Title of Invention

A METHOD OF ASSIGNING FREQUENCY SUBBANDS IN A COMMUNICATION SYSTEM AND APPARATUS THEREOF

Abstract For quasi-orthogonal multiplexing in an OFDMA system, multiple (M) sets of traffic channels are defined for each base station. The traffic channels in each set are orthogonal to one another and may be pseudo-random with respect to the traffic channels in each of the other sets. The minimum number of sets of traffic channels (L) is used to support a given number of (U) terminals selected for data transmission, where and . Each terminal transmits data and pilot symbols on its traffic channel. A base station receives data transmissions from all terminals and may perform receiver spalial processing on received symbols with spatial filter matrices to obtain detected data symbols. The spatial filter matrix for each subband may be derived based on channel response estimates for all terminals transmitling on that subband.
Full Text MULTIPLEXING FOR A MULTI-CARRIER CELLULAR COMMUNICATION
SYSTEM
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Patent Application Serial
No. 60/580,810, filed June 18, 2004, which is incorporated herein by reference in their entirety.
BACKGROUND
I. Field
[0002] The present invention relates generally to data communication, and more
specifically to data transmission in a multi-carrier multiple-access communication
system.
II. Background
[0003] A multiple-access system can concurrently support communication for
multiple terminals on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. Multiple terminals may simultaneously transmit data on the reverse link and/or receive data on the forward link. This may be achieved by multiplexing the multiple data transmissions on each link to be orthogonal to one another in time, frequency, and/or code domain. Complete orthogonality is typically not achieved in most instances due to various factors such as channel conditions, receiver imperfections, and so on. Nevertheless, the orthogonal multiplexing ensures that the data transmission for each terminal minimally interferes with the data transmissions for the other terminals.
[0004] A multi-carrier communication system utilizes multiple carriers for data
transmission. The multiple carriers may be provided by orthogonal frequency division multiplexing (OFDM), discrete multi tone (DMT), some other multi-carrier modulation techniques, or some other construct. OFDM effectively partitions the

overall system bandwidth into multiple (K) orthogonal frequency subbands. These subbands are also referred to as tones, sub-carriers, bins, frequency channels, and so on. Each subband is associated with a respective sub-carrier that may be modulated with data.
[0005] An orthogonal frequency division multiple access (OFDMA) system is a
multi-access system that utilizes OFDM. An OFDMA system may use time and/or frequency division multiplexing to achieve orthogonality among multiple data transmissions for multiple terminals. For example, different terminals may be allocated different subbands, and the data transmission for each terminal may be sent on the subband(s) allocated to the terminal. By using disjoint or non-overlapping subbands for different terminals, interference among the multiple terminals may be avoided or reduced, and improved performance may be achieved.
[0006] The number of subbands available for data transmission is limited (to K) by
the OFDM structure used for the OFDMA system. The limited number of subbands places an upper limit on the number of terminals that may transmit simultaneously without interfering one another. In certain instances, it may be desirable to allow more terminals to transmit simultaneously, e.g., to better utilize the available system capacity. There is therefore a need in the art for techniques to concurrently support more terminals in an OFDMA system.
SUMMARY
[0007] Techniques that can support simultaneous transmission for more terminals
than the number of orthogonal transmission units (or orthogonal dimensions) available in the system are described herein. Each such "transmission unit" may correspond to a group of one or more subbands in one or more symbol periods, and is orthogonal to all other transmission units in frequency and time. These techniques are called "quasi-orthogonal multiplexing" and may be used to more fully utilize additional capacity that may be created in a spatial dimension by employing multiple antennas at a base station. These techniques can also reduce the amount of interference observed by each terminal, which may improve performance.
[0008] In an embodiment of quasi-orthogonal multiplexing that is suitable for an
OFDMA system, multiple (M) sets of traffic channels are defined for each base

station in the system. Each set contains multiple (N) traffic channels, e.g., one traffic channel for each orthogonal transmission unit available in the system. Each traffic channel is associated with the particular orthogonal transmission unit (e.g., the particular subbands) to use for each transmission interval. For a frequency hopping OFDMA (FH-OFDMA) system, each traffic channel may be associated with an FH sequence that pseudo-randomly selects different subbands in different transmission intervals or hop periods. The traffic channels in each set are orthogonal to one another and may be pseudo-random with respect to the traffic channels in each of the other M-l sets. A total of M-N traffic channels are then available for use in the system. The minimum number of sets of traffic channels (L) may be used to support a given number of (U) terminals selected for data transmission. Each terminal may be assigned a traffic channel selected from the L sets of traffic channels.
[0009] Each terminal transmits data symbols (which are modulation symbols for
data) on its traffic channel. Each terminal also transmits pilot symbols, (which are modulation symbols for a pilot) on its traffic channel to allow a base, station to estimate the response of the wireless channel between the terminal and the base station. The U terminals may transmit simultaneously on their assigned traffic channels.
[0010] The base station receives data transmissions from the U terminals and obtains
a vector of received symbols for each subband in each symbol period. The base station may derive a spatial filter matrix for each subband based on channel response estimates obtained for all terminals transmitting on that subband. The base station may perform receiver spatial processing on the received symbol vector for each subband with the spatial filter matrix for that subband to obtain detected data symbols, which are estimates of the data symbols sent by the terminals using the subband.
[0011] Various aspects and embodiments of the invention are described in further
detail below.

BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The features and nature of the present invention will become more apparent
from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:
[0013] FIG. 1 shows multiple terminals and a base station in an OFDMA system;
[0014] FIG. 2 illustrates frequency hopping in the OFDMA system;
[0015] FIG. 3 shows M sets of FH sequences for quasi-orthogonal multiplexing;
[0016] FIG. 4 shows a process for assigning FH sequences to U terminals;
[0017] FIG. 5 shows a block diagram of a single-antenna terminal and a multi-
antenna terminal; and
[0018] FIG. 6 shows a block diagram of the base station.
DETAILED DESCRIPTION
[0019] The word "exemplary" is used herein to mean "serving as an example,
instance, or illustration." Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
[0020] The quasi-orthogonal multiplexing techniques described herein may be used
for various multi-carrier communication systems, e.g., an OFDM-based system such as an OFDMA system. These techniques may also be used for single-antenna and multi-antenna systems. A single-antenna system utilizes one antenna for data transmission and reception. A multi-antenna system utilizes one or multiple antennas for data transmission and multiple antennas for data reception. These techniques may also be used for time division duplexed (TDD) and frequency division duplexed (FDD) systems, for the forward and reverse links, and with or without frequency hopping. For clarity, quasi-orthogonal multiplexing is described below for the reverse link of a multi-antenna FH-OFDMA system.
[0021] FIG. 1 shows multiple terminals 1 lOa through 1 lOu and a base station 120 in
an OFDMA system 100. A base station is generally a fixed station that communicates with the terminals and may also be referred to as an access point or some other terminology. A terminal may be fixed or mobile and may also be referred

to as a mobile station, a wireless device, or some other terminology. The terms "terminal" and "user" are also used interchangeably herein. Base station 120 is equipped with multiple (R) antennas for data transmission and reception. A terminal may be equipped with one antenna (e.g., terminal HOa) or multiple antennas (e.g., terminal HOu) for data transmission and reception. The R antennas at base station 120 represent the multiple-input (MI) for transmissions on the forward link and the multiple-output (MO) for transmissions on the reverse link. If multiple terminals are selected for simultaneous transmission, then the multiple antennas for these selected terminals collectively represent the multiple-output for forward link transmissions and the multiple-input for reverse link transmissions.
[0022] FIG. 2 illustrates frequency hopping (FH) transmission scheme 200 that may
be used for the OFDMA system. Frequency hopping can provide frequency diversity against deleterious path effects and randomization of interference. With frequency hopping, each terminal/user may be assigned a different FH sequence that indicates the particular subband(s) to use in each "hop" period. An FH sequence may also be called a hop pattern or some other terminology. A hop period is the amount of time spent on a given subband, may span one or multiple symbol periods, and may also be called a transmission interval or some other terminology. Each FH sequence may pseudo-randomly select subbands for the terminal. Frequency diversity is achieved by selecting different subbands across the K total subbands in different hop periods. FH sequences and traffic channels may be viewed as convenient ways of expressing assignment of subbands.
[0023] The FH sequences for different users in communication with the same base
station are typically orthogonal to one another so that no two users use the same subband in any given hop period. This avoids "intra-cell" or "intra-sector" interference among the terminals communicating with the same base station (assuming that orthogonality is not destroyed by some other factor). The FH sequences for each base station may be pseudo-random with respect to the FH sequences for nearby base stations. Interference between two users communicating with two different base stations occurs whenever the FH sequences for these users select the same subband in the same hop period. However, this "inter-cell" or "inter-sector" interference is randomized due to the pseudo-random nature of the FH sequences.

[0024] For the embodiment shown in FIG. 2, the subbands usable for data
transmission are arranged into N groups. Each group contains S subbands, where in general N>1, S>1, and N-S^K. The subbands in each group may be contiguous, as shown in FIG. 2. The subbands in each group may also be noncontiguous, e.g., uniformly distributed across the K total subbands and evenly spaced apart by S subbands. Each user may be assigned one group of S subbands in each hop period. Data symbols may be time division multiplexed with pilot symbols, which are known a priori by both the terminal and base station, as shown in FIG. 2.
[0025] Interference may be avoided or reduced among all users communicating with
the same base station if their FH sequences are orthogonal to one another. In this case, the users are assigned non-overlapping groups of subbands or, equivalently, a subband is only used by at most one user at any given time. Complete orthogonality is typically not achieved due to channel conditions, receiver imperfections, unsynchronized timing at the terminals, and so on. The loss of orthogonality may cause inter-carrier interference (ICI) and inter-symbol interference (ISI). However, the ICI and ISI may be small in comparison to the interference that would be observed if the users are not assigned orthogonal FH sequences.
[0026] The number of subband groups available for data transmission is limited, e.g.,
to N for the embodiment shown in FIG. 2. If one subband group is assigned to each user, then more than N users may be supported by time division multiplexing (TDM) the users and allowing different sets of up to N users to transmit on up to N groups of subbands in different hop periods. More than N orthogonal transmission units may thus be created in the frequency and time domains, where each transmission unit is orthogonal to all other transmission units in frequency and time. The transmission units may also be viewed as orthogonal dimensions. The time division multiplexing of users may be undesirable since it reduces the amount of time available for data transmission, which may then limit the data rates achievable by the users.
[0027] In certain instances, it may be desirable to support more users than the
number of available orthogonal transmission units. For example, additional capacity may be created in the spatial dimension by employing multiple antennas at the base station. The base station may then be able to support more users with the additional capacity. However, the number of orthogonal transmission units available in the OFDMA system is determined by the system design and is typically limited and

finite for a given system bandwidth and a given time duration. For simplicity, the following description assumes that time division multiplexing is not used and N orthogonal transmission units are available in the system, although this is not a requirement for quasi-orthogonal multiplexing. Once all of the available transmission units have been assigned to users, it is no longer possible to support additional users while still maintaining orthogonality among all of the users.
[0028] Quasi-orthogonal multiplexing can allow more users to simultaneously
communicate on the reverse link, e.g., to more fully utilize the additional capacity created by the multiple antennas at the base station. In an embodiment, multiple (M) sets of FH sequences are defined for each base station. Each set contains N FH sequences, or one FH sequence for each orthogonal transmission unit available in the system. A total of M • N FH sequences are then available for use in the system.
[0029] FIG. 3 shows M sets of FH sequences that may be used for quasi-orthogonal
multiplexing. The first FH sequence in each set is indicated by the darkened boxes on a frequency-time plane for that set. The remaining N -1 FH sequences in each set may be vertical and circular shifted versions of the first FH sequence in the set. The N FH sequences in each set are orthogonal to one another. Thus, no interference is observed among N data transmissions sent simultaneously by N users assigned with the N FH sequences in any given set (assuming no loss of orthogonality due to other factors). The FH sequences in each set may also be pseudo-random with respect to the FH sequences for each of the M -1 other sets. In this case, data transmissions sent simultaneously using the FH sequences in any one set would observe randomized interference from data transmissions sent using the FH sequences in the other M -1 sets. The M sets of N FH sequences may be generated in various manners.
[0030] hi one embodiment, the N FH sequences for each set are derived based on a
pseudo-random number (PN) code assigned to that set. For example, the 15-bit short PN codes defined by IS-95 and IS-2000 may be used. The PN code may be implemented with a linear feedback shift register (LFSR). For each hop period, the LFSR is updated and the content of the LFSR is used to select the subbands for the N FH sequences in the set. For example, a binary number corresponding to the B least significant bits (LSBs) in the LFSR may be denoted as PNt(t), where B = log2(N),

i is an index of the M sets of FH sequences, and t is an index for hop period. The N FH sequences in set t may then be defined as:
fifi) = ([PNt(t) + i] mod N) +1 , for I = 1 ... M and i = 1 ... N, Eq (1)
where i is an index for the N FH sequences in each set; and ft>i(t) is the i-th FH sequence in set £.
The +1 in equation (1) accounts for an indexing scheme that starts with T instead of '0'. The FH sequence fei(t) indicates the particular subband(s) to use for each hop
period t.
[0031] To simplify implementation, the M PN codes used for the M sets of FH
sequences may be defined to be different time shifts of a common PN code. In this case, each set is assigned a unique time shift, and the PN code for that set may be identified by the assigned time shift. The common PN code may be denoted as PN(t), the time shift assigned to set i may be denoted as AT£, and the binary
number in the LFSR for set i may be denoted as PN(t + AT,). The N FH sequences in set £ may then be defined as:
ft.(t) = ([FN(t + AT,) + /] mod N) +1 , for I = 1 ... M and i = 1 ... N. Eq(2)
[0032] In another embodiment, the M sets of FH sequences are defined based on M
different mapping tables, one table for each set. Each mapping table may implement a random permutation of an input. Each mapping table receives an index i for the i-th FH sequence in the set associated with the table and provides the subband(s) to use for this FH sequence in each hop period t. Each mapping table may be defined to be pseudo-random with respect to the other M -1 mapping tables.
[0033] The M sets of N FH sequences may also be defined and generated in other
manners, and this is within the scope of the invention.
[0034] FH sequences may be assigned to the users in a manner to reduce the amount
of intra-cell interference observed by all of the users. For simplicity, the following description assumes that one orthogonal transmission unit is assigned to each user selected for transmission. If the number of users selected for data transmission (U) is less than or equal to the number of orthogonal transmission units (or U ^ N ), then

the U users may be assigned orthogonal FH sequences in one set. If the number of users is greater than the number of orthogonal transmission units (or U > N ), then additional FH sequences from one or more other sets may be used. Since the FH sequences from different sets are not orthogonal to one another and thus result in intra-cell interference, the smallest number of sets should be used at any given moment. The minimum number of sets (L) needed to support U users may be expressed as:

L —

.Eq(3)

where "f~x~|" denotes a ceiling operator that provides an integer value that is equal to or
greater than x.
[0035] If L sets of FH sequences are used for U users, then each user will observe
interference from at most L-l other users at any given moment and is orthogonal to at least U - (L -1) other users. If U is much larger than L, which is typically the case, then each user observes interference from a small number of users at any given moment. The U users may then be viewed as somewhat orthogonal, or "quasi-orthogonal", with one another.
[0036] FIG. 4 shows a flow diagram of a process 400 for assigning FH sequences to
users with quasi-orthogonal multiplexing. Initially, the number of users selected for data transmission (U) is determined (block 412). The minimum number of sets of FH sequences (L) needed to support all of the selected users is then determined (block 414). If each selected user is assigned one FH sequence and if each set contains N FH sequences, then the minimum number of sets may be determined as shown in equation (3). L sets of FH sequences are then selected from among M sets of FH sequences available for use (block 416). Each selected user is then assigned one (or possibly multiple) FH sequences from the L sets of FH sequences (block 418).
[0037] The U selected users may be assigned FH sequences from the L sets in
various manners, m one embodiment, users with similar received signal qualities are assigned FH sequences in the same set. Received signal quality may be quantified by a signal-to-interference-and-noise ratio (SINR) or some other measurement. For this

embodiment, the U users may be ranked based on their SINRs, e.g., from highest SINR to lowest SINR. One user may be processed at a time, in sequential order based on the ranking, and assigned an FH sequence from a first set of FH sequences. Another set of FH sequences is used whenever all FH sequences in the first set have been assigned. This embodiment can map users with similar channel conditions to the same FH sequence set. For example, users located closer to the base station may achieve higher SINRs and may be assigned FH sequences in one set. Users located farther away from the base station (or "sector-edge" users) may achieve lower SINRs and may be assigned FH sequences in another set. This embodiment may also facilitate power control of the users. For example, the sector-edge users may cause more interference to users in other sectors and may be directed to transmit at lower power levels.
[0038] In another embodiment, users with different received SINRs are assigned FH
sequences in the same set. This embodiment may improve detection performance for users transmitting simultaneously using FH sequences in the same set. In yet another embodiment, users are categorized based on then" "margins." Margin is the difference between the received SINR and the required SINR for a given rate and captures the excess SINR available for that rate. Users with larger margins are more likely to be decoded correctly than users with lower margins. Users with different margins may be assigned FH sequences in different sets, which may improve the likelihood of separating the users. For example, users with large margins may be detected and decoded first, the interference caused by these users may be estimated and canceled, then users with lower margins may be detected and decoded next, and so on. In yet another embodiment, users are multiplexed based on their spatial signatures. Users with uncorrelated signatures can be more easily separated using receiver spatial processing, as described below, even though these users may collide in time and frequency. Various combinations of spatial signatures for different groups of users may be evaluated to identify uncorrelated signatures. Users may also be categorized and multiplexed in other manners.
[0039] Quasi-orthogonal multiplexing may be used with or without power control.
Power control may be implemented in various manners. In one power control scheme, the transmit power of each user is adjusted such that the received SINR for the user, as measured at the base station, is maintained at or near a target SINR. The

target SINR may, in turn, be adjusted to achieve a particular level of performance, e.g., 1% packet error rate (PER). This power control scheme adjusts the amount of transmit power used for a given data transmission so that interference is minimized while still achieving the desired level of performance. In another power control scheme, the received SINR for each user is maintained within a range of SINRs. In yet another power control scheme, the received signal power for each user is maintained near a target value or within a range of values.
[0040] Frequency-hopping quasi-orthogonal frequency division multiple access (FH-
QOFDMA) is a multiple-access scheme that uses quasi-orthogonal multiplexing (or M sets of N FH sequences) to support U users concurrently, where U may be greater than N. FH-QOFDMA has some advantages over conventional FH-OFDMA, which uses only one set of N FH sequences for all users. For a small number of users with U N, various techniques may be used to mitigate the deleterious effects of the intra-cell interference, as described below.
[0041] If the base station is equipped with multiple antennas for data reception, then
the data transmissions from the U users may be separated using various receiver spatial processing techniques. Referring back to FIG. 1, a single-input multiple-output (SMO) channel is formed between single-antenna terminal HOa and multi-antenna base station 120. The SIMO channel for terminal 1 lOa may be characterized
by-an-Rxl channel response vector hflCM). for each subband, which may be
expressed as:
= l... K, Eq(4)

where A; is an index for subband, and hai(k,t), for z = l ... R, is the coupling or
complex channel gain between the single antenna'at terminal 1 lOa and the R antennas at base station 120 for subband k in hop period t.
[0042] A multiple-input multiple-output (MIMO) channel is formed between multi-
antenna terminal HOu and multi-antenna base station 120. The MIMO channel for terminal HOu may be characterized by an RxT channel response matrix Ha(£,f) for each subband, which may be expressed as:
S.(*,0 = Ql,.i(*,0 &.,2(*.0 - feT(M)] , for k = l ... K, Eq(5)
where huj(k,t), for j — \ ... T, is the channel response vector between antenna j at
terminal HOu and the R antennas at base station 120 for subband k in hop period t. Each channel response vector hH>y(£,0 contains R elements and has the form shown in
equation (4).
[0043] In general, each terminal may be equipped with one or multiple antennas and
may be assigned S subbands in each hop period, where S > 1. Each terminal would then have one set of channel response vectors for each antenna, with each vector set containing S channel response vectors for the S subbands assigned to the terminal for hop period t. For example, if terminal m is assigned S subbands with indices k through k + S -1 in hop period t, then the vector set for each antenna./ of terminal m would contain S channel response vectors hmj(k,ty through hmj(k + S-l,t) for
subbands k through k + S -1, respectively. These S channel response vectors are indicative of the channel response between antenna j at terminal m and the R antennas at the base station for the S subbands assigned to terminal m. The subband index k for terminal m changes in each hop period and is determined by the FH sequence assigned to terminal m.
[0044] The channel response vectors for the U terminals selected for simultaneous
data transmission are typically different from one another and may be viewed as "spatial signatures" for these U terminals. The base station may estimate the channel response vectors for each terminal based on pilot symbols received from the terminal, which may be time division multiplexed with data symbols as shown in FIG. 2.

[0045] For simplicity, the following description assumes that L = U/N and L
single-antenna terminals m{ through mL are assigned to each subband group in each hop period. An RxL channel response matrix H(fc,f) may be formed for each subband k in each hop period t based on the L channel response vectors for the L terminals using subband k in hop period t, as follows:
forfc = l... K, Eq(6)
where hmt(k,t), for ^ = 1 ... L, is the channel response vector for the ^-th terminal
using subband k in hop period t. The channel response matrix H(£,0 for each subband in each hop period is dependent on the specific set of terminals assigned to that subband and hop period.
[0046] The "received" symbols at the base station for each subband k in each symbol
period n of each hop period t may be expressed as:
r(k,t,n) = R(k,t)-\(k,t,n) + n(k,t,n) , forfc = l... K, Eq(7)
where \.(k,t,ri) is a vector with L "transmit" symbols sent by the L terminals on
subband k in symbol period n of hop period t; r(k,t,n) is a vector with R received symbols obtained via the R antennas at the
base station for subband k in symbol period n of hop period t\ and Vi(k,t,n) is a noise vector for subband k in symbol period n of hop period t.
""•For-simplicity, the channel response matrix H(/M) is assumed to be constant for an entire hop period and is not a function of symbol period n. Also for simplicity, the noise may be assumed to be additive white Gaussian noise (AWGN) with a zero mean vector and a covariance matrix of

and I is the identity matrix.

[0047] K transmit symbol vectors, \(k,t,n) for k = l ... K, are formed for the K
subbands in each symbol period of each hop period. Because different sets of terminals may be assigned to different subbands in a given hop period, as determined by their FH sequences, the K transmit symbol vectors \(k,t,n) for each symbol period of each hop period may be formed by different sets of terminals. Each vector x(£,^n) contains L transmit symbols sent by the L terminals using subband k in symbol period n of hop period t. In general, each transmit symbol may be a data symbol, a pilot symbol, or a "zero" symbol (which is a signal value of zero).
[0048] K received symbol vectors, r(k,t,n) for k = l ... K, are obtained for the K
subbands in each symbol period of each hop period. Each vector r(k,t,n) contains R received symbols obtained via the R antennas at the base station for one subband in one symbol period. For a given subband k, symbol period n, and hop period t, thej-th transmit symbol in the vector x(£,/,n) is multiplied by the/-th vector/column of the channel response matrix H(M) to generate a vector rj(k,t,n). The L transmit symbols in x(/c,*,«), which are sent by L different terminals, are multiplied by the L columns of H(&,*) to generate L vectors r^(k,t,n) through rL(k,t,n), one vector ±j(k,t,ri) for each terminal. The vector r(Ar,?,«) obtained by the base station is
L
composed of the L vectors ^(k,t,n) through rL(k,t,n), or r(k,t,n) = ^jrj(k,t,n).
Each received symbol in r(k,t,n) thus contain a component of each of the L transmit symbols in x(&, t, w). The L transmit symbols sent simultaneously by the L terminals on each subband k in each symbol period n of each hop period t thus interfere with one another at the base station.
[0049] The base station may use various receiver spatial processing techniques to
separate out the data transmissions sent simultaneously by the L terminals on each subband in each symbol period. These receiver spatial processing techniques include a zero-forcing (ZF) technique, a minimum mean square error (MMSE) technique, a maximal ratio combining (MRC) technique, and so on.
[0050] For the zero-forcing technique, the base station may derive a spatial filter
matrix M^(k,t) for each subband & in each hop period t, as follows:

r-H*(A:,0 , Eq(8)
where " H " denotes a conjugate transpose. The base station estimates the channel response matrix H(fc,f) for each subband, e.g., based on pilots transmitted by the
terminals. The base station then uses the estimated channel response matrix H(k,t) to derive the spatial filter matrix. For clarity, the following description assumes no estimation error so that H(^»0 = H(&jO . Because Jl(k,f) is assumed to be constant across hop period t, the same spatial filter matrix Mrf(k,t) may be used for all symbol
periods in hop period t.
[0051] The base station may perform zero-forcing processing for each subband k in
each symbol period n of each hop period t, as follows:
where ±tf(k,t,n) is a vector with L "detected" data symbols for subband k in symbol
period n of hop period t; and ntf(k,t,n) is the noise after the zero-forcing processing.
A detected data symbol is an estimate of a data symbol sent by a terminal.
[0052] For the MMSE technique, the base station may derive a spatial filter matrix
Mmmse(k, t) for each subband k in each hop period t, as follows:
Mmmse(M) = [H*(*,0-H(M + ^-ir:-HV,0 . Bq(10)
If the covariance matrix q> of the noise is known, then this covariance matrix may be
used in place of a2 -I in equation (10).
[0053] The base station may perform MMSE processing for each subband k in each
symbol period n of each hop period t, as follows:
R(k,t)^(k,t,n) + n(k,t,n)] , Eq(ll)
where J)mmse(k,t) is a diagonal vector containing the diagonal elements of a matrix
[M^foO-SC*,*)], or Dmmse(A:,0 = diag[Mmnise(^0-H(A,0]; and nmmie (£,/,«) is the noise after the MMSE processing.
The symbol estimates from the spatial filter Mmmse(k,t) are unnormalized estimates of the transmit symbols in x(k,t,ri) . The multiplication with the scaling matrix
BmLe(^>0 provides normalized estimates of the transmit symbols.
[0054] For the MRC technique, the base station may derive a spatial filter matrix
Mmrc(k,t) for each subband k in each hop period t, as follows:
Mra),(M) = H*(*,0 • Eq(12)
[0055] The base station may perform MRC processing for each subband k in each
symbol period n of each hop period t, as follows:
\mrc(k,t,ri) = Dl(£,0-Mmre(fc,0-r(*,f,n) ,
)^(k,t>n) + n(k,t,n)] , Eq(13)
where Dmrc(k,t) is a diagonal vector containing the diagonal elements of a matrix
nmrc(k,t, ri) \s the inoise after the MRC processmg.
[0056] In general, different sets of terminals may be assigned to different subband
groups in a given hop period, as determined by then: FH sequences. The N terminal sets for the N subband groups in a given hop period may contain the same or different numbers of terminals. Furthermore, each terminal set may contain single-antenna terminals, multi-antenna terminals, or a combination of both. Different sets
of terminals (which may again contain the same or different numbers of terminals) may also be assigned to a given subband in different hop periods. The channel response matrix H(&,*) for each subband in each hop period is determined by the set of terminals using that subband hi that hop period and contains one or more vectors/columns for each terminal transmitting on that subband hi that hop period. The matrix H(&,0 may contain multiple vectors for a terminal using multiple antennas to transmit different data symbols to the base station.
[0057] As shown above, the multiple data transmissions sent simultaneously from up
to L terminals on each subband k in each symbol period n of each hop period t may be separated by the base station based on their uncorrelated spatial signatures, which are given by their channel response vectors hmt(k,t). This allows FH-QOFDMA to
enjoy higher capacity when the number of antennas used for data reception increases. Furthermore, FH-QOFDMA reduces the amount of intra-cell interference observed on each subband in each hop period so that better utilization of the additional capacity created in the spatial dimension can be achieved.
[0058] FIG. 5 shows a block diagram of an embodiment of single-antenna terminal
1 lOa and multi-antenna terminal 1 lOu. At single-antenna terminal 1 lOa, an encoder/ modulator 514a receives traffic/packet data (denoted as {da}*) from a data source
512a and possibly overhead/signaling data from a controller 540a, processes (e.g., encodes, interleaves, and symbol maps) the data based on one or more coding and modulation schemes selected for terminal llOa, and provides data symbols (denoted as {xa}) for terminal llOa. Each data symbol is a modulation symbol, which is a complex value for a point in a signal constellation for a modulation scheme (e.g., M-PSKorM-QAM).
[0059] A symbol-to-subband mapper 520a receives the data symbols and pilot
symbols and provides these symbols onto the proper subband(s) in each symbol period of each hop period, as determined by an FH control from an FH generator 522a. FH generator 522a may generate the FH control based on an FH sequence or a traffic channel assigned to terminal llOa. FH generator 522a may be implemented with look-up tables, PN generators, and so on. Mapper 520a also provides a zero symbol for each subband not used for pilot or data transmission. For each symbol
period, mapper 520a outputs K transmit symbols for the K total subbands, where
each transmit symbol may be a data symbol, a pilot symbol, or a zero symbol.
[0060] An OFDM modulator 530a receives K transmit symbols for each symbol
period and generates a corresponding OFDM symbol for that symbol period. OFDM modulator 530a includes an inverse fast Fourier transform (IFFT) unit 532 and a cyclic prefix generator 534. For each symbol period, IFFT unit 532 transforms K transmit symbols to the time domain using a K-point IFFT to obtain a "transformed" symbol that contains K time-domain samples. Each sample is a complex value to be transmitted in one sample period. Cyclic prefix generator 534 repeats a portion of each transformed symbol to form an OFDM symbol that contains N + C samples, where C is the number of samples being repeated. The repeated portion is often called a cyclic prefix and is used to combat ISI caused by frequency selective fading. An OFDM symbol period (or simply, a symbol period) is the duration of one OFDM symbol and is equal to N + C sample periods. OFDM modulator 53 Oa provides a stream of OFDM symbols to a transmitter unit (TMTR) 536a. Transmitter unit 536a processes (e.g., converts to analog, filters, amplifies, and frequency upconverts) the OFDM symbol stream to generate a modulated signal, which is transmitted from an antenna 538a.
[0061] At multi-antenna terminal HOu, an encoder/modulator 514u receives traffic/
packet data (denoted as {du}) from a data source 512u and possibly
overhead/signaling data from a controller 540u, processes the data based on one or more coding and modulation schemes selected for terminal llOu, and provides data symbols (denoted as {xu}) for terminal HOu. A demultiplexer (Demux) 516u demultiplexes the data symbols into T streams for the T antennas at terminal HOu, one data symbol stream {xuj} for each antenna, and provides each data symbol
stream to a respective symbol-to-subband mapper 520u. Each mapper 520u receives the data symbols and pilot symbols for its antenna and provides these symbols onto the proper subband(s) in each symbol period of each hop period, as determined by an FH control generated by an FH generator 522u based on an FH sequence or a traffic • channel assigned to terminal 1 lOu. Up to T different data symbols or pilot symbols may be sent from the T antennas in each symbol period on each subband assigned to terminal 1 lOu. Each mapper 520u also provides a zero symbol for each subband not
used for pilot or data transmission and, for each symbol period, outputs K transmit symbols for the K total subbands to a corresponding OFDM modulator 530u.
[0062] Each OFDM modulator 530u receives K transmit symbols for each symbol
period, performs OFDM modulation on the K transmit symbols, and generates a corresponding OFDM symbol for the symbol period. T OFDM modulators 530ua through 530ut provide T streams of OFDM symbols to T transmitter units 536ua through 536ut, respectively. Each transmitter unit 536u processes its OFDM symbol stream and generates a corresponding modulated signal. T modulated signals from transmitter units 536ua through 536ut are transmitted from T antennas 538ua through 538ut, respectively.
[0063] Controllers 540a and 540u direct the operation at terminals HOa and HOu,
respectively. Memory unit 542a and 542u provide storage for program codes and data used by controllers 540a and 540u, respectively.
[0064] FIG. 6 shows a block diagram of an embodiment of base station 120. The
modulated signals transmitted by the U terminals selected for data transmission are received by R antennas 612a through 612r, and each antenna provides a received signal to a respective receiver unit (RCVR) 614. Each receiver unit 614 processes (e.g., filters, amplifies, frequency downconverts, and digitizes) its received signal and provides a stream of input samples to an associated OFDM demodulator (Demod) 620. Each OFDM demodulator 620 processes its input samples and provides received symbols. Each OFDM demodulator 620 typically includes a cyclic prefix removal unit and a fast Fourier transform (FFT) unit. The cyclic prefix removal unit removes the cyclic prefix in each received OFDM symbol to obtain a received transformed symbol. The FFT unit transforms each received transformed symbol to the frequency domain with a K-point FFT to obtain K received symbols for the K subbands. For each symbol period, R OFDM demodulators 620a through 620r
provide R sets of K received symbols for the R antennas to a receive (RX) spatial
processor 630.
[0065] Receive (RX) spatial processor 630 includes K subband spatial processors
632a through 632k for the K subbands. Within RX spatial processor 630, the received symbols from OFDM demodulators 620a through 620r for each symbol period are demultiplexed into K vectors of received symbols, r(k,t,n) for
k = l ... K, which are provided to the K spatial processors 632. Each spatial
processor 632 also receives a spatial filter matrix M(k,t) for its subband, performs
receiver spatial processing on r(k,t,n) with M(k,t) as described above, and
provides a vector \(k,t,n) of detected data symbols. For each symbol period, K
spatial processors 632 through 632k provide K sets of detected data symbols in K
vectors t(k,t,n) for the K subbands to a subband-to-symbol demapper 640.
[0066] Demapper 640 obtains the K sets of detected data symbols for each symbol
period and provides detected data symbols for each terminal m onto a stream {xm}
for that terminal, where me [a ... u}. The subbands used by each terminal are determined by an FH control generated by an FH generator 642 based on the FH sequence or traffic channel assigned to that terminal. A demodulator/decoder 650 processes (e.g., symbol demaps, deinterleaves, and decodes) the detected data
^
symbols {Jcm} for each terminal and provides decoded data {dm} for the terminal.
[0067] A channel estimator 634 obtains received pilot symbols from OFDM
demodulators 620a through 620r and derives a channel response vector for each antenna of each terminal transmitting to base station 120 based on the received pilot symbols for the terminal. A spatial filter matrix computation unit 636 forms a channel response matrix H(Ar,tf) for each subband in each hop period based on the channel response vectors of all terminals using that subband and hop period. Computation unit 636 then derives the spatial filter matrix M(k,t) for each subband of each hop period based on the channel response matrix H(fc,f) for that subband and hop period and further using the zero-forcing, MMSE, or MRC technique, as described above. Computation unit 636 provides K spatial filter matrices for the K subbands in each hop period to K subband spatial processors 632a through 632k.
[0068] A controller 660 directs the operation at base station 120. A memory unit 662
provides storage for program codes and data used by controller 660.
[0069] For clarity, quasi-orthogonal multiplexing has been specifically described for
the reverse link of a frequency hopping OFDMA system. Quasi-orthogonal multiplexing may also be used for other multiple-carrier communication systems whereby the multiple subbands may be provided by some means other than OFDM.
[0070] Quasi-orthogonal multiplexing may also be used for the forward link. For
example, a terminal equipped with multiple antennas may receive data transmission from multiple base stations (e.g., one data symbol from each of the multiple base stations on each subband in each symbol period). Each base station may transmit to the terminal using a different FH sequence that the base station assigned to the terminal. The FH sequences used by the different base stations for the terminal may not be orthogonal to one another. Multiple base stations may send multiple data symbols on the same subband in the same symbol period to the terminal whenever these FH sequences collide. The terminal may use receiver spatial processing to separate out the multiple data symbols sent simultaneously on the same subband in the same symbol period by the multiple base stations.
[0071] The quasi-orthogonal multiplexing techniques described herein may be
implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used for quasi-orthogonal multiplexing at a transmitting entity (e.g., as shown in FIG. 5) may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. The processing units used for quasi-orthogonal multiplexing at a receiving entity (e.g., as shown in FIG. 6) may also be implemented within one or more ASICs, DSPs, and so on.
[0072] For a software implementation, the quasi-orthogonal multiplexing techniques
may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit (e.g., memory unit 542a or 542u in FIG. 5 or memory unit 662 in FIG. 6) and executed by a processor (e.g., controller 540a or 540u in FIG. 5 or controller 660 in FIG. 6). The memory unit may be implemented within the processor or external to the processor.
[0073] 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 will be readily apparent to those skilled in the
art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
WHAT IS CLAIMED IS:



We Claim:
1. A method of assigning frequency subbands in a communication system (100),
comprising:
determining L sets of traffic channels to use for U terminals selected for data transmission to a base station (120), where L is greater than one and U is one or greater, wherein each set includes multiple traffic channels that are orthogonal to one another, and wherein the traffic channels in each set are not orthogonal to the traffic channels in each of the L-l other sets; and
assigning the U terminals with the traffic channels in the L sets, wherein each traffic channel is associated with one or more frequency subbands to use for data transmission in each transmission interval, and wherein data transmissions for the U terminals are sent using the traffic channels assigned to the U terminals.
2. The method as claimed in claim 1, wherein the system utilizes frequency hopping (FH), and wherein each traffic channel in each set is associated with a respective FH sequence that pseudo-randomly selects different frequency subbands in different transmission intervals for the traffic channel.
3. The method as claimed in claim 1, wherein the traffic channels in each set use frequency subbands that are pseudo-random with respect to frequency subbands used by the traffic channels in each of the L-l other sets.
4. The method as claimed in claim 1, wherein L is a minimum number of sets to support the U terminals.
5. The method as claimed in claim 1, wherein each set includes N traffic channels, where N is greater than one and L times N is equal to or greater than U.
6. The method as claimed in claim 5, wherein one set of traffic channels is selected if U is less than or equal to N.
7. The method as claimed in claim 5, wherein
(Formula Removed)
denotes a ceiling operator that provides an integer value equal to or greater than x.

8. The method as claimed in claim 1,
wherein the U terminals are arranged into L groups of terminals, one group of terminals for each of the L sets of traffic channels, and wherein each group of terminals is assigned traffic channels from a respective set of traffic channels.
9. The method as claimed in claim 8, wherein the U terminals are arranged into L groups based on received signal qualities achieved for the U terminals.
10. The method as claimed in claim 9, wherein each group includes terminals having similar received signal qualities.
11. The method as claimed in claim 8, wherein the U terminals are arranged into L groups based on margins achieved by the U terminals, wherein a margin for a terminal is indicative of a difference between a received signal quality achieved by the terminal and a required signal quality for the terminal.
12. The method as claimed in claim 8, wherein the U terminals are arranged into L groups based on spatial signatures of the U terminals, and wherein a spatial signature for a terminal is determined by a channel response for the terminal.
13. The method as claimed in claim 2, wherein the L sets of traffic channels are associated with L pseudo-random number (PN) codes, one PN code for each set of traffic channels, and wherein FH sequences for the traffic channels in each set are generated based on the PN code for the set.
14. The method as claimed in claim 13, wherein the L PN codes for the L sets of traffic channels are different time shifts of a common PN code.
15. The method as claimed in claim 1, wherein frequency subbands to use for each set of traffic channels are determined based on a respective mapping table.
16. An apparatus in a communication system (100), comprising:
a controller operative to:

determine L sets of traffic channels to use for U terminals selected for data transmission to a base station (120), where L is greater than one and U is one or greater, wherein each set includes multiple traffic channels that are orthogonal to one another, and wherein the
traffic channels in each set are not orthogonal to the traffic channels in each of the L-l other sets, and assign the U terminals with the traffic channels in the L sets, wherein each traffic channel is associated with one or more frequency subbands to use for data transmission in each transmission interval, and wherein data transmissions for the U terminals are sent using the traffic channels assigned to the U terminals.
17. The apparatus as claimed in claim 16, wherein the system (100) utilizes frequency hopping (FH), and wherein each traffic channel in each set is associated with a respective FH sequence that pseudo-randomly selects different frequency subbands in different transmission intervals for the traffic channel.
18. A method of transmitting data in a communication system , comprising:
obtaining a traffic channel to use for data transmission to a base station (120), wherein the traffic channel is selected from among L sets of traffic channels for the base station, where L is greater than one, wherein each set includes multiple traffic channels that are orthogonal to one another, wherein the traffic channels in each set are not orthogonal to the traffic channels in each of the L-1 other sets, and wherein the traffic channel is associated with one or more frequency subbands to use for data transmission in each transmission interval; and mapping data symbols onto the one or more frequency subbands belonging to the traffic channel.
19. The method as claimed in claim 18, wherein the system utilizes frequency hopping (FH), and wherein each traffic channel in each set is associated with a respective FH sequence that pseudo-randomly selects different frequency subbands in different transmission intervals for the traffic channel.
20. The method as claimed in claim 18, wherein each set includes N traffic channels, and wherein L is a minimum number of sets to support U terminals selected for data transmission, where N is greater than one, U is one or greater, and L times N is equal to or greater than U.
21. The method as claimed in claim 18,

wherein pilot symbols are mapped onto the one or more frequency subbands belonging to the traffic channel, and wherein the data symbols and the pilot symbols are transmitted using time division multiplexing (TDM).
22. The method as claimed in claim 18, wherein the data symbols and the pilot symbols are transmitted from one antenna.
23. The method as claimed in claim 18,
wherein the data symbols are demultiplexed into multiple streams for multiple antennas, and wherein the data symbols for each stream are mapped onto the one or more frequency subbands belonging to the traffic channel and further transmitted from an associated antenna .
24. An apparatus in a communication system , comprising:
a controller operative to obtain a traffic channel to use for data transmission to a base station (120), wherein the traffic channel is selected from among L sets of traffic channels for the base station (120), where L is greater than one, wherein each set includes multiple traffic channels that are orthogonal to one another, wherein the traffic channels in each set are not orthogonal to the traffic channels in each of the L-l other sets, and wherein the traffic channel is associated with one or more frequency subbands to use for data transmission in each transmission interval; and
a mapping unit operative to map data symbols onto the one or more frequency subbands belonging to the traffic channel.
25. A terminal comprising the apparatus as claimed in claim 24.
26. A base station comprising the apparatus as claimed in claim 24.
27. The method as claimed in claim 1,
wherein data transmissions are received on the traffic channels assigned to the U terminals and are processed to recover data sent by the U terminals to the base station (120).
28. The method as claimed in claim 1, wherein L is a minimum number of sets to
support the U terminals.

29. The method as claimed in claim 27, wherein the processing the data transmissions
comprises
obtaining a group of received symbols for each of K frequency subbands used for data transmission, each group including R received symbols for R antennas, where R and K are each greater than one,
performing spatial processing on the group of received symbols for each frequency subband to obtain a group of detected data symbols for the frequency subband, and
demultiplexing K groups of detected data symbols for the K frequency subbands in each symbol period to obtain detected data symbols for each of the U terminals.
30. The method as claimed in claim 27,
wherein a channel estimate is obtained for each of the U terminals based on pilot symbols received from the terminal, and wherein spatial processing is performed for the received data transmissions based on channel estimates for the U terminals.
31. The method as claimed in claim 27,
wherein a channel response matrix is formed for each of K frequency subbands based on channel estimates for a group of one or more terminals using the frequency subband, where K is one or greater;
wherein a spatial filter matrix is derived for each of the K frequency subbands based on the channel response matrix for the frequency subband, and
wherein spatial processing for each frequency subband is performed with the spatial filter matrix for the frequency subband.
32. The method as claimed in claim 31, wherein the spatial filter matrix for each frequency subband is further derived based on a zero-forcing (ZF) technique.
33. The method as claimed in claim 31, wherein the spatial filter matrix for each frequency subband is further derived based on a minimum mean square error (MMSE) technique.

34. The method as claimed in claim 31, wherein the spatial filter matrix for each frequency subband is further derived based on a maximal ratio combining (MRC) technique.
35. The apparatus as claimed in claim 16, wherein
a processing unit (660) is operative to process data transmissions received on the traffic channels assigned to the U terminals.
36. The apparatus as claimed in claim 35, wherein the processing unit comprises
a spatial processor (630) operative to obtain a group of received symbols for each of K frequency subbands used for data transmission and to perform spatial processing on the group of received symbols for each frequency subband to obtain a group of detected data symbols for the frequency subband, wherein each group of received symbols includes R received symbols for R antennas, where R and K are each greater than one, and a demultiplexer (630) operative to demultiplex K groups of detected data symbols for the K frequency subbands in each symbol period to obtain detected data symbols for each of the U terminals.
37. The apparatus as claimed in claim 36,
wherein a channel estimator (634) is operative to form a channel response matrix for each of the K frequency subbands based on channel estimates for a group of one or more terminals using the frequency subband;
wherein a computation unit (636) is operative to derive a spatial filter matrix for each of the K frequency subbands based on the channel response matrix for the frequency subband, and
wherein the spatial processor(630) is operative to perform spatial processing on the group of received symbols for each frequency subband with the spatial filter matrix for the frequency subband.
38. A base station (120) comprising the apparatus as claimed in claim 16.

Documents:

7913-delnp-2006-abstract.pdf

7913-DELNP-2006-Assignment.pdf

7913-DELNP-2006-Claims-(10-07-2012).pdf

7913-delnp-2006-Claims-(22-05-2013).pdf

7913-delnp-2006-claims.pdf

7913-delnp-2006-Correspondance Others-(07-05-2013).pdf

7913-DELNP-2006-Correspondence Others-(10-07-2012).pdf

7913-delnp-2006-Correspondence Others-(22-05-2013).pdf

7913-delnp-2006-Correspondence-Others-(28-05-2013).pdf

7913-DELNP-2006-Correspondence-Others.pdf

7913-delnp-2006-description (complete).pdf

7913-DELNP-2006-Drawings-(10-07-2012).pdf

7913-delnp-2006-drawings.pdf

7913-delnp-2006-Form-1-(22-05-2013).pdf

7913-delnp-2006-form-1.pdf

7913-delnp-2006-form-18.pdf

7913-delnp-2006-Form-2-(22-05-2013).pdf

7913-delnp-2006-form-2.pdf

7913-DELNP-2006-Form-3-(10-07-2012).pdf

7913-delnp-2006-Form-3-(28-05-2013).pdf

7913-DELNP-2006-Form-3.pdf

7913-delnp-2006-form-5.pdf

7913-delnp-2006-GPA-(07-05-2013).pdf

7913-DELNP-2006-GPA-(10-07-2012).pdf

7913-delnp-2006-gpa.pdf

7913-delnp-2006-pct-220.pdf

7913-delnp-2006-pct-237.pdf

7913-delnp-2006-pct-304.pdf

7913-delnp-2006-pct-311.pdf

7913-delnp-2006-pct-search report.pdf

7913-DELNP-2006-Petition-137-(10-07-2012).pdf


Patent Number 259412
Indian Patent Application Number 7913/DELNP/2006
PG Journal Number 11/2014
Publication Date 14-Mar-2014
Grant Date 12-Mar-2014
Date of Filing 27-Dec-2006
Name of Patentee QUALCOMM INCORPORATED
Applicant Address 5775 MOREHOUSE DRIVE, SAN DIEGO, CALIFORNIA 92121-1714, USA
Inventors:
# Inventor's Name Inventor's Address
1 ARAK SUTIVONG 8840 COSTA VERDE BOULEVARD, #3439 SAN DIEGO, CALIFORNIA 92122, USA
2 AVNEESH AGRAWAL 7891 DOUG HILL, SAN DIEGO, CALIFORNIA 92127, USA
PCT International Classification Number H04L 5/02
PCT International Application Number PCT/US2005/021056
PCT International Filing date 2005-06-14
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/887,710 2004-07-08 U.S.A.
2 60/580,810 2004-06-18 U.S.A.