WO2010048129A1

WO2010048129A1 - Method and apparatus for performing uplink transmission techniques with multiple carriers and reference signals

Info

Publication number: WO2010048129A1
Application number: PCT/US2009/061251
Authority: WO
Inventors: Erdem Bala; Sung-Hyuk Shin; Philip J. Pietraski; Guodong Zhang; Joseph S. Levy; Kyle Jung-Lin Pan
Original assignee: Interdigital Patent Holdings, Inc.
Priority date: 2008-10-20
Filing date: 2009-10-20
Publication date: 2010-04-29
Also published as: TW201125304A; AR073834A1

Abstract

A method and apparatus are described for performing uplink (UL) transmission techniques with multiple carriers. Multiple transmission techniques with low cubic metric (CM), especially for cell-edge wireless transmit/receive units (WTRUs), are preferred for long term evolution advance (LTE-A) systems. Layer shifting and multiplexing of precoded pilots can be carried out in the uplink.

Description

[0001] METHOD AND APPARATUS FOR PERFORMING UPLINK

TRANSMISSION TECHNIQUES WITH MULTIPLE CARRIERS AND REFERENCE SIGNALS

[0002] FIELD OF INVENTION

[0003] This application is related to wireless communications.

[0004] BACKGROUND

[0005] In a long term evolution (LTE) system, single carrier frequency division multiple access (SC-FDMA) is used for uplink (UL) transmissions due to the smaller cubic metric (CM) or peak-to-average power ratio (PAPR). An SC-FDMA transmission is similar to an orthogonal frequency division multiplexing (OFDM) transmission except that the modulated data is first spread with a discrete Fourier transform (DFT), and then mapped to consecutive subcarriers in an inverse fast Fourier transform (IFFT) block. To improve the frequency domain scheduling of SC- FDMA, a similar multiple access scheme referred to as clustered DFT spread FDMA (CL-DFTS-FDMA) has been proposed. In this case, the DFT-spread symbols do not have to be mapped to consecutive subcarriers. Instead, the data may be mapped to non-contiguous clusters, where a cluster consists of a number of consecutive subcarriers.

[0006] The maximum bandwidth supported in LTE is 20 MHz. To get data rates of up to lGb/s, carrier aggregation has been proposed. In carrier aggregation, carriers of bandwidth 20 MHz or less are aggregated and used for transmission. The aggregated carriers may be contiguous or non-contiguous.

[0007] An LTE UL reference signal (RS) is based on Zadoff-Chu sequences which belong to the family of constant amplitude zero auto-correlation (CAZAC) sequences. The cyclic shifts of a root CAZAC sequence are orthogonal to each other and the cross-correlation between different root sequences is low. When the UL is based on an SC transmission, as in LTE, the RSs are time multiplexed with data, (i.e., RSs are transmitted in separate OFDM symbols. For example, in LTE there are two slots per subframe or transmission time interval (TTI). Each slot may have 7 OFDM symbols, and the middle OFDM symbol, (the forth OFDM symbol in a time slot), is used for pilot transmission.

[0008] Multiplexing of RSs from different antennas of a WTRU has been previously studied. Some possible methods may be multiplexing with frequency division multiplexing (FDM), (including multiplexing in frequency RSs from different antennas), multiplexing with code division multiplexing (CDM) including multiplexing RSs from different antennas with orthogonal codes in frequency and/or time, or any combination thereof.

[0009] In LTE, multiple antennas may be used for UL transmission. With multiple antennas, closed or open loop precoding and transmit diversity may be used. The current design of the RS, also called a pilot, in an LTE system for the UL assumes a single transmit antenna. When multiple antennas are used, new reference signals for the additional antennas will be required. [0010] When multiple antennas are supported for UL transmission, data modulation reference signals (DMRS) may be precoded similar to data. Also, RSs from different antennas of a WTRU and from multiple WTRUs may be multiplexed. Lastly, sounding reference signals (SRS) from different antennas of a WTRU and from multiple WTRUs may be multiplexed.

[0011] When carrier aggregation is used for UL transmission, large CM or

PAPR arises as a problem. Thus, multiple access schemes with low CM, especially for cell-edge wireless transmit/receive units (WTRUs), are preferred for LTE- advance (LTE-A) systems. A method and apparatus for efficiently performing codeword-to-carrier mapping is desired.

[0012] SUMMARY

[0013] A method and apparatus are described for performing UL transmission techniques with multiple carriers. Multiple transmission techniques with low CM, especially for cell-edge WTRUs, are preferred for LTE-A systems. A method for performing efficient codeword-to-carrier mapping is also described. Furthermore, a method and apparatus are described for reference signaling in UL transmissions in LTE. The method and apparatus includes multiplexing precoded pilots, multiplexing multiple WTRUs in UL multi-user multiple -input multiple -output (MU-MIMO), and multiplexing SRS.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:

[0016] Figure 1 shows a codeword-to-carrier mapping scheme;

[0017] Figure 2 shows multiplexing with orthogonal codes (CDM);

[0018] Figure 3 shows multiplexing in frequency (FDM); and

[0019] Figure 4 shows multiplexing with FDM and CDM;

[0020] Figure 5 shows an example of a block diagram of an evolved Node-B

(eNodeB); and

[0021] Figure 6 shows an example of a block diagram of a WTRU.

[0022] DETAILED DESCRIPTION

[0023] When referred to hereafter, the terminology "wireless transmit/receive unit (WTRU)" includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment.

[0024] When referred to hereafter, the terminology "evolved Node-B (eNodeB)" includes but is not limited to a base station, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. [0025] A list of possible combinations of multiple access schemes for cases where there is a single carrier, (i.e., no aggregation or aggregated carriers), is found in Table 1 below. Note that SC-FDMA is a special case of clustered DFT-S-FDMA where the number of clusters is 1.

Table 1

[0026] There is a relationship between the number of codewords and the number of aggregated carriers. Figure 1 shows a codeword-to-carrier mapping scheme. In Figure 1, there are groups of contiguous carriers and the groups are noncontiguous. When there are multiple codewords for a given WTRU, several codeword-to-carrier mapping schemes may be implemented.

[0027] In a first scheme, each codeword is fed into a separate DFT block, then mapped to subcarriers in an IFFT block, and then transmitted on a given component carrier or a group of contiguous carriers. The inputs to the DFT blocks are different codewords. The output of an IFFT block may be mapped to several contiguous carriers or a single carrier.

[0028] In a second scheme, one codeword may be input to two or more DFT blocks, (e.g., a codeword is interleaved over different DFT blocks). In this case, a codeword is transmitted over different carriers and may benefit from frequency diversity.

[0029] In a third scheme, a codeword may hop over several carriers, (i.e. not all carriers are used at a given time). [0030] In a fourth scheme, when multiple antennas are used for spatial multiplexing/precoding, layer permutation using large delay cyclic delay diversity (CDD) over multiple carriers may be used.

[0031] In a fifth scheme, if OFDMA is used at the air interface, the codeword- to-carrier mapping methods may also be used except that DFT precoding before IFFT in SC-FDMA is not applied in OFDMA.

[0032] The codeword-to-carrier mapping is related to the used physical downlink control channel (PDCCH) format.

[0033] In one embodiment, there is one PDCCH for a carrier. A codeword may be transmitted on a single carrier. Alternatively, pieces of a codeword may be transmitted on different carriers. There may be more than one PDCCH for a codeword.

[0034] In another embodiment, there is one PDCCH for a set of carriers. A codeword is transmitted on the carriers for which the PDCCH allocates the transmission resources. There may be a single PDCCH for a codeword. Alternatively, pieces of a codeword may be transmitted on different sets of carriers. There may be more than one PDCCH for a codeword.

[0035] In yet another embodiment, there is one PDCCH for a codeword. The

PDCCH may allocate resources on one or more carriers for the codeword. The modulation order, coding rate, and other parameters for different carriers may be the same or different which may result in a larger PDCCH format. [0036] The details for performing MIMO precoding with bandwidth aggregation in a codeword-to-carrier mapping scheme are provided below. [0037] In LTE, precoding is combined with large delay CDD so that each layer experiences similar SNR. Precoding with large delay CDD is defined where the matrix W is the precoding matrix and the matrices D and U are known to those of ordinary skill in the art and defined in the standard. [0038] For example, Equation (1)

may be shown to be equivalent to:

Equation (2) where Ψ^(d_Λxl(£)) is a cyclically permuted version of d by k times. Thus, different columns of the precoding matrix are used to precode a layer on different subcarriers. This improves the diversity because now all layers are transmitted through all eigendirections of the channel instead of a fixed layer to eigendirection mapping. [0039] When there are several carriers, (the same is also true with one carrier), the large delay CDD may be applied after the DFT spreading. It is possible to enable/disable large delay CDD for different carriers.

[0040] Applying large delay CDD after DFT spreading may increase the

PAPR; for example when the precoding matrix W is just an identity matrix. To keep the PAPR the same and still benefit from the advantages of transmitting a layer through several eigendirections, data streams (i.e., streams of modulation symbols) may be multiplexed before the DFT operation, (i.e., in the time domain). For example, suppose that there are two data streams denoted as Xl and X2. When layer multiplexing (or layer shifting) is applied, the input to the first DFT may be XIl, X21, X13, X23, ..., and the input to the second DFT may be X12, X22, X14, X24, where Xab denotes the b'th symbol in the a'th layer. After the DFT spreading, the precoding matrix W and delay matrix D may be applied. Note that, in this example, the modulation symbols are multiplexed in time domain. The modulation symbols may be multiplexed (layer-shifted) block by block such that each block of modulation symbols correspond to the amount of data comprising, for example, one orthogonal frequency division multiplexing (OFDM) symbol or one time slot. [0041] In another scheme, un-precoded reference signals may be transmitted in the UL to enable channel estimation by the eNodeB. Alternatively, precoded reference signals may be transmitted. This may allow the eNodeB to directly estimate the effective channel. Also, precoded/beamformed pilots may have enhanced received signal-to-interference and noise ratio (SINR). [0042] Using precoded pilots may result in more efficient usage of the cyclic shifts of a root sequence. The number of required orthogonal sequences becomes equal to the number of data streams, not the number of antennas. This may also reduce the pilot overhead. [0043] Design of Precoded RSs

[0044] Precoding of the RSs may be done in a similar way to precoding of data.

On each subcarrier, the vector of pilot coefficients is multiplied by the precoding matrix. The term precoding is used in a general context such that beamforming is also a kind of precoding, possibly rank-1 and wideband. As an example, pi and p2 are two cyclic -shifted CAZAC sequences with zero autocorrelation, i.e. they are derived from the same root sequence by applying different cyclic shifts. The lengths of these sequences are L. Thus, the sequences may be mapped to L subcarriers after being precoded. W is the precoding matrix with size (Nt x N_s), where Nt is the number of transmit antennas and N_s is the number of data streams. On a given subcarrier k, the corresponding pilot coefficients are multiplied by the precoding matrix. The size of the vector that contains the pilot coefficients is (N₈ x 1). This operation is shown in Equation (3) for two data streams and two transmit antennas as follows:

- Pkl^wl ⁺ Pk2^w2 . Equation (3)

[0045] Then, from each antenna, the coefficient tki is transmitted where i = 1,

..., Nt. When orthogonal sequences are used as reference signals, the same matrix may be used to precode the entire pilot sequence in order to maintain the orthogonality between the sequences.

[0046] The precoded pilot sequences may be multiplexed by applying multiplexing techniques as described below.

[0047] Multiplexing of the precoded pilots by CDM in frequency domain

[0048] The precoded pilots may be multiplexed with CDM in the frequency domain, (i.e., orthogonal sequences are used as reference signals). Specifically, orthogonal sequences may be derived from the cyclic shifts of the same root sequence. The number of sequences is equal to the number of data streams. On each subcarrier, the corresponding coefficient from the precoded CAZAC sequence is transmitted. This multiplexing technique is illustrated in Figure 2 for two data streams, (two orthogonal sequences), where the shading represents a different sequence.

[0049] Multiplexing of the precoded pilots using CDM in frequency and time domains

[0050] To increase the number of pilots, time domain spreading may also be used in addition to applying CDM in the frequency domain. In LTE, UL RS is carried in one OFDM symbol in each of the two slots in a subframe. The orthogonal pilot sequences, after being precoded, may be spread over two or more OFDM symbols by using orthogonal codes, such as Walsh codes. For example, if spread over two OFDM symbols, (where each OFDM symbol is in one slot as in LTE), the

spreading matrix may be used for time domain spreading. If spread over

1 1

2π 4π three OFDM symbols, the spreading matrix \ e ³ e ³ may be used. As an

Aπ 2π

1 e

1 1 example, time domain spreading with may be implemented by using a 1 -1 precoded pilot sequence that is mapped to the corresponding subcarriers after being multiplied by 1 in the first OFDM symbol that is used to transmit reference signals (denoted as RS-OFDM) and by 1 in the second RS-OFDM symbol. Additionally, the same precoded pilot sequence may be mapped to the corresponding subcarriers after being multiplied by 1 in the first RS-OFDM symbol and by -1 in the second RS- OFDM symbol.

[0051] When time domain spreading is used in addition to CDM in frequency domain, the time domain spreading sequence should also be known by the WTRU in addition to the base sequence and the cyclic shift.

[0052] Multiplexing of the precoded pilots in frequency domain (FDM)

[0053] The precoded RSs can also be multiplexed in frequency domain as shown in Figure 3. Reference signal corresponding to one of the antenna ports may be transmitted on a given subcarrier. For example, at subcarrier k, the first precoded reference signal is transmitted, which is equivalent to setting pk2 = 0. With frequency domain multiplexing, the same pilot sequences can be used for all data streams because orthogonality is achieved in the frequency domain. In this case, the length of the root sequence may be L/m, where L is the number of subcarriers used for data transmission and m is the repetition factor, i.e. the number of antenna ports or data streams.

[0054] Multiplexing of the precoded pilots in frequency and code domains

(CDM and FDM)

[0055] This is a combination of multiplexing precoded pilots in frequency domain and code domain. A set of subcarriers are allocated for the transmission of two or more specific precoded reference signals. The precoded reference signals are multiplexed in code domain as explained above and mapped to these subcarriers. Different sets of subcarriers are allocated for the transmission of other precoded reference signals. An example is given herein in Figure 4. The odd-numbered subcarriers are allocated for the transmission of two precoded reference signals (precoded reference signals 1 and 2). These two reference signals may be generated by precoding two orthogonal sequences (e.g., with a precoding matrix). The even- numbered subcarriers may similarly be used to transmit two other precoded reference signals (precoded reference signals 3 and 4). In this example, the length of the root sequence becomes L/2 because every other subcarrier is used to transmit the sequence.

[0056] Multiplexing of the precoded pilots in time (TDM)

[0057] Precoded pilots can be multiplexed in time domain only as well. In this case, different precoded RSs can be transmitted in different OFDM symbols. [0058] Multiplexing in MU-MIMO

[0059] When MU-MIMO is used in a UL transmission, the antennas and the

WTRU may be multiplexed. In one option, if every WTRU transmits a single stream, then the above methods can be applied as if each WTRU is a different stream. In another option, if multiple streams per WTRU are allowed, the same methods may still be used.

[0060] Signaling of the cyclic shift index

[0061] When multiple antennas are used for UL transmission, the cyclic shifts of the sequences (those are used for frequency domain spreading) may be signaled to the WTRU. With precoded pilots, the required number of cyclic shifts is equal to the number of data streams but not the number of the transmit antennas. This means that the number might change dynamically, so the control signaling format should be designed appropriately to be able to accommodate all possible options. Some control channel format design options are described below.

[0062] If separate UL grant formats are used for MU-MIMO and single-user

MIMO (SU-MIMO) respectively, the following embodiments may be implemented. [0063] For a SU-MIMO UL grant, the cyclic shifts may be configured by higher layer signaling. The configuration may be cell-specific or WTRU- specific. The cyclic shifts may be predetermined and may not change. One UL grant format which has a reserved place for up to the maximum number of data streams may be used, but this may result in inefficiency. Different UL grant formats for different number of data streams may be used. For example, if up to four data streams are supported, then four different formats may be designed. This may result in increased number of blind detections. Implicit signaling of the cyclic shifts may be used wherein there is one UL grant format and the eNodeB signals the index of the first cyclic shift. The others may be found by applying a formula, for example consecutive cyclic shifts may be used.

[0064] For a MU-MIMO UL grant, if there is a restriction on MU-MIMO such that the number of data streams is limited to 1, then the cyclic shift is signaled. If there is no such restriction, then methods set forth above for SU-MIMO may be used.

[0065] If the same control signaling format is used for SU-MIMO and MU-

MIMO, then the cyclic shifts may be signaled and methods set forth above may be used.

[0066] The orthogonal sequence index may be determined if time domain spreading is used for pilots. This may be signaled in a cell-specific or WTRU-specific manner. Alternatively an orthogonal sequence index may also be derived from other parameters.

[0067] The root sequences and cyclic shifts may be changed inside a subframe or between subframe. "Cyclic shift group hopping" may occur among groups of cyclic shifts. For example, if there are 6 cyclic shifts and 2 of them are used at a given time, hopping pattern may be {cl,c2}; {c3,c4}; {cl,c4}, and the like. Each cyclic shift may also be hopped independently from each other, i.e., there is no grouping. The hopping patterns may be either fixed or configured by WTRU-specific or cell- specific signaling.

[0068] Open Loop precoding

[0069] One form of precoding is open loop precoding where a precoding matrix/vector may be selected without any feedback. As an example, for high speed WTRUs, it may not be practical to have the eNodeB select the precoder to be used in the UL. When open loop precoding is used, and if the precoding is wideband or the same precoding matrix/vector is used over a large number of subcarriers, the above methods for multiplexing precoded RS may be used. Alternatively, if the precoding matrix/vector is used over narrowband or a small number of subcarriers, for example, per subcarrier, then non-precoded RS may be used. Open and closed loop precoding may be configured by higher layer signaling and then the corresponding RS transmission scheme may be used. [0070] RS for OFDMA

[0071] When single carrier transmission is used, RSs are transmitted by time multiplexing with data as shown above, (i.e., one or more OFDM symbols are used just for RS). In the case that the UL grant is for an OFDMA transmission, RSs may be confined to resource element (RE) boundaries rather than spanning an entire symbol. In this case, similar to the downlink, RSs may be transmitted in several OFDM symbols. The above methods may similarly be used in OFDM transmission as well.

[0072] In order to have the effective channel estimate per layer determined by the eNodeB, certain REs or groups of REs may be reserved for different rows (or columns) of the precoding matrix used. The channel estimate for each layer could then be determined by using different sets of REs. The REs may be separated in time and/or frequency.

[0073] Alternatively, the pilots may be precoded and signaled the same way as the data (simultaneously on a set of REs) except that different sequences are used that have good correlation properties.

[0074] The number and location of REs may depend on the environmental factors or geometry such as speed or signal-to-noise ratio (SNR) and the number of layers. The REs used for sending RS may be signaled as part of broadcast, cell- specific or WTRU specific signaling.

[0075] SC and OFDMA transmission may be configured by higher layer signaling. The corresponding RS transmission scheme is used. [0076] Sounding RS (SRS) multiplexing [0077] The aforementioned methods may be used to multiplex the SRS among different WTRUs and different antennas of a WTRU. SRS transmission may be precoded or non-precoded. In LTE, the maximum bandwidth supported is 20 MHz. To increase the bandwidth, several component carriers may be aggregated, for example two component carriers of 20 MHz. When several component carriers are used in UL, then the WTRU power might not be enough to sound all component carriers at the same time. In this case, time multiplexing may be used where different component carriers are sounded at different times. Also, frequency multiplexing may be used where different bands of the component carriers are sounded. Additionally, a combination of the two may be used. [0078] RS transmission for the UL control channel

[0079] In the UL control channel, open-loop transmission such as transmit diversity may be used. In this case, un-precoded pilots from all antennas instead of precoded pilots may be required. The same methods as for RS of UL data channel may be used where the precoding matrix can be thought of an identity matrix and

[0080] Figure 5 is an example of a block diagram of an eNodeB 500. The eNodeB 500 includes a MIMO antenna 505, a receiver 510, a processor 515 and a transmitter 520. The MIMO antenna 505 includes antenna elements 505i, 5052, 5053 and 5054. Although there are four (4) antenna elements depicted in Figure 5, an extension to more or less antenna elements may be implemented and should be apparent to those skilled in the art.

[0081] Figure 6 is an example of a block diagram of a WTRU 600. The WTRU

600 includes a MIMO antenna 605, a receiver 610, a processor 615 and a transmitter 620. The MIMO antenna 605 includes antenna elements 605i, 605₂, 605₃ and 605₄. Although there are four (4) antenna elements depicted in Figure 6, an extension to more or less antenna elements may be implemented and should be apparent to those skilled in the art. The WTRU 600 performs MIMO uplink transmissions. [0082] The processor 615 in the WTRU 600 is configured to perform any embodiments disclosed above. For example, the processor 615 may be configured to generate modulation symbols, map the modulation symbols to at least two layers for spatial multiplexing while performing layer shifting in time domain such that the modulation symbols in one input stream are multiplexed over multiple layers, and perform DFT spreading on the layer-shifted modulation symbols. The processor 615 may be configured to apply a precoding matrix before or after performing the DFT spreading after layer- shifting (i.e., layer-multiplexing) the modulation symbols. The processor 615 may be configured to perform layer shifting of the modulation symbols block by block. One block of modulation symbols comprise one OFDM symbol or one time slot. The processor 615 may be configured to generate a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence, and map the precoded reference signals on a plurality of subcarriers.

[0083] The processor 615 in the WTRU 600 may be configured to generate a plurality of precoded reference signals, wherein each reference signal includes an orthogonal pilot sequence that is cyclically shifted from the orthogonal sequence of the other reference signals, and apply CDM on the reference signals in frequency domain based on the cyclic shift separation between the reference signals. The orthogonal pilot sequences may be spread over a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain. [0084] Embodiments.

[0085] 1. A method, implemented by a WTRU, of performing MIMO uplink transmissions.

[0086] 2. The method of embodiment 1 comprising generating modulation symbols.

[0087] 3. The method of embodiment 2 comprising mapping the modulation symbols to at least two layers for spatial multiplexing while performing layer shifting in time domain such that the modulation symbols in one input stream are multiplexed over multiple layers. [0088] 4. The method of embodiment 3 comprising performing DFT spreading on the layer-shifted modulation symbols.

[0089] 5. The method of embodiment 4 comprising performing OFDM processing on the DFT-spread modulation symbols to generate OFDM symbols on multiple layers.

[0090] 6. The method of embodiment 5 comprising transmitting the OFDM symbols through multiple antennas.

[0091] 7. The method as in any one of embodiments 3-6, further comprising applying a precoding matrix after layer shifting the modulation symbols in time domain.

[0092] 8. The method of embodiment 7 wherein the modulation symbols are layer-shifted block by block.

[0093] 9. The method of embodiment 8 wherein modulation symbols in one block are processed for transmission in one OFDM symbol.

[0094] 10. The method of embodiment 8 wherein modulation symbols in one block are processed for transmission in one time slot.

[0095] 11. The method as in any one of embodiments 2-10, further comprising generating a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence.

[0096] 12. The method of embodiment 11 comprising mapping the precoded reference signals on a plurality of subcarriers.

[0097] 13. The method of embodiment 1 comprising generating a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence.

[0098] 14. The method of embodiment 13 comprising mapping the precoded reference signals on a plurality of subcarriers.

[0099] 15. The method as in any one of embodiments 13-14, wherein the reference signals are CAZAC sequences. [00100] 16. The method of embodiment 15 wherein the reference signals are based on Zadoff-Chu sequences.

[00101] 17. The method as in any one of embodiments 13-16, further comprising spreading the precoded pilot sequences over a plurality of OFDM symbols in time domain.

[00102] 18. The method of embodiment 17 wherein the precoded pilot

sequences are spread over two OFDM symbols by using a matrix

[00103] 19. A WTRU for performing MIMO uplink transmissions.

[00104] 20. The WTRU of embodiment 19 comprising a processor configured to generate modulation symbols.

[00105] 21. The WTRU of embodiment 20 wherein the processor is configured to map the modulation symbols to at least two layers for spatial multiplexing while performing layer shifting in time domain such that the modulation symbols in one input stream are multiplexed over multiple layers. [00106] 22. The WTRU of embodiment 21 wherein the processor is configured to perform DFT spreading on the layer-shifted modulation symbols. [00107] 23. The WTRU of embodiment 22 wherein the processor is configured to perform OFDM processing on the DFT-spread modulation symbols to generate OFDM symbols on multiple layers.

[00108] 24. The WTRU of embodiment 23 comprising multiple antennas for transmitting the OFDM symbols.

[00109] 25. The WTRU as in any one of embodiments 21-24, wherein the processor is configured to apply a precoding matrix after layer -shifting the modulation symbols.

[00110] 26. The WTRU as in any one of embodiments 20-25, wherein the processor is configured to perform layer shifting of the modulation symbols block by block.

[00111] 27. The WTRU of embodiment 26 wherein modulation symbols in one block are processed for transmission in one OFDM symbol.

[00112] 28. The WTRU of embodiment 26 wherein modulation symbols in one block are processed for transmission in one time slot.

[00113] 29. The WTRU as in any one of embodiments 20-28, wherein the processor is configured to generate a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence, and map the precoded reference signals on a plurality of subcarriers.

[00114] 30. The WTRU of embodiment 19 comprising multiple antennas.

[00115] 31. The WTRU of embodiment 30 comprising a processor configured to generate a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence, and map the precoded reference signals on a plurality of subcarriers.

[00116] 32. The WTRU of embodiment 31 wherein the reference signals are

CAZAC sequences.

[00117] 33. The WTRU of embodiment 32 wherein the reference signals are based on Zadoff-Chu sequences.

[00118] 34. The WTRU as in any one of embodiments 31-33, wherein the processor is configured to spread the precoded pilot sequences over a plurality of

OFDM symbols in time domain.

[00119] 35. The WTRU of embodiment 34 wherein the precoded pilot

sequences are spread over two OFDM symbols by using a matrix

[00120] Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).

[00121] Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine.

[00122] A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light- emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB) module.

Claims

CLAIMS What is claimed is:

1. A method, implemented by a wireless transmit/receive unit (WTRU), of performing multiple-input multiple -output (MIMO) uplink transmissions, the method comprising: generating modulation symbols; mapping the modulation symbols to at least two layers for spatial multiplexing while performing layer shifting in time domain such that the modulation symbols in one input stream are multiplexed over multiple layers; performing discrete Fourier transform (DFT) spreading on the layer-shifted modulation symbols; performing orthogonal frequency division multiplex (OFDM) processing on the DFT-spread modulation symbols to generate OFDM symbols on multiple layers; and transmitting the OFDM symbols through multiple antennas.

2. The method of claim 1 further comprising: applying a precoding matrix after layer shifting the modulation symbols in time domain.

3. The method of claim 1 wherein the modulation symbols are layer- shifted block by block.

4. The method of claim 3 wherein modulation symbols in one block are processed for transmission in one orthogonal frequency division multiplexing (OFDM) symbol.

5. The method of claim 3 wherein modulation symbols in one block are processed for transmission in one time slot.

6. The method of claim 1 further comprising: generating a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence; and mapping the precoded reference signals on a plurality of subcarriers.

7. A method, implemented by a wireless transmit/receive unit (WTRU), of performing multiple-input multiple -output (MIMO) uplink transmissions, the method comprising: generating a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence; and mapping the precoded reference signals on a plurality of subcarriers.

8. The method of claim 7 wherein the reference signals are constant amplitude zero auto-correlation (CAZAC) sequences.

9. The method of claim 7 wherein the reference signals are based on Zadoff-Chu sequences.

10. The method of claim 7 further comprising: spreading the precoded pilot sequences over a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain.

11. The method of claim 10 wherein the precoded pilot sequences are

spread over two OFDM symbols by using a matrix

12. A wireless transmit/receive unit (WTRU) for performing multiple-input multiple -output (MIMO) uplink transmissions, the WTRU comprising: a processor configured to generate modulation symbols, map the modulation symbols to at least two layers for spatial multiplexing while performing layer shifting in time domain such that the modulation symbols in one input stream are multiplexed over multiple layers, perform discrete Fourier transform (DFT) spreading on the layer- shifted modulation symbols, and performing orthogonal frequency division multiplex (OFDM) processing on the DFT-spread modulation symbols to generate OFDM symbols on multiple layers; and multiple antennas for transmitting the OFDM symbols.

13. The WTRU of claim 12 wherein the processor is configured to apply a precoding matrix after layer- shifting the modulation symbols.

14. The WTRU of claim 12 wherein the processor is configured to perform layer shifting of the modulation symbols block by block.

15. The WTRU of claim 14 wherein modulation symbols in one block are processed for transmission in one orthogonal frequency division multiplexing (OFDM) symbol.

16. The WTRU of claim 14 wherein modulation symbols in one block are processed for transmission in one time slot.

17. The WTRU of claim 12 wherein the processor is configured to generate a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence, and map the precoded reference signals on a plurality of subcarriers.

18. A wireless transmit/receive unit (WTRU) for performing multiple-input multiple -output (MIMO) uplink transmissions, the WTRU comprising: multiple antennas; and a processor configured to generate a plurality of precoded reference signals by applying a precoding matrix to reference signals that are generated by cyclically shifting a root sequence, and map the precoded reference signals on a plurality of subcarriers.

19. The WTRU of claim 18 wherein the reference signals are constant amplitude zero auto-correlation (CAZAC) sequences.

20. The WTRU of claim 18 wherein the reference signals are based on Zadoff-Chu sequences.

21. The WTRU of claim 18 wherein the processor is configured to spread the precoded pilot sequences over a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain.

22. The WTRU of claim 21 wherein the precoded pilot sequences are spread

over two OFDM symbols by using a matrix