CN103647744A - Communication method based on OFCDM (Orthogonal Frequency and Code Division Multiplexing) and modulation-demodulation of related domain - Google Patents

Abstract

The invention relates to a communication method based on OFCDM (Orthogonal Frequency and Code Division Multiplexing) and modulation-demodulation of a related domain, belonging to the technical field of communication anti-jamming. According to the method provided by the invention, based on an OFCDM system, a sending terminal carries out the related domain modulation on a sending bit in a time-frequency domain formed by a coherent bandwidth and a coherent time, a receiving terminal carries out the related domain demodulation on a received data block, and the sending bit is demodulated according to correlation values of the two data blocks. Compared with the OFCDM system, the communication method has the advantages that the link of the receiving terminal is simple, and a good BER (Bit Error Rate) performance can be realized just by carrying out related modulation-demodulation in a time-frequency coherent channel without knowing the spreading code block selected by the sending terminal and channel estimation and frequency domain balance, so that the system complexity is lowered.

Description

A kind of communication means based on OFCDM and domain of dependence modulation /demodulation

Technical field

The invention belongs to Communication Anti-Jamming Techniques field, relate to orthogonal frequency and code division multiplexing (Orthogonal Frequency and Code Division Multiplexing, OFCDM) technology and domain of dependence modulation-demodulation technique.

Background technology

Orthogonal frequency and code division multiplexing (Orthogonal Frequency and Code Division Multiplexing, OFCDM) be a kind of based on MC-CDMA (Multi-carrier Code Division Multiple Access, MC-CDMA) and the technology of OFDM (Orthogonal Frequency Division Multiplexing, OFDM).OFCDM essence is the same with MC-CDMA, the lower character rate of each subcarrier transmission, and the multipath that can effectively suppress so to be mainly present in broad-band channel disturbs.The complete block diagram of OFCDM system as shown in Figure 1, is with the difference of ofdm system, and first OFCDM carries out two-dimensional expansion before the subcarrier mapping of transmitting terminal, after the solution subcarrier mapping of receiving terminal, carries out two-dimentional despreading.If the transmitting-receiving two-end of OFCDM system will successfully communicate, receiving terminal must carry out channel estimating and must know the local frequency expansion sequence of transmitting terminal, otherwise cannot eliminate channel effect and realize receiving terminal despreading.

Coherence bandwidth is an important parameter that characterizes multipath channel characteristic, and within the scope of coherence bandwidth, multipath channel has constant gain and linear phase, and the decline of signal is height correlation, can think decline approximately equal; And if signal bandwidth is greater than coherence bandwidth, the channel magnitude value that surpasses so two frequencies of coherence bandwidth at interval is similar to independently, and now in signal bandwidth, channel magnitude changes greatly.Also be an important parameter that characterizes multipath channel coherence time, within coherence time, can think that channel is correlated with in time domain, and the time interval surpasses two data of coherence time, can think that the time domain channel that they experience is separate.

Summary of the invention

The present invention be take OFCDM system as basis, according to the coherence bandwidth calculating, at transmitting terminal, to sending bit, carries out domain of dependence modulation, at receiving terminal, carries out domain of dependence demodulation, according to the correlation of two code blocks, demodulates transmission bit.

Whole system link of the present invention as shown in Figure 3, comprising: digitlization information source, coherence bandwidth and calculating coherence time, generating orthogonal spread spectrum code block, domain of dependence modulation, FFT/IFFT, add/go the modules such as CP module, channel, correlation value calculation, normalization factor calculating, correlation normalization, judgement demodulation and output.

Detailed technology scheme of the present invention is as follows:

A communication means based on OFCDM and domain of dependence modulation /demodulation, comprises the following steps:

Step 1: according to the maximum delay σ of channel _τand Doppler frequency shift f _dthe coherence bandwidth B of computing system _c=1/ σ _τwith T coherence time _c=1/f _d.Have determined coherence bandwidth and coherence time the domain of dependence size of channel, then zygote carrier spacing Δ f and sampling time t _scalculate the sub-carrier number N that coherence bandwidth is crossed at frequency domain _fwith the lasting timeslot number N of coherence time in time domain _t, as shown in Figure 2.

Step 2: as shown in Figure 2, the domain of dependence size calculating according to step 1, determines that orthogonal spectrum expansion code block size is L * N _t, L=N wherein _f/ 2.The orthogonal intersection set of blocks generating is P={P ₁p ₂p _k, every two different spread spectrum code blocks quadrature mutually wherein.

Step 3: determine according to the total sub-carrier number of system and spreading code block size the bit number M that every frame can send, and produce M position information bit by digitlization information source.

Step 4: domain of dependence modulation.Its detailed process as shown in Figure 4.

If information bit b _m=1,

Steps A: 2 spread spectrum code block P of random selection from orthogonal spectrum expansion code block _iwith P _j(i=j), the transmission information after domain of dependence modulation is [P _ip _j].

If information bit b _m=0,

Step B: 2 spread spectrum code block P of random selection from orthogonal spectrum expansion code block _iwith P _j(i ≠ j), the transmission information after domain of dependence modulation is [P _ip _j].

Step 5: the data after domain of dependence modulation are carried out to IFFT conversion, and send after adding CP.Send data and after channel, arrive receiving terminal.

Step 6: receiving terminal preliminary treatment.The signal receiving is removed to CP, and then FFT transforms to frequency domain.

Step 7: press spreading code block size L * N _t, get respectively two adjacent data R ₁=[y ₁; y ₂; y _l] and R ₂=[y _l+1; y _l+2; y _2L], wherein L is the frequency domain length of spread spectrum code block, y _l=H _lx _l, l=1 ..., L is that length is 1 * N _tvector, represent to receive the capable data of l of data block, x _lthe capable data of l of each data block after the relevant spread spectrum of expression transmitting terminal, H _lfor corresponding frequency domain channel data.

Step 8: domain of dependence demodulation.

Step 8-1: calculate correlation.Correlation $D=|R_1*R_2^H|=\left|\underset{l=1}{\overset{l=L}{\mathrm{\Σ}}}{y}_l{y}_{L+l}^H\right|.$

Step 8-2: calculate correlation normalization factor.Correlation normalization factor

Step 8-3: correlation normalization.Correlation after normalization

Step 8-4: judgement.If

the information bit of adjudicating before domain of dependence modulation is " 1 "; If

the information bit of adjudicating before domain of dependence modulation is " 0 ".

The invention has the beneficial effects as follows:

The invention provides a kind of communication means based on OFCDM and domain of dependence modulation /demodulation, this technology be take OFCDM system as basis, in the time-frequency domain forming in coherence bandwidth and coherence time, carry out domain of dependence modulation, each information bit distributes two spread spectrum code blocks, if information bit is " 1 ", two spread spectrum code blocks are relevant, if information bit is " 0 ", two spread spectrum code blocks are uncorrelated.At receiving terminal, carry out domain of dependence demodulation, the code block correlation according to after normalization, rules out corresponding information bit.

Compare OFCDM system, receiving terminal link of the present invention is simple, do not need the spread spectrum code block of knowing that transmitting terminal is selected, do not need to carry out channel estimating and frequency domain equalization yet, as long as be correlated with in the relevant channel of time-frequency, modulation /demodulation can reach good BER performance, greatly reduces system complexity.The BER performance of proof system under multipath channel is along with the increase gradually of the channel degree of correlation only can approach the BER performance through awgn channel gradually in emulation, and the BER performance under flat fading is better than the BER performance of only passing through awgn channel.

Accompanying drawing explanation

Fig. 1 is the holonomic system block diagram of OFCDM system.

Fig. 2 is obtained the schematic diagram of orthogonal spectrum expansion code block size by domain of dependence size.

Fig. 3 is the system block diagram of domain of dependence modulation and demodulation in the present invention's OFCDM system used.

Fig. 4 is the flow chart of the domain of dependence modulation that proposes of the present invention.

Embodiment

A kind of communication means based on OFCDM and domain of dependence modulation /demodulation of the present invention, to be transmitting terminal carry out domain of dependence modulation to its main innovation in coherence bandwidth and the time-frequency domain that forms coherence time, receiving terminal does not need the spread spectrum code block of knowing that transmitting terminal is selected, do not need to carry out channel estimating and frequency domain equalization, only according to the correlation of code block, carry out demodulation yet.When the channel degree of correlation is higher, system can obtain good BER performance.

A communication means based on OFCDM and domain of dependence modulation /demodulation, comprises the following steps:

Step 1: according to the maximum delay σ of channel _τand Doppler frequency shift f _dthe coherence bandwidth B of computing system _c=1/ σ _τwith T coherence time _c=1/f _d.Have determined coherence bandwidth and coherence time the domain of dependence size of channel, then zygote carrier spacing Δ f and sampling time t _scalculate the sub-carrier number N that coherence bandwidth is crossed at frequency domain _fwith the lasting timeslot number N of coherence time in time domain _t, as shown in Figure 2.

Step 2: as shown in Figure 2, the domain of dependence size calculating according to step 1, determines that orthogonal spectrum expansion code block size is L * N _t, L=N wherein _f/ 2.The orthogonal intersection set of blocks generating is P={P ₁p ₂p _k, every two different spread spectrum code blocks quadrature mutually wherein.

Step 3: determine according to the total sub-carrier number of system and spreading code block size the bit number M that every frame can send, and produce M position information bit by digitlization information source.

Step 4: domain of dependence modulation.Its detailed process as shown in Figure 4.

If information bit b _m=1,

Steps A: 2 spread spectrum code block P of random selection from orthogonal spectrum expansion code block _iwith P _j(i=j), the transmission information after domain of dependence modulation is [P _ip _j].

If information bit b _m=0,

Step B: 2 spread spectrum code block P of random selection from orthogonal spectrum expansion code block _iwith P _j(i ≠ j), the transmission information after domain of dependence modulation is [P _ip _j].

Step 5: the data after domain of dependence modulation are carried out to IFFT conversion, and send after adding CP.Send data and after channel, arrive receiving terminal.

Step 6: receiving terminal preliminary treatment.The signal receiving is removed to CP, and then FFT transforms to frequency domain.

Step 7: press spreading code block size L * N _t, get respectively two adjacent data R ₁=[y ₁; y ₂; y _l] and R ₂=[y _l+1; y _l+2; y _2L], wherein L is the frequency domain length of spread spectrum code block, y _l=H _lx _l(l=1 ..., be L) that length is 1 * N _tvector, represent to receive the capable data of l of data block, x _lthe capable data of l of each data block after the relevant spread spectrum of expression transmitting terminal, H _lfor corresponding frequency domain channel data.

Step 8: domain of dependence demodulation.

Step 8-1: calculate correlation.Correlation $D=|R_1*R_2^H|=\left|\underset{l=1}{\overset{l=L}{\mathrm{\Σ}}}{y}_l{y}_{L+l}^H\right|.$

Step 8-2: calculate correlation normalization factor.Correlation normalization factor

Step 8-3: correlation normalization.Correlation after normalization

Step 8-4: judgement.If the information bit of adjudicating before domain of dependence modulation is " 1 "; If

the information bit of adjudicating before domain of dependence modulation is " 0 ".

Claims (1)

1. the communication means based on OFCDM and domain of dependence modulation /demodulation, comprises the following steps:

Step 1: according to the maximum delay σ of channel _τand Doppler frequency shift f _dthe coherence bandwidth B of computing system _c=1/ σ _τwith T coherence time _c=1/f _d; Have determined coherence bandwidth and coherence time the domain of dependence size of channel, then zygote carrier spacing Δ f and sampling time t _scalculate the sub-carrier number N that coherence bandwidth is crossed at frequency domain _fwith the lasting timeslot number N of coherence time in time domain _t;

Step 2: the domain of dependence size calculating according to step 1, determine that orthogonal spectrum expansion code block size is L * N _t, L=N wherein _f/ 2; The orthogonal intersection set of blocks generating is P={P ₁p ₂p _k, every two different spread spectrum code blocks quadrature mutually wherein;

Step 3: determine according to the total sub-carrier number of system and spreading code block size the bit number M that every frame can send, and produce M position information bit by digitlization information source;

Step 4: domain of dependence modulation; Its detailed process is as follows:

If information bit b _m=1,

Steps A: 2 spread spectrum code block P of random selection from orthogonal spectrum expansion code block _iwith P _j, and i=j, the transmission information after domain of dependence modulation is [P _ip _j];

If information bit b _m=0,

Step B: 2 spread spectrum code block P of random selection from orthogonal spectrum expansion code block _iwith P _j, and i ≠ j, the transmission information after domain of dependence modulation is [P _ip _j];

Step 5: the data after domain of dependence modulation are carried out to IFFT conversion, and send after adding CP; Send data and after channel, arrive receiving terminal;

Step 6: receiving terminal preliminary treatment; The signal receiving is removed to CP, and then FFT transforms to frequency domain;

Step 7: press spreading code block size L * N _t, get respectively two adjacent data R ₁=[y ₁; y ₂; y _l] and R ₂=[y _l+1; y _l+2; y _2L], wherein L is the frequency domain length of spread spectrum code block, y _l=H _lx _l(l=1 ..., be L) that length is 1 * N _tvector, represent to receive the capable data of l of data block, x _lthe capable data of l of each data block after the relevant spread spectrum of expression transmitting terminal, H _lfor corresponding frequency domain channel data;

Step 8: domain of dependence demodulation; Detailed process is as follows:

Step 8-1: calculate correlation, correlation $D=|R_1*R_2^H|=\left|\underset{l=1}{\overset{l=L}{\mathrm{\Σ}}}{y}_l{y}_{L+l}^H\right|;$

Step 8-2: calculate correlation normalization factor, correlation normalization factor

Step 8-3: correlation normalization, the correlation after normalization

Step 8-4: judgement;

the information bit of adjudicating before domain of dependence modulation is " 1 "; If

the information bit of adjudicating before domain of dependence modulation is " 0 ".

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