to remove pilot frequency modulation from the received pilot symbols to obtain an observation of the observations of the pilot subcarriers. The computer program product of claim 69, wherein the instructions for processing the observations comprise: processing the observations based on a minimum mean square error (MMSE) technique to obtain the first and second channel estimates Instructions. The computer program product of claim 68, wherein the instructions for processing the second input samples comprise: instructions for processing the second input samples to obtain observations of the pilot frequency subcarriers; The observations are processed to obtain instructions for the third and fourth channel estimates. The computer program product of claim 72, wherein the instructions for processing the second input samples to obtain an observation comprise: performing OFDM demodulation on the second input samples to obtain the pilot frequency subcarriers An instruction to receive the pilot symbol; and an instruction to remove pilot frequency modulation from the received pilot symbols to obtain an observation of the observations of the pilot subcarriers. The computer program product of claim 72, wherein the instructions for processing the observations comprise: processing the observations based on a minimum mean square error (MMSE) technique to obtain the third and fourth channel estimates Instructions.