Pilot signal transmission for an orthogonal frequency division wireless communication system

Description

BACKGROUND

I. Field

This document generally relates to wireless communication and, but not limited to, transmission of pilot information in an orthogonal frequency division wireless communication system.

II. Background

[0002] An orthogonal frequency division multiple access (OFDMA) system uses orthogonal frequency division multiplexing (OFDM). OFDM is a multi-carrier modulation technique that divides the overall system bandwidth into multiple (N) orthogonal frequency subcarriers. These subcarriers may also be called tones, bins, and frequency channels. Each subcarrier may be modulated with data. A maximum of N modulation symbols may be transmitted on a total of N subcarriers in each OFDM symbol period. These modulation symbols are converted into the time domain using an N-point inverse fast Fourier transform (IFFT) to generate a transformed symbol that includes N time-domain chips or samples.

[0003] In a frequency hopping communication system, data is transmitted on different frequency subcarriers at different time intervals, which may be referred to as hopping periods. These frequency subcarriers may be provided by orthogonal frequency division multiplexing, other multi-carrier modulation techniques, or some other approach. Using frequency hopping, data transmission jumps from one subcarrier to another subcarrier in a manner

53 / 59P27325PL00 pseudorandom. These hopping provide frequency diversity and allow the data transmission to be more immune to harmful path influences such as narrowband interference, jamming, fading, and so on.

[0004] An OFDMA system can support multiple mobile stations simultaneously. In a frequency hopping OFDMA system, data transmission for a given mobile station may be performed on a traffic channel that is associated with a specific frequency hopping (FH) sequence. This FH sequence indicates the use of a specific subcarrier for data transmission in each hop period. Multiple data transmissions may be made simultaneously for multiple mobile stations on multiple traffic channels that are associated with different FH sequences. These FH sequences may be specified to be orthogonal to each other such that only one traffic channel, and therefore only one data transmission, uses each subcarrier for each hop period. By using orthogonal FH sequences, multiple data transmissions do not substantially interfere with each other while taking advantage of frequency diversity.

[0005] Accurate estimation of the wireless channel between a transmitter and a receiver is typically necessary in order to recover data transmitted over the wireless channel. Channel estimation is usually done by sending a remote control from the transmitter and measuring the remote control at the transmitter. The pilot signal is made up of pilot symbols that are known in advance by both the transmitter and the receiver. The receiver can therefore estimate the channel response based on the received symbols and known symbols.

[0006] A portion of each transmission from any particular mobile station to a base station, often referred to as an uplink transmission, during a hop period is allocated to transmit pilot symbols. Basically, the number of symbols

The pilot determines the quality of the channel estimation, and therefore the performance determined by the packet error rate. The use of pilot symbols, however, reduces the effective data rate that can be achieved. That is, the more bandwidth is allocated to the pilot information, the less bandwidth remains available for data transmission.

[0007] One type of FH-OFDMA system is a block hop system, in which multiple mobile stations are allocated to a group of contiguous frequencies and symbol periods. In such a system it is important that the pilot information is reliably received from the mobile station, at the same time reducing the bandwidth that is allocated for the pilot information since the block has a limited amount of symbols and tones available for use for both data and pilot transmission.

[0008] Reference is made to WO 2005/015797 which discloses a radio communication device in which a delay dispersion measuring part uses a received signal to form a delay profile and measures the delay dispersion indicative of the delay dispersion. The mobility rate estimating part estimates, based on the electric power reception variation of the pilot symbol, the traveling speed of the mobile station device that transmitted the pilot symbol. Another cell interference measuring part uses a pilot symbol to measure interference to another cell caused by a signal transmitted from a cell other than the cell to which the local device belongs. The pilot pattern information producing part produces the pilot information by selecting a pilot pattern where the position of the pilot symbol in the frame is most desirable, according to delay dispersion, traveling speed and other cell interference.

53 / 59P27325PL00

[0009] Furthermore, attention is drawn to US 2003/072254, which describes an apparatus for limiting the number of pilot symbols in a MIMO-OFDM communication system and for improving channel estimation in such a system. For each transmit antenna at the OFDM transmitter, pilot symbols are coded to be unique to the transmit antenna. The coded pilot symbols are then inserted into an OFDM frame to form a planar diamond pattern, with these diamond networks for different transmit antennas using the same frequencies but offset by one symbol in the time domain. At the OFDM receiver, the channel response is estimated for the center symbol in each diamond of the diamond lattice using two-dimensional interpolation. The estimated channel responses are smoothed in the frequency domain. The channel responses of the remaining symbols are then estimated by frequency domain interpolation.

Finally, attention should be paid to JIWOONG CHOI ET AL: Design of the optimum pilot pattern for channel estimation in OFDM systems GLOBAL TELECOMMUNICATIONS CONFERENCE, 2004. GLOBECOM '04. IEEE DALLAS, TX, USA NOVEMBER 29-DECEMBER 3, 2004, PISCATAWAY, NJ, USA, IEEE, November 29, 2004 (2004-11-29), Pages 3661-3665, ΧΡ010758420

ISBN: 0-7803-8794-5

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a wireless communication device as set forth in claim 1 and a pilot symbol transmission method as set forth in claim 12. Embodiments of the invention are claimed in the dependent claims.

[0012] In an embodiment, pilot symbol patterns for pilot symbols transmitted from a mobile station are provided

53 / 59P27325PL00 or base station. The pattern allows for improved reception and demodulation of transmitted pilot symbols.

[0013] In additional embodiments, schemes are provided for improving the ability to multiplex pilot symbols without the interference and / or interaction of other mobile stations in the same sector of the base station at the same frequencies and time slots in an OFDM system.

[0014] In further embodiments, schemes are provided for reducing the interaction or interference of pilot symbols transmitted from other mobile stations in neighboring cells at the same frequencies and time slots in an OFDM system.

[0015] In other embodiments, methods of modifying pilot symbol patterns are provided. Also, in other additional embodiments, methods of generating pilot symbols are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The features, nature, and advantages of the present embodiments may become more apparent from the detailed description provided below when considered in conjunction with the drawings, wherein like reference numerals identify corresponding elements throughout the text, and wherein:

[0017] Fig. 1 illustrates a multiple access wireless communication system according to an embodiment;

[0018] Fig. 2 is a spectrum allocation scheme for a multiple access wireless communication system according to an embodiment;

[0019] Fig. 3A is flowcharts of a pilot assignment scheme according to an embodiment;

53 / 59P27325PL00

[0020] FIG. 3BA is block diagrams of a pilot assignment scheme according to another embodiment;

[0021] Fig. 4A shows a pilot symbol scrambling scheme according to an embodiment;

[0022] Fig. 4A is a pilot symbol scrambling scheme in accordance with another embodiment;

[0023] Fig. 5 illustrates a base station with multiple sectors in a multiple access wireless communication system according to an embodiment;

[0024] Fig. 6 illustrates a multiple access wireless communication system in accordance with another embodiment;

[0025] Fig. 7 is a block diagram of an embodiment of a transmitter circuit and a receiver circuit in a multiple-input-multiple-output multiple access wireless communication system;

[0026] Fig. 8 is a flowchart of a pilot symbol generation method according to an embodiment; and

[0027] Fig. 9 is a flowchart of a method of modifying pilot symbol patterns according to an embodiment;

DETAILED DESCRIPTION

[0028] Fig. 1 shows a multiple access wireless communication system according to an embodiment. Base station 100 includes a plurality of groups 102, 104, and 106 antennas, each of which includes one or more antennas. In Fig. 1, only one antenna is shown for each antenna group 102, 104, and 106, however, multiple antennas may be used for each antenna group that corresponds to a sector of base station 100. Mobile station 108 communicates with antenna 104, with antenna 104 transmitting information to mobile station 108 over the forward link 114 and receiving information from mobile station 108 over reverse link 112.

53 / 59P27325PL00

Mobile station 110 communicates with antenna 106, with antenna 106 transmitting information to mobile station 110 via forward link 118 and receiving information from mobile station 110 via reverse link 116.

[0029] Each group of antennas 102, 104 and 106, and / or the area where they are designated to communicate, is typically referred to as a base station sector. In an exemplary embodiment, each of the antenna groups 102, 104, and 106 is designated to communicate with a mobile station in a sector of sectors 120, 122 and 124, respectively, of areas within the coverage of base station 100.

[0030] The base station may be a fixed station used for communicating with the terminals, and may also be referred to as access point, Node B, or by some other nomenclature. The mobile station may also be called a mobile station, user equipment (UE), wireless communication device, terminal, access terminal, or some other nomenclature.

[0031] Fig. 2 is a spectrum allocation scheme for a wireless multiple access system. A plurality of OFDM symbols 200 are allocated on T symbol periods and on S frequency subcarriers. Each OFDM symbol 200 includes one symbol period of T symbol periods and a frequency tone or subcarrier of S subcarriers.

[0032] In a frequency hopping OFDM system, one or more symbols 200 may be assigned to a given mobile station. In an embodiment of an allocation scheme as shown in Fig. 2, one or more hop regions, e.g., hop region 202, of symbols to a group of mobile stations for uplink communication. In each hop region, the symbol assignment may be randomized to limit potential interference and provide frequency diversity to harmful path influences.

53 / 59P27325PL00

[0033] Each hop area 202 includes symbols 204 which are assigned to one or more mobile stations that are in communication with a base station sector and are assigned to the hop area. In other embodiments, each hop region is assigned to one or more mobile stations. During each hopper period or frame, the position of the hop region 202 with respect to the T symbol periods and the S subcarriers changes according to the hopping sequence. In addition, the assignment of symbols 204 for individual mobile stations in the hop area 202 may vary for each hop area.

[0034] A hopping sequence may pseudo-randomly, randomly, or in accordance with a predetermined sequence, select the position of the hop region 202 for each hop region. Hop sequences for different sectors of the same base station are designed to be orthogonal to each other in order to avoid intracellular interference between mobile stations communicating with the same base station. In addition, the hop sequences for each base station may be pseudo-random with respect to the hop sequences for nearby base stations. This can help to randomize the intercellular interference between mobile stations communicating with other base stations.

[0035] For uplink communication, some of the symbols 204 of the hop area 202 are assigned to pilot symbols that are transmitted from the mobile stations to the base station. The assignment of pilot symbols to symbols 204 should preferably support space division multiple access (SDMA), where signals from different mobile stations overlapping in the same hop region may be split due to multiple receive antennas in a sector or base station, provided there is sufficient different mobile stations corresponding to the spatial diversity of signatures. In order to

To extract and demodulate the signals of different mobile stations more precisely, the respective uplink channels should be carefully estimated. Thus, it may be desirable that the pilot symbols on the reverse link allow the separation of pilot signatures of different mobile stations at each receiving antenna within a sector to sequentially apply multi-antenna processing to pilot symbols received from different mobile stations.

[0036] Block hopping may be used for both the forward link and the reverse link, or only for the reverse link depending on the system. It should be noted that while Fig. 2 shows a hop region 200 of seven symbol periods in length, the length of a hop region 200 may be any desired value, may vary in size between hopper periods, or between different hop regions within a given hopper period.

[0037] It should be noted that while the embodiment of Fig. 2 is described in terms of using block hopping, the position of the block need not be changed from one hop to another, or need not be changed at all.

[0038] Figs. 3A and 3B are block diagrams of pilot assignment schemes in accordance with several embodiments. Hop regions 300 and 320 are defined by T symbol periods and by S subcarriers or tones. The hop area 300 includes pilot symbols 302 and the hop area 320 includes pilot symbols 322, with the remaining symbol and tone period combinations available for data symbols and other symbols. In an embodiment, pilot symbol locations for each hop region, i.e., group N_s adjacent tones for N._T. subsequent OFDM symbols should have pilot tones located near the edges of the hop region. This is a general rule of thumb as typical channels in wireless applications are relatively slow time and functions

Thus, a first order channel approximation, e.g., a first order Taylor expansion, along the time and frequency hopping region provides information regarding the channel conditions that is sufficient to estimate the channel for a given mobile station. In such case, it is preferable to estimate the channel parameter pair for correct reception and demodulation of symbols from mobile stations, namely channel constant component, zero-order Taylor expansion term, and linear component, first-order Taylor expansion term, of the channel along the time and frequency range of the channel. Basically, the accuracy of the DC component estimation is independent of the pilot location. The accuracy of the linear component estimation is generally preferably achieved with pilot tones located at the edges of the hop region.

[0039] Pilot symbols 302 and 322 are distributed over adjacent clusters 304, 306, 308, and 310 (Fig. 3A) and

324, 326, 328, and 330 (Fig. 3B) pilot symbols. In an embodiment, each cluster 304, 306, 308, and 310 (Fig. 3A) and 324, 326, 328, and 330 (Fig. 3B) within a hop region has a fixed number, and often the same number, of pilot symbols in a given hop area. jump. The use of clusters 304, 306, 308 and 310 (Fig. 3A) and 324, 326, 328 and 330 (Fig. 3B) of adjacent pilot symbols may in an embodiment consider the effect of multi-user interference caused by inter-carrier interference that results from large Doppler delay and / or symbol spreads. Moreover, if pilot symbols from mobile stations scheduled in the same hop region are received at substantially different power levels, the signals of the stronger mobile station may generate a significant amount of interference to the weaker mobile station. The amount of interference is greater on the edge, e.g. subcarrier 1 and subcarrier S, of the hop region, and also on the edge of OFDM symbols, e.g. periods 1 and T of symbols when crosstalk is caused by

Excessive delay spread, ie, when the portion of the channel energy concentrated in channel response pulses (taps) that exceeds the cyclic OFDM symbol prefix becomes significant. Thus, if the pilot symbols are disposed only at the edges of the hop region, degradation in channel estimation accuracy and discrepancy in interference estimation may occur. Thus, as shown in Fig. 3A and 3B, the pilot symbols are placed close to the edges of the jump region, however avoiding that all pilot symbols are located at the edges of the jump region.

[0040] In Fig. 3A, a hop region 300 is comprised of pilot symbols 302. For channels with distinct frequency selectivity instead of time selectivity, pilot symbols 302 are distributed over adjacent pilot symbol clusters 304, 306, 308, and 310, with each pilot symbol cluster 304, 306, 308, and 310 including multiple symbol periods and one frequency tone. . The frequency tone is preferably selected to be close to the edges of the frequency range of the hop region 300, but not exactly at the edge. In the embodiment in Fig. 3A, none of the pilot symbols 302 in a given cluster is on edge frequency tones, and in each cluster only a pilot symbol may be in the edge of the symbol period.

[0041] One rationale for the horizontal shape of adjacent pilot symbol clusters for pilot symbols 302 is that for channels with higher frequency selectivity, the first order (linear) component may be stronger in the frequency domain than in the time domain.

It should be noted that the one or more pilot symbols in each cluster, in the embodiment of Fig. 3A, may be on a different tone than one or more pilot symbols in a different cluster. For example, cluster 304 may be on tone S and cluster 306 may be on tone S1.

53 / 59P27325PL00

In Fig. 3B, for channels with explicit time selectivity rather than frequency selectivity, pilot symbols 322 are arranged in clusters 324, 326, 328, and 330 of adjacent pilot symbols, each including multiple frequency tones but having the same period of time. jump area symbol 320. OFDM symbols at the edges of hop region 320, those having a maximum tone, e.g., S tone, or a minimum tone, e.g. tone 1 of the frequency range that defines the S sub-carriers may be included as part of the pilot symbols as there may be pilot symbols 322 that are located at the edges of the hop region 320. However, in the embodiment shown in Fig. 3B, only one pilot symbol in each cluster may be assigned to the maximum or minimum frequency subcarrier.

[0044] In the embodiment shown in Fig. 3B, a channel with higher time selectivity may have a conventional pattern that can be obtained by rotating 90 ° the pattern chosen for channels with higher frequency selectivity (Fig. 3A).

[0045] It should be noted that one or more pilot symbols in each cluster, in the embodiment of Fig. 3B, may be assigned to a different symbol period than one or more pilot symbols in a different cluster. For example, cluster 324 may be in a different symbol period T than cluster 326.

[0046] Further, as shown in the embodiments in Figs. 3A and 3B, pilot patterns are provided such that clusters 304, 306, 308, and 310 (Fig. 3A) and 324, 326, 328, and 330 (Fig. 3B) are preferably symmetrical with respect to the center of the jump region. Symmetry of the clusters about the center of the hop region may provide improved simultaneous channel estimation with respect to the time and frequency response of the channel.

[0047] It should be noted that although Figs. 3A and 3B show four pilot symbol clusters per

Hop region, fewer or more clusters may be used in each hop region. In addition, the number of pilot symbols per pilot symbol cluster may also vary. The total number of pilot symbols and pilot symbol clusters is a function of the number of pilot symbols required by the base station to correctly demodulate data symbols received on the uplink and to estimate the channel between the base station and the mobile station. Each cluster does not need to have the same number of pilot symbols either. The number of mobile stations that may be multiplexed in a single hop region may, in the embodiment, be equal to the number of pilot symbols in a hop region.

[0048] Moreover, while Figs. 3A and 3B show pilot symbol clusters for either channels having frequency selectivity or time selectivity, the pilot pattern may be such that there are clusters for frequency selective channels as well as clusters for time selective channels including same pilot pattern, e.g., some clusters arranged in the cluster pattern 304, 306, 308 or 310, and some clusters arranged in the cluster pattern 324, 326, 328, or 330.

[0049] In some embodiments, the pilot pattern selected to be used may be based on the conditions for which the channel is optimized. For example, for channels that may have a high speed of movement, e.g. vehicle speed, mobile stations, a time selective pilot pattern may be preferred, while for low velocity mobile stations, e.g. pedestrian speed, a time selective pilot pattern may be used. frequency selective pilot. In another embodiment, the pilot pattern may be selected based on channel conditions, a determination made after a predetermined number of hopper periods.

[0050] Referring to Figs. 4A and 4B, pilot allocation schemes according to further embodiments are illustrated. In Fig. 4A,

The hop region 400 includes symbols Ci,_qr C.₂,_q, and Cs 1, pilot deployed on cluster 402; C4_rq, C_2rq, and C6,_q, distributed over cluster 404; C.₇,_q, C8,_q, and C._9rq, distributed over cluster 406; and C._10rq, shh,_qr and Ci2_rq distributed in the cluster 408. In an embodiment, in order to increase spatial diversity in the hop regions where multiple mobile stations provide overlapping pilot symbols, the pilot symbols of different mobile stations should be multiplexed in the same OFDM symbol period and toned. the pilot symbols were generally orthogonal when received by the base station cluster antennas.

[0051] In Fig. 4A, each of the symbols C_lrq, C_2rq, C_3rq, C_4rq, C_5rq, C6,_q, c₇,_qr C._8rqf C._9iq, C₁₀,_q, C_llrq_f and C.₁₂,_q the pilot is assigned to a plurality of mobile stations of the hop area 400, i.e., each symbol period includes a plurality of pilot symbols, from a number of different mobile stations. Each of the pilot symbols in a pilot symbol cluster, e.g., cluster 402, 404, 406, and 408, is generated and transmitted such that a pilot symbol receiver in the cluster, e.g., base station, can receive them to be orthogonal with respect to to pilot symbols from every other mobile station in the same cluster. This may be achieved by applying a predetermined phase shift, e.g., a scalar function to multiply, each of the samples constituting the pilot symbols transmitted by each of the mobile stations. To ensure orthogonality, the scalar products of the vectors representing the sequence of scalar functions in each cluster for each base station may be zero.

[0052] Moreover, in some embodiments, it is preferred that the pilots of each cluster are orthogonal to the pilots of each other hop region cluster. This can be provided in the same way that orthogonality is provided for pilot symbols in each cluster from a different mobile station, by using a different

Sequence of scalar functions for the pilot symbols of each mobile station in each pilot symbol cluster . The mathematical determination of orthogonality may be done by selecting multiple scalar sequences for each of the pilot symbols for a specific cluster for a specific mobile station whose vector is orthogonal, e.g. the dot product is zero, with respect to the vector representing the sequence of scalar multiples used for pilot symbols of other mobile stations in all clusters and the same mobile station in other clusters.

[0053] In an embodiment, the number of mobile stations that may be served where pilot symbol orthogonality is provided within each of the clusters is equal to the number of pilot symbols that are per pilot symbol cluster.

[0054] In the embodiments of Figs. 4A and 4B, the qth user of Q overlapping users, 1 <q <Q, uses a sequence S of size N_F.where N_F. is the total number of pilot tones (in Figs. 4A and 4B, N_F. =12) :

(i) here (^T.) denotes a transposition of a matrix containing sequences. As mentioned above, the sequences of the scalar functions in each pilot symbol cluster should be different for different mobile stations in order to obtain consistent estimates of the corresponding channels by reducing interference between pilot symbols. Furthermore, the sequences should be linearly independent as it is preferred that no sequence or vector is a linear combination of the remaining sequences. Mathematically, it can be determined such that the matrix NP χ Q s = [ą ... s_e] (2) is the row of the full column. Note that in expression (2) above, the matrix N_p.

This means that the number

The overlapping mobile stations should not exceed the total number of pilot symbols in the hop region.

[0055] Based on the above, any full-order S sequence set of Q sequences allows consistent channel estimation. However, in another embodiment, the actual estimation accuracy may depend on the correlation property S. In an embodiment, as can be determined using equation (1), performance may be improved when any two sequences are (guasi-) orthogonal to each other in the presence of the S-channel. . Mathematically, this condition can be defined by ® 0 for all Κρ, ίίβ, ($) where H_k is a complex channel gain corresponding to the angle pilot symbol, l <kdNp. In a channel that is invariant in time and frequency = H.₂ = ... = Hnp condition (3) reduces to the requirement of mutually orthogonal sequences:

u, for all \ <p, q <Q, (4) k = 1 it may be impractical to impose this condition on any possible channel implementation from a typical channel set. In fact, expression (3) may be satisfied when the channel exhibits limited time and frequency selectivity, which is the case of pedestrian channels with a relatively small delay spread. However, the conditions may be substantially different in vehicle channels and / or channels with a significant delay spread, thus causing performance degradation.

[0056] As mentioned with reference to Figs. 3A and 3B, the pilot allocation patterns consist of several clusters of pilot symbols located near the edges of a hop region, each cluster being contiguous with time (Fig. 3A) and / or frequency (Fig. 3B). As the channel variations within each cluster are substantially limited due to the continuous nature of the pilot symbols over time and frequency and the continuity of the channel over time and frequency. So, providing orthogonality varies

The sequences in each cluster allow condition (3) to be satisfied. A potential disadvantage of this is that the number of overlapping mobile stations that may be orthogonal in each cluster is limited to the size of the cluster, denoted herein N_c. In the example shown in Figs. 4A and 4B, N_c = 3, thus up to Q = 3 mobile stations can be orthogonally separated in such an embodiment. In fact, a relatively small number of Q is sufficient in many practical scenarios. When Q> N_c, it can be difficult to maintain orthogonality of all the mobile stations in each cluster as there may be some interference between symbols. Therefore, the approximate orthogonality may be sufficient, with some loss in efficiency for time and frequency varying channels if Q> N_c.

[0057] In an embodiment, the design parameter set for the scalar function sequence S = [Si ... S_Q] can be defined by:

* Any two sequences are orthogonal over the entire pilot symbol set, thus satisfying = 0 for all l <p, g <Q, (5) and = l * Consecutive groups of N_c The sequences are such that any two sequences in the group are orthogonal to each other in the pilot cluster:

+ \ źp, q £ ηπη ((<+ 1) 0 <n0 <l <M_C.. (6) * All items Sk,_q all sequences have substantially equal absolute values, e.g., approximately the same power.

Where's m_c is the total number of clusters of size N_c, so that the number of pilots N_F. = M_C.N_C..

[0058] In an embodiment, the sequences S = [Si ... S_Q] are created using exponential functions so that by

Each sequence was provided with the same energy per symbol. Moreover, in this embodiment, it can be provided that the groups N_c the sequences will be mutually orthogonal over each cluster, regardless of cluster size, as the exponents are not limited to specific multiples, and with sequences used in every other cluster among all pilot symbols, by (i) specifying exponential sequences within each cluster, and (ii) populating parts inside a cluster in clusters. This can be seen in equation (7), where the base of the Discrete Fourier Transform (DFT) Ν χ N is defined.

<td></td><td></td><td></td><td></td><td> 1</td><td> 1</td><td></td><td> 1</td><td></td>

<td>F (W) =</td><td>Incl</td><td>^F.M in j. ^F.», M</td><td> =</td><td>12 ^ 1 e ^N</td><td></td><td></td><td>e ^N</td><td> (7)</td>

<td></td><td> _^F.M.</td><td></td><td></td><td>.2 ^ _e *</td><td>e *</td><td></td><td>e »</td><td></td>

The above expression (7) can be written in a compact

[0059] the embodiments as follows:

S- [ą ..... (8) where &lt;·&gt;_:,_1:0 stands for a matrix block made up of columns 1 through Q of the original matrix. The more general form of S can be expressed as:

where U is any identity matrix of N_c χ N_c (V * V = I_NF), and V is any identity matrix of M_c χ M_c (V * V = I_MC) .

[0060] In an embodiment, the number of mobile stations that may be served where pilot symbol orthogonality is ensured within each of the clusters is equal to the number of pilot symbols that are per pilot symbol cluster.

[0061] In an example, the exponential functions used to multiply the pilot symbol samples are generated from

Discrete Fourier Transform function which is well known. In embodiments where a Discrete Fourier Transform function is used to generate symbols for transmission, an additional phase shift is used when creating symbols using the Discrete Fourier Transform function in generating symbols for transmission.

[0062] In the embodiments of Figs. 4A and 4B, the scalar products of the vectors representing the sequence of scalar functions in each cluster for each base station may be zero. However, in other embodiments, this is not the case. The arrangement may be such that only guasiorthogonality is provided between the sequences of scalar functions in each cluster for each mobile station.

[0063] Moreover, in situations where the number of mobile stations assigned to the hop region is less than the number of pilot symbols assigned to the hop region, the scalar shifts may still be decoded at the base station to use to perform interference estimation. Therefore, these pilot symbols can be used for interference estimation because they are orthogonal or guasi-orthogonal with respect to pilot symbols by other mobile stations assigned to the hop region.

[0064] Fig. 5 shows a base station with multiple sectors in a multi-user wireless communication system according to an embodiment. Base station 500 includes multiple antenna groups 502, 504, and 506. In FIG. 5, only one antenna is shown for each antenna group 502, 504, and 506, however multiple antennas may be used. Multiple antennas from each group of antennas 502, 504, and 506 may be used to provide spatial diversity at the base station for signals transmitted from mobile stations in a corresponding sector, in addition to spatial diversity.

53 / 59P27325PL00 provided for different physical locations of different mobile stations.

[0065] Each antenna group 502, 504 and 506 of base station 500 is configured to communicate with mobile stations in the sector to be covered by base station 500. In the embodiment of Fig. 5, antenna group 502 covers sector 514, antenna group 504 covers sector 516 and antenna group 506 covers sector 518. In each sector, as described with reference to Fig. 4, pilot symbols transmitted from mobile stations can be accurately demodulated and used for channel estimation and for other functionalities at the base station due to orthogonality or approximate orthogonality between all inter-sector pilot symbol clusters.

[0066] However, intra-sector interference may exist for mobile stations close to a sector edge, e.g., for mobile station 510 which is near the edge of sectors 514 and 516. In that case, pilot symbols from mobile station 510 may have lower powers than symbols. pilot from other mobile stations in both sectors 514 and 516. In such a situation, mobile station 510 would eventually benefit from receiving using the antennas of both sectors, especially when its channel signals to the serving sector, i.e. of sector 516, may fade out if power is boosted from antenna 504. In order to take full advantage of the reception from antenna 502 of sector 514, an accurate channel estimate of mobile station 510 between antenna 502 of sector 514 should be provided. However, if the same or substantially the same sequences are used for scalar multiples of pilot symbols in different sectors with the present pilot structure, pilot symbols transmitted by mobile station 510 may conflict with pilot symbols transmitted by mobile station 508, which is scheduled at sector 514 in this the same hop area in which mobile station 510 is scheduled in sector 516. Also, in some instances

Depending on the power control strategy used by the base station to control the mobile stations, the power level of the symbols from the mobile station 508 may substantially exceed the signal level of the mobile station 510 in antenna group 502 of sector 514, especially when the mobile station 508 is nearby. base station 500.

[0067] In order to combat the intra-sector interference that may arise, scrambling codes for mobile stations may be used. The scrambling code may be unique for individual mobile stations or it may be the same for each of the mobile stations communicating with a particular sector. In an embodiment, these special scrambling codes allow antenna group 502 to see the composite channel of mobile stations 508 and 510.

[0068] In the event that one mobile station is assigned to an entire hop area, user specific scrambling sequences may be provided such that each mobile station in a given sector uses the same pilot sequence; the construction of these sequences is described with reference to Figs. 4A and 4B. In the example of Fig. 5, mobile stations 508, 510, and 512 may have different user-specific scrambling sequences, and thus, sufficient channel estimation may be achieved.

[0069] In the event that multiple mobile stations are, or may be, assigned to the same hop area, two methods may be used for intra-cluster interference mitigation. First, user-specific scrambling sequences can be used if size N_c the cluster is greater than or equal to the number of overlapping mobile stations in each sector Q times the number of sectors in the cell. If so, different sets of Q different user-specific scrambling codes may be assigned to different sectors.

53 / 59P27325PL00

[0070] However, if the size of N_c cluster is smaller than the number of overlapping mobile stations in each sector Q times the number of sectors in a cell, this may be important if the purpose of system design is to preserve N_c In order to maintain limited pilot overhead, user-specific scrambling codes may not be effective in reducing inter-cell interference. In such a case, a sector specific scrambling sequence may be used in conjunction with a user specific scramble sequence.

[0071] A sector-specific scramble sequence is a sequence X_s = [X_{2f p} Xnp, _s]^vol N_p complex functions that multiply the individual elements of the sequence S = [Si ... S_Q], for all mobile stations in the same sector. In a cell consisting of S sectors, a set of S sector-specific scramble sequences X and X_s can be used to multiply the sequence S = [Si ... S_Q] mobile stations. In this case, mobile stations in different sectors, e.g. sectors 514 and 516, which may include mobile stations that use the same user-specific scrambling sequences S = [Si ... S_Q] may differ due to different sector-specific X scrambles_s2 and X_s2used to multiply a user-specific scramble sequence.

[0072] As with user-specific encryption, it is preferred that all entries of X₂X_s have approximately equal absolute values ​​in order to maintain approximately equal power between the pilot symbols. In other embodiments, it is preferable that entries Xi, ..., X_s were such that any pair of pilot symbols in the pilot symbol cluster corresponding to any two combinations of user-specific and sector-specific scramble sequences satisfy condition (3). One approach to selecting the content of each sector specific X sequence₂ Xs consists of

Exhaustive sequence lookup such that the elements of each sequence are derived from some constant module constellation (PSK) such as QPSK, 8-PSK. The selection criterion may be based on the worst-case variance of the channel estimation error corresponding to the worst combination of mobile stations from different sectors and different user-specific scrambling that is based on a potential channel environment. The channel estimation error may be calculated analytically based on the statistical properties of the channel. Specifically, a channel estimate covariance matrix trace that adopts a channel correlation structure based on a predicted fading model and parameters such as mobile station speed, which determines the time selectivity, and propagation delay spread, which determines frequency selectivity. The analytical expressions for the minimum achievable channel estimation error depending on a given actual channel correlation structure are known in the art. Other similar criteria can also be used to optimize the selection of X,. . . , Xs

[0073] In an embodiment where quadrature amplitude modulation is used as the modulation scheme, a set of sector-specific scramble sequences X₂ , ..., X_sthat can be used are shown in Table 1 below. Each entry in the table specifies the I and Q components of each X_for, l &lt;sńS and l &lt;k &lt;N_P. for S = 3 and N_P. = 12.

53 / 59P27325PL00

Table

<td> 04</td><td> (+1,+0)</td><td> (+0,+1)</td><td>o + V</td>

<td></td><td>o + -1-</td><td>+ o +</td><td>o +</td>

<td>ABOUT</td><td> +</td><td>(+ o, + l)</td><td> (+0,-1)</td>

<td>&lt;Τί</td><td>about</td><td>+ o +</td><td> (+1,+0)</td>

<td>WHAT</td><td>o +</td><td> (+0,-1)</td><td>(Τ + Ό-)</td>

<td></td><td> (+1,+0}</td><td>o + +</td><td> +</td>

<td>IN</td><td>o + k</td><td>o + +</td><td>1 k +</td>

<td>LU</td><td>o +</td><td> 1 +</td><td>+ k +</td>

<td>•and·</td><td>o + k +</td><td> (+1,+0)</td><td>o + k +</td>

<td>cU</td><td>o + k +</td><td>o + V</td><td>o + k +</td>

<td> 04</td><td>o + i — l +</td><td>o + +</td><td>o + k 1</td>

<td>t-4</td><td>+ i — l +</td><td> {+1,+0}</td><td>+ k O +</td>

<td>Λί</td><td>7 ω</td><td>Cs] 11 cn</td><td>What II</td>

53 / 59P27325PL00

[0074] In an embodiment where quadrature amplitude modulation is used as the modulation scheme, a set of sector-specific scramble sequences X_k The Xs that may be used are shown in Table 1 below. Each entry in the table specifies the I and Q components of each X_Fr., 1 &lt;s ^ S and l &lt;k &lt;N_P. for S = 3 and N_P. = 12. [0075] In some embodiments, each cell in the communication network can use the same sequences for sector specific scramble sequences.

[0076] Fig. 6 shows a wireless multiple access system 600 in accordance with another embodiment. In the event that the same sets of user-specific and sector-specific scrambling sequences are used in multiple cells, e.g., cells 602, 604, and 606, interference from neighboring cells may lead to degradation in channel estimation accuracy due to pilot symbol collisions. For example, the channel estimation in the sector of interest may be distorted by the channel of a mobile station from a neighboring cell which mobile station has the same user and sector specific encryption. To avoid this distortion, cell-specific encryption in addition to user-specific and sector-specific encryption may be used. The cell specific encryption scheme may be specified by Y_c = [Yi,_c Ynp, _s] 7 which is a scalar function vector that multiplies the corresponding pilot symbol sequence for each mobile station in the cell. Complete sequence of Z pilot symbols_(q,_s,_c) = [Z_lr(q_rs_rc) / ··· / Z_Np, (_q,_s, c) ~ \^T. r that corresponds to a mobile station with a coding specific for the qth coding user in the nth sector of the c-th cell can be determined as follows. If sector-specific encryption is used:

53 / 59P27325PL00 ^ k ^ N_p, 1 &lt;^ S, c = 1,2 (10)

If sector-specific encryption is not used:

lźkSN_P., IźsźS, c = 1,2 "... (11)

[0077] As already mentioned, the use of sector specific encryption is recommended when Q&gt; 1 and not recommended when Q = 1.

[0078] Contrary to user and sector specific encryption, no particular optimization of cell specific scrambling sequences needs to be used. The two design parameters that can be used are that:

* All elements of a cell-specific encryption sequence have equal modules.

* Cell-specific encryption sequences vary widely from cell to cell.

[0079] In the absence of a predetermined assignment of cell-specific scramble sequences in a network of base stations, (pseudo) random cell-specific scrambles from some constellations of constant modulus (PSK) may be used in the formation of the Y cell-specific sequences. such as QPSK, 8-PSK. To further increase the randomization of the cell-specific encryption and to avoid bad fixed combinations of the encryption sequences, the cell-specific encryption may be changed periodically in a (pseudo) random manner. In some embodiments, each frame, super frame, or multiple frames or super frames may be changed periodically.

[0080] Fig. 7 is a block diagram of an embodiment of a transmitter circuit 710 and a receiver circuit 750 in a MIMO system 700. At transmitter circuit 710, traffic data for multiple data streams is provided from data source 712 to data source 712.

53 / 59P27325PL00 of a transmitted data (TX) processor 714. In an embodiment, each data stream is transmitted via a respective transmit antenna. TX data processor 714 formats, codes, and interleaves the run data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

[0081] The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. Typically, the pilot data is a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot data and coded data for each data stream are then modulated (i.e., a symbol mapping) based on the specific modulation scheme (e.g. BPSK, QSPK, M-PSK or MQAM) selected for this data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by the instructions performed on the provided by controller 130.

[0082] The modulation symbols for all data streams are then provided to TX processor 720, which may then process the modulation symbols (e.g., for OFDM). TX processor 720 then provides N_T. modulation symbol streams to N_T. transmitters (TMTR) from 722a to 722t. Each transmitter 722 receives and processes a corresponding symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and frequency-upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. N_T. modulated signals from transmitters 722a through 722t are then transmitted from the N_T. antennas from 124a to 124t, respectively.

53 / 59P27325PL00

[0083] At receiver circuit 750, the transmitted modulated signals are received at N_K. antennas 752a through 752r, and the received signal from each antenna 752 is provided to an appropriate receiver (RCVR) 754. Each receiver 754 conditions (e.g., filters, amplifies, and frequency downconverts) the corresponding received signal, and converts the conditioned signal to digital form into to provide samples, and then processes the samples to provide the corresponding received symbol stream.

[0084] RX data processor 760 then receives and processes the N_r received symbol streams from N_K. receivers 754 based on the specific receiver processing technique to provide N_T. symbol streams detected. The processing performed by RX data processor 760 is described in more detail below. Each detected symbol stream includes symbols that are estimates of modulation symbols transmitted for the corresponding data stream. RX data processor 760 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing performed by RX data processor 760 is complementary to that performed by TX processor 720 and TX data processor 714 in transmitter circuit 710.

[0085] RX processor 760 may determine the estimate of the channel response between N_T. transmitting antennas and N_K. receiving antennas, e.g. based on pilot information multiplexed with traffic data. RX processor 760 may identify pilot symbols according to pilot patterns stored in memory, e.g., memory 772 that identify a frequency subcarrier and a symbol period assigned to each pilot symbol. In addition, user-specific, sector, and cell-specific scrambling sequences can be stored in memory so that they can be used by the RX 760 processor to multiply

53 / 59P27325PL00 of received symbols, such that appropriate decoding can take place.

[0086] The response estimation generated by RX processor 760 can be used to perform spatial, spatial / temporal processing at a receiver, adjusting power levels, changing modulation rate or schemes, or other actions. RX processor 760 may further estimate the signal to noise and interference (SNR) ratios of the detected symbol streams, and possibly other channel characteristics, and provide these quantities to the controller 770. RX data processor 760 or controller 770 may further determine an operational SNR estimate for the system. Controller 770 then provides channel state information (CSI), which may include various types of information regarding the communication link and / or the received data stream. For example, the CSI information may include only operational SNR. The CSI information is then processed by TX data processor 778, which also receives traffic data for multiple data streams from data source 776, modulated by modulator 780, conditioned by transmitters 754a through 754r, and transmitted back to transmitter circuit 710.

[0087] At transmitter circuit 710, modulated signals from receiver circuit 750 are received by antennas 724, conditioned by receivers 722, demodulated by demodulator 740, and processed by RX data processor 742 to recover CSI information reported by the receiver circuitry. The reported CSI information is then passed to controller 730 and used to (1) determine the data rate and coding and modulation schemes to be used for the data streams and (2) generate various control signals for TX data processor 714 and TX processor 720.

[0088] Controllers 730 and 770 direct the operation of the transmitter circuit and receiver circuit, respectively. Memories 732 and 772

53 / 59P27325PL00 provide for the storage of program codes and data used by controllers 730 and 770, respectively. Memories 732 and 772 store pilot patterns in terms of cluster locations, user specific scramble sequences, sector specific scramble sequences if used, and specific scramble sequences. cells, if used. In some embodiments, multiple pilot patterns are stored in each memory so that the transmitter can transmit and the receiver can receive both frequency selective and time selective pilot patterns. A combination of pilot patterns having clusters geared to time selective channels and frequency selective channels may also be used. This allows the transmitter to transmit a specific pattern based on a parameter, such as a random sequence, or in response to stand and base instructions.

[0089] Processors 730 and 770 may then select which of the pilot patterns, user specific scramblers, sector specific scramblers, and cell specific scramblers to be used in the transmission of pilot symbols.

[0090] At the receiver, various processing techniques may be used to process the N_R received signals to detect N_T. transmitted symbol streams. These receiver processing techniques can be grouped into two basic categories (i) spatial and time-space receiver processing techniques (which are also referred to as equalization techniques) and (ii) receiver processing technique successive clearing / correcting and interference suppression (which is also referred to as Receiver processing tuner successively eliminating interference or successively eliminating).

53 / 59P27325PL00

[0091] Although Fig. 7 shows a MIMO system, the same system may be used in a multi-input-single-output system in which multiple transmit antennas, e.g., those at a base station, transmit one or more symbol streams to a single-output device. an antenna, e.g. of a mobile station. Also, the one-output-one input antenna system can be used in the same way as described with reference to Fig. 7.

[0092] Fig. 8 is a flowchart of a pilot symbol generation method according to an embodiment. Multiple pilot symbol clusters are selected for transmission over a hop region time from a particular mobile station, block 800. All of these pilot symbol clusters may be adapted to be transmitted on a frequency-selective channel (Fig. 3A), time-selective channel (Fig. 3B), or a combination of clusters, some of which are suitable for transmission on a frequency selective and time selective channel.

[0093] Once the pilot symbol clusters are selected, a decision is made as to whether the base station cluster in which the mobile station is communicating supports or is communicating with multiple mobile stations, block 802. This determination may be based on a priori knowledge of the network. where the mobile station is located. Alternatively, the information may be communicated from the base station sector as part of the pilot information or network messages.

[0094] If the cluster does not support communication, or is not currently communicating with multiple mobile stations, then scalar functions are applied on pilot symbols that are unique within the cluster with which the mobile station is communicating, block 804. In an embodiment, the scalar functions for each sector may be stored in the mobile station and used depending on the sector identification signal that is part of its part of its pilot information or broadcast messages.

53 / 59P27325PL00

[0095] If the cluster does not support communication with multiple mobile stations then scalar functions are applied to pilot symbols that are unique to the mobile station, block 806. In some embodiments, the scalar functions for each mobile station may be based on its unique identifier being used. for registration or delivered to the device at the time of production.

[0096] When scalar functions that are unique to either the sector in which the mobile station is communicating or the mobile station itself are applied to pilot symbols, another sequence of scalar functions, block 808, is applied to the pilot symbols. Scalar function sequence relates to the cell. in which the mobile station communicates. This scalar function may change over time if each cell is not specifically assigned scalar functions that are known or provided to mobile stations. After this operation, pilot symbols can be communicated from the mobile station to the base station.

[0097] The scalar functions discussed with respect to Fig. 8 may, in an exemplary embodiment, include a phase shift of each of the samples that constitute the pilot symbols. As mentioned with reference to Fig. 4A, 4B, 5 and 6, the scalar functions are selected such that each pilot symbol cluster is orthogonal to each different pilot symbol set from the same mobile station in other pilot symbol clusters and in the same and different pilot symbol clusters for other mobile stations. the same sector of the base station.

[0098] Furthermore, each block described with reference to Fig. 8 may be implemented as one or more instructions in a computer readable medium such as memory, which are executed by a processor, controller, or other electronic circuitry.

[0099] Fig. 9 is a flowchart of a method of modifying pilot symbol patterns according to an example

53 / 59P27325PL00 execution. Information regarding channel conditions is received, block 900. The information may include SNRs in one or more sectors of the base stations, channel selectivity at the base station, the desired type of traffic, pedestrian or circular for which the base station is to be optimized, delay spread, or otherwise. channel properties. In addition, the information may relate to time periods, may be part of the normal maintenance operations with respect to the base station or network of base stations, may be based on increased load on the base station or network of base stations, or other periods.

[0100] The information is analyzed to determine the channel conditions of a sector or base station, block 902. The analysis may be a determination as to whether a given channel is frequency selective, time selective, or a combination of both. The analysis is then used to determine a pilot symbol pattern to be communicated from mobile stations that are able to communicate with the sector or base station, block 904. All these pilot symbol clusters may be adapted to be transmitted on a frequency-selective channel (Fig. 3A), a time-selective channel (Fig. 3B), or a combination of clusters, some of which are adapted to be transmitted on a frequency-selective and time-selective channel. The selected specific pilot pattern may then be used by all mobile stations that are in communication with the base station or sector until diagnostics are performed again for the base station or sector.

[0101] To implement a particular pilot pattern in mobile stations communicating at the base station or base station sector, an instruction may be transmitted from the base station or sector to the mobile stations as part of an initialization or configuration procedure. In some embodiments, information such as which pilot pattern, user specific scramble sequence, scramble sequence

The sector-specific and / or cell-specific scramble sequence to be used may be transmitted in a preamble of one or more data packets that are transmitted from the base station to the mobile station at regular intervals or during initialization or configuration.

[0102] Note that the analysis may also be used to determine the number of pilot symbols to be transmitted in each pilot symbol cluster and pilot symbol groupings. In addition, each block described with reference to Fig. 9 may be implemented as one or more instructions on a computer readable medium such as memory or removable medium which is implemented by a processor, controller, or other electronic circuitry.

[0103] The techniques described herein may be practiced in a variety of ways. For example, the techniques may be implemented in hardware, software, or a combination thereof. For hardware implementation, the processing units in the base station or mobile station may be implemented in one or more special purpose integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), programmable logic gate matrix (FPGA), processors, controllers, microcontrollers, microprocessors, other electronic devices designed to perform the functions described in this document, or combinations thereof.

[0104] For a software implementation, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Software codes 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

53 / 59P27325PL00 processor via various means that are known in the art.

[0105] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments may be apparent to those skilled in the art, and the general principles set forth herein may be applied to other embodiments without departing from the scope of the invention as defined in the appended claims. Thus, the present invention is not intended to be limited to the embodiments set forth herein, but is intended to conform to the broadest scope consistent with the principles and novel features set forth herein.