CN1543101A - Method for separating user data from training sequence in multicarrier system - Google Patents

Method for separating user data from training sequence in multicarrier system Download PDF

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CN1543101A
CN1543101A CNA031177735A CN03117773A CN1543101A CN 1543101 A CN1543101 A CN 1543101A CN A031177735 A CNA031177735 A CN A031177735A CN 03117773 A CN03117773 A CN 03117773A CN 1543101 A CN1543101 A CN 1543101A
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training sequence
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user data
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CN100373831C (en
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唐友喜
赵宏志
李少谦
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University of Electronic Science and Technology of China
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Abstract

This invention discloses a separation method for user data and the measurement sequence based on time frequency synchronization in a multicarrier system which re-establishes signals of the received measurement sequence to balance out the part interference of the re-established measurement sequence from the received signal sum based on a channel estimation result and part signals after balanced out is demodulated. This invention also can be realized by software programming or related hardware circuit is processed.

Description

The separation method of user data and training sequence in a kind of multicarrier system
Technical field
The invention belongs to the field of the communication technology, the known training sequence of utilizing that particularly is used for the communication technology is carried out the method that temporal frequency is synchronous and user data separates with training sequence.
Background technology
OFDM is owing to have the message transmission rate height, and the anti-multipath interference performance is strong, and the spectrum efficiency advantages of higher more and more comes into one's own, and it successfully is used for wired, radio communication.As: among DAB, DVB, EEE802.11a and the HyperL AN/2, in the IEEE802.16 that is formulating at present, also related to the OFDM technology in a large number.This new modulation technique of OFDM also can be used in the mobile communication system of a new generation.Use the OFDM technology will improve the transmission data rate and the spectrum efficiency of the third generation mobile communication system greatly, and have good ability of anti-multipath, cochannel interference and impact noise ability, see document: Bingham, J.A.C., " Multicarrier modulation for data transmission:an idea whose time has come, " IEEE CommunicationsMagazine, Volume:28 Issue:5, May 1990, Page (s): 5-14; And document: Yun Hee Kim; Iickho Song; Hong Gil Kim; Taejoo Chang; Hyung Myung Kim, " Performance analysis of a coded OFDM system in time-varying multipathRayleigh fading channels; " Vehicular Technology, IEEE Transactions on, Volume:48 Issue:5, Sept.1999, Page (s): 1610-1615 is described.
OFDM is divided into time synchronized and Frequency Synchronization synchronously.The purpose of time synchronized is to find out the border of each OFDM symbol in the serial data stream of receiving; And the purpose of Frequency Synchronization is to obtain and correct the frequency shift (FS) of receiving end.One of weakness of OFDM technology be to the requirement of time and Frequency Synchronization particularly Frequency Synchronization require more much higher than single-carrier system.The general system of employing OFDM technology that requires is no more than 2% of its subcarrier spacing in the receiving terminal frequency shift (FS), sees document van de Beek, J.J.; Sandell, M.; Borjesson, P.O., " ML estimation of time and frequency offset in OFDM systems; " Signal Processing, IEEETransactions on, Volume:45 Issue:7, July 1997, and Page (s): 1800-1805 is described.
In the OFDM technology; disturb for eliminating intersymbol interference and cochannel; generally the adding protection is protected the general requirement of gap length 2 times or 4 times greater than channel impulse response length at interval before each OFDM symbol, and protection content at interval generally is the part of OFDM symbol.
The method for synchronous of conventional OFDM has two kinds:
1) utilizes protection interval and the intersymbol correlation of OFDM, can realize time and Frequency Synchronization.Referring to document van deBeek, J.J.; Sandell, M.; Borjesson, P.O., " ML estimation of time and frequency offset in OFDM systems; " Signal Processing, IEEE Transactions on, Volume:45 Issue:7, July 1997, Page (s): 1800-1805.
2) make a start with training sequence filling OFDM symbol, following dual mode can be arranged: training sequence is placed in the protection at interval of OFDM; B) training sequence is placed on the protection at interval of OFDM before.Receiving end is asked the relevant time synchronized of carrying out to received signal and known training sequence:
3) make a start training sequence is superimposed upon on the OFDM useful data, referring to document Tufvesson, F.; Edfors, O.; Faulkner, M., " Time and frequency synchronization for OFDM using PN-sequence preambles; " Vehicular TechnologyConference, 1999.VTC 1999-Fall.IEEE VTS 50th, Volume:4,1999, Page (s): 2203-2207.Be about to training sequence and be superimposed upon on the OFDM useful data, form protection then at interval, receiving end is utilized the correlation of training sequence to ask and is correlated with and carries out time synchronized.
But above-mentioned OFDM protection method for designing at interval all has shortcoming, and the shortcoming of method (1) is exactly that the correlation peak of receiving end is not obvious, and the scope of its frequency offset estimating has only 1/2 of ofdm system subcarrier spacing.The shortcoming of method (2) is to be time-division (perhaps frequency division) multiplexed form between training sequence and the OFDM initial data, causes the decline of data transmission efficiency; Method 3) do not causing data transmission efficiency to descend and not under the prerequisite of occupying volume external system bandwidth, receiving end can obtain correlation peak preferably in.
Method 3) specific embodiment in traditional transmitter and receiver:
ρ represents the relative power of training sequence in the present embodiment, be the percentage that training sequence power accounts for gross power, training sequence is a training sequence, training sequence adopts CAZAC (Constant Amplitude Zero Auto-Correlation) sequence, the CAZAC sequence has the good period correlation properties, and the amplitude of sequence all remains constant in time domain and frequency domain, can not cause PAPR (peak to average power ratio) problem.Based on above-mentioned characteristic, the CAZAC sequence especially is suitable for and is used for channel estimating and temporal frequency is synchronous in ofdm system, and the CAZAC sequence comprises a variety of, and relatively more commonly used have Milewski sequence, Frank-Zadoff sequence and a Chu sequence.
As shown in Figure 1: user's data is at first carried out data-modulated in module 1, and the data after the modulation are carried out power division in module 2, inserts guiding in module 3 then, sends into module 4 again and carries out the IFFT conversion, finishes the multi-carrier modulation function; While training sequence process module 9 is carried out after the power division and the signal after the multi-carrier modulation superposes, and enters module 5 interpolations and protects time slots, passes through up-conversion module 6 at last, serves antenna 7 and launches.
At said method 3) traditional receiver in shown in figure (1); the signal that antenna 7 receives at first carries out down-conversion in module 10; sending into synchronization module 11 then, to carry out temporal frequency synchronous; through past protection time slot module 12; FFT conversion module 13; signal after the multicarrier demodulation enters module 14 and guides extraction; enter channel estimation module 15 again; finish channel estimation function; the signal multiplication that the inverse estimated and the module 13 of winning the confidence again come out; promptly finish the function of received signal being carried out the channel fading compensation, carry out demodulation process in module 17 at last
The defective of traditional method of reseptance is because training sequence has certain interference to data, causes the energy efficiency of emission data lower.Compare under the harsh conditions in channel variation, in order to carry out the correct time Frequency Synchronization in receiving end, need make a start suitably strengthen transmit in the shared power of training sequence, but when carrying out channel estimating and data demodulates, receiving end inevitably strengthened the interference of training sequence simultaneously to data-signal, the deterioration that this has just caused systematic function has caused the increase of system mistake probability.If but the power of minimizing training sequence, peak value can be not obvious when receiving end was carried out related operation, reduced synchronization performance.
Summary of the invention
Task of the present invention provides a kind of separation method of high performance training sequence and user data in a kind of multicarrier system, promptly adopt separation method of the present invention, under the channel variation condition of severe, the make a start power of enhancing training sequence that can be suitable, receiver obtains net synchronization capability accurately whereby, while can reduce to the interference to user data of training sequence minimum, makes under the situation that system is abominable in channel variation and training sequence power strengthens and still obtains BER performance preferably.
Innovation part of the present invention is: 1) receiving terminal is after finishing synchronizing function, at first the received signal of training sequence is rebuild according to synchronous result, 2) because the inaccuracy of channel estimating, for fear of the information that does not belong to interference is originally deducted from received signal, the present invention adopts the way of part interference cancellation to offset the interference of training sequence to data-signal, promptly according to accuracy of channel estimation, a part interference cancellation factor is multiply by in interference to the training sequence rebuild, 3) from total received signal, deduct the training sequence of reconstruction, carry out corresponding demodulation work again, just obtained the performance higher than direct demodulation.
According to the separation method of temporal frequency synchronous training sequence and user data in a kind of multicarrier system of the present invention, as shown in Figure 3, it comprises:
1) receiver is according to the signal r advanced line time Frequency Synchronization of known training sequence c to receiving;
2) r is carried out FFT (quick Fourier transformation), obtain the total received signal sequence R of receiving terminal;
3) from R, extract the pilot sequence X that inserts making a start, adopt the Wiener filtering method to obtain channel estimation results H ~ = ω 0 · R X · X * , ω wherein 0Be interpolation filter coefficient, R XThe guide symbol that expression receives, X *Expression the gripping altogether of the guide symbol that sends of making a start;
It is characterized in that it also comprises the following step:
4) training sequence c is carried out the FFT conversion and obtain sequence C, C and above-mentioned channel estimation results
Figure A0311777300061
Multiply each other, obtain the reconstruction signal of C
Figure A0311777300062
Promptly C ~ = ρ · C · H ~ , Wherein ρ is the power factor of training sequence;
5) will Multiply by part interference cancellation factor lambda, promptly C ~ ′ = C ~ · λ ;
6) from total received signal R, deduct the interference of part training sequence, the signal S after obtaining separating, S = R - C ~ ′ . Need to prove that the channel estimation methods that process of the present invention adopts can be a Wiener filtering, also can be linear interpolation, perhaps other known channel estimation methods do not influence generality of the present invention; In addition, λ ∈ (0,1) wherein, the λ occurrence is by the order of accuarcy decision of channel estimating, and λ value principle is: make BER (bit error rate) minimum of system.
Just can realize later separation purpose of the present invention through aforesaid operations.
Essence of the present invention is to rebuild the training sequence of process channel effect at receiving terminal, and deducts the part interference of rebuilding training sequence from the summation signals that receives, and then data-signal is carried out demodulation.
From above-mentioned steps as can be seen, adopt separation method of the present invention, the interference to user data of training sequence can be reduced to minimumly, make under the situation of system's and training sequence power enhancing abominable and still obtain higher performance in channel variation.
Description of drawings
Fig. 1 is traditional transmitter fundamental diagram based on training sequence
Wherein, the 1st, modulating unit, the 2nd, the data-signal power distributing unit, the 3rd, insert guide unit; the 4th, IFFT (contrary discrete Fourier transform (DFT)) unit, the 5th, add protection time slot unit, the 6th, the up-conversion unit; the 7th, antenna, the 8th, CAZAC sequence generation unit, the 9th, training sequence power distributing unit.
Fig. 2 is traditional operation of receiver schematic diagram based on training sequence
Wherein, the 7th, antenna, the 10th, down-converter unit, the 11st, lock unit, the 12nd, go to protect the time slot unit, the 13rd, the FFT unit, the 14th, extract the guide symbol unit, the 15th, channel estimating unit, the 16th, channel fading compensating unit, the 17th, data demodulation unit.
Fig. 3 is the flow chart of key step of the present invention
Wherein ρ represents the relative power of training sequence.
Fig. 4 is a transmitter fundamental diagram of the present invention
Wherein, the 1st, modulating unit; the 2nd, the data-signal power distributing unit, the 3rd, insert guide unit, the 4th, IFFT (contrary discrete Fourier transform (DFT)) unit; the 5th, add protection time slot unit; the 6th, up-conversion unit, the 7th, antenna, the 8th, CAZAC sequence generation unit; the 9th, training sequence power distributing unit, the 13rd, FFT converter unit.
Fig. 5 is the fundamental diagram of receiver of the present invention
Wherein, the 7th, antenna, the 10th, down-converter unit; the 11st, lock unit, the 12nd, go to protect the time slot unit, the 13rd, the FFT unit; the 14th, extract the guide symbol unit; the 15th, channel estimating unit, the 16th, channel fading compensating unit, the 17th, data demodulation unit; the 8th, CAZAC sequence generation unit; the 9th, training sequence power distributing unit, the 13rd, FFT converter unit, the 18th, part interference cancellation unit.
Fig. 6 is the performance chart of one embodiment of the present of invention
Wherein, transverse axis is represented signal to noise ratio, unit is DB, the longitudinal axis is represented bit error rate, article two, curve all is that the power ratio at training sequence is the policy result under 0.5 the condition, the curve representation of top does not adopt under the situation of inventive method of the present invention, and the performance curve of system, the curve representation of below adopt the performance curve of system under the situation of separation method of the present invention.
Embodiment:
Below to provide a concrete OFDM configuration down, the performing step of this patent.Need to prove: the parameter in the following example does not influence the generality of this patent.
We select M.1225 channel for use; FFT length selects 4096; the protection time slot is got 1/4th of OFDM symbol lengths; training sequence is selected the CHU sequence; the cycle 4096 of CHU sequence; data-modulated is selected the BPSK modulation; ρ chooses a bigger power factor 0.5; the power of training sequence that has been suitable enhancing; the guiding pattern is selected the steering signal pattern of rectangle for use; channel estimating adopts the channel estimation methods of first-order linear interpolation, and for the ease of comparing, part interference cancellation factor lambda gets 0.65 and 0 respectively.
User data signal at first carries out the BPSK modulation in module 1, carries out power division in module 2 then, and module 3 is pressed rectangle guiding pattern and inserted guiding; Module 8 produces needed training sequence CHU sequence simultaneously; carry out the training sequence power division through module 9 again; carry out 4096 FFT conversion by module 13; superpose with the data-signal that inserts guiding afterwards; stack result is sent into module 4 carry out 4096 IFFT conversion; by adding protection time slot module 5, up-conversion module 6 is served antenna 7 emissions at last.As shown in Figure 4.
The signal that receiver antenna receives at first carries out down-conversion by unit 10, sending into synchronization module 11 then, to carry out temporal frequency synchronous, synchronously later signal is again through past protection time slot unit 12, enter FFT converter unit 13 and finish the demodulation function of multi-carrier modulation, from the signal of demodulation, extract guide symbol and 15 carry out the first-order linear channel estimating in the unit; Receiving end is carried out the reconstruction of training sequence received signal simultaneously, produces 4096 the used CHU sequence of making a start by training sequence generator unit 8 earlier, and the sequence that produces be multiply by amplitude factor
Figure A0311777300081
Carry out the FFT conversion by unit 13 again, training sequence and channel estimation results after will rebuilding then multiply each other, multiply by part interference cancellation factor ω then, the part that deducts training sequence again from total received signal is disturbed, promptly finish the function of interference cancellation unit 18, reduce the interference of training sequence to data-signal, from the data message after the FFT demodulation, deduct the training sequence information behind the interference cancellation, just obtained than direct demodulation data message more accurately, the output result of this data message and channel estimation module is got reciprocal multiplication, just remove the channel fading of data message, the signal after the compensation is exported at last by data demodulation unit 17.As shown in Figure 5.
Part interference cancellation factor lambda get respectively 0.65 and 0 two kind of situation under system the BER performance curve as shown in Figure 6, we are as can be seen from figure, the curve representation of top does not adopt under the situation of inventive method of the present invention, it is the performance curve of λ=0, the curve representation of below adopts under the situation of separation method of the present invention, i.e. the performance curve of λ=0.65 system.Adopt separation method of the present invention, can reduce the influence of training sequence, increase substantially the performance of system, huge using value is arranged at real wireless communication system to the data demodulation.

Claims (4)

1, the separation method of user data and training sequence in a kind of multicarrier system, it comprises following step:
1) receiver is according to the signal r advanced line time Frequency Synchronization of known training sequence c to receiving;
2) r is carried out FFT (quick Fourier transformation), obtain the total received signal sequence R of receiving terminal;
3) from R, extract the pilot sequence X that inserts making a start, adopt the Wiener filtering method to obtain channel estimation results H ~ = ω 0 · R X · X * , ω wherein 0Be interpolation filter coefficient, R XThe guide symbol that expression receives, X *Table
Gripping altogether of the guide symbol that showing makes a start sends;
It is characterized in that it also comprises the following step:
4) training sequence c is carried out the FFT conversion and obtain sequence C, C and above-mentioned channel estimation results Multiply each other, obtain the reconstruction signal of C Promptly C ~ = ρ · C · H ~ , Wherein ρ is the power factor of training sequence;
5) will
Figure A031177730002C5
Multiply by part interference cancellation factor lambda, promptly C ~ ′ = C ~ · λ ;
6) from total received signal R, deduct the interference of part training sequence, the signal S after obtaining separating, S = R - C ~ ′ .
2, according to the separation method of user data and training sequence in the described a kind of multicarrier system of claim 1, it is characterized in that described channel estimation methods can be a Wiener filtering, also can be linear interpolation, perhaps other known channel estimation methods.
3, according to the separation method of user data and training sequence in the described a kind of multicarrier system of claim 1, it is characterized in that described part interference cancellation factor lambda, λ ∈ (0,1), the λ occurrence is by the decision of the order of accuarcy of channel estimating, and λ value principle is to make BER (bit error rate) minimum of system.
4, according to the separation method of user data and training sequence in claim 1 or the 3 described a kind of multicarrier systems, it is characterized in that described part interference cancellation factor lambda can be 0.65.
CNB031177735A 2003-04-29 2003-04-29 Method for separating user data from training sequence in multicarrier system Expired - Fee Related CN100373831C (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101188592B (en) * 2007-11-29 2012-08-08 北京邮电大学 Synchronization method and system for multi-carrier system
CN104618041A (en) * 2014-12-31 2015-05-13 北京邮电大学 Channel data playback method and device

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100362571B1 (en) * 1999-07-05 2002-11-27 삼성전자 주식회사 Frequency offset compensation apparatus and method using pilot symbol in orthogonal frequency division multiplex system
CN1248439C (en) * 2002-08-22 2006-03-29 上海交通大学 Method for realizing frequency synchronization in orthogonal FDM system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101188592B (en) * 2007-11-29 2012-08-08 北京邮电大学 Synchronization method and system for multi-carrier system
CN104618041A (en) * 2014-12-31 2015-05-13 北京邮电大学 Channel data playback method and device

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