CN101521531A - Method of enhancing down-link performance of TD-LTE by antenna selection - Google Patents

Abstract

The invention provides a method of enhancing the down-link performance of TD-LTE, which relates to a wireless communication system. The method comprises the following steps that the number of antennae to be selected is confirmed on the basis of a maximized capacity criterion; the antenna subset selection and the minimum singular value calculation are carried out; the precoding matrix and the signal-to-noise ratio are solved on the basis of a ZF criterion; transmission antennae are selected on the basis of a minimum error rate criterion; and finally, a base station finishes the sending of downward information. When the relativity of an antenna unit at the sending terminal exists, the number of the antennae is confirmed on the basis of the maximized capacity criterion, the transmission antennae are selected on the basis of the minimum error rate criterion, and the adverse effect to MIMO and the precoding from the antenna relativity can be eliminated or weakened, thereby the capacity of the down-link of the TD-LTE system is increased, and the error ratio of the TD-LTE system is reduced; in addition, the number of radio frequency parts at the sending terminal of the TD-LTE system can be reduced, the dimensionality of the matrix which is involved in calculation during the treatment of MIMO can be ensured to be less, and the realization complexity and the cost are also reduced.

Description

A kind of method of utilizing day line options to strengthen the TD-LTE down-link performance

Technical field

The present invention relates to wireless communication technology field, relate in particular to a kind of method that strengthens TD-LTE downlink system performance.

Background technology

Along with the develop rapidly of computer technology, the network communications technology, the needs of broadband high-speed data communication services constantly increase.Because the finiteness of available radio spectrum resource, high data rate can only be realized by signal processing efficiently.According to the information theory result, wireless multiple-input, multiple-output (MIMO) system can improve the capability of communication system and the availability of frequency spectrum significantly under the situation that does not increase bandwidth.Because the huge capacity potentiality of mimo system become the important technology that solves the wireless high-speed data transmission.At present, general hypothesis channel is that coefficient is independent identically distributed multiple gaussian variable in the MIMO research, simplifying the system model studied, and do not consider that the correlation between the antenna element (abbreviating Antenna Correlation as) is to the influence of systematic function in the multiaerial system.The down link (base station is to travelling carriage) of third generation mobile communication system LTE (Long Term Evolution) has adopted the MIMO technology, but Antenna Correlation can cause the performance of mimo system obviously to descend; In addition, the LTE down link also utilizes the complexity of precoding reduction receiver (travelling carriage), and precoding is influenced seriously by Antenna Correlation also.Therefore, the Antenna Correlation problem of solution LTE down link is extremely important.

It line options technology is selected part antenna (antenna subset) from the antenna array of emission/receiving terminal, make the antenna subset selected performance of bringing into play and the effect of using whole antennas to communicate quite or approaching.Existing a lot of about the algorithm of sky line options, as high specific emission/selective reception technology, based on the selection algorithm of heap(ed) capacity, based on selection algorithm of minimum bit-error rate or the like.But be applied to exist the research of sky line options of LTE system of Antenna Correlation also fewer, also do not have preferably algorithm application in having the LTE system of MIMO and precoding.The present invention is directed to very duplexing LTE system (TD-LTE system), a kind of Antenna Selection Algorithem that is applied to exist the TD-LTE down link of Antenna Correlation is proposed, under the prerequisite that satisfies user's transmission quality or power system capacity, find less number of transmit antennas to be used for transmission, this scheme can better be improved systematic function and reduce system cost.

Summary of the invention

The present invention is directed to the middle transmitting terminal Antenna Correlation of third generation mobile communication system TD-LTE down link (having MIMO and precoding) to the influence of systematic function and from saving the system cost aspect, come the feasibility of enhanced system performance to explore adopting a day line options in the TD-LTE down link that has Antenna Correlation.Propose a kind of Antenna Selection Algorithem, when there is correlation in the transmitting terminal antenna element, carried out the performance (capacity, the error rate etc.) that day line options strengthens the TD-LTE system down link.

The realization the technical solution adopted in the present invention is, a kind of antenna selecting method when existing correlation, the transmitting terminal antenna element has been proposed, (1) base station obtains the channel information of implementing day line options: utilize the reciprocity of up-downgoing channel in the TD-LTE system, the channel information that obtains according to up link

, estimate the channel matrix of down link; (2) based on the definite antenna number that need choose of maximum capacity criterion:, utilize the maximum capacity criterion to calculate suitable number of transmit antennas t according to the channel information that has estimated; (3) antenna subset is selected: select t antenna and form an antenna subset St from Mt transmitting antenna; (4) utilize singular value decomposition to calculate minimum singular value: the channel matrix H of antenna subset St correspondence is calculated in the base station _t, and carry out singular value decomposition, calculate minimum singular value according to the singular value decomposition result then; (5) ask pre-coding matrix and signal to noise ratio based on the ZF criterion: derive optimum pre-coding matrix Mt according to ZF (ZF) criterion, further estimate received signal to noise ratio SNR; (6) select transmit antenna based on the minimum bit-error rate criterion: calculate minimum singular value r based on the minimum bit-error rate criterion _MinMaximum antenna subset, the antenna of this subclass correspondence are used for transmitting, and these antenna is the transmit antenna of selection, and the base station is finished downlink information and sent.

This method is by selecting transmit antenna based on the definite antenna number that need choose of maximum capacity criterion with based on the minimum bit-error rate criterion, after when there is correlation in the transmitting terminal antenna element, carrying out day line options, can eliminate or weaken the adverse effect of Antenna Correlation, thereby increase the capacity of TD-LTE system down link and reduce error rate of system MIMO and precoding; In addition, can also reduce TD-LTE system transmitting terminal radio-frequency devices (as power amplifier, frequency conversion etc.) number and cost; Simultaneously, also can make the matrix dimension that participates in calculating in the MIMO processing littler, reduce and realize complexity.

Description of drawings

Fig. 1 main implementation step of the present invention

Fig. 2 adopts the capacity simulation result of TD-LTE down link after the inventive method

Fig. 3 adopts the error rate simulation result of TD-LTE down link after the inventive method

Embodiment

Be illustrated in figure 1 as the main implementation step schematic diagram that strengthens TD-LTE downlink system performance methodology.Embodiment is as follows:

The first step: obtain downlink channel information H

Suppose in the base station to finish channel estimating to receive channel (up link, promptly travelling carriage is to the base station) with the method for various maturations

Because the reciprocity of up-downgoing channel in the TDD system, the propagation characteristic that is uplink downlink is basic identical, thereby the channel parameter of up-downgoing channel is basic identical, and the transmission that base station up reception estimated channel impulse response can be directly applied to down direction is handled, and vice versa.

Like this,

If number of transmit antennas is Mt (Mt 〉=2), the reception antenna number is Mr, and then the dimension of H is Mr * Mt.Then can draw the channel matrix of down link.

Second step: based on the definite number of transmit antennas t that need choose of maximum capacity criterion

Obtaining under the channel H situation, can draw maximum channel capacity based on the maximum capacity criterion and be

$C=\max \underset{i=1}{\overset{r}{\mathrm{\Σ}}}{\log }_2(1+{\mathrm{\γ}}_i{\mathrm{\λ}}_i)---\left(1\right)$

Wherein, r is the order of matrix H, λ _i(i=1,2 ..., r) be matrix H H ^*Nonzero eigenvalue, γ _i(i=1,2 ..., r) being the optimum transmit power apportioning cost of one group of each antenna, * is a Matrix Conjugate commentaries on classics value.

According to the maximum capacity criterion as can be known, selected antenna number is the order of matrix H, i.e. t=r, and the order of matrix H is as the antenna number of selecting.

The 3rd step: antenna subset is selected

From Mt transmitting antenna, select t antenna arbitrarily and form an antenna subset St, recomputate the channel matrix H of antenna subset St correspondence _t(Mr * t dimension), these needs remove does not choose the row of antenna correspondence to get final product in the matrix H.

The 4th step: to channel matrix H _tUtilize singular value decomposition to calculate minimum singular value λ _Min

At first to channel matrix H _tCarry out singular value decomposition

$H_t=U_t{\mathrm{\Σ}}_t{V}_t^{*}---\left(2\right)$

Wherein, U _tFor Mr * Mr ties up unitary matrice, it is classified as

Characteristic vector; V _tFor t * t ties up unitary matrice, it is classified as

Characteristic vector; ∑ _tFor Mr * t ties up matrix, diagonal entry is a matrix H _tSingular value, all the other elements are 0.

The result knows according to singular value decomposition, can be directly from the matrix ∑ _tDiagonal entry in select reckling to obtain minimum singular value λ _Min

The 5th step: ask pre-coding matrix and signal to noise ratio based on ZF (ZF) criterion

According to ZF (ZF) criterion, can derive pre-coding matrix Mt and be

$M_t=H_t^{*}{\left(H_t{H}_t^{*}\right)}^{-1}---\left(3\right)$

Behind precoding and channel, the signal to noise ratio snr of received signal is

$\mathrm{SNR}=\frac{{\mathrm{<figure-callout\; id="0"\; label="E\; s\; tN"\; filenames="A200910103519E00101.png,A200910103519E00102.png"\; state="\{\{state\}\}">E</figure-callout>}}_s}{{\mathrm{tN}}_{}}{\left|\right|M_t\left|\right|}^2---\left(3\right)$

Wherein, E _sBe symbol power, N ₀Be noise variance.Can obtain according to matrix properties

$\mathrm{SNR}\&GreaterEqual;{\mathrm{\&lambda;}}_{\min }^2\frac{E_s}{{\mathrm{tN}}_0}---\left(5\right)$

From following formula as seen, increase the minimum singular value λ of channel _MinCan improve signal to noise ratio snr, thereby reduce the error rate, vice versa.

The 6th step: select transmit antenna based on the minimum bit-error rate criterion

Go on foot and to find from the 5th, if the minimum singular value λ of the antenna subset of the 3rd step selection _MinBigger, the then corresponding error rate can be less, and vice versa.Like this, select transmit antenna to be equivalent to based on the minimum bit-error rate criterion and seek out minimum singular value r _MinMaximum antenna subset.

For each transmitting antenna subclass that the 3rd step was selected, the 4th step of foundation is obtained each subclass respective channels matrix H _tMinimum singular value r _Min, can obtain like this (

) individual minimum singular value, from the definite minimum singular value r of said method _MinIn select the antenna subset of maximum correspondence, the antenna of this subclass correspondence is used for transmitting, these antenna is the transmit antenna of selection.

Below with a concrete application example effect that the present invention improves power system capacity, the error rate is compared explanation, according to the TDD-LTE system environments of 3GPP standard code, utilize MATLAB that the method for the invention is carried out simulation analysis.Sample frequency 1.6e6Hz, 256 subcarriers, subcarrier spacing 6.25KHz, actual carrier number 240 (using 15 data subcarriers of each user for 16 users), OFDM symbol period length 160 μ s, the circulating prefix-length 8.75 μ s of using.Hypothesis base station number of transmit antennas is 4 in the emulation, and the reception antenna number is 4, and channel estimating is desirable (correctly).R is the antenna coefficient correlation, and general r and antenna distance d, wavelength X are relevant with angle spread Λ, satisfy r (d) ≈ exp (23 Λ ²d ²), one group of antenna phase relation numerical value is directly got in emulation.

Figure 2 shows that and adopt that the capacity of TD-LTE down link improves the result behind the said method, (2a) be depicted as the method that adopts prior art, (2b) be depicted as and adopt method of the present invention in the capacity improvement after the sky line options pass through under the different coefficient correlations at the capacity after day line options of pass through under the different coefficient correlations.Figure 3 shows that and adopt behind the said method error rate of TD-LTE down link to improve the result, (3a) be depicted as the error rate improvement of adopting method of the present invention is passed through day line options when coefficient correlation 0.2 after, (3b) be depicted as and adopt method of the present invention when coefficient correlation 0.7, to improve by the error rate after the sky line options.From Fig. 2, Fig. 3 as can be seen, owing to adopt the method for the invention in the TDD-LTE down link, its capacity and the error rate all have bigger improvement, have strengthened the TD-LTE down-link performance.Adopt the method for enhancing of the present invention TD-LTE down-link performance, not only can enhanced system performance (capacity and the error rate), improve communication quality, saved channel resource, improved the efficiency of transmission of channel, can also reduce system cost.

The above; only be better embodiment of the present invention, but protection scope of the present invention is not limited thereto, anyly is familiar with the people of this technology in the disclosed technical scope of the present invention; the conversion that can expect easily and replacement all should be included in the protection category of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (4)

1, a kind of method of utilizing day line options to strengthen the LTE down-link performance is characterized in that this method comprises the steps: that (1) base station according to the channel information that up link obtains, estimates the channel matrix H of down link; (2), utilize the maximum capacity criterion to calculate antenna number t according to channel matrix H; (3) from all transmitting antennas, select t antenna arbitrarily and form an antenna subset St; (4) to the channel matrix H of antenna subset St correspondence _tCarry out singular value decomposition, calculate minimum singular value; (5) ask pre-coding matrix Mt and received signal to noise ratio based on Zero Forcing; (6) select transmit antenna according to minimum bit-error rate.

2, method according to claim 1 is characterized in that, is the order of channel matrix H according to the selected antenna number t of maximum capacity criterion in the step (2).

3, method according to claim 1 is characterized in that, step (4) specifically comprises, according to the channel matrix H of antenna subset St correspondence _tCarry out singular value decomposition, obtaining diagonal entry is matrix H _tSingular value, all the other elements are 0 matrix ∑ _t, from the matrix ∑ _tDiagonal entry in select minimum value as minimum singular value.

4, method according to claim 1 is characterized in that, the minimum singular value that increases channel reduces the error rate, and step (6) comprises that specifically the antenna of selecting maximum antenna subset correspondence from minimum singular value is as transmit antenna.

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