MX2008005459A - Pilot symbol transmission in wireless communication systems - Google Patents

Abstract

Pilot symbols transmitted from different sectors of a same base station are multiplied with a same cell specific scrambling code and a first code having low cross correlation and second codes having low cross correlation. The second code is constant over the length of the first code, but may vary for repetitions of the first code.

Description

"TRANSMISSION OF PILOT SYMBOLS IN WIRELESS COMMUNICATIONS SYSTEMS" FIELD OF THE INVENTION The present document refers in general terms to wireless communications and, among other things, to pilot transmission in wireless communications.

BACKGROUND OF THE INVENTION A wireless communications system may use multiple transmit antennas at a base station or a user station in order to transmit symbols or other information. The use of multiple transmit antennas improves the receiver's ability to decode symbols since multiple versions of the same symbol are available for use in decoding the transmissions. An orthogonal frequency division multiple access system (OFDMA) uses orthogonal frequency division multiplexing (OFDM - orthogonal frequency division multiplexing). OFDM is a multiple carrier modulation technique that divides the General bandwidth of the system into multiple (N) orthogonal frequency subcarriers. These subcarriers are also called tones, groups and frequency channels. Each subcarrier is associated with a respective subcarrier that can be modulated with data. Up to N modulation symbols may be sent by the total N subcarriers in each OFDM symbol period. These modulation symbols are converted into the time domain with a fast N-point inverse transform (IFFT) in order to generate a transformed symbol containing N chips or samples in the time domain. In a communication system with frequency variation by jumps, the data is transmitted by different subcarriers of frequency in different time intervals, which can be referred to as "periods of frequency variation by jumps". These frequency subcarriers may be provided by orthogonal frequency division multiplexing, other multiple carrier modulation techniques, or some other constructions. With the frequency variation by jumps, the high data transmission of subcarrier in subcarrier in a pseudo-random manner. This variation by hopping provides frequency diversity allows the data transmission to better withstand the harmful effects of the path such as narrow band interference, jamming or fading, and so on. An OFDMA system can support multiple mobile stations simultaneously. For an OFDMA system of frequency variation by jumps, a data transmission can be sent for a specific mobile station by a "traffic" channel that is associated with a specific sequence of variation of frequency by jumps (FH - frequency hopping). This sequence of FH orders you to use the specific subcarrier for the transmission of data in each period of variation by jumps. Multiple data transmissions for multiple mobile stations can be sent simultaneously over multiple traffic channels that are associated with different FH sequences. These FH sequences can be defined to be orthogonal to one another such that only one traffic channel, and consequently only one data transmission, uses each subcarrier in each hop variation period. By using orthogonal FH sequences, multiple data transmissions generally do not interfere with each other and simultaneously enjoy the benefits of frequency diversity. Normally a precise calculation of a wireless channel between a transmitter and a receiver is required in order to recover the data sent through the wireless channel. Typically, the channel calculation is performed by sending a pilot from the transmitter and measuring the pilot in the receiver. The pilot signal is made up of pilot symbols that are known to both the transmitter and the receiver. Consequently, the receiver can calculate in the channel response based on the received symbols and the known symbols. A code division multiple access (CDMA) system has a universal frequency reuse that makes it possible for mobile users to receive and send the same signal simultaneously to and from multiple base stations or sectors of a base station. Smooth and softer transfers in CDMA systems are techniques by which mobiles close to cells, and the sector in the case of smoother transfer limits, communicate the same signals transmitted to more than one base station or sector of a base station . Smoother and softer transfers provide better communication quality and a smoother transition compared to conventional hard transfer. Smooth and softer transfers are intrinsic to a CDMA system, since the signals transmitted from different users occupy the same allocation of time and frequency. Different users can be separated based on the respective distribution firms. Supporting smooth and softer transfers in multiple access orthogonal systems such as TDMA, FDMA and OFDMA is much more difficult and often requires special planning. For example, in order to provide diversity, a specific cell encryption code is used in the forward link in order to randomize the interference from the surrounding cells. Frequently, the encryption code is different between sectors in the same cell (ie, Node B). When the specific cell encryption code is applied to the downlink OFDM based radio access, each modulation symbol of the pilot channel suffers inter-sector interference. The influence of the inter-sector interference the pilot channel is particularly significant for a transfer user. However, the channel calculation using the pilot channel in the inter-sector diversity does not improve compared to the case with a link connection due to inter-sector interference.

Consequently, the improvement in the channel calculation is essential, especially in inter-sector switching. Therefore, there is a need to find efficient approaches to provide an improved channel calculation for the different sectors in OFDMA systems.

BRIEF DESCRIPTION OF THE INVENTION In some aspects, a wireless communication apparatus comprises a memory and a circuit coupled to the processor. The memory is configured to store at least a first sequence of a group of first sequences, which have a low cross-correlation with one another, of a first long and at least two second sequences of a group of second sequences, which have a low correlation crossed one with another, a second long that is different from the first long. The circuit is configured to multiply pilot symbols to be transmitted from a plurality of groups of antennas using at least a first sequence and at least two second sequences. In another aspect, a method for transmitting pilot symbols comprises multiplying the first pilot symbols by a first antenna group using a first sequence of a group of first sequences, having a low cross-correlation with each other, and at least two second sequences of a group of second sequences, which have a low cross-correlation with each other, and multiply the second pilot symbols for a second group of antennas using a third sequence of the group of first sequences and at least two fourth sequences of the group of second sequences. The first and second pilot symbols can be transmitted. In additional aspects, a processor-readable medium may include instructions executable by one or more processors. The instructions can execute one or more aspects of the aforementioned method. In a further aspect, an apparatus for transmitting pilot symbols comprises means for multiplying the first pilot symbols for a first group of antennas using a first sequence of a group of first sequences, which have a low cross-correlation with one another, and at least two second sequences of a group of second sequences, which have a low correlation with one used with another, and means for multiplying second pilot symbols for a second group of antenna using a third sequence of the group of first sequences and at least two fourth sequences of the group of second sequences. The apparatus may also include one or more transmitters configured to transmit the first and second pilot symbols. Next, various aspects and modalities are described in detail. The applications also provide methods, processors, transmitter units, receiver units, base stations, terminals, systems, and / or other devices and elements that implement various aspects, modalities and characteristics, as described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS The features, nature and advantages of the present embodiments may become apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters are correspondingly identified throughout of the same and in which: Figure 1 illustrates a multiple access wireless communications system according to one modality; Figure 2 illustrates a spectrum allocation scheme for a multiple access wireless communications system according to one embodiment; Figure 3 illustrates aspects of a multiple access wireless communications system; Figure 4 illustrates a block diagram of aspects of a transmitter system and a receiver system in a multi-input multiple-input multiple-access wireless communications system, - Figure 5 illustrates a flowchart of aspects of a transmission method of pilot; and Figure 6 illustrates a block diagram of aspects of portions of a multiple sector base station.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1, a multiple access wireless communications system according to one embodiment is illustrated. A base station 100 includes multiple groups of antennas 102, 104 and 106 each including one or more antennas. In Figure 1, only one antenna is shown for each group of antennas 102, 104 and 106, however, one or multiple antennas may be used for each group of antennas corresponding to a sector of the base station 100. Mobile station 108 is located in communication with the antenna 104, where the antenna 104 transmits information to the mobile station 108 through the forward link 114 and receives information from the mobile station 108 through a reverse link 112. The mobile station 110 is in communication with the antenna 106, where the antenna 106 transmits information to the mobile station 110 through the forward link 118 and receives information from the mobile station 110 through the reverse link 116. Each group of antennas 102, 104 and 106 and / or the area in which they are designed to communicate frequently is referred to as a sector of the base station. In the embodiment, each of the groups of antennas 102, 104 and 106 is designed to communicate with the mobile stations in a sector, sectors 120, 122 and 124, respectively, of the areas covered by the base station 100. With object to allow efficient processing of the data symbols, the base station 100 can transmit pilot symbols from sectors 102, 104 and 106 that can be identified as being different from each other. In some aspects, this can be done even if the pilots are transmitted on the same subcarriers and at about the same time from two sectors at a time. For example, this can be done by multiplying the pilot symbols of each sector by a common encryption code for the cell and a first code with low cross-correlation, for example, an orthogonal code, which is specific to the particular sector. In this way, the interference for pilot symbols transmitted from a given sector decreases with respect to any other sector. In addition to the first code for the sector, a second code with low cross-correlation can be used, for example, an orthogonal, quasi-orthogonal code, or a PN code, for each portion of the code that is repeated in a given OFDM symbol. Also, the second code with low cross-correlation is selected in such a way that the pilot symbols transmitted from a certain sector code with low cross-correlation with respect to the pilot symbols transmitted from another sector of the same cell or a different cell. A base station may be a fixed station used to communicate with the terminals and may also be referred to as, include some or all of the functionality of, an access point, a Node B, or some other terminology. A mobile station may also be referred to as, and include some or all of the functionality of, a mobile station, a user equipment, a wireless communication device, terminal, access terminal or some other terminology. As used herein, in communication with the antenna or group of antennas, it generally refers to the antenna or group of antennas that is responsible for the transmission to a mobile station. In the case of a transmission from a mobile station, multiple groups of antennas can be used to receive transmissions that include the use of soft combinations or other types of combinations. It should be noted that although Figure 1 graphically represents physical sectors, that is, having different groups of antennas for different sectors, other approaches can be used. For example, multiple fixed "beams" can be used, each of which covers different areas of the cell in the frequency space instead of, or in combination of, or in combination with, physical sectors. Such an approach is graphically depicted and described in the U.S. Patent Application. Serial No. [not yet assigned], Registration Number No. 050917, entitled "Adaptive Sectorization In Cellular System", and recorded as of the date hereof, and which is incorporated in the present for reference in its entirety. In such a case, different "beams" can be assigned different encryption and code sequences with low cross-correlation as described herein. As described above, a first code with low cross-correlation is used to multiply the pilot symbols in each sector that is orthogonal or quasi-orthogonal to another first code with low cross-correlation used to multiply the pilot symbols from another sector of the cell . In addition, a second code with low cross-correlation is used to multiply the pilot symbols after multiplication by the first code in each sector. This second code with low cross-correlation, which can be any number of orthogonal or quasi-orthogonal codes, is used to multiply the length of the first code, with a different second code with low cross-correlation used in a single sector. This is illustrated in Table 1 shown below: In the examples in Table 1, the pilots occupy the tones f, f ?, Í4, faith, faith, fio, fi2, and f in a given OFDM symbol for all sectors of a given cell. An encryption code to be specific may or may not be applied. In some aspects, this specific cell encryption code can be applied as S (0), S (2), S (4), S (6), S (8), S (10), S (12) and S (14) This is then multiplied by a first code? (0), x (2), V 4), W? (6), W? (8), W? (10), x (12) and Wx (14) for sector 1, a first code 2 (0), W2 (2), 2 (4), 2 (6), 2 (8), 2 (10), W2 (12) and W2 (14) for sector 2 , and a first code 3 (0), 3 (2), 3 (4), 3 (6), W3 (8), 3 (10), W3 (12) and 3 (14). In some aspects, the first and / or second codes W1; 2 and 3 can be alsh or Exponential codes. Also, each of the first codes generally has a length that is less than a number of tones used for the pilot symbols. For example, the codes i, 2 and 3 can have a long four, such that each first code is repeated twice in each OFDM symbol for each sector. That is, the first code used to multiply the pilot symbols for the subcarriers f0, f ?, fi, and fe, and the first code used to multiply the pilot symbols for the subcarriers f8, fio, fi? And fi4 is identical. The signal received in the tone i for the user is determined by S (i) (Wx (i) PN (i) H? (I) + W2 (i) PN (i) H2 (i) + 3 (i) PN (i) H3 (i)) + noise, where Hi, H2 and H3 are the channels coming from sectors 1, 2 and 3, respectively. However, Wi, 2 and 3 can be orthogonal or quasi-orthogonal to each other in the tones. { 0,2,4,6} , the two products between Wi (i) Hj. (i), 2 (i) H2 (i) and 3 (i) H3 (i) may not be orthogonal or quasi-orthogonal, if some channel Hi, H2 or H3 shows significant variations in the set of tones. { 0, 2, 4, 6, 8, 10, etc. ..}. . In some cases, due to the channel variation, two of W? (I) H? (I), 2 (i) H2 (i) and 3 (i) H3 (i) currently provide a very high correlation. In this case, there will be no suppression of the interference derived from the pilots of the two sectors. In order to address such situations, the second PN code may be constant during the length of the first code. In some aspects, the second code would take a pseudo-random value for the tones f0, f ?, f ^ Y, and another value for the tones f8, fio, fi? and fi4 - This generates that even if? (i) H? (i), 2 (i) H2 (i) and W3 (i) H3 (i) from two sectors have a high correlation, this correlation has a different phase for different frequency regions due to the PN code used, and through different instances of time. When interpolating in frequency or time, the different phases will be averaged in order to provide a low general correlation. Although the second codes may be constant for the length of the first code, they may vary for other subcarriers that extend beyond the length of the first code in the same sector. It should be noted that the second codes may be different for each sector. Alternatively, the second codes may be the same in each sector, but they have a different order in each sector as they are applied to the different pilot subcarriers in order to make sure that no pilot symbol is multiplied by the same second code. In addition, the sectors can use different combinations of some of the same codes or some of the different codes. In some cases, it may be desired that the pilots have to occupy the same set of tones in different sectors. Therefore, if the variation of pilot jumps is used, we have to make sure that it is the same for different sectors. Referring to Figure 3, a multiple access wireless communications system according to another embodiment is illustrated. A multiple access wireless communications system 600 includes multiple cells, for example, cells 602, 604 and 606. In the embodiment of Figure 3, each cell 602, 604 and 606 may include multiple sectors, not shown, which are in communication with mobile stations 620. As described above, each cell 602, 604 and 606 may use a specific cell encryption code. different to multiply pilot symbols transmitted from their sectors. Each sector may operate after agreement with any of the aspects and use any of the features described herein. Referring to Figure 4, a block diagram of a mode of a transmitter system 810 and a receiver system 850 in a MIMO 800 system is illustrated. In the transmitter system 810, the traffic data for a certain number of data streams is provides from a data source 812 to the transmission data processor (TX) 814. In one embodiment, each data stream is transmitted by a respective transmission antenna. The data processor TX 814 formats, encodes and distributes the traffic data for each data flow based on a particular coding scheme selected for that data stream to provide coded data. The data encoded for each data flow can be multiplexed with pilot data or using OFDM techniques. Typically, the pilot data is a known data pattern that is processed in a known manner and that can be used in the receiver system to calculate the channel response. Then, the multiplexed pilot data and the coded data for each data stream are modulated (i.e., mapped by symbol) based on a particular modulation scheme (eg, BPSK, QPSK, M-PSK, or M- QAM) selected for that data stream to provide modulation symbols. The data rate, coding and modulation for each data stream can be determined by instructions executed or provided by the 830 processor. The modulation symbols for all data streams are then provided to a TX 820 processor, which can process additionally the modulation symbols (for example, for OFDM). Next, the TX 820 processor provides Nt modulation symbol streams to Nt transmitters (TMTR) 822a to 822t. Each transmitter 822 receives and processes a respective symbol stream to provide one or more analog signals and also conditions (eg, amplifies, filters and over converts) the analog signals in order to provide a modulated signal suitable for transmission over the MIMO channel . Then, Nt modulated signals are transmitted from the transmitters 822a to 822t from Nt antennas 824a to 824t, respectively. In receiver system 850, the transmitted modulated signals are received by NR antennas 852a to 852r and the received signal from each antenna 852 is provided to a respective receiver (RCVR) 854. Each receiver 854 conditions (eg, filters, amplifies and subverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples in order to provide a flow of corresponding "received" symbols. Then, an RX data processor 860 receives and processes the received symbol streams from receiver NRs 854 based on a particular receiver processing technique in order to provide Nt streams of "detected" symbols. The processing by the RX 860 data processor is described in more detail below. Each stream of detected symbols includes symbols that are calculations of the transmitted modulation symbols for the corresponding data stream. Then, the RX 860 data processor demodulates, groups and decodes each stream of detected symbols to retrieve the traffic data for the data stream. Processing by the RX 818 data processor is complementary to that performed by the TX 820 processor and the TX 814 processor in a transmitter system 810. The RX 860 processor can derive or a calculation of the channel response between the antennas transmission Nt and the reception NR, for example, based on the pilot information multiplexed with the traffic data. The RX processor 860 can identify the pilot symbols according to pilot patterns stored in the memory, for example, memory 872, which identify the frequency subcarrier and the symbol period assigned to each pilot symbol. In addition, the cell encryption code and the specific sector codes, for example, the second codes with low cross-correlation, can be stored in the memory in such a way that they can be used by the RX 860 processor to multiply the received symbols so that appropriate decoding can occur. The channel response calculation generated by the RX 860 processor can be used to execute space, space / time processing on the receiver, adjust power levels, change rates or modulation schemes, or other actions. The RX 860 processor can also calculate the noise and signal-to-interference ratios (SNRs) of detected symbol flows, and possibly other channel characteristics, and provide these quantities to an 870 processor. The RX 860 data processor or the processor 870 can further derive a calculation of the "operational" SNR for the system. Next, the processor 870 provides channel state information (CSI), which may comprise various types of information regarding the communication link and / or the data stream received. For example, the CSI may comprise only the operational SNR. Then, the CSI is processed by a data processor of TX 878, is modulated by a modulator 880, conditioned by the transmitters 854a to 854r, and transmitted again to the transmitter system 810. In the transmitter system 810, the modulated signals from the receiving system 850 are received by the antennas 824, conditioned by the receivers 822, demodulated by a demodulator 840 and processed by an RX data processor 842 to recover the CSI reported by the receiving system. Then, the reported CSI is provided to the 830 processor and used to (1) determine the data rates and coding and modulation schemes to be used by the data streams and (2) generate various controls for the data processor of the data processor. TX 814 and the TX 820 processor. Alternatively, the CSI may be used by the processor 870 to determine the modulation schemes and / or coding rates for the transmission, along with other information. This can then be provided to the transmitter that uses this information, which can be quantified to provide later transmissions to the receiver. The processors 830 and 870 direct the operation in the transmitter and receiver systems, respectively.

The memories 832 and 872 provide storage for program and data codes used by the processors 830 and 870, respectively. The memories 832 and 872 store the specific cell encryption sequence and the first and second codes with low cross-correlations. The processors 830 and 870 can then use the specific cell encryption sequence and the first and second codes with low cross-correlation to multiply the pilot symbols for each sector, as appropriate. In the receiver, various processing techniques can be used to process the NR received signals in order to detect the Nt transmitted symbol streams. These receiver processing techniques can be grouped into two main categories (i) spatial receiver and space-time processing techniques (which are also referred to as equalization techniques); and (ii) receiver processing technique of "successive cancellation / equalization and interference cancellation" (which is also referred to as receiver processing technique of "successive interference cancellation" or "successive cancellation"). Although Figure 4 describes a MIMO system, the same system can be applied to a multiple input and individual output system in which multiple transmit antennas, for example, those in a base station, transmit one or more symbol streams to a device. of individual antenna, for example, a mobile station. Also, a single-input individual output antenna system can be used in the same manner as described with respect to FIG. 4. Referring to FIG. 5, a flow diagram of a method of pilot symbol assignment according to FIG. with one modality A plurality of pilot symbols, block 900 is generated. Then, the first code for the sector is used to multiply the samples of the pilot symbols, block 902. A second code for the sector is then applied to the pilot symbols, block 904. In some cases, the second code is constant for the entire length of the first code. In other cases the second code can be of any length and vary more or less the length of the first code. In addition, multiple instances of the first code can be multiplied by different second codes. Then, the multiplied symbols, block 906, are transmitted. Referring to Figure 6, a block diagram of aspects of portions of a multiple sector base station is illustrated. A base station may include multiple sectors, only two being shown here for purposes of illustration. However, any number of sectors may be used, for example, three as graphically depicted in Figure 1. Each sector includes a means for multiplying pilot symbols with a first code and a second code, blocks 1000 and 1004, respectively. Each code is different from the other and both can have the same length, using different second codes for each group of pilot symbols multiplied by the first code. A pair of respective transmitters is used to transmit the multiplied pilot symbols, blocks 1002 and 1006, respectively. The techniques described herein can be implemented by various means. For example, these techniques can be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units in a base station or mobile station can be implemented within specific application integrated circuits (ASICs application specific integrated circuits), digital signal processors (DSPs), digital signals (DSPDs -digital signal processing devices), programmable logic devices (PLDs), programmable field gate arrays (FPGAs - field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For a software implementation, the techniques described herein may be implemented with instructions (eg, procedures, functions, etc.) that may be used by one or more processors to perform the functions described herein. The instructions can be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it may be communicatively coupled to the processor through various means as is known in the art. The above description of the described embodiments is provided to the person skilled in the art in order to make or use the present invention. Various modifications to these embodiments may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without being insulated from the spirit or scope of the invention. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but to grant it the broadest scope consistent with the principles and novel features described herein.

Claims (31)

1. NOVELTY OF THE INVENTION Having described the invention as antecedent, the content of the following claims is claimed as property
2. CLAIMS 1. A wireless communication apparatus, characterized in that it comprises: a memory configured to store at least a first sequence of a group of first sequences, having a low cross-correlation with each other, a first long and at least two second sequences of a group of second sequences, which have a low cross-correlation with each other, of a second length different from the first length; and a circuit coupled to the memory, the circuit configured to multiply pilot symbols to be transmitted from each plurality of groups of antennas using at least a first sequence and at least two second sequences. The wireless communication apparatus according to claim 1, characterized in that the memory is further configured to store an encryption sequence and wherein the processor is further configured to multiply the pilot symbols with the encryption sequence.
3. 3. The wireless communication apparatus according to claim 2, characterized in that the encryption sequence comprises a single encryption sequence.
4. The wireless communication apparatus according to claim 1, characterized in that the circuit comprises a processor.
5. The wireless communication apparatus according to claim 1, characterized in that the circuit is further configured to modulate each pilot symbol with a carrier frequency according to a predetermined pattern.
6. The wireless communication apparatus according to claim 5, characterized in that the predetermined pattern is the same for each group of antennas 7.
7. The wireless communication apparatus according to claim 6, characterized in that the circuit is configured to vary the predetermined pattern in the over time.
8. The wireless communication apparatus according to claim 1, characterized in that each group of antennae corresponds to a different sector of a base station.
9. 9. The wireless communication apparatus according to claim 1, characterized in that the first sequence is an alsh code.
10. 10. The wireless communication apparatus according to claim 1, characterized in that the group of first sequences are orthogonal codes.
11. The wireless communication apparatus according to claim 1, characterized in that the group of second sequences are sequences of PN.
12. 12. The wireless communication apparatus according to claim 1, characterized in that the group of second sequences are exponential codes.
13. A method for transmitting pilot symbols, characterized in that it comprises: multiplying first pilot symbols for a first group of antennas using a first sequence of a group of first sequences, having a low cross-correlation with each other, and at least two second sequences of a group of second sequences, which have a low cross-correlation with one another; multiplying second pilot symbols for a second group of antennas using a third sequence from the group of first sequences and at least two fourth sequences from the group of second sequences; transmit the first pilot symbol from the first group of antennas; and transmit the second pilot symbol from the second group of antennas.
14. The method according to claim 13, further characterized in that it comprises: multiplying the first pilot symbols and the second pilot symbols by an encryption sequence; multiplying the third pilot symbols by a third group of antennas using one of the first group of sequences and at least two second sequences of the group of second sequences; transmit the third pilot symbol from the third group of antennas.
15. 15. The method according to claim 13, further characterized by comprising modulating each pilot symbol with a carrier frequency in accordance with a predetermined pattern.
16. The method according to claim 15, characterized in that the predetermined pattern is the same for each group of antennas.
17. The method according to claim 16, further characterized in that it comprises varying the predetermined pattern with the passage of time.
18. The method according to claim 13, further characterized in that each group of antennas corresponds to a different sector of a base station.
19. 19. The method according to claim 13, characterized in that the first and third orthogonal sequences are alsh codes.
20. The method according to claim 13, characterized in that the group of first sequences are orthogonal codes.
21. The method according to claim 13, characterized in that the group of second sequences are PN sequences.
22. 22. The method according to claim 13, characterized in that the group of second sequences are exponential codes.
23. 23. A wireless communication apparatus, characterized in that it comprises: means for multiplying the first pilot symbols for a first group of antennas using a first sequence of a group of first sequences, having a low cross-correlation with each other and at least two second sequences of a group of second sequences, which have a low cross-correlation with one another; means for multiplying the second pilot symbols by a second group of antennas using a third sequence of the group of first sequences and at least two fourth sequences of the group of second sequences;
24. a first transmitter configured to transmit the first pilot symbols from a first group of antennas; and a second transmitter configured to transmit the second symbols from a second group of antennas. The apparatus according to claim 23, further characterized in that it comprises means for modulating each pilot symbol with a carrier frequency according to a predetermined pattern.
25. 25. The apparatus according to claim 23, further characterized in that it comprises means for varying the predetermined pattern with the passage of time.
26. 26. The apparatus according to claim 23, characterized in that each group of antennas corresponds to a different sector of a base station.
27. 27. The apparatus according to claim 23, characterized in that the first and second sequences are alsh codes.
28. 28. The apparatus according to claim 23, characterized in that the group of first sequences are orthogonal codes.
29. 29. The apparatus according to claim 23, characterized in that the group of second sequences are sequences of, PN.
30. 30. The apparatus according to claim 23, characterized in that the group of second sequences are exponential codes.
31. 31. A processor-readable medium including instructions thereon which can be used by one or more processors, characterized in that the instructions comprise: instructions for multiplying the first pilot symbols for a first group of antennas using a first sequence of a group of first sequences, which have a low cross-correlation with each other and at least two second sequences of a group of second sequences, which have a low cross-correlation with one another; instructions for multiplying the second pilot symbols for a second group of antennas using a third sequence of the group of first sequences and at least two fourth sequences of the group of second sequences; instructions for transmitting the first pilot symbols from a first group of antennas; and instructions for transmitting the second pilot symbols from a second group of antennas.