CN102291165B - Zero-forcing detection method for multi-input multi-output system - Google Patents

Abstract

The invention discloses a zero-forcing detection method for a multi-input multi-output system. The zero-forcing detection method comprises the following steps of: weighting a received signal and normalizing the antenna gain of each receiving antenna to obtain a weighted received signal r'; and 2, inputting the weighted received signal r' into a formula, i.e., (HHH)-1HH of the conventional zero-forcing detection method to obtain a sending signal detection value, wherein H refers to a channel matrix. According to the zero-forcing detection method, noise energies sensed during signal detection of a baseband module of a multi-receiving antenna system are equal, so that loss of the detection performance caused by unequal branch noises and gains is remedied, and the system performance is enhanced.

Description

ZF detection method in the multi-input multi-output system

Technical field

The present invention relates to a kind of wireless communication system detection technique, particularly a kind of ZF detection method in the multi-input multi-output system that can eliminate inter-antenna interference in multi-input multi-output system (Multiple-Input Multiple-Output the is called for short MIMO) system fully.

Background technology

As breakthrough theory and technology in the wireless communication field in recent years, multiple-input and multiple-output (Multiple-Input Multiple-Output, MIMO) wireless communication system disposes a plurality of antennas simultaneously in the transmitting-receiving both sides, by making full use of wireless channel multipath transmisstion characteristic, can be under the condition that does not increase spectral bandwidth and transmitted power, effectively improve capacity of communication system and communication quality, and gradually at 3GPP LTE, IEEE 802.16e, constantly show up prominently in the emerging wireless communication systems such as IEEE 802.11n, become a key technology in the next generation mobile communication system.

The prerequisite that receiver carries out input is that receiver has completely channel condition information (Channel State Information, CSI), this can realize in common mimo system.Detection method optimum in the SDM system is maximum likelihood (Maxmimum Likelihood, ML) detect, yet detecting, ML need do exhaustive search to all possible emission signal vector is arranged, the method complexity is counted exponential increase along with the data bit of number of transmit antennas and each symbol correspondence usually, and this is difficult to realize in the system of many antennas high order modulation.The detection method of two class suboptimums is linearity test methods and based on the nonlinear method of decision-feedback in the MIMO input.The linearity test method is separated the signal that different antennae sends by the one-level linear filtering, then the signal that separates is carried out independent detection, typical method has ZF (Zero-Forcing, ZF) and least mean-square error (Minimum Mean Square Error, MMSE) method etc., Paulraj, " Introduction to Space-Time Wireless Communications " book that R.Nabar and D.Gore collaborate has detailed introduction and derivation to these methods.As shown in Figure 2, traditional ZF detection method all is to suppose that the noise power of each antenna receiving branch of receiving terminal and gain equate.But in real system,, may cause noise power and gain between the receiving branch unequal owing to following reason:

1. the radio frequency link module specification difference of each reception antenna branch road makes that the thermal noise of generation of branch road is unequal

2. each receiving branch is received interference in various degree, makes that extraneous noise power is unequal

3. when each antenna branch was used independently automatic gain control, each branch road had caused branch gain difference and noise power unequal to the amplification coefficient difference of noise.

If in detection, do not consider these factors, will make the detection decreased performance.

Summary of the invention

Goal of the invention: technical problem to be solved by this invention is assumed condition implacable situation in reality in detecting at traditional ZF, and the ZF detection method in a kind of multi-input multi-output system of improved low complex degree is provided.

Technical scheme: the invention discloses the ZF detection method in a kind of multi-input multi-output system, may further comprise the steps:

Step 1 is weighted processing by r to received signal the antenna gain of each reception antenna is carried out normalization, obtains the received signal r ' after the weighting;

Step 2 is with the traditional ZF detection method formula (H of the input of the received signal r ' after the weighting ^HH) ^-1H ^HObtain to send value detection signal

Wherein H is a channel matrix.

Step 1 of the present invention may further comprise the steps:

Step 11 is considered multiaerial system, and the antenna gain difference of every reception antenna uses following formula to calculate the interference noise variance that enters each reception antenna receiving terminal:

E[(G ₁n ₁) ^*(G ₁n ₁) ^*]=(G ₁σ ₁) ², E[(G _in _i) ^*(G _in _i) ^*]=(G _iσ _i) ², G wherein ₁The antenna gain of representing the 1st antenna, G _iThe antenna gain of representing i root antenna, G ₁n ₁Expression enters the receiving terminal interference noise of the 1st antenna, G _in _iExpression enters the receiving terminal interference noise of i root antenna; (G _in _i) ^*Expression G _in _iConjugate complex number, E[(G _in _i) ^*(G _in _i) ^*] represent the receiving terminal interference noise that enters i root antenna to be asked variance, (G _iσ _i) ²Represent its interference noise variance yields.G _iValue can not estimate separately, use G herein _iConsidered the difference of every receiving antenna gain to show the method.

Step 12 is introduced weight coefficient w _i:

w _iRepresent the weight coefficient of i root antenna with respect to the 1st antenna receiving terminal interference noise;

Step 13, r=[r to received signal ₁r ₂L r _N] ^TBe weighted, obtain the received signal after the weighting:

R '=[w ₁r ₁w ₂r ₂L w _Nr _N] ^T, wherein N represents the receiving terminal antenna amount, T represents that vectorial to received signal r carries out transposition.

In the step 2 of the present invention, send value detection signal

Principle of the present invention: send out N for a M and receive system, traditional ZF detection method, received signal vector r:

r＝Hx+n，

Wherein, x is a transmitting terminal primary signal vector, is the unknown at receiving terminal; N is the channel white noise.

Received signal vector wherein:

$r=\left[\begin{array}{c}{r}_1\\ r_2\\ M\\ r_N\end{array}\right],$ N represents the receiving terminal antenna amount.

Channel matrix H is:

$H=\left[\begin{array}{cccc}{H}_{11}& H_{12}& L& H_{1M}\\ H_{21}& H_{22}& L& H_{2M}\\ M& M& O& M\\ H_{N1}& H_{N2}& L& H_{\mathrm{NM}}\end{array}\right],$ M represents the transmitting terminal antenna amount.

According to traditional ZF detection method, then can instead thus release emission signal vector

${\hat{x}}_{\mathrm{ZF}}=\left[\begin{array}{c}{x}_1\\ x_2\\ M\\ x_M\end{array}\right]={\left(H^{H}H\right)}^{-1}{H}^{H}r.$

But consider that receiving terminal has N reception antenna, each reception antenna all has different antenna gains, and the annoyance level difference that is subjected to, extraneous noise power difference, and the present invention has introduced receiving antenna gain G _i(i=1,2 ..., N).

Introduce receiving antenna gain G _iAfter, received signal r can be expressed as r=H _GX+n _G, wherein:

$H_G=\left[\begin{array}{cccc}{G}_1{H}_{11}& {G_{1}H}_{12}& L& {G_{1}H}_{1M}\\ {G_{2}H}_{21}& {G_{2}H}_{22}& L& {G_{2}H}_{2M}\\ M& M& O& M\\ G_N{H}_{N1}& {G_{N}H}_{N2}& L& {G_{N}H}_{\mathrm{NM}}\end{array}\right],$ $n_G=\left[\begin{array}{c}{G}_1{n}_1\\ G_2{n}_2\\ M\\ G_N{n}_N\end{array}\right].$

H _GAnd n _GIn G _iCan not estimate separately, only show different antenna gains channel and The noise, so when channel is estimated, H _GThere is not essential distinction with the channel matrix H in the conventional method, and n _GNo longer be a value, but one is measured together.The present invention makes the normalization of receiving terminal interference noise vector by being weighted processing to received signal at receiving terminal, makes it satisfy the service condition of traditional ZF detection method.This method provides a kind of and has introduced receiving antenna gain G _iAfter a kind of ZF detection method of modified model low complex degree.

At first calculate the interference noise variance that enters each reception antenna receiving terminal:

E[(G ₁n ₁) ^*(G ₁n ₁) ^*]＝(G ₁σ ₁) ²，E[(G _in _i) ^*(G _in _i) ^*]＝(G _iσ _i) ²。

G wherein ₁The antenna gain of representing the 1st antenna, G _iThe antenna gain of representing i root antenna, G ₁n ₁Expression enters the receiving terminal interference noise of the 1st antenna, G _in _iExpression enters the receiving terminal interference noise of i root antenna; (G _in _i) ^*Expression G _in _iConjugate complex number, E[(G _in _i) ^*(G _in _i) ^*] represent the receiving terminal interference noise that enters i root antenna to be asked variance, (G _iσ _i) ²Represent its interference noise variance yields.G _iValue can not estimate separately, use G herein _iConsidered the difference of every receiving antenna gain to show the method.Then introduce weight coefficient w _i:

$w_i=\frac{{\mathrm{<figure-callout\; id="1"\; label="G"\; filenames="HDA0000089247180000013.png"\; state="\{\{state\}\}">G</figure-callout>}}_1{\mathrm{\&sigma;}}_1}{G_i{\mathrm{\&sigma;}}_i}.$

w _iRepresent the weight coefficient of i root antenna with respect to the 1st antenna.

By the w that obtains _iR=[r to received signal ₁r ₂L r _N] ^TBe weighted, obtain the received signal r ' after the weighting:

$r^{\&prime;}=\left[\begin{array}{c}{w}_1{r}_1\\ w_2{r}_2\\ M\\ w_N{r}_N\end{array}\right].$

Finished after the weighting to received signal, just can suppose that at receiving terminal the gain of each reception antenna is identical value with receiving noise, purpose is and can detects by traditional ZF detection method, obtains sending more accurately value detection signal::

${\hat{z}}_{\mathrm{ZF}}={\left(H^{H}H\right)}^{-1}{H}^H{r}^{\&prime;}.$

Based on the ZF detection method in traditional mimo system, make full use of the difference of the interference noise that multiple receive antenna gain causes at receiving terminal, obtain the ratio of gains of the ratio of gains of different receiving terminal interference noises as reception antenna, and be weighted to received signal, thereby use traditional ZF detection method to detect to transmitting, it is characterized in that, traditional ZF ZF detection method is to be based upon on the identical basis of gain of each reception antenna of hypothesis, yet in fact, the gain of each reception antenna all is different, have small difference, and the received interference noise of each reception antenna also has nothing in common with each other, this improved ZF detection method reaches normalized purpose is carried out in the gain of each antenna exactly by receiving end signal is weighted, and makes it meet the assumed condition of traditional Z F detection method.

Beneficial effect: the present invention improves one's methods by this, can be so that receiver be weighted optimization at receiving terminal, the noise energy that makes baseband module experience when carrying out input equates, does not wait the loss of the detection performance that causes thereby remedied the branch road noise with gaining.The present invention is applicable to other communication systems multiple-input and multiple-output mimo system and that can be modeled as mimo system.

Description of drawings

Below in conjunction with the drawings and specific embodiments the present invention is done further to specify, above-mentioned and/or otherwise advantage of the present invention will become apparent.

Fig. 1 is the block diagram of the MIMO communication system implemented of embodiment.

Fig. 2 is the flow chart of traditional ZF detection method.

Fig. 3 is the flow chart of ZF detection method of the present invention.

Embodiment

Below by drawings and Examples the present invention is carried out elaboration.

Detection method of the present invention is applicable to mimo system, or can be modeled as other communication systems of mimo system.For example, the present invention can directly be used on any one subcarrier of multi-I/O OFDM (MIMO-OFDM) system, also can be used for the Multiuser Detection of code division multiple access system.

Fig. 1 is a M transmit antennas, the block diagram of the MIMO communication system that the M receipts N of N root reception antenna sends out.At transmitting terminal, input traffic becomes signal through signal encoding and modulation, through forming the baseband signal of multidiameter delay after string and the conversion,, transmit simultaneously from many antennas respectively through different modulators at last if there is space-time coding collar joint then to carry out space-time code; Through after the wireless multipath fading, received simultaneously by many antennas from after the signal of many different transmit antennas and the noise stack, through generation multidiameter delay baseband signal after the demodulation; Channel estimator can estimate channel condition information by interting pilot signal at interval etc. in the signal, thereby recovers initial data from baseband signal.The relation of the baseband signal input and output of this system can be expressed as:

r＝Hx+n。

Wherein, x=[x ₁x ₂L x _M] ^TThe expression emission signal vector, M represents the number of transmitting antenna, [] ^TThe transposition of representing matrix or vector, x _iExpression is from the signal of i root antenna emission; N=[n ₁n ₂L n _N] ^TThe expression noise vector, N represents the number of reception antenna, n _iRepresent the signal noise that i root reception antenna receives;

R=[r ₁r ₂L r _N] ^TThe expression received signal vector, r _iRepresent the signal that i root reception antenna receives; H is the channel matrix of a N * M, can be expressed as:

$H=\left[\begin{array}{cccc}{H}_{11}& H_{12}& L& H_{1M}\\ H_{21}& H_{22}& L& H_{2M}\\ M& M& O& M\\ H_{N1}& H_{N2}& L& H_{\mathrm{NM}}\end{array}\right],$

Wherein, the element h of the capable j row of i _{I, j}To the channel fading factor the i root reception antenna, the value of H can be estimated to draw by the channel estimation module recursion from the j transmit antennas in expression.The present invention relates to MIMO signal estimating part shown in Figure 1 and input part.

Fig. 2 shows the flow chart of traditional ZF detection method in the MIMO communication system, is used for the MIMO input part of Fig. 1.The prerequisite that tradition ZF detection method is suitable for is that N reception antenna of hypothesis all has identical antenna gain, identical ideal conditionss such as outside noise power, like this, by channel estimation module, can estimate channel matrix H, thereby pass through formula:

${\hat{z}}_{\mathrm{ZF}}={\left(H^{H}H\right)}^{-1}{H}^{H}r.$

Estimate the estimated value of the x that transmits Finish the MIMO input.

Yet actual conditions are that each reception antenna all is discrepant in the MIMO communication system, and different antenna gains is all arranged, can receive different outside noise power, if still use following formula to detect, can cause detection decreased performance to a certain degree, influence the operate as normal of communication system.For this reason, the present invention has introduced weighting to received signal and has adjusted the factor, and flow process as shown in Figure 3.

Because the gain difference of each reception antenna, received noise level are also just different, the white noise n among the receiving side signal journey r=Hx+n has just become vector n; The receiving gain of supposing i root antenna is G _i, then white noise n can be expressed as:

n＝[G ₁n ₁?G ₂n ₂?L?G _Nn _N] ^T。

At first, in channel estimation module shown in Figure 1, need estimate, calculate the variance of receiving terminal white noise noise signal:

E[(G ₁n ₁) ^*(G ₁n ₁) ^*]＝(G ₁σ ₁) ²，E[(G _in _i) ^*(G _in _i) ^*]＝(G _iσ _i) ²；

Then introduce weight coefficient w _i:

$w_i=\frac{{\mathrm{<figure-callout\; id="1"\; label="G"\; filenames="HDA0000089247180000013.png"\; state="\{\{state\}\}">G</figure-callout>}}_1{\mathrm{\&sigma;}}_1}{G_i{\mathrm{\&sigma;}}_i},$

Make the noise vector n of receiving terminal carry out normalization according to the 1st antenna; Order then:

r′＝[w ₁r ₁?w ₂r ₂?L?w _Nr _N] ^T，

Promptly allow the received signal r of i root antenna _iMultiply by weighted factor w _iThe value of channel matrix H is still estimated to draw by the channel estimation module recursion.Be weighted adjustment through the received signal to each antenna, become constant n again after the white noise vector n normalization of receiving terminal, satisfied the service condition of traditional ZF detection method formula, the testing result after then improving is:

${\hat{x}}_{\mathrm{ZF}}={\left(H^{H}H\right)}^{-1}{H}^H{r}^{\&prime;}.$

Embodiment

The performance comparison result of method provided by the invention and conventional method.Abscissa is represented signal to noise ratio (snr), that ordinate is represented is bit error rate (BER), the transmitting antenna of this system and reception antenna number are 4, channel is independent identically distributed MIMO flat Rayleigh fading channel, the modulation system that is adopted is QPSK, no chnnel coding, the noise power ratio after process reception antenna different gains is amplified 40: 30: 10: 1, simulation result shows that method provided by the invention compares with the conventional method performance, and performance boost is comparatively obvious.

If only the amount of calculation with a CM division is the unit of method complexity, ignore addition and subtraction, comparison, selection etc. and relatively simply handle, the complexity of a kind of follow-on ZF detection method then provided by the invention is suitable with the complexity of traditional ZF detection method.On the basis of raising system detection performance, significantly do not improve the system-computed complexity.

The invention provides the thinking and the method for the ZF detection method in a kind of multi-input multi-output system; the method and the approach of this technical scheme of specific implementation are a lot; the above only is a preferred implementation of the present invention; should be understood that; for those skilled in the art; under the prerequisite that does not break away from the principle of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.The all available prior art of each part not clear and definite in the present embodiment is realized.

Claims (1)

1. the ZF detection method in the multi-input multi-output system is characterized in that, may further comprise the steps:

Step 1 is weighted processing by r to received signal the antenna gain of each reception antenna is carried out normalization, obtains the received signal r' after the weighting;

Step 2 is with the input of the received signal r' after weighting formula (H ^HH) ^-1H ^HObtain to send value detection signal Wherein H is a channel matrix;

Step 1 may further comprise the steps:

Step 11, use following formula to calculate the interference noise variance that enters each reception antenna receiving terminal:

E[(G ₁n ₁) * (G ₁n ₁) ^*]=(G ₁σ ₁) ², E[(G _in _i) * (G _in _i) ^*]=(G _iσ _i) ², G wherein ₁The antenna gain of representing the 1st antenna, G _iThe antenna gain of representing i root antenna, G ₁n ₁Expression enters the receiving terminal interference noise of the 1st antenna, G _in _iExpression enters the receiving terminal interference noise of i root antenna; (G _in _i) ^*Expression G _in _iConjugate complex number, E[(G _in _i) * (G _in _i) ^*] represent the receiving terminal interference noise that enters i root antenna to be asked variance, (G _iσ _i) ²Represent its interference noise variance yields;

Step 12 is introduced weight coefficient w _i:

w _iRepresent the weight coefficient of i root antenna with respect to the 1st antenna receiving terminal interference noise;

Step 13, r=[r to received signal ₁r ₂... r _N] ^TBe weighted, obtain the received signal after the weighting

R'=[w ₁r ₁w ₂r ₂... w _Nr _N] ^T, wherein N represents the receiving terminal antenna amount, T represents that vectorial to received signal r carries out transposition;

In the step 2, send value detection signal

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