CN102833046A - Adaptive modulation method for distributed multi-antenna system - Google Patents

Abstract

The invention relates to an adaptive modulation (AM) method design and performance evaluation for a wireless distributed multi-antenna system (DAS). Under the constraint condition of a target bit error rate (BER), the system frequency spectrum efficiency is maximized to respectively design two AM schemes of a discrete rate and a continuous rate. By aiming at the discrete rate AM, an adaptive switching threshold based on precise BER is provided. Compared with the traditional AM based on an approximate threshold, the AM method disclosed by the invention can obtain high frequency spectrum efficiency. A channel model comprising path loss, shadow fading and Rayleigh fading is designed by considering the practical situation of DAS. On the basis, the computation expression of a continuous rate AM frequency spectrum efficiency, a discrete rate AM frequency spectrum efficiency and the average BER is given so as to provide an effective method for system performance evaluation. An Matlab (matrix laboratory) simulation platform shows that the designed AM method can satisfy the target BER requirement, and the continuous rate AM method is better than a discrete rate AM method. In addition, due to the providing of an improved threshold, the discrete rate AM can be used for realizing the high frequency spectrum efficiency if being compared with the traditional AM method. In addition, the provided frequency spectrum efficiency has good consistency with the average BER calculation and simulation, and the system performance can be effectively evaluated.

Description

Self-adaptive modulation method in the distributed multi-antenna system

Technical field

The invention belongs to wireless communication field, relate to the adaptive modulation scheme design of radio communication, relate to speed and the design of discrete velocity self-adaptive modulation method continuously in the distributed MIMO system in particular.

Background technology

At present; Wireless communication technology has been widely used in the social life each side; And various wireless communication data business present volatile growth to capacity requirement; Especially the wireless access of the Internet and multimedia application have surpassed the data rate that prior art is supported to the information throughput growth of requirement, and a kind of important technology that makes data rate be able to effectively to increase is exactly to settle multiple antenna at system's transmitting terminal and receiving terminal; It is multiple-input and multiple-output (MIMO, Multiple Input and Mu1tiple Output) technology.Research shows; Use the MIMO technology of many antennas can make full use of space resources; Under the situation that does not increase system bandwidth and the total transmitting power of antenna, can resist the influence of wireless channel decline effectively, improve the availability of frequency spectrum and the channel capacity of system widely; Become one of key technology of third generation partner program (3GPP, 3rd Generation Partnership Project) LTE.

And along with the growing tension of frequency spectrum resource and the sustainable growth of user's request, conventional cellular systems has occurred switching frequently, has disturbed problems such as increase, cost raising, can't satisfy the demand for development of the system of following radio communication.In recent years, distributing antenna system has caused the extensive concern of academia as a kind of emerging technology.No matter distributing antenna system is improving power system capacity; Reduce transmitting power and still all demonstrate the incomparable advantage of conventional cellular systems at aspects such as reducing switching times, reduction outage probability; The desirable replacement scheme that is considered to conventional cellular systems has become following radio communication and has had one of direction of development prospect.At present, existing research shows with centralized MIMO to be compared, and it has higher capacity, sub-district average coverage rate and anti-fading ability.

Technology for self-adaptively transmitting can be according to the requirement of wireless communications environment and service quality (QoS); The various parameters that dynamically change transmitting terminal improve resource utilization ratio; To obtain higher system throughput and capacity, be widely used in the wireless communication system as a kind of strong technology that improves the transmission system frequency spectrum.

Based on this, this patent will provide Adaptive Modulation in the wireless distributed multiaerial system (AM) algorithm design, with the variation of Adaptive matching wireless channel, effectively improve throughput of system and data transmission rate.

Technology for self-adaptively transmitting has obtained fairly perfect research in single carrier a single aerial system (SI SO).People such as A.J.Goldsmith have provided the closed expression of average BER and average spectral efficiency (ase) (ASE) to carrying out performance evaluation based on the Adaptive Transmission of different transmission plan (comprising variable bit rate, variable power, average error bit rate (BER) constraint, instantaneous BER constraint) in the SISO system.A.Maaref is generalized to the SISO adaptive modulation technology in the mimo system of Space Time Coding, and has carried out the performance evaluation of discrete velocity adaptive modulation scheme under the firm power.X.Yu has studied the adaptive modulation scheme of mimo system based on incomplete channel condition information (CSI), has provided the accurate expression of average BER of this system and ASE.Yet above-mentioned adaptive modulation scheme all is to design to centralized SISO/MIMO system, and distributing antenna system (DAS) is carried out the Adaptive Modulation design seldom.Only there is rapid fading unlike centralized mimo system; DAS is because transmitting antenna is distributed in the zones of different of sub-district; Transmitting terminal will experience different large scale slow fadings to the mobile terminal, make the design of distributed MIMO system self-adaption modulation scheme have certain degree of difficulty.

Therefore; The present invention will be to wireless DAS system; Study its adaptive modulation scheme and corresponding algorithm design thereof---promptly under constant power and instantaneous mistake BER constraints; Through maximization system spectral efficiency (SE), design two kinds of self-adaptive modulation methods of continuous speed and discrete velocity, wherein the self adaptation change-over gate limit value of discrete velocity AM scheme will obtain according to target BER.Consider that existing threshold value is based on approximate BER and obtains, so that the AM scheme can not reflect actual modulation case exactly accordingly, brings the SE of system limited.For this reason, designed a kind of self adaptation handoff threshold and corresponding AM method, can obtain high spectrum efficiency than AM based on common approximate threshold based on accurate BER.To the DAS actual conditions; Designed the channel model that comprises path loss, shadow fading and Rayleigh fading; And, provided the computing formula of continuous rate AM spectrum efficiency and dispersion ratio AM spectrum efficiency and average BER, for system performance testing provides effective appraisal procedure based on this model.Utilize the Matlab emulation platform to carry out the performance test of AM method, its result shows that the AM method that is designed all can satisfy target BER requirement, and wherein rate AM is owing to need not the limit value of rate continuously, and its SE will be apparently higher than dispersion ratio AM method.And carry compares with existing AM method based on the AM method of improving thresholding, also can realize higher spectrum efficiency.In addition, the spectrum efficiency of being given and average BER calculate also and to obtain consistently preferably with emulation, thereby assess for the DAS systematic function effective method are provided.

Below will combine accompanying drawing that the object of the invention and characteristic are described in detail through specific embodiment, these specific embodiments be illustrative, do not have restricted.

Summary of the invention

The present invention be directed to distributing antenna system, carried out its Adaptive Modulation algorithm design, comprise continuously and two kinds of adaptive modulation schemes of discrete velocity.Purpose is under the constraints of constant power and target bit, utilizes the AM method that is designed can obtain the very big raising of the SE of system.Following steps have been adopted in the DAS adaptive modulation scheme design that the present invention proposes:

(1) DAS model and channel model have been provided.

The distributing antenna system model is shown in accompanying drawing 1.

Accompanying drawing 1 has provided the physical model of distributing antenna system, the border circular areas that it is D that cell unit is modeled as a radius, and each remote antenna (RA) at random is placed in the diverse location of sub-district, is designated as RA _i(i=1,2 ...., N), be connected to a CPU (MCU) through specific transmission channel (optical fiber). be without loss of generality, suppose that each portable terminal (MT) all has L antenna.

If RA _iSelection is used for transmitting, and the expression formula that moves the reception signal of receiving terminal so can be expressed as:

expression formula 1

Wherein, y _i ^(j)For moving the reception signal of receiving terminal j root reception antenna, E _sFor sending the power of signal, compound channel matrix h _iIn element h _i ^(j)Be RA _iAnd the channel coefficients between the mobile receiving terminal j root reception antenna; X is from RA _iThe signal and the energy normalized of sending are 1.It is that 0 variance is N that each element among the noise matrix z is obeyed average ₀Multiple Gaussian distribution.

Since the architectural characteristic of distributing antenna system, h _i ^(j)Represent in order to drag in the present invention:

${h_i}^{\left(j\right)}={{\mathrm{\κ}}_i}^{\left(j\right)}\sqrt{L_i{S}_i}$ Expression formula 2

In the formula, κ _i ^(j)Represented RA _iAnd the small scale rapid fading between the j root reception antenna of mobile terminal, i.e. amplitude | κ _i ^(j)| be Rayleigh fading, thereby | κ _i ^(j)| ²Obeys index distribution.L _iAnd S _iRepresent RA respectively _iAnd path loss between the mobile terminal and shadow fading, wherein path loss can be expressed from the next:

$L_i={\left(\frac{d_0}{d_i}\right)}^{{\mathrm{\β}}_i}$ Expression formula 3

Wherein, β _iThe expression path loss index, d ₀Be reference distance, d _iBe RA _iAnd the distance between the MT.

Can obtain the effective noise of system receiving terminal (SNR) than doing by expression formula 1 and expression formula 2

${\mathrm{\γ}}_i=\underset{j=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\γ}}_i^{\left(j\right)}={\mathrm{\Ω}}_i\underset{j}{\overset{L}{\mathrm{\Σ}}}{\left|h_i^{\left(j\right)}\right|}^2$ Expression formula 4

Wherein, The instantaneous output signal-to-noise ratio (SNR) of

expression j root reception antenna,

By existing document, in conjunction with expression formula 4, can try to achieve the receiving terminal effective signal-to-noise ratio and obey the normal distribution of logarithm Rayleigh, its probability density function (PDF) can be expressed as:

$f_{{\mathrm{\γ}}_i}\left(\mathrm{\γ}\right)={\∫}_0^{\∞}\frac{L^{L-1}{\mathrm{\γ}}^{L-1}}{\mathrm{\Γ}\left(L\right){\mathrm{\τ}}^L}\mathrm{Exp}(-\frac{\mathrm{L\γ}}{\mathrm{\τ}})\frac{\mathrm{\ξ}}{\sqrt{2}{\mathrm{\π\; \σ}}_i\mathrm{\τ}}\mathrm{Exp}[-\frac{{(10\mathrm{Lg\τ}-{\mathrm{\μ}}_i-10\mathrm{LgL})}^2}{2{\mathrm{\σ}}_i^2}]\mathrm{D\τ}$ Expression formula 5

Wherein, σ _i(in dB) is 10lgS _iStandard deviation,

Consider that there is integration in this formula, so can't directly be used for carrying out the Performance Evaluation of system.A logarithm normal distribution capable of using for this reason is similar to and replaces above-mentioned Rayleigh logarithm normal distribution, and is specific as follows:

$f_{{\mathrm{\γ}}_i}\left(\mathrm{\γ}\right)\≅\frac{\mathrm{\ξ}}{\sqrt{2\mathrm{\π}}{\widehat{\mathrm{\σ}}}_i\mathrm{\γ}}\mathrm{Exp}(-\frac{{(10\mathrm{Lg\γ}-{\widehat{\mathrm{\μ}}}_i)}^2}{2{\widehat{\mathrm{\σ}}}_i})$ Expression formula 6

In the formula;

is the average of APPROXIMATE DISTRIBUTION, can be expressed as

wherein ψ () be Euler psi function; And the variance of APPROXIMATE DISTRIBUTION is

wherein ζ () be Reimann zeta function.

(2) rate adaptation modulation scheme design continuously among the DAS

For M-ary orthogonal Modulation and Amplitude Modulation (M-QAM), its approximate BER formula can be represented with following formula:

Ber (n, γ) _Appro.≈ 0.2exp (g _nγ) expression formula 7

In the formula, for square M-QAM, g _nEqual 1.6/ (M _n-1), for rectangle M-QAM, g _nEqual 6/ (5M _n-4), wherein BPSK is the special circumstances of rectangle M-QAM.Common adaptive modulation scheme design just is based on this approximate BER and obtains the self adaptation handoff threshold, so that can not reflect real modulation case exactly, thereby spectrum efficiency is limited.

Equal target BER (BER through setting above-mentioned instantaneous BER ₀) can carry out continuous rate AM conceptual design.Promptly by expression formula 7 and BER ₀,, can try to achieve the spectrum efficiency of continuous rate Adaptive Modulation through inverting

For square M-QAM:

${\mathrm{SE}}_{\mathrm{Continu}}={\mathrm{Log}}_2(-\frac{1.6\mathrm{\γ}}{\mathrm{Ln}({\mathrm{BER}}_0/0.2)}+1)$ Expression formula 8

For rectangle M-QAM:

${\mathrm{SE}}_{\mathrm{Continu}}={\mathrm{Log}}_2(-\frac{1.2\mathrm{\γ}}{\mathrm{Ln}({\mathrm{BER}}_0/0.2)}+0.8)$ Expression formula 9

(3) discrete velocity adaptive modulation scheme design among the DAS

One of this patent content is to satisfy under the target BER condition at instantaneous BER, comes discrete rate AM scheme through the maximization average spectral efficiency (ase).Through target setting BER is BER ₀, we are divided into several intervals, [γ to instantaneous SNR _n, γ _N+1), n=0,1 ... .., N-1 is γ wherein ₀=0, γ _N+1=+∞, N are the total number of system modulation mode.Planisphere size M for discrete M-QAM _nCan be defined as { M ₀=0, M ₁=2 ..., M _n=2 ^2n-2, n=2 ..., N-1}, when instantaneous SNR between [γ _n, γ _N+1) when interval, system has planisphere with selection and is of a size of M _nModulation system, corresponding message transmission rate b _n=log ₂M _nBit/s.

Under additive Gaussian noise (AWGN) channel, accurately the BER formula of M-QAM modulation system can be expressed as

$\mathrm{Ber}{(n,\mathrm{\γ})}_{\mathrm{Exact}}=\underset{m}{\mathrm{\Σ}}{\mathrm{\α}}_m\mathrm{Erfc}\left(\sqrt{{\mathrm{\β}}_m\mathrm{\γ}}\right)$ Expression formula 10

Expression formula 10 is set at target BER, then can obtains the accurate threshold value γ of SNR _{N_exact}=BER _Exact ^-1(BER ₀).Obvious γ _N-exactCalculating comparatively complicated.Only adopt first (this paper is called suboptimum BER formula) in 10 formulas of expression to simplify the calculating of SNR threshold value for this reason, obtain suboptimum SNR threshold value

γ _N-suboptimal=[erfc ^-1(BER ₀/ α ₁] ²/ β ₁Expression formula 11

This is owing to when hanging down SNR, often adopts low-order-modulated mode BPSK, QPSK, and the BER formula of these modulation systems only comprises one, when high SNR, often adopts high-order modulating, and first of its BER formula occupied an leading position; So suboptimum threshold value γ that is proposed _N-suboptimalWith accurate threshold value γ _N-exactHas the good goodness of fit.And common approximate threshold value differs bigger.For this reason, table 1 has provided BER ₀Be under 0.01 the situation, the self adaptation handoff threshold that calculates by accurate, suboptimum and approximate BER formula respectively.γ ₁, γ ₂, γ ₃, γ ₄, γ ₅, γ ₆And γ ₇Respectively according to BPSK, QAM, 8QAM, 16-QAM32-QAM, 64-QAM and 128-QAM obtain.It is as shown in the table, γ _N-suboptimalAnd γ _N-exactNumerical value is identical, the γ that this expression is carried _N-suboptimalCan be to replace γ exactly _N-exactYet, the approximate γ that common AM is adopted _{N-approximate}But with essence gate limit value γ _N-exactBetween have very big difference, this will cause the SE loss.

Table 1 self adaptation handoff threshold

	γ l	γ 2	γ 3	γ 4	γ 5	γ 6	γ 7
								γ n-exact	2.7059	5.4119	15.2839	24.5613	60.6553	94.0884	226.7062
γ n-suboptimal	2.7059	5.4119	15.2839	24.5613	60.6553	94.0884	226.7062
								γ n-approximate	2.9957	5.6170	17.9744	28.0850	77.8890	1177950	317.5476

In following analysis, do not lose accuracy again in order to simplify calculating, the improvement threshold of being carried (being expression formula 11) will be used to DAS and carry out the self-adaptive modulation method design, thereby can obtain higher spectrum efficiency.

Below in conjunction with accompanying drawing and embodiment the present invention is further described:

Fig. 1 is the DAS structural representation

Fig. 2 is for adopting the DAS systematic schematic diagram of Adaptive Modulation

Fig. 3 is a DAS adaptive modulation scheme spectrum efficiency

Fig. 4 adopts the spectrum efficiency of two kinds of thresholdings and different modulating mode for the DAS adaptive modulation scheme

Fig. 5 is a DAS adaptive modulation scheme average error bit rate

Embodiment

The DAS self-adaptive modulation method that the present invention proposes is verified through the Matlab platform, can find out that from simulation result this method can obtain higher spectrum efficiency, thereby frequency is imitated and performance test provides effective ways for system improves.Provide the technical scheme of concrete enforcement below:

(1) based on the DAS of sky line options

The native system transmitting terminal comes transmission signals according to the best antenna of channel information selective channel condition of feedback, promptly selects maximum that root RA of output signal-to-noise ratio (SNR) _iCome transmission signals, reach maximization to obtain received signal to noise ratio.Sending criterion can be by following model representation:

γ=max{ γ ₁..., γ _NExpression formula 12

Because the distance between each RA is bigger, so can think γ ₁..., γ _NBetween separate.Utilize the expression formula 6 can be in the hope of the cumulative distribution function of γ:

$F_{\mathrm{\γ}}\left(\mathrm{\γ}\right)=\underset{i=0}{\overset{N}{\mathrm{\Π}}}{F}_{{\mathrm{\γ}}_i}\left(\mathrm{\γ}\right)=\underset{i=0}{\overset{N}{\mathrm{\Π}}}[1-\frac{1}{2}\mathrm{Erfc}\left(\frac{10\mathrm{Lg\γ}-{\widehat{\mathrm{\μ}}}_i}{2{\widehat{\mathrm{\σ}}}_i}\right)]$ Expression formula 13

To the following formula differentiate, the PDF that we can obtain γ is:

$f_{\mathrm{\γ}}\left(\mathrm{\γ}\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\left[f_{{\mathrm{\γ}}_i}\left(\mathrm{\γ}\right)\underset{k=1,k\≠i}{\overset{N}{\mathrm{\Π}}}{F}_{{\mathrm{\γ}}_k}\left(\mathrm{\γ}\right)\right]$ Expression formula 14

(2) the continuous rate AM average spectral efficiency (ase) of DAS

By probability density function and expression formula 8 and 9 of system's effective signal-to-noise ratio, the average SE that utilizes the Guass-Hernite numerical integration can try to achieve the continuous rate adaptation modulation of DAS does

expression formula 15

Wherein, t _nAnd H _nBe distributed as N _rPolynomial basic point of rank Hermite and weight coefficient.This SE expression formula is that the continuous rate adaptation modulation of DAS provides spectrum efficiency computational methods comparatively accurately, for the systematic function assessment provides effective ways.

(3) spectrum efficiency of DAS dispersion ratio AM and average BER

The average SE of A.DAS adaptive modulation scheme

The average SE of system is defined as N interval censored data transmission rate and the sum of products respective bins probability, thereby combines the adaptive threshold value that obtains according to expression formula 14, and the average SE that can try to achieve DAS is:

$\stackrel{\‾}{\mathrm{SE}}=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{b}_n\·[F_{\mathrm{\γ}}\left({\mathrm{\γ}}_{n+1}\right)-F_{\mathrm{\γ}}\left({\mathrm{\γ}}_n\right)]$ Expression formula 16

The spectrum efficiency that can be obtained discrete velocity AM by expression formula 13 and expression formula 16 embodies formula.

The average BER of B.DAS adaptive modulation scheme

The average BER of system can accurately be calculated by the ratio of average errored bit number and overall average transmitted bit number, promptly by following formula definition:

$\stackrel{\‾}{\mathrm{BER}}=\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{b}_n\·{\mathrm{BER}}_n/\stackrel{\‾}{\mathrm{SE}}$ Expression formula 17

BER wherein _nFor system is in n interval average BER, promptly

Because there is integration in this expression formula, fails to provide BER _nClosed expression.For this reason, the present invention adopts the Newton-Cotes numerical integration to simplify the calculating of above-mentioned expression formula.The Newton-Cotes numerical integration is that definite integral is uniformly-spaced got basic point and utilized weight coefficient to sue for peace and represent in integral domain, can obtain following closed expression thus:

${\mathrm{BER}}_n\≅\underset{m}{\mathrm{\Σ}}{\mathrm{\α}}_m(\mathrm{Erfc}\left(\sqrt{B_m\mathrm{\γ}}\right)F_{\mathrm{\γ}}\left(\mathrm{\γ}\right){|}_{{\mathrm{\γ}}_n}^{{\mathrm{\γ}}_{n+1}}+\sqrt{\frac{{\mathrm{\β}}_m}{\mathrm{\π}}}\·\mathrm{Ah}\underset{j=0}{\overset{U}{\mathrm{\Σ}}}{W}_j\frac{\mathrm{Exp}(-{\mathrm{\β}}_m{\mathrm{\γ}}_j)}{\sqrt{\mathrm{\γ}}}{F}_{\mathrm{\γ}}\left({\mathrm{\γ}}_j\right))$ Expression formula 18

A and W in the formula _jBe respectively constant and the weight coefficient corresponding, and h is the equally spaced length of integral domain with U

Can get the average BER of system, the i.e. average BER closed expression of DAS dispersion ratio AM to expression formula 18 and 16 substitution expression formulas 17.Thereby effective calculation is provided for the BER Performance Evaluation of system.

The present invention proposes two kinds of self-adaptive modulation methods of DAS and corresponding performance estimating method.The advantage of extracting method in order to embody utilizes the Matlab platform to carry out emulation testing.For discrete AM among the DAS, it adopts 7 kinds of modulation systems such as BPSK, 4QAM, 8QAM, 16QAM, 32QAM, 64QAM and 128QAM. and accompanying drawing 3, accompanying drawing 4 and accompanying drawing 5 have provided the spectrum efficiency of the AM of DAS system and the Performance Evaluation of average BER.Accompanying drawing 3 has provided the continuous speed AM of system, the spectrum efficiency of discrete velocity AM and the shannon capacity of this system, and wherein the SE of discrete velocity AM is obtained by the suboptimum thresholding.By finding out among the figure; Continuously speed AM has higher spectrum efficiency with respect to discrete velocity AM, and this is because the latter receives limited modulation system restriction, so speed only can reach the high modulation mode transmission rate that is allowed; And the former does not have the restriction of rate, so performance will be got well.But their final speed is all less than hump speed---shannon capacity.In addition, the SE curve that obtains by the suboptimum thresholding can with simulation curve obtain consistent preferably, thereby verified that the present invention puies forward the validity of SE Performance Calculation method.Can be known that by accompanying drawing 4 the suboptimum thresholding has higher spectrum efficiency with respect to approximate threshold, this is because the suboptimum thresholding γ that carries _N-suboplimalExtraordinary accuracy is arranged, and its value will be lower than common approximate threshold γ _{N-approximate}, the probability that such adaptive modulation scheme that designs is selected high-order modulating is with higher, so the self-adaptive modulation method SE that is carried will be apparently higher than the existing AM method based on approximate threshold.By also obtaining among the figure: adopting 7 kinds of modulation systems than adopting 4 kinds of modulation systems has higher SE.Accompanying drawing 5 has provided average BER theory of system and simulation curve.Can be found out that by this figure average BER all is lower than target BER, the Adaptable System that is promptly designed can satisfy qos requirement, and average BER accurate Theory value obtains extraordinary consistent with simulation value.But the approximation theory value is then apparently higher than simulation value, and this is because of the upper bound derivation of equation of approximation theory value by BER.The above results shows that the BER Performance Calculation method of carrying also is effective.

The content of not doing in the application of the present invention to describe in detail belongs to this area professional and technical personnel's known prior art.

Claims (4)

1. Adaptive Modulation (AM) method design in the distributed multi-antenna system (DAS) is characterized in that comprising that step is following:

(1) sets up distributed multi-antenna system model and channel model.

(2) utilize accurate bit error rate (BER) formula and the approximate BER formula of M-QAM under the Gaussian channel, provide the suboptimum change-over gate limit value and the approximate threshold value of Adaptive Modulation.

(3), provide the design of DAS dispersion ratio self-adaptive modulation method based on the suboptimum threshold value; And by being similar to the design that the BER formula obtains the continuous rate self-adaptive modulation method of distributed multi-antenna system;

(4) characteristic of channel, the BER formula of M-QAM and the threshold value of acquisition of combination distributed multi-antenna system provide DAS dispersion ratio AM spectrum efficiency (SE) and average BER expression formula, for the systematic function assessment provides computational methods.

2. distributed multi-antenna system self-adaption modulation algorithm design according to claim 1 is characterized in that said step (1) comprising:

(1a) among the DAS because each spaced antenna is different apart from the distance of receiving terminal; So must consider that each remote antenna to the different large scale slow fading that reception antenna experienced, is a channel that comprises shadow fading, path loss and Rayleigh rapid fading here to this Channel Modeling.

(1b) according to the described wireless distributed multiple antenna communication of step (1a), the effective received signal to noise ratio γ of the system that obtains and its probability density function (PDF).

3. according to claim 1 and 2 described DAS Adaptive Modulation algorithm design schemes, it is characterized in that said step (2) comprising:

(2a) design the continuous rate adaptation modulation scheme of distributed multi-antenna system according to target BER and M-QAM approximate formula.And utilize the effectively PDF of received signal to noise ratio of step (1b), by means of the Guass-Hernite numerical integration, the spectrum efficiency enclosed that can obtain continuous speed AM is calculated.Thereby effective calculation is provided for the Performance Evaluation of continuous speed AM.

(2b) for the dispersion ratio AM of distributed multi-antenna system conceptual design: at first design the accurate BER formula that the AM threshold value is utilized M-QAM under the Gaussian channel one by one, keep leading term, and to make it be target BER, can try to achieve and be used for the suboptimum threshold value that AM switches.Compare with the common threshold value that obtains based on the approximate BER formula of exponential function, the threshold value of carrying has better accuracy, can obtain better consistent with the precision gate limit value.Based on this suboptimum threshold value, design distribution formula multiaerial system dispersion ratio AM method.This method based on the AM method of approximate threshold, can obtain higher spectrum efficiency than usually.

4. according to claim 1 and 3 described DAS dispersion ratio AM methods for designing, it is characterized in that said step (3) comprising:

(3a) according to dispersion ratio adaptive threshold value in distributed multi-antenna system channel characteristic described in the step (1) and the step (2b), the enclosed that provides DAS dispersion ratio Adaptive Modulation spectrum efficiency is calculated.But since the complexity of DAS channel and effective signal-to-noise ratio PDF, the very difficult closed expression that directly provides the average BER formula of system.

The accurate calculating of (3b) adopting the newton-cotes Numerical Integral Formulas to come the average BER of simplified system can obtain the approximate average BER closed expression of DAS dispersion ratio AM, for system's BER Performance Evaluation provides direct calculation method.

The self-adaptive modulation method performance of (3c) utilizing Matlab emulation platform test to be designed, its result verification the validity of institute's extracting method.Promptly put forward the AM method and all can satisfy target BER requirement, have bigger SE to improve than common AM method.And the SE that is given and BER closed expression also provide effective ways for the Systems Theory assessment.

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