CN101521531B - 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 antennaeThe 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 antennaeto 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 signa 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 downwl-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 antenard 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 tnae 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 bhe 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. e 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 antenna selective enhancement 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 processed to realize by efficient signal.According to the information theory result, wireless multiple-input, multiple-output (MIMO) system can be in the situation that do not increase capacity and the availability of frequency spectrum that bandwidth improves communication system significantly.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 (referred to as Antenna Correlation) is on the impact 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 affected seriously by Antenna Correlation also.Therefore, the Antenna Correlation problem of solution LTE down link is extremely important.

Antenna Selection Technology is selected part antenna (antenna subset) from the antenna array of transmitting/receiving end, make the antenna subset the selected performance of bringing into play and the effect of using whole antennas to communicate quite or approach.Existing a lot of about the algorithm of sky line options, such 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 etc.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 come 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) on the impact of systematic function and from saving the system cost aspect, the feasibility that adopts day line options to strengthen systematic function in the TD-LTE down link that has Antenna Correlation is explored.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 to choose of maximum capacity criterion: according to the channel information that has estimated, utilize the maximum capacity criterion to calculate suitable number of transmit antennas t; (3) antenna subset selection: from Mt transmitting antenna, select t antenna and form an antenna subset St; (4) utilize singular value decomposition to calculate minimum singular value: channel matrix H corresponding to antenna subset St calculated in the base station _t, and carry out singular value decomposition, then calculate minimum singular value according to the singular value decomposition result; (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: the antenna subset that calculates the minimum singular value maximum based on the minimum bit-error rate criterion, antenna corresponding to this subset is used for transmitting, these antenna is the transmit antenna of selection, and the base station is finished downlink information and sent.

The method is by selecting transmit antenna based on the definite antenna number that need to 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 Antenna Correlation to the adverse effect of MIMO and precoding, thereby increase the capacity of TD-LTE system down link and reduce error rate of system; In addition, can also reduce TD-LTE system transmitting terminal radio-frequency devices (such as power amplifier, frequency conversion etc.) number and cost; Simultaneously, also can make the matrix dimension that participates in calculating in the MIMO processing less, 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 BER 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, namely 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, the channel impulse response that the base station uplink receiving is estimated can be directly applied to the transmission processing of down direction, and vice versa.

Like this,

If number of transmit antennas is Mt(Mt 〉=2), the reception antenna number is Mr, 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 to choose of maximum capacity criterion

Obtaining in 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 that Matrix Conjugate turns 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 selection

From Mt transmitting antenna, select arbitrarily t antenna and form an antenna subset St, recomputate channel matrix H corresponding to antenna subset St _t(Mr * t dimension), these needs remove does not choose row corresponding to antenna 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

$H_t=U_t{\mathrm{\Σ}}_t{V}_t^{*}$

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 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 that receives signal is

$\mathrm{SNR}=\frac{E_s}{\mathrm{<figure-callout\; id="0"\; label="t\; N"\; filenames="H2009101035191E00021.png"\; state="\{\{state\}\}">t</figure-callout>}{N}_{}{}_0}{\left|\right|M_t\left|\right|}^2---\left(4\right)$

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

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

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 _MinLarger, then the corresponding error rate can be less, and vice versa.Like this, select transmit antenna to be equivalent to the antenna subset of seeking out the minimum singular value maximum based on the minimum bit-error rate criterion.

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

Individual minimum singular value is selected antenna subset corresponding to maximum from the minimum singular value that said method is determined, the antenna that this subset is corresponding is used for transmitting, and 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, reality uses carrier number 240(for 16 users, 15 data subcarriers of each user), OFDM symbol period length 160 μ s, circulating prefix-length 8.75 μ s.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, general r and antenna distance d, wavelength X and angle spread

Relevant, satisfy

, 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 at the capacity after day line options of pass through under the different coefficient correlations, (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.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.Can find out from Fig. 2, Fig. 3, owing to adopting the method for the invention in the TDD-LTE down link, its capacity and the error rate have larger improvement, have strengthened the TD-LTE down-link performance.Adopt the method for enhancing TD-LTE down-link performance of the present invention, not only can strengthen systematic function (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; be better embodiment of the present invention only, but protection scope of the present invention is not limited to this, 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 (2)

1. a method of utilizing antenna selective enhancement LTE down-link performance is characterized in that, the 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) according to channel matrix H, utilize the maximum capacity criterion to calculate antenna number t, namely the order of matrix H is as antenna number; (3) from all transmitting antennas, select arbitrarily t antenna and form an antenna subset St, calculate channel matrix H corresponding to antenna subset St _t(4) channel matrix H corresponding to antenna subset St _t, according to formula:

Carry out singular value decomposition, calculate minimum singular value, 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 matrix H _tSingular value, it is the reception antenna number that all the other elements are 0, Mr; (5) ask pre-coding matrix Mt and received signal to noise ratio based on Zero Forcing, wherein, the Zero Forcing pre-coding matrix is , behind precoding and channel, the signal to noise ratio snr that receives signal is:

, the minimum singular value that increases channel is improved signal to noise ratio, reduces the error rate, wherein, and E _sBe symbol power, N ₀Be noise variance; (6) from minimum singular value, select antenna corresponding to antenna subset corresponding to maximum to be used for transmitting.

2. method according to claim 1 is characterized in that, step (4) is specially: directly from the matrix ∑ _tDiagonal entry in select reckling to obtain minimum singular value.

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