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

Abstract

The invention discloses an adaptive polarization-QAM joint modulation method for improving power amplifier energy efficiency. Aiming at the problem that power amplifier nonlinear distortion reduces energy efficiency in an OFDM system, the present invention first provides an OFDM system model based on an adaptive polarization-QAM joint modulation method, that is, adding a polarization modulation branch in an OFDM system based on QAM modulation Secondly, the present invention analyzes the influence of power amplifier nonlinear distortion on QAM modulation, and utilizes the characteristic not affected by power amplifier nonlinear distortion that polar modulation has, and obtains the respective closed formula of QAM modulation and polar modulation bit error rate untie. Finally, the present invention provides an implementation method of adaptive polarization-QAM joint modulation, that is, utilizing the respective performance advantages of QAM modulation and polar modulation in the linear region and nonlinear region of the power amplifier, and transforming it into a restricted optimization problem. For the data rate requirement of the sending end at a certain moment, the system adaptively adjusts the order of the two modulation methods, thereby improving the energy efficiency of the power amplifier. The invention can effectively overcome the problem of energy efficiency reduction caused by the nonlinear distortion of the power amplifier, and improve the energy efficiency of the power amplifier in the OFDM system.

Description

An Adaptive Polarization-QAM Joint Modulation Method for Improving Power Amplifier Energy Efficiency

technical field

The invention belongs to the technical field of wireless communication, and in particular relates to an adaptive polarization-QAM joint modulation technology and the influence of nonlinear effects of power amplifiers in OFDM systems on energy efficiency. Specifically, it is an OFDM system power amplifier energy efficiency improvement method based on adaptive polarization-QAM joint modulation.

Background technique

In an Orthogonal Frequency Division Multiplexing (OFDM) system, the power amplifier (Power Amplifier: PA), which is a key component of the OFDM system transmitting unit, is the main part of energy consumption, accounting for about 10% of the total energy consumption of the terminal. 60%-70%, but the energy conversion efficiency of the power amplifier is only 5%-10% under this high energy consumption. This is because the power amplifier needs to work in the linear region to avoid nonlinear distortion, and the energy conversion efficiency in the linear region is low. In addition, the peak-to-average ratio characteristic of the OFDM signal will further increase the requirements on the linearity of the power amplifier, making it more difficult to avoid nonlinear distortion of the power amplifier.

At present, there have been some researches on suppressing nonlinear distortion of power amplifiers and improving energy efficiency of power amplifiers in wireless communication. The first type of method starts with changing the signal characteristics, and reduces the peak-to-average ratio of the OFDM signal through limiting, filtering, coding, etc., thereby reducing the impact of the nonlinearity of the power amplifier on the OFDM signal. However, this type of method mostly makes the power amplifier work in the linear region, thus limiting the improvement of the energy efficiency of the power amplifier. The second type of method starts from eliminating the nonlinear distortion of the power amplifier, and uses feedforward, negative feedback, pre-distortion and other technologies to linearize the nonlinear power amplifier. However, due to the memory effect of the power amplifier, it is difficult to completely eliminate the nonlinear distortion. At the same time, eliminating the distortion will also lose some energy. Therefore, this method also limits the improvement of the energy efficiency of the power amplifier. The third type of method starts with changing the way information is carried. For example, the polarization state of the signal has the characteristic that it is not affected by the nonlinearity of the power amplifier. Accordingly, polarization modulation (Polarization Modulation: PM) can be used to transmit data to overcome the nonlinearity of the power amplifier. The effect of distortion. However, compared with quadrature amplitude modulation (Quadrature Amplitude Modulation: QAM), polar modulation has a higher bit error rate in the linear region of the power amplifier, and its energy efficiency is lower than that of QAM modulation under the same energy consumption. Therefore, polar modulation alone can only Improve the energy efficiency of the power amplifier in the non-linear region of the power amplifier. In addition, the above three types of research on suppressing nonlinear distortion and improving power amplifier energy efficiency are all aimed at the condition of fixed data rate. In practical applications, it is impossible to make real-time optimization for the changing data rate requirements of the transmitter, and there are certain limitations.

Contents of the invention

Aiming at the nonlinear distortion effect existing in the power amplifier, the invention provides an adaptive polarization-QAM joint modulation method suitable for OFDM systems. This method utilizes the respective advantages of QAM modulation and polar modulation in the linear region and nonlinear region of the power amplifier, combines the two modulation techniques, and effectively improves the energy efficiency of the power amplifier in the OFDM system by adjusting the modulation order.

When the power amplifier is in the linear region, the QAM modulation bit error rate (Symbol Error Rate: SER) is lower than that of polar modulation, and QAM modulation can obtain higher energy efficiency under the condition that the power amplifier consumes the same energy; and when the power amplifier is in the nonlinear region , QAM modulation is affected by the nonlinear distortion of the power amplifier, and bit errors occur, but the polar modulation has the characteristic that it is not affected by the nonlinear distortion of the power amplifier. Therefore, the modulation order of QAM modulation and polar modulation can be adaptively adjusted according to the operating point of the power amplifier determined by the current data rate requirement of the transmitting end, so as to continuously optimize the energy efficiency of the power amplifier in the OFDM system. That is, when the data rate requirement is low and the power amplifier is in the linear region, more data is transmitted with QAM modulation, and the QAM modulation order is higher than the polarization modulation order; and when the data rate requirement increases, the power amplifier enters the nonlinear region Finally, reduce the QAM modulation order and increase the polar modulation order, thereby reducing the impact of nonlinear distortion on the OFDM system and improving the energy efficiency of the power amplifier. The present invention comprehensively utilizes the respective advantages of QAM modulation and polar modulation in the linear region and nonlinear region, and when the power amplifier is located in different working areas and working points due to the changing data rate requirements of the transmitting end, the self-adaptive QAM modulation and polar modulation The modulation order ensures that the power amplifier can have a high effective data rate regardless of whether it works in the linear region or the nonlinear region, thereby optimizing the energy efficiency of the power amplifier.

An adaptive polarization-QAM joint modulation method that can adaptively adjust the modulation order of the two modulation modes of QAM modulation and polar modulation according to changing data rate requirements, thereby improving the energy efficiency of OFDM system power amplifiers. The specific steps are as follows:

Step 1: adding a polar modulation branch in the traditional OFDM system based on QAM modulation;

The transmitted information is encoded to obtain a binary digital sequence, and the corresponding data rate is R. The adaptive unit determines the optimal modulation order M _Qk and M _Pk of QAM modulation and polar modulation on the kth subcarrier in the current system, and the corresponding The allocation of the data rate R _Q of the upper branch and the data rate R _P of the lower branch is completed.

For the upper branch data with a rate of R _Q , the OFDM system sequentially completes a series of operations such as QAM modulation, Inverse Fast Fourier Transform (IFFT), and digital-to-analog conversion, and then enters the power amplifier; It is the lower branch data of R _P. First, the binary digital sequence is mapped to the polarization constellation point on the Poincaré sphere through the polarization modulation constellation mapping unit, and then the output signal of the power amplifier is sequentially performed power division and phase shifting operations, thereby completing Polar modulation process. Finally, the horizontally polarized component E _H and the vertically polarized component E _V are transmitted through the horizontally polarized antenna and the vertically polarized antenna respectively.

Step 2: Solve the closed-form solutions of the respective bit error rates of QAM modulation and polar modulation in the OFDM system under the influence of the nonlinearity of the power amplifier;

In the present invention, the power amplifier power series model is used to characterize the nonlinearity of the power amplifier, then the OFDM signal modulated by QAM will be affected by the nonlinear distortion of the power amplifier, coupled with the noise in the channel, a code error will occur when the QAM demodulation is performed at the receiving end . The polar modulation is not affected by the nonlinear distortion of the power amplifier, and can use the distorted OFDM signal to transmit information, so the bit error rate of the polar modulation is only related to the noise in the channel.

Step 3: realization of adaptive polarization-QAM joint modulation method;

In the present invention, the energy efficiency of the power amplifier is defined as the ratio of the correct data rate R _m to the total input power P _total of the power amplifier. Therefore, the adaptive polarization-QAM joint modulation method in the present invention can be summarized as a restricted optimization problem. It can be seen from the optimization problem that for the data rate requirement R of the transmitting end at a certain moment, the optimal power amplifier energy efficiency is determined by the QAM modulation order M _Q , the polarization modulation order _MP and the output power back-off value of the power amplifier (Output Back Off:OBO) are jointly determined by the three. Therefore, after determining the working area and working point of the power amplifier at this time, the energy efficiency of the power amplifier in the OFDM system can be improved by adaptively adjusting the respective modulation orders of QAM modulation and polar modulation.

Advantages of the present invention:

1. The adaptive polarization-QAM joint modulation method in the present invention not only uses the amplitude and phase characteristics (signal scalar characteristics) of QAM modulation to carry information, but also uses the polarization state attribute of the signal to carry information, making full use of Vector properties of the signal polarization domain.

2. In the present invention, the influence of the nonlinear distortion of the power amplifier on the energy efficiency is considered, and an adaptive polarization-QAM joint modulation method based on the adaptive modulation order is adopted in the OFDM system. For the data rate requirement of the sending end at a certain moment, it is transformed into a restrictive optimization problem, and the energy efficiency of the power amplifier in the OFDM system is improved by selecting the optimal modulation order to transmit data.

3. Compared with the OFDM system using fixed-order QAM modulation or polar modulation, the power amplifier energy efficiency performance of the adaptive polarization-QAM joint modulation in the present invention can be optimized to a certain extent.

Description of drawings

Fig. 1 is the OFDM system transmitter model based on adaptive polarization-QAM joint modulation method adopted in the present invention;

Fig. 2 is the OFDM system receiver model based on adaptive polarization-QAM joint modulation method adopted in the present invention;

Fig. 3 is the bit error rate performance of polar modulation and QAM modulation in the linear region of power amplifier among the present invention;

Fig. 4 is the bit error rate performance of polar modulation and QAM modulation in power amplifier nonlinear region in the present invention;

Fig. 5 shows the optimal QAM modulation and polar modulation order determined by the adaptive joint modulation method, the power amplifier output power fallback value and the corresponding power amplifier energy efficiency when the data rate requirement of the transmitting end changes in the present invention;

Fig. 6 is the power amplifier energy efficiency comparison of the OFDM system adopting the adaptive joint modulation method in the present invention and the OFDM system adopting fixed-order QAM modulation and polar modulation under different bit error rate threshold requirements;

detailed description

The present invention will be further described in detail below in conjunction with the accompanying drawings.

The invention is an adaptive polarization-QAM joint modulation method that can adaptively adjust the modulation orders of two modulation modes, QAM modulation and polar modulation, according to changing data rate requirements, thereby improving the energy efficiency of OFDM system power amplifiers.

In the OFDM system, the power amplifier, which is a key component of the OFDM system transmitting unit, is the main part of energy consumption, accounting for about 60%-70% of the total energy consumption of the terminal, but the energy conversion efficiency of the power amplifier is only 5%-10%, this is because the power amplifier needs to work in the linear region to avoid nonlinear distortion, and the energy conversion efficiency in the linear region is low. In addition, the peak-to-average ratio characteristic of the OFDM signal will further increase the requirements on the linearity of the power amplifier, making it more difficult to avoid nonlinear distortion of the power amplifier.

In order to reduce the influence of the non-linear effect of the power amplifier on the energy efficiency of the power amplifier in the OFDM system, the present invention proposes an adaptive polarization-QAM joint modulation method based on the adaptive modulation order to improve the energy efficiency performance of the power amplifier in the OFDM system. The specific implementation is as follows: when the data rate requirement is low and the power amplifier is in the linear region, more data is transmitted with QAM modulation, and the QAM modulation order is higher than the polar modulation order; and when the data rate requirement increases, the power amplifier enters After the nonlinear zone, the bit error rate of QAM modulation increases, and when it exceeds a certain bit error rate threshold, the order of QAM modulation is reduced, the order of polar modulation is increased, and more data is transmitted with polar modulation, thereby reducing nonlinearity The impact of distortion on the OFDM system, and improve the energy efficiency of the power amplifier.

The self-adaptive polarization-QAM joint modulation method for improving the power amplifier energy efficiency of the OFDM system proposed in the present invention includes the simultaneous use of two modulation modes of QAM modulation and polarization modulation in the traditional OFDM system, and the respective bit error rates of QAM modulation and polarization modulation The solution of the closed-form solution, the realization process of the adaptive polarization-QAM joint modulation method, the simulation analysis of bit error rate and power amplifier energy efficiency performance, etc., are as follows:

Step 1: using QAM modulation and polar modulation in the OFDM system at the same time;

The transmitter model of the OFDM system using adaptive polarization-QAM joint modulation is shown in Figure 1, in which the upper branch completes the QAM modulation, and the lower branch completes the polarization modulation. In the figure, the adaptive unit determines the optimal modulation order of QAM modulation and polar modulation according to the current data rate requirements of the sending end and completes the data rate allocation; the QAM modulation unit performs QAM modulation on the binary digital sequence allocated by the upper branch; the OFDM signal processing unit Complete a series of operations such as serial-to-parallel conversion, inverse fast Fourier transform, parallel-to-serial conversion, and digital-to-analog conversion; the power amplifier amplifies the input signal; the band-pass filter filters out the intermodulation in the output signal of the power amplifier that falls outside the frequency band of the original signal component; the polarization modulation unit is divided into three parts, in which the constellation mapping unit completes the mapping of the binary number sequence to the polarization state constellation point on the Poincaré sphere, and the power divider divides the output signal of the power amplifier into two signal components and sets the corresponding amplitude The phase shifter sets the phase difference of the two signal components; the vertically and horizontally polarized antennas transmit the two signal components. The specific process is as follows:

At the sending end of the system, for the data rate requirement R at a certain moment, the adaptive modulation order unit determines the optimal modulation order M _Qk and M _Pk of QAM modulation and polar modulation on the kth subcarrier in the current system, corresponding Complete the data rate allocation of the upper branch R _Q and the lower branch R _P , where N is the number of subcarriers in the OFDM system.

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Equation (1) represents the correct data rate that the upper branch can achieve under ideal conditions, but when the OFDM signal x(t) carrying QAM modulated data passes through the power amplifier, the nonlinear distortion of the power amplifier will affect the correct data rate of the upper branch Thus affecting the energy efficiency of the system. Therefore, the present invention uses a power series form with clear physical meaning and strong universality to characterize the nonlinear power amplifier, and studies its influence on the performance of the OFDM system based on the polarization-QAM joint modulation method.

For a power amplifier in the form of a power series, the relationship between its input signal x(t) and output signal y(t) can be expressed as:

y(t)＝a ₁ x(t)+a ₃ x ³ (t) (3)

In the formula, a ₁ and a ₃ are the output polynomial coefficients of the nonlinear power amplifier, which are related to the hardware characteristics of the nonlinear power amplifier.

For the OFDM signal x(t) at the input end of the power amplifier in the present invention, its time-domain form can be expressed as

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Where X _k represents the data symbol on the kth subcarrier, T represents the OFDM symbol period, and N represents the number of subcarriers.

Then the signal at the output of the power amplifier can be expressed as:

$\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}\underset{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}\underset{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

y(t) contains several kinds of intermodulation products introduced by the original signal and nonlinear power amplifier. After the mixed signal y(t) is passed into the band-pass filter, the signal components far away from the OFDM frequency band in the above formula are filtered out, and the output signal of the band-pass filter is y'(t).

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}\underset{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

At this time, the serial signal y'(t) still contains the amplified original signal and several intermodulation products falling within the frequency band of the original OFDM signal.

In the lower branch of polarization modulation, the digital sequence R _P is mapped into the M _P -order polarization state constellation through the polarization state Polarized state It can be represented by the polarization phase descriptor (δ _i ,φ _i )(δ _i ∈[0,π/2),φ _i ∈[0,2π)). In order to add the information carried by the polarization state to the OFDM signal at the output end of the power amplifier, it is necessary to make the signal y'(t) pass through the power dividing unit and the phase shifting unit in sequence. Therefore, the power dividing network and the phase shifting network can be respectively used by the transfer function and Expressed as:

${\stackrel{<span\; class="notranslate">\; \&Right\; Arrow;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; cos\&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ {\mathrm{<span\; class="notranslate">\; sin\&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Among them, the power divider controls the amplitude ratio of the signal, and the phase shifter controls the phase difference of the signal, so the polarization state information carried by the polarization modulation is used in the lower branch can be uniquely determined by the following formula.

After the signal y'(t) passes through the power dividing network and the phase shifting network, the transmitted signal vectors at the vertically and horizontally polarized antenna ports are:

From this, the polarization phase descriptor of the transmitted signal vector can be obtained as:

${\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; V</span>}}<span\; class="notranslate">\; |</span>}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; |</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

It can be seen that the transmitted signal on the same subcarrier All signal components including the distorted signal and the undistorted signal still have the same parameters as the power dividing network and the phase shifting network when transmitting, that is, the polarization state of the signal does not change, so it can be proved that the polarization state can be independent of the power amplifier Influence of non-linear characteristics. Finally, the two orthogonally polarized components E _H and E _V of the signal can be transmitted by a pair of horizontal-vertical orthogonal dual-polarized antennas.

Step 2: Solve the closed-form solutions of the respective bit error rates of QAM modulation and polar modulation in the OFDM system under the influence of the nonlinearity of the power amplifier;

The receiver model of OFDM system based on adaptive polarization-QAM joint modulation method is shown in Figure 2. Since the polar modulation unit changes the original amplitude and phase information of the signal when the polar modulation is performed at the transmitting end, the polar information in the signal should be directly extracted from the _orthogonal polarization components E _H and EV at the receiving end , and use the polarization matching and combining technology to realize polarization demodulation, restore the information carried by the polarization state and at the same time restore the amplitude ratio and phase difference of the OFDM signal based on QAM modulation, and then through the fast Fourier transform, QAM Demodulation and other operations to restore all data information.

Because the present invention focuses on the relationship between the modulation order and energy efficiency under changing data rate requirements, the present invention considers the AWGN channel without affecting the adaptive modulation method. Let r(t) be the signal at the receiving end of OFDM without polarization modulation, then r(t) can be approximately considered to be composed of the OFDM signal y'(t) containing the original signal and the distorted signal and the additive Gaussian white in the channel The noise n(t) consists of, namely:

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

Perform FFT transformation on the signal on the kth subcarrier at the receiving end, then the symbol on the kth subcarrier at the receiving end can be expressed as:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}\\ <span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\underset{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}}\underset{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}\\ <span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}\\ <span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; N</span>}}\underset{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\\ <span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{<span\; class="notranslate">\; |</span>}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ <span\; class="notranslate">\; +</span>\underset{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&NotEqual;</span>\mathrm{<span\; class="notranslate">\; k</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

In the formula, the expressions of Q _k and U ₃ (N,k) are as follows:

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; k</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 16</span>}<span\; class="notranslate">\; )</span>$

The first item in formula (14) is the desired signal, the second and third items are the in-band distortion and out-of-band extension signal formed by intermodulation respectively, and the fourth item is noise. It can be seen that the power amplifier not only linearly amplifies the original OFDM signal, but also produces new frequency components due to the cubic component of the nonlinear power amplifier at the transmitter. For a subcarrier of a certain frequency, some of the new frequency components fall within the frequency band of the subcarrier and become in-band distorted signals, while the rest of the signals fall outside the frequency band of the subcarrier and become out-of-band extension signals. It can be seen that The nonlinearity of the power amplifier at the transmitting end will generate a large number of interference signal components, which will significantly increase the bit error rate at the receiving end.

For the received signal on the kth subcarrier, the SINR is:

${\mathrm{<span\; class="notranslate">\; SINR</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{{\mathrm{<span\; class="notranslate">\; IM</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 17</span>}<span\; class="notranslate">\; )</span>$

where P _K is the expected signal energy, is the energy of the intermodulation component, is the noise energy. It can be seen that the existence of intermodulation components reduces the signal-to-interference-noise ratio at the receiving end, thereby increasing the bit error rate at the receiving end.

At this time, the bit error rate of the signal applied to the M _Qk order QAM modulation on the kth subcarrier of the OFDM system is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; (</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; SINR</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 18</span>}<span\; class="notranslate">\; )</span>$

SER _Qk ＝1-(1-P _b ) ² ＝2P _b -P _b ² (19)

For polar modulation, the bit error rate on each subcarrier k after the AWGN channel can be expressed as:

${\mathrm{<span\; class="notranslate">\; SER</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 20</span>}<span\; class="notranslate">\; )</span>$

Where M _Pk is the polarization modulation order of the lower branch; is the joint probability density function of the latitude and longitude of the polarization state of the receiving end on the Poincare sphere after adding Gaussian white noise to the channel. Its expression is:

Among them, SNR is the polarization modulation signal-to-noise ratio, that is, the ratio of the power amplifier output power P _OUT to the Gaussian white noise power N ₀ .

It can be seen from formulas (18)-(21) that for the closed-form solutions of QAM modulation and polar modulation BER, both are directly related to the corresponding modulation order.

Step 3: realization of adaptive polarization-QAM joint modulation method;

The energy efficiency of the nonlinear power amplifier is determined by the correct data rate and the total energy consumed by the power amplifier, which represents the correct number of data bits per joule of energy transmission. The main goal of the present invention is to improve the energy efficiency of the nonlinear power amplifier. For the QAM modulation of the upper branch, when the power amplifier is in the linear region, its bit error rate performance is lower than that of polar modulation, and the QAM modulation energy efficiency performance is better at this time; if the data rate of the sending end increases and the power amplifier enters the nonlinear region, the power amplifier The output signal contains a large number of distortion components, and the bit error rate of QAM modulation increases greatly. If the polarization state has the characteristic that it is not affected by the nonlinearity of the power amplifier, and a part of the data rate is transferred to the polarization modulation of the lower branch, then On the basis of ensuring a certain bit error rate threshold, the modulation order of the upper and lower branches can be adaptively adjusted, thereby optimizing the energy efficiency of the power amplifier.

In the present invention, the energy efficiency of the power amplifier is defined as the ratio of the correct data rate R _m to the total input power P _total of the power amplifier, so the adaptive modulation mechanism can be transformed into the following restrictive optimization problem:

$\underset{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; k</span>}}}{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}\mathrm{<span\; class="notranslate">\; \&eta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; l</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; three</span>}<span\; class="notranslate">\; )</span>$

s.t.

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; SER</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; SER</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; four</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 25</span>}<span\; class="notranslate">\; )</span>$

{SER _Qk ,SER _Pk }≤SER _th (26)

0≤P _IN ≤P _ISA (27)

0≤{M _Qk ,M _Pk }≤2 ^R (28)

In the formula, R is the data rate requirement of the transmitting end at a certain moment, SER _th is the bit error rate threshold that both the upper and lower branches need to meet, P _IN is the input power of the power amplifier, and P _ISA is the input power of the power amplifier saturation point.

For the radio frequency power amplifier MRF6S21050L used in the present invention, it can be seen from the simulation that the power amplifier consumes the total energy P _total can be expressed as the following function of the power amplifier input power P _IN :

P _total ＝5×10 ^-4 P _IN ³ -6×10 ^-3 P _IN ² +0.04P _IN +41 (29)

It can be seen from formula (24) that the correct data rate R _m at a certain moment is determined by the total data rate R at that time, the modulation orders M _Q , _MP of the upper and lower branches, and the bit error rates SER _Q , SER _P. The total energy consumed by the power amplifier P _total is determined by the input power P _IN of the power amplifier, but P _IN cannot intuitively represent the operating point of the power amplifier, that is, whether the power amplifier works in the linear region or the nonlinear region. Therefore, it should be characterized by the power amplifier output power backoff value OBO, as shown in formula (30), where P _OUT is the input power of the power amplifier, and P _OSA is the output power at the saturation point of the power amplifier.

OBO＝P _OSA /P _OUT (30)

The relationship between P _IN and P _OUT is as follows:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; \&beta;</span>}}^{\mathrm{<span\; class="notranslate">\; \&infin;</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 31</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; A</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 32</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formulas (23)(24)(30) that for the input data rate R at a certain moment at the transmitting end, the optimal power amplifier energy efficiency is determined by M _Q , _MP , and OBO. Therefore, the modulation order of QAM modulation and polar modulation can be adaptively adjusted according to the operating point of the power amplifier determined by the current data rate requirement of the transmitting end, so as to continuously optimize the energy efficiency of the power amplifier in the OFDM system.

Step 4: Performance analysis of bit error rate and power amplifier energy efficiency;

In order to evaluate the performance advantage of the adaptive polarization-QAM joint modulation method in improving the energy efficiency of the power amplifier, the present invention provides corresponding simulation analysis.

Simulation results:

Figure 3 and Figure 4 show the bit error rate comparison of polar modulation and QAM modulation at different SNRs when the power amplifier is located in the linear region and nonlinear region respectively. When the OBO value is 12dB, the power amplifier is in the linear region; and when the OBO value is 6dB, the power amplifier is in the nonlinear region. It can be seen from the figure that for QAM modulation, when the power amplifier is in the linear region, its SER performance is better than polar modulation, but when the power amplifier enters the nonlinear region, due to the influence of the nonlinear distortion of the power amplifier, the QAM modulation performance deteriorates significantly . For polar modulation, although the bit error rate performance is not as good as that of QAM modulation in the linear region when the power amplifier is in the linear region, if the power amplifier enters the nonlinear region, because the polar modulation has the characteristic that it is not affected by the nonlinear distortion of the power amplifier. , can effectively utilize the nonlinear distortion signal of the power amplifier, so the polar modulation can work in the nonlinear region with higher energy conversion efficiency.

Based on the above analysis and simulation results, the adaptive mechanism in the present invention is set as follows. When the data rate requirement at the sending end is low at a certain moment and the power amplifier is in the linear region, the bit error rate performance of QAM modulation is better than that of polar modulation, so QAM modulation is preferred to transmit data bits, and the upper branch transmits more information. However, when the demand for data rate increases and the power amplifier enters the nonlinear region, the performance of QAM modulation will drop rapidly due to the influence of nonlinear distortion. If the set bit error rate threshold is exceeded, more data rate will be handed over to the polar modulation of the lower branch. After transmission, the polarization modulation order of the lower branch increases. Based on the above adaptive modulation mechanism, it is possible to achieve the purpose of combating the nonlinear distortion of the power amplifier and optimizing the energy efficiency of the power amplifier.

Figure 5 shows that when the input data rate of the transmitter changes from 200bit/s to 1000bit/s, in the OFDM system based on the adaptive polarization-QAM joint modulation method, the QAM modulation order, polarization modulation order, and input power fallback value and the distribution curve of the energy efficiency value of the power amplifier. In the simulation, it is assumed that there are 100 subcarriers, the bandwidth is 20MHz, and it works in the 5.15GHz frequency band. The optional order of QAM modulation is 4th order, 16th order, and 64th order, and the optional order of polar modulation is 2nd order, 4th order, 8th order, 16th order, 32nd order, and 64th order. The set bit error rate threshold is 10 ^-3 . As for the power amplifier MRF6S21050L used in the present invention, when the OBO value is greater than 10dB, the power amplifier works in the linear region, and when the OBO value is less than 10dB, the power amplifier works in the nonlinear region.

From Figure 5(a)(b), we can see that when the data rate requirement R is less than 700bit/s, as the data rate increases, the QAM modulation order continues to rise while the polarization modulation order remains relatively low. low state. When the data rate exceeds 700bit/s, the PM modulation order increases and the polarization modulation order decreases. It can be seen from Figure 5(c) that the OBO value of the power amplifier continues to decline, and when the data rate reaches 700bit/s, the OBO value reaches a critical point of 10dB, that is, when the data rate exceeds 700bit/s, the power amplifier enters the nonlinear region . When the input data rate increases to 500bit/s or 700bit/s, it can be seen that the order of QAM modulation increases and the order of polar modulation decreases. This is because the power amplifier is in the linear region at this time, and the performance of QAM modulation is better than that of polar modulation. , in order to ensure higher energy efficiency, the system adaptively selects the QAM modulation of the upper branch to transmit a higher data rate; and when the data rate continues to increase to 800bit/s, it can be seen that the QAM modulation order decreases and extremely The modulation order continues to rise. This is because as the input data rate increases, the power amplifier gradually enters the nonlinear region, and the QAM modulation of the upper branch is seriously affected by the nonlinear distortion of the power amplifier, while the polarization modulation of the lower branch is insensitive to the nonlinear distortion of the power amplifier. characteristics, so the system self-adaptively increases the order of polar modulation, and continuously achieves the goal of optimizing the energy efficiency of the power amplifier. From Figure 5(d), we can see that even when the power amplifier enters the nonlinear region, the energy efficiency of the power amplifier continues to increase, that is, the number of correct data bits per joule of energy transmission continues to increase. This also proves that when the adaptive polarization-QAM joint modulation method proposed in the present invention is applied to an OFDM system, it can overcome the problem of energy efficiency reduction caused by the nonlinearity of the power amplifier caused by the change of the input data rate at the sending end, and continuously optimize the power amplifier. efficiency.

Figure 6 shows the power amplifier energy efficiency performance comparison between the adaptive polarization-QAM joint modulation method and the fixed 16th-order QAM modulation and polarization modulation under different bit error rate threshold requirements. Change the bit error rate threshold from 10 ^-7 to 10 ^-2 while still working in an OFDM system with 100 sub-carriers, a bandwidth of 20MHz, and a frequency band of 5.15GHz. It can be seen from the figure that if the restriction on the threshold value of the bit error rate is relaxed, although the error code words may increase, the energy efficiency of the power amplifier can continue to increase, and the energy efficiency of the adaptive polarization-QAM joint modulation method will also increase. Significantly better than QAM modulation and polar modulation. This is because, for an OFDM system applying the adaptive polarization-QAM joint modulation method, when the power amplifier works in the nonlinear region, the polarization property of the carrier can be used to transmit information, and at the same time, it can also be used for the QAM modulation of the upper and lower branches. The PM modulation adaptively selects the optimal modulation order, thereby reducing the impact of the nonlinearity of the power amplifier on OFDM performance and improving the energy efficiency of the power amplifier. The simulation results show that the energy efficiency of the OFDM system using adaptive polarization-QAM joint modulation method is about twice that of the OFDM system using 16QAM modulation under the same bit error rate threshold.

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.