CN101087285A - A synchronization method for new generation of wireless mobile communication system - Google Patents

Abstract

The invention belongs to field of communication technique, especially a synchronization method in new wireless mobile communication system which can be used in OFDM modulating system of digital broadcasting TV system, wireless mobile communication system. The invention provides a new OFDM multi-carrier communication system synchronization method whose calculating complexity, performance is perfect. The method uses superposed pseudo-random sequence which possesses perfect relativity to protection band sub carrier, and pseudo-random sequence is distributed with weak energy, and the pseudo-random sequence and local sequence generate synchronization signal on receiving end. The invention is accurate, probability of synchronization is high, and performance of system can not be affected.

Description

Method for synchronous in a kind of new generation of wireless mobile communication system

Technical field:

The invention belongs to communication technical field, simultaneous techniques in the OFDM multi-carrier communications systems particularly of new generation.Can be applied in the system of employing OFDM modulation such as digital broadcast television system, mobile radio system.

Background technology:

The target of next-generation mobile communications is that high transfer rate more, the higher availability of frequency spectrum can be provided, based on such target, and the OFDM of multi-carrier scheme (the being called for short OFDM) successful Application of technology in existing communication system, the OFDM technology is chosen as the core modulation-demodulation technique of next-generation mobile communications.

The OFDM technology is that the information code current that speed is very high is divided into many low speed code streams, carries out the technology of parallel transmission on the subchannel of one group of quadrature.Adopt the OFDM technology can expand the width of subchannel transmission symbol, thus the design of equalizer in the simplified receiver greatly.Simultaneously, the OFDM technology adopts guardtime to remove intersymbol interference effectively at interval, disturbs thereby overcome the multipath that is shorter than TGI.On the other hand, the OFDM technology is utilized the orthogonality between subcarrier, has improved the availability of frequency spectrum effectively.This is the major advantage of OFDM technology.

But ofdm system is very responsive to synchronous error.In wireless transmission link, under the channel conditions of chromatic dispersion decline, fast moving, demodulating end need learnt sequence of operations such as just can finishing FFT operation and channel estimating under the accurately synchronous prerequisite.

Generally speaking, whether simultaneous techniques adopts Given information to form method for synchronous and blind synchronization method that synchronizing signal can be divided into prior information according to it.The former can be divided into the method for synchronous that adopts PN sequence or pilot tone to carry out, the method for synchronous that adopts protection to carry out at interval again.Adopt protection to carry out synchronous method for awgn channel time synchronized better performances at interval, then can not guarantee good performance for the multipath Rayleigh channel of high-speed mobile; Adopt protection to carry out synchronously at interval simultaneously, its frequency lock-in range is less.Adopt pilot tone to realize in the DVB-T system, using synchronously more, undesirable on the performance when translational speed is higher, can occur.Adopting the PN sequence is the also all well and good method of present popular performance synchronously; Generally whether independently take time slot and it can be divided into parallel PN sequence method for synchronous and serial PN sequence method for synchronous according to the PN sequence.In order to realize third generation mobile communication system high speed data transfers, up-to-date method adopts parallel PN sequence to carry out method for synchronous exactly.Yet because the PN sequence that adopts is superimposed upon on the information symbol, this has produced interference to information symbol.Though Liying Song, YouxiTang, Hongzhi Zhao, Shaoqian Li, etc, Optimum partial interference canceling factor pilot assistantcoherent OFDM system with partial power training sequences synchronization, The 14 ^ThIEEE 2003international symposium on Personal, Indoor and Mobile Radio CommunicationProceedings, pp:1906-1910. proposed a kind ofly to eliminate the method that part is disturbed, but this method has implied a condition: promptly to the change of receiver structure; And document Fredrik Tufvesson, Mike Faulkner, Peter Hoeher and Ove Edfors, OFDM time and frequency synchronization by spread spectrum pilot technique, IEEEConference, 1999. and document Steinga B.A, etc, Frame synchronization using superimposed sequence, Proc.IEEE ISIT ' 97, ULM, Germany, 1997, pp:489. adopting at different synchronous phases selects for use the different-energy factor can realize really synchronously with the method for adjusting stack PN sequence energy, but caused the influence to systematic function, especially needed under high-speed mobile environment fast synchronously, this method more is not suitable for.A kind of Weak energy parallel Barker code frame synchronous method has been proposed in patent 200510035894.9, it is 32 parallel Barker code that this method is utilized length, its energy is reduced to very weak situation, produce frame synchronizing signal thus, this method can obtain frame synchronization performance preferably really, but synchronizing signal can not obtain Frequency Synchronization thus.This patent considers that from another angle the PN sequence is to obtain synchronizing signal.

Summary of the invention:

The objective of the invention is: propose the method for synchronous in a kind of third generation mobile communication system.This method not only computation complexity is very low, and net synchronization capability is fine.

For achieving the above object, the present invention proposes method for synchronous in a kind of third generation mobile communication system.Its technical scheme is: select for use N continuous sub-carriers group to serve as the synchronous detecting symbol in the boundary belt at system information passband two ends; the pseudo random sequence that will have good autocorrelation performance is superimposed upon on N the interior subcarrier of boundary belt; and distributing more weak energy, the training sequence of weak energy produces synchronizing signal to obtain frame synchronization thus.

Synchronization principles of the present invention is described in detail as follows:

Step 1: select the pseudo random sequence c[k that length is the good autocorrelation performance of having of N].This sequence is superimposed upon in time domain on the boundary belt of ofdm signal, and pseudo random sequence is assigned with extremely weak energy ρ in this process, and remaining energy distribution is to the symbol d[k of boundary belt] on.For sub-carrier number is N _cOfdm system, in awgn channel, baseband receiving signals can be expressed as:

$r[k-\mathrm{\τ}]=s[k-\mathrm{\τ}]+n[k-\mathrm{\τ}]$

$=(\sqrt{\mathrm{\ρ}}c[k-\mathrm{\τ}]+\sqrt{1-\mathrm{\ρ}}d[k-\mathrm{\τ}])e^{j(\frac{2\mathrm{\π\ϵk}}{N_c}+\mathrm{\θ})}+n[k-\mathrm{\τ}]$ (1)

Wherein, ρ is the ratio of institute's superimposed pilot energy and transmission symbol gross energy; N[k] be white complex gaussian noise, θ is a carrier phase, and ε is a normalization frequency deviation to be estimated, and τ is a timing position to be estimated.Transmit and the power of noise is respectively σ _s ²And σ _n ²

What is particularly worth mentioning is that, in this patent, the energy ρ that pseudo random sequence is distributed can be very a little less than; Because this pseudo random sequence is to be added on the subcarrier in the boundary belt; and do not transmit information symbol in the boundary belt; all with zero filling (be d[k]=0); so; in fact; the pseudo random sequence of this stack just is equivalent to independently take this time slot; with other adopt the serial PN sequence synchronized algorithm independently take time slot different be; the energy that pseudo random sequence in this patent is distributed only is few part of whole symbol energy, and the energy that general serial pseudo random sequence symbol is distributed then is the energy of whole symbol.Certainly, if to this pseudo random sequence distribute strong energy or all energy also can, as long as the shared sub-carrier number of this pseudo random sequence is few, can not bring obvious influence to the performance of boundary belt yet.This patent core concept different that Here it is with other conventional algorithms.Especially in this patent pseudo random sequence is placed in the boundary belt, this is the thought that existing all conventional synchronized algorithms do not have employing.

Step 2: received signal has by local pseudo random sequence despreading:

$c^{*}\left[k\right]r[k+\mathrm{\τ}]=\sqrt{\mathrm{\ρ}}{c}^{*}\left[k\right]c[k+\mathrm{\τ}]e^{j(\frac{2\mathrm{\π\ϵk}}{N_c}+\mathrm{\θ})}+{\sqrt{1-\mathrm{\ρ}}c}^{*}\left[k\right]d[k+\mathrm{\τ}]e^{j(\frac{2\mathrm{\π\ϵk}}{N_c}+\mathrm{\θ})}+n^{\′}[k+\mathrm{\τ}]---\left(2\right)$

For frame synchronization, suppose that two slide relative position τ between the sequence are integer.In order to carry out in formula (2), can regarding noise jamming as for last two synchronously.

Step 3 can obtain following signal by the despread signal of receiving terminal:

$\mathrm{cor}[k,\mathrm{\τ}]=\frac{1}{N\sqrt{\mathrm{\ρ}}}\underset{l=1}{\overset{N}{\mathrm{\Σ}}}r[k+l+\mathrm{\τ}]c^{*}[l+\mathrm{\τ}]---\left(3\right)$

If the estimated value of bag zero-time is

, as the output cor[k of detector,

] greater than appointed threshold value , then the original position of sign synchronization is found in expression.Wherein, c ^*[.] expression is to c[.] get conjugation.

The present invention has the pseudo random sequence of only distributing less energy of good autocorrelation performance at the transmitting terminal of ofdm communication system by stack in the time domain boundary belt; realized that DVB-T 2K system at first obtains frame synchronization under the situation that does not still obtain time synchronized and Frequency Synchronization, thereby improved the travelling performance of system.

Be with the difference of prior art maximum: the first, pseudo random sequence and boundary belt internal information are parallel, that is: pseudo random sequence is superimposed upon on the boundary belt internal information; The second, Die Jia pseudo random sequence is only distributed the energy (institute's distribute energy can be very weak energy, also can be more intense energy) of the part of gross energy, thereby different with conventional method.Three, owing to this pseudo random sequence is superimposed upon in the boundary belt, and the interior data of boundary belt are often with zero filling, so the pseudo random sequence of this stack only produces certain influence to boundary belt; Because this stacking pseudorandom sequence is very short, only take several subcarriers, and the energy that is distributed again extremely a little less than, so overlying training sequence is very little to the interference of useful information and system in this patented technology.Four, the pseudo random sequence of selecting for use in this patented technology can be very short, as: selecting length for use is 5 Barker code.Five, synchronized algorithm difference.

The present invention is applicable to and adopts all to adopt OFDM to carry out carrying out frame synchronization and time synchronized in the communication system for modulation, especially is applicable in European digital terrestrial television (DVB-T) system.Though technology of the present invention is primarily aimed at the system of frequency division multiple access, but any engineer with knowledge background such as signal processing, communications, can design corresponding frame synchronization or time synchronism apparatus at code division multiple access and time division multiple access according to the present invention, it all should be included in thought of the present invention and the scope.

Description of drawings:

Fig. 1 has provided in this patent N of stacking pseudorandom sequence subcarrier schematic diagram in boundary belt.Because this stacking pseudorandom sequence is different with conventional serial method for synchronous, with patent " a kind of Weak energy parallel Barker code frame synchronous method " (number of patent application: 200510035894.9) Barker code is superimposed upon on the useful information symbol also different.

Embodiment:

Below by concrete enforcement technical scheme of the present invention is further described.

Step 1: in order to reduce the influence to boundary belt, selecting length for use is 5 Barker code; This Barker code is superimposed upon on the boundary belt subcarrier adjacent with information symbol in the transmitting terminal time domain, and distributes more weak energy, getting ρ is 0.025, and promptly the ratio of institute's superimposed pilot energy and transmission symbol gross energy is 0.025.

Step 2: the signal that will comprise Barker code information is launched, by 20 Rayleigh multipath channels stipulating in the European DVB-T standard, the speed of its travelling carriage is 120km/h, channel signal to noise ratio snr=6dB, and carry out demodulation to received signal according to formula (2), obtain basic demodulation cell signal.

Step 3: can obtain synchronizing signal at receiving terminal through type (3), and obtain frame synchronization by adaptive threshold is set.Emulation shows that this algorithm accurate synchronization probability can reach 99%.

Claims (5)

1, the present invention relates to simultaneous techniques in a kind of new generation of wireless mobile communication system, it is characterized in that comprising the steps:

Step 1: select the pseudo random sequence c[k that length is the good autocorrelation performance of having of N].This sequence is superimposed upon in time domain on the boundary belt of ofdm signal, and pseudo random sequence is assigned with extremely weak energy ρ in this process, and remaining energy distribution is to the information symbol d[k of boundary belt] on.For sub-carrier number is N _cOfdm system, in awgn channel, baseband receiving signals can be expressed as:

$r[k-\mathrm{\τ}]=s[k-\mathrm{\τ}]+n[k-\mathrm{\τ}]$

$=\left(\sqrt{\mathrm{\ρ}}c\right[k-\mathrm{\τ}]+\sqrt{1-\mathrm{\ρ}}d[k-\mathrm{\τ}\left]\right)e^{j(\frac{2\mathrm{\π\ϵk}}{N_c}+\mathrm{\θ})}+n[k-\mathrm{\τ}]---\left(1\right)$

Wherein, ρ is the ratio of institute's stacking pseudorandom sequence energy and transmission symbol gross energy; N[k] be white complex gaussian noise, θ is a carrier phase, and ε is a normalization frequency deviation to be estimated, and τ is a timing position to be estimated.Transmit and the power of noise is respectively σ _s ²And σ _n ²

Step 2: received signal has by local pseudo random sequence despreading:

$c^{*}\left[k\right]r[k+\mathrm{\τ}]=\left(\sqrt{\mathrm{\ρ}}{c}^{*}\right[k\left]c\right[k+\mathrm{\τ}]e^{j(\frac{2\mathrm{\π\ϵk}}{N_c}+\mathrm{\θ})}+\sqrt{1-\mathrm{\ρ}}{c}^{*}[k\left]d\right[k+\mathrm{\τ}\left]\right)e^{j(\frac{2\mathrm{\π\ϵk}}{N_c}+\mathrm{\θ})}+n^{\′}[k+\mathrm{\τ}]---\left(2\right)$

For frame synchronization, suppose that two slide relative position τ between the sequence are integer.In order to carry out in formula (2), can regarding noise jamming as for last two synchronously.

Step 3: the despread signal by receiving terminal can obtain following signal:

$\mathrm{cor}[k,\mathrm{\τ}]=\frac{1}{N\sqrt{\mathrm{\ρ}}}\underset{l=1}{\overset{N}{\mathrm{\Σ}}}r[k+l+\mathrm{\τ}]c^{*}[l+\mathrm{\τ}]---\left(3\right)$

If the estimated value of bag zero-time is

Output when detector

Greater than appointed threshold value , then the original position of sign synchronization is found in expression.Wherein, c ^*[.] expression is to c[.] get conjugation.

2, said as claim 1, the simultaneous techniques in a kind of new generation of wireless mobile communication system is characterized in that: the pseudo random sequence of this stack is to be superimposed upon in the boundary belt on the subcarrier in the transmitting terminal time domain.

3, said as claim 1, the simultaneous techniques in a kind of new generation of wireless mobile communication system is characterized in that: this is superimposed upon the energy that the pseudo random sequence on the subcarrier is distributed in the boundary belt and can adjusts as required.

4, said as claim 1, the simultaneous techniques in a kind of new generation of wireless mobile communication system is characterized in that: the method formula (3) that produces synchronizing signal can be changed.

5, said as claim 1, the simultaneous techniques in a kind of new generation of wireless mobile communication system is characterized in that: the thought of this method for synchronous not only can be used for the multicarrier system of OFDM modulation, and can be used for systems such as CDMA, TDMA.

Images