CN106534008A - Power compensation MMSE equalization method for wireless multipath channel - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and discloses a power compensation MMSE equalization method of a wireless multipath channel; comprising: performing A/D sampling on data transmitted through a wireless multipath channel to obtain received sampling data; Perform MMSE estimation on the multipath channel to obtain the frequency domain filter coefficients of the wireless multipath channel, determine the filter error power spectrum and compensation direction of the MMSE estimation; correct the frequency domain filter coefficients of the wireless multipath channel, and obtain the error compensation Frequency-domain filter coefficients; according to the frequency-domain filter coefficients after error compensation, frequency-domain equalization is performed on the frequency-domain sampling data to obtain frequency-domain equalized data; thereby obtaining actual received data; with better performance and more Low complexity and easy engineering implementation.

Description

Power Compensated MMSE Equalization Method for Wireless Multipath Channel

technical field

The invention belongs to the technical field of wireless communication, and in particular relates to a power compensation MMSE (Minimum Mean Squared Error, minimum mean square error) equalization method of a wireless multipath channel.

Background technique

Due to the limitation of communication capabilities, traditional combat methods can only rely on the situational awareness, command and control capabilities, maneuverability, lethality, survivability and quantity of each combat unit to form its combat effectiveness, while network-centric warfare uses advanced Communication and network technology mainly rely on the cooperation and coordination among combat units to generate combat effectiveness. The battlefield situation is changing rapidly and the amount of communication data is huge. Therefore, combat troops have higher requirements for traditional military communication stations in terms of transmission rate, channel bandwidth, communication distance, mobile reception, communication networking and anti-interference capabilities.

However, the symbol crosstalk caused by the frequency selective fading caused by multipath seriously affects the reliability of broadband wireless communication. Broadband high-speed data transmission is very sensitive to channel time variation, and the increase in bandwidth will make the sampling interval smaller than the channel delay spread, thus resulting in frequency selective fading in a multipath environment. At the same time, the high-speed relative movement between wireless communication devices will cause the Doppler frequency shift effect, and the Doppler effect makes the transmission channel change rapidly with time, thus causing time-selective fading of the channel. Therefore, the wireless broadband mobile communication system will suffer from inter-symbol interference due to the influence of channel time-frequency dual selective fading. Inter-symbol interference will deteriorate the received signal, increase the bit error rate, and reduce system performance. Unable to continue working properly.

Contents of the invention

The invention provides a power compensation MMSE equalization method of a wireless multipath channel, which has better performance, lower complexity and is easy for engineering realization.

In order to achieve the above object, the present invention adopts the following technical solutions to achieve.

A power compensation MMSE equalization method of a wireless multipath channel, said method comprising the steps of:

Step 1, obtaining the intermediate frequency data to be sent, the intermediate frequency data is transmitted through the wireless multipath channel, and A/D sampling is performed on the data transmitted through the wireless multipath channel to obtain the received sampling data;

Step 2, using the training sequence to perform MMSE estimation on the wireless multipath channel to obtain the frequency domain filter coefficients of the wireless multipath channel, and determine the MMSE estimated filter coefficient according to the frequency domain filter coefficients of the wireless multipath channel The power spectrum of the device error and the direction of compensation;

Step 3, modifying the frequency domain filter coefficients of the wireless multipath channel according to the filter error power spectrum and the compensation direction, to obtain the frequency domain filter coefficients after error compensation;

Step 4, performing fast Fourier transform on the received sampling data to obtain frequency domain sampling data, and performing frequency domain equalization on the frequency domain sampling data according to the frequency domain filter coefficient after the error compensation, Obtain the data after frequency domain equalization;

Step 5: Inverse Fourier transform is performed on the frequency-domain equalized data to obtain time-domain sampling data, thereby obtaining actual received data.

Features and further improvements of the technical solution of the present invention are:

(1) In step 1,

Obtain the intermediate frequency data {a _k } that needs to be sent, the intermediate frequency data is transmitted through the wireless multipath channel, A/D sampling is performed on the data transmitted through the wireless multipath channel, and the received sampling data _{ rm } is obtained; and :

Among them, k=0,1,...,(M ₁ -1), M ₁ is the number of points after intermediate frequency sampling; m=0,1,...,(M-1), M is A/D sampling points, and M=M ₁ ; h(i) is the impulse response of the wireless multipath channel, n(i) is the additive noise, and T is the intermediate frequency sampling period.

(2) _The frequency-domain filter coefficient W after error compensation in step 3 is:

Wherein, l=0, 1, 2, ..., (M ₂ -1), M ₂ is the number of frequency domain filter coefficients, and M ₂ =M, is the filter error power spectrum, is the conjugate of H _l , SNR is the signal-to-noise ratio, ^σ2 is the variance of the additive noise, h represents the impulse response of the wireless multipath channel, Represents the mean value of the radian values of the impulse response of the wireless multipath channel, express request the symbolic value of The value of -1 or 1 indicates the compensation direction.

(3) In step 5, the actual received data {z _m } is obtained as:

Among them, R _l is the frequency domain sampling data, W _l is the frequency domain filter coefficient after error compensation.

The invention proposes a power compensation MMSE equalization method of wireless multipath channel, uses training sequence to carry out channel estimation, calculates MMSE power error value and compensation direction, and updates the equalization coefficient. Compared with the existing equalization method, the equalization method proposed by the invention has better performance, low complexity and is easy to implement in engineering.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a schematic flow diagram of a power compensation MMSE equalization method for a wireless multipath channel provided by an embodiment of the present invention;

FIG. 2 is a schematic block diagram of the principle of an equalization method based on a CPM modulated signal provided by an embodiment of the present invention;

Fig. 3 is the setting method of the Chu synchronization sequence provided by the embodiment of the present invention;

4 is a schematic diagram of a data frame structure after data recombination of a Chu synchronization sequence and a CPM modulated signal provided by an embodiment of the present invention;

Fig. 5 is the first schematic diagram of the simulation results under the SUI6 channel provided by the embodiment of the present invention;

Fig. 6 is the second schematic diagram of the simulation results under the SUI6 channel provided by the embodiment of the present invention;

Fig. 7 is the third schematic diagram of the simulation results under the SUI6 channel provided by the embodiment of the present invention;

FIG. 8 is a schematic diagram of bit error performance under different Doppler frequency shifts of the power compensation MMSE equalization method provided by the embodiment of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The adaptive equalizer based on the pilot training sequence generally includes two working modes, namely training mode and tracking mode. In the training mode, the traditional method is that the transmitting end transmits a known, fixed-length pilot training sequence, so that the equalizer at the receiving end can calculate the channel estimation value through the distorted received signal and the known transmitted signal, according to the channel estimation value Adjust the coefficients of the equalization filter to near the optimum value to realize compensation for channel distortion. A typical pilot training sequence is a binary pseudo-random sequence or a string of pre-specified data bits, followed by user data transmitted immediately after the pilot training sequence. When designing the pilot training sequence, it is required that even under the worst channel conditions, the equalizer can obtain correct filter coefficients through this sequence. This ensures that the filter coefficients of the equalizer are close to the optimum value after receiving the pilot training sequence. The time span of the whole process from adjusting parameters to forming convergence of the equalizer is a function of the equalizer algorithm, structure and channel change rate. In order to ensure that inter-symbol interference can be effectively eliminated, the equalizer needs to be trained periodically. The tracking mode is to receive the real user data and start the transmission of useful information between the two sides of the communication. This method is called adaptive equalization with training. However, in practical applications, especially in wireless mobile communications, the change of channel characteristics is often very drastic. In order to enable the equalizer to track the change of channel characteristics and effectively eliminate intersymbol interference, the transmitter has to The training sequence is sent periodically.

Based on comprehensive consideration of various factors such as the performance requirements of the communication system, channel characteristics, and implementation complexity, in practical applications, the adaptive equalizer generally uses the Zero-Forcing (ZF) equalization algorithm and the simplified MMSE equalization algorithm.

In the existing technical solution, when the frequency fading of the channel is relatively flat, the effect of ZF equalization and MMSE equalization is not much different. However, when the channel has a deep fading pole in the frequency domain, ZF equalization will amplify the noise, and MMSE equalization will not cause the channel noise to be excessively amplified, and the performance is better than zero-forcing equalization. However, there will be some residual intersymbol interference after MMSE equalization. If the residual intersymbol interference is eliminated, the bit error rate will be further reduced and the performance will be improved. The MMSE-RISIC (ResidualISI Cancellation) algorithm uses feedback operations to effectively remove residual intersymbol interference, but the disadvantage is that it increases the computational complexity.

The embodiment of the present invention provides a power compensation MMSE equalization method of a wireless multipath channel, as shown in FIG. 1 , the method includes the following steps:

Step 1: Acquire intermediate frequency data to be sent, the intermediate frequency data is transmitted through a wireless multipath channel, and A/D sampling is performed on the data transmitted through the wireless multipath channel to obtain received sampled data.

In step 1, obtain the intermediate frequency data {a _k } that needs to be sent. The intermediate frequency data is transmitted through the wireless multipath channel, and A/D sampling is performed on the data transmitted through the wireless multipath channel to obtain the received sampled data {r _m }; and:

Among them, k=0, 1,..., (M ₁ -1), M ₁ is the number of points after intermediate frequency sampling; m=0, 1,..., (M-1), M is A/D sampling , and M=M ₁ ; h(·) is the impulse response of the wireless multipath channel, n(·) is the additive noise, and T is the intermediate frequency sampling period.

Step 2, using the training sequence to perform MMSE estimation on the wireless multipath channel to obtain the frequency domain filter coefficients of the wireless multipath channel, and determine the MMSE estimated filter coefficient according to the frequency domain filter coefficients of the wireless multipath channel The power spectrum of the device error and the direction of compensation.

Step 3: Correct the frequency domain filter coefficients of the wireless multipath channel according to the filter error power spectrum and the compensation direction to obtain error compensated frequency domain filter coefficients.

The frequency domain filter coefficient W _l after error compensation in step 3 is:

Wherein, l=0, 1, 2, ..., (M ₂ -1), M ₂ is the number of frequency domain filter coefficients, and M ₂ =M, is the filter error power spectrum, is the conjugate of H _l , SNR is the signal-to-noise ratio, ^σ2 is the variance of the additive noise, h represents the impulse response of the wireless multipath channel, Represents the mean value of the radian values of the impulse response of the wireless multipath channel, express request the symbolic value of The value of -1 or 1 indicates the compensation direction.

Step 4, performing fast Fourier transform on the received sampling data to obtain frequency domain sampling data, and performing frequency domain equalization on the frequency domain sampling data according to the frequency domain filter coefficient after the error compensation, Obtain the data after frequency domain equalization.

Step 5: Inverse Fourier transform is performed on the frequency-domain equalized data to obtain time-domain sampling data, thereby obtaining actual received data.

In step 5, the actual received data {z _m } is obtained as:

Among them, R _l is the frequency domain sampling data, W _l is the frequency domain filter coefficient after error compensation.

Exemplarily, the technical solution of the present invention is described below through simulation of specific examples.

The functional block diagram of the equalization method based on CPM (Continue Phase Modulation) signal modulation is shown in Figure 2. The Chu sequence is mainly used for wireless multipath channel estimation, equalization, frequency offset and phase offset estimation.

First, the Chu sequence in this embodiment is described:

The Chu sequence belongs to the CAZAC (Constant Amplitude Zero Auto-Correlation) sequence, which is a non-binary complex sequence with excellent characteristics of constant amplitude and zero autocorrelation. CAZAC sequences have the characteristics of sharp correlation peaks and zero side lobes. CAZAC sequences are often used in synchronization algorithms in communication systems. CAZAC sequences have the following properties:

Constant envelope characteristic: CAZAC sequence amplitude of any length is constant.

Ideal periodic autocorrelation characteristics: After any CAZAC sequence is shifted by n bits, when n is not an integer multiple of the period of the CAZAC sequence, the shifted sequence is not correlated with the original sequence.

Good cross-correlation: Cross-correlation and partial correlation values are close to 0.

Low peak-to-average ratio characteristic: The signal composed of any CAZAC sequence has a very low ratio of the peak value to its mean value.

After Fourier transform, it is still a CAZAC sequence: any CAZAC sequence is still a CAZAC sequence after Fourier transform. The Chu synchronization sequence used in the embodiment of the present invention is:

The setting method of the Chu synchronization sequence is shown in Figure 3. The setting method of the Chu synchronization sequence here is to use these two training sequences for channel estimation, which can ensure that the two sequences in the received signal are not affected by other information signals. The effect of diameter expansion. The transmitting end and the receiving end work independently, so the receiving end does not know when the transmitted data arrives at the receiving end, and the receiving end needs to process to obtain the time when the transmitted data arrives at the receiving end.

Therefore, the time synchronization information can be obtained by using the two training symbols before each frame. When performing time synchronization estimation, the time domain estimation value of the channel can be obtained, and the frequency domain value of the channel estimation can be obtained after performing FFT transformation. Using the frequency domain value of channel estimation, channel equalization is performed on the data after time and carrier frequency offset correction in the frequency domain to offset the influence of the channel on the signal.

Further, as shown in FIG. 4, the data frame structure after data recombination of the Chu sequence and the CPM modulated signal and the simulation parameters of this embodiment, each data frame is composed of two Chu synchronization symbols, two data symbols and It consists of 200us frequency switching protection, and the Chu synchronization symbols and data symbols have a 22.22us cyclic prefix for anti-multipath delay.

Obtain the intermediate frequency data {a _k } that needs to be sent, the intermediate frequency data is transmitted through the wireless multipath channel, A/D sampling is performed on the data transmitted through the wireless multipath channel, and the received sampling data _{ rm } is obtained; and :

Among them, k=0, 1,..., (M ₁ -1), M ₁ is the number of points after intermediate frequency sampling; m=0, 1,..., (M-1), M is A/D sampling , and M=M ₁ ; h(·) is the impulse response of the wireless multipath channel, n(·) is the additive noise, and T is the intermediate frequency sampling period.

Due to the existence of cyclic prefixes, {a _k } can be assumed to be periodic. For any integer L, a _k = a _k±LM , and h(mT)=h((m±LM)T) for the impulse response. In the discrete domain, formula (2) can be expressed as:

R _l = H _l 4 _l + V _l , l = 0, 1, 2, ..., (M-1) (3)

In formula (3):

After frequency domain equalization, the output signal in the time domain is:

in That is, R _l is the FFT transformation of the received signal {r _m }.

If the zero-forcing equalization algorithm is used, the coefficients of the filter can be obtained by the following formula:

If the minimum mean square error (MMSE) criterion is used, the coefficients of the filter can be obtained by the following formula

If the traditional MMSE algorithm is used, there is The average error power spectrum, so an improvement can be made to the MMSE algorithm. The improved filter coefficients are:

express request the symbolic value of The value of -1 or 1 is used to determine the direction of MMSE algorithm error power spectrum compensation.

All simulations in the embodiment of the present invention are based on the data frame structure shown in FIG. 4 , and the channel model used in the simulation is mainly based on multipath Rayleigh fading channel+Gaussian noise. The multipath Rayleigh fading channel model is SUI 6 (Strong hilly): tau=[0 14000 20000]*1e-9, pdb=[0 -10 -14]. Among them, tao is the path delay vector, and pdb is the amplitude attenuation vector. The following simulation results are based on various equalization algorithm simulations of the sui6 channel.

Fig. 5 is the simulation result (frequency offset 150Hz) under the SUI6 channel, Fig. 6 is the simulation result (frequency offset 100Hz) under the SUI6 channel, Fig. 7 is the simulation result (frequency offset 50Hz) under the SUI6 channel; from Fig. 5, Fig. 6 and Fig. 7, it can be seen that when the bit error rate is at the level of 10 ^-2 , the zero-forcing equalization algorithm, the MMSE equalization algorithm and the MMSE equalization algorithm based on power compensation of the present invention all have a certain resistance to multipath and Doppler frequency shift Function, MMSE algorithm has about 3dB bit error gain than zero-forcing equalization algorithm performance, and the improved power error compensation MMSE equalization algorithm of the present invention has about 8dB bit error gain than zero-forcing equalization algorithm, thus it can be seen that MMSE equalization algorithm is carried out effectively The power error compensation is very good against channel multipath fading and Doppler frequency shift.

Fig. 8 is the bit error performance of the power error compensation MMSE equalization algorithm provided by the present invention under different Doppler frequency shifts. From the simulation results in Fig. 8, it can be seen that the improved MMSE equalization algorithm for the CPM signal can withstand a maximum of 100 Hz. Puller shift.

The above-mentioned embodiment proposes a new type of single-carrier frequency domain equalization based on power spectrum compensation of a continuous phase modulation (Continue Phase Modulation, CMP) signal based on the existing minimum mean square error (Minimum Mean Squared Error, MMSE) equalization technology Algorithm, based on the MMSE equalization algorithm, uses the known training sequence to estimate the channel, determines the MMSE power error value and the direction of the error value according to the channel estimation value, updates the equalization filter coefficients, and eliminates the residual inter-symbol interference; it can effectively remove the residual code Interference, improve demodulation performance, and has the advantages of simplicity, low computational complexity, and easy engineering implementation.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (4)

1. power back-off MMSE equalization methods of a kind of wireless multi-path channels, it is characterised in that methods described comprises the steps：

Step 1, obtains the intermediate frequency data for needing to send, and the intermediate frequency data is transmitted through wireless multi-path channels, wireless to process Data after multi-path channel transmission carry out A/D samplings, obtain the sampled data for receiving；

The wireless multi-path channels are carried out MMSE estimations using training sequence by step 2, obtain the frequency of the wireless multi-path channels Domain filter coefficient, according to the frequency domain filter coefficient of the wireless multi-path channels, determines the filter error work(that MMSE estimates Rate is composed and compensation direction；

Step 3, according to the filter error power spectrum and compensation direction, the frequency domain filter system to the wireless multi-path channels Number is modified, and obtains the frequency domain filter coefficient after error compensation；

Step 4, carries out fast Fourier transform to the sampled data for receiving, and obtains frequency domain sample data, and according to institute The frequency domain filter coefficient after error compensation is stated, frequency domain equalization is carried out to the frequency domain sample data, after obtaining frequency domain equalization Data；

Data after the frequency domain equalization are carried out inverse Fourier transform, obtain time domain sampled data by step 5, so as to obtain reality The receiving data on border.

2. a kind of power back-off MMSE equalization methods of wireless multi-path channels according to claim 1, it is characterised in that step In rapid 1,

Obtain the intermediate frequency data { a for needing to send_k, the intermediate frequency data is transmitted through wireless multi-path channels, to through wireless multi-path Data after transmission carry out A/D samplings, obtain the sampled data { r for receiving_m}；And：

$r_m=\underset{k=0}{\overset{M_1-1}{\Σ}}{a}_{k}h(mT-kT)+n\left(mT\right)$

Wherein, k=0,1 ..., (M₁- 1), M₁For the points after if sampling；M=0,1 ..., (M-1), M is A/D samplings Points, and M=M₁；Shock responses of the h () for wireless multi-path channels, n () are additive noise, and T is the if sampling cycle.

3. a kind of power back-off MMSE equalization methods of wireless multi-path channels according to claim 2, it is characterised in that step Frequency domain filter coefficient W in rapid 3 after error compensation_lFor：

$W_l=\frac{H_l^{*}}{|H_l{|}^2+1/SNR}-sign(\∠\stackrel{\‾}{h})*\frac{{\mathrm{\σ}}^2}{|H_l{|}^2+1/SNR},l=0,1,2,\mathrm{...},M_2-1$

Wherein, l=0,1,2 ..., (M₂- 1), M₂For the number of frequency domain filter coefficient, and M₂=M,For filter Ripple device error power is composed, For H_lConjugation, SNR is signal to noise ratio, σ²For additive noise Variance, h represents the shock response of wireless multi-path channels,Represent wireless multi-path channels shock response radian value it is equal Value, Expression is askedValue of symbol,Value be -1 or 1, represent compensation Direction.

4. a kind of power back-off MMSE equalization methods of wireless multi-path channels according to claim 3, it is characterised in that step In rapid 5, actual receiving data { z is obtained_mBe：

$z_m=\frac{1}{M}\underset{l=0}{\overset{M-1}{\Σ}}{W}_l{R}_l\exp (-j2\mathrm{\π}\frac{ml}{M})$

Wherein, R_lFor frequency domain sample data, W_lFor the frequency domain filter coefficient after error compensation.