MXPA06014943A - Multiplexing for amulti-carrier cellular communication system - Google Patents

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 spatial processing on received symbols with spatial filter matrices to obtain detected data symbols. The spatial filter matrix for each sub band maybe derived based on channel response estimates for all terminals transmitting on thatsub band.

Description

"MULTIPLEXION FOR A CELLULAR MULTIPLE CARRIER COMMUNICATIONS SYSTEM" FIELD OF THE INVENTION The present invention relates in general terms to data communications, and more specifically to the transmission of data in a multiple-carrier multiple access communications system.

BACKGROUND OF THE INVENTION A multiple access system can concurrently support communications for multiple terminals for 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 coming from the terminals to the base stations. Multiple terminals can simultaneously transmit data through the reverse link and / or receive data through the forward link. This can be achieved by multiplexing the multiple data transmissions per link so that they are orthogonal to one another in the time domain, frequency, and / or code. Typically, complete orthogonality is not achieved in most cases due to various factors such as channel conditions, receptor imperfections, and so on. However, orthogonal multiplexing ensures that the data transmission for each terminal minimally interferes with the data transmissions for the other terminals. A multi-carrier communication system uses multiple carriers for data transmission. Multiple carriers can be provided by Orthogonal Frequency Division Multiplexing (OFDM - Orthogonal Frequency Division Multiple Access), discrete multi-tone (DMT - discrete multi tone), some other multiple carrier modulation techniques, or some other construction. The OFDM effectively partitions the bandwidth of the system in general into multiple (K) orthogonal frequency subbands. These sub-bands are also referred to as tones, sub-carriers, groups, frequency channels, and so on. Each subband is associated with a respective subband that can be modulated with the data. An orthogonal frequency division multiple access (OFDMA) system is a multiple access system that uses OFDM. An OFDM system can use multiplexing by time division and / or frequency to achieve orthogonality between multiple data transmissions for multiple terminals. For example, different sub-bands can be assigned to different terminals, and data transmission for each terminal can be sent by the sub-band (s) assigned to the terminal. By adjusting disjointed or non-superimposed subbands to different terminals, interference between multiple terminals can be avoided or reduced, and improved performance can be achieved. 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 that place an upper limit the number of terminals find that they can transmit simultaneously without interfering with each other. In some cases, it may be desirable to allow more terminals to transmit simultaneously, for example, to better utilize the capacity of the available system. Therefore, there is a need in the art for techniques that concurrently support more terminals in an OFDM system.

BRIEF DESCRIPTION OF THE INVENTION [0002] Techniques to support simultaneous transmission for more terminals than the number of orthogonal transmission units (or orthogonal dimensions) available in the system are described herein. Each "transmission unit" may correspond to a group of one or more subbands in one or more periods of symbols, and is orthogonal to all other transmission units in time and frequency. These frequencies are called "quasi-orthogonal multiplexing" and can be used to more fully utilize the additional capacity that can be created in a spatial dimension by employing multiple antennas in a base station. These techniques can also reduce the amount of interference present in each terminal, which can improve performance. In a quasi-orthogonal multiplexing mode 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, for example, 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 be used for each transmission interval. For an OFDMA system with variations by frequency hopping (FH-OFDMA - frequency hopping OFDMA), each traffic channel can be associated with a sequence of FH that selects pseudo-randomly different subbands in different transmission intervals or periods of variation by jumps . The traffic channels in each set are orthogonal to each other and can 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 available for use in the system. The minimum number of sets of traffic channels (L) can be used to support a certain number of (U) terminals selected for data transmission. Each terminal can be assigned a traffic channel selected from the L sets of traffic channels. Each terminal transmits data symbols (which are modulation symbols for the data) by its traffic channel. Each terminal also transmits the pilot symbols (which are modulation symbols for a pilot) by its traffic channel in order to allow a base station to calculate the response of the wireless channel between the terminal and the base station. The U terminals can transmit simultaneously through their assigned traffic channels. The base station receives data transmissions from the U terminals and obtains a vector of symbols received for each subband in each symbol period. The base station can derive a spatial center matrix for each subband based on the channel response calculations obtained for all terminals transmitting on that subband. The base station can perform receiver spatial processing by the vector of received symbols for each subband with the spatial filter matrix for that subband to obtain the detected data symbols, which are calculations of the data symbols sent by the terminals that they use the subband. In the following, various aspects and embodiments of the invention are described in detail.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics 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 are correspondingly identified throughout the description. same and where: Figure 1 shows multiple terminals and a base station in a communication link system; Figure 2 illustrates the variations by frequency hopping in the OFDMA station; Figure 3 shows M sets of FH sequences for quasi-orthogonal multiplexing; Figure 4 shows a process for assigning sequences from FH to U terminals; Figure 5 shows a block diagram of an individual antenna terminal and a multiple antenna terminal; and Figure 6 shows a block diagram of the base station.

DETAILED DESCRIPTION OF THE INVENTION The words "by way of example" are used in the present to refer to "that serve as example, instance, or illustration". Any modality or design described herein "by way of example" does not necessarily have to be interpreted as being preferred or advantageous over other modalities or designs. The quasi-orthogonal multiplexing techniques described herein can be used for various multi-carrier communication systems, for example, an OFDM-based system such as an OFDMA system. These techniques can also be used for single antenna and multiple antenna systems. An individual antenna system uses an antenna that for the transmission and reception of data. A multiple antenna system uses one or multiple antennas for data transmission and multiple antennas for data reception. These techniques can also be used for duplicate time division systems (TDD - time division duplexed) and frequency division duplicates (FDD - frequency division time), for forward and reverse links, and with or without variations due to frequency jumps. . For the sake of clarity, the quasi-orthogonal multiplexing for the reverse link of a multiple antenna FH-OFDMA system is described below. Figure 1 shows multiple terminals 110a to HOu and a base station 120 in an OFDMA system 100. A base station is usually a fixed station that communicates with the terminals and can 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. The base station 120 is equipped with multiple (R) antennas for the transmission and reception of data. A terminal may be equipped with an antenna (e.g., terminal 110a) or multiple antennas (e.g., terminal HOu) for transmitting and receiving data. The R antennas in the base station 120 represent the multiple inputs (MI) for the transmissions by the reverse link. If multiple terminals are selected for simultaneous transmission, then the multiple antennas for these selected terminals collectively represent the multiple outputs for the forward link transmissions and the multiple inputs for the reverse link transmissions. Figure 2 illustrates the scheme of 200 transmission of variations by frequency hopping (FH) that can be used for the OFDMA system. Variations by frequency hopping can provide frequency diversity against the harmful effects of the path and the randomization of interference. With the variations by frequency jumps, each terminal / user can be assigned a different sequence of FH indicates the particular subband (s) to be used in each period of "variation by jumps". An FH sequence can also be called skip pattern or some other terminology. A period of variations by breaks is the amount of time spent in a certain sub-band, it can expand one or multiple periods of symbols, and it can also be called a transmission interval or some other terminology. Each FH sequence can pseudo-randomly select subbands for the terminal. The frequency diversity is achieved by selecting different subbands in the K total subbands in different periods of variations by jumps. The FH sequences and traffic channels can be viewed as convenient ways to express the allocation of subbands. The FH sequences for different users in communication with the same base station are typically orthogonal to one another so that neither of the two users uses the same subband at any given hop variation period. This avoids "intra-cell" or "intra-sector" interference between terminals communicating with the same base station (assuming orthogonality is not destroyed by some other factor). The FH sequences for each base station can be pseudo-random with respect to the FH sequences for the nearby base stations. Interference between two users communicating with two different base stations occurs at any time that the FH sequences for these users select the same subband in the same period of variations per hop. However, this "inter-cell" or "inter-sector" interference is randomized due to the pseudo-random nature of the FH sequences. For the modality shown in Figure 2, the usable subbands for data transmission are configured in N groups. Each group contains S sub-bands, where in general N >; 1, S = l, and N-S = K. The subbands in each group can be contiguous, as shown in Figure 2.

The subbands in each group can also be non-contiguous, for example, evenly distributed in the K total subbands and spaced evenly by S subbands. Each user can be assigned a group of S subbands in each period of variations per hop. The data symbols can be multiplexed by time division with the pilot symbols, which are known a priori both by the terminal and by the base station, as shown in Figure 2. Interference can be avoided or reduced among all users that communicate with the same base station if their FH sequences are orthogonal to each other. In this case, the users are assigned non-superimposed groups of sub-bands or, equivalently, a sub-band is used only at the most by a user at any given moment. Typically, complete orthogonality is not achieved due to channel conditions, receiver imperfections, timing not synchronizing to terminals, and so on. The loss of orthogonality can cause inter-carrier interference (ICI) and inter-symbol interference (ISI). However, the ICI and the ISI may be small compared to the interference that would be present if the users were not assigned orthogonal FH sequences.

The number of groups of sub-bands available for data transmission is limited, for example, to N for the modality shown in Figure 2. If a group of sub-bands is assigned to each user, then multiplexing by time division (TD - multiplexing time division) can support more than N users to transmit up to N groups of subbands in different periods of variations per hop. Consequently, more than N orthogonal transmission units can be created in the domains of time and frequency, where each transmission unit is orthogonal with respect to the other transmission units in time and frequency. The transmission units can also be viewed as orthogonal dimensions. Multiplexing by time division of users may be undesirable because it reduces the amount of time available for data transmission, which may then limit the data rates available by users. In some cases, it may be desirable to support more users than the number of orthogonal transmission units available. For example, additional capacity can be created in the spatial dimension by using multiple antennas in the base station. Then, the base station may be able to support more users with 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 certain duration. For the sake of simplicity, the following description assumes that time division multiplexing is not used and that N orthogonal transmission units are available in the system, although it is not a requirement for quasi-orthogonal multiplexing. Once all the available transmission units have been assigned to users, it is no longer possible to support additional users while maintaining the orthogonality among all users. The quasi-orthogonal multiplexing can allow more users to communicate simultaneously over the reverse link, for example, in order to more fully utilize the additional capacity created by the multiple antennas in the base station. In one embodiment, multiple (M) sets of FH sequences are defined for each base station. Each set contains N FH sequences for each orthogonal transmission unit available in the system. Therefore, M-N FH sequences are available for use in the system. Figure 3 shows M sets of FH sequences can be used for quasi-orthogonal multiplexing. The first FH sequence in each set is indicated by the - - boxes shaded in a plane time-frequency for that set. The remaining N-l FH sequences in each set can be alternate vertical and circular versions of the first FH sequence in the set. The N sequences of FH in each set are orthogonal to each other. Consequently, there is no interference between the N transmissions of data sent simultaneously by the N assigned users with the N FH sequences in any given set (assuming there is no loss of orthogonality due to other factors). The sequences of FH in each set can also be pseudo-random with respect to the FH sequences for each of the other M-l sets. In this case, the data transmissions sent simultaneously are used FH sequences in any set would present a randomized interference derived from the data transmissions sent using the FH sequences in the other M-l sets. The M sets of the N FH sequences can be generated in various ways. In one embodiment, the N FH sequences for each set are derived based on a pseudo-random number code (PN-pseudo-noise) assigned to that set. For example, the 15-bit short PN codes defined by the IS-95 and IS-2000 standards can be used. The PN code can be increased with a linear feedback shift register (LSFR linear feedback shift register). For each hop variation period, the LSFR is updated and the content of the LSFR is used to select the subbands for the N FH sequences in the set. For example, a binary number corresponding to the least significant B bits (LSBs - less significant bits) in the LSFR can be noted as PNt (t) = where B = log2 (N), l is an index of the M sets of sequences of FH, yt is an index for the period of variations by jumps. Therefore, the N sequences of FH in the set <; they can be defined as: { [PN, (t) + i] mod N) +1, for l = 1 ... M ei = l ... N, Eq. (1) where i is an index for the N FH sequences in each set; and ft, i. { t) is the i-th sequence of FH in the set f. The +1 in equation (1) represents an indexing scheme that starts with 1 'instead of? 0'. The sequence of FH f (, i (t) indicates the particular subband (s) to be used for each period of variations by jumps t In order to simplify the implementation, the M PN codes used for the M sets of FH sequences can be defined to be different - time variations of a PN code In this case, each set is assigned a unique time variation, and the PN code for that set can be identified by the assigned time variation The PN code can be denoted as PN (t), the time variation assigned to the set l can be noted as ?? (, and the binary number in the LFSR for set i can be noted as PN. { t + ?? (). The N sequences of FH in set I can be defined as: f /, i { t) = ([PN, (t + ??,) + i] mod N) +1, for i = 1 ... M ei = l ... N, Eq. (2) In another modality, the M sets of FH sequences are defined based on different M mapping tables, one table for each set. Each mapping table can implement a random permutation of an entry. Each mapping table receives an index i for the i-th sequence of FH in the set associated with the table and provides the subband (s) to be used for this sequence of FH in each period of variations by jumps t. Each mapping table can be defined as pseudo-random with respect to the other M-l mapping tables. The M sets of N FH sequences can also be defined and generated in other ways, and this is within the scope of the invention. FH sequences can be assigned to users in order to reduce the amount of present intra-cell interference observed by all users. For the sake of simplicity, the following description assumes that an 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 U users can be assigned orthogonal FH sequences in a 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 sets can be used. Since the FH sequences from different sets are not orthogonal to one another and consequently result in intra-cell interference, the smallest number of sets should be used at any time. The minimum number of sets (L) needed to support U users can be expressed as: where "[x]" denotes a roof operator that provides an integer value that is equal to a greater than x. FH sequences sets are used by U users, then each user will observe interference derived at most from other L-l users at any time and is orthogonal to at least the other U- (L-1) users. If U is much larger than L, which is typically the case, then each user observes interference derived from a small number of users at any time. Then, the U users can be visualized as orthogonal, or "quasi-orthogonal", with each other. Figure 4 shows a flow chart of a process 400 allocating 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 (L) sequences necessary to support all selected users is determined later (block 414). If each selected user is assigned an FH sequence and if each set contains N FH sequences, then the minimum number of sets can be determined as shown in equation (3). Then, L sequences of FH are selected among M sets of FH sequences available for use (block 416). Then, each selected user is assigned one (or possibly multiple) FH sequences from L sets of FH sequences (block 418). The selected users can be assigned FH sequences from L sets in various ways. In one embodiment, users with similar received signal qualities are assigned FH sequences in the same set. The received signal quality can be quantified by a signal-to-interference-noise (SINR) or some other measurement. For this morality, U users can be classified based on their SINRs, for example, from the highest SINR to the lowest SINR. One user can be processed at a time, in sequential order based on the classification, and an FH sequence can be assigned from a first set of FH sequences. Another set of FH sequences is used at any time in which all the FH sequences have been assigned in the first set. This mode can map users with similar channel conditions to the same set of FH sequences. For example, users located closer to the base station can achieve higher SINRs and can be assigned FH sequences in a set. Users located further away from the base station (or "edge of the sector" users) can achieve lower SINRs and can be assigned FH sequences in another set. This modality can also facilitate the power control of the users. For example, sector edge users may be more interfering with users in other sectors and may be directed to transmit at lower power levels. In another modality, users with different received SINRs are assigned FH sequences in the same set. This mode can improve the detection performance for users transmitting simultaneously using FH sequences in the same set. Even in another modality, users are categorized based on their "margins". The margin of the difference between the SINR received and the SINR required for a given rate and captures the excess of SINR available for that rate. Users with larger margins are more likely to decode correctly than users with lower margins. Users with different margins can be assigned FH sequences in different sets, which can improve the probability of separating users. For example, users with large margins can be detected and decoded first, the interference caused by these users can be calculated and canceled, then users with lower margins can be detected and decoded then, and so on. Even in another modality, users are multiplexed based on their spatial signatures. Users with uncorrelated signatures can be separated more easily using receiver spatial processing, as described below, even though these users may collide in time and frequency. Various combinations of spatial signatures can be evaluated for different user groups in order to identify uncorrelated signatures. Users can also be categorized and multiplexed in other ways. Quasi-orthogonal multiplexing can be used with or without power control. Power control can be implemented in various ways. In a power control scheme, the transmit power for each user is adjusted such that the received SINR for the user, measured at the base station, is maintained at or near an objective SINR. The target SINR can, in turn, be adjusted to achieve a particular performance level, for example, a packet error rate (PER - packet error rate) of 1%. 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 SINR received for each user is maintained within a range of SINRs. Even in another power control scheme, the received signal strength for each user remains close to a value or within a range of target values.

Multiple access by quasi-orthogonal frequency division with variations by frequency hopping (FH-QOFDMA - frequency-hopping quasi-orthogonal frequency multiple division access) is a multiple access scheme that uses quasi-orthogonal multiplexing (or M sets of N). FH sequences) to support U users concurrently, where U can be greater than N. The FH-QOFDMA has some advantages over the conventional FH-OFDMA, which uses only a set of N FH sequences for all users. For a small number of users with U = N, only one set of FH sequences is needed, and FH-QOFDMA degenerates to and is identical to the conventional FH-QOFDMA. However, the FH-QOFDMA is limited to only one set of FH sequences and may not be able to fully utilize the additional capacity created in the spatial dimension by using multiple antennas in the base station. In contrast, the FH-QOFDMA can use multiple sets of FH sequences to support more users who take advantage of the additional capacity. Although the U users are strictly non-orthogonal to each other in the domains of frequency and time with the FH-QOFDMA when U > N, various techniques can be used to mitigate the harmful effects of intra-cell interference, as described below.

- - If the base station is equipped with multiple antennas for the reception of data, then the data transmissions from the U users can be separated using various spatial receiver processing techniques. Referring again to Figure 1, a single-input multiple-output (SIMO) channel is formed between the single antenna terminal 110a and the multiple antenna base station 120. The SIMO channel for terminal 110a can be characterized by a vector ha. { k, t) of channel response Rxl for each subband, which can be expressed as: ha (k, t) for k = 1 ... K, Eq. (4) where k is an index for subband, and haij (k, t), for i = l ... R, is the coupling or complex channel gain between the individual antenna at terminal 110a and the R antennas at the base station of 120 for subband k in the period of variations by jumps t. A multi-input multiple-input (MIMO) channel is formed between the multiple antenna terminal HOu and the multiple antenna base station 120. The MIMO channel for the HOu terminal can be characterized by a .u matrix. { k, t) of the RxT channel response for each subband, which can be expressed as: Hu (Jc, t) = [hu, i (Jc, t) hUf2, t) ... hu, T (k, t) ], for k = 1 ... K, Eq. (5) where hu, j (, t), for j '= 1, ... T, is the channel response vector between antenna j in the terminal HOu and the R antennas at base station 120 for subband k in the period of variations by jumps t. Each vector hUrj. { k, t) of channel response contains R elements and has the form shown in equation (4). In general, each terminal can be equipped with one or multiple antennas and can be assigned S sub-bands in each period of variations by jumps, where S = l. Each terminal would have a set of channel response vectors for each antenna, each set of vectors S containing channel response vectors for the S subbands assigned to the terminal for the period of variations per hop t. For example, if the terminal m is assigned S subbands with indices ka Jc + S-1 in the period of variations by jumps t, then the set of vectors for each antenna j of the terminal m would contain S of response actors of channel hm, j (k, t) to hm, j (Jc + S-1, t), for the subbands ka íc + Sl, respectively. These S channel response vectors are indicative of the channel response between antenna j at terminal m and the R antennas at base station for the S subbands assigned to terminal m. The index k of subband for the terminal m also each period of variations by jumps and is determined by the sequence of FH assigned to the terminal m. The channel response vectors for the U terminals selected for simultaneous data transmission are typically different from one another and can be visualized as "spatial signatures" for these U terminals. The base station can calculate the channel response vectors for each terminal based on the pilot symbols received from the terminal, which can be multiplexed by time division with data symbols as shown in Figure 2. For the sake of simplicity, the following description assumes that L = U / N and L individual antenna terminals J¾ to mL are assigned to each group of subbands in each period of variations by jumps. A channel response matrix H (k, t) RxL can be formed for each subband k in each period of variations by hopping t based on the L channel response vectors for the L terminals using the subband k in the period of variations by jumps t, as explained below: H (k, t) = [hml (k, t) hm2 (k, t) hmL (k, t)],,? ^ ') ?? <; - h ", L (k, t) for k = 1 ... K, Eq. (6) where ... L, is the channel response vector for the ith terminal used by subband k in the period of variations by jumps t. The channel response matrix H (^, t) for each subband in each period of variations per hop is dependent on the specific set of terminals assigned to that subband and the period of variations per hop. The symbols "received" in the base station for each subband k in each period of symbols n of each period of variations by jumps t can be expressed as: r (k, t, n) = R [k, t) -x. k, t, n) + n (k, t, n), for = 1 ...?, Eq. (7) where (J, t, n) is a vector with L symbols of "transmission" sent by L terminals by subband k in period n of symbols of the period of variations by jumps t; and r (k, t, n) is a vector with R received symbols obtained by the R antennas at the base station for subband k in period n of symbols of the period of variations by jumps t; and n (k, t, n) is a noise vector for subband k in period n of symbols of the period of variations by jumps t. For the sake of simplicity, the channel response matrix H (k, t) is assumed to be constant for a whole period of variations per hop and is not a function of the period of symbols n. Also for the sake of simplicity, it can be assumed that the noise is additive white Gaussian noise (AWGN - additive white Gaussian noise) with a zero mean vector and a covariance matrix of (pnm = s2 ·? _, Where a2 is the variance of the noise and I_ is the identity matrix K vectors of transmission symbols, x (k, t, n) for k = 1 ... K, is formed for the K subbands in each symbol period of each period of variations by jumps Because different sets of terminals can be assigned to different subbands in a given period of variations per hop, as determined by their FH sequences, the K vectors of transmission symbols x {k, tfn) for each period of symbols of each period of variations by jumps can be formed by different sets of terminals. Each vector x. { k, t, n) contains L transmission symbols sent by the L terminals using the subband k in the period of symbols n of the period of variations by jumps t. In general, each transmission symbol may be a data symbol, a pilot symbol, or a "zero" symbol (which is a zero signal value). K vectors of received symbols, r (k, t, n) for? = 1 ... K, are obtained for the K subbands in each symbol period of each period of variations by jumps. Each vector r_. { krt, n) contains R received symbols obtained by the R antennas at the base station for a subband in a symbol period. For a given subband k, period of symbols n, and period of variations by jumps t, the jth symbol of transmission in vector x. { k, t, n) is multiplied by the (th) jth vector / column of the channel response matrix H (k, t) to generate a vector r_j (k, t, n). The L transmission symbols in x (k, t, n), which are sent by L different terminals, are multiplied by the L columns of H (k, t) to generate L vectors r_i (k, t, n) to rL (?, t, n), a vector Tj [k, t, n) for each terminal. The vector r (k, t, n) obtained by the base station is composed of the L L vectors rj (/ c, t, n) to rL (k, t, n), or r. { k, t, n) = j (k, t, ri).

Each symbol received in r (k, t, n) consequently contains a component of each of the L transmission symbols in x (J, t, n). The L transmission symbols sent simultaneously by the L terminals in each subband k in each period of symbols n of each period of variations by jumps t consequently interfere with each other in the base station. The base station may use various receiver spatial processing techniques to separate the data transmissions sent simultaneously by the L terminals for each subband in each symbol period. These receiver spatial processing techniques include a ZF (zero-forcing) technique, a minimum square root mean error (MMSE minimum mean square error), a maximum ratio combining (MRC) technique, etc. For the zero force technique, the base station can derive a matrix of spatial filter Mzf (k, t) for each subband k in each period of variations by jumps t, as explained below: Mzf (/, t) = [HH (k, t) -H. { k, t)] -1-HH (k, t), Eq. (8) where "H" denotes a conjugate transpose. The base station calculates the channel response matrix? (?,?) For each subband, for example, based on the pilots transmitted by the terminals. Then, the base station uses the channel response matrix B_ (k, t) to derive the spatial filter matrix. For the sake of clarity, the following description assumes that there are no calculation errors so that fí. { k, t) = H (k, t). Because it is assumed that H (k, t) is constant in the waiting period t, the same spatial filter matrix Mzf (Jc, t) can - - used for all symbol periods in the waiting period t. The base station can perform forced processing to zero for each subband k in each symbol period n of each waiting period t, as explained below: = [HH (k, t) -H. { k, t)] _1-HH (^, t) · [H (/, t) -x. { k, t, n) + n. { k, t, n)} = x. { k, t, n) + nzf (k, t, n), Eq. (9) where Lf (Jc, t, n) is a vector with L data symbols "detected" for subband k in the period of symbols n of the period of variations by jumps t; and nZf (k, t, n) is the noise after the forced to zero process. A detected data symbol is a calculation of a data symbol sent by a terminal. For the MMSE technique, the base station can derive a spatial filter matrix MmmSe (k, t) for each subband k in each period of variations by t breaks, as explained below: Mmmse (k, t) = ÍHH ( k, t) ·? (,?) + s2 ·?] _ 1 · ?? (^) Ec. (10) If the covariance matrix is known (pnm of the noise, then this covariance matrix can be used in place of s2) · I in equation (10).

- - The base station can perform the MMSE processing for each subband k in each period of symbols n of each period of variations by jumps t, as explained below: mm, (*, n) =. (k, t) | Mmmse (k, t) | _ r (k, t, n), = D-mlmse (k, t) | Mmmxe (k, t) | [H (k, t) | x ( k, í, n) + n (k, /, = x (k, t, n) + nmmse (k, f, n), where Dmmse (i, t) is a diagonal vector that contains the diagonal elements of a matrix lWmmse. { what you. { k, t)], or -K (k, t)]; Y nmse. { k, t, n) is the noise after processing of MMSE. The symbol calculations derived from the filter spatial Mmm.se (k, t) are non-normalized calculations of the transmission symbols in x (k, t, n). Multiplication with the scale matrix D_1mm.se. { k, t) provides calculations standardized transmission symbols.

For the MRC technique, the base station can derive a spatial filter matrix Mmrc (k, t) for each subband k in each period of variation of jumps t, as It is explained below: Mmre (*, t) = HH (k, t) Eq. (12) The base station can perform the processing of MRC for each subband k in each period n of symbols of each period of variations by jumps t, as is - - explains below: = (fc, /) · Fe. (13) = x (k, t, ri) + nmrc (k, t, n), where Dmrc. { k, t) is a diagonal vector that contains the diagonal elements of a matrix Í H (k, t) -E. { k, t)], or Dmrc (^, t) = diag [HH (^, t) -H (k, t)]; Y nmrc (?, t, n) is the noise after processing of MRC.

In general, different sets can be assigned from terminals to different subband groups in a determined period of variations by breaks, as determined by its FH sequences. The N sets terminals for the N subband groups in a given period of variations by breaks may contain same or different numbers of terminals. In addition, each Terminal set can contain antenna terminals individual, multiple antenna terminals, or a combination of both. Different sets of terminals (which may contain the same or different terminal numbers) can also be assigned to a certain subband in different periods of variations by jumps. The channel response matrix H (k, t) for Each sub-band in each period of variations per jump is determines by the set of terminals that this subband uses in that period of variations by jumps and contains one or more vectors / columns for each terminal that transmits for that subband in that period of variations by jumps. The matrix H (k, t) can contain multiple vectors for a terminal that uses multiple antennas to transmit different data symbols to the base station. As shown above, the multiple data transmissions sent simultaneously from up to L terminals in each subband k in each symbol period n of each hop variation period t can be separated by the base station based on their uncorrelated spatial signatures, which are determined by their channel response vectors ml (k, t). This allows the FH-QOFDMA to enjoy a greater capacity when the number of antennas used for the reception of data is increased. In addition, the FH-QOFDMA reduces the amount of intra-cell interference observed by each subband in each period of variations per hopping so that the utilization of the additional capacity created in the spatial dimension can be achieved. Figure 5 shows a block diagram of an individual antenna terminal mode 110a and the multi-antenna terminal HOu. In the individual antenna terminal 110a, an encoder / modulator 514a receives the traffic / packet data (denoted as. {Da.}.) From a data source 512a and possibly supplementary information / signaling data from a controller 540a, processes (eg, encodes, distributes, and maps by symbols) the data based on one or more modulation schemes selected for the terminal 110a, and provides data symbols (denoted as { xa.}. ) for terminal 110a. Each data symbol is a modulation symbol, which is a complex value for a point in a signal constellation for a modulation scheme (for example, M-PSK or M-QAM). A mapper 520a from symbol to subband receives the data symbols and pilot symbols and provides these symbols for the appropriate subband (s) in each symbol period of each period of variations per hop, as determined for an FH control from a 522a generator of FH. The FH generator 522a can generate the FH control based on an FH sequence or a traffic channel assigned to the terminal 110a. The generator 522a of FH can be implemented with query tables, PN generators, and so on. The mapper 520a also provides a zero symbol for each subband not used for pilot or data transmission. For each symbol period, the mapper 520a outputs K transmission symbols for the total K subband, where each transmission symbol can be a data symbol, a pilot symbol, or a zero symbol. An OFDM modulator 530a receives K transmission symbols for each symbol period and generates a corresponding OFDM symbol for that symbol period. The OFDM modulator 530a includes a reverse fast Fourier transform unit 532 (IFFT - inverse Fourier transform phase) and a cyclic prefix generator 534. For each symbol period, the IFFT unit 532 transforms K transmission symbols in the time domain using a K-point IFFT to obtain a "transformed" symbol containing K samples in the time domain. Each sample is a complex value that is transmitted in a sample period. The cyclic prefix generator 534 repeats a portion of each transformed symbol so as to form an OFDM symbol containing N + C samples, where C is the number of samples that is repeated. The repeated portion is often called the cyclic prefix and is used to combat ISI caused by selective frequency fading. A period of OFDM symbols (or simply, a period of symbols) is the duration of an OFDM symbol and is equal to N + C sample periods. The OFDM modulator 530a provides a flow of OFDM symbols to a transmitter unit (TMTR) 536a. The transmitter unit 536a processes (eg, converts to analog, filters, amplifies, and overconverts in frequency) the OFDM symbol stream to generate a modulated signal, which is transmitted from an antenna 538a. In the multi-antenna terminal HOu, an encoder / modulator 514u receives traffic / packet data (denoted as { Du.}.) From a 512u data source and possibly supplementary information / signaling data from a controller. 540u, processes the data based on one or more coding and modulation schemes selected for the HOu termina, and provides data symbols (denoted as { xu.}.) for the llOu terminal. A demultiplexer (Demux) 516u demultiplexes the data symbols into T streams for the T antennas at the terminal llOu, a stream of data symbols. { xu, j} for each antenna, and provides each data symbol stream to a respective mapper 520u from symbol to subband. Each mapper 520u receives the data symbols and pilot symbols for its antenna and provides these symbols for the appropriate subband (s) in each symbol period of each period of variations per hop, as determined by the FH control generated by a 522u generator of FH based on a sequence of FH or a traffic channel assigned to terminal llOu. Up to T different data symbols or pilot symbols may be sent from the T antennas in each symbol period for each subband assigned to the terminal llOu. Each mapper 520u also provides a zero symbol for each subband not used for the pilot or data transmission and, for each symbol period, outputs K as transmission symbols for the total K subbands to a corresponding OFDM modulator 530u. Each OFDM modulator 530u receives K transmission symbols for each symbol period, performs OFDM modulation by the K transmission symbols, and generates a corresponding OFDM symbol for the symbol period. The T modulators of OFDM 530ua to 530ut provide T OFDM symbol flows to the T transmitter units 536ua to 536ut, respectively. Each transmitting unit 536u processes its flow of OFDM symbols and generates a corresponding modulated signal. The T modulated signals from the transmitter units 536ua to 536ut are transmitted from T antennas 538ua to 538ut, respectively. The controllers 540a to 540u direct the operation at terminals 110a and llOu, respectively. The memory unit 542a and 542u provide storage of program and data codes used by the controllers 540a and 540u, respectively. Figure 6 shows a block diagram of a mode of the base station 120. The modulated signals transmitted by the U terminals selected for data transmission are received by the R antennas 612a to 612r, and each antenna provides a received signal to a respective receiving unit (RCVR) 614. Each receiving unit 614 processes (e.g., filters, amplifies, sub-frequency, and digitizes) its received signal and provides a flow of input samples in an associated OFDM demodulator (Demod) 620. Each OFDM demodulator 620 processes its input samples and provides the received symbols. Each OFDM demodulator 620 typically includes a cyclic prefix removal unit and a fast Fourier transform (FFT) unit. The cyclic prefix elimination unit removes the cyclic prefix in each received OFDM symbol to obtain a received transformed symbol. The FFT unit transforms each transformed symbol received in the frequency domain with an FFT of K points to obtain K received symbols for the K subbands. For each symbol period, R OFDM demodulators 620a to 620r provide R sets of K received symbols for the R antennas to a spatial processor 630 of reception (RX) · The spatial reception processor (RX) 630 includes K sub-band spatial processors 632a to 632k for the K subbands. Within the R 630 spatial processor, the received symbols from the OFDM demodulators 620a to 620r for each symbol period are demultiplexed in K vectors of received symbols r_ (k, t, n) for k = l ..., the which are provided to the K space processors 632. Each spatial processor 632 also receives a spatial filter matrix M (k, t) for its subband, performs spatial processing of receiver in r (.k, t, n) with M (k, t) as described previously, and provides a vector x (k, t, n) of the detected data symbols. For each symbol period, K spatial processors 632 through 632k provide K sets of data symbols detected in K vectors x. { k, t, n) for the K subbands in a demapping machine 640 from subband to symbol. The demapper 640 obtains the K sets of detected data symbols for each symbol period and provides the detected data symbols for each terminal m in a stream. { xm} for that ends, where m 6 { to ... u} . The subbands used by each terminal are determined by an FH control generated by a FH generator 642 based on the FH sequence or traffic channel assigned to that terminal. A demodulator / decoder 650 processes (eg, unmasks by symbols, groups, and decodes) the detected data symbols. { xm} for each terminal and provides the decoded data. { d m } for the terminal. A channel calculator 634 obtains received pilot symbols from the OFDM demodulators 620a to 620r and derives a channel response vector for each antenna of each terminal transmitting to the base station 120 based on the pilot symbols received for the terminal. A spatial filter matrix calculation unit 636 forms an H channel response matrix (k, t) for each subband in each hop variation period based on the channel response vectors of all terminals that use that subband and period of variations by jumps. Then, the calculation unit 636 derives the spatial filter matrix M (.k, t) for each subband of each hop variation period based on the H channel response matrix (A:, t) for that subband and period of variations by jumps and also uses the forced zeroing technique, MMSE, or MRC technique, as described above. The calculation unit 636 provides K spatial filter matrices for the K subbands in each period of variations by jumps to K spatial processors of subband 632a to 632k. A controller 660 directs the operation in the base station 120. A memory unit 662 provides storage for the program and data codes used by the controller 600. For the sake of clarity, the quasi-orthogonal multiplexing has been specifically described for the link Inverse of an OFDMA system with variations by frequency jumps. Quasi-orthogonal multiplexing can also be used for other multiple carrier communications systems whereby multiple subbands can be provided by some means other than OFDM. The quasi-orthogonal multiplexing can also be used for the forward link. For example, a terminal equipped with multiple antennas can receive a data transmission from multiple base stations (eg, a data symbol from each of the multiple base stations for each subband in each symbol period). Each base station can transmit to the terminal using a different FH sequence than the base station assigned to the terminal. The FH sequences used by the different base stations for the terminal may be non-orthogonal to one another. Multiple base stations can send multiple data symbols for the same subband in the same symbol period to the terminal at any time these FH sequences collide. The terminal may use receiver spatial processing to separate the multiple data symbols sent simultaneously by the same subband in the same symbol period by multiple base stations. The quasi-orthogonal multiplexing techniques described herein can be implemented by various means. For example, these techniques can be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used for quasi-orthogonal multiplexing in a transmitting entity (eg, as shown in Figure 5) can be implemented within one or more specific application integrated circuits (ASICs - application specific integrated circuit), digital signal processors (DSPs - digital signal processor), digital signal processing devices (DSPDs -digital signal processing devices), programmable logic devices (PLDs), programmable field gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. Processing units used for quasi-orthogonal multiplexing can also be implemented in a receiving entity (e.g., as shown in Figure 6) within one or more ASICs, DSPs, and so on. For a software implementation, quasi-orthogonal multiplexing techniques can be implemented with modules (e.g., procedures, functions, etc.) that perform the functions described herein. The software codes may be stored in a memory unit (for example, the memory unit 542a or 542u in Figure 5 or the memory unit 662 in Figure 6) and may be executed by a processor (e.g., the 540a driver or 540u in Figure 5 or controller 660 in Figure 6). The memory unit can be implemented inside the processor or external to the processor. The above description of the embodiments described is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these modalities will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without being insulated from the spirit or scope of the invention. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but should encompass the broadest scope consistent with the principles and novel features described herein.

Claims (46)

1. NOVELTY OF THE INVENTION Having described the invention as antecedent, the content of the following claims is claimed as property CLAIMS 1. A method for assigning frequency subbands in a communication system using orthogonal frequency division multiplexing (OFDM), characterized in that it comprises: determining L sets of traffic channels to be used for U terminals selected for data transmission, where L and U are each one or greater, where each set includes multiple traffic channels that are orthogonal to each other, and where the traffic channels in each set are not orthogonal to the traffic channels in each of the other Ll sets; and allocating the U terminals with the traffic channels in the joint Ls, where each traffic channel is associated with one or more frequency sub-bands to be used for the transmission of data in each transmission interval, and where the data transmissions for The U terminals are sent using the traffic channels assigned to the U terminals.
2. 2. The method according to claim 1, characterized in that the system uses variations by frequency hopping (FH), and where 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 according to claim 1, characterized in that the traffic channels in each set use frequency sub-bands that are pseudo-random with respect to the frequency sub-bands used by the traffic channels in each of the other L-1 sets.
4. The method according to claim 1, characterized in that L is a minimum number of sets to support the U terminals.
5. The method according to claim 1, characterized in that 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 according to claim 5, characterized in that a set of traffic channels is selected if U is less than or equal to N.
7. 7. The method according to claim 5, characterized in that L = [U / N], where [x] denotes a roof operator that provides an integer value equal to or greater than x.
8. The method according to claim 1, further characterized by comprising: configuring the U terminals in L groups of terminals, a group of terminals for each of the L sets of traffic channels, where each group of terminals is assigned channels of traffic from a respective set of traffic channels.
9. The method according to claim 8, characterized in that the U terminals are configured in L groups based on the received signal qualities reached for the U terminals.
10. The method according to claim 9, characterized in that each group includes terminals having similar received signal qualities.
11. The method according to claim 8, characterized in that the U terminals are configured in L groups based on margins reached by the U terminals, where a margin for a terminal is indicative of a difference between a received signal quality reached by the terminal and a signal quality requested for the terminal.
12. The method according to claim 8, characterized in that the U terminals are configured in L groups based on spatial signatures of the U terminals, where a spatial signature for a terminal is determined by a channel response for the terminal.
13. The method according to claim 2, characterized in that the L sets of traffic channels are associated with L pseudo-random number (PN) codes, a PN code for each set of traffic channels, and where the sequences of FH for the traffic channels in each set are generated based on the PN code for the set.
14. 14. The method according to claim 13, characterized in that the L PN codes for the L sets of traffic channels are different time variations of a common PN code.
15. The method according to claim 1, characterized in that the frequency sub-bands to be used for each set of traffic channels are determined based on a respective mapping table.
16. 16. An apparatus in a communication system using orthogonal frequency division multiplexing (OFDMA), characterized in that it comprises: an operating controller for determining L sets of traffic channels to be used for the U terminals selected for data transmission, where L and U are each one or more, where each set includes multiple traffic channels that are orthogonal to each other, and where the traffic channels in each set are not orthogonal to the traffic channels in each of the others Ll sets; and allocating the U terminals with the traffic channels in the joint Ls, where each traffic channel is associated with one or more frequency sub-bands to be used for the transmission of data in each transmission interval, and where the data transmissions for The U terminals are sent using the traffic channels assigned to the U terminals.
17. The method according to claim 16, characterized in that the system uses variations by frequency hopping (FH), and where each traffic channel in each set is associated with a respective FH sequence that selects pseudo-randomly different frequency subbands in different transmission intervals for the traffic channel.
18. 18. An apparatus in a communication system using orthogonal frequency division multiplexing (OFDMA), characterized in that it comprises: means for determining L sets of traffic channels to be used for the U terminals selected for data transmission, where L and U are each one or greater, where each set includes multiple traffic channels that are orthogonal to each other, and where the traffic channels in each set are not orthogonal to the traffic channels in each of the other Ll sets; and means for assigning the U terminals to the traffic channels in the joint Ls, where each traffic channel is associated with one or more frequency subbands to be used for the transmission of data in each transmission interval, and where the transmissions of data for the U terminals are sent using the traffic channels assigned to the U terminals.
19. The apparatus according to claim 18, characterized in that the system uses variations by frequency hopping (FH), and where 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. 20. A method for transmitting data in a communication system using orthogonal frequency division multiplexing (OFDMA), characterized in that it comprises: obtaining a traffic channel to be used for data transmission, where the traffic channel is selected from among L sets of traffic channels, where L is one or more, where each set includes multiple traffic channels that are orthogonal to each other, where the traffic channels in each set are not orthogonal to the traffic channels in each of the other Ll sets, and where the traffic channel is associated with one or more frequency subbands to be used for the transmission of data in each transmission interval; and mapping the data symbols in the frequency subband (s) belonging to the traffic channel.
21. The method according to claim 20, characterized in that the system uses variations by frequency hopping (FH), and where each traffic channel in each set is associated with a respective FH sequence that selects pseudo-randomly different frequency subbands in different transmission intervals for the traffic channel.
22. The method according to claim 20, characterized in that each set includes N traffic channels, and where 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.
23. 23. The method according to claim 20, further characterized by comprising: mapping pilot symbols in the frequency subband (s) belonging (n) to the traffic channel, where data and pilot symbols are transmitted using division multiplexing of time (TDM).
24. 24. The method according to claim 23, characterized in that the data and pilot symbols are transmitted from an antenna.
25. The method according to claim 20, further characterized in that it comprises: demultiplexing the data symbols into multiple streams for multiple antennas, and where the data symbols for each stream are mapped into one or more frequency subbands belonging (n) to traffic channel and are also transmitted to an associated antenna.
26. 26. An apparatus in a communication system using orthogonal frequency division multiplexing (OFDM), characterized in that it comprises: an operating controller for obtaining a traffic channel to be used for data transmission, where the traffic channel is selected from between L sets of traffic channels, where L is one or greater, where each set includes multiple traffic channels that are orthogonal to each other, where the traffic channels in each set are not orthogonal to the traffic channels in each of the other L-1 sets, and where the traffic channel is associated with one or more frequency sub-bands to be used for the transmission of data in each transmission interval; and an operational mapping unit for mapping the data symbols in the frequency subband (s) belonging to the traffic channel.
27. 27. A terminal comprising the apparatus according to claim 26.
28. 28. A base station comprising the apparatus according to claim 26.
29. 29. An apparatus in a communication system using orthogonal frequency division multiplexing (OFDM), characterized in that comprises: means for obtaining a traffic channel to be used for data transmission, where the traffic channel is selected from among L sets of traffic channels, where L is one or more, where each set includes multiple traffic channels that are orthogonal to each other, where the traffic channels in each set are not orthogonal to the traffic channels in each of the other L-1 sets, and where the traffic channel is associated with one or more frequency sub-bands to be used for the transmission of data in each transmission interval; and means for mapping the data modulation symbols in the frequency subband (s) belonging to the traffic channel.
30. 30. A method for receiving data in a communication system using orthogonal frequency division multiplexing (OFDM), characterized in that it comprises: determining assigned traffic channels to U selected terminals for data transmission, where a traffic channel is assigned to each terminal and is selected from among L sets of traffic channels, where L and U are each one or greater, where each set includes multiple traffic channels that are orthogonal to each other, and where the traffic channels in each set are not orthogonal to the traffic channels in each of the other Ll sets; and processing the data transmissions received in the traffic channels assigned to the U terminals.
31. The method according to claim 30, characterized in that the system uses variations by frequency hopping (FH), and where each traffic channel in each set is associated with a respective FH sequence that selects pseudo-randomly different frequency subbands in different transmission intervals for the traffic channel.
32. The method according to claim 30, characterized in that each set includes N traffic channels, where N is greater than one and L times N is equal to or greater than U, and where L is a minimum number of sets to support the terminal U .
33. 33. The method according to claim 30, characterized in that the processing of the data transmissions comprises: obtaining a group of received symbols for each of the K frequency sub-bands used for data transmission, including each group R received symbols for R antennas, where R and K are each one of them greater than one, perform spatial processing in the group of symbols received for each frequency sub-band in order to obtain a group of detected data symbols for the frequency sub-band, and demultiplex K groups of data symbols detected for the K frequency sub-bands in each symbol period in order to obtain the detected data symbols for each of the terminal U's.
34. 34. The method according to claim 33, further characterized in that it comprises: obtaining a channel calculation for each of the terminals. U-terminals based on the pilot symbols received from the terminal, and where spatial processing is carried out n base in the channel calculations for the U terminals.
35. 35. The method according to claim 33, further characterized by comprising: forming a channel response matrix for each of the K frequency sub-bands based on the channel calculations for a group of one or more terminals using the subband of frequency; and deriving a spatial filter matrix for each of the K frequency sub-bands based on the channel response matrix for the frequency sub-band, and where spatial processing for each frequency sub-band is performed with the spatial filter matrix for the frequency sub-band.
36. 36. The method according to claim 35, characterized in that the spatial filter matrix for each frequency sub-band is further divided based on a ZF-zero-forcing technique.
37. 37. The method according to claim 35, characterized in that the spatial filter matrix for each frequency sub-band is further derived based on a minimum square root mean error (MMSE) technique.
38. 38. The method according to claim 35, characterized in that the spatial filter matrix for each frequency sub-band is further derived based on a maximum ratio combining (MRC) technique.
39. 39. An apparatus in a communication system using orthogonal frequency division multiplexing (OFDM), characterized in that it comprises: an operating controller for determining the traffic channels assigned to the U terminals selected for data transmission, where a channel of traffic is assigned to each terminal and selected from among L sets of traffic channels, where L and U are each one or greater, where each set includes multiple traffic channels that are orthogonal to each other, and where the channels traffic in each set are not orthogonal to the traffic channels in each of the other Ll sets; and an operational processing unit for processing the data transmissions received by the traffic channels assigned to the U terminals.
40. 40. The apparatus according to claim 39, characterized in that the processing unit comprises: a spatial processor operative to obtain a group of symbols received for each of the K sub-bands of frequencies used for the transmission of data and for performing spatial processing in the group of symbols received for each frequency sub-band, where each group of received symbols includes R symbols received for R antennas, where R and K are each greater than one, an operational demultiplexer for demultiplexing K groups of data symbols detected for the K frequency sub-bands in each symbol period in order to obtain the detected data symbols for each of the U terminals.
41. 41. The apparatus according to claim 40, further characterized in that it comprises: an operational channel calculator for forming a channel response matrix for each of the K frequency sub-bands based on the channel calculations for a group of one or more terminals that use the frequency sub-band; and an operational calculation unit for deriving a spatial filter matrix for each of the K frequency sub-bands based on the channel response matrix for the frequency sub-band, and where the spatial processing is operative to perform the spatial processing in the group of symbols received for each frequency sub-band with the spatial filter matrix for the frequency sub-band.
42. 42. A base station comprising the apparatus - - according to claim 39.
43. 43. A terminal comprising the apparatus according to claim 39.
44. 44. An apparatus in a communication system using orthogonal frequency division multiplexing (OFDM), characterized in that it comprises: means for determining assigned traffic channels; to the U terminals selected for data transmission, where a traffic channel is assigned to each terminal and selected from L sets of traffic channels, where L and U are each one or greater, where each set includes multiple traffic channels that are orthogonal to each other, and where the traffic channels in each set are not orthogonal to the traffic channels in each of the other Ll sets; and means for processing the data transmissions received by the traffic channels assigned to the U terminals.
45. 45. The apparatus according to claim 44, characterized in that the processing means comprises: means for obtaining a group of received symbols for each of the K frequency sub-bands used for data transmission, including each group R received symbols for R antennas , where R and K are each greater than one, means for performing spatial processing in the group of symbols received for each frequency sub-band in order to obtain a group of detected data symbols for the frequency sub-band, and to demultiplex K groups of detected data symbols for the K frequency sub-bands in each symbol period in order to obtain the detected data symbols for each of the U terminals.
46. 46. The apparatus according to claim 45, characterized in that it further comprises: means for forming a channel response matrix for each of the K subbands based on the channel calculations for a group of one or more terminals using the subband of frequencies; and means for deriving a spatial filter matrix for each of the K frequency sub-bands based on the channel response matrix for the frequency sub-band, and where the spatial processing for each frequency sub-band is performed with the filter matrix space for the frequency sub-band.