CN104639489A - Joint sidelobe suppression method and device based on bipolar coding and windowing - Google Patents

Abstract

The invention discloses a joint sidelobe suppression method and a joint sidelobe suppression device based on bipolar coding and windowing. Baseband data generated by a digital information source module are coded by a channel of a channel coding module; after being subjected to serial-to-parallel conversion of a modulation mapping and serial-to-parallel conversion module of a modulation mapping module, the baseband data are sent into a bipolar coding module; the bipolar coding module carries out bipolar coding on parallel data in sequence and then sends the parallel data into an IFFT transformation module for IFFT transformation; the data subjected to the IFFT transformation are sent into a parallel-to-serial conversion module for parallel-to-serial conversion after passing through a raised cosine window of a windowing module and are then sent into a radio frequency module to form a final OFDM modulation signal. According to the method, the sidelobe suppression performance can be improved under the conditions that the calculation complexity is not increased and interference is not introduced, so that the interference of a cognitive user on a main user is suppressed to the maximum extent.

Description

Side lobe suppression method and device is combined based on bipolar coding and windowing

Technical field

The invention belongs to communication technical field, be specifically related to a kind ofly combine side lobe suppression method and device based on bipolar coding and windowing.

Background technology

Along with the continuous growth of wireless traffic, frequency spectrum resource becomes growing tension.Therefore, in the communication technology from now on, how to improve the availability of frequency spectrum and become one of subject matter needing to solve.In order to maximize the availability of frequency spectrum as much as possible, Chinese scholars proposes cognitive radio technology.Cognitive radio technology requires that cognitive user can utilize the untapped frequency range of primary user (idle frequency range) to communicate, and the interference of cognitive user to primary user is controlled within tolerable scope.OFDM technology is widely used in a wireless communication system, it has the higher availability of frequency spectrum, and the parameter such as subcarrier modulation modes, occupied bandwidth can control flexibly, therefore OFDM technology is applied in the requirement that effectively can meet cognitive radio technology in cognitive radio technology.But ofdm modulation signal exists larger out-of-band power to be revealed, therefore at cognitive user transmitting terminal, close primary user simply and take OFDM subcarrier corresponding to frequency range and still can cause larger secondary lobe interference to primary user, cause primary user can not proper communication.Therefore, at cognitive user transmitting terminal, the attenuation outside a channel adopting certain technology to accelerate OFDM power spectrum seems especially important.

Publication number is in the Chinese patent application " frequency spectrum coexistence method and frequency spectrum processing device for ofdm system " of CN103581917, propose a kind of method by inserting Interference Cancellation subcarrier at target frequency bands (namely needing to produce the frequency range of frequency spectrum groove) two ends and produce frequency spectrum groove, suppressed sidelobes disturbs.But the computation complexity of this method is higher, be unfavorable for real-time application, and when adopting less counteracting subcarrier, Sidelobe Suppression effect is poor.

Publication number is in the Chinese patent application " a kind of OFDM cognitive radio system and nonopiate active side lobe suppression method " of CN103117977, propose a kind of method inserting Interference Cancellation subcarrier in nonopiate position, the method performance is compared traditional Interference Cancellation subcarrier method and is increased in Sidelobe Suppression performance, but such a method introduces inter-sub-carrier interference, and increase computation complexity further, be unfavorable for real-time application.

Summary of the invention

Technical problem to be solved by this invention is to provide a kind ofly combines side lobe suppression method and device based on bipolar coding and windowing, it can improve Sidelobe Suppression performance when not increasing computation complexity and not introducing interference, thus suppresses cognitive user to the interference of primary user to greatest extent.

For solving the problem, the present invention is achieved by the following technical solutions:

Combine a side lobe suppression method based on bipolar coding and windowing, comprise following steps:

(1) produce independent memoryless base band data, wherein independent memoryless referring between each base band data is separate, and the value of each base band data is equiprobable;

(2) chnnel coding is carried out to base band data;

(3) carry out modulation to the data after coding to map, obtain the data after M modulation mapping;

(4) carry out serioparallel exchange to the data after modulation mapping, the data of M serial are transformed into the parallel data on v road, the number of every channel parallel data is N;

(5) successively bipolar coding is carried out to v channel parallel data;

(6) form v OFDM symbol after carrying out IFFT conversion respectively to the v circuit-switched data after bipolar coding, what the IFFT of each OFDM symbol converted counts as N;

(7) v the OFDM symbol obtained after being converted by IFFT carries out windowing respectively, and wherein windowed function is raised cosine windows;

(8) OFDM symbol of the v after windowing is carried out parallel-serial conversion;

(9) rf modulations is carried out to serial data, form final ofdm modulation signal.

The modulation carried out in above-mentioned steps (3) is mapped as 16QAM modulation and maps.

1 circuit-switched data in v channel parallel data in above-mentioned steps (5) after bipolar coding meets a _{i, 2k}=-a _{i, 2k-1}, k=1,2, N/2+1.

The mathematic(al) representation of the raised cosine windows described in above-mentioned steps (7) is:

$w_n=\left\{\begin{array}{cc}0.5+0.5\cos \left(\mathrm{\&pi;}\frac{n}{\mathrm{\&beta;N}}\right),& 0\&le;n<\mathrm{\&beta;N}\\ 1,& \mathrm{\&beta;}\&le;n<N\\ 0.5+0.5\cos \left(\mathrm{\&pi;}\frac{n-N}{\mathrm{\&beta;N}}\right),& N\&le;n<(1+\mathrm{\&beta;})N\end{array}\right.$

In formula, w _nfor raised cosine windows, β is the rolloff-factor of window function, and N is counting of IFFT conversion, and n is the sample number of window function sequence.

Combine a side lobe suppression device based on bipolar coding and windowing, be made up of digital source module, channel coding module, modulation mapping block, serioparallel exchange module, bipolar coding module, IFFT conversion module, windowing module, parallel serial conversion module and radio-frequency module; The input of modulation mapping block is sent into after the output channel coding module of digital source module, the output of modulation mapping block is through the input of serioparallel exchange module and bipolar coding module, the output of bipolar coding module is connected through the input of IFFT conversion module with windowing module, and the output of windowing module connects the input of radio-frequency module.

Above-mentioned modulation mapping block is that 16QAM modulates mapping block.

Compared with prior art, tool of the present invention has the following advantages:

(1) what realize ofdm system by bipolar coding and windowing process combines Sidelobe Suppression, and it does not need complicated computational process, thus can improve Sidelobe Suppression performance when not increasing hardware implementing complexity.

(2) be hardware implementing platform with FPGA, improve the parallel processing capability of system, add the integrated level of system, reduce cost and power consumption.

(3) the OFDM symbol subcarrier modulation modes involved by method that the present invention proposes is 16QAM, and adjacent sub-carrier carries identical bit information, serves the effect of frequency diversity, contributes to the error performance of raising system.

Accompanying drawing explanation

Fig. 1 combines side lobe suppression method flow chart based on bipolar coding and windowing in cognitive OFDM.

Fig. 2 is based on the structured flowchart of combining side lobe suppression device of bipolar coding with windowing in cognitive OFDM.

Fig. 3 is the structured flowchart of channel coding module.

Fig. 4 is the structured flowchart of bipolar coding module.

Fig. 5 is the Sidelobe Suppression performance simulation comparison diagram of this method and conventional method.

Fig. 6 is the error performance simulation comparison figure of this method and conventional method.

Embodiment

The power spectrum function of an OFDM symbol can be calculated by following formula:

$S_x\left(f\right)=\underset{i=0}{\overset{N-1}{\mathrm{\&Sigma;}}}\frac{{\left|X_i\left(f\right)\right|}^2}{T_S}---\left(1\right)$

In formula, i represents i-th subcarrier of an OFDM symbol, T _sbe the duration of an OFDM symbol, N is the sub-carrier number of an OFDM symbol, and f is the frequency range that an OFDM symbol occupies.X _if () is the frequency spectrum function of the i-th subcarrier before bipolar coding and windowing, it can be calculated by following formula:

$X_i\left(f\right)=\sqrt{N}{T}_S\cos \left(\mathrm{\&pi;i}\right)\left[\frac{\sin \mathrm{\&pi;}(f{T}_{S}N-i)}{\mathrm{\&pi;}(f{T}_{S}N-i)}\right]---\left(2\right)$

As can be seen from formula (2), the single OFDM subcarrier spectrum before bipolar coding and windowing only with speed decline, thus out-of-band radiation power is comparatively large, causes larger secondary lobe interference.

After bipolar coding, the frequency spectrum function that the subcarrier pair of i-th and the i-th+1 sub-carrier wave composition is formed is:

$X_i\left(f\right)-X_{i+1}\left(f\right)=-\sqrt{N}{T}_S\left[\frac{\sin \mathrm{\&pi;}(f{T}_{S}N-i)}{\mathrm{\&pi;}(f{T}_{S}N-i-1)(f{T}_{S}N-i)}\right]---\left(3\right)$

As can be seen from formula (3), the frequency spectrum of the subcarrier pair after bipolar coding with speed decline, fall off rate is obviously accelerated, and thus reduces out-of-band radiation power, inhibits secondary lobe to disturb.

The OFDM symbol formed after bipolar coding and IFFT conversion is sent into windowing module and carries out windowing operation, the out-of-band power rate of decay of OFDM symbol frequency spectrum can be accelerated further, thus suppressed sidelobes interference further.For raised cosine window, the OFDM symbol power spectrum function after windowing is:

$S_{\mathrm{RC}}\left(f\right)=S_x\left(f\right)\frac{\cos \left(\mathrm{\&beta;\&pi;f}{T}_S\right)}{1-4{\mathrm{\&beta;}}^2{f}^2{T}_S}---\left(4\right)$

In formula, β is the rolloff-factor of window function.As can be seen from formula (4), the power spectrum function of the OFDM symbol after windowing with rate attenuation, thus windowing operation can further suppressed sidelobes interference.

Based on above principle, a kind of designed by the present invention combines side lobe suppression method based on bipolar coding and windowing, as shown in Figure 1, comprises following steps:

(1) base band data digital source module sent is sent into channel coding module and is carried out chnnel coding, to correct the burst error that may cause in transmission process.

(2) by coding after data send into 16QAM modulate mapping block carry out modulation map, obtain modulate map after data, be set to by coding after data send into 16QAM modulate mapping block carry out modulation map, obtain modulation mapping after data, be set to c _index, index=1,2 ... M, M are the data amount check after modulation maps, and index is the data subscript after modulation maps.

(3) data after modulation being mapped carry out serioparallel exchange, the data of M serial are transformed into the parallel data a on v road _i,j, i=1,2 ... v, j=1,2 ... N, the number of each channel parallel data is N.Following relation is met: M=vN between M, v, N.In the preferred embodiments of the present invention, M=1280, v=10, N=128.

(4) data after modulation being mapped are sent into bipolar coding module and are carried out bipolar coding, make 1 circuit-switched data in the v channel parallel data after encoding meet a _{i, 2k}=-a _{i, 2k-1}, k=1,2, N/2+1.

(5) parallel data after bipolar coding is sent into IFFT conversion module and carry out IFFT conversion, counting as N of IFFT conversion.V OFDM symbol is formed after IFFT conversion.

(6) 10 OFDM symbol after being converted by IFFT are sent into windowing modules and are carried out windowing, and what finally complete bipolar coding and windowing combines Sidelobe Suppression process.Because the Sidelobe Suppression performance of raised cosine window is better than other window functions, the window function of therefore windowing module adopts raised cosine window to realize, and the mathematic(al) representation of raised cosine window is:

$w_n=\left\{\begin{array}{cc}0.5+0.5\cos \left(\mathrm{\&pi;}\frac{n}{\mathrm{\&beta;N}}\right),& 0\&le;n<\mathrm{\&beta;N}\\ 1,& \mathrm{\&beta;}\&le;n<N\\ 0.5+0.5\cos \left(\mathrm{\&pi;}\frac{n-N}{\mathrm{\&beta;N}}\right),& N\&le;n<(1+\mathrm{\&beta;})N\end{array}\right.---\left(5\right)$

In formula, β is the rolloff-factor of window function, and N is counting of IFFT conversion.In the preferred embodiment of the present invention, β=0.125, N=128.

(7) send into radio-frequency module after the OFDM symbol after windowing being carried out parallel-serial conversion, form final ofdm modulation signal.Step (1) can suppress the side-lobes power of ofdm modulation signal to (6).

Side lobe suppression device is combined based on bipolar coding and windowing based on a kind of designed by said method, as shown in Figure 2, mapping block, serioparallel exchange module, bipolar coding module, IFFT conversion module, windowing module, parallel serial conversion module and radio-frequency module composition is modulated primarily of digital source module, channel coding module, 16QAM.The output of digital source module is connected with the input of channel coding module.The input that output and the 16QAM of channel coding module modulate mapping block is connected.The output that 16QAM modulates mapping block is connected with the input of serioparallel exchange module.The output of serioparallel exchange module is connected with the input of bipolar coding module.The output of bipolar coding module is connected with the input of IFFT conversion module.The output of IFFT conversion module is connected with the input of windowing module.The output of windowing module is connected with the input of parallel serial conversion module.The output of parallel serial conversion module is connected with the input of radio-frequency module.

Above-mentioned digital source module, channel coding module, 16QAM modulate mapping block, serioparallel exchange module, bipolar coding module, IFFT conversion module, parallel serial conversion module and windowing module and all can realize on fpga chip.Fpga chip adopts the virtexIV series xc4v55 chip of ISE company, this chip internal be integrated with a large amount of distributed RAM for realizing logical design, block RAM stores for data high-speed, PLL for the management of clock, embedded multiplier for the process of digital signal, high-speed transceiver for data communication etc., there is the advantages such as parallel processing capability Qiang ﹑ fast operation, this Di of Cheng ﹑ reliability are high, flexible in programming.Radio-frequency module is existing, buys obtain from market.

Digital source module is used for producing binary baseband data and delivers to channel coding module, and digital source module is held COM Debug Assistant to be transferred on FPGA plate in binary data source by RS232 interface by PC and realized.

Channel coding module is used for carrying out chnnel coding to the binary baseband data that digital source is sent here, with correcting digital signal issuable random error in transmission process.Channel coding module adopt (2,1,7) convolution code, its structure as shown in Figure 3, in figure, for XOR gate, D1-D6 is six grades of shift registers.This module coding efficiency is 1/2, and constraint length is 7.Channel coding module is realized on FPGA by Verilog hardware description language.

The base band binary data that 16QAM modulation mapping block is used for channel coding module to send here carries out 16QAM modulation and maps, be mapped on corresponding OFDM subcarrier by base band binary data, after mapping, OFDM subcarrier carries the information MAP of 4bit.16QAM is modulated mapping block and is realized on FPGA by Verilog hardware description language.

Serioparallel exchange module is used for changing a circuit-switched data circulation of serial into parallel multichannel data, to adapt to the requirement of OFDM transmission mechanism.Serioparallel exchange module is realized on FPGA by verilog hardware description language.

Bipolar coding module is used for the parallel data stream after by serioparallel exchange and carries out bipolar coding, and its structure as shown in Figure 4.This module makes in a channel parallel data, and the polarity of rear data is contrary with the polarity of previous data, thus makes the adjacent sub-carrier of an OFDM symbol carry opposite polarity data.In structure as shown in Figure 4, in input data sequence write RAM module, data export by RAM module under the effect of read address counter.Send into odd even judge module after data export, the parity of odd even judge module to the count value of read address counter judges, the data of odd address directly export, and the data of even address export after getting complement code module, realize the process of bipolar coding.Bipolar coding module is realized on FPGA by Verilog hardware description language.

IFFT module is used for the parallel data after by serioparallel exchange and bipolar coding and carries out IFFT conversion, forms OFDM symbol.Counting as N=128 of IFFT conversion.IFFT module is realized on FPGA by the IP kernel calling Xilinx company.

The OFDM symbol that windowing module is used for IFFT module to send carries out windowing process, disturbs with further suppressed sidelobes.The window function that windowing module adopts is raised cosine window.Windowing module is realized on FPGA by the IP kernel calling Xilinx company.

Parallel serial conversion module is used for the parallel data stream after by windowing and converts serial data stream to, and parallel serial conversion module is realized on FPGA by Verilog hardware description language.

Radio-frequency module is used for the OFDM symbol of serial to carry out D/A conversion and rf modulations, forms final ofdm modulation signal.Radio-frequency module is existing, buys obtain from market.

This side lobe suppression method has carried out simulation comparison to the method and traditional direct closedown subcarrier method in Matlab simulated environment.Simulation parameter arranges as follows: system subcarrier number is 128, and subcarrier sequence number corresponding to the frequency range that primary user takies is 9-12, and subcarrier modulation modes is 16QAM, and channel is awgn channel.Simulation result as shown in Figure 5.From simulation result, the method for directly closing subcarrier can produce the notch depth of approximately-20dB, and the method inserting Interference Cancellation subcarrier (AIC) can produce the notch depth of about-25dB, is slightly better than directly closing subcarrier method.Rejection can be promoted to-30dB by bipolar coding method, and rejection can be promoted to-35dB by the bipolar coding that this patent proposes combines suppression method with windowing.Obviously, the method that this patent proposes improves Sidelobe Suppression performance when not increasing computation complexity.

The method of the error performance of the method and traditional direct closedown subcarrier has been carried out simulation comparison by this side lobe suppression method in Matlab simulated environment.Simulation parameter arranges as follows: system subcarrier number is 128, subcarrier sequence number corresponding to the frequency range that primary user takies is 9-12, the OFDM subcarrier modulation modes that this method adopts is 16QAM, conventional method is QPSK, but the OFDM adjacent sub-carrier adopted due to this method transmits identical data message, and therefore this method is identical with the message transmission rate of conventional method.Simulation result as shown in Figure 6.As can be seen from simulation result, the error performance of this method is better than conventional method, this is because the OFDM adjacent sub-carrier that this method adopts transmits identical data message after bipolar coding, serve the effect of frequency diversity, thus improve the error performance of system.

Claims (6)

1. combine a side lobe suppression method based on bipolar coding and windowing, it is characterized in that, comprise following steps:

(1) independent memoryless base band data is produced;

(2) chnnel coding is carried out to base band data;

(3) carry out modulation to the data after coding to map, obtain the data after M modulation mapping;

(4) carry out serioparallel exchange to the data after modulation mapping, the data of M serial are transformed into the parallel data on v road, the number of every channel parallel data is N;

(5) successively bipolar coding is carried out to v channel parallel data;

(6) form v OFDM symbol after carrying out IFFT conversion respectively to the v circuit-switched data after bipolar coding, what the IFFT of each OFDM symbol converted counts as N;

(7) v the OFDM symbol obtained after being converted by IFFT carries out windowing respectively, and wherein windowed function is raised cosine windows;

(8) OFDM symbol of the v after windowing is carried out parallel-serial conversion;

(9) rf modulations is carried out to serial data, form final ofdm modulation signal.

2. according to claim 1ly a kind ofly combine side lobe suppression method based on bipolar coding and windowing, it is characterized in that, the modulation carried out in step (3) is mapped as 16QAM modulation and maps.

3. according to claim 1ly a kind ofly combine side lobe suppression method based on bipolar coding and windowing, it is characterized in that, 1 circuit-switched data in the v channel parallel data in step (5) after bipolar coding meets a _{i, 2k}=-a _{i, 2k-1}, k=1,2, N/2+1.

4. according to claim 1ly a kind ofly combine side lobe suppression method based on bipolar coding and windowing, it is characterized in that, the mathematic(al) representation of the raised cosine windows described in step (7) is:

$w_n=\left\{\begin{array}{cc}0.5+0.5\cos \left(\mathrm{\&pi;}\frac{n}{\mathrm{\&beta;N}}\right),& 0\&le;n<\mathrm{\&beta;N}\\ 1,& \mathrm{\&beta;}\&le;n<N\\ 0.5+0.5\cos \left(\mathrm{\&pi;}\frac{n-N}{\mathrm{\&beta;N}}\right),& N\&le;n<(1+\mathrm{\&beta;})N\end{array}\right.$

In formula, w _nfor raised cosine windows, β is the rolloff-factor of window function, and N is counting of IFFT conversion, and n is the sample number of window function sequence.

5. combine side lobe suppression device based on a kind of designed by said method based on bipolar coding and windowing, it is characterized in that, be made up of digital source module, channel coding module, modulation mapping block, serioparallel exchange module, bipolar coding module, IFFT conversion module, windowing module, parallel serial conversion module and radio-frequency module; The input of modulation mapping block is sent into after the output channel coding module of digital source module, the output of modulation mapping block is through the input of serioparallel exchange module and bipolar coding module, the output of bipolar coding module is connected through the input of IFFT conversion module with windowing module, and the output of windowing module connects the input of radio-frequency module.

6. according to claim 5ly a kind ofly combine side lobe suppression device based on bipolar coding and windowing, it is characterized in that, described modulation mapping block is that 16QAM modulates mapping block.