CN103973619A - Signal transmission method for single-carrier modulation with time-frequency domain combination - Google Patents

Abstract

The invention relates to a signal transmission method for single-carrier modulation with time-frequency domain combination and belongs to the technical field of digital information transmission. The method comprises the steps that channel coding and constellation labeling are sequentially conducted on information generated by a sending end and mapped symbols are obtained; the mapped symbols are combined into a data block, a pilot carrier composed of a plurality of UWs is inserted into the front end of the data block, and a UW is inserted into the rear end of the data block, so that a time-frequency domain combined single-carrier modulation symbol block is formed; operations such as symbol synchronization, frequency synchronization and frequency-domain balance are accomplished by a receiving end through the pilot carrier at the front end of the data block and the UW at the rear end of the data block in the received time-frequency domain combined single-carrier modulation symbol block, and constellation inverse labeling, channel decoding and original information recovery are sequentially conducted. The method keeps the advantage of low complexity of the SC-FDE technology, estimation of a channel response by the receiving end is more accurate, the system processing efficiency is higher, and the method is more suitable for a broadband wireless mobile communication system.

Description

A kind of method for transmitting signals that adopts time domain and frequency domain combined single-carrier modulated

Technical field

The invention belongs to digital information transmission technical field, relate in particular to the single-carrier modulated technology in wideband wireless mobile communication system.

Background technology

In wideband wireless mobile communication system, transmit and in communication process, tend to be subject to that various objects in environment causedly block, absorb, the impact of reflection, refraction and diffraction, form mulitpath signal component and arrive receiver.The signal component in different paths has different propagation delays, phase place and amplitude, and is attached with interchannel noise, and their stack can make composite signal cancel out each other or strengthen, and causes serious decline.This decline can make the reception signal of receiver produce distortion, reduces the reliability of communication.In addition, if transmitter or receiver, in relative-movement state, due to the existence of Doppler effect, receive signal and can produce even more serious distortion.Traditional time domain equalization can be eliminated intersymbol interference (the InterSymbol Interference that multipath brings, hereinafter to be referred as ISI), the waveform that it utilizes time waveform that equalizer produces to go direct correction to distort, makes to comprise that the impulse response of the whole system of equalizer meets without intersymbol interference condition.Because computation complexity and the maximum delay of time domain equalization is extended to proportional relation, the implementation complexity that this has increased time domain equalization system greatly, has limited its application in wideband wireless mobile communication.(expansion of so-called maximum delay, just refers to the difference of maximum transmitted time delay and minimum transfer time delay, and the difference of last distinguishable delay time signal and first delay time signal time of advent, is exactly in fact the time of pulse stretching.)

The transport stream signal journey of OFDM (Orthogonal Frequency Division Multiplexing, hereinafter to be referred as OFDM) system as shown in Figure 1.The laggard planetary mapping of encoding of information source channel obtains data flow, then data flow is converted to multidiameter delay data block and data block is carried out to inverse fast fourier transform (Inverse Fast Fourier Transform, hereinafter to be referred as IFFT) data block is transformed into time domain, the last rear ofdm signal that forms of Cyclic Prefix (Cyclic Prefix, hereinafter to be referred as CP) that inserts before each data block of time domain is launched; Ofdm signal arrives receiving terminal after by transmission, receiving terminal carries out fast fourier transform (Fast Fourier Transform after removing CP to the received signal, hereinafter to be referred as FFT) convert back frequency domain, through the laggard planetary inverse mapping of equilibrium, channel decoding, recover raw information (stay of two nights).

Above-mentioned transmission method is a kind of efficient modulation system, and owing to having, the advantage such as the availability of frequency spectrum is high, anti-frequency selective fading is widely applied to the every field of wideband wireless mobile communication to this transmission method.But, OFDM also have peak-to-average power ratio (Peak to Average Power Ratio, hereinafter to be referred as PAPR) excessive, to deficiencies such as frequency deviation sensitivities.With respect to OFDM, method as another kind of effectively antagonism channel fading characteristic in wideband wireless mobile communication, single carrier frequency domain equalization (Single Carrier-Frequency Domain Equalization, hereinafter to be referred as SC-FDE) carried out, the transport stream signal journey of its system as shown in Figure 2, comprises following step:

1) information that transmitting terminal will be sent is carried out chnnel coding and constellation mapping, the information after being shone upon successively;

2), to after the block sort after above-mentioned mapping, at every front end, add after CP forms SC-FDE symbol and launch;

3) receiving terminal receives above-mentioned SC-FDE symbol from channel;

4) to removing the CP in SC-FDE symbol after above-mentioned SC-FDE sign synchronization, obtain the data block in SC-FDE symbol;

5) above-mentioned data block is carried out to FFT operation, be converted to frequency domain;

6) utilize channel estimating channel information out, the above-mentioned data that are converted in frequency domain are carried out to equilibrium, obtain the frequency domain data after equilibrium;

7) frequency domain data after equilibrium is carried out to IFFT operation, convert it back to time domain;

8) data that convert back in time domain are carried out recovering prime information (stay of two nights) after constellation inverse mapping, channel decoding.

Above-mentioned SC-FDE method is compared OFDM following advantage:

What the first, SC-FDE transmitted in channel is the signal of directly modulating in time domain, envelope is multi-system phase shift keying (Multiple Phase Shift Keying, hereinafter to be referred as MPSK) or M-ary orthogonal amplitude modulation(PAM) (Multiple QuadratureAmplitude Modulation, hereinafter to be referred as MQAM) signal, envelope is more constant, PAPR is low, and ofdm signal is piled up by a series of sub-carrier signal, when its each sub-carrier phase is identical, can produce very high PAPR.Therefore,, with respect to OFDM, SC-FDE has reduced radio frequency cost.

The second, different from the ofdm system of non-self-adapting, SC-FDE can not adopt coding to carry out contrary frequency selectivity.

Three, SC-FDE is insensitive to carrier wave frequency deviation, the cost of Frequency Synchronization while having reduced to receive signal.

Contrast by Fig. 1 and Fig. 2 is visible, single carrier frequency domain equalization is to be developed by the OFDM based on FFT, it is that the data of serial transmitting-receiving are divided into the piecemeal of formed objects at receiving terminal, each piecemeal is carried out to FFT processing and obtain frequency domain representation, at frequency domain, by the result of channel estimating channel gain divided by this frequency on each frequency, after equilibrium, with IFFT processing, recover time-domain signal and carry out decoding.(so-called channel estimating is exactly by the model parameter estimation of certain channel model of supposition process out from receive data.)

SC-FDE frame structure as shown in Figure 3.The one piece of data at each data block end is copied to be placed on before this data block and make CP, to eliminate ISI.The CP of each data block and front end thereof forms a SC-FDE symbol.Due to the not intellectual of CP, SC-FDE method is difficult to utilize that CP carries out synchronously, channel estimating and the operation such as balanced, allows to realize these functions, and its algorithm complex is also higher.

Summary of the invention

The object of the invention is, for overcoming the weak point of prior art, to propose a kind of method for transmitting signals that adopts time domain and frequency domain combined single-carrier modulated.This method has not only retained the low advantage of single-carrier wave frequency domain equalization technology transmitting terminal complexity, and makes receiving terminal more accurate to the estimation of channel response, is more suitable in wideband wireless mobile communication system.

The method for transmitting signals of the single-carrier modulated that employing that the present invention proposes is time domain and frequency domain combined, comprises the following steps:

1) information transmitting terminal being produced is carried out chnnel coding and constellation mapping, a plurality of symbols after being shone upon successively;

2) a plurality of symbols after above-mentioned mapping are formed to a parallel data block;

3) each data block is carried out to TFU-SCM modulation: establishing UW is a reference sequences; At described data block front end, insert the pilot tone being formed by one or more UW, and in rear end, insert a UW and do protection interval, the UW of data block and rear end forms fft block, by channels transmit goes out after forming a time domain and frequency domain combined single-carrier modulated symbol (being called for short TFU-SCM symbol) piece by pilot blocks and fft block;

4) receiving terminal extracts the pilot tone of data block front end from the TFU-SCM symbolic blocks receiving, and carries out sign synchronization and Frequency Synchronization;

5) complete after sign synchronization and carrier synchronization, the frequency domain of each frequency of channel while utilizing described pilot tone to estimate corresponding TFU-SCM symbolic blocks by channel gains;

6) delete the pilot tone of the front end in each TFU-SCM symbolic blocks, obtain each fft block;

7) described fft block is carried out to Fourier transform, obtain the frequency-region signal that time domain fft block is corresponding;

8) utilize the frequency domain gain in (5) to carry out equalization operation to described frequency-region signal, obtain the frequency-region signal after equilibrium;

9) frequency-region signal after described equalization operation is carried out to IFFT operation, remove the UW of each fft block rear end, obtain the data block after recovering;

10) data block after above-mentioned recovery is carried out to constellation inverse mapping, channel decoding successively, obtain raw information.

Feature and the advantage of the method for transmitting signals of the single-carrier modulated that employing that the present invention proposes is time domain and frequency domain combined are:

The present invention claims that this technology is time domain and frequency domain combined single-carrier modulated (Time domain and Frequency domainUnited-Single Carrier Modulation, hereinafter to be referred as TFU-SCM) technology.TFU-SCM is with special word (UniqueWord; hereinafter to be referred as UW) cyclic suffix that forms does protection interval, the special training sequence that forms with one or more UW is made pilot tone (can select neatly according to the requirement of systematic function the number of UW in pilot tone) and formed TFU-SCM symbol; by the operation at frequency domain to pilot tone; can at receiving terminal, carry out synchronously easily the operations such as channel estimating and equilibrium.

The present invention has adopted in time domain and has added pilot tone, but at frequency domain, utilize that pilot tone is carried out synchronously, the single-carrier modulated technology of channel estimating and the operation such as balanced resist wideband wireless mobile communication in by multipath transmisstion, and the problems such as channel fading brought such as Doppler frequency deviation.

The present invention can select the number of UW in pilot tone neatly according to the requirement of systematic function, by the operation at frequency domain to pilot tone, can at receiving terminal, carry out synchronously easily the operations such as channel estimating and equilibrium.So not only retain the low advantage of single-carrier wave frequency domain equalization technology transmitting terminal complexity, and made receiving terminal more accurate to the estimation of channel response.Under the channel condition of frequency selective fading or time selective fading, still there is very good performance.Compare existing method for transmitting signals, the inventive method is more suitable in wideband wireless mobile communication system.

Accompanying drawing explanation

Fig. 1 is the system flow block diagram of existing OFDM technology.

Fig. 2 is the system flow block diagram of existing SC-FDE technology.

Fig. 3 is the SC-FDE frame structure schematic diagram in existing SC-FDE technology.

Fig. 4 is the TFU-SCM symbolic construction block diagram in the method for transmitting signals that proposes of the present invention.

Fig. 5 is the FB(flow block) that in the method for transmitting signals that proposes of the present invention, signal sends.

Fig. 6 is the FB(flow block) that in the method for transmitting signals that proposes of the present invention, signal receives.

Embodiment

The present invention proposes a kind of method for transmitting signals that adopts time domain and frequency domain combined single-carrier modulated by reference to the accompanying drawings and embodiment be described in detail as follows:

A kind of method for transmitting signals that adopts time domain and frequency domain combined single-carrier modulated that the present invention proposes, is characterized in that, the method comprises the following steps:

1) information transmitting terminal being produced is carried out chnnel coding and constellation mapping, a plurality of symbols after being shone upon successively;

2) a plurality of symbols after above-mentioned mapping are formed to a data block;

3) each data block is carried out to TFU-SCM modulation: establishing UW is a reference sequences; At described data block front end, insert the pilot tone being formed by one or more UW, and in rear end, insert a UW and do protection interval, the UW of data block and rear end forms fft block, by channels transmit goes out after forming a time domain and frequency domain combined single-carrier modulated symbol (being called for short TFU-SCM symbol) piece by pilot blocks and fft block;

4) receiving terminal extracts the pilot tone of data block front end from the TFU-SCM symbolic blocks receiving, and carries out sign synchronization and Frequency Synchronization;

5) complete after sign synchronization and carrier synchronization, the frequency domain of each frequency of channel while utilizing described pilot tone to estimate corresponding TFU-SCM symbolic blocks by channel gains;

6) delete the pilot tone of the front end in each TFU-SCM symbolic blocks, obtain each fft block;

7) described fft block is carried out to Fourier transform, obtain the frequency-region signal that time domain fft block is corresponding;

8) utilize 5) in frequency domain gain described frequency-region signal is carried out to equalization operation, obtain the frequency-region signal after equilibrium;

9) frequency-region signal after described equalization operation is carried out to IFFT operation, remove the UW of each fft block rear end, obtain the data block after recovering;

10) data block after above-mentioned recovery is carried out to constellation inverse mapping, channel decoding successively, obtain raw information.

As shown in Figure 4, as seen from Figure 4, the symbol of a TFU-SCM comprises two parts to the structure of above-mentioned TFU-SCM symbol: the pilot blocks that a part is comprised of one or more UW, another part is by data block and a fft block that UW forms below thereof.

A kind of embodiment that adopts the method for transmitting signals of time domain and frequency domain combined single-carrier modulated that the present invention proposes, as shown in Figure 5,6, comprises the following steps:

1) information that transmitting terminal will be sent is carried out chnnel coding and constellation mapping successively, a plurality of symbols after being shone upon;

The mode of chnnel coding wherein can be convolution code (Convolutional Code, CC), low density parity check code (Low Density Parity Check, LDPC), Reed Solomon code (Reed Solomon, RS) etc.

Information after chnnel coding is carried out to constellation mapping, its mapping mode can enter phase shift keying (Binary PhaseShift Keying for two, hereinafter to be referred as BPSK), Quadrature Phase Shift Keying (Quadrature Phase Shift Keying, hereinafter to be referred as QPSK), 16 quadrature amplitude modulation (16-Quadrature Amplitude Modulation, hereinafter to be referred as 16QAM), 64 quadrature amplitude modulation (64-Quadrature Amplitude Modulation, hereinafter to be referred as 64QAM) and 256 quadrature amplitude modulation (256-Quadrature Amplitude Modulation, hereinafter to be referred as 256QAM) etc.

2) a plurality of symbols after above-mentioned mapping are formed to parallel data block;

3) each data block is carried out to TFU-SCM modulation: it is a reference sequences that UW is set; At above-mentioned data block front end, insert a plurality of symbol pilot tones that formed by one or more UW, and at a UW of rear end insertion, the UW of data block and rear end forms fft block, by pilot blocks and fft block, form (as shown in the empty frame of Fig. 5) after a time domain and frequency domain combined single-carrier modulated (TFU-SCM) symbolic blocks, after the TFU-SCM symbolic blocks component frame signal of Jiang Ge road, by channel, send.The generative process of concrete TFU-SCM symbolic blocks is as follows:

3-1) generate UW sequence, in the present embodiment, UW chooses Chu sequence (being proposed by David C.Chu) or Frank-Zadoff sequence (being combined proposition by R.L.Frank with S.A.Zadoff) as UW sequence, its length is 2 positive integer time power, and length maximum is no more than 256.When UW is used as protection interval, UW sequence length is not less than the length of channel maximum delay.For example, when system bandwidth is 10MHz, UW length can get 64, comprises 4 UW in the pilot blocks of the present embodiment.

Length be homophase (In-phase, hereinafter to be referred as the I) road of UW sequence of U (U is positive integer) and quadrature (Quadrature, hereinafter to be referred as Q) road signal respectively by following formula produce (:

I[n]＝cos(θ[n]) (1)

Q[n]＝sin(θ[n]) (2)

Wherein n is the arbitrary integer within the scope of 0 to U-1.

Wherein phase theta [n] can have two kinds of selections, when producing Frank-Zadoff sequence, gets θ [n]=θ _frank[n], when producing Chu sequence, θ [n]=θ _chu[n].

θ _frankthe expression formula of [n] is:

${\mathrm{\θ}}_{\mathrm{Frank}}[n=p+q\sqrt{U}]=\frac{2\mathrm{\πpqr}}{\sqrt{U}}---\left(3\right)$

$p=\mathrm{0,1},...,\sqrt{U}-1---\left(4\right)$

$q=\mathrm{0,1},...,\sqrt{U}-1---\left(5\right)$

R=1 wherein, 3 or with coprime integer;

θ _chuthe expression formula of [n] is:

${\mathrm{\θ}}_{\mathrm{chu}}\left[u\right]=\frac{{\mathrm{\πn}}^2}{U}---\left(6\right)$

n＝0,1,...,U-1 (7)

3-2) in above-mentioned each channel parallel data piece rear end, insert a UW and do protection interval, data block and UW form fft block;

3-3) fft block front end insert by one or more UW form pilot blocks (systematic function requires higher, the UW number in pilot blocks the more, but the number of UW is no more than 4), by pilot blocks and fft block, form a TFU-SCM symbol, as shown in Figure 4;

4) receiving terminal receives the frame signal that above-mentioned each road TFU-SCM symbol forms, and the frame signal receiving is split as to the TFU-SCM symbol of multidiameter delay by corresponding building form, and from time domain and frequency domain combined single-carrier modulated symbolic blocks, extract the pilot tone of data block front end, carry out sign synchronization and Frequency Synchronization;

5) complete after sign synchronization and carrier synchronization, the frequency domain of each frequency of channel while utilizing above-mentioned pilot tone to estimate corresponding time domain and frequency domain combined single-carrier modulated symbolic blocks by channel gains; The present embodiment channel estimating adopts the channel estimation method based on discrete Fourier transform (DFT) (Discrete Fourier Transform, hereinafter to be referred as DFT).

The channel estimation method of DFT is as follows:

When the present embodiment sends each symbol, the frequency response of channel is constant, and the length of the UW in pilot blocks is L (positive integer that L is 2 time power, and maximum is no more than 256), with { x _m(wherein, x represents the signal in time domain; M is the arbitrary integer within the scope of 0 to L-1) represent { y for UW in the pilot tone receiving _m(wherein, y represents the signal in time domain; M is the arbitrary integer within the scope of 0 to L-1) represent.First, respectively to x _mand y _mcarry out L point FFT computing, obtain sequence { X _k(wherein, X represents the signal in frequency domain; K is the arbitrary integer within the scope of 0 to L-1) and { Y _k(wherein, X represents the signal in frequency domain; K is the arbitrary integer within the scope of 0 to L-1), the frequency response estimated value H of each subchannel _k(wherein, k is the arbitrary integer within the scope of 0 to L-1) can be obtained by following formula:

$H_k=\frac{Y_k}{X_k},0\≤k\≤L-1$

Adopt Frequency domain interpolation to obtain the Frequency Response of M (M is positive integer, and its value equals the length of fft block) sub-channels.To { H _kcarrying out L point IFFT computing, the tail of sequence that is L in the length obtaining adds 0 to length M, then carries out M point FFT computing, just obtains the frequency response estimated value of M sub-channels (wherein, i is the arbitrary integer within the scope of 0 to M-1).

For improving systematic function, can make pilot signal comprise a plurality of UW, channel is repeatedly estimated, then average as the Frequency Response of subchannel, finally carry out the frequency response that Frequency domain interpolation obtains whole subchannels.At transmitting terminal, sending continuously the individual UW of N (N is positive integer), as pilot blocks, averages to N estimated value:

${\hat{H}}_k=\frac{1}{N}\underset{n=1}{\overset{N}{\mathrm{\Σ}}}\frac{{Y_k}^{\left(n\right)}}{X_k},0\≤k\≤M-1$

Wherein, n is the arbitrary integer between 0 to N-1.

6) symbol synchronization information that basis obtains carries out the pilot tone in each TFU-SCM symbol and fft block separated, and the pilot tone of deleting the front end in each time domain and frequency domain combined single-carrier modulated symbolic blocks, obtains each fft block;

7) above-mentioned fft block is carried out to Fourier transform, obtain the frequency-region signal that time domain fft block is corresponding;

8) utilize 5) in frequency domain gain above-mentioned frequency-region signal is carried out to equalization operation, obtain the frequency-region signal after equilibrium;

Channel equalization adopts ZF (Zero Forcing, hereinafter to be referred as ZF) equalization algorithm.

ZF equalization algorithm is as follows:

The basic skills of ZF is that transmitting terminal sends a training sequence, there is accordingly a desirable acceptance value, this training sequence is subject at receiving terminal, obtaining disturbed value after the interference of ISI channel, then this ideal value is compared to the equalizing coefficient that obtains filter with disturbed value, from frequency domain, exactly the frequency response of disturbed signal is multiplied by a frequency response function (frequency response of sef-adapting filter), makes it to equal the desirable frequency response that receives signal.

Equalizing coefficient is expressed as:

$W_{l=}\frac{1}{H_l}$

Wherein, H _lfrequency response estimated value for each subchannel; L is nonnegative integer.

9) frequency-region signal after above-mentioned equilibrium is carried out to IFFT operation, remove the UW of each data block rear end, by the data block obtaining after recovering.Through above-mentioned Dui Ge road TFU-SCM symbol, carry out, after time domain and frequency domain combined single carrier demodulation process, multidiameter delay data block being merged into serial data.Described single carrier demodulation is as shown in Fig. 6 dotted line frame (step 4～9);

10) data block after above-mentioned recovery is carried out to constellation inverse mapping, channel decoding successively, obtain raw information.Wherein constellation inverse mapping, channel decoding are according to carrying out (specific implementation is known technology) with the corresponding constellation mapping of transmitting terminal, channel coding method.

Claims (1)

1. adopt a method for transmitting signals for time domain and frequency domain combined single-carrier modulated, it is characterized in that, the method comprises the following steps:

1) information that transmitting terminal will be sent is carried out chnnel coding and constellation mapping successively, a plurality of symbols after being shone upon;

2) a plurality of symbols after above-mentioned mapping are formed to a parallel data block;

3) each data block is carried out to TFU-SCM modulation: establishing UW is a reference sequences; At above-mentioned data block front end, insert the pilot tone being formed by several UW, and at a UW of rear end insertion, the UW of data block and rear end forms fft block, by pilot blocks and fft block, form a time domain and frequency domain combined single-carrier modulated symbolic blocks, after the TFU-SCM symbolic blocks component frame signal of Jiang Ge road, by channel, send;

4) receiving terminal extracts the pilot tone of data block front end from the time domain and frequency domain combined single-carrier modulated symbolic blocks receiving, and carries out sign synchronization and Frequency Synchronization;

5) complete after sign synchronization and carrier synchronization, the frequency domain of each frequency of channel while utilizing described pilot tone to estimate corresponding time domain and frequency domain combined single-carrier modulated symbolic blocks by channel gains;

6) delete the pilot tone of the front end in each time domain and frequency domain combined single-carrier modulated symbolic blocks, obtain each fft block;

7) described fft block is carried out to Fourier transform, obtain the frequency-region signal that time domain fft block is corresponding;

8) utilize the frequency domain gain in (5) to carry out equalization operation to above-mentioned frequency-region signal, obtain the frequency-region signal after equilibrium;

9) frequency-region signal after above-mentioned equilibrium is carried out to IFFT operation, remove the UW of each data block rear end, by the data block obtaining after recovering;

10) data block after above-mentioned recovery is carried out to constellation inverse mapping, channel decoding successively, obtain raw information.