HK1112350A - Capacity based rank prediction for mimo design - Google Patents

Description

Capacity-based rank prediction for MIMO designs

Technical Field

[0001] The present disclosure relates generally to communication, and more specifically to determining how to allocate data streams to be transmitted via multiple channels, such as a multiple-input multiple-output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) communication system.

Background

[0002] In a wireless communication system, an RF modulated signal from a transmitter may reach a receiver via a number of propagation paths. The characteristics of the propagation path typically change over time due to a number of factors, such as fading and multipath effects. To provide diversity against deleterious path effects and improve performance, multiple transmit and receive antennas may be used. If the propagation paths between the transmitting and receiving antennas are linearly independent (i.e., transmission on one path cannot form a linear combination with transmission on the other path), which is generally true to at least some extent, then the likelihood of correctly receiving a data transmission increases as the number of antennas increases. In general, as the number of transmit and receive antennas increases, diversity increases and performance improves.

[0003]Multiple Input Multiple Output (MIMO) communication systems using multiple N _T ) Transmitting antenna and a plurality (N) _R ) The antennas are received for transmission of data. From N _T A transmitting antenna and N _R A MIMO channel formed by multiple receive antennas can be decomposed into N _S A separate channel, wherein N _S ≤min{N _T ，N _R }. N may also be substituted _S Each of the independent channels is referred to as a spatial subchannel (or a transmission channel) of the MIMO channel and corresponds to one dimension. MIMO systems can improve performance (e.g., increase transmission capacity) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.

[0004]For a full rank (fullrank) MIMO channel, where N _S ＝N _T ≤N _R From N may be _T Each of the transmit antennas transmits a separate data stream. The transmitted data streams may experience different channel conditions (e.g., different fading and multipath effects) and may achieve different signal-to-noise-and-interference ratios (SNRs) for a given amount of transmit power. Furthermore, if successive interference cancellation is used at the receiverTo recover the transmitted data stream(as described below), then, depending on the particular order in which the data streams are recovered, different SNRs for the data streams may be obtained. Thus, different data rates may be supported by different data streams depending on the achieved SNR for the different data streams. Since the channel conditions typically change over time, the data rate supported by each data stream also changes over time.

[0005] The MIMO design has two modes of operation-Single Codeword (SCW) and Multiple Codeword (MCW).

[0006] In MCW mode, the transmitter may independently encode data transmitted on each spatial layer at potentially different rates. The receiver uses a Successive Interference Cancellation (SIC) algorithm that operates as follows: the first layer is decoded, then after re-encoding and multiplying the encoded first layer by the "estimated channel", its contribution is subtracted from the received signal, then the second layer is decoded, and so on. This "onion-peeling" approach means that each successively decoded layer sees an increased signal-to-noise ratio (SNR) and therefore can support higher rates. The MCW design approach with SIC achieves capacity without error propagation. The drawbacks of this design result from the load of "managing" the rate of each spatial layer- (a) increased CQI feedback (one CQI per layer); (b) Increased ACK/NACK messaging (one per layer); (c) Complexity in Hybrid ARQ (HARQ) because each layer may stop at a different transmission; (d) Performance sensitivity of SIC to channel estimation errors with increased Doppler and/or low SNR; and (e) increased decoding latency requirements because a subsequent layer cannot be decoded before a previous layer is decoded.

[0007] In conventional SCW mode design, the transmitter encodes data transmitted at "the same data rate" on each spatial layer. The receiver may use a low complexity linear receiver such as a minimum mean square solution (MMSE) or Zero Frequency (ZF) receiver, or a non-linear receiver such as a QRM for each tone.

[0008] The SCW design overcomes the implementation problems of the MCW design mentioned above. The disadvantage is that the SCW mode cannot support MCW rates in spatially correlated channels or line of sight (LOS) channels with high K-factors. Both of these scenarios result in a loss of channel rank or an increase in the number of channel states and increased inter-layer interference. This greatly reduces the effective SNR for each spatial layer. Thus, the data rate supported by each layer is reduced, which reduces the overall data rate.

[0009] The K factor is the ratio of LOS channel power to non-LOS channel power. Rank is the number of eigenmodes in a channel with non-zero energy. The number of states is the ratio of the largest eigenvalue to the smallest eigenvalue of the MIMO channel.

[0010] Accordingly, there is a need in the art for techniques for allocating data streams to be dynamically transmitted via multiple channels, such as multiple-input multiple-output (MIMO), orthogonal Frequency Division Multiplexing (OFDM) communication systems.

Disclosure of Invention

[0011] In one aspect, a method of rank prediction (rank prediction) includes: calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission; calculating a signal-to-noise ratio (SNR) for each tone from the MIMO channel matrix; mapping the SNR for each tone to yield an effective SNR for each layer transmission; additive White Gaussian Noise (AWGN) capacities corresponding to these effective SNRs were calculated and represented as Cap1, cap2, cap3, cap4; selecting the highest Cap from the highest Cap; the rank is selected according to the selected absolute highest Cap.

[0012] In one aspect, a wireless communication device comprises: means for calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission; means for calculating a signal-to-noise ratio (SNR) for each tone from the MIMO channel matrices; means for mapping the SNR of each tone to produce an effective SNR for each layer transmission; means for calculating and representing Additive White Gaussian Noise (AWGN) capacities corresponding to the effective SNRs as Cap1, cap2, cap3, cap4; means for selecting an absolute highest Cap from the highest Caps; means for selecting a rank according to the selected absolute highest Cap.

[0013] In one aspect, a processor is programmed to perform a method of rank prediction, the method comprising: calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission; computing a signal-to-noise ratio (SNR) for each tone according to the MIMO channel matrix; mapping the SNR for each tone to produce an effective SNR for each layer transmission; additive White Gaussian Noise (AWGN) capacities corresponding to these effective SNRs were calculated and represented as Cap1, cap2, cap3, cap4; selecting the Cap with the highest absolute value from the caps with the highest absolute value; the rank is selected according to the selected absolute highest Cap.

[0014] In one aspect, a computer-readable medium embodies a method of rank prediction, the method comprising: calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission; calculating a signal-to-noise ratio (SNR) for each tone according to the MIMO channel matrix; mapping the SNR for each tone to produce an effective SNR for each layer transmission; additive White Gaussian Noise (AWGN) capacities corresponding to these effective SNRs were calculated and represented as Cap1, cap2, cap3, cap4; selecting the highest Cap from the highest Cap; the rank is selected according to the selected absolute highest Cap.

[0015] Various aspects and embodiments of the disclosure are described in further detail below.

Drawings

[0016] The features and nature of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

[0017] figure 1 shows a conventional SCW transmitter;

[0018] fig. 2 shows an SCW transmitter with rank prediction in accordance with an embodiment;

[0019]FIG. 3 shows an embodiment M _T Cyclic multiplexing technique of =4,m =2,b = 1;

[0020]FIG. 4 shows an embodiment M _T A block cyclic multiplexing technique of =4,m =2,b = 4; and

[0021] fig. 5 shows a block diagram for capacity-based rank prediction according to an embodiment.

Detailed Description

[0022] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

[0023] The performance-based rank prediction techniques described herein may be used for various communication systems such as Code Division Multiple Access (CDMA) systems, wideband CDMA (WCDMA) systems, direct sequence CDMA (DS-CDMA) systems, time Division Multiple Access (TDMA) systems, frequency Division Multiple Access (FDMA) systems, high Speed Downlink Packet Access (HSDPA) systems, orthogonal Frequency Division Multiplexing (OFDM) based systems, orthogonal Frequency Division Multiple Access (OFDMA) systems, single-input single-output (SISO) systems, multiple-input multiple-output (MIMO) systems, and so forth.

[0024] OFDM is a multi-carrier modulation technique that effectively partitions the overall system bandwidth into multiple (NF) orthogonal subbands. These subbands are also referred to as tones, subcarriers, bins, and frequency channels. With OFDM, each subband is associated with a respective subcarrier that is modulated with data. Up to NF modulation symbols are transmitted on the NF subbands during each OFDM symbol period. These modulation symbols are converted to the time domain using an NF-point Inverse Fast Fourier Transform (IFFT) prior to transmission to obtain a "converted" symbol comprising NF chips.

[0025] The SCW design overcomes the disadvantages of the MCW design. However, the SCW mode cannot support MCW rates in spatially correlated channels or line of sight (LOS) channels with high K factors. Both of these scenarios result in a loss of channel rank or an increase in the number of channel states and increased inter-layer interference. This greatly reduces the effective SNR for each spatial layer. Thus, the supported data rate per layer is reduced, which reduces the overall data rate. The "effective SNR" (approximately) is proportional to the geometric mean of the SNR averaged over all tones.

[0026] One way to reduce inter-layer interference is to reduce the number of spatial layers transmitted within the low rank channel and trade off inter-layer interference against MIMO gain. For example, reducing the number of layers transmitted from four to 3 (i.e., reducing the rank from 4 to 3) may greatly increase the effective SNR of the three layers, thus greatly increasing the data rate supported by each layer. The net effect is that a three-layer transmission can actually have a higher spectral efficiency than a four-layer transmission.

[0027] In one embodiment, the SCW design effectively trades off inter-layer interference and MIMO gain to maximize overall spectral efficiency. This may be achieved via rank prediction, where in addition to carrier quality versus interference (CQI), the receiver feeds back the best number of transmission layers to match the channel rank.

Conventional SCW transmitter

[0028]Fig. 1 shows a conventional SCW transmitter 100. Depending on the Packet Format (PF) 108, 110 specified by the rate prediction algorithm 112, the bits 102 are turbo encoded by 104 and QAM mapped by 106. The encoding process is the same as for Single Input Single Output (SISO) designs. These encoded symbols are then decomposed 114 into M _T On layer 116, and then spatially mapped 118 to M _T An OFDM modulator 120 and M _T An antenna 122. The OFDM processing by each transmit antenna then proceeds in the same manner as SISO, after which the signal is transmitted into a MIMO wireless channel. The rate prediction algorithm uses 4-bit CQI feedback 124 from the receiver 126 every 5 msec. The CQI is a metric of the effective SNR/spatial layer and is measured at the receiver. The spatial mapping is done in a manner that ensures that the SNR of each layer is similar. As explained above, this embodimentPerformance in low rank channelsThe middle is worsened.

SCW transmitter with rank prediction function

[0029] According to one embodiment, a Single Codeword (SCW) design with rank prediction functionality is described below. The algorithm for strong rank prediction will be given below. The performance of the SCW design with low complexity MMSE receiver & rank prediction function is similar to the multi-codeword (MCW) design with Successive Interference Cancellation (SIC) function for SNR < 15dB (90% users). Without HARQ, SCW is better than MCW, since MCQ is more sensitive to channel estimation errors. These factors make SCW more attractive for MIMO due to lower implementation complexity and overhead compared to MCW.

[0030] For SNR between 15 and 20dB (10% of users), the performance gap between SCW and MCW is less than 1.0dB for the low K channels and 2-5dB for the high K channels. Performance degradation at high SNR is reduced to 1-2dB for high K channels by using dual polarized antennas. In fact, even at high SNR, the SCW design is within two dB of the MCW design. Without HARQ, the performance of MCW is worse than SCW at SNR < 15dB due to the increased sensitivity of SIC to channel estimation errors.

[0031] Fig. 2 shows an SCW transmitter with rank prediction function according to an embodiment. Depending on the Packet Format (PF) 208, 210 specified by the rate prediction algorithm 212, the bits 202 are turbo encoded by 204 and mapped by 206 QAM.

[0032]In one embodiment, the encoded symbols are then decomposed by 214 into M streams 216 or layers (1 ≦ M _T ) Above, where M228 is the 2-bit integer 1 ≦ M specified by the feedback of the receiver 226 per 5msec, in addition to the 5-bit CQI224 _T . M streams 216 are then spatially mapped 218 to M _T An OFDM modulator 220 and M _T An antenna 222.

Spatial mapping

[0033]Spatial mapper (precoder) 218Is a M _T A xm matrix P (k) that maps M symbols to M for each OFDM tone k _T An antenna. For the precoderSeveral options are possible. Consider an M _R ×M _T MIMO channel H (K). These precoder matrices may be selected such that the frequency selectivity of the equivalent channel matrix H (k) P (k) is improved over H (k). The decoder may use the increased frequency selectivity to obtain frequency diversity gain.

[0034] In one embodiment, the precoder matrix is a permutation matrix of:

wherein II (0), II (1), II (M) _T -1) is from the identity matrix I _MT×MT M obtained from the M column of _T The xm sub-permutation matrix, and B is a parameter controlling the frequency selectivity of the equivalent channel.

[0035]According to one embodiment, if M _T =4, m =2, then:

[0036]for B =1, this results in a strategy of cyclic multiplexing in two layers, as shown in fig. 3, where the vertically lined boxes 302 correspond to symbols from layer 1 and the horizontally lined boxes 304 correspond to symbols from layer 2. FIG. 3 shows M _T Cyclic multiplexing of =4, M =2, b = 1. The vertical axis 306 represents the antenna. The horizontal axis 308 represents tones.

[0037]For B =4, this results in a strategy for block round-robin multiplexing in two layers, as shown in fig. 4, where the vertical line-filled boxes 402 correspond to symbols from layer 1 and the horizontal line-filled boxes 404 correspond to symbols from layer 2. FIG. 4 shows M _T Block cyclic multiplexing of =4,m =2, B = 4. The vertical axis 406 represents an antenna. Horizontal axis 408 represents pitch.

[0038] An increase in B results in a decrease in the frequency selectivity of the equivalent channel, which is desirable when weak codes are used. Furthermore, the parameter B is very sensitive to channel interleaver selection, and therefore can be optimized later.

[0039] The cyclic multiplexing improves frequency diversity regardless of the channel delay spread. In the presence of a strong turbo code, the performance of CM (M = 1) approaches Space Time Transmit Diversity (STTD). However, STTD may be significantly better than CM for very high PFs or for control channels using weak convolutional codes.

[0040] In one embodiment, the precoder matrix is a generic delay diversity matrix of:

[0041]wherein Θ is _MT×M Is from M _T ×M _T M obtained by M columns of DFT matrix _T xM sub-DFT matrix, and Δ _MT×MT Is M _T ×M _T Is represented by the (j, j) th item

[0042] The parameter δ is a delay parameter that also controls the frequency selectivity of the channel, and N is the number of OFDM tones. We note that for M =1, the precoding matrix described above achieves "pure" delay diversity. Strictly speaking, delay diversity performs worse than cyclic multiplexing (and STTD) and has poor performance in LOS channel conditions for high PF. The only advantage of using delay diversity is that it can benefit from improved SISO channel estimation gain in very low SNR (SNR < -5 dB) and for high mobility (> 120 kmph) scenarios. In these channel scenarios, cyclic multiplexing cannot benefit from SISO channel estimation gains.

[0043] Packet format

[0044] Current SISO designs use 7 PFs with spectral efficiency of [0.5,1,1.5,2.0,2.5,3.0,4.0] bps/Hz. In SCW designs using one layer transmission, granularity in Spectral Efficiency (SE) should be sufficient. However, when all four layers are used for transmission, this would translate to a spectral efficiency of [2,4,6,8, 10, 12, 16], with SE granularity on the order of 2-4 bps/Hz. The result of this coarse granularity is a data rate loss because these users are limited to transmitting at a much lower data rate than their achievable SE. It should be noted that the SIC-enabled MCW design does not have this granularity problem, since the rate of each layer can be independently adjusted, resulting in an overall finer spectral efficiency granularity.

Bao Ge Formula (II)	Modulation	In a frame The next generation Code rate	Spectral efficiency of each layer after transmission of N frames
				1	2	3	4	5	6

0	2	1/4	0.50	0.25	0.17	0.13	0.10	0.08
									1	2	3/8	0.75	0.38	0.25	0.19	0.15	0.13
2	2	1/2	1.00	0.50	0.33	0.25	0.20	0.17
									3	4	5/16	1.25	0.63	0.42	0.31	0.25	0.21
4	4	3/8	1.50	0.75	0.50	0.38	0.30	0.25
									5	4	7/16	1.75	0.88	0.58	0.44	0.35	0.29
6	4	1/2	2.00	1.00	0.67	0.50	0.40	0.33
									7	4	9/16	2.25	1.13	0.75	0.56	0.45	0.38
8	6	5/12	2.50	1.25	0.83	0.63	0.50	0.42
									9	6	11/24	2.75	1.38	0.92	0.69	0.55	0.46
10	6	1/2	3.00	1.50	1.00	0.75	0.60	0.50
									11	6	13/24	3.25	1.63	1.08	0.81	0.65	0.54
12	6	7/12	3.50	1.75	1.17	0.88	0.70	0.58
									13	6	5/8	3.75	1.88	1.25	0.94	0.75	0.63
14	6	2/3	4.00	2.00	1.33	1.00	0.80	0.67
									15	6	17/24	4.25	2.13	1.42	1.06	0.85	0.71

Table 1: package format for SCW design with rank prediction functionality

[0045] Table 1 shows a packet format for an SCW design with rank prediction functionality according to one embodiment. Table 1 shows PFs with SEs targeting the first through sixth transmissions. Targeting the first transmission, 16 PFs per layer with SE-ranging from 0.5 bps/Hz/layer to 4.25 bps/Hz/layer in 0.25 bps/Hz/layer increments are provided. When the third transmission is targeted, the maximum achievable SE-per layer is 1.42 bps/Hz/layer. SE between 1.42 bps/Hz/layer and 2.13 bps/Hz/layer can be achieved by targeting the second transmission, while SE greater than 2.13 bps/Hz/layer can be achieved by targeting the first transmission with reduced HARQ benefits.

[0046] In another embodiment, more PS # with SE/layer > 4.25bps/Hz may be added, so that higher SE can be obtained by targeting the third transmission and benefit from HARQ gain. In this case, a CQI of 6 bits may be needed to ensure that PF granularity is captured.

Capacity-based rank prediction algorithm

[0047]Fig. 5 shows a block diagram of a capacity-based rank prediction according to an embodiment. For the k-th tone, H (k) P ₄ (k) 502 to H (k) P ₁ (k) 508 are input to MMSE512 to MMSE518, respectively. MMSE512 to MMSE518 Generation of SNR separately ₄ (k) 522 to SNR ₁ (k) 528. SNR is measured ₄ (k) 522 to SNR ₁ (k) 528 are input to Cap mappers 532 through 538, respectively. Cap mapper 532 to Cap mapper 538 to generate EffSNR, respectively ₄ 542 to EffSNR ₁ 548 and separately generating Cap ₄ 552 to Cap ₁ 558. Mixing Cap ₄ 552 to Cap ₁ 558 is input to a decision unit 570. Decision unit 570 produces a rank 572.

[0048]Will EffSNR ₁ 542 to EffSNR ₄ 548 and the rank 572 are input to a select&A quantization unit 574. The selection being made&The quantization unit 574 generates a 5-bit CQI576.

[0049] According to one embodiment, the capacity-based rank prediction algorithm works in the following way:

[0050]1. on each tone, 4 × 4, 4 × 3,4 × 2, and 4 × 1 MIMO channel matrices (H (k) P) are computed corresponding to the {1,2,3,4} layer transmission ₁ (k)、H(k)P ₂ (K)、H(k)P ₃ (k) And H (k) P ₄ (k) In that respect Post-processing SNR (SNR) for {1,2,3,4} layer transmission for each tone assuming an MMSE receiver ₁ (k)、SNR ₂ (k)、SNR ₃ (k)、SNR ₄ (k) Calculated as:

if we assume other receivers, such as QRM-MLD or IDD, these post-processing SNRs are computed in different ways.

[0051]2. The capacity-unlimited mapping is then used to produce an effective SNR averaged over all tones for the {1,2,3,4} layer transmission. We denote them as EffSNR ₁ 、EffSNR ₂ 、 EffSNR ₃ 、EffSNR ₄ . The Additive White Gaussian Noise (AWGN) capacities corresponding to these effective SNRs are denoted as Cap ₁ 、Cap ₂ 、Cap ₃ 、Cap ₄ 。

[0052]3, select the best rank/layer to maximize the overall spectral efficiency, i.e.

And then feeds back a CQI of 5 bits, wherein,

[0053] it will be appreciated by those of ordinary skill in the art that known techniques for calculating Additive White Gaussian Noise (AWGN) capacity may be used.

[0054] The techniques described herein may be used for various OFDM-based systems as well as other systems. The rank prediction techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing unit for performing interference control may be implemented as: one or more Application Specific Integrated Circuits (ASICs), digital Signal Processors (DSPs), digital Signal Processing Devices (DSPDs), programmable Logic Devices (PLDs), field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

[0055] For a software implementation, the interference control techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes are stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

[0056] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (20)

1. A method of rank prediction, comprising:

calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission;

calculating a signal-to-noise ratio (SNR) for each tone based on the MIMO channel matrix;

mapping the SNR of each tone to produce an effective SNR for each layer transmission;

an Additive White Gaussian Noise (AWGN) capacity corresponding to the effective SNR is calculated and represented as Cap ₁ 、Cap ₂ 、Cap ₃ 、Cap ₄ ；

Selecting an absolute highest Cap from the highest Caps; and

the rank is selected according to the absolute highest Cap selected.

2. The method of claim 1, further comprising:

the quality indicator is transmitted according to the selected rank.

3. The method of claim 2, wherein the quality indicator is a carrier quality to interference (CQI) ratio.

4. The method of claim 1, wherein the number of layer transmissions is four.

5. The method of claim 1, wherein the SNR is calculated as:

where k is the kth tone, H (k) P ₁ (k)、H(k)P ₂ (k)、H(k)P ₃ (k) And H (k) P ₄ (k) Corresponding to 1,2,3,4) layer transport.

6. The method of claim 1, wherein the mapping is not limited in capacity.

7. The method of claim 1, wherein the selected rank is selectedThe calculation is as follows:

8. the method of claim 7, wherein the quality indicator CQI is calculated as:

where effSNR is the effective SNR for the selected rank.

9. A wireless communication device, comprising:

means for calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission;

means for calculating a signal-to-noise ratio (SNR) for each tone from the MIMO channel matrix;

means for mapping the SNR for each tone to produce an effective SNR for each layer transmission;

for calculating and representing an Additive White Gaussian Noise (AWGN) capacity corresponding to the effective SNR as Cap ₁ 、Cap ₂ 、Cap ₃ 、Cap ₄ The module of (1);

means for selecting an absolute highest Cap from the highest Cap; and

means for selecting a rank according to the selected absolute highest Cap.

10. The wireless communication device of claim 9, further comprising:

means for transmitting a quality indicator according to the selected rank.

11. The wireless communication device of claim 9, wherein the number of layer transmissions is at least two.

12. The wireless communication device of claim 10, wherein the quality indicator is a carrier quality to interference ratio.

13. A processor programmed to perform a method of rank prediction, the method comprising:

calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission;

calculating a signal-to-noise ratio (SNR) for each tone from the MIMO channel matrix;

mapping the SNR of each tone to produce an effective SNR for each layer transmission;

computing and representing an Additive White Gaussian Noise (AWGN) capacity corresponding to the effective SNR as Cap ₁ 、Cap ₂ 、Cap ₃ 、Cap ₄ ；

Selecting an absolute highest Cap from the highest Cap; and

the rank is selected according to the absolute highest Cap selected.

14. The processor of claim 13, wherein the method further comprises:

the quality indicator is transmitted according to the selected rank.

15. The processor of claim 13, wherein the number of layer transmissions is at least two.

16. The processor of claim 14, wherein the quality indicator is a carrier quality to interference ratio.

17. A computer-readable medium embodying a method of rank prediction, the method comprising:

calculating a MIMO channel matrix for each tone corresponding to the multi-layer transmission;

calculating a signal-to-noise ratio (SNR) for each tone from the MIMO channel matrix;

mapping the SNR of each tone to produce an effective SNR for each layer transmission;

calculating and representing an Additive White Gaussian Noise (AWGN) capacity corresponding to the effective SNR as Cap ₁ 、Cap ₂ 、Cap ₃ 、Cap ₄ ；

Selecting an absolute highest Cap from the highest Caps; and

the rank is selected according to the absolute highest Cap selected.

18. The computer readable medium of claim 17, wherein the method further comprises:

the quality indicator is transmitted according to the selected rank.

19. The computer readable medium of claim 17, wherein the number of layer transmissions is at least two.

20. The computer readable medium of claim 18, where the quality indicator is a carrier quality to interference ratio.