CN1201500C - Synchronization capture method of downline in CDMA system - Google Patents

Abstract

The present invention discloses a synchronous capturing method applied to the downlink of a CDMA communication system and a broadcasting channel receiver for realizing the method. The method mainly comprises: a broadcasting channel is added to the downlink, and a unique code is input into the fixed time slot of a broadcasting channel frame; the broadcasting channel receiver of a mobile station first finds out an energy concentrated position occurring in the main peak of each sign, and then the judgment moment of each sign is determined according to the position so as to judge the signs; subsequently, the unique code is detected by a unique code matched filter which sends out synchronous information when the unique code is detected. The present invention is realized by the broadcasting channel, a matched filter structure and sliding correlated technology so as to rapidly realize the synchronous reception of the downlink, and the present invention has the advantages of high synchronous precision, simple method and easy realization.

Description

The synchronization capture method of down link in the code division multiple access system

Technical field

The present invention relates to any code division multiple access (CDMA) wireless communication technology field that contains, relate in particular to a kind of synchronization capture method in the receiver apparatus of cdma communication system.

Background of invention

In recent years, cdma system was owing to had big capacity, soft capacity, soft handover, high speech quality and low transmitting power and special advantages such as anti-interference and secret is developed rapidly it, and became the one preferred technique of third generation cellular communication system.

CDMA is a kind of modulation and multiple access interconnection technique based on spread spectrum communication.In cdma communication system, the used signal of different user transmission information is not to distinguish by frequency difference or time slot difference, but distinguishes with different separately coded sequences.Receiver can be selected the signal that uses the predetermined codes type with correlator in a plurality of CDMA signals.Other signal that uses different sign indicating number types is because different with the local sign indicating number type that produces of receiver and can not be by demodulation.

Usually in cdma system, no matter be base station transmitter or mobile radio station transmitter all with the digital information spread-spectrum of spreading code to transmission, and receiving equipment utilizes local spreading code to the relevant despreading of spread-spectrum signal, solves Useful Information.To realize exactly synchronously local spreading code and the spreading code that receives structurally, in full accord on frequency and the phase place.Cdma system except carrier synchronization that general digital communication system is arranged, bit synchronization, frame synchronization, spreading code be that it is peculiar synchronously.Therefore, the stationary problem of spread spectrum system is more more complicated than general digital communication system.

In general, in transmitter and receiver, adopt the clock frequency source of high accuracy and high stability, can remove the unsteadiness of many frequencies and phase place.But owing to objectively exist many prior inestimable uncertain factors, especially in mobile communication, these uncertain factors all have randomness, can not compensate in advance, can only eliminate by synchro system.Therefore synchro system is indispensable in cdma system, and is very important.

Summary is got up, and causes probabilistic time uncertainty and frequency uncertainty of mainly containing, and is summarized as follows:

1, the distance between transceiver causes the phase difference that the delay of propagation produces.

2, the frequency difference that causes of the relative instability of transceiver clock frequency.

3, the Doppler frequency-shift that causes of transceiver relative motion.

4, the frequency that causes of multipath effect and the variation of phase place.

So, spreading code be divided into two steps synchronously: the one, catch, i.e. the frequency and the phase place of the local spreading code of coarse adjustment make local spreading code and receive the spreading code phase difference less than a symbol width Tc.The 2nd, follow the tracks of, promptly adjust the phase place of local spreading code automatically, make it and receive spreading code frequency and phase place precise synchronization.

Traditional cdma system catching method has a variety of, for example sliding correlation method, sequence estimation method, matched filter method etc., and what wherein fundamental sum was the most frequently used is sliding correlation method.

Slip correlation capturing functional-block diagram is referring to Fig. 1.In practice, the spreading code that often uses is m sequence or Gold sequence.Spreading code has good autocorrelation performance, and when cycle N was very big, auto-correlation function was very big and submaximum is very little, utilized correlator to calculate the correlation function value of received signal spreading code and local spreading code, and differentiated phase difference in view of the above.When phase difference during greater than Tc, the signal that integration exports decision device to is lower than decision threshold, at this moment sends a stepping pulse signal.When two yards relative time differences hour, the amplitude output signal of envelope detector is very big, signal level behind the integration is higher than decision threshold, send a trace pulse signal after the decision circuit judgement, but the time difference that shows two yards of transmitting-receivings is in following range, start tracking circuit, synchro system is in tracking mode.

The slip correlation capturing is the order correlometer algorithm to two spreading codes, fairly simple, but shortcoming is when the time of two spreading codes or phase place have big difference, and is particularly long to the capture time of long code, thereby must the employing measure limit capture range and accelerate capture time.

Above sliding correlation method be to calculate auto-correlation function value R (τ) in the cycle at spreading code, and determine thus and realization catching spreading code.But, be that long code is when sliding correlation capturing to spreading code, must carry out correlation intergal to receiving code and local code in one of long code complete cycle, and it is relevant to ask for the correlation function value peak value to need progressively to slide, the shortcoming of bringing thus is that capture time is oversize and realization is complicated.

In the IS-95 cdma system, the guiding spreading code is to be 215 long code in the cycle, and chip speed is 1.2288Mcps, if having no under the condition of time reference, it is unpractical solving catching of spreading code with sliding correlation method.Therefore the down channel of IS-95 cdma system is provided with pilot channel, and the mobile radio station adjustment also is synchronized with the spreading code of pilot channel, and send with same spreading code phase place.

Summary of the invention

For solving existing the problems referred to above and defective in the prior art, the object of the present invention is to provide a kind of new downlink synchronization method for catching that is used for code division multiple address communication system.

The method that the present invention is to use broadcast channel, matched filter structure and sliding window to combine realizes the synchronous reception of down link fast, and synchronization accuracy is very high, and method is simple, is easy to realize.

Objects and advantages of the present invention are by the description of the downlink synchronization method for catching of following mobile communication cdma system, and it is more and more obvious to become.

Downlink synchronization method for catching of the present invention is mainly by using broadcast channel, matched filter and slip correlation technique to realize.The realization of this method may further comprise the steps:

1) in down link, add broadcast channel, and in broadcast channel frame fixedly time slot put unique word; When mobile radio station broadcast channel receiver detects unique word, just can determine frame alligning information.

2) in order to overcome the influence of multidiameter fading channel, the broadcast channel synchronisation loop is at first found out the position of the concentration of energy that the main peak of each symbol occurs, determine each symbol judgement of broadcast channel receiver constantly according to this position then, if judgement is correct, after the unique word matched filter detects unique word, just can provide a synchronizing information more accurately.

Brief Description Of Drawings

Fig. 1 is a kind of slip correlation capturing schematic diagram.

Fig. 2 shows the structural representation of the mobile radio station broadcast channel receiver of the method according to this invention design.

Fig. 3 shows the synchronization loop schematic diagram of the method according to this invention design.

Implement mode of the present invention

The present invention will be described in detail below by embodiment and accompanying drawing.

Referring to Fig. 2, the broadcast channel receiver by demodulator 22 and low pass filter 23, is sent into output I road, the Q road value of matched filter 24,24 with received signal 21 then, and after quadratic sum computing 25, output signal is sent into synchronization loop.

The synchronization loop detailed structure as shown in Figure 3.Detailed process is as follows:

Preestablish a threshold value V0, its value is decided according to practical experience, for example can be half of main peak signal value.Signal by 25 outputs after the computing compares at comparator 301 and this fixed threshold V0.When a value surpasses thresholding V0, this is designated as T0 constantly, and skips 2I again The sample value of width is initial moment T=T0+ITc with this constantly, and choosing of I will be considered actual channel circumstance, is advisable with all peak positions that can skip this symbol.

If being entered the data that postpone accumulator 302 constantly, T is designated as D _T,

By postponing 302 in accumulator

$\underset{i=0}{\overset{K}{\mathrm{\Σ}}}{D}_{T+i\×\mathrm{NTc}}$ Value deposit among the RAM, be designated as R[1];

$\underset{i=0}{\overset{K}{\mathrm{\&Sigma;}}}{D}_{T+i\&times;\mathrm{NTc}+\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}}$ Value deposit among the RAM, be designated as R[2];

$\underset{i=0}{\overset{K}{\mathrm{\&Sigma;}}}{D}_{T+i\&times;\mathrm{NTc}+\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}\&times;2}$ Value deposit among the RAM, be designated as R[3];

·

·

·

$\underset{i=0}{\overset{K}{\mathrm{\&Sigma;}}}{D}_{T+i\&times;\mathrm{NTc}+\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}\&times;(2N-1)}$ Value deposit among the RAM, be designated as R[2N];

Wherein N is the length of broadcast channel spreading code, and note 2N is because receiver adopts is 2 times of chip speed.The purpose of memory 303 is exactly constantly accumulator to be tired out first value that at T+KNTc to write RAM, $T+\mathrm{KNTc}+\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}$ Constantly the 2nd value write RAM, up to $T+\mathrm{KNTc}+\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}\&times;(2N-1)$ Constantly 2N value write RAM.More than operation promptly is that the circulation of the correspondence position value of K+1 symbol is added up.Choosing of K wants to guarantee that circulation is added to most symbols of broadcast frame, so that can detect unique word at next frame.Unique word is placed on the end of broadcast frame.

In order to L is window width, and sliding step is that 1 sliding window 304 slides in 2N value in RAM from front to back, every slip once calculate primary energy and, find out the window of energy and maximum (Emax); Following this position of window of meter is counted Location, and (each number in RAM all has a positional number, a total 2N number, positional number correspondence 1,2,3 ... 2N, the positional number that writes earlier is little).

Comparator 305 is sent in the output of sliding window 304, as if Emax＜E0, does not promptly capture most of symbol of broadcast channel frame, then returns and enters search condition again; As if Emax＞E0, promptly capture most of symbol of broadcast channel frame, then exist $T+\mathrm{FT}+\mathrm{Location}\&times;\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}+i\&times;\mathrm{NTc}$ The moment, differential ference spiral device 306 beginning differential ference spirals, $T+\mathrm{FT}+(\mathrm{Location}+L)\&times;\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}+i\&times;\mathrm{NTc}$ Moment differential ference spiral finish, and $T+\mathrm{FT}+(\mathrm{Location}+L)\&times;\frac{\mathrm{<figure-callout\; id="2"\; label="Tc"\; filenames="C0081877300101.png"\; state="\{\{state\}\}">Tc</figure-callout>}}{2}+i\&times;\mathrm{NTc}$ Constantly to each symbol judgement, i=0 wherein, 1 ... K, and each decision value sent into unique word matched filter 307.

After unique word matched filter 307 detects unique word, enter counter 308, if detect unique word again through FT ms (frame length) THE DETECTION OF UNIQUE circuit, pass through FT again, the THE DETECTION OF UNIQUE circuit detects unique word again, and Counter Value 308 is 3, illustrates that continuous 3 frames all detect unique word at the same position of broadcast frame, finish synchronous seizure so, sent a synchronizing signal 27.

After seizure is finished synchronously, postpone Q * NTc+GapTc time, the Traffic Channel receiver is started working, and Q is relevant with the time slot that unique word is placed in the broadcast channel frame here, and Gap is the protection interval between broadcast channel frame and the traffic channel frame.Catch constantly every process FT ms synchronously later on,, all give professional receiver synchronizing information again if broadcast channel receiver synchronization loop detects unique word.

If there is the time synchronized loop less than 4 frames all not detect unique word, so professional receiver is kept former synchronous regime; If the time of continuous 4 frames, synchronization loop does not all detect unique word, and then professional receiver cuts out, and broadcasting receiver is caught again synchronously.

Claims (3)

1. synchronization capture method that is applied to the down link of cdma communication system is characterized in that this method may further comprise the steps at least:

In down link, add broadcast channel, and in broadcast channel frame fixedly time slot place the unique word be exclusively used in synchronous seizure; The broadcast channel receiver behind demodulation, low-pass filtering, matched filtering and related operation, is sent into synchronization loop with the signal that receives; Synchronization loop is at first found out the position of the concentration of energy that the main peak of each symbol occurs, and determines moment that each symbol is adjudicated according to this position then, and carries out symbol judgement; Secondly detect this unique word through the unique word matched filter, then provide synchronizing information if detect.

2. method according to claim 1 provides synchronizing information after it is characterized in that described unique word matched filter is continuous and detecting unique word three times.

3. mobile radio station broadcast channel receiver of implementing the described method of claim 1 is characterized in that this receiver comprises at least:

Demodulator, low pass filter, matched filter, related operation device and synchronization loop, wherein received signal after demodulation, low-pass filtering and matched filtering, is carried out related operation successively, and the output signal after the computing is sent into synchronization loop;

Synchronization loop comprises first comparator, delay accumulation device, memory module, sliding window module and second comparator, differential ference spiral device, unique word matched filter, counter; Form the connection of series connection form between described first comparator, delay accumulation device, memory module, sliding window module and second comparator, differential ference spiral device, unique word matched filter, the counter in order, another output of second comparator is connected with the input of synchronization loop; Synchronization loop moment of finding out the position of the concentration of energy that the main peak of each symbol occurs with first comparator, delay accumulation device, memory module, sliding window module and second comparator and determining according to this position each symbol is adjudicated wherein, separate the mediation symbol judgement with the differential ference spiral device, detect this unique word with unique word matched filter and counter, and provide synchronizing information.

Images