CN101166040B - Cell searching synchronization method base on time domain processing - Google Patents

Abstract

The invention discloses a method for synchronizing search of local areas based on time domain process, which applies a phase difference of two TDM CPICH to identify a harass code set in a data frame sent at the transmitting end and extra masks are not needed, so it will not increase interference to other local areas and reduces complexity of related test operation to frequency domain of OFDM signals. The invention can shorten the improved local area search time or improved correct probability of local search by reducing the calculation amount through simplified algorithm.

Description

Cell searching synchronization method based on the time domain processing

Technical field

The present invention relates to improve cellular mobile system cell searching synchronization method based on the CDMA multiple carrier modulation technique.

Background technology

The OFDM technology is acknowledged as the key technology in the new generation of wireless communication system, and it is highly resistant to intersymbol interference (ISI) and the multipath fading that multipath causes.CDMA obtains spreading gain and improves antijamming capability by user data being carried out spread spectrum.Coming into one's own owing to it possesses bigger power system capacity of two kinds of technology in conjunction with the CDMA multiple carrier technology.

In cellular mobile system, when the user has just begun start or handover, need carry out Cell searching and find only sub-district to communicate synchronously based on the CDMA multiple carrier modulation.Document Y.ISHII, K.HIGUCHI, and M.SAWAHASHI, " Three-Step Cell Search Algorithm EmployingSynchronization and Common Pilot Channels for OFCDM Broadband Wireless Access " IEICE TRANS.COMMUN, VOL.E85-B, the method of some Cell searchings has been described among NO.12 DEC 2002 and the patent WO03/049344 " MULTI-CARRIER TRANSMISSION/RECEPT ION APPARTUS ", but they have used SCH (synchronizing channel (channel when frame designs, SCH and the incomplete quadrature of other data channels, when the probability of success that will improve search, when improving the SCH channel power, can cause very big interference to other data channels.So document M.TANNO, H.ATARASHI, K.HIGUCHI, andM.SAWAHASHI, " Three-Step Cell Search Algorithm Exploiting Common Pilot Channelfor OFCDM Broadband Wireless Access " IEICE TRANS.COMMUN., VOL.E86-B, NO.1 JAN 2003 has announced a kind of SCH channel that do not use, only utilize the method for pilot channel, its CPICH (pilot channel) and other data channels of this sub-district reach complete quadrature by time division multiplexing.The shortcoming of the document is: (i) because its in two time-multiplexed CPICH channels has covered the grouping that one deck mask is used to discern cell scrambling, and the interference in the time of can increasing the data despreading to other sub-districts.(ii) each scrambler group identification and scrambler identification all need the reception data after local candidate's mask and the FFT demodulation to carry out coherent detection, just can know corresponding district scrambler group by candidate's mask of finding out the correlation maximum.The operand that FFT demodulation in this process brings is bigger.

Summary of the invention

Switch at the sub-district in the CDMA multiple carrier cellular system, the present invention proposes a kind of cell searching synchronization method of handling based on time domain, be used for reducing the interference of pilot channel and reducing searching algorithm complexity and search time.

The cell searching synchronization method that the present invention proposes based on the time domain processing, processing procedure is:

Transmitting terminal is planned the Pi value that is used to discern the scrambler group, by P ₀The phase difference planning that begins each Pi is followed successively by 0, N/2, N/2 ², N/2 ²+ N/2, N/2 ³, N/2 ³+ N/2 ... N/2 ^M, N/2 ^M+ N/2 ..., be total to N _GRPIndividual, wherein, carrier number N=N _C, N _GRP＜N _C/ 2, described N _GRPBe the CSSC carrier number, described N _CCarrier number for the OFDM symbol;

In the transmission Frame of transmitting terminal, except data symbol, pilot channel 1 and pilot channel 2 respectively take an OFDM symbol period and other data time division multiplexinges at frame head and postamble in each frame; Different sub-districts adopts different scramblers to carry out spread spectrum, the signal of identical sub-district adopts identical cell scrambling to carry out spread spectrum with different channel orthogonal codes, the phase place difference of the cell scrambling that the OFDM data symbol of different time slots is adopted in each frame signal utilizes the phase difference of the cell scrambling of pilot channel 1 and pilot channel 2 to judge the cell scrambling group;

Receiving terminal carries out Autocorrelation Detection to received signal, by finding that maximum correlation value detects symbol time slot and FFT window;

Receiving terminal allows OFDM symbol and its previous OFDM symbol of receiving not multiply each other before the FFT, then product is carried out the FFT computing of part, whole value of output

Store, constantly carry out same operation, up to having experienced a frame N along time domain _SIndividual OFDM symbol detects the maximum in the value of storage this moment

Wherein, the time slot of the corresponding frame head of k, the corresponding CSSC code character of Pi;

Local all CSSC sign indicating numbers are all carried out the IFFT computing, store then, CSSC time-domain symbol for the CPICH channel that receives is carried out coherent detection by correlator and local all time domain CSSC values, and the local candidate CSSC sign indicating number of detected value maximum is exactly current cell scrambling; Normal data communication is carried out in the sub-district that turns to then and select.

If remove the influence of channel fading and other interference, detecting

Maximum before can pass through multiple averaging earlier.

Because the present invention has only adopted the phase difference identification scrambler group of two time division multiplexing CPICH channels in the frame design of the data that transmitting terminal transmits, such benefit is not need extra mask to discern the scrambler group, therefore can not increase the weight of the interference to other sub-districts.The present invention has reduced the complexity of ofdm signal frequency domain coherent detection computing, will shorten time of improving Cell searching or the correct probability that improves Cell searching by the minimizing of shortcut calculation amount of calculation.

Description of drawings

Fig. 1 is the P in order to judgement cell scrambling group _iThe allocative decision schematic diagram of value

Fig. 2 is the frame structure of transmitting terminal data of the present invention and the multiplex mode schematic diagram of pilot channel;

Fig. 3 is in the carrier wave of the present invention's OFDM symbol of each time slot in transmitting terminal one frame data, the distribution condition of CSSC code phase, and in the configuration schematic diagram of the CSSC of pilot channel phase place;

Fig. 4 carries out the flow chart of Cell searching at receiving terminal for the present invention;

Fig. 5 for the present invention in second stage of Cell searching, cell scrambling group acknowledge and frame synchronization stage, the flow chart of shortcut calculation;

Fig. 6 for the principle of part fft algorithm of the present invention and and complete fft algorithm concern schematic diagram;

Fig. 7 has illustrated that general OFDM frequency-region signal correlation technique and the present invention propose frequency domain correlation technique schematic flow sheet.

Embodiment

The present invention is in the transmission Frame of transmitting terminal, and except data symbol, pilot channel 1 (CPICH1) and pilot channel 2 (CPICH2) respectively take an OFDM symbol period and other data time division multiplexinges at frame head and postamble in each frame.

Different sub-districts adopts different scramblers to carry out spread spectrum, the signal of identical sub-district adopts identical cell scrambling (CSSC) to carry out spread spectrum with different channel orthogonal codes (CSOC), but the phase place difference of the cell scrambling that the OFDM data symbol of different time slots is adopted in each frame signal, utilize the phase difference of the cell scrambling of pilot channel CPICH1 and CPICH2 to judge the cell scrambling group, need not so some CPICH channels are carried out the mask operation again, increase presence of intercell interference.

Frame design above corresponding can all utilize formula for every adjacent two OFCDM symbols at receiving terminal

$s_{P_I}\left(k\right)=\underset{n=0}{\overset{N_C-1}{\mathrm{\Σ}}}{r}_{n-P_i}(k-1)r_n^{*}\left(k\right)\{r_{-p_i}=r_{N_C-P_I}i>0\}$

Carry out related operation and obtain the identification of cell scrambling group. The subcarrier in frequency domain sequence number that is illustrated in k OFDM symbol of time domain and k-1 OFCDM symbol differs and is P _iData between the output of being correlated with, N _CBe the carrier number of OFDM symbol, by finding pairing k of maximum correlation value and P _iCan find out corresponding frame boundaries starting point time slot and CSSC code character, the algorithm principle that CSSC code character that Here it is detects.

The characteristic that algorithm principle that detects at the CSSC code character and receiving terminal data-signal all need to carry out the FFT demodulation can be designed one two step shortcut calculation and reduce amount of calculation.

At first can simplify top scrambler group detection calculations, can find that be P with adjacent two through output sequence number behind the value circular convolution on the OFDM symbol subcarrier in frequency domain after the FFT demodulation by the principle of computing of frequency domain circular convolution and time domain multiplication computing equivalence _iValue (i=1,2 ... N _GRPN _GRPBe scrambler group number) our coherent detection output valve of needing just

So for circular convolution computing with frequency domain

Can further pass through

$\stackrel{\‾}{s\left(k\right)}=\mathrm{FFT}(\stackrel{\‾}{R\left(K\right)}\·*\stackrel{\‾}{R(K-1)})$

Obtain.

Be not have FFT demodulation time domain OFDM symbolic vector before,

Be to carry out FFT computing output vector Middle sequence number is P _iThat scalar value, relative like this and top per two symbols need N _GRPRelated operation is discerned the cell scrambling group, only needs N here _CInferior multiplying need not in addition with top the same as each data FFT data demodulates, and it is just passable that two products that do not have a time domain OFDM symbol before the FFT demodulation are carried out the FFT computing, so finally the FFT operand is constant, the multiplication computation complexity has reduced N relatively _GRPDoubly.This moment multiplication algorithm complexity and M.TANNO, H.ATARASHI, K.HIGUCHI, the method for mentioning in the document of and M.SAWAHASHI is compared the same, but saves a large amount of add operations.

Secondly can design P _iValue simplify top calculating once more

The FFT operand.At first can know from FFT fast algorithm principle, if the sequence number of the point of being asked comes together in FFT computing output, then the value of these points can by to FFT computing simplify and obtain, if use the N point FFT fast algorithm of decimation in frequency (DIF), the value of exporting the sequence number that comes point together differs successively from the near to the remote according to the position and is N/2, N/2 ², N/2 ³。。。。。2,1, the be separated by value of near more sequence number of sequence number differs big more.Suppose that here N is 2 K power.Allow N _GRPIndividual P _IRespectively and the preceding N of the N point FFT computing of decimation in frequency (DIF) output _GRPThe value of the sequence number of individual point equates, P _iBetween value differ closely and be N/2, N/2 to differing far successively ², N/2 ³。。。。。2,1, can keep maximum distance interval always, meet the phase difference P that we require two adjacent C PICH channels _iThe requirement of the big more easy more judgement of value.Also can allow corresponding in addition

All come FFT computing output

Preceding N in the vector _GRPIndividual, then can use the FFT computing of simplification to obtain

After taking this method, the multiplication that each FFT relates to and the amount of addition operations once more by N _CLog ₂N _C(just M.TANNO, H.ATARASHI, K.HIGUCHI, the amount of calculation that the FFT data of the method for mentioning in the document of and M.SAWAHASHI are separated) is reduced to N successively _GRP(log ₂N _GRP+ 2N/N _GRP-2),

Multiplication computation amount is few with the index demultiplication.If be used for 1024 subcarriers, scrambler is divided into 64 groups, the multiplication that so each FFT relates to and the amount of addition operations are kept to 256 and 2432 successively by 10240 and 5120, reduce multiple and are about 40 times and 2 times successively.

The data that for the detection of cell scrambling also generally are each subcarrier on the CPICH1 channel that will receive are relevant with all local CSSC candidate codewords, and the code word that correlation is the highest is exactly the code word of current area.According to the constant principle of time-frequency two territory power, formula can be directly passed through in proposition in time domain in this patent

$X_{{\mathrm{RC}}_i}\left(0\right)=\underset{n=0}{\overset{N_C-1}{\mathrm{\Σ}}}{r}_n{c_{n,i}}^{*}$

Obtain the value of their frequency domain coherent detection.c _{N, i}The local time thresholding through the CSSC sign indicating number after the IFFT computing of expression exists in the internal memory because the FFT computing of this step can be carried out in advance, disregards so this part FFT amount of calculation can be omitted.Whole process is compared with conventional method and is saved a FFT computing.

The two step shortcut calculation first steps that the present invention proposes only need two signals that do not have the FFT demodulation that receive are carried out N _CInferior multiplying each other just can obtain the coherent detection output valve that we want with product FFT computing

Saved the amount of addition operations of general coherent detection; Next allows N _GRPIndividual

In P _iRespectively with the preceding N of the N point FFT computing of decimation in frequency output _GRPThe value of the sequence number of individual point equates, utilizes the algorithm principle of FFT, if N before requiring _GRPThe correlation that individual needs detect All will carry out the FFT demodulation and carry out coherent detection then as long as carry out in the computing of part FFT and the general related algorithm each symbol, FFT multiplication and the amount of addition operations are reduced by at least 1/2 ^MDoubly; Directly the signal on the pilot channel of local all scramblers after the IFFT processing and reception is carried out the coherent detection computing by circular convolution and the constant principle of time-frequency two territory power in OFDM receiving terminal time domain at last and replace the frequency domain coherent detection, the centre need not FFT and handles, and directly can detect the current area scrambler.

Below further specify processing procedure of the present invention by a specific embodiment, suppose to be applied to a carrier number N=N _C, the cell scrambling number is N _GRP, contain N in the frame _SIn the middle of the Frame design of the transmitting terminal of the multi-carrier mobile communication system of individual OFDM symbol and cell search process, method and the programming of receiving terminal.

Earlier to being used to discern the P of scrambler group _iValue plan.Fig. 1 has illustrated a N=N _C, the sub-district is around code character number=N _GRPThe time correspondence the phase difference P of two CPICH channels _iThe planning situation of value, P as seen from the figure _iValue by P ₀Begin to be followed successively by

0、N/2、N/2 ²、N/2 ²+N/2。。。N/2 ^M、N/2 ^M+N/2、。。。、

Be total to N _GRPIndividual, N wherein _GRP＜N _C/ 2.This value and the preceding N that exports according to DIF algorithm computation N point FFT _GRPThe sequence number value of individual point is identical

Then the data of input are carried out the frame design as shown in Figure 2.The data symbol of two pilot channels goes in the data symbol and the data symbol time division multiplexing being inserted into end to end of each frame.

Next CSSC is at phase assignments scheme such as Fig. 3 of each OFDM symbol time slot the time.The phase place that CSSC differs on each adjacent OFDM data symbol carrier wave is all identical, and the CSSC phase place of CPICH2 channel is 0, CPICH1 channel CSSC phase place P _i, it is determined by the scrambler group under the CSSC.

At P _iValue and frame design after the sign indicating number allocative decision is handled, can constructed corresponding CDMA multiple carrier transmitter process according to this standard, the data of input are handled emission.

At receiving terminal, receiver carries out Cell searching by following process.As shown in Figure 4

Phase I at first, the GI by to received signal carries out Autocorrelation Detection, by finding that maximum correlation value detects symbol time slot and FFT window.

At the algorithm of second stage as shown in Figure 5.Allow OFDM symbol and its previous OFDM symbol of receiving not multiply each other before the FFT, then product is carried out the FFT computing of part, whole value of output

Store, constantly carry out same operation, up to having experienced a frame N along time domain _SIndividual OFDM symbol detects the maximum in the value of storage this moment

The time slot of the frame head of k correspondence, P _iCorresponding CSSC code character.If remove the influence of channel fading and other interference, also can be through detecting after the multiple averaging

Maximum.

Fft algorithm about part obtains explanation in Fig. 6.Fig. 6 is the fft algorithm flow process of normal N=8, if just calculate the value of preceding two points as can be seen, it is just passable only to need to calculate its calculating that relates to, the computing that dotted line comprised among Fig. 6 just, it is the part of complete fft algorithm, but keeps away a large amount of multiplyings that relate among the FFT cleverly.For N=N _C, the point of calculating is at preceding N _GRP(N _GRP＜=N _C/ 2) be suitable for too.

Phase III CSSC detects and can utilize the local all candidate CSSC sign indicating numbers and the coherent detection of CPICH2 channel.At first local all CSSC sign indicating numbers are all carried out the IFFT computing, store then, for the CSSC time-domain symbol of the CPICH channel that receives by as all time domain CSSC value coherent detections of correlator and this locality of Fig. 7 (b), the local candidate CSSC sign indicating number of detected value maximum is exactly that current sub-district is around sign indicating number.Whole like this Cell searching flow process just is through with, and normal data communication is carried out in the sub-district that begins to turn to and select.

Above-mentioned embodiment describes the present invention with preferred embodiment, but the example of this visualization of just lifting for the ease of understanding should not be considered to be limitation of the scope of the invention.Equally, according to the description of technical scheme of the present invention and preferred embodiment thereof, can make various possible being equal to and change or replacement, and all these changes or replacement all should belong to the protection range of claim of the present invention.

Claims (2)

1. cell searching synchronization method of handling based on time domain is characterized in that this method comprises:

Transmitting terminal is planned the Pi value that is used to discern the scrambler group, by P ₀The phase difference planning that begins each Pi is followed successively by 0, N/2, N/2 ², N/2 ²+ N/2, N/2 ³, N/2 ³+ N/2 ... N/2 ^M, N/2 ^M+ N/2 ..., be total to N _GRPIndividual, wherein, carrier number N=N _C, N _GRP＜N _C/ 2, described N _GRPBe the CSSC carrier number, described N _CCarrier number for the OFDM symbol;

In the transmission Frame of transmitting terminal, except data symbol, pilot channel 1 and pilot channel 2 respectively take an OFDM symbol period and other data time division multiplexinges at frame head and postamble in each frame; Different sub-districts adopts different scramblers to carry out spread spectrum, the signal of identical sub-district adopts identical cell scrambling to carry out spread spectrum with different channel orthogonal codes, the phase place difference of the cell scrambling that the OFDM data symbol of different time slots is adopted in each frame signal utilizes the phase difference of the cell scrambling of pilot channel 1 and pilot channel 2 to judge the cell scrambling group;

Receiving terminal carries out Autocorrelation Detection to received signal, by finding that maximum correlation value detects symbol time slot and FFT window;

Receiving terminal allows OFDM symbol and its previous OFDM symbol of receiving not multiply each other before the FFT, then product is carried out the FFT computing of part, whole value of output Store, constantly carry out same operation, up to having experienced a frame N along time domain _SIndividual OFDM symbol detects the maximum in the value of storage this moment

Wherein, the time slot of the corresponding frame head of k, the corresponding CSSC code character of Pi;

Local all CSSC sign indicating numbers are all carried out the IFFT computing, store then, CSSC time-domain symbol for the CPICH channel that receives is carried out coherent detection by correlator and local all time domain CSSC values, and the local candidate CSSC sign indicating number of detected value maximum is exactly current cell scrambling; Normal data communication is carried out in the sub-district that turns to then and select.

2. method according to claim 1 is characterized in that, if remove the influence of channel fading and other interference, is detecting

Maximum before can pass through multiple averaging earlier.

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