CN103001916A - 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, relate in particular to a kind of time domain shaping methods of ofdm communication system, be used for reducing the loss of the information energy that system communication causes because crossing the border.
Background technology
OFDM (OFDM, Orthogonal Frequency Division Multiplexing) is a kind of multi-carrier broadband digital modulation technique.The characteristics such as the 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 realize by Fast Fourier Transform Inverse (IFFT) or fast Fourier transform (FFT).In traditional ofdm system, after the input bit sequence is finished serial to parallel conversion, according to the modulation system that adopts, finish corresponding modulation mapping, form 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 the D/A conversion, obtain the time domain waveform of OFDM modulated signal.Receiving terminal docks first time receiving territory signal and carries out the A/D conversion, removes cyclic prefix CP, obtains the sampled sequence of OFDM modulated signal, this sampled sequence is made FFT namely obtain former modulation intelligence sequence.
Thereby ofdm system forms protection interval GI by introducing Cyclic Prefix; effectively resist because intersymbol interference (the Inter-Symbol Interference that multidiameter delay brings; abbreviation ISI) and between subcarrier disturb (Inter-Carrier Interference is called for short ICI).But wide protection section blanking time meeting is so that the system effectiveness variation, thereby low protection interval OFDM scheme occurred again.In any case in some cases, signal still can be crossed and protect blanking time, thereby the signal energy loss occurs, and ISI and ICI.
Summary of the invention
It is existing owing to signal is crossed the signal energy loss problem that the protection interval occurs that technical problem to be solved by this invention is to overcome existing ofdm communication system; a kind of time domain shaping methods of ofdm communication system is provided; thereby reduce the loss of the information energy that causes because crossing the border in the system communication, improve systematic function.
The present invention specifically solves the problems of the technologies described above by the following technical solutions:
A kind of time domain shaping methods of ofdm communication system,
At the transmitting terminal of ofdm communication system, the frequency-region signal of institute's the transmission of data of obtaining behind the Digital Modulation is carried out following processing: the odd term of described frequency-region signal be multiply by-1, and even item remains unchanged, and obtains new frequency-region signal; This new frequency-region signal is carried out inverse fast Fourier transform; The odd term of the signal that will obtain through inverse fast Fourier transform multiply by-1, and even item remains unchanged, and obtains the time domain reshaping signal of final the transmission of data;
At the receiving terminal of ofdm communication system, carry out following processing for the time domain reshaping signal of the transmission of data that receives: the odd term of described time domain reshaping signal be multiply by-1, and even item remains unchanged, and obtains new time-domain signal; This new time-domain signal is carried out fast Fourier transform; The odd term of the signal that will obtain through fast Fourier transform multiply by-1, and even item remains unchanged, and obtains the frequency-region signal of institute's the transmission of data.
The data division that the present invention is directed to the OFDM frame structure carries out the time domain shaping, and signal energy is concentrated on the mid portion of OFDM symbol, and the both sides portion of energy is less, thereby has effectively reduced because of the cross the border loss of the information energy that causes of signal, has improved systematic function.
Description of drawings
Fig. 1 is the frame structure of ofdm communication system;
Fig. 2 a is the flow chart of basic OFDM time domain shaping scheme transmitting terminal;
Fig. 2 b is the flow chart of basic OFDM time domain shaping scheme receiving terminal;
Fig. 3 a is the flow chart of DCO-OFDM time domain shaping scheme transmitting terminal;
Fig. 3 b is the flow chart of DCO-OFDM time domain shaping scheme receiving terminal;
Fig. 4 a be the cycle be 127 pseudo random sequence after the BPSK modulation, by the frequency domain figure that traditional wireless OFDM method obtains, Fig. 4 b is the time-domain diagram that obtains;
Fig. 5 a be the cycle be 127 pseudo random sequence after the BPSK modulation, adopt the inventive method to carry out the frequency domain figure that the time domain shaping obtains, Fig. 5 b is the time-domain diagram that obtains;
Fig. 6 a be the cycle be 63 pseudo random sequence after the BPSK modulation, by the frequency domain figure that traditional DCO-OFDM method obtains, Fig. 6 b is the time-domain diagram that obtains;
Fig. 7 a be the cycle be 63 pseudo random sequence after the BPSK modulation, adopt the inventive method to carry out the frequency domain figure that the time domain shaping obtains, Fig. 7 b is the time-domain diagram that obtains.
Embodiment
Below in conjunction with accompanying drawing technical scheme of the present invention is elaborated:
Thinking of the present invention is that existing ofdm communication system is improved, data division to the OFDM frame structure carries out the time domain shaping, signal energy is concentrated on the mid portion of OFDM symbol, and the both sides portion of energy is less, thereby reduces because of the cross the border loss of the information energy that causes of signal.The structure of ofdm signal frame as shown in Figure 1, the present invention only carries out shaping to wherein data division, other parts are constant.The present invention specifically adopts following methods:
At the transmitting terminal of ofdm communication system, the frequency-region signal of institute's the transmission of data of obtaining behind the Digital Modulation is carried out following processing: the odd term of described frequency-region signal be multiply by-1, and even item remains unchanged, and obtains new frequency-region signal; This new frequency-region signal is carried out inverse fast Fourier transform; The odd term of the signal that will obtain through inverse fast Fourier transform multiply by-1, and even item remains unchanged, and obtains the time domain reshaping signal of final the transmission of data;
At the receiving terminal of ofdm communication system, carry out following processing for the time domain reshaping signal of the transmission of data that receives: the odd term of described time domain reshaping signal be multiply by-1, and even item remains unchanged, and obtains new time-domain signal; This new time-domain signal is carried out fast Fourier transform; The odd term of the signal that will obtain through fast Fourier transform multiply by-1, and even item remains unchanged, and obtains the frequency-region signal of institute's the transmission of data.
The time domain waveform that adopts such scheme to obtain is to the shaping of the time domain waveform that draws by traditional OFDM method in fact, namely the 0th arrives
Individual point is successively to right translation
Individual, the
Put successively to left to N-1
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 can be used for the OFDM of incoherent system such as optical communication system.For ease of public understanding, the below is respectively take wireless OFDM communication system and DCO-OFDM(direct current biasing light OFDM) communication system further specifies technical solution of the present invention as example.
For wireless OFDM communication system, the transmitting terminal of system carries out first the Digital Modulation of the modes such as QAM or QPSK to communication data, the digital signal that is about to be transmitted converts the mapping of subcarrier amplitude and phase place to, the frequency-region signal sequence of the institute's the transmission of data after obtaining modulating, be designated as: X (k) (k=0,1 ..., N-1); With 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, with odd term X (2m+1) (m=0,1 ..., N/2-1) multiply by-1, obtain new frequency-region signal; The frequency-region signal that this is new carries out getting x'(n after the 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); With sequence x ' even item x'(2r (n)) (r=0,1 ..., N/2-1) constant, odd term x'(2r+1) (r=0,1 ..., N/2-1) multiply by-1, obtain after the final shaping time-domain signal x (n) (n=0,1 ..., N-1).Above-mentioned shaping flow process is shown in Fig. 2 a.The time-domain signal of transmitting terminal after with shaping adds protection interval (or Cyclic Prefix), forms the OFDM symbol, then adds synchronizing sequence when framing, and channel estimation sequence etc. obtain baseband signal and output.
System receiving terminal is for the baseband signal that receives, advanced line time synchronously, the decimal frequency multiplication is estimated and correct after, obtain the time-domain signal x after the shaping " (n) (n=0; 1 ..., N-1); with burst x " (n) (and n=0,1 ... N-1) odd term x " (2m+1) (m=0,1 ...; N/2-1) multiply by-1, even item x " (2m) (m=0,1,, N/2-1) remain unchanged, obtain new time-domain signal; This new time-domain signal is carried out getting X after the N point FFT computing " (k) (k=0,1 ..., N-1); With burst X " (k) (k=0,1 ...; the odd term X N-1) " (2r+1) (r=0,1 ... N/2-1) multiply 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. behind Digital Modulation that will transmit.Above-mentioned flow process is shown in Fig. 2 b.To frequency domain signal X ' (k) (k=0,1 ..., N-1) carry out corresponding digital demodulation, the data bit flow that can obtain transmitting.
The tradition optical transmission system, receiving terminal adopts direct-detection, the light signal strength that produces is relevant with input electrical signal, information is carried on the luminous intensity, require input electrical signal non-negative, and OFDM is bipolar signal, so will realize the application of OFDM technology in optical transmission system, then requiring the OFDM symbol is arithmetic number.Wherein a kind of method is to adopt DCO-OFDM(direct current biasing light OFDM) method.For the DCO-OFDM communication system, the frequency-region signal x (n) of transmitting terminal transmitted information bit stream behind Digital Modulation (n=1 ..., N/2-1) need correspondingly shine upon to realize the real number of OFDM symbol, the frequency-region signal behind the real number
The mapping expression formula as follows:
Similarly, with burst
Odd term s (2m+1) (m=0,1 ..., N/2-1) multiply 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 carry out after the N point IFFT computing the time-domain signal sequences y ' (n) (and n=0,1 ..., N-1); With the odd term y ' of time-domain signal sequences y ' (n) (2r+1) (r=0,1 ..., N/2-1) multiply by-1, even item y ' (2r) (r=0,1 ..., N/2-1) remain unchanged, obtain after the final shaping time-domain signal y (n) (n=0,1 ..., N-1).Above-mentioned flow process is shown in Fig. 3 a.The time-domain signal y (n) of transmitting terminal after with shaping adds protection interval (or Cyclic Prefix), forms the OFDM symbol, then adds synchronizing sequence when framing, and channel estimation sequence etc. obtain baseband signal and output.
System receiving terminal is for the baseband signal that receives, advanced line time synchronously, the decimal frequency multiplication is estimated and correct after, obtain the time-domain signal y after the shaping " (n) (n=0,1 ..., N-1); With burst y " (n) (n=0,1 ..., odd term y N-1) " (2m+1) (m=0,1 ..., N/2-1) multiply by-1, even item y " (2m) (m=0,1 ..., N/2-1) constant, obtain new time-domain signal; This new time-domain signal is carried out getting s after the N point FFT computing " (n) (n=0,1 ..., N-1); With frequency-region signal sequence s " odd term s (n) " (2r+1) (r=0,1 ..., N/2-1) multiply by-1, even item s " (2r) (r=0,1 ..., N/2-1) remain unchanged; obtain burst s ' (n) (n=0,1 ..., N-1); The number of winning the confidence sequence s ' (n)
,
Be the frequency-region signal of transmitting terminal institute the transmission of data behind Digital Modulation.Above-mentioned flow process is shown in Fig. 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 traditional wireless OFDM communication system, DCO-OFDM communication system are contrasted with the wireless OFDM communication system, the DCO-OFDM communication system that adopt the inventive method.Fig. 4 a, Fig. 4 b be respectively the cycle be 127 pseudo random sequence after the BPSK modulation, the frequency domain figure and the time-domain diagram that obtain by traditional wireless OFDM method; Fig. 5 a, Fig. 5 b be respectively the cycle be 127 pseudo random sequence after the BPSK modulation, adopt the inventive method to carry out frequency domain figure and the time-domain diagram that the time domain shaping obtains; Fig. 6 a, Fig. 6 b be respectively the cycle be 63 pseudo random sequence after the BPSK modulation, the frequency domain figure and the time-domain diagram that obtain by traditional DCO-OFDM method; Fig. 7 a, Fig. 7 b be respectively the cycle be 63 pseudo random sequence after the BPSK modulation, adopt the inventive method to carry out frequency domain figure and the time-domain diagram that the time domain shaping obtains.Can find out that from Fig. 4 b and Fig. 5 b Fig. 5 b is the translation of Fig. 4 b in fact, with the concentration of energy of the signal mid portion at the OFDM symbol, the both sides portion of energy is less, like this when crossing the border appears in signal, signal energy loss just less also minimizes on the impact of system.Similarly, can be found out by Fig. 6 b and Fig. 7 b that in the DCO-OFDM communication system, time domain shaping scheme of the present invention also so that the concentration of energy of OFDM symbol at mid portion, when signal crosses the border, can reduce the impact on system so equally, guarantees the performance of system.
Claims (3)
1. the time domain shaping methods of an ofdm communication system is characterized in that,
At the transmitting terminal of ofdm communication system, the frequency-region signal of institute's the transmission of data of obtaining behind the Digital Modulation is carried out following processing: the odd term of described frequency-region signal be multiply by-1, and even item remains unchanged, and obtains new frequency-region signal; This new frequency-region signal is carried out inverse fast Fourier transform; The odd term of the signal that will obtain through inverse fast Fourier transform multiply by-1, and even item remains unchanged, and obtains the time domain reshaping signal of final the transmission of data;
At the receiving terminal of ofdm communication system, carry out following processing for the time domain reshaping signal of the transmission of data that receives: the odd term of described time domain reshaping signal be multiply by-1, and even item remains unchanged, and obtains new time-domain signal; This new time-domain signal is carried out fast Fourier transform; The odd term of the signal that will obtain through fast Fourier transform multiply by-1, and even item remains unchanged, and obtains the frequency-region signal of institute's the transmission of data.
2. the time domain shaping methods of ofdm communication system as claimed in claim 1 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, with the frequency-region signal of institute's the transmission of data of obtaining behind the Digital Modulation
X(
k) (
k=0,1 ...,
N-1) is divided into even item
X(2
m) (
m=0,1 ...,
N/ 2-1) and odd term
X(2
m+ 1) (
m=0,1 ...,
N/ 2-1); Keep even item
X(2
m) (
m=0,1 ...,
N/2-1) constant, with odd term
X(2
m+ 1) (
m=0,1 ...,
N/ 2-1) multiply by-1, obtain new frequency-region signal; The frequency-region signal that this is new carries out getting after the N point IFFT computing
(
n=0,1 ...,
N-1); Again with sequence
Be divided into even item
(
r=0,1 ...,
N/ 2-1), odd term
(
r=0,1 ...,
N/ 2-1); With sequence
Even item
(
r=0,1 ...,
N/ 2-1) constant, odd term
(
r=0,1 ...,
N/ 2-1) multiply by-1, obtain after the final shaping time-domain signal x (
n) (
n=0,1,
N-1);
At the receiving terminal of wireless OFDM communication system, with the time-domain signal after the shaping
(
n=0,1,
N-1) odd term
(
m=0,1 ...,
N/ 2-1) multiply by-1, even item
(
m=0,1 ...,
N/ 2-1) remain unchanged, obtain new time-domain signal; This new time-domain signal is carried out getting after the N point FFT computing
(
k=0,1 ...,
N-1); With burst
(
k=0,1 ...,
N-1) odd term in
(
r=0,1 ...,
N/ 2-1) multiply by-1, keep even item
(
r=0,1 ...,
N/ 2-1) constant, obtain 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 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, with the frequency-region signal of the institute's the transmission of data behind Digital Modulation and the real number
Odd term
s(2
m+ 1) (
m=0,1 ...,
N/ 2-1) multiply by-1, even item
s(2
m) (
m=0,1 ...,
N/ 2-1) remain unchanged, obtain new frequency-region signal; This new frequency-region signal is carried out getting the time-domain signal sequence after the N point IFFT computing
(
n=0,1 ...,
N-1); With the time-domain signal sequence
Odd term
(
r=0,1 ...,
N/ 2-1) multiply by-1, even item
(
r=0,1 ...,
N/2-1) remain unchanged, obtain the time-domain signal after the final shaping
(
n=0,1 ...,
N-1);
At the receiving terminal of direct current biasing light ofdm communication system, with the time-domain signal after the shaping that receives
(
n=0,1 ...,
N-1) odd term
(
m=0,1 ...,
N/ 2-1) multiply by-1, even item
(
m=0,1 ...,
N/ 2-1) constant, obtain new time-domain signal; This new time-domain signal is carried out getting after the N point FFT computing
(
n=0,1 ...,
N-1); With the frequency-region signal sequence
Odd term
(
r=0,1 ...,
N/ 2-1) multiply by-1, even item
(
r=0,1 ...,
N/ 2-1) remain unchanged, obtain burst
(
n=0,1 ...,
N-1); The number of winning the confidence sequence
The 1st ~
,
, be the frequency-region signal of transmitting terminal institute the transmission of data behind Digital Modulation.
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| CN103281273A (en) * | 2013-05-30 | 2013-09-04 | 东南大学 | Direct-current offset optimization method of multi-carrier visible light communication system |
| CN104901918A (en) * | 2015-06-15 | 2015-09-09 | 电子科技大学 | Method for generating OFDM (orthogonal frequency division multiplexing) data sequence based on Chirp signal and synchronization method |
| CN105471799A (en) * | 2015-11-26 | 2016-04-06 | 上海交通大学 | Sidelobe suppression prefix-based DWDM-OFDM implementation method and system thereof |
| US11090763B2 (en) | 2017-10-20 | 2021-08-17 | Concept Laser Gmbh | Build material application device for an apparatus for additively manufacturing three-dimensional components |
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| US11090763B2 (en) | 2017-10-20 | 2021-08-17 | Concept Laser Gmbh | Build material application device for an apparatus for additively manufacturing three-dimensional components |
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