GB2467916A - Vector perturbation multi-antennae multi-user communication using a power scaling matrix - Google Patents

Abstract

The invention concerns power allocation method in a multiple input multiple output (MIMO) system employing precoding. Information for transmission is represented by a data vector, d, comprising corresponding data for each of the multi-antennae. A perturbation vector, 1, is applied to the data vector in order to generate a perturbed data vector, s, (see e.g. equation 22). A power scaling matrix (e.g. GN, equation 16) is used in the computation of the perturbation vector (see e.g. equation 20). The power scaling matrix is preferably a diagonal matrix representing at least the noise power of each receiver. In one embodiment, the invention enables a check to be made, prior to transmission, to determine whether a scheduled multiantenna transmission can be provided with a level of transmit power which is sufficient and also lies below the maximal level of the system.

Description

WIRELESS COMMUNICATIONS METHODS AND APPARATUS

Field of the Invention

The present invention is in the field of wireless communication and particularly, though not exclusively, the field of multiple input multiple output (MIMO) communications.

Background of the Invention

In multiple input multiple output (MIMO) systems employing precoding, channel knowledge is used at the transmitter in order to enhance link quality.

Power control in the downlink of cellular wireless networks is an important optimization task of a base station (BS) controller. Since unnecessary high transmit power from a BS may cause significant interferences to other users in other cells; the capacity of the whole network may be reduced remarkably. Therefore, minimizing transmit power is a mandatory task of BS.

In practice, transmit power of a base station in cellular networks is often fixed to a certain maximum value; so that the amounts of interference to other cells can be estimated by other base stations. If the actual transmit power is smaller than that maximal value, the users of the neighbouring cells will potentially have higher signal to interference plus noise ratio and thus the cellular network could have higher capacity.

Vector perturbation (VP) precoding is a power-efficient multiuser (MU) precoding technique for multiple-input multiple-output (MIMO) downlink, compared to other precoding techniques such as zero-forcing (ZF) and Tomlinson-Harashima (TH) precoding. One such technique is described in a paper by B. M. Hochwald, C. B. Peel, and A. L. Swindlehurst, "A vector-perturbation technique for near-capacity multiantenna multiuser communication -Part II: Perturbation," IEEE Trans. Comm., vol. 53, pp. 537- 544, March 2005. The whole contents of this paper is incorporated herein by way of reference, which paper will hereinafter be referred to as Hochwald et al. However, power allocation has not been solved in Hochwald et al. in which it is remarks that power allocation is an important subject for further studies. More particularly, Hochwald et al. does not discuss how to handle users with differing average received signal power, for example for use in systems where there are many users, and some are much nearer to the access point than others.

We will now analyse below the problems associated with power allocation for multiuser VP precoding, by first reviewing the VP technique and ana'ysing the major difficulties.

The analysis will focus on the zero-forcing version of VP techniques.

LetM be the number transmit antennas at the BS. We shall assume, without loss of generality, that the number of users is equal to the number of transmit antennas at the BS. Furthermore, we will assume that each user has a single receive antenna.

The mathematical system model of MU-MIMO transmissions using non-linear VP precoding can be described by =FfP(d+ri)+n (1) where d, I v and n are the transmit, perturbation, receive, and noise vectors, respectively; H and P are the combined channel matrix of all users and precoding matrix. The combined channel matrix of all users is hereafter also referred to as channel matrix. The channel matrix is obtained by stacking users' channel vectors h ( = 1...,M), where h1 = [h,1 h2... hIM], h is the channel coefficients between k-th transmit antenna (k = L... .. M) to -th user (i = ... .. M).

The ZF precoder uses a precoding matrix P = ft1.Since the precoding matrix P is generally non-unitary, the transmit power, even though minimized by the perturbation vector, may increase significantly. Therefore, the transmit vector P(d + TI) is normalized by its norm such that the actual transmit signal is d � rl x= (2) Where = tIP(d � ri) 112. (3) Thus, the complete transmit-receive signal relation reads = JfP(d + ri) � ii (4) where p is the transmit power.

The VP precoder minimizes the normalisation factor by perturbing the data vector with a complex integer vector 1 such that I. = arg rninP(d +i1') 112 (5) where r is a constant to guarantee that a simple modulo operation can uniquely recover the perturbation signal at the receivers. A full description ofT is decribed in Hochwald et al. In order to recover the transmitted data, at the receivers, the value of y should be known, either by explicit signalling, side information or any other means. However, since the value of y is dependent on each user data vector, it is not possible to send the value of y for every data vector. Hochwald et al. suggests that the expected value of y, denoted by E.,, could be used at the receiver instead of the instantaneous value of y Now we discuss our problems of interest: 1. Can a BS support a set of users in MU-MIMO transmission if the transmit power of base stations has a fixed limit? 2. How to allocate transmit power to users' signals to meet certain individual BER requirements? 3. How to select suitable adaptive modulation and coding (AMC) schemes for users sharing the same resource block? We also have to take into consideration practical issues: users' receivers have different noise (i.e. thermal noise plus interference) powers and their channels have different statistics, for example due to different velocity, direction of movement, and so on.

In a conventional single-user transmission, the power is allocated to a user's signal by a power scaling factor A. Experienced system designers may extend this approach for multi-user transmission using zero-forcing VP since users have no inter-user interference. Let A be a power allocation factor of i-th user to adjust its transmit power.

Thus the transmit signal for a user i is A1(d1 + tic).

Let A = diag(Aj,A A). The transmit-receive signals in (5) becomes = =HPft(d 4-rl)+ (6) \ y where I is still calculated by (4). With power scaling factors, the transmit power normalization factory is computed as y lPA(d + ri) 9. (7) To safely meet the SNR requirements of all users, experienced system designers may select a maximum transmit power so that that all users may receive strong enough signals in a best-effort manner.

We summarize the power allocation approach presented above in the Table 1 below.

This method will be referred to hereinafter as the conventional power allocation technique.

Table 1: Algorithm I -Conventional power allocation technique Step 1: Calculate precoding matrix P = H_t.

Step 2: Calculate perturbation vector I 1. = ar.g mnllDP(d +irl') W, (8) Step 3: Calculate the normalized power allocation factors X, according to *SPJR1 (9) where is the average requested SNR of user. Let = nn (10 (11 A dag(A12., , A). (12 Step 4: Formulate transmit vectors (13) s = :x PA(d + r1) i.y where y 11PA(d + r1) O. To detect the transmitted signal, receivers must know their own power scaling factors.

The power scaling factor could be sent to user's receiver by pilot signals for example.

The instantaneous received SNR of user 1 is = tx SNR1 (14) If the average of the instantaneous SNR SNRLt,,,r is smaller than the requested value then QoS of user i cannot be satisfied. Unfortunately, the conventional power allocation provides no means to predict whether SNRIrJ is larger than NR or not. That is the first drawback of the conventional approach. Second, simulation results show that the power efficiency of the conventional method is very poor. For example, as shown in Figure 1 the average uncoded BER of conventional method is illustrated for two multi-user communication scenarios, where all the users have the same unit channel powers, but have different noise powers. By comparing the slopes of the BER curves of the two tested cases and that of the standard setting, where all users have the same noise powers, we conclude that the conventional power allocation method does not achieve full spatial transmit diversity. Thus, even when the transmit power is set at maximal value, the average received SNR of all users could be smaller than the required values due to the power inefficiency of the conventional technique.

Summary of the Invention

The invention strives to overcome the disadvantages referred to above.

According to a first aspect of the invention there is provided a method of processing information prior to emission thereof on a multi-antenna emission, said information being a data vector comprising corresponding data from multiple users for each antenna of said multi-antenna emission, the method comprising applying a perturbation to said data vector in order to generate a perturbed data vector, said perturbation being expressible as a perturbation vector, wherein a power scaling matrix is included in the computation of the perturbation vector.

In one embodiment a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multi-user transmissions. If the power required for multi-user transmission is less than the maximal power of the system, the transmission will take place. Otherwise, a new set of users is selected and the check for sufficient power is repeated for the new set of users. Sufficient transmit power is achieved if: Pa + �= P where p, is a function of SNR p, is a power offset is a maximum transmit power and the transmit power offset p is calculated from the equation: = 10 io.g1 iOIogj (dB) where G is a channel power matrix specified in the equation Cc = d.ag(a1,o..., c) GN a power scaling matrix a2 is the noise power at i-th receiver.

cr2 is the channel power of i-th receiver M is the number of transmit antennae p is conveniently determined from a look-up table.

In one embodiment the perturbation vector is calculated from the equation: I.arg rr4nPG(d + ri!) 2 where 1 is the perturbation vector P is the precoding matrix the power scaling matrix d is the transmit vector r is a constant.

In one embodiment the precoding matrix P = H1 where H is the channel matrix.

The method may include the step of calculating an instantaneous transmit power normalization y derived from the equation: = OllPG(d + TI) ll and calculation wherein a transmit vector s is generated in accordance with the equation: = The power scaling matrix GN: may be expressed as: th ag (u,1.. 2 **. a) In a further embodiment the perturbation vector is calculated from the equation:-I arg niInOPA1d + Tir) 112.

wherein 1 is the perturbation vector P is the precoding matrix A is the power scaling matrix d is the transmit vector y is a constant and the power scaling matrix: (1 pj.1 ______ Adag . wherein P1 = SNR1/p0 wherein p0 = SNRN).

As in the embodiment described earlier sufficient transmit power is achieved if: P0 + �= Prrx where p. is a power offset is a maximum transmit power.

However, the transmit power offset p is calculated differently this time from the equation: PLn.

= taceUt) 2 According to a second aspect of the invention there is provided a signal processing apparatus for processing information for multi-antenna communication apparatus, said information being a data vector comprising data for each antenna of said multi-antenna emission, the signal processing apparatus comprising a precoder for precoding said data vector, the precoder comprising perturbation means for applying a perturbation to said data vector in order to generate a perturbed data vector, said perturbation being expressible as a perturbation vector, wherein a power scaling matrix is included in the computation of the perturbation vector.

The signal processor may include embodiments incorporating features defined by the accompanying claims to the signal processing apparatus.

According to a further aspect of the invention there is provided a storage medium storing executable instructions which, when executed on general purpose controlled communications apparatus, causes the apparatus to become configured to perform the method of processing information defined by the accompanying method.

Brief description of the drawings

Further preferred features of these aspects of the invention will now be set forth by way of the following description of specific embodiments of the invention, provided by way of example only, with reference to the accompanying drawings in which: Figure 1 is a graph depicting the performance of Bit Error Rate (BER) against SNR for different diagonal noise power matrices G employing a conventional power allocation technique using Algorithm I and Figure 2 is a graph similar to Figure 1 comparing power efficiencies for Algortihm I against Algorithm II, Algorithm II being in accordance with an embodiment of the present invention.

Figure 3 illustrates an exemplary wireless communications device incorporating a specific embodiment of the invention; and Figure 4 illustrates a precoding method in accordance with a specific embodiment of the invention.

Specific embodiments of the present invention will be described in further detail on the basis of the attached diagrams. It will be appreciated that this is by way of example only, and should not be viewed as presenting any limitation on the scope of protection sought.

Firstly the theory behind the solution to the problem of power allocation in multi-user vector perturbation precoding will be described.

Let h, be the channel coefficients between k-th transmit antenna (k = 1 M) to i-th user ( L...M). Also, let be the variance of noise power at each receiver. In general, the noise and channel variance of users are different, depending on the users' locations and noise power (it means thermal noise plus interference) levels.

It is reasonable to assume that the channels between any transmit antennas to a specific user have the same power, i.e. h (k M) have the same variance For the purpose of illustration and without loss of generality, we shall assume that all users request the same data rate and the same BER, (or the same SINR). Other transmission scenarios can be developed from the subject invention. For example, if some users request a higher bit rate than others, these users also need another SINR to achieve the same BER.

Our aim is to design a power allocation method, which is more power efficient than the conventional technique, while the average received SNR of all users can be predicted.

In this way, once the multi-user transmission is in progress, the BS can confidently provide users with requested QoS. Let

zri)' (15) = (16) Then the channel matrix H can be written as H GCfI, where all the elements of ii have the same unit average power.

In one embodiment the transmit power is allocated according to the noise power only.

In particular, the user's signals are scaled by the square root of its noise power. Let = Th' and P = H. Consequently, the transmit-receive vectors are related as =4Gt(HPGN(d+t1) +n1. (17) The perturbation vector is calculated by I arg n1InIIPGN(d 4-ri') III. (18) Different from the conventional method, the power scaling matrix is included in the computation of perturbation vector. The reason is that at the transmitter, the transmitted vector experiences a precoding matrix PGN, but not P only. (See, for example, the applicant's co-pending application GB 0901089.3, the whole contents of which are incorporated herein by way of reference.) Simulation results will be presented below showing that the method, in accordance with the embodiment of the invention, to calculate the perturbation vector actually achieves full spatial transmit diversity; and thus the method has much better performance than the conventional method.

Now we discuss how to predict average received SNR of users when they have different channel and noise powers. For given values of noise and channel powers of users, we first calculate the upper bound on the power offset with respect to the standard case, where all the channel and noise powers are 1. The upper bound to the power offset is given as = lO!og (rrace(Gc24)) iOtog0 (dB). (19) Then the total transmit power can be found by adding the power offset and Pc (function of SNR) the transmit power of the standard case. The value of p0 should be known a priori, either by field measurements or simulations, and stored in the look-up

table.

The description of one embodiment of the power allocation method according the invention is summarized in Table 2.

Table 2: Algorithm II -Proposed power allocation method Step 1: From required BER, calculate transmit power offset pj, by equation (20) and p0 from a look-up table.

Step 2: Check whether a BS has sufficient transmit power to support multi-user transmission: if P0 + P �= multi-user transmission will be taken place. Otherwise, select another set of users and go back to Step 1.

Step 3: Set transmit power P is either p0 + p, or depending on the system design.

Step 4: Calculate precoding matrix P Step 5: Calculate optimal perturbation vector I g flI4flIIIPGAV(d � TIF) OF2 (20) Step 6: Calculate instantaneous transmit power normalization OIPGN(d + ri) Q (21) Step 7: Generate transmit vector s.(PGN(d+TI) (22) Step 8: Request SINR feedback from users after a certain period and adjust transmit power if necessary.

The most important Steps of Algorithm fl are in Steps 1, 2 and 5. The long-term transmit power in Step 7 is pre-calculated in Step 1, based on a prediction in equation (20). Because the transmit power may be higher than actually requested, it can be adjusted to the right value by SINR feedback from users in Step 8.

Note that the expected value E7 of y, can be used in Algorithm Il. In this case, BS can calculate the value E. for a certain period, until a reliable estimate of E is obtained.

In Algorithm II, we have given a specific example, in which all users require the same SNR. In the systems, different users may request different SNR values for different type of services such as voice or video communications. In this case, the system scheduler may assign users using the same service into the same resource block.

Nevertheless, Algorithm II can be generalized for more general setting, when users require a different BER.

Table 3: Algorithm Ill -Proposed power allocation method -Generalization Step 1: From users' requested BER, find corresponding SNR SNR ( 1, ,M) from the look-up table of the standard case (all users have the same unit noise and channel powers). Calculate: transmit power offset p by equation (20).

= niln(SNRt, ".. SNR), (23 = SiVR1Jp0, (24 (25 (11 _____ A = dug j 7]J (26 .2 = tace(A) = (27 Step 2: Check whether a BS has sufficient transmit power to support multi-user transmission: if p + P, �= (in dB), multi-user transmission will be taken place. Otherwise, select another set of users and go back to Step 1.

Step 3: Set transmit power P (in dB) is either P0 + p-or depending on the system design.

Step 4: Calculate precoding matrix P H_t Step 5: Calculate optimal perturbation vector I = arg n nOIIPA(d + TI') tIP. (28 Step 6: Calculate instantaneous transmit power normalization = flItPA(d + TI) IF (29 Step 7: Generate transmit vector s = PA(d + I) (30 Step 8: Request SINR feedback from users after a certain period and reduce transmit power if necessary.

Note that if all users request the same BER, then P = I in equation (25) for all users; Algorithm Ill reduces to Algorithm II.

The newly proposed power allocation method can provide a way to guarantee that a multi-user transmission is whether successful or not before the actual transmission takes place. This is opposite to the conventional technique, which is based on best-effort only and provides no guarantee for successful transmission. Secondly, the new approach is much more power efficient than the conventional method. This conclusion will be further supported in Example section.

Our new power allocation method is to compute the transmit power needed to support successful multi-user transmission. This information is very beneficial in order to reduce the interference to neighbour cells in cellular networks. In orthogonal frequency division multiplexing (OFDM) systems, by minimizing the transmit powers of subcarriers, the un-used power can be assigned to other subcarriers for other users, who need more powers. Another application of our method is to select users such that the BS can provide enough transmit power for successful transmission. Additionally, the system can select suitable modulation and coding schemes so that the transmit power is still under the maximal transmit power of the base station.

We will present the power efficiency and the prediction accuracy of our proposed technique with emphasis on Algorithm it, it means all users request the same BER. The simulated system has 4 transmit antennas at BS, 4 users. Uncoded BER will be presented. All users use the same constellation, either 4QAM or 16QAM. Channels have Rayleigh fading, with no correlation at transmitter.

Figure 2 compares the BER of the conventional and the proposed power allocation method, when the users have different noise powers, and have the same unit channel power. The results show the BER curves associated with our method have the same slope as that of the standard case (all users have the same unit channel and noise powers). This fact indicates that our method achieves full spatial diversity of multiple transmit antennas. Therefore, the BER due to our method is much better than the conventional method. In Figure 2, the SNR improvements are about 9 and 11 dB for the two tested scenarios, at BER of iO.

Now we verify the prediction accuracy of our method, by following steps 1 and 2 in Algorithm II. We assume that the maximal transmit power of the system is 24 dB and an average uncoded BER of 1O_2 is the target BER of all users. For the conventional method, a transmission is considered successful if the required SNR is smaller than 24 dB; otherwise this transmission is failed. For our method, the required transmit power is always predicted. Thus there will be no failed transmissions. However, it is possible that the predicted transmit power is larger than 24 dB, but the actual transmit power needed is less than 24 dB. In this case, the prediction is considered inaccurate.

Simulation results are given in Table 4 for totally 24 simulations, including 12 simulations with 4QAM and the other 12 simulations for 16QAM. From the results, we find that by using conventional power allocation method and 4QAM, 6 out of 12 multi-user transmissions fail due to the average transmit SNR needed is larger than 24 dB.

With 1 6QAM, the number of failed transmissions is even higher, 8 out of 12.

Table 4: Comparison of conventional and proposed power allocation methods T.tPredicted Predicted Sim. Channel Noise power power transmit Prediction PredictionTramissi01 No. power G Algo. I Algo. offset power Error accuracy without 1dB) (dB' Algo. II Alga. Il (dB) prediction ___________ ___________ ______ ______ (dB) (dB) _______ _______ __________ ____________ ____________ 4QAM, maximal transmit power 24 dB ________ ________ ___________ 1 1 1 1 1 1 1 1 1 14.4 14.4 0.0 14.4 0.0 Accurate Successful 2 8 4 2 1 1 1 1 1 21.5 10 -3.3 11.1 1.1 Accurate Successful 3 16 1/2 8 4 1 1 1 1 26.5 9.5 -2.2 12.2 2.7 Accurate Failed 4 1 4 2 1 1 1 1 1 20.5 12.3 -1.6 12.8 0.5 Accurate Successful 1/4 2 4 Y2 1 2 1 4 32.5 17.6 5.2 19.6 2.0 Accurate Failed 6 8 4 2 1 1 2 1 4 29.5 13 1.1 15.5 2.5 Accurate Failed 7 1 1 1 1 1 2 1 4 26.9 16.7 3.0 17.4 0.7 Accurate Failed 8 2 1 4 1 1 2 1 4 29.2 14.9 2.3 16.7 1.8 Accurate Failed 9 16 2 8 4 1 8 2 1 30.1 11.9 0.6 15.0 3.1 Accurate Failed 16 8 8 4 1/4 1/2 1/8 1 17.2 1.5 -10.7 3.7 2.2 Accurate Successful 11 16 2 8 4 2 1/2 1/4 1 16.2 5.5 -7.8 6.6 1.1 Accurate Successful 12 4 2 8 16 1/4 1/2 1/8 1 16.3 2.7 -10.1 4.3 1.6 Accurate Successful ___________ ___________ 16QAM, maximal transmit power 24 dB ________ ________ __________ 13 1 1 1 1 1 1 1 1 19.1 19.1 0.0 19.1 0.0 Accurate Successful 14 8 4 2 1 1 1 1 1 25 15.1 -3.3 15.8 0.7 Accurate Failed 16 1/2 8 4 1 1 1 1 30 15.2 -2.2 16.9 1.7 Accurate Failed 16 1 1 1 1 1 2 1 4 29.5 21.6 3.0 22.1 0.5 Accurate Failed 17 2 1 4 1 1 2 1 4 29.1 20.3 2.3 21.4 1.1 Accurate Failed 18 8 4 2 1 1 2 1 4 29.4 18.5 1.1 20.2 1.7 Accurate Failed 19 1/4 2 4 1/2 1 2 1 4 36,3 22.8 5.2 24.3 1.5 Inaccurate Failed 16 2 8 4 1 8 2 1 33.6 17.6 0.6 19.7 2.1 Accurate Failed 21 8 1 16 4 1 8 2 1 37.6 20.2 3.3 22.4 2.2 Accurate Failed 22 16 2 8 4 2 1/2 1/4 1 19.8 10.5 -7.8 11.3 0.8 Accurate Successful 23 16 8 8 4 1/4 1/2 1/8 1 21.1 7 -10.7 8.4 1,4 Accurate Successful 24 4 2 8 16 1/4 1/2 1/8 1 20 8 -10.1 9.0 1.0 Accurate Successful By using our prediction method, in only 1 out of 24 tested cases, simulation number 19, the prediction is inaccurate. In simulation, the predicted transmit power is 24.3 dB, which is slightly higher than the maximal transmit power of the system, 24 dB.

Nevertheless, by comparing the required SNR to support the same BER of 1O, our method can save more than 10 dB over the conventional technique.

Therefore, we can conclude that our proposed power allocation method is much more power efficient than the convention method, while our method can predict with high accuracy rate whether a multi-user transmissions successful or not before the actual transmissions happen.

The present invention will now be described with reference to an implementation of a wireless communication device. Figure 3 illustrates such a device 100, such as found at a mobile base station.

The wireless communication device 100 illustrated in Figure 3 is generally capable of being used in a MIMO context, to establish a MIMO communications channel with one or more other devices and, in accordance with a specific embodiment of the invention, to take account of channel information so as to derive a pre-coding scheme appropriate to the quality of the channel. The reader will appreciate that the actual implementation of the wireless communication device is non-specific, in that it could be a base station or a user terminal.

Figure 3 illustrates schematically hardware operably configured (by means of software or application specific hardware components) as a wireless communication device 100.

The receiver device 100 comprises a processor 120 operable to execute machine code instructions stored in a working memory 124 and/or retrievable from a mass storage device 122. By means of a general purpose bus 130, user operable input devices 136 are capable of communication with the processor 120. The user operable input devices 136 comprise, in this example, a keyboard and a mouse though it will be appreciated that any other input devices could also or alternatively be provided, such as another type of pointing device, a writing tablet, speech recognition means, or any other means by which a user input action can be interpreted and converted into data signals.

Audio/video output hardware devices 138 are further connected to the general purpose bus 130, for the output of information to a user. Audio/video output hardware devices 138 can include a visual display unit, a speaker or any other device capable of presenting information to a user.

Communications hardware devices 132, connected to the general purpose bus 130, are connected to antennas 134. In the illustrated embodiment in Figure 3, the working memory 124 stores user applications 126 which, when executed by the processor 120, cause the establishment of a user interface to enable communication of data to and from a user. The applications in this embodiment establish general purpose or specific computer implemented utilities that might habitually be used by a user.

Communications facilities 128 in accordance with the specific embodiment are also stored in the working memory 124, for establishing a communications protocol to enable data generated in the execution of one of the applications 126 to be processed and then passed to the communications hardware devices 132 for transmission and communication with another communications device, It will be understood that the software defining the applications 126 and the communications facilities 128 may be partly stored in the working memory 124 and the mass storage device 122, for convenience, A memory manager could optionally be provided to enable this to be managed effectively, to take account of the possible different speeds of access to data stored in the working memory 124 and the mass storage device 122.

On execution by the processor 120 of processor executable instructions corresponding with the communications facilities 128, the processor 120 is operable to establish communication with another device in accordance with a recognised communications protocol.

The specific embodiment performs a method to enable more efficient power allocation.

Figure 4 illustrates the steps of precoding a data vector in accordance with a specific embodiment of the invention. In the first step (step 140) of the method, a check is made to determine whether a BS has sufficient transmit power to support multi-user transmission. If there is, one proceeds to step 142 to set the transmit power. Step 144 involves the calculation of the precoding matrix and step 146 calculating the optimal perturbation matrix. From these results the instantaneous transmit power consumption is calculated in step 148 after which the transmit vector can be calculated in step 150.

An additional step, not shown in Figure 4, is the request for SNIR feedback from users after a certain period and a reduction of transmit power is necessary.

Claims (28)

1. CLAI MS: 1. A method of processing information prior to emission thereof on a multi-antenna emission, said information being a data vector comprising corresponding data from multiple users for each antenna of said multi-antenna emission, the method comprising applying a perturbation to said data vector in order to generate a perturbed data vector, said perturbation being expressible as a perturbation vector, wherein a power scaling matrix is included in the computation of the perturbation vector.
2. 2. A method as claimed in claim 1 wherein the perturbation vector is calculated from the equation: I = arg w nIIPGy(d + ri!) P. where I is the perturbation vector P is the precoding matrix GN the power scaling matrix d is the transmit data vector r is a constant.
3. 3. A method as claimed in claim 1 or 2 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions.
4. 4. A method as claimed in claim 3 wherein sufficient transmit power is achieved if: where p is a function of SNR p is a power offset Prx is a maximum transmit power.
5. 5. A method as claimed in claim 4 wherein the transmit power offset p is calculated from the equation: = 10 to,g1 (tr.c(GGJ) 10 tog0 (t:) (dB) where G is a channel power matrix is specified in equation = GN a power scaling matrix a2 ri is a variance of noise power at i-th user's receiver.-is a channel power of i-th user M is the number of transmit antennae.
6. 6. A method as claimed in claim 4 or claim 5 wherein Po is determined from a look-up table.
7. 7. A method as claimed in any one of claims 1 to 6 wherein the precoding matrix P = ft1 where H is the channel matrix.
8. 8. A method as claimed in any one of claims 1 to 7, wherein the method includes the step of calculating an instantaneous transmit power normalization y derived from the equation: = lPGy(d + ri F.
9. 9. A method as claimed in claim 8 wherein a transmit vector s is generated in accordance with the equation: s= jPGN(d+rt)
10. 10. A method as claimed in claim 2, or any one of claims 3 to 9 when dependent on claim 2 wherein the power scaling matrix GN: GM o).
11. 11. A method as claimed in claim 1 wherein the perturbation vector is calculated from the equation:-I. .arg ni4nllllPA(d + rL) F. wherein I is the perturbation vector P is the precoding matrix A is the power scaling matrix d is the transmit vector -r is a constant.
12. 12. A method as claimed in claim 11 wherein the power scaling matrix: (1 P*t4� ______ -ftj wherein SNR/p0 wherein = rr.ki(SNR. .... SNR).
13. 13. A method as claimed in claims 11 or claim 12 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions.
14. 14. A method as claimed in claim 13, when dependent on claim 12, wherein sufficient transmit power is achieved if: ft0 + �= where p is a power offset is a maximum transmit power.
15. 15. A method as claimed in claim 14 wherein the transmit power offset p is calculated from the equation: = trace(A) 16. A method as claimed in any one of claims 11 to 15 wherein the precoding matrix P = ft1 where H is the channel matrix.17. A method as claimed in any one of claims 11 to 16 wherein the method includes the step of calculating an instantaneous transmit power normalization v derived from the equation: = OOPA(d + Tfl 002 18. A method as claimed in claim 17 wherein a transmit vectors is generated in accordance with the equation: s= IPA(d+'vl) 19. A storage medium storing executable instructions which, when executed on general purpose controlled communications apparatus, causes the apparatus to become configured to perform the method claimed in any one of claims 1 to 18.20. A signal processing apparatus for processing information for a multi-antenna communication apparatus, said information being a data vector comprising data of multiple users for each antenna of said multi-antenna emission, the signal processing apparatus comprising a precoder for precoding said data vector, the precoder comprising perturbation means for applying a perturbation to said data vector in order to generate a perturbed data vector, said perturbation being expressible as a perturbation vector, wherein a power scaling matrix is included in the computation of the perturbation vector.21. A signal processing apparatus as claimed in claim 20, wherein the perturbation vector is calculated from the equation: I = arg n1liPG1(d + ri') D2 where 1. is the perturbation vector P is the precoding matrix GN is the power scaling matrix d is the transmit vector r is a constant.22. A signal processing apparatus as claimed in claim 20 or 21 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions.23. A signal processing apparatus as claimed in claim 22 wherein sufficient transmit power is achieved if: 7' -7'. -7' tLO -X where p is a function of SNR p. is a power offset is a maximum transmit power.24. A signal processing apparatus as claimed in claim 23 wherein the transmit power offset p is calculated from the equation: = 10 iog 1OIog (M=t;i) (dB) where G is a channel matrix a power scaling matrix o-, is a variance of noise power at each receiver.M is the number of transmit antennae.25. A signal processing apparatus as claimed in claim 23 or claim 24 wherein p0 is determined from a look-up table, the values of p0, having been pre-determined bycomputer simulation or field measurements.26. A signal processing apparatus as claimed in any one of claims 20 to 25 wherein the precoding matrix P = ft1 where H is the channel matrix.27. A signal processing apparatus as claimed in any one of claims 20 to 26, wherein an instantaneous transmit power normalization y is derived from the equation: = lJPG.(d + r1) . 28. A signal processing apparatus as claimed in claim 27 wherein a transmit vector s is generated in accordance with the equation: = jPGr(d + Ti) 29. A signal processing apparatus as claimed in claim 21, or any one of claims 22 to 28 when dependent on claim 21 wherein the power scaling matrix GN: dag(a1.. 2 **. o).30. A signal processing apparatus as claimed in claim 20 wherein the perturbation vector is calculated from the equation:-I arg raEnOPA(d + TIE) Z wherein 1 is the perturbation vector P is the precoding matrix A is the power scaling matrix d is the transmit vector -r is a constant.31. A signal processing apparatus as claimed in claim 30 wherein the power scaling matrix (iii ______ dagu 2 \L wherein SNRJp0 wherein p0 min(SNR. ..SNR).32. A signal processing apparatus as claimed in claims 30 or claim 31 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions.33. A signal processing apparatus as claimed in claim 32, when dependent on claim 12, wherein sufficient transmit power is achieved if: Po+Pth<_Priax where p is a power offset Pr--is a maximum transmit power.34. A signal processing apparatus as claimed in claim 33 wherein the transmit power offset p. is calculated from the equation: Pi,Lo = trace(A) 35. A signal processing apparatus as claimed in any one of claims 30 to 34 wherein the precoding matrix P I-F1 where H is the channel matrix.36. A signal processing apparatus as claimed in claim 30 wherein an instantaneous transmit power normalization y derived from the equation: y = DPA(d + r1) F. 37. A method as claimed in claim 36 wherein a transmit vector s is generated in accordance with the equation: s= (PA(d+L) ijr 38. A signal carrying computer receivable information, the information defining computer executable instructions which, when executed on a general purpose computer controlled communication apparatus, causes the apparatus to become configured to perform the method of any of claims 1 to 18.Amendments to the claims have been filed as followed CLAIMS: 1. A method of processing information prior to emission thereof on a multi-antenna emission, said information being a data vector comprising corresponding data from multiple users for each antenna of said multi-antenna emission, the method comprising applying a perturbation to said data vector in order to generate a perturbed data vector, said perturbation being expressible as a perturbation vector, wherein a transmit power is pre-computed without knowing the value of said perturbation vector, said transmit power kept constant for any channel matrices for a certain period and a power scaling matrix is included in the computation of said perturbation vector, 2. A method as claimed in claim 1 wherein the perturbation vector is calculated from the equation: where 1 is the perturbation vector p is the precoding matrix GN the power scaling matrix d is the transmit data vector is a constant. * * S ** S3. A method as claimed in claim 1 or 2 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions. S. * S* . 4. A method as claimed in claim 3 wherein sufficient transmit power is achieved if: * .S SS * S where p is a function of SNR b is a power offset is a maximum transmit power.5. A method as claimed in claim 4 wherein the transmit power offset p is calculated from the equation: iO'LJog 10 1Jog (dB) where G is a channel power matrix is specified in equation Cc. = GN a power scaling matrix a2 ri is a variance of noise power at i-th user's receiver.a2 hini is a channel power of i-th user M is the number of transmit antennae.6. A method as claimed in claim 4 or claim 5 wherein p is determined from a look-up table. S.... : 7. A method as claimed in any one of claims Ito 6 wherein the precoding matrix S... * S S...*:*:: P=H1 where H is the channel matrix. S.8. A method as claimed in any one of claims Ito 7, wherein the method includes the step of calculating an instantaneous transmit power normalization y derived from the equation: Y IGN(d --rI) . 9. A method as claimed in claim 8 wherein a transmit vector s is generated in accordance with the equation: s = PGN(d+ ) 10. A method as claimed in claim 2, or any one of claims 3 to 9 when dependent on claim 2 wherein the power scaling matrix GN: = I 11. A method as claimed in claim 1 wherein the perturbation vector is calculated from the equation:-I = argmnlPA(d + I') I12 wherein 1 is the perturbation vector p is the precoding matrix A is the power scaling matrix *S.. * * * * Sd is the transmit vector S... * .. * S S * S*t is a constant. *S * S * S..S*55S*SS12. A method as claimed in claim 11 wherein the power scaling matrix: ( p11 ______ Adiag) wherein P1 wherein p0 = rxthiSNR1, .,SNR).13. A method as claimed in claims 11 or claim 12 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions.14. A method as claimed in claim 13, when dependent on claim 12, wherein sufficient transmit power is achieved if: p+ ;1,:p where p is a power offset p,, is a maximum transmit power.15. A method as claimed in claim 14 wherein the transmit power offset p is calculated from the equation: c *..S * . * S. * S...
16. 16. A method as claimed in any one of claims 11 to 15 wherein the precoding matrix P ft1 where H is the channel matrix. * S * S..
17. 17. A method as claimed in any one of claims 11 to 16 wherein the method includes the step of calculating an instantaneous transmit power normalization y derived from the equation: V = -irI) IP.
18. 18. A method as claimed in claim 17 wherein a transmit vector s is generated in accordance with the equation: s=
19. 19. A storage medium storing executable instructions which, when executed on general purpose controlled communications apparatus, causes the apparatus to become configured to perform the method claimed in any one of claims 1 to 18.
20. 20. A signal processing apparatus for processing information for a multi-antenna communication apparatus, said information being a data vector comprising data of multiple users for each antenna of said multi-antenna emission, the signal processing apparatus comprising a precoder for precoding said data vector, the precoder comprising perturbation means for applying a perturbation to said data vector in order to generate a perturbed data vector, said perturbation being expressible as a perturbation vector, wherein the apparatus is configured to pre-compute a transmit power without knowing the value of said perturbation vector, to keep said transmit power constant for any channel matrices for a certain period and a power scaling matrix is included in the computation of said perturbation vector.
21. 21. A signal processing apparatus as claimed in claim 20, wherein the perturbation vector is calculated from the equation: * S* I = arg nlrillPC,,,r(d+ i!) I11. * *.where I is the perturbation vector P is the precoding matrix GN the power scaling matrix d is the transmit vector is a constant.
22. 22. A signal processing apparatus as claimed in claim 20 or 21 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions.
23. 23. A signal processing apparatus as claimed in claim 22 wherein sufficient transmit power is achieved if: Po+ Pub<-Pnwx where p is a function of SNR p is a power offset p is a maximum transmit power.
24. 24. A signal processing apparatus as claimed in claim 23 wherein the transmit power offset p, is calculated from the equation: gto 1Utog0;ML_i4) (dB) where G is a channel matrix GN a power scaling matrix a r is a variance of noise power at each receiver.M is the number of transmit antennae. S.. I * *Si,.. I
25. 25. A signal processing apparatus as claimed in claim 23 or claim 24 wherein p0 is S.'.., determined from a look-up table, the values of P, having been pre-determiried bycomputer simulation or field measurements.
26. 26. A signal processing apparatus as claimed in any one of claims 20 to 25 wherein the precoding matrix P = ft1 where H is the channel matrix.
27. 27. A signal processing apparatus as claimed in any one of claims 20 to 26, wherein an instantaneous transmit power normalization y is derived from the equation: y -IPG1,1(d --rI)IP.
28. 28. A signal processing apparatus as claimed in claim 27 wherein a transmit vector s is generated in accordance with the equation:S29. A signal processing apparatus as claimed in claim 21, or any one of claims 22 to 28 when dependent on claim 21 wherein the power scaling matrix GN: 30. A signal processing apparatus as claimed in claim 20 wherein the perturbation vector is calculated from the equation:-I = arg 9,nIllPA( d + r I') 1112. * . **:::* wherein 1 is the perturbation vector P is the precoding matrix A is the power scaling matrix * d is the transmit vector t is a constant.31 A signal processing apparatus as claimed in claim 30 wherein the power scaling matrix: ( Pi Pw44 2 2 wherein p = SAR/p0 wherein p rrnin(SIVR1, ,5pjJ) 32. A signal processing apparatus as claimed in claims 30 or claim 31 wherein a check is made to determine whether a multi-antenna emission has sufficient transmit power to support multiple-user transmissions.33. A signal processing apparatus as claimed in claim 32, when dependent on claim 12, wherein sufficient transmit power is achieved if: + Pt&b �= where is a power offset * S * :.: is a maximum transmit power.*:*::* 34. A signal processing apparatus as claimed in claim 33 wherein the transmit power offset p is calculated from the equation:SO5-, t ___ * *** L * a 35. A signal processing apparatus as claimed in any one of claims 30 to 34 wherein the precoding matrix P = H where H is the channel matrix.36. A signal processing apparatus as claimed in claim 30 wherein an instantaneous transmit power normalization y derived from the equation: IIIPA(d + L) fP.37. A method as claimed in claim 36 wherein a transmit vector s is generated in accordance with the equation: s PA(dfTI) 4)Y 38. A signal carrying computer receivable information, the information defining computer executable instructions which, when executed on a general purpose computer controlled communication apparatus, causes the apparatus to become configured to perform the method of any of claims 1 to 18. * * S S. * S... * S S... * S. * S * * ** S. * S * S..S I *