CN106209717A - A kind of adaptive polarization QAM combined modulation method of hoisting work exoergic effect - Google Patents

Abstract

The invention discloses the adaptive polarization QAM combined modulation method of a kind of hoisting work exoergic effect.Reducing this problem of efficiency for power amplifier non-linear distortion in ofdm system, first the present invention gives ofdm system model based on adaptive polarization QAM combined modulation method, i.e. adds polarization modulation branch road in ofdm system based on QAM modulation；Secondly, the present invention analyzes the impact on QAM modulation of the power amplifier non-linear distortion, and utilizes the characteristic not affected by power amplifier non-linear distortion that polarization modulation has, and has obtained the closed solutions of QAM modulation and polarization modulation each bit error rate.Finally, The present invention gives the implementation method of adaptive polarization QAM combined modulation, i.e. utilize each comfortable power amplifier linear zone of QAM modulation and polarization modulation and the performance advantage of inelastic region, be translated into restricted optimization problem.For the data-rate requirements of a certain moment transmitting terminal, system self-adaption adjust the exponent number of two kinds of modulation systems, thus hoisting work exoergic is imitated.The problem that the efficiency that the present invention can effectively overcome power amplifier non-linear distortion to bring reduces, promotes power amplifier efficiency in ofdm system.

Description

A kind of adaptive polarization QAM combined modulation method of hoisting work exoergic effect

Technical field

The invention belongs to wireless communication technology field, particularly to adaptive polarization QAM combined modulation technology and OFDM The nonlinear effect of the power amplifier impact on efficiency in system.Specifically, it is a kind of based on adaptive polarization QAM combined modulation Ofdm system power amplifier efficiency method for improving.

Background technology

In OFDM (Orthogonal Frequency Division Multiplexing:OFDM) system In, it is that the energy disappears as the power amplifier (Power Amplifier:PA) of key components in ofdm system transmitter unit The major part of consumption, accounts for the 60%-70% of terminal total energy consumption, but the energy conversion efficiency of power amplifier is only under this high energy consumption 5%-10%, this is because power amplifier needs to be operated in linear zone thus avoids non-linear distortion, and the energy of linear zone conversion effect Rate is relatively low.Additionally, the high peak-to-average power ratio characteristic that ofdm signal has can increase the requirement to the power amplifier linearity further, make to avoid merit Put non-linear distortion and become more difficult.

At present, some researchs about suppression power amplifier non-linear distortion with hoisting work exoergic effect are had in wireless communications. First kind method is started with from changing signal characteristic, by amplitude limit, filter, the mode such as coding reduces the peak-to-average force ratio of ofdm signal, from And reduce the non-linear impact on ofdm signal of power amplifier.But this class method makes power amplifier be operated in linear zone more, thus limits The lifting of power amplifier efficiency.Equations of The Second Kind method is to start with from elimination power amplifier non-linear distortion, uses feedforward, negative feedback, predistortion etc. Technology carries out linearization process to nonlinear power amplifier.But owing to power amplifier exists memory effect, it is difficult to accomplish to be completely eliminated non-linear Distortion, eliminates distortion simultaneously and also can lose part energy, and the most this kind of method also limit the lifting of power amplifier efficiency.3rd class Method is then that the mode from the carrying of change information is started with, and the polarized state of such as signal has not spy by power amplifier non-linear effects Property, polarization modulation (Polarization Modulation:PM) transmission data can be used accordingly thus overcome power amplifier non-thread The impact of property distortion.But compared to quadrature amplitude modulation (Quadrature Amplitude Modulation:QAM), polarization is adjusted The system bit error rate in power amplifier linear zone is higher, and under conditions of consuming identical energy, efficiency is less than QAM modulation, is therefore used alone pole Change modulation to imitate at power amplifier inelastic region hoisting work exoergic.Additionally, above three class suppression non-linear distortions and hoisting work exoergic The research of effect is both under conditions of fixed data rate, in actual applications cannot be for the data speed of transmitting terminal change Rate demand makes real-time optimization, has some limitations.

Summary of the invention

The non-linear distortion effects existed for power amplifier, the invention provides a kind of self adaptation be applicable to ofdm system Polarization QAM combined modulation method.The method utilizes each comfortable power amplifier linear zone of QAM modulation and polarization modulation and inelastic region Two kinds of modulation techniques are combined by advantage, effectively promote the power amplifier efficiency in ofdm system by adjusting order of modulation.

When power amplifier is in linear zone, the QAM modulation bit error rate (Symbol Error Rate:SER) is less than polarization modulation, Under the conditions of power amplifier consumes identical energy, QAM modulation can obtain higher energy efficiency；And when power amplifier is in inelastic region, QAM modulation is affected by power amplifier non-linear distortion there is error code, but polarization modulation has and do not affected by power amplifier non-linear distortion Characteristic.Therefore, it can the power amplifier operating point that the data-rate requirements according to currently transmitted end determines and be adaptively adjusted QAM modulation With the order of modulation of polarization modulation, thus the power amplifier efficiency in Continuous optimization ofdm system.I.e. relatively low when data-rate requirements, merit Putting when being positioned at linear zone, more data QAM modulation be transmitted, QAM modulation exponent number is higher than polarization modulation exponent number；And work as Data-rate requirements raises after making power amplifier enter inelastic region, reduces QAM modulation exponent number, improves polarization modulation exponent number, thus drop The low nonlinearity distortion impact on ofdm system, improves power amplifier efficiency.The present invention comprehensively utilizes QAM modulation with polarization modulation each In the advantage of linear zone Yu inelastic region, when the data-rate requirements of transmitting terminal change makes power amplifier be positioned at different working areas and work When putting, by the order of modulation of self adaptation QAM modulation Yu polarization modulation, it is ensured that no matter power amplifier is operated in linear zone or non-thread Can be provided with higher effective data rate during property district, thus optimize power amplifier efficiency.

A kind of can be according to data-rate requirements adaptive adjustment QAM modulation and two kinds of modulation methods of polarization modulation of change The order of modulation of formula, thus improve the adaptive polarization QAM combined modulation method of ofdm system power amplifier efficiency, concrete steps are such as Under:

Step one: add polarization modulation branch road in tradition ofdm system based on QAM modulation；

Obtain sequence of binary digits encoded to transmitting information, corresponding data rate is R, determines through adaptive unit Order of modulation M that in current system, on kth subcarrier, QAM modulation is optimum with polarization modulation_QkWith M_Pk, complete accordingly to prop up Circuit-switched data speed R_QWith lower branch data speed R_PDistribution.

It is R for speed_QUpper branch data, ofdm system successively it is completed QAM modulation, fast Fourier contravariant Power amplifier is entered after changing the sequence of operations such as (Inverse Fast Fourier Transform:IFFT), digital-to-analogue conversion；And for Speed is R_PLower branch data, first pass through polarization modulation constellation mapping unit and complete sequence of binary digits on Poincare sphere The mapping of polarization constellation point, then carries out merit successively and divides and phase shift operation, thus complete polarization modulation mistake power amplifier output signal Journey.Finally, by horizontal polarized components E_HWith perpendicular polarisation components E_VLaunched with vertical polarized antenna by horizontally-polarized antenna respectively Go out.

Step 2: QAM modulation and polarization modulation each bit error rate closed solutions in ofdm system under power amplifier non-linear effects Solve；

In the present invention, utilize power amplifier power series model to characterize power amplifier non-linear, then the ofdm signal through QAM modulation can be subject to Affect to power amplifier non-linear distortion, add the noise in channel, there will be error code when receiving terminal carries out QAM demodulation.And pole Change modulation and there is the characteristic not affected by power amplifier non-linear distortion, it is possible to use the ofdm signal transmission information of distortion, therefore The polarization modulation bit error rate is the most relevant with the noise in channel.

Step 3: the realization of adaptive polarization QAM combined modulation method；

In the present invention, the energy efficiency of power amplifier is defined as proper data rate R_mWith power amplifier input general power P_totalRatio Value.Therefore the adaptive polarization QAM combined modulation method in the present invention can be summarized as a restricted optimization problem.From excellent It can be seen that for data-rate requirements R of a certain moment transmitting terminal, optimum power amplifier efficiency is by QAM modulation rank in change problem Number M_Q, polarization modulation exponent number M_PAnd output rollback value (the Output Back Off:OBO) three of power amplifier determines jointly. Therefore, after determining power amplifier working area now and operating point, by self-adaptative adjustment QAM modulation and the respective tune of polarization modulation Exponent number processed, it is possible to promote the power amplifier efficiency in ofdm system.

Advantages of the present invention:

1, the adaptive polarization QAM combined modulation method in the present invention not only used amplitude and the phase place of QAM modulation Characteristic (signal post flow characteristic) carries information, also uses the polarized state attribute of signal to carry information, takes full advantage of The vectorial property in polarizations territory.

2, the present invention considers the non-linear distortion impact on efficiency of power amplifier, and uses in an ofdm system based on certainly Adapt to the adaptive polarization QAM combined modulation method of order of modulation.For the data-rate requirements of a certain moment transmitting terminal, will It is converted into restricted optimization problem, transmits data by selected optimal modulation exponent number, thus promotes power amplifier energy in ofdm system Effect.

3, compared with the ofdm system using fixing exponent number QAM modulation or polarization modulation, the adaptive pole in the present invention The power amplifier performance efficiency changing QAM combined modulation can obtain certain optimization.

Accompanying drawing explanation

Fig. 1 is the ofdm system transmitting terminal mould based on adaptive polarization QAM combined modulation method used in the present invention Type；

Fig. 2 is the ofdm system receiving terminal mould based on adaptive polarization QAM combined modulation method used in the present invention Type；

Fig. 3 is polarization modulation and the QAM modulation bit error rate performance in power amplifier linear zone in the present invention；

Fig. 4 is polarization modulation and the QAM modulation bit error rate performance in power amplifier inelastic region in the present invention；

Fig. 5 be in the present invention when transmitting terminal data-rate requirements changes, adaptive combined modulator approach determine Excellent QAM modulation and polarization modulation exponent number, power amplifier output rollback value and corresponding power amplifier efficiency；

Fig. 6 be the present invention uses the ofdm system of adaptive combined modulator approach with use fixing exponent number QAM modulation with The power amplifier efficiency contrast under different threshold bit error rate require of the ofdm system of polarization modulation；

Detailed description of the invention

Below in conjunction with accompanying drawing, the present invention is described in further detail.

The present invention be a kind of can be according to data-rate requirements adaptive adjustment QAM modulation and the polarization modulation two of change Plant the order of modulation of modulation system, thus improve the adaptive polarization QAM combined modulation method of ofdm system power amplifier efficiency.

In an ofdm system, it is energy resource consumption as the power amplifier of key components in ofdm system transmitter unit Major part, account for the 60%-70% of terminal total energy consumption, but the energy conversion efficiency of power amplifier be only 5%-under this high energy consumption 10%, this is because power amplifier needs to be operated in linear zone thus avoids non-linear distortion, and the energy conversion efficiency of linear zone is relatively Low.Additionally, the high peak-to-average power ratio characteristic that ofdm signal has can increase the requirement to the power amplifier linearity further, make to avoid power amplifier non- Linear distortion becomes more difficult.

In order to reduce power amplifier nonlinear effect to the impact of power amplifier efficiency in ofdm system, the present invention propose employing based on The adaptive polarization QAM combined modulation method of Adaptive Modulation exponent number improves the power amplifier performance efficiency of ofdm system.Specifically It is accomplished by when data-rate requirements is relatively low, and power amplifier is positioned at linear zone, more data QAM modulation is transmitted, QAM modulation exponent number is higher than polarization modulation exponent number；And after data-rate requirements rising makes power amplifier enter inelastic region, QAM modulation The bit error rate rises, and then reduces QAM modulation exponent number after exceeding certain threshold bit error rate, improves polarization modulation exponent number, will be more Data polarization modulation is transmitted, thus reduces the non-linear distortion impact on ofdm system, improves power amplifier efficiency.

The adaptive polarization QAM combined modulation method promoting ofdm system power amplifier efficiency proposed in the present invention, including Using QAM modulation and two kinds of modulation systems of polarization modulation in conventional OFDM systems, QAM modulation is each missed with polarization modulation simultaneously Solving of the closed solutions of code check, the process that realizes of adaptive polarization QAM combined modulation method, the bit error rate and power amplifier performance efficiency The contents such as simulation analysis, specific as follows:

Step one: the most simultaneously use QAM modulation and two kinds of modulation systems of polarization modulation；

Use the ofdm system transmitting terminal model of adaptive polarization QAM combined modulation as it is shown in figure 1, wherein to go up branch road complete Becoming QAM modulation, lower branch road completes polarization modulation.In figure, adaptive unit determines QAM according to currently transmitted end data rate requirement Modulation and polarization modulation optimal modulation exponent number complete data rate allocation；The binary system that upper branch road is distributed by QAM modulation unit Serial No. carries out QAM modulation；Ofdm signal processing unit completes serial to parallel conversion, Fast Fourier Transform Inverse, parallel serial conversion, number The sequence of operations such as modular transformation；Input signal is amplified by power amplifier；Band filter filters in power amplifier output signal Fall at the out-of-band intermodulation component of original signal；Polarization modulation unit is divided into three parts, and wherein constellation mapping unit completes binary system Serial No. is to the mapping of polarized state constellation point on Poincare sphere, and power amplifier output signal is divided into two component of signals by power splitter And corresponding Amplitude Ratio parameter is set, the phase shifter arranges the phase contrast of two component of signals；Vertical and horizontal poliarizing antenna is then by two Individual component of signal is launched.Idiographic flow is as follows:

At system transmitting terminal, for data-rate requirements R in a certain moment, Adaptive Modulation exponent number unit determine currently Order of modulation M that in system, on kth subcarrier, QAM modulation is optimum with polarization modulation_QkWith M_Pk, complete branch road R accordingly_QWith Lower branch road R_PData rate allocation, in formula, N is ofdm system subcarrier number.

$R_Q=\underset{k=0}{\overset{N-1}{\Σ}}{\log }_2{M}_{Qk}---\left(1\right)$

$R_P=\underset{k=0}{\overset{N-1}{\Σ}}{\log }_2{M}_{Pk}---\left(2\right)$

Formula (1) characterizes and ideally goes up the proper data rate that branch road can reach, but when carrying QAM modulation number According to ofdm signal x (t) proper data rate of branch road can be affected through power amplifier, the non-linear distortion of power amplifier thus affect System energy efficiency.Therefore, the present invention utilizes explicit physical meaning and has the power series form non-linear merit of sign of stronger universality Put, and study its impact on ofdm system performance based on polarization QAM combined modulation method.

For the power amplifier of power series form, the relation between its input signal x (t) and output signal y (t) can represent For:

Y (t)=a₁x(t)+a₃x³(t) (3)

A in formula₁、a₃It is the output multinomial coefficient of nonlinear power amplifier, relevant with the ardware feature of nonlinear power amplifier.

For ofdm signal x (t) of power amplifier input in the present invention, its forms of time and space can be expressed as

$x\left(t\right)=\underset{k=0}{\overset{N-1}{\Σ}}{X}_k{e}^{j2\mathrm{\π}kt/T}---\left(4\right)$

Wherein X_kRepresenting the data symbol on kth subcarrier, T represents the OFDM symbol cycle, and N represents number of sub carrier wave.

Then power amplifier output end signal can be expressed as:

$y\left(t\right)=a_1\underset{k=0}{\overset{N-1}{\Σ}}{X}_k{e}^{j2\mathrm{\π}kt/T}+\frac{3a_3}{4}\underset{k_1,k_2,k_3}{\Σ}{X}_{k_1}{X}_{k_2}{X}_{k_3}{e}^{j(k_1+k_2-k_3)2\mathrm{\π}t/T}+\frac{3a_3}{4}\underset{k_1,k_2,k_3}{\Σ}{X}_{k_1}{X}_{k_2}{X}_{k_3}{e}^{j(k_1+k_2+k_3)2\mathrm{\π}t/T}---\left(5\right)$

Y (t) comprises primary signal and the several intermodulation component of nonlinear power amplifier introducing.Mixed signal y (t) is passed through After band filter, filtering the signal component away from OFDM frequency band in above formula, band filter output signal is y'(t).

$y^{\′}\left(t\right)=a_1\underset{k=0}{\overset{N-1}{\Σ}}{X}_k{e}^{j2\mathrm{\π}kt/T}+\frac{3a_3}{4}\underset{k_1,k_2,k_3}{\Σ}{X}_{k_1}{X}_{k_2}{X}_{k_3}{e}^{j(k_1+k_2-k_3)2\mathrm{\π}t/T}---\left(6\right)$

Now serial signal y'(t) in still to comprise the primary signal of amplification several with fall in former ofdm signal frequency band Intermodulation component.

And under polarization modulation in branch road, Serial No. R_PIt is mapped to M by polarized state_PRank polarized state constellationPolarized stateBy polarization phases, son (δ can be described_i,φ_i)(δ_i∈[0,π/2),φ_i∈[0,2 π)) represent.And in order to realize being added on the ofdm signal of power amplifier outfan carried for polarized state information, then need to make letter Number y'(t) sequentially pass through merit subdivision and phase-shifting unit.Therefore, it can power division network and phase-shift network are used transmission function respectivelyWithIt is expressed as:

${\stackrel{\→}{F}}_i=\left[\begin{array}{c}{\mathrm{cos\δ}}_i\\ {\mathrm{sin\δ}}_i\end{array}\right]---\left(7\right)$

The wherein Amplitude Ratio of power splitter control signal, the phase contrast of phase shifter control signal, therefore descends branch road to utilize polarization The polarized state information of modulation carryingUniquely can be determined by following formula.

Signal y'(t) after power division network with phase-shift network, at the transmitting signal of vertically and horizontally poliarizing antenna port Vector is:

It is hereby achieved that the polarization phases launching signal phasor describes son it is:

${\mathrm{\δ}}_E=arctan\left(\frac{\left|E_V\right|}{\left|E_H\right|}\right)={\mathrm{\δ}}_i---\left(11\right)$

As can be seen here, the transmitting signal on same subcarrierInclude all letters of distorted signal and non-distorted signal Number composition still has the polarized state of the parameter identical with phase-shift network with power division network, i.e. signal and does not change when launching Become, thus may certify that polarized state can not be affected by power amplifier nonlinear characteristic.Finally, two orthogonally polarized components of signal E_HWith E_VCan be launched by a pair horizontal vertical quadrature dualpolarized antenna.

Step 2: QAM modulation and polarization modulation each bit error rate closed solutions in ofdm system under power amplifier non-linear effects Solve；

Ofdm system receiving terminal model based on adaptive polarization QAM combined modulation method is as shown in Figure 2.Owing to sending out Penetrating end when carrying out polarization modulation, polarization modulation unit changes the original amplitude of signal and phase information, therefore should at receiving terminal This is first by orthogonally polarized component E_HWith E_VPolarization information in extracting directly signal, and utilize polarization Match merging technology to realize Polarization demodulation, has also recovered the Amplitude Ratio of ofdm signal based on QAM modulation while reducing polarized state institute carrying information With phase contrast, then operate via fast Fourier transform, QAM demodulation etc. successively, thus recover total data information.

Because the present invention pays close attention under the data-rate requirements of change, the relation between order of modulation and energy efficiency, Therefore, under conditions of not impacting self-adaptive modulation method, the present invention considers awgn channel.Order is removed polarization modulation and is held The OFDM receiving end signal of information carrying breath is r (t), then can be approximately considered r (t) by the OFDM comprising primary signal and distorted signal Signal y'(t) additive white Gaussian noise n (t) composition additional with channel, it may be assumed that

R (t)=y'(t)+n (t) (13)

At receiving terminal, signal on kth subcarrier is carried out FFT, then on receiving terminal kth subcarrier, symbol is permissible It is expressed as:

$\begin{array}{c}{Y}_k=\frac{1}{N}\underset{m=0}{\overset{N-1}{\Σ}}r\left(m\right)e^{-j2\mathrm{\π}km/N}\\ =\frac{1}{N}\underset{m=0}{\overset{N-1}{\Σ}}{a}_1\underset{l=0}{\overset{N-1}{\Σ}}{X}_l{e}^{j2\mathrm{\π}lm/N}{e}^{-j2\mathrm{\π}km/N}+\frac{1}{N}\underset{n=0}{\overset{N-1}{\Σ}}\frac{3a_3}{4}\underset{k_1,k_2,k_3}{\Σ}{X}_{k_1}{X}_{k_2}{X}_{k_3}{e}^{j(k_1+k_2-k_3)2\mathrm{\π}m/N}{e}^{-j2\mathrm{\π}km/N}\\ +\frac{1}{N}\underset{m=0}{\overset{N-1}{\Σ}}n\left(m\right)e^{-j2\mathrm{\π}km/N}\\ =\frac{a_1}{N}\underset{l=0}{\overset{N-1}{\Σ}}{X}_l{Q}_{l-k}+\frac{3a_3}{4N}\underset{k_1{k}_2{k}_3}{\Σ}{Q}_{k_1+k_2-k_3-k}+N_k\\ =a_1{X}_k+\frac{3a_3}{4N}{U}_3(N,k)X_{k_1}{X}_{k_2}{X}_{k_3}{|}_{k_1+k_2-k_3=k}{Q}_0\\ +\underset{k_1+k_2-k_3\≠k}{\overset{N-1}{\Σ}}{X}_{k_1}{X}_{k_2}{X}_{k_3}{Q}_{k_1+k_2-k_3-k}+N_k\end{array}---\left(14\right)$

In formula, Q_kWith U₃(N, expression formula k) is as follows:

$Q_k=\underset{m=0}{\overset{N-1}{\Σ}}{e}^{j2\mathrm{\π}km/N}---\left(15\right)$

$U_3(N,k)=\frac{3}{2}(2kN-2k^2+2k+N^2-N)---\left(16\right)$

In formula (14), Section 1 is desired signal, and Section 2 and Section 3 are respectively inband distortion and the band that intermodulation is formed External expansion signal, Section 4 is noise.It can be seen that because transmitting terminal nonlinear power amplifier exists cubic term component, therefore power amplifier Former ofdm signal has not only carried out linear amplification, and the intermodulation between the subcarrier of different frequency simultaneously also creates new frequency and divides Amount.For the subcarrier of some frequency, the frequency component that some of them are new falls in this sub-carrier band, becomes in band Distorted signal, remaining signal then falls outside this sub-carrier band, becomes band external expansion signal, it can be seen that transmitting terminal power amplifier non- Linearly can produce a large amount of interference signal component, make the bit error rate of receiving terminal dramatically increase.

For the reception signal on kth subcarrier, its Signal to Interference plus Noise Ratio is:

${\mathrm{SINR}}_K=\frac{P_K}{P_{{\mathrm{IM}}_K}+P_{N_K}}---\left(17\right)$

P in formula_KFor desired signal energy,For intermodulation component energy,For noise energy.As can be seen here, intermodulation divides The existence of amount reduces receiving terminal Signal to Interference plus Noise Ratio, so that the receiving terminal bit error rate increases.

Now, ofdm system kth subcarrier is applied M_QkThe bit error rate of the signal of rank QAM modulation is:

$P_b=2(1-\frac{1}{\sqrt{M_{Qk}}})Q\left(\sqrt{\frac{3{\log }_2{M}_{Qk}}{M_{Qk}-1}\·{\mathrm{SINR}}_k}\right)---\left(18\right)$

SER_Qk=1-(1-P_b)²=2P_b-P_b ² (19)

And for polarization modulation, the bit error rate on each subcarrier k after awgn channel can be expressed as:

${\mathrm{SER}}_{Pk}=\frac{1}{N}\underset{i=0}{\overset{N-1}{\Σ}}{P}_e^i---\left(20\right)$

Wherein M_PkFor lower branch road polarization modulation exponent number；It is after channel adds white Gaussian noise, receiving terminal polarization shape State is at the joint probability density function of Poincare ball upper warp and woof degree.Its expression formula is:

Wherein SNR is polarization modulation signal to noise ratio, i.e. power amplifier output P_OUTWith white Gaussian noise power N₀Ratio.

From formula (18)-(21), for the closed solutions of QAM modulation Yu the polarization modulation bit error rate, both with corresponding Order of modulation directly related.

Step 3: the realization of adaptive polarization QAM combined modulation method；

The energy efficiency of nonlinear power amplifier is together decided on by the gross energy of correct data rate with power amplifier consumption, characterizes every The just data bit number of Joule energy transmission, the main target of the present invention is just an up the energy efficiency of nonlinear power amplifier.Right In the QAM modulation of upper branch road, when power amplifier is positioned at linear zone, its bit error rate performance is less than polarization modulation, now QAM modulation efficiency Performance is more excellent；If transmitting terminal data rate increase makes power amplifier enter inelastic region, then power amplifier output signal comprises substantial amounts of mistake True component, the QAM modulation bit error rate is significantly increased, if utilize that polarized state has not by the characteristic of power amplifier non-linear effects, will A portion data rate transfers to lower branch road polarization modulation to transmit, then on the basis of can ensure that certain threshold bit error rate, The order of modulation of the upper and lower branch road of self-adaptative adjustment, thus optimize power amplifier efficiency.

The energy efficiency of power amplifier is defined as proper data rate R by the present invention_mWith power amplifier input general power P_totalRatio Value, therefore Adaptive Modulation mechanism can be converted into following restricted optimization problem:

$\underset{M_{Qk},M_{Pk}}{max}\mathrm{\η}=\frac{R_m}{P_{total}}---\left(23\right)$

s.t.

$R_m=\underset{k=0}{\overset{N-1}{\Σ}}\[{\log }_2{M}_{Qk}(1-{\mathrm{SER}}_{Qk})\]+\underset{k=0}{\overset{N-1}{\Σ}}\[{\log }_2{M}_{Pk}(1-{\mathrm{SER}}_{Pk})\]---\left(24\right)$

$R=\underset{k=0}{\overset{N-1}{\Σ}}\[{\log }_2{M}_{Qk}+{\log }_2{M}_{Pk}\]---\left(25\right)$

{SER_Qk,SER_Pk}≤SER_th (26)

0≤P_IN≤P_ISA (27)

0≤{M_Qk,M_Pk}≤2^R (28)

In formula, R is a certain moment transmitting terminal data-rate requirements, SER_thThe threshold bit error rate met it is both needed to for upper and lower branch road Value, P_INFor power amplifier input power, P_ISAFor power amplifier saturation point input power.

For radio-frequency (RF) power amplification MRF6S21050L used in the present invention, from emulation, power amplifier consumes gross energy P_totalCan To be expressed as power amplifier input power P_INSuch as minor function:

P_total=5 × 10^-4P_IN ³-6×10^-3P_IN ²+0.04P_IN+41 (29)

From formula (24), proper data rate R in a certain moment_mTotal data rate R time thus with upper and lower two Order of modulation M of branch road_Q、M_PWith bit error rate SER_Q、SER_PDetermine.And power amplifier consumes gross energy P_totalBy power amplifier input power P_IN Determine, but P_INPower amplifier operating point, i.e. power amplifier be cannot intuitively characterize and linear zone or inelastic region are operated in.Therefore should be diligent Put output rollback value OBO to characterize, as shown in formula (30), wherein P_OUTFor power amplifier input power, P_OSAFor power amplifier saturation point Output.

OBO=P_OSA/P_OUT (30)

And P_INWith P_OUTBetween relation be shown below:

$P_{OUT}=P_{OSA}-P_{IN}{\mathrm{\β}}^2{e}^{\mathrm{\β}}{\∫}_{\mathrm{\β}}^{\mathrm{\∞}}{e}^{-t}{t}^{-1}dt---\left(31\right)$

$\mathrm{\β}=\frac{P_{OSA}}{P_{IN}}---\left(32\right)$

From formula (23) (24) (30), the input data rate R in moment a certain for transmitting terminal, optimum power amplifier energy Effect is by M_Q、M_P, OBO determine.Therefore, it can the power amplifier operating point self adaptation that the data-rate requirements according to currently transmitted end determines Ground adjustment QAM modulation and the order of modulation of polarization modulation, thus the power amplifier efficiency in Continuous optimization ofdm system.

Step 4: the bit error rate is analyzed with power amplifier performance efficiency；

In order to assess the adaptive polarization QAM combined modulation method performance advantage in hoisting work exoergic efficacious prescriptions face, this Bright give corresponding simulation analysis.

Simulation result:

Fig. 3 Yu Fig. 4 represents when power amplifier is positioned at linear zone and inelastic region respectively, polarization modulation from QAM modulation different Bit error rate contrast under signal to noise ratio.When OBO value is 12dB, power amplifier is positioned at linear zone；And when OBO value is 6dB, power amplifier is positioned at Inelastic region.It can be seen that for QAM modulation, when power amplifier is positioned at linear zone, its SER performance is better than polarization modulation, But after power amplifier enters inelastic region, owing to being affected by power amplifier non-linear distortion, therefore QAM modulation performance significantly deteriorates. And for polarization modulation, although when power amplifier is positioned at linear zone bit error rate performance not as the QAM modulation performance of linear zone of existing together good, If but power amplifier enters inelastic region, because polarization modulation has the characteristic not affected by power amplifier non-linear distortion, and can be effectively sharp With the non-linear distortion signal of power amplifier, therefore polarization modulation can be operated in the inelastic region with higher-energy conversion efficiency.

Analyzing and simulation result based on above, the adaptation mechanism in the present invention arranges as follows.When a certain moment transmitting terminal Data-rate requirements is relatively low, and when power amplifier is positioned at linear zone, QAM modulation bit error rate performance is better than polarization modulation, the most preferentially uses QAM modulation transmission data bit, upper branch road transmission more information.And make power amplifier enter inelastic region when data-rate requirements raises Afterwards, QAM modulation is affected performance by non-linear distortion and is declined rapidly, if exceeding the threshold bit error rate of setting, then and will be more Data rate transfers to lower branch road polarization modulation to transmit, and lower branch road polarization modulation exponent number increases.Based on above Adaptive Modulation Mechanism, can reach to resist power amplifier non-linear distortion, optimize the purpose of power amplifier efficiency.

Fig. 5 represent transmitting terminal input data rate by 200bit/s when 1000bit/s changes, based on adaptive pole Change in the ofdm system of QAM combined modulation method, QAM modulation exponent number, polarization modulation exponent number, input power rollback value and merit The distribution curve of exoergic valid value.Emulation assumes there are 100 subcarriers, carries a width of 20MHz, be operated in 5.15GHz frequency range.QAM Modulating optional exponent number is 4 rank, 16 rank, 64 rank, and the optional exponent number of polarization modulation is 2 rank, 4 rank, 8 rank, 16 rank, 32 rank, 64 rank. The threshold bit error rate arranged is 10^-3.And for the power amplifier MRF6S21050L used in the present invention, when OBO value is more than 10dB, Power amplifier is operated in linear zone, and when OBO value is less than 10dB, power amplifier is operated in inelastic region.

From Fig. 5 (a) (b), it will be seen that when data-rate requirements R is less than 700bit/s, along with data rate Increase, QAM modulation exponent number persistently rises and polarization modulation exponent number maintains relatively low state.When data rate is more than 700bit/s After, PM order of modulation rises and polarization modulation exponent number declines.It can be seen that power amplifier OBO value continuous decrease from Fig. 5 (c), and When data rate reaches 700bit/s, OBO value reaches 10dB critical point, i.e. after data rate is more than 700bit/s, power amplifier I.e. enter inelastic region.When input data rate rises to 500bit/s or 700bit/s, it can be seen that QAM modulation exponent number rises And polarization modulation exponent number declines, this is because now power amplifier is positioned at linear zone, the performance of QAM modulation is better than polarization modulation, in order to Ensureing higher energy efficiency, the selection of system self-adaption allows the QAM modulation of branch road transmit higher data rate；And when number When continuing to increase to 800bit/s according to speed, it can be seen that QAM modulation exponent number declines and polarization modulation exponent number persistently rises.This is Because along with the increase of input data rate, power amplifier steps into inelastic region, and upper branch road QAM modulation is non-by serious power amplifier Linear distortion affects, and the polarization modulation of lower branch road has the characteristic insensitive to power amplifier non-linear distortion, and therefore system is adaptive The exponent number of the lifting polarization modulation answered, persistently reaches to optimize the purpose of power amplifier efficiency.And it will be seen that be from Fig. 5 (d) Make when power amplifier enters inelastic region, and the energy efficiency of power amplifier the most persistently increases, the just data ratio of i.e. every Joule energy transmission Special number persistently increases.This adaptive polarization-QAM combined modulation method also demonstrating present invention proposition is applied in ofdm system Time, can overcome because of the transmitting terminal input data rate power amplifier that causes of change is non-linear thus problem that bring efficiency reduces, Continuous optimization power amplifier efficiency.

Fig. 6 represents under different threshold bit error rate requirement, adaptive polarization QAM combined modulation method be fixed on 16 rank QAM modulation contrasts with the power amplifier performance efficiency of polarization modulation.Make threshold bit error rate from 10^-7To 10^-2Change, still works simultaneously There are 100 subcarriers at one, carry a width of 20MHz, be operated in the ofdm system of 5.15GHz frequency range.It can be seen that If relaxing the restriction to threshold bit error rate value, although mistake code word may be caused to increase, but the energy efficiency of power amplifier can continue Increasing, the efficiency of adaptive polarization QAM combined modulation method is also significantly better than QAM modulation and polarization modulation simultaneously.This be because of For, for the ofdm system of an application self-adapting polarization QAM combined modulation method, when power amplifier is operated in inelastic region, The polarization properties transmission information of carrier wave can be utilized, can also be QAM modulation and the PM modulation self adaptive of upper and lower branch road simultaneously Selecting optimum order of modulation, thus reduce the non-linear impact on OFDM performance of power amplifier, hoisting work exoergic is imitated.Emulation knot Fruit shows, under same threshold bit error rate value, the efficiency of the ofdm system of application self-adapting polarization QAM combined modulation method is about Twice for the ofdm system of application 16QAM modulation.

Claims (3)

1. an adaptive polarization QAM combined modulation method for hoisting work exoergic effect, is applied in ofdm system, and its feature exists In, including:

For adapting to the power amplifier performance efficiency different from inelastic region in linear zone, use the most simultaneously QAM modulation and Two kinds of modulation systems of polarization modulation；

On the operating point that power amplifier is different, for obtaining the highest power amplifier efficiency, determined QAM modulation at transmitting terminal by adaptive unit Optimal modulation exponent number respective with polarization modulation, and complete upper and lower branch data rate-allocation.

Method the most according to claim 1, it is characterised in that in described ofdm system, when power amplifier is positioned at inelastic region Comprise the method for solving of inband distortion and the QAM modulation bit error rate closed solutions of out-of-band distortion simultaneously, including:

The power amplifier being pointed to inelastic region at transmitting terminal power series model is described, after receiving terminal is to removing polarization information Signal on kth subcarrier carries out N point FFT, then on kth subcarrier, symbol can be expressed as:

In formula, a₁With a₃It is the single order in power amplifier power series model and three level numbers, Q_kWith U₃(N, expression formula k) is as follows:

Then on kth subcarrier, the Signal to Interference plus Noise Ratio of QAM modulation can be expressed as:

P in formula_KFor desired signal energy,For intermodulation component energy,For noise energy.

Now, ofdm system kth subcarrier is applied M_QkThe bit error rate of the signal of rank QAM modulation is:

SER_Qk=1-(1-P_b)²=2P_b-P_b ² (6)。

Method the most according to claim 2, it is characterised in that the reality of self-adaptive modulation method in described adaptive unit Existing, including:

The energy efficiency of power amplifier is defined as proper data rate R_mWith power amplifier input general power P_totalRatio, thus adaptive Combined modulation method is answered to be converted into following restricted optimization problem:

s.t.

{SER_Qk,SER_Pk}≤SER_th (4)

0≤P_IN≤P_ISA (5)

0≤{M_Qk,M_Pk}≤2^R (6)

In formula, η is power amplifier efficiency, M_QkWith M_PkIt is respectively in ofdm system the tune of QAM modulation and polarization modulation on kth subcarrier Exponent number processed, SER_QkWith SER_PkBeing respectively QAM modulation and the respective bit error rate of polarization modulation on kth subcarrier, N is OFDM system System subcarrier number, R is the data-rate requirements of currently transmitted end, SER_thFor threshold bit error rate value, P_INFor power amplifier input work Rate, P_ISAFor power amplifier saturation point input power.

For adaptive polarization QAM combined modulation method, power amplifier can be determined according to the data-rate requirements of currently transmitted end Operating point, by the order of modulation of self-adaptative adjustment QAM modulation Yu polarization modulation, thus optimize the power amplifier energy in ofdm system Effect.