CN103001915B

CN103001915B - Time domain reshaping method of asymmetric limiting light orthogonal frequency division multiplexing (OFDM) communication system

Info

Publication number: CN103001915B
Application number: CN201210500613.2A
Authority: CN
Inventors: 陈健; 马新凤
Original assignee: Nanjing Post and Telecommunication University
Current assignee: Nanjing Post and Telecommunication University; Nanjing University of Posts and Telecommunications
Priority date: 2012-11-30
Filing date: 2012-11-30
Publication date: 2015-01-28
Anticipated expiration: 2032-11-30
Also published as: CN103001915A

Abstract

The invention discloses a time domain reshaping method of an asymmetric limiting light orthogonal frequency division multiplexing (OFDM) communication system and belongs to the technical field of communication. Aiming at the problem of signal energy loss of an existing asymmetric limiting light OFDM communication system due to the fact that signals cross a protection time interval, time domain reshaping is performed on a data portion of an OFDM frame structure, signal energy is concentrated on the middle portion of an OFDM symbol, two sides of the OFDM symbol has little energy, and the time domain reshaping method effectively reduces the information energy loss caused by border-crossing of the signals and improves system performance.

Description

A kind of time domain shaping methods of asymmetric amplitude limit light ofdm communication system

Technical field

The present invention relates to communication technical field, particularly relate to a kind of asymmetric amplitude limit light OFDM(AOC-OFDM) the time domain shaping methods of communication system, for reducing the loss of the information energy caused because crossing the border in system communication.

Background technology

OFDM (OFDM, Orthogonal Frequency Division Multiplexing) is a kind of multi-carrier broadband digital modulation technique.The features such as OFDM technology has good antijamming capability, and the availability of frequency spectrum is high, and transmission capacity is large, the quadrature modulation in each subchannel and demodulation are realized by Fast Fourier Transform Inverse (IFFT) or fast Fourier transform (FFT).In traditional ofdm system, after input bit sequence completes serial to parallel conversion, according to the modulation system adopted, completing and modulate mapping accordingly, forming modulation intelligence sequence pair, to this information to carrying out IFFT, calculate the time domain sample sequence of OFDM modulated signal, add cyclic prefix CP, remake D/A conversion, obtain the time domain waveform of OFDM modulated signal.Receiving terminal first docks receipts time-domain signal and carries out A/D conversion, removes cyclic prefix CP, obtains the sampled sequence of OFDM modulated signal, make FFT namely obtain former modulation intelligence sequence to this sampled sequence.

Ofdm system is by introducing Cyclic Prefix thus forming protection interval GI; effectively resist intersymbol interference (the Inter-Symbol Interference because multidiameter delay brings; be called for short ISI) and inter-sub-carrier interference (Inter-Carrier Interference is called for short ICI).But wide protection section interval time can make poor system efficiency, because of and there is low protection interval OFDM scheme.In any case in some cases, signal still can be crossed and protect interval time, thus occurs that signal energy is lost, and ISI and ICI.As the one of optical OFDM system, there is this problem in existing asymmetric amplitude limit light ofdm communication system equally.

Summary of the invention

Technical problem to be solved by this invention is that overcoming the signal existed in existing asymmetric amplitude limit light ofdm communication system crosses protection interval time thus the deficiency causing signal energy to be lost; a kind of time domain shaping methods of asymmetric amplitude limit light ofdm communication system is provided; signal energy can be made to concentrate on the mid portion of OFDM symbol; both sides portion of energy is less, thus reduces to cross the border the loss of the information energy caused because of signal.

The present invention is concrete by the following technical solutions:

A time domain shaping methods for asymmetric amplitude limit light ofdm communication system,

At the transmitting terminal of asymmetric amplitude limit light ofdm communication system, by transmitted data through digital modulation and do correspondingly map process after frequency-region signal sequence in s(4 m+ 1) ( m=0,1 ..., n/ 4-1) item is multiplied by , by s (4 m+ 3) ( m=0,1 ..., n/ 4-1) item is multiplied by , obtain new frequency-region signal; Time-domain signal sequence is obtained after N point IFFT computing is carried out to this new frequency-region signal ( n=0,1 ..., n-1); By burst 's (4 m+ 3) ( m=0,1 ..., n/ 4-1) item is multiplied by-1, (4 m+ 1) ( m=0,1 ..., n/ 4-1) item remains unchanged, and obtains the time-domain signal sequence after shaping ( n=0,1 ..., n-1);

At the receiving terminal of asymmetric amplitude limit light ofdm communication system, by the time-domain signal sequence received ( n=0,1 ..., n-1) ( m=0,1 ..., n/ 4-1) item is multiplied by-1, ( m=0,1 ..., n/ 4-1) item remains unchanged, and obtains new time-domain signal; Frequency-region signal sequence is obtained after N point FFT computing is carried out to this new time-domain signal ( n=0,1 ..., n-1); By frequency-region signal sequence in ( r=0,1 ..., n/ 4-1) item is multiplied by , ( r=0,1 ..., n/ 4-1) item is multiplied by , obtain frequency-region signal sequence ( n=0,1 ..., n-1); Get frequency-region signal sequence in , , namely transmitting terminal transmit the frequency-region signal of data after digital modulation.

The data division that the present invention is directed to existing asymmetric amplitude limit light OFDM frame structure carries out time domain shaping, signal energy is concentrated on the mid portion of OFDM symbol, both sides portion of energy is less, thus effectively reduces because signal crosses the border the loss of the information energy caused, and improves systematic function.

Accompanying drawing explanation

Fig. 1 is the frame structure of ofdm communication system;

Fig. 2 a is the process chart of transmitting terminal in time domain shaping methods of the present invention;

Fig. 2 b is the process chart of receiving terminal in time domain shaping methods of the present invention;

Fig. 3 a to be the cycle be 63 pseudo random sequence after BPSK modulation, the frequency domain figure obtained by traditional ACO-OFDM method, Fig. 3 b is the time-domain diagram obtained;

Fig. 4 a to be the cycle be 63 pseudo random sequence after BPSK modulation, adopt the frequency domain figure that the inventive method obtains, Fig. 4 b is the time-domain diagram obtained.

Embodiment

Below in conjunction with accompanying drawing, technical scheme of the present invention is described in detail:

The frame structure of ofdm communication system as shown in Figure 1, thinking of the present invention only carries out shaping to wherein data division, and make signal energy concentrate on the mid portion of OFDM symbol, both sides portion of energy is less, thus reduce to cross the border the loss of the information energy caused because of signal, improve systematic function; Other parts do not change.

Tradition optical transmission system, receiving terminal adopts direct-detection, the light signal strength produced is relevant with input electrical signal, information is carried in luminous intensity, require input electrical signal non-negative, and OFDM is bipolar signal, so the application of OFDM technology in optical transmission system will be realized, then require that OFDM symbol is arithmetic number.Wherein an approach adopts ACO-OFDM modulation technique.In ACO-OFDM communication system, data bit flow is carried out the digital modulation of the modes such as QAM or QPSK by transmitting terminal, and the digital signal being about to be transmitted converts the mapping of subcarrier amplitude and phase place to, obtain after modulating transmit the frequency-region signal of data , then right do the mapping be shown below, obtain ,

。

Adopt the ACO-OFDM communication system of the inventive method, transmitting terminal is by frequency-region signal sequence in s(4 m+ 1) ( m=0,1 ..., n/ 4-1) item is multiplied by , will s(4 m+ 3) (m=0,1 ..., n/ 4-1) item is multiplied by , obtain new frequency-region signal; Time-domain signal sequence is obtained after N point IFFT computing is carried out to this new frequency-region signal ( n=0,1 ..., n-1); By burst 's (4 m+ 3) ( m=0,1 ..., n/ 4-1) item is multiplied by-1, (4 m+ 1) ( m=0,1 ..., n/ 4-1) item remains unchanged, and obtains the time-domain signal sequence after shaping ( n=0,1 ..., n-1).Above-mentioned handling process as shown in Figure 2 a.

At receiving terminal, by the time-domain signal sequence received ( n=0,1 ..., n-1) ( m=0,1 ..., n/ 4-1) item is multiplied by-1, ( m=0,1 ..., n/ 4-1) item remains unchanged, and obtains new time-domain signal; Frequency-region signal sequence is obtained after N point FFT computing is carried out to this new time-domain signal ( n=0,1 ..., n-1); By frequency-region signal sequence in ( r=0,1 ..., n/ 4-1) item is multiplied by , ( r=0,1 ..., n/ 4-1) item is multiplied by , obtain frequency-region signal sequence ( n=0,1 ..., n-1); Get frequency-region signal sequence in , , namely transmitting terminal transmit the frequency-region signal of data after digital modulation.Above-mentioned handling process as shown in Figure 2 b.Receiving terminal is to frequency-region signal carry out corresponding digital demodulation, the initial data that transmitting terminal transmits can be obtained.

Fig. 3 a to be the cycle be 63 pseudo random sequence after BPSK modulation, the frequency domain figure obtained by traditional ACO-OFDM method, Fig. 3 b is the time-domain diagram obtained; Fig. 4 a to be the cycle be 63 pseudo random sequence after BPSK modulation, adopt the frequency domain figure that the inventive method obtains, Fig. 4 b is the time-domain diagram obtained.As can be seen from Fig. 3 b, Fig. 4 b, in ACO-OFDM communication system, adopt time domain shaping methods of the present invention, make the energy of OFDM symbol less in both sides part, like this when signal crosses the border, the impact on system can be reduced, thus the performance of the system of guarantee.

Claims

1. a time domain shaping methods for asymmetric amplitude limit light ofdm communication system, is characterized in that,

At the transmitting terminal of asymmetric amplitude limit light ofdm communication system, by transmitted data through digital modulation and do correspondingly map process after frequency-region signal sequence in s(4 m+ 1) ( m=0,1 ..., n/ 4-1) item is multiplied by , by s (4 m+ 3) ( m=0,1 ..., n/ 4-1) item is multiplied by , obtain new frequency-region signal; Time-domain signal sequence is obtained after N point IFFT computing is carried out to this new frequency-region signal ( n=0,1 ..., n-1); By burst 's (4 m+ 3) ( m=0,1 ..., n/ 4-1) item is multiplied by-1, (4 m+ 1) ( m=0,1 ..., n/ 4-1) item remains unchanged, and obtains the time-domain signal sequence after shaping ( n=0,1 ..., n-1), N is the integer can divided exactly by 4;