CN103001916B - Time domain reshaping method of orthogonal frequency division multiplexing (OFDM) communication system - Google Patents
Time domain reshaping method of orthogonal frequency division multiplexing (OFDM) communication system Download PDFInfo
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Abstract
The invention discloses a time domain reshaping method of an orthogonal frequency division multiplexing (OFDM) communication system. The method is used for reducing information energy loss caused by border crossing in system communication and belongs to the technical field of communication. The method includes conducting time domain reshaping on a data portion of an OFDM frame structure and enabling signal energy to be collected at the middle portion of OFDM symbols with less energy on two lateral portions. Therefore, the method effectively reduces information energy loss caused by signal border crossing and improves system performance. The time domain reshaping method is simple to achieve and capable of being used in various OFDM communication systems.
Description
Technical field
The present invention relates to communication technical field, particularly relate to a kind of time domain shaping methods of ofdm 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.
Summary of the invention
Technical problem to be solved by this invention is to overcome crosses protection interval due to signal and the signal energy loss problem that occurs existing for existing ofdm communication system; a kind of time domain shaping methods of ofdm communication system is provided; thus the loss of the information energy caused because crossing the border in reduction system communication, improve systematic function.
The present invention specifically solves the problems of the technologies described above by the following technical solutions:
A time domain shaping methods for ofdm communication system,
At the transmitting terminal of ofdm communication system, to obtain after digital modulation transmit data frequency-region signal carry out following process: the odd term of described frequency-region signal is multiplied by-1, and even item remains unchanged, and obtains new frequency-region signal; Inverse fast Fourier transform is carried out to this new frequency-region signal; The odd term of the signal obtained through inverse fast Fourier transform is multiplied by-1, and even item remains unchanged, and obtains the time domain reshaping signal of final transmission data;
At the receiving terminal of ofdm communication system, the time domain reshaping signal for the transmission data received carries out following process: the odd term of described time domain reshaping signal is multiplied by-1, and even item remains unchanged, and obtains new time-domain signal; Fast Fourier transform is carried out to this new time-domain signal; The odd term of the signal obtained through fast Fourier transform is multiplied by-1, and even item remains unchanged, and obtains the frequency-region signal of transmitted data.
The data division that the present invention is directed to OFDM frame structure carries out time domain shaping, signal energy is concentrated on the mid portion of OFDM symbol, and 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 flow chart of basic OFDM time domain shaping aspect transmitting terminal;
Fig. 2 b is the flow chart of basic OFDM time domain shaping aspect receiving terminal;
Fig. 3 a is the flow chart of DCO-OFDM time domain shaping aspect transmitting terminal;
Fig. 3 b is the flow chart of DCO-OFDM time domain shaping aspect receiving terminal;
Fig. 4 a to be the cycle be 127 pseudo random sequence after BPSK modulation, the frequency domain figure obtained by traditional wireless OFDM method, Fig. 4 b is the time-domain diagram obtained;
Fig. 5 a to be the cycle be 127 pseudo random sequence after BPSK modulation, the frequency domain figure adopting the inventive method to carry out time domain shaping to obtain, Fig. 5 b is the time-domain diagram obtained;
Fig. 6 a to be the cycle be 63 pseudo random sequence after BPSK modulation, the frequency domain figure obtained by traditional DCO-OFDM method, Fig. 6 b is the time-domain diagram obtained;
Fig. 7 a to be the cycle be 63 pseudo random sequence after BPSK modulation, the frequency domain figure adopting the inventive method to carry out time domain shaping to obtain, Fig. 7 b is the time-domain diagram obtained.
Embodiment
Below in conjunction with accompanying drawing, technical scheme of the present invention is described in detail:
Thinking of the present invention improves existing ofdm communication system, time domain shaping is carried out to the data division of OFDM frame structure, signal energy is concentrated 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.As shown in Figure 1, the present invention only carries out shaping to data division wherein to the structure of ofdm signal frame, and other parts are constant.The present invention specifically adopts following methods:
At the transmitting terminal of ofdm communication system, to obtain after digital modulation transmit data frequency-region signal carry out following process: the odd term of described frequency-region signal is multiplied by-1, and even item remains unchanged, and obtains new frequency-region signal; Inverse fast Fourier transform is carried out to this new frequency-region signal; The odd term of the signal obtained through inverse fast Fourier transform is multiplied by-1, and even item remains unchanged, and obtains the time domain reshaping signal of final transmission data;
At the receiving terminal of ofdm communication system, the time domain reshaping signal for the transmission data received carries out following process: the odd term of described time domain reshaping signal is multiplied by-1, and even item remains unchanged, and obtains new time-domain signal; Fast Fourier transform is carried out to this new time-domain signal; The odd term of the signal obtained through fast Fourier transform is multiplied by-1, and even item remains unchanged, and obtains the frequency-region signal of transmitted data.
The time domain waveform adopting such scheme to obtain is the shaping to the time domain waveform drawn by traditional OFDM method in fact, namely the 0th arrives
individual point is successively to right translation
individual, the
to N-1 point successively to left
individual, so just signal energy is concentrated on the mid portion of OFDM symbol.
The inventive method can be used for traditional wireless OFDM communication system, also may be used for incoherent system as the OFDM in optical communication system.For ease of public understanding, below respectively for wireless OFDM communication system and DCO-OFDM(direct current biasing light OFDM) communication system is further described technical solution of the present invention.
For wireless OFDM communication system, the transmitting terminal of system first carries out the digital modulation of the modes such as QAM or QPSK to communication data, 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 sequence of data, be designated as: X (k) (k=0,1 ..., N-1); By frequency domain signal X (k) (k=0,1 ..., N-1) be divided into even item X (2m) (m=0,1 ..., N/2-1) and odd term X (2m+1) (m=0,1 ..., N/2-1); Maintenance even item X (2m) (m=0,1 ..., N/2-1) constant, by odd term X (2m+1) (m=0,1 ..., N/2-1) and be multiplied by-1, obtain new frequency-region signal; X'(n is obtained after this new frequency-region signal being carried out N point IFFT computing) (n=0,1 ..., N-1); Again sequence x ' (n) is divided into even item x'(2r) (r=0,1 ..., N/2-1), odd term x ' (2r+1) (r=0,1 ..., N/2-1); Even item x'(2r by sequence x ' (n)) (r=0,1 ..., N/2-1) and constant, odd term x'(2r+1) (r=0,1 ..., N/2-1) and be multiplied by-1, obtain time-domain signal x (the n) (n=0 after final shaping, 1 ..., N-1).Above-mentioned shaping flow process as shown in Figure 2 a.Time-domain signal after shaping is added protection interval (or Cyclic Prefix) by transmitting terminal, forms OFDM symbol, then adds synchronizing sequence when framing, channel estimation sequence etc., obtain baseband signal and export.
System receiving terminal is for the baseband signal received, advanced line time is synchronous, decimal frequency multiplication is estimated and after correcting, obtain the time-domain signal x after shaping " (n) (n=0; 1 ..., N-1); " (n) (n=0 by burst x, 1 ..., N-1) odd term x " (2m+1) (and m=0; 1; ..., N/2-1) " (the 2m) (m=0 that is multiplied by-1, even item x, 1,, N/2-1) remain unchanged, obtain new time-domain signal; X is obtained after N point FFT computing is carried out to this new time-domain signal " (k) (k=0,1 ..., N-1); By burst X " (k) (k=0,1 ...; and N-1) in odd term X " (2r+1) (and r=0,1 ... N/2-1) be multiplied by-1, keep even item X " (2r) (r=0,1; ..., N/2-1) constant, obtain final frequency domain signal X ' (k) (k=0; 1; ..., N-1), i.e. the transmitting terminal frequency-region signal of Serial No. after digital modulation that will transmit.Above-mentioned flow process as shown in Figure 2 b.To frequency domain signal X ' (k) (k=0,1 ..., N-1) and carry out corresponding digital demodulation, transmitted data bit flow can be obtained.
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 a kind of method adopts DCO-OFDM(direct current biasing light OFDM) method.For DCO-OFDM communication system, frequency-region signal x (n) of transmitting terminal transmitted information bit stream after digital modulation (n=1 ..., N/2-1) and need correspondingly map the real number realizing OFDM symbol, the frequency-region signal after real number
mapping expression formula as follows:
Similarly, by burst
odd term s (2m+1) (m=0,1 ..., N/2-1) and be multiplied by-1, even item s (2m) (m=0,1 ..., N/2-1) remain unchanged, obtain new frequency-region signal; To this new frequency-region signal to carry out after N point IFFT computing time-domain signal sequences y ' (n) (and n=0,1 ..., N-1); By odd term y ' (the 2r+1) (r=0 of time-domain signal sequences y ' (n), 1 ..., N/2-1) and be multiplied by-1, even item y ' (2r) (r=0,1 ..., N/2-1) remain unchanged, obtain time-domain signal y (the n) (n=0 after final shaping, 1 ..., N-1).Above-mentioned flow process as shown in Figure 3 a.Time-domain signal y (n) after shaping is added protection interval (or Cyclic Prefix) by transmitting terminal, forms OFDM symbol, then adds synchronizing sequence when framing, channel estimation sequence etc., obtain baseband signal and export.
System receiving terminal is for the baseband signal received, and advanced line time is synchronous, decimal frequency multiplication is estimated and after correcting, obtain the time-domain signal y after shaping " (n) (n=0,1 ..., N-1); By burst y " (n) (n=0,1 ..., N-1) odd term y " (2m+1) (m=0,1 ..., N/2-1) and be multiplied by-1, even item y " (2m) (m=0; 1 ..., N/2-1) constant, obtain new time-domain signal; S is obtained after N point FFT computing is carried out to this new time-domain signal " (n) (n=0,1 ..., N-1); By frequency-region signal sequence s " the odd term s of (n) " (2r+1) (r=0,1 ..., N/2-1) and be multiplied by-1, even item s " (2r) (r=0; 1 ..., N/2-1) remain unchanged; obtain burst s ' (n) (n=0; 1 ..., N-1); Get of burst s ' (n)
,
be transmitting terminal transmit the frequency-region signal of data after digital modulation.Above-mentioned flow process as shown in Figure 3 b.Right
carry out corresponding digital demodulation, namely obtain the original data bits stream that transmitting terminal transmits.
In order to verify the effect of the inventive method, respectively the wireless OFDM communication system of traditional wireless OFDM communication system, DCO-OFDM communication system and employing the inventive method, DCO-OFDM communication system are contrasted.Fig. 4 a, Fig. 4 b to be the cycle be respectively 127 pseudo random sequence after BPSK modulation, the frequency domain figure obtained by traditional wireless OFDM method and time-domain diagram; Fig. 5 a, Fig. 5 b to be the cycle be respectively 127 pseudo random sequence after BPSK modulation, adopt the inventive method to carry out frequency domain figure that time domain shaping obtains and time-domain diagram; Fig. 6 a, Fig. 6 b to be the cycle be respectively 63 pseudo random sequence after BPSK modulation, the frequency domain figure obtained by traditional DCO-OFDM method and time-domain diagram; Fig. 7 a, Fig. 7 b to be the cycle be respectively 63 pseudo random sequence after BPSK modulation, adopt the inventive method to carry out frequency domain figure that time domain shaping obtains and time-domain diagram.As can be seen from the translation that Fig. 4 b and Fig. 5 b, Fig. 5 b is Fig. 4 b in fact, by the mid portion of the concentration of energy of signal in OFDM symbol, both sides portion of energy is less, like this when crossing the border appears in signal, it is just less that signal energy is lost, and also minimizes on the impact of system.Similarly, can be found out by Fig. 6 b and Fig. 7 b, in DCO-OFDM communication system, time domain shaping aspect of the present invention also makes the concentration of energy of OFDM symbol at mid portion, like this when signal crosses the border, can reduce the impact on system equally, ensure the performance of system.
Claims (3)
1. a time domain shaping methods for ofdm communication system, is characterized in that,
At the transmitting terminal of ofdm communication system, to obtain after digital modulation transmit data frequency-region signal carry out following process: the odd term of described frequency-region signal is multiplied by-1, and even item remains unchanged, and obtains new frequency-region signal; Inverse fast Fourier transform is carried out to this new frequency-region signal; The odd term of the signal obtained through inverse fast Fourier transform is multiplied by-1, and even item remains unchanged, and obtains the time domain reshaping signal of final transmission data;
At the receiving terminal of ofdm communication system, the time domain reshaping signal for the transmission data received carries out following process: the odd term of described time domain reshaping signal is multiplied by-1, and even item remains unchanged, and obtains new time-domain signal; Fast Fourier transform is carried out to this new time-domain signal; The odd term of the signal obtained through fast Fourier transform is multiplied by-1, and even item remains unchanged, and obtains the frequency-region signal of transmitted data.
2. the time domain shaping methods of ofdm communication system as claimed in claim 1, it is characterized in that, described ofdm communication system is wireless OFDM communication system, and described time domain shaping methods is specific as follows:
At the transmitting terminal of wireless OFDM communication system, by obtain after digital modulation transmit the frequency domain signal X (k) of data, k=0,1 ..., N-1, be divided into even item X (2m), m=0,1 ..., N/2-1, with odd term X (2m+1), m=0,1 ..., N/2-1; Keep even item X (2m), m=0,1 ..., N/2-1, constant, by odd term X (2m+1), m=0,1 ..., N/2-1, is multiplied by-1, obtains new frequency-region signal; X'(n is obtained after this new frequency-region signal being carried out N point IFFT computing), n=0,1 ..., N-1; Again by sequence x'(n) be divided into even item x'(2r), r=0,1 ..., N/2-1, odd term x'(2r+1), r=0,1 ..., N/2-1; By sequence x'(n) even item x'(2r), r=0,1 ..., N/2-1 is constant, odd term x'(2r+1), r=0,1 ..., N/2-1, be multiplied by-1, obtain time-domain signal x (n) after final shaping, n=0,1 ... N-1;
At the receiving terminal of wireless OFDM communication system, the time-domain signal x by after shaping " (n), n=0; 1 ... N-1, odd term x " (2m+1), m=0,1 ... N/2-1, is multiplied by-1, even item x " (2m); m=0,1 ...; N/2-1, remains unchanged, and obtains new time-domain signal; X is obtained after N point FFT computing is carried out to this new time-domain signal " (k), k=0,1 ..., N-1; By burst X " (k), k=0,1 ...; and N-1, in odd term X " (2r+1), r=0,1,, N/2-1, is multiplied by-1, keeps even item X " and (2r); r=0,1 ..., N/2-1; constant, obtains final frequency domain signal X ' (k), k=0; 1 ..., N-1.
3. the time domain shaping methods of ofdm communication system as claimed in claim 1, it is characterized in that, described ofdm communication system is direct current biasing light ofdm communication system, and described time domain shaping methods is specific as follows:
At the transmitting terminal of direct current biasing light ofdm communication system, by digital modulation and after real number transmit the frequency-region signal of data
odd term s (2m+1), m=0,1 ..., N/2-1, is multiplied by-1, even item s (2m), m=0, and 1 ..., N/2-1, remains unchanged, and obtains new frequency-region signal; To this new frequency-region signal to carry out after N point IFFT computing time-domain signal sequences y ' (n), n=0,1 ..., N-1; By time-domain signal sequences y ' the odd term y'(2r+1 of (n)), r=0,1,, N/2-1, is multiplied by-1, even item y'(2r), r=0,1,, N/2-1, remains unchanged, obtain time-domain signal y (n) after final shaping, n=0,1,, N-1;
At the receiving terminal of direct current biasing light ofdm communication system, the time-domain signal y by after the shaping that receives " (n), n=0,1; ..., N-1, odd term y " (2m+1), m=0,1 ... N/2-1, is multiplied by-1, even item y " (2m); m=0,1 ...; N/2-1, constant, obtain new time-domain signal; S is obtained after N point FFT computing is carried out to this new time-domain signal " (n), n=0,1 ..., N-1; By frequency-region signal sequence s " the odd term s of (n) " (2r+1), r=0,1 ..., N/2-1, is multiplied by-1, even item s " (2r), r=0,1 ..., N/2-1, remains unchanged; obtain burst s ' (n), n=0, and 1 ..., N-1; Get of burst s ' (n)
, obtain x ' (n),
be transmitting terminal transmit the frequency-region signal of data after digital modulation.
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| CN104901918B (en) * | 2015-06-15 | 2019-01-18 | 电子科技大学 | The method and synchronous method of OFDM data sequence are generated based on Chirp signal |
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