CN103227768A - Application of novel ICI self-eliminating method in OFDM modulation - Google Patents

Abstract

The invention discloses a method applied to an OFDM (Orthogonal Frequency Division Multiplexing) modulation system. Combination signal processing is performed in a frequency domain and a time domain. The system consists of an OFDM modulator, namely a sending end, and an OFDM demodulator, namely a receiving end. The method comprises the steps that before the sending end performs iFFT (Inverse Fast Fourier Transform), information is transmitted at even subcarriers, and 0 is filled in odd subcarriers; or the information is transmitted at the odd subcarriers, and 0 is filled in the odd subcarriers; or data is transmitted at the subcarriers capable of being divided exactly by 4, and 0 is filled in the rest of subcarriers to ensure that an effect of ICI (Inter-Carrier Interference) is further eliminated. A time domain waveform subjected to the processing has symmetry, and can be compressed; an opposite course is performed at the receiving end, and the waveform is subjected to reduction and FFT (Fast Fourier Transform) according to the symmetry; on the premise that the channel transmission efficiency is not reduced, the effect of the ICI can be reduced significantly, and a channel utilization ratio is not changed basically; and a core concept of the method is that adjacent subcarrier terms are compressed in the frequency domain in order to eliminate the effect of the ICI, and the time domain waveform is compressed in the time domain according to the symmetry in order to improve the channel transmission efficiency.

Description

A kind of new application of ICI self elimination method in the OFDM modulation

Technical field

The method that the present invention proposes, (Orthogonal Frequency Division Multiplexing OFDM) in the modulation, belongs to the mobile communication technology field to can be applicable to OFDM.

Technical background

At OFDM/QAM(QAM, Quadrature Amplitude Modulation, quadrature amplitude modulation) in the transmission system, the Doppler frequency displacement that frequency selective fading that mobile multipath channel causes and high-speed mobile cause is two principal elements that influence transmission reliability.Move Doppler's (Doppler) frequency displacement cause and the reference frequency difference between the transceiver, all can produce frequency deviation, frequency deviation can cause disturbing (ICI) between subcarrier in the OFDM symbol; A thinking that reduces the ICI influence is, adopt various algorithms to estimate the Doppler frequency shift value, manage to calculate the ICI size then, and manage to eliminate, but when channel conditions deteriorate, it is very difficult accurately to estimate frequency deviation value, especially under mobile environment, the influence of Doppler frequency shift effect is dynamic change, is difficult to accurate tracking, the combined effect of multipath and interchannel noise, can obviously reduce algorithm effect, especially to high order modulation (as 16QAM, 64QAM), when signal to noise ratio (snr) was not high, improvement effect was relatively poor.

Another thinking that reduces the ICI influence is, modulation improves to OFDM, fundamentally eliminates the influence of frequency deviation to ICI, and these class methods are called the ICI self elimination method, and its essence is that modulation improves to OFDM, eliminates the basic reason that produces ICI.The most classical a kind of ICI self elimination method is, before carrying out iFFT, make adjacent odd even subcarrier opposite number each other, promptly with the identical information of a pair of odd even subcarrier transmission, claim adjacent sub-carriers to repeat (Adjacent Sub-carrier Repeat, ASR) method again.From eliminating the OFDM modulating system, can obviously reduce the ICI influence based on the ICI of ASR, but it is original 50% to cause modulation efficiency (or channel utilization) to be reduced to, and loses more than gain.

Summary of the invention

Goal of the invention of the present invention: when carrying out the OFDM modulation, handle, fundamentally eliminate the influence of ICI, and do not reduce bandwidth availability ratio to transmission performance by the allied signal of frequency domain and time domain.

Technical scheme of the present invention is: make discovery from observation, odd subcarriers is filled out the time domain waveform of the OFDM symbol after 0, its first half and latter half are identical, utilize this characteristic, only need send the first half of OFDM symbol at transmitting terminal, utilize above characteristic to recover compressed time domain waveform at receiving terminal.Also can transmit data in odd subcarriers, even subcarriers fills out 0; Perhaps expand this paper scheme, can be by the 4 subcarrier transmitting datas of dividing exactly, all the other subcarriers fill out 0, make it further eliminate the influence of ICI.

For this reason, the present invention proposes: in even subcarriers transmission data, odd subcarriers fills out 0, has so just removed the influence that all odd subcarriers are brought, and comprises the adjacent sub-carrier that influence is bigger.

In conventional ofdm communication system, suppose because Doppler effect or because the carrier deviation normalized value that causes of crystal oscillator deviation is ε.Under the additive Gaussian channel situation, the restituted signal of k subcarrier of receiving terminal can be described as:

$Z_k=X_k{\mathrm{<figure-callout\; id="0"\; label="S"\; filenames="HDA00003126189100012.png"\; state="\{\{state\}\}">S</figure-callout>}}_0+\underset{i=0,i\&NotEqual;k}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_i{S}_{k-i}+N_k,k=\mathrm{0,1},...,N-1---\left(1\right)$

Wherein N is the carrier wave sum, X _kBe to upload defeated data at k subcarrier, X _kS ₀Be the useful signal part, N _kIt is additive Gaussian noise; S _K-iBe that i subcarrier given k the ICI influence value size that subcarrier brings, can be expressed as:

$S_{k-i}=\frac{\sin \left[\mathrm{\&pi;}(k-i+\mathrm{\&epsiv;})\right]}{N\sin \left[\frac{\mathrm{\&pi;}}{N}(k-i+\mathrm{\&epsiv;})\right]}\&CenterDot;\exp \left[\mathrm{j\&pi;}(1-1/N)(k-i+\mathrm{\&epsiv;})\right]---\left(2\right)$

Wherein ε=Δ f/fs is the normalization carrier wave frequency deviation.When not having carrier wave frequency deviation (ε=0), S ₀=1, S _K-i=0, there is not the influence of ICI this moment.When having frequency deviation, S _K-i≠ 0,

Be total ICI interference value.Observe S _K-iWaveform finds that to distracter contribution maximum is S _K-i=+1, the item of-1 o'clock correspondence, and these two just in time be the adjacency of current k subcarrier; If do not send this two adjacent sub-carrier items, i.e. X in modulated terminal _K-1=X _K+1=0, then fundamentally eliminated two maximum in the ICI interference value.In the OFDM modulated terminal, if at k=0,2 ... 4, N-sends signal on the subcarrier, at k=1,3,5 ..., N-3, not sending signal on the N-1 subcarrier (is X _k=0, k=1,3,5 ..., N-3 N-1), just can reach basic I CI from the purpose of eliminating.

But, at k=1,3,5 ..., do not send signal on the N-1 subcarrier, can make data quantity transmitted reduce half, promptly channel utilization has reduced half.But, (be the ICI self elimination method that proposes above X _k=0, k=1,3,5 ..., N-1) in the output signal expression formula of substitution OFDM modulator, we have found a peculiar phenomenon: two parts are identical before and after the time domain waveform of output OFDM symbol.We claim that this phenomenon is the symmetry of time domain waveform.Utilize symmetry, can be on time domain waveform as another be reduce, recover according to symmetry again at demodulating end.Through after the above-mentioned processing, channel utilization is identical with conventional ofdm system.

Also can transmit data in odd subcarriers, even subcarriers fills out 0; Perhaps expand said method, can be by the 4 subcarrier transmitting datas of dividing exactly, all the other subcarriers fill out 0, make it further eliminate the influence of ICI.Emulation and experiment test show that this scheme can significantly reduce the influence of ICI under the prerequisite that does not reduce Channel Transmission efficient.

The core concept that suppresses the ICI self elimination method of adjacent sub-carrier is: on frequency domain the adjacent sub-carrier item is compressed, to eliminate the influence of ICI; On time domain, utilize symmetry compression time domain waveform, to improve Channel Transmission efficient.

The symmetry of time domain waveform is derived as follows.

In the OFDM modulation, can be expressed as through the output signal after N point inverse discrete Fourier transform/inverse fast fourier transform (iDFT/iFFT) module:

$x\left(n\right)=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}X\left(k\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\mathrm{nk}\right),n=\mathrm{0,1},...,N-1---\left(3\right)$

Wherein N is an even number, because of odd subcarriers is filled with 0, and X (1)=X (3)=...=X (2n+1)=...=X (N-3)=X (N-1)=0, substitution (3) formula:

$x\left(n\right)=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)n\right),n=0,1,...,N-1$

$=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)n\right),n=\mathrm{0,1},...,N/2-1$

$=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)n\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;i}\right),n=\mathrm{0,1},...,N/2-1$

$=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)(n+N/2)\right),n=\mathrm{0,1},...,N/2-1---\left(4\right)$

$=x(n+N/2)$

X (n)=x (n+N/2), front and back two parts of expression time domain waveform x (n) are identical.

Suppressing the application principle of ICI self elimination method in the OFDM modulation of adjacent sub-carrier sees shown in Figure 1; It is a kind of improved OFDM transmission system, is made of improved OFDM modulator (transmitting terminal) and improved ofdm demodulator (receiving terminal).

At transmitting terminal, data flow is admitted to nQAM mapper (Mapper) earlier and carries out the planisphere mapping, and N/2 is to data in output, sends into 2 times of up-samplers then, and N is to data in output; This N satisfies the condition that suppresses adjacent sub-carrier to data:

X _K≠0,k=0,2,...,4N-,X _k≠0,k=0,2,...,4N-,

X _k=0,k=1,3,...,5N-,X _k=0,k=1,3,...,5N-,

This N is transfused to N point inverse discrete Fourier transform/inverse fast fourier transform (iDFT/iFFT) module to parallel data, and the output duration is T _SThe OFDM symbol, through behind the parallel serial conversion, the time domain waveform of two parts identical (symmetry) before and after becoming; After this waveform process waveform compressor compresses, the output duration is T _S/ 2 time-domain signal; After this signal process prefixing (CP) processing and the quadrature modulation module, export a brand-new OFDM modulated signal.

The processing procedure of demodulator is the inverse process of said process substantially.

Beneficial effect of the present invention is: compare with conventional OFDM modulating system, the present invention can reduce significantly between subcarrier and to disturb (ICI) to receiving Effect on Performance, especially move, under the multipath scene, and channel utilization is basic consistent with conventional OFDM modulating system; Compare with typical ICI self elimination method, channel utilization has improved nearly one times, and on the elimination effect of ICI to the reception performance impact, two kinds of methods are equally matched.

Description of drawings

Fig. 1 is the OFDM modulation demodulation system theory diagram that adopts the present invention program's correspondence

Fig. 2 is conventional ofdm system and the contrast of 2 rank ICI of the present invention ICI distracter in the corresponding ofdm system of cancellation scheme

Fig. 3 is that Fig. 3 is an ofdm signal spectral decomposition schematic diagram under the different schemes, from scheming as can be seen useful signal and the situation of change of ICI interference signal under different frequency deviations under the frequency domain

Fig. 4 is the following 4 kinds of option b ER performance comparison of Dan Jing, Gaussian channel

Fig. 5 is the following 3 kinds of option b ER performance comparison of rural multipath (RAX) channel

Fig. 6 is the following 2 kinds of option b ER performance comparison of city multipath (TUX) channel.

Specific embodiments

1 basic scheme

The application principle of the ICI self elimination method of inhibition adjacent sub-carrier in the OFDM modulation as shown in Figure 1, at transmitting terminal, data flow is admitted to nQAM mapper (Mapper) earlier and carries out the planisphere mapping, N/2 is to data in output, the N point inverse discrete Fourier transform/inverse fast fourier transform (iDFT/iFFT) of 2 times of up-samplings, and process then module.Data behind up-sampling, the even subcarriers correspondence be data, odd subcarriers is filled with 0, after the iDFT/iFFT module, output length is T _SThe OFDM symbol, front and back two parts of this symbol time domain waveform identical (symmetry).

Behind the IDFT, the expression formula of output signal is:

$x\left(n\right)=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}X\left(k\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\mathrm{nk}\right),n=\mathrm{0,1},...,N-1---\left(5\right)$

Wherein N is an even number, because of odd subcarriers is filled with 0, and X (1)=X (3)=...=X (2n+1)=...=X (N-3)=X (N-1)=0, substitution (1) formula:

$x\left(n\right)=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)n\right),n=0,1,...,N-1$

$=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)n\right),n=\mathrm{0,1},...,N/2-1$

$=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)n\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;i}\right),n=\mathrm{0,1},...,N/2-1$

$=\frac{1}{N}\underset{i=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}X\left(2i\right)\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003126189100012.png,HDA00003126189100021.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;}}{N}\left(2i\right)(n+N/2)\right),n=\mathrm{0,1},...,N/2-1---\left(6\right)$

$=x(n+N/2)$

X (n)=x (n+N/2), front and back two parts of expression time domain waveform x (n) are identical, thus, x (n) sequence can be carried out the time domain compression.

Also can adopt odd subcarriers transmission be data, even subcarriers by 0 scheme of filling, be the negative symmetries of front and back two parts at this moment through the OFDM symbol of exporting behind the iDFT/iFFT.

Utilize before and after the OFDM symbol identical or this characteristic on the contrary of two parts, half that can a transmission OFDM symbol waveform in data compressing module, second half is compressed.Before carrying out iFFT, because adjacent sub-carrier filled out 0, make channel utilization descend half, but OFDM meet and has been compressed half on the time domain, make the identical of channel utilization and conventional OFDM transmission system.But after adjacent sub-carrier is removed, can eliminate the influence of the ICI that frequency deviation causes.

The expansion of 2 high-orders

Above-mentioned basic scheme also can be carried out the more expansion of high-order, for example, and only can be by the 4 subcarrier transmitting data symbols of dividing exactly in carrier number, on other aspect, fill 0, through the OFDM symbol waveform behind the iFFT, be that the cycle is identical with Ts/4, can be with all the other 3/4 waveform compressions.Such high-order expansion meeting can bring better influence for ICI from the elimination aspect than basic scheme before, when not considering that CP influences, because of on time domain waveform being compressed, can not reduce band efficiency; But, because meeting all after each compression will be added CP,, when expanding too much, will produce obvious influence to channel utilization to eliminate intersymbol interference (ISI).Simultaneously, when realizing, the high-order expansion can consume more hardware resource.But, in this programme, what transmit on a lot of subcarriers all is 0, can utilize this characteristic, improves the IDFT algorithm, reduces requirement to resource with this.In actual applications, can utilize and can or be come transmission information by 4 subcarriers of dividing exactly by 2, other subcarriers fill out 0, can take into account ICI like this and eliminate contradiction between effect, resource consumption and the channel utilization.

3ICI is to the influence of performance of BER

In conventional ofdm communication system, suppose because Doppler effect or because the carrier deviation normalized value that causes of crystal oscillator deviation is ε.Under the additive Gaussian channel situation, can be described as at the restituted signal of k subcarrier of receiving terminal:

$Z_k={\mathrm{<figure-callout\; id="0"\; label="X\; k\; S"\; filenames="HDA00003126189100012.png"\; state="\{\{state\}\}">X</figure-callout>}}_k{S}_{}{}_0+\underset{i=0,i\&NotEqual;k}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_i{S}_{k-i}+N_k,k=\mathrm{0,1},...,N-1---\left(7\right)$

Wherein N is the carrier wave sum, and Xk uploads defeated data at k subcarrier, N _kBe pairing additive Gaussian noise, S _K-iBe that i subcarrier given k the ICI influence value size that subcarrier brings, can be expressed as:

$S_{k-i}=\frac{\sin \left[\mathrm{\&pi;}(k-i+\mathrm{\&epsiv;})\right]}{N\sin \left[\frac{\mathrm{\&pi;}}{N}(k-i+\mathrm{\&epsiv;})\right]}\&CenterDot;\exp \left[\mathrm{j\&pi;}(1-1/N)(k-i+\mathrm{\&epsiv;})\right]---\left(8\right)$

Wherein ε=Δ f/fs is the normalization carrier wave frequency deviation.Formula (7) right half part first term is needed useful signal, when not having carrier wave frequency deviation (ε=0), and S ₀=1, S _I-k=0, there is not the influence of ICI this moment.

The basic I CI that proposes for the present invention is from elimination system (2 rank scheme), and the restituted signal of k subcarrier of receiving terminal can be described as:

$Z_k^{\&prime;}={\mathrm{<figure-callout\; id="0"\; label="X\; k\; S"\; filenames="HDA00003126189100012.png"\; state="\{\{state\}\}">X</figure-callout>}}_k{S}_{}{}_0+\underset{i=0,i\&NotEqual;k/2}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{X}_{2i}{S}_{k-2i}+N_k,k=\mathrm{0,2,4},...,N-2---\left(9\right)$

Z' _k＝0，k=1，3，5，...,N-3,N-1

Wherein N is the carrier wave sum, X _kBe to upload defeated data at k subcarrier, N _kBe pairing additive Gaussian noise, S _K-2iBe that 2i subcarrier given k the ICI interference value that subcarrier brings.

Fig. 2 is that conventional system and 2 rank ICI eliminate the S of system certainly _I-kThe mould value relatively, total sub-carrier number N=16 among the figure, it is useful signal S that frequency deviation ε is taken as 0.15 and 0.3,7 work song carrier wave ₀The S of 2 rank ICI elimination systems _K-2iThe S of mould value and conventional system _K-iThe mould value is compared, and quantity has reduced 1 times, and 2 points (adjacent sub-carriers of 7 work song carrier waves) of mould value maximum have not had.

In the formula (7), first is useful signal, and second is total distracter; Fig. 3 is an ofdm signal spectral decomposition schematic diagram, and solid line is 7 work song spectrums of carrier, and chain-dotted line is the frequency spectrum of interfering sub-carrier in the conventional system, and void is scribed ss the present invention 2 rank ICI from the frequency spectrum of eliminating the system interference subcarrier.The imaginary point vertical line is the situation when not having frequency deviation, and this moment, the interference value of two kinds of systems all was 0; Solid vertical line is the situation of frequency deviation ε=0.3 o'clock, and the present invention's this moment 2 rank ICI are significantly less than the interference value of conventional system from the interference value of eliminating system.

According to the theory diagram of Fig. 1, the present invention program has been carried out emulation.Simulation parameter is: N=1024, available subcarrier are 880, and balanced way is the linear interpolation method based on Comb Pilot, select the QPSK mapping mode.

The scene description that emulation is adopted is:

Scheme 1: conventional ofdm system, receiving terminal do not adopt the ICI removing method.

Scheme 2: 2 rank ICI of the present invention are from the elimination system, and receiving terminal does not adopt the ICI removing method.

Scheme 3: 4 rank ICI of the present invention are from the elimination system, and receiving terminal does not adopt the ICI removing method.

Scheme 4: adjacent odd even subcarrier each other the ICI of opposite number from sterilizing system, i.e. ASR(Adjacent Sub-carrier Repeat) system.Promptly two adjacent carriers transmit a pair of data symbol, and what transmit on the odd point subcarrier is the negate symbol of even number point subcarrier symbol.At receiving terminal, the demodulation value of two adjacent carriers of transmission same-sign is adjudicated the data symbol that is transmitted jointly.Under the same map mode, its channel efficiency has descended 50%, and is consistent with top 3 kinds of situations in order to make channel efficiency, must adopt the 16QAM mapping.

Fig. 4 represent above-mentioned four kinds of schemes under Dan Jing (with respect to multipath) condition, the result of different carrier frequency deviation.Respectively emulation single footpath ε=0(be equivalent to Gaussian channel), under ε=0.3 situation, the bit error rate of 4 kinds of schemes (BER) performance; ε=0 o'clock, the performance of BER of scheme 1,2,3 much at one, the bit error rate of scheme 4 is higher than system 1,2,3, this is that when signal to noise ratio was identical, the noise robustness of QPSK was better than 16QAM because under Gaussian channel; ε=0.3 o'clock, adopted ICI to be starkly lower than scheme 1 from the BER of the scheme 2,3,4 of cancellation scheme, wherein, adopted the present invention 4 rank ICI minimum from the bit error rate of the scheme 3 of cancellation scheme, next be 2 rank ICI of the present invention from cancellation scheme, the poorest is adjacent odd even subcarrier each other the ICI of opposite number from disappearing scheme.

Simulation result shows that under the situation that does not reduce band efficiency, the present invention program's error rate rate performance is along with the raising of exponent number can be become better and better.

Under mobile multipath channel environment, simulated channel adopts the 6 tap TUX channels (city multipath channel) and the RAX channel (rural multipath channel) of the classics that define in the 3GPP TR25.943 consensus standard.For the size of the Doppler frequency deviation under the more different mobile channels, it is the normalization maximum Doppler frequency offset that this paper defines ε d, and ε d is the maximum Doppler frequency offset of channel and the ratio of subcarrier spacing.

Bit error rate (BER) performance of Fig. 5 representation scheme 1,2,4 under the RAX channel model, simulated environment is ε d=0.01, ε d=0.2, the smaller and bigger two kinds of situations of corresponding Doppler frequency deviation.Simulation result shows that the BER performance of the present invention program under the RAX channel model is better than scheme 1,4.

Fig. 6 representation scheme 2,4 under the TUX channel model, the BER performance of ε d=0.01 and ε d=0.2, the smaller and bigger two kinds of situations of corresponding Doppler frequency deviation respectively.The result shows that the ICI that the present invention proposes under the TUX channel model is better than scheme 4 from the BER of cancellation scheme performance.

4 band efficiency analyses

The band efficiency of conventional ofdm system is (ignoring the influence of CP):

${\mathrm{\&eta;}}_b=\frac{N\&CenterDot;{\log }_{2}M}{T_s\&CenterDot;B}\mathrm{bit}/(s\&CenterDot;\mathrm{Hz})---\left(10\right)$

The adjacent odd even subcarrier L rank ICI of opposite number each other is the band efficiency (ignoring the influence of CP) of L rank ASR scheme from cancellation scheme:

${\mathrm{\&eta;}}_b=\frac{N/L\&CenterDot;{\log }_{2}M}{T_s\&CenterDot;B}\mathrm{bit}/(s\&CenterDot;\mathrm{Hz})---\left(11\right)$

L of the present invention rank ICI is from the band efficiency (ignoring the influence of CP) of cancellation scheme:

${\mathrm{\&eta;}}_b=\frac{N/L\&CenterDot;{\log }_{2}M}{T_s/L\&CenterDot;B}=\frac{N\&CenterDot;{\log }_{2}M}{T_s\&CenterDot;B}\mathrm{bit}/(s\&CenterDot;\mathrm{Hz})---\left(12\right)$

Wherein, N is the carrier wave number, and Ts is through the OFDM symbol lengths behind the IDFT/IFFT, and M is the system number of the qam mode of employing, the channel width of B for using.Wherein L refers to the exponent number of high-order expansion, and for example L=4 is per 4 same data of sub-carrier transmission in the ASR scheme, is the subcarrier transmitting data of carrier number aliquot 4 in the present invention program, and all the other fill 0.

Comparison expression (10), (11), (12) as can be known, under same map mode (being that nQAM is identical), the present invention program's band efficiency is identical with conventional ofdm system, be the ASR scheme band efficiency L doubly.

When considering the influencing of CP, the present invention program's bandwidth availability ratio slightly reduces, and factor of influence β is:

$\mathrm{\&beta;}=\frac{T_s}{T_s+L\&CenterDot;T_{\mathrm{CP}}}---\left(13\right)$

Conventional ofdm system can be regarded the system of L=1 as; Consider that the CP duration is 1/16 a situation of OFDM symbol duration, 2 rank ICI then of the present invention are that 94.4%, 4 rank ICI of conventional ofdm system is 85% of a conventional ofdm system from the bandwidth availability ratio of cancellation scheme from the bandwidth availability ratio of cancellation scheme.

Take into account the elimination effect certainly of bandwidth availability ratio and ICI, 2 rank ICI of the present invention are best from the combination property of cancellation scheme.

More than show and described basic principle of the present invention and principal character and advantage of the present invention.The technical staff of the industry should be appreciated that; the present invention is not restricted to the described embodiments; that describes in the foregoing description and the specification just illustrates principle of the present invention; without departing from the spirit and scope of the present invention; the present invention also has various changes and modifications; these changes and improvements all fall in the claimed scope of the invention, and the claimed scope of the present invention is defined by its equivalent of appending claims.

Claims (4)

1. the application of new ICI self elimination method in the OFDM modulation, by the OFDM modulator is that transmitting terminal and ofdm demodulator are that receiving terminal constitutes, it is characterized in that, at transmitting terminal, subcarrier is divided into even subcarriers and odd subcarriers, only send information in even subcarriers, odd subcarriers fills out 0, perhaps conversely: utilize symmetry that time domain waveform is compressed then:

A, in even subcarriers transmission information, odd subcarriers fills out 0, its process is as follows, at transmitting terminal, data flow is admitted to nQAM mapper (Mapper) earlier and carries out the planisphere mapping, N/2 is to data in output, sends into 2 times of up-samplers then, N is to data in output; This N satisfies the condition that suppresses adjacent sub-carrier to data:

X _k≠0,k＝0,2,4,...,N-2

X _k＝0,k＝1,3,5,...,N-1

This N is transfused to N point inverse discrete Fourier transform/inverse fast fourier transform (iDFT/iFFT) module to parallel data, and the output duration is T _SThe OFDM symbol, through behind the parallel serial conversion, the time domain waveform of two parts identical (symmetry) before and after becoming; After this waveform process waveform compressor compresses, the output duration is T _S/ 2 time-domain signal; After this signal process prefixing (CP) processing and the quadrature modulation module, export a brand-new OFDM modulated signal, the processing procedure of demodulator then is the inverse process of said process;

B, in odd subcarriers transmission information, even subcarriers fills out 0, its process is as follows, at transmitting terminal, data flow is admitted to nQAM mapper (Mapper) earlier and carries out the planisphere mapping, N/2 is to data in output, sends into 2 times of up-samplers then, N is to data in output; This N satisfies the condition that suppresses adjacent sub-carrier to data:

X _k≠0,k=1,3,5,...,N-1

X _k=0,k=0,2,4,...,N-2

This N is transfused to N point inverse discrete Fourier transform/inverse fast fourier transform (iDFT/iFFT) module to parallel data, and the output duration is T _SThe OFDM symbol, through behind the parallel serial conversion, the time domain waveform of identical, the opposite in sign (symmetry) of two parts absolute value before and after becoming; After this waveform process waveform compressor compresses, the output duration is T _S/ 2 time-domain signal; After this signal process prefixing (CP) processing and the quadrature modulation module, export a brand-new OFDM modulated signal, the processing procedure of demodulator then is the inverse process of said process.

2. a kind of new application of ICI self elimination method in the OFDM modulation according to claim 1 is characterized in that behind the inverse discrete Fourier transform (IDFT), the expression formula of output signal is:

Wherein N is an even number, because of odd subcarriers is filled with 0, and X (1)=X (3)=...=X (2n+1)=...=X (N-3)=X (N-1)=0, substitution (1) formula:

X (n)=x (n+N/2), front and back two parts of expression time domain waveform x (n) are identical, thus, x (n) sequence can be carried out the time domain compression;

Also can adopt odd subcarriers transmission be data, even subcarriers by 0 scheme of filling, be the negative symmetries of front and back two parts at this moment through the OFDM symbol of exporting behind the iDFT/iFFT.

3. a kind of new application of ICI self elimination method in the OFDM modulation according to claim 1 is characterized in that after receiving terminal was expanded (decompression), FFT module through waveform, the restituted signal of k subcarrier can improve and be described as:

Z' _k＝0，k=1，3，5，...,N-3,N-1

Wherein N is the carrier wave sum, X _kBe to upload defeated data at k subcarrier, Nk is pairing additive Gaussian noise, S _K-2iBe that 2i subcarrier given k the ICI interference value that subcarrier brings.

4. according to claim 1 or the 2 or 3 described a kind of new application of ICI self elimination method in the OFDM modulation, it is characterized in that, can carry out more high-order expansion, at transmitting terminal, can uploaded transmission information by 4 even subcarriers that divide exactly, all the other subcarriers fill out 0; Utilizing symmetry that time domain waveform is carried out 4 multiplication of voltages then contracts.

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