CN1909403A - Pilot frequency creating method in multiple-input and multiple-output system - Google Patents

Abstract

The invention relates to a pilot generating method of multi-input multi-output system, wherein said method comprises: at the sender, receiving the signal channel informant feedback from the receiver to obtain the signal channel damping matrix; using signal channel estimate method to obtain the signal channel estimate error; using signal channel signal checking method, based on output check optimized mode, to obtain the relationship between the signal channel estimate error and the signal channel matrix; based on said relationship, fixing the mode of pilot, and based on the pilot mode and the signal channel damping matrix, generating pilot.

Description

Pilot frequency creating method in the multi-input multi-output system

Technical field

The present invention relates to the pilot frequency creating method under a kind of MIMO (multiple-input and multiple-output) system, more specifically, the present invention relates to a kind of pilot frequency creating method under relative MIMO system, be applicable to that high-speed radiocommunication system under the various honeycomb systems and high throughput wireless local area network system, particularly correlation are strong or have the MIMO communication system of slow time-varying characteristics.

Background technology

MIMO (multiple-input and multiple-output) multiaerial system adopts a plurality of antennas in emission or receiving terminal, utilizes the redundancy of user's attitude information or space channel on one's own initiative, can improve the capacity of system effectively.Along with mimo system the manifesting of critical role in wireless system, the pilot design under the MIMO environment becomes the research topic of being paid close attention to gradually.Under the MIMO environment, when utilizing designed pilot frequency sequence to carry out channel estimating, not only to estimate each transmitting antenna to the reception antenna time-domain information, also to estimate the space characteristics difference of each antenna with correspondence.Therefore, when the pilot frequency sequence of design mimo system, not only to consider the design of each transmitting antenna pilot frequency sequence, also should consider the contact between each antenna pilot sequences.

In mimo system, each antenna is pilot signal transmitted simultaneously, also can part antenna transmission pilot signal, and other antenna transmission data-signals.Fig. 1 shows several pilot signals and the data-signal arrangement at each antenna and each symbol period.Gray circles is represented pilot tone among the figure, and white circle is represented data-signal, and transverse axis is a time shaft, different transmit antennas that respectively value is corresponding on the longitudinal axis.Wherein, modal load mode is the pairing mode of Fig. 1 (a), in some symbol periods, and each antenna or all transmit pilot signal, or equal data signal, the present invention launches based on this model.

When carrying out the design of pilot frequency sequence, find the solution the channel estimation errors matrix according to different channel estimation methods, the pattern according to this matrix mean square deviation minimum designs pilot frequency sequence then.The flow chart of conventional method pilot design as shown in Figure 3, in step 31, obtain channel estimating according to selected channel estimation method, in step 32, deduct the channel true value with channel estimating, obtain channel estimation errors, in step 33, obtain the channel channel estimation errors and minimize expression formula,, try to achieve pilot frequency sequence according to described expression formula in step 34.

Yet the channel estimating mean square deviation only is an estimated performance tolerance on the one hand, can not comprehensively react the quality of channel estimating.Such as, if adopt the ZF method to carry out channel estimating, its channel estimating mean square deviation is determined by the energy and the pilot frequency sequence of noise fully so, and it is irrelevant with the characteristic of channel, therefore, when generating pilot frequency sequence, can't further improve performance for estimating channel in conjunction with the characteristic of channel.

In fact, for zero forcing algorithm, the different characteristics of channel adapts to different pilot frequency sequences." MIMO channelestimation:optimal training and tradeoffs between estimationtechniques " that the people write (ICC 2004-IEEE International Conference onCommunications such as Mehrzad Biguesh, Alex B.Gershman, vol.27, no.1, June 2004, pp.2658-2662) the yardstick zero forcing algorithm has been proposed, it multiplies each other with a scalar scale factor and channel estimating, utilize channel information, choose suitable scale factor, can reduce the evaluated error of channel.Even have identical mean square deviation, when input, its influence of different channel estimation errors also is different.The present invention utilizes the ZF signal detection algorithm, analyzes the influence of channel estimation errors for input, when channel estimation errors and channel mutually during quadrature, and the pairing interfering energy minimum of channel estimation errors.Therefore only utilize the channel estimating mean square deviation to generate pilot frequency sequence and have certain one-sidedness.

In the actual environment, there is certain correlation in the channel between dual-mode antenna.Under relevant MIMO environment, the correlation properties of channel change slower in time, and this slow component of channel can be fed back transmitting terminal, carry out pilot design to generate pilot tone, to improve the precision that subsequent channel is estimated.As " OptimalSignal Design For Estimation Of Correlated MIMO Channels " that the people write (Proc.of ICC such as Jayesh H.Kotecha and Akbar M.Sayeed, 2004, pp.3170-3174) disclosed in, under relevant environment, re-constructed channel model, as shown in Figure 2, it is relevant that it is shown transmitting terminal with channel table, the long-pending form that the independent channel part is relevant with receiving terminal.When generating pilot frequency sequence, the mutual information maximization pattern of received signal and channel fading and mean square error minimum combined design pilot frequency sequence.Yet, the problem of this method demand dematrix mark and determinant combined optimization, complexity is too high, and the document has only provided the approximate solution under high s/n ratio and the low signal-to-noise ratio.

Summary of the invention

Consider that the problems referred to above have proposed the present invention.The present invention relates to a kind of pilot frequency creating method under relative MIMO system, be applicable to that high-speed radiocommunication system under the various honeycomb systems and high throughput wireless local area network system, particularly correlation are strong or have the MIMO communication system of slow time-varying characteristics.

To achieve these goals, proposed the pilot frequency creating method in a kind of multi-input multi-output system, described method comprises: at transmitting terminal, receive from the channel information of receiving terminal feedback and obtain the channel fading matrix; Utilize channel estimation methods to obtain channel estimation errors; Utilize the channel signal detection method, detect optimization model, obtain the incidence relation of channel estimation errors and channel matrix according to output; According to incidence relation, determine the pattern of pilot design by determined channel fading matrix of the channel signal detection method that is adopted and pilot matrix; And generate pilot tone according to described pilot design pattern and described channel fading matrix.

Preferably, described channel signal detection method is the ZF method.

Preferably, described output detection optimization model is to make channel estimation errors disturb minimum pattern to the signal that detects output.

Preferably, the described channel estimation errors that makes is that channel estimation errors is at channel inverse matrix upslide shadow minimal mode to one of minimum pattern of the signal interference that detects output.

Preferably, described channel estimation errors is at channel inverse matrix upslide shadow minimal mode: the long-pending energy minimum that makes channel errors and channel matrix pseudoinverse.

It is preferably, described that to make channel estimation errors disturb another minimum pattern to the signal that detects output be the parallel pattern of channel estimation errors and channel matrix.

Preferably, the parallel pattern of described channel estimation errors and channel matrix is to make the negative that be projected as mould value maximum of channel estimation errors matrix on channel matrix.

Preferably, based on the slow time-varying characteristics of channel, described channel matrix adopts the correlated channels matrix to represent, and adopts previous channel matrix to be used as substituting of current required channel matrix.

Description of drawings

Below in conjunction with the detailed description of preferred embodiment of accompanying drawing to being adopted, above-mentioned purpose of the present invention, advantage and feature will become apparent by reference, wherein:

Fig. 1 (a), 1 (b) and 1 (c) show the figure that is transmitted in the load mode of each antenna and each symbol period according to the pilot frequency sequence of prior art and data;

Fig. 2 shows the figure according to the virtual correlated channels model of prior art;

Fig. 3 shows the flow chart based on the pilot frequency creating method of channel estimation errors according to prior art;

Fig. 4 shows the schematic diagram according to the system model that is used for the generation of relative MIMO system pilot tone of the embodiment of the invention;

Fig. 5 shows the flow chart based on the pilot frequency creating method of input according to the embodiment of the invention;

Fig. 6 shows the flow chart based on a specific implementation process of the pilot frequency creating method of input according to the embodiment of the invention;

Fig. 7 shows the principle schematic according to the channel relevancy pilot design pattern one of the embodiment of the invention;

Fig. 8 shows the principle schematic according to the channel similitude pilot design pattern two of the embodiment of the invention; And

Fig. 9 and Figure 10 are the curve chart that shows the Monte-Carlo Simulation result.

Embodiment

The preferred embodiments of the present invention are described below with reference to the accompanying drawings.

Used a kind of pilot design pattern relevant in the pilot frequency creating method of the present invention with channel information, the pilot frequency sequence optimized Algorithm that it is different from the past, only from channel estimating performance, the present invention is further found the solution the result of input by channel estimation value, analyze of the influence of channel estimation errors matrix, proposed the channel similitude pattern and the corresponding generation method of pilot frequency sequence design signal detection performance.The present invention combines the characteristic of channel when generating pilot frequency sequence, can generate corresponding pilot frequency sequence according to different channels.

Particularly, the present invention considers the characteristic of channel when the design pilot frequency sequence, and it generates corresponding pilot frequency sequence at different channels, and its system model as shown in Figure 4.When generating pilot tone, the channel information that transmitting terminal utilizes receiving terminal to feed back to by feedback channel is adjusted the phase place and the power of pilot tone, and is inserted in the middle of the data, goes out by each antenna transmission through beam forming and radio frequency amplification back.

If mimo system has N transmitting antenna, M reception antenna, M 〉=N wherein, there is certain correlation in the transmitting terminal of mimo system.After matched filtering and sampling, obtaining received signal is X.

X＝HP+N _P (1)

Wherein each row of X is corresponding channel that each reception antenna receives, its each row the are corresponding symbol that same symbol period received, H is the channel matrix of M * N dimension, its element [H] _IjCorresponding i transmitting antenna is to the channel fading between j reception antenna, and wireless channel is for equalling the Rayleigh channel that declines.N _PBe the additive Gaussian noise of zero-mean, the spatial domain white noise, obedience N (0, N ₀I _N) distribute.P is each antenna pilot transmitted vector, the element p of the capable j row of its i _IjCorresponding i antenna is at j the frequency pilot sign that symbol period sent.

The influence of channel estimation errors for input will be described below.

Traditional method is when design and generation pilot frequency sequence, only considered the influence of pilot frequency sequence for the channel estimating mean square deviation, channel estimating is for the input service, the present invention has further analyzed the influence of channel estimation errors for input, thereby draws a kind of pilot frequency sequence Design Mode of similitude maximum.

The present invention proposes the pilot frequency sequence design method based on input, and its flow chart in step 51, obtains channel estimating according to selected channel estimation method as shown in Figure 5

In step 52, use channel estimating

Deduct channel true value H, obtain channel estimation errors E, be i.e. the channel estimation errors matrix

$E=H-\hat{H}$

Channel can be expressed as

$H=\hat{H}-E---\left(2\right)$

Here, the method for designing difference with traditional pilot signal is: the present invention has further contemplated the influence of channel estimating for input when designing and generate pilot frequency sequence, its pattern is to reduce the negative effect of channel estimation errors matrix as far as possible.In step 53, obtain the output of Channel Detection according to different channel signal detection algorithms.If the signal of emission is S, through after the signal fadeout, the signal that antenna receives is

Y＝HS+N _s

N wherein _sZero-mean, additivity, Gauss, the spatial domain white noise received for reception antenna.Utilize the ZF method to carry out input, obtain

$\hat{S}={\hat{H}}^{+}Y={\hat{H}}^{+}(\mathrm{HS}+N_s)$

Wherein Channel estimating

Pseudoinverse, ${\hat{H}}^{+}={\hat{H}}^H{\left(\hat{H}{\hat{H}}^H\right)}^{-1}.$ If, obtain testing result with (2) formula substitution following formula

$\hat{S}={\hat{H}}^{+}Y={\hat{H}}^{+}(\hat{H}-E)S+{\hat{H}}^{+}{N}_s=S-{\hat{H}}^{+}\mathrm{ES}+{\hat{H}}^{+}{N}_s---\left(3\right)$

In step 54, by described signal detecting result, analyze the influence of channel estimation errors to input, determine the pattern of pilot design according to the pattern of signal detection performance optimum.(3) in the formula Be the estimated value to S, first S of its right-hand member is the symbol that sends, and is that we wish during the design pilot frequency sequence, should increase the value estimated S as far as possible and exist Middle proportion.In the formula second Relevant with channel estimation errors, the 3rd by noise

Cause.

Design to generate pilot tone in step 55 pair pilot tone, the flow chart of the specific implementation method of pilot design as shown in Figure 6.In step 61, determine the optimization pattern of pilot design, its main purpose is to reduce the negative effect of channel estimation errors E in input.In step 62, what determine selection is pattern one or pattern two.As with second Regard interference as,, then should make in order to increase the ratio of S

Value as far as possible little, thus, the present invention proposes the pattern one shown in step 63: channel estimation errors will be introduced in embodiment one at channel inverse matrix upslide shadow minimal mode.If do not regard interference as with second, when When approaching unit matrix, channel estimation errors not only can not reduce the performance of detection, the performance that can strengthen detecting on the contrary, for this reason, the present invention derives the pattern two shown in step 64: the parallel pattern of channel estimation errors and channel matrix, will in embodiment two, introduce.Finally, use one of selected pattern one and pattern two and generate pilot tone.

(embodiment one)

As mentioned above, when regarding interference as with second in (3) formula, in order to reduce this influence, should make its energy minimum, obtain pattern one: channel estimation errors is at channel inverse matrix upslide shadow minimal mode

min{‖EH ⁺‖ ²}

In pattern one, comprised the information of channel H, when the design pilot frequency sequence,, design and generate corresponding pilot frequency sequence according to the different characteristics of channel.

In real system, can't obtain the information of instantaneous channel matrix H, during realization, replace instantaneous channel matrix with the correlated channels matrix.In certain time interval, channel has similar characteristic, in order to reduce the operand of finding the solution correlation matrix, and the required channel information in the time of can utilizing last channel information to do the optimization pilot frequency sequence.

If adopt the ZF method to carry out channel estimating, so, channel estimation errors is

E＝N _PP ⁺

E and H ⁺Product energy minimum can be expressed as

$\min \left\{{\left|\right|N_P{P}^{+}{H}^{+}\left|\right|}^2\right\}=\min \left\{\mathrm{tr}\left({\left(P^{+}{H}^{+}\right)}^H{N_P}^H{N}_P\left(P^{+}{H}^{+}\right)\right)\right\}$

$={\mathrm{\σ}}_x^2\min \left\{\mathrm{tr}\left({\left(P^{+}{H}^{+}\right)}^H\left(P^{+}{H}^{+}\right)\right)\right\}$

$={\mathrm{\σ}}_x^2\min \left\{\mathrm{tr}\right[{\left(\mathrm{HP}\right)}^{{+}^H}{\left(\mathrm{HP}\right)}^{+}\left]\right\}$

$={\mathrm{\σ}}_x^2\min \left\{\mathrm{tr}\right[{\left\{\left(\mathrm{HP}\right){\left(\mathrm{HP}\right)}^H\right\}}^{+}\left]\right\}$

According to the characteristic of mark as can be known, make E and H ⁺Product energy minimum, then

(HP)(HP) ^H＝I。

Can make P=H ⁺, following formula just can be met.

Fig. 7 has provided this pilot design physical interpretation.Transverse axis among Fig. 7 is the antenna sequence number, and the longitudinal axis is the average power of each transmitting antenna.Fig. 7 (a) is the average power of each antenna channel, Fig. 7 (b) by the average power of each antenna pilot sequences of correspondence.Pilot tone is the pseudoinverse of channel matrix, that is to say that the channel fading energy is high more, and the average energy of its respective antenna pilot frequency sequence is low more.Therefrom we can see an interesting phenomenon, and design is during pilot frequency sequence, and for the poor more channel of performance, by it is distributed pilot energy high more, the requirement of this and water-filling algorithm is just in time opposite.

(embodiment two)

From (3) formula as can be seen, when When approaching unit matrix, channel estimation errors not only can not reduce the performance of detection, and the performance that can strengthen detecting makes on the contrary

Signal to noise ratio improve. Approaching unit matrix can be expressed as

$-{\hat{H}}^{+}E=\mathrm{cI}\&DoubleRightArrow;-E=c\hat{H}\&DoubleRightArrow;-E=c(H+E)\&DoubleRightArrow;E=\frac{-\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="A20051008939600142.png,A20051008939600161.png"\; state="\{\{state\}\}">c</figure-callout>}}{1+c}H$

Wherein c is a positive number.As can be seen, when channel estimation errors and channel matrix have similar characteristic, and the mould value of the projection of E on H can improve the performance of input when being negative from following formula.Therefore, the present invention proposes pattern two: the parallel pattern of channel estimation errors and channel matrix.

Fig. 8 has provided the schematic diagram of pattern in the present embodiment, i row vector in the vectorial i representation unit battle array among the figure ,-e _hExpression Middle corresponding vector is in signal detecting result

In, after superposeing, both multiply each other with S, represented the signal section of testing result.(a) among the figure-e _hHave equidirectional with i, the vector after both additions has higher amplitude, and corresponding red line part among (b) figure has increased S and existed

Middle ratio improves output signal-to-noise ratio.(c) figure and (d) figure then provided opposite situation.

As mentioned above, the present invention proposes the method that a kind of basis pilot design pattern relevant with channel information generates pilot tone, the pilot frequency sequence optimized Algorithm that it is different from the past is only from channel estimating performance; The present invention is further found the solution the result of input by channel estimation value, analyze the influence of channel estimation errors matrix to signal detection performance, has proposed the channel similitude pattern and the respective design method of pilot frequency sequence design.The present invention combines the characteristic of channel when design and generation pilot frequency sequence, can be according to the corresponding pilot frequency sequence of different channel design.

It should be noted that, although above is that example shows the present invention with the ZF method, but apparent, thought of the present invention can be applied to other detection methods, as long as in its pilot frequency sequence design, consider of the influence of channel estimation errors matrix to signal detection performance.

Fig. 9 and Figure 10 have provided 10000 times Monte-Carlo Simulation result.Transmitting terminal and receiving terminal have 2 antennas, the noise Gaussian distributed, and the noise signal on each reception antenna is separate, sends symbol and adopts the BPSK modulation system, and each transmission symbol constantly is separate.Channel is a falt fading channel.Compared the performance of carrying out input after the channel estimating that algorithm of the present invention and prior art algorithm obtain in the emulation.Channel estimating and input all adopt zero forcing algorithm, and channel is constant in short-term.Pilot frequency sequence is selected unit matrix for use in the traditional algorithm.

When Fig. 9 was channel estimating, signal to noise ratio was 10dB, during input, and under the variable situation of signal to noise ratio, the performance comparison of inventive method and conventional method.When Figure 10 was input, signal to noise ratio was 10dB, during channel estimating, and under the variable situation of signal to noise ratio, the performance comparison of inventive method and art methods.When the channel estimating signal to noise ratio was 10dB, the signal to noise ratio of input was high more, and the relative traditional algorithm of the present invention is good more.When the input signal to noise ratio was 10dB, the signal to noise ratio of channel estimating was low more, and the relative traditional algorithm of the present invention is good more.

Although below show the present invention in conjunction with the preferred embodiments of the present invention, one skilled in the art will appreciate that under the situation that does not break away from the spirit and scope of the present invention, can carry out various modifications, replacement and change to the present invention.Therefore, the present invention should not limited by the foregoing description, and should be limited by claims and equivalent thereof.

Claims (8)

1, the pilot frequency creating method in a kind of multi-input multi-output system, described method comprises:

At transmitting terminal,

Reception obtains the channel fading matrix from the channel information of receiving terminal feedback;

Utilize channel estimation methods to obtain channel estimation errors;

Utilize the channel signal detection method, detect optimization model, obtain the incidence relation of channel estimation errors and channel matrix according to output;

According to incidence relation, determine the pattern of pilot design by determined channel fading matrix of the channel signal detection method that is adopted and pilot matrix; And

Generate pilot tone according to described pilot design pattern and described channel fading matrix.

2, method according to claim 1 is characterized in that described channel signal detection method is the ZF method.

3, method according to claim 2 is characterized in that it is to make channel estimation errors disturb minimum pattern to the signal that detects output that described output detects optimization model.

4, method according to claim 3 is characterized in that: the described channel estimation errors that makes is that channel estimation errors is at channel inverse matrix upslide shadow minimal mode to one of minimum pattern of the signal interference that detects output.

5, method according to claim 4 is characterized in that described channel estimation errors is at channel inverse matrix upslide shadow minimal mode: the long-pending energy minimum that makes channel errors and channel matrix pseudoinverse.

6, method according to claim 3 is characterized in that: described to make channel estimation errors disturb another minimum pattern to the signal that detects output be the parallel pattern of channel estimation errors and channel matrix.

7, method according to claim 6 is characterized in that the parallel pattern of described channel estimation errors and channel matrix is to make the negative that be projected as mould value maximum of channel estimation errors matrix on channel matrix.

8, according to any described method of claim 1 to 7, it is characterized in that the slow time-varying characteristics based on channel, described channel matrix adopts the correlated channels matrix to represent, and adopts previous channel matrix to be used as substituting of current required channel matrix.

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