In mobile communication system, when UE (subscriber equipment) switched on, it did not know where it be in and it is in which sub-district.Therefore for travelling carriage, the first step is a search of initial zone, sets up the communication linkage with the base station.In common cdma system, the task of search of initial zone is normally searched for some cell-specific sign indicating numbers that are called as synchronous code.Structure of this yard and detection method thereof be the characteristic properties of different system normally.
Detection of complex and search time are the problems of being concerned about most.That uses at present has several cdma systems, as TD-SCDMA (time-division-synchronization code multi-address division system, UTRA TDD/FDD (UMTS (Universal Mobile Telecommunications System) terrestrial wireless inserts time division duplex/Frequency Division Duplexing (FDD)) system, and CDMA2000 (IS-95)) system, they use different small region search methods.
In the TD-CDMA system, synchronous code (SYNC) is sent out at down link pilot timeslot (DwPTS).Content among the SYNC is one group of Gold code (Gold code).Gold code is designed to neighbor identification, thereby is easier to cell measurement.
During search of initial zone, UE at first receives a subframe (5ms) signal.Moving window utilizes known Gold code sequence (using 19 sign indicating numbers at least) then, and the uncertainty with 1/19th is searched the maximal correlation peak value between two protection periods (guard period).For this purpose, 19 matched filters (or any similar devices) are by the use that walk abreast, and they mate with 19 synchronous codes respectively.Determine DwPTS then.In case travelling carriage obtains DwPTS, it can be proceeded other and obtain operation.
In UTRA TDD/FDD system, use the synchronizing channel (SCH) that is loaded with Primary Synchronisation Code and secondary synchronization code.Primary Synchronisation Code is identical and be sent out in main SCH to each sub-district in the system.Inferior SCH is made up of the sequence of the various combination with secondary synchronization code, and with neighbor identification, these secondary synchronization code and main SCH are parallel to be sent.
During search of initial zone, UE uses Primary Synchronisation Code to obtain and the signal slot synchronization of strong sub-district.A matched filter (or any similar devices) is used to this purpose, promptly with to the identical Primary Synchronisation Code in all sub-districts is complementary.UE uses the sequence of secondary synchronization code to search frame synchronization and discerns in 32 code characters one then.Signal by making reception is relevant with all possible secondary synchronization code sequence in the position of secondary synchronization code, detects subsynchronous sequence.In case travelling carriage has obtained subsynchronous sequence, it can be proceeded other and obtain operation.In this system, two kinds of sign indicating number sequences are used.
In CDMA2000 (or IS95) system, a public code multiplexed pilot (pilot) that is used for all users is provided, a known PN sequence is used to pilot tone.The different time mode shifter of this sequence is used in different sub-districts, thereby they can be discerned well.This pilot channel is shared by all Traffic Channels, and it is synchronous that the travelling carriage of working in base station overlay area uses this synchronizing channel to obtain initial time.
When powering up, travelling carriage is searched on the optimized frequency of forward pilot channel (F-PICH).For example, can carry out this search by making the local short code that produces and the signal correction of reception.This process proceeds to discovery " coupling ".The forward pilot channel that the mobile station in selecting correlation is the highest is corresponding to the strongest base station of signal.In case obtain the forward pilot channel, travelling carriage just can demodulation forward synchronizing channel (F-SYNC).This is possible, because F-SYNC makes its frame border always aim at the conversion of the PN of forward pilot channel (Pseudo-Random Noise Code) (roll-over).In other words, the F-SYNC frame border always departs from the PN deviation value of a corresponding F-PICH from system time.The system time that travelling carriage departs from according to PN and sends in Sync Channel Message is regulated its internal clocking.In case travelling carriage obtains system timing, it can be proceeded other and obtain operation.
In said system, because synchronous code or equivalent code length, the synchronous code quantity of each sub-district is big, and synchronous code detection of complex and search of initial zone consumed time are long.
Embodiment.
According to the present invention, Fig. 1 shows frame structure and the design of using of SYNC (synchronously) sign indicating number in the TD-SCDMA system.As shown in Figure 1, the SYNC sign indicating number is placed on DwPTS, and service signal interrupts here.Usually, the SYNC code is that 64 chips (chip) are long, 19 codes of definition in the TD-SCDMA system.
In the present invention, to adopt selected a kind of classification (hierarchical) sequence be synchronous code and repeat at each frame.By forming this hierarchical sequence, as subcode 1 and subcode 2 in conjunction with two short codes that are called as subcode.A plurality of subcodes 2 are arranged.As shown in Figure 1, a hierarchical sequence is that the SYNC sign indicating number multiply by subcode 2 formation by subcode 1.The different choice of these two sign indicating numbers can produce the cell-specific synchronous code, is used for neighbor identification.Suppose that 1 pair of all sub-district of subcode are all identical, and give subcode 2 of each cell allocation, each sub-district will have a cell-specific SYNC sign indicating number.Therefore, two step Cell searchings based on these two subcodes of identification have improved complexity and search time greatly.The process of search of initial zone will be described in detail in the back.
In the prior art, in order to discern different sub-districts, if the sub-district can be identified by their synchronous code, this will be favourable.But if use different synchronous codes, travelling carriage must simultaneously or in a sequence be searched for all sign indicating numbers, causes high complexity and/or long search time.
Therefore, as mentioned above, the present invention solves this problem by utilizing a kind of special synchronous code design.At first, in one embodiment of the invention, described synchronous code, promptly hierarchical sequence comprises a short subcode 1 and a lot of quadrature subcode 2, and short subcode 1 is for being identical in the whole system scope, and quadrature subcode 2 is that each sub-district is exclusive, and length may be longer.Therefore, travelling carriage only need be searched for subcode 1 in the first step.This can be by the signal and subcode 1 relevant finishing that makes reception, and will find continuous relevant peaks in each sub-district, and this is public because of 1 pair of whole network of subcode.Because this sign indicating number is short, so this is not very complicated.Then, finish the detection of subcode 1 after, detection window can be reduced to the peripheral region of the relevant peaks of finding.In this zone, travelling carriage is attempted by a signal that receives and the relevant subcode 2 of discerning of all possible sign indicating number.In the present invention, because the first step causes search window reduced, its complexity reduces.After relevant with all full SYNC sign indicating numbers, the highest relevant peaks is determined, and the subcode 2 that is used for this peak also is determined, thereby the sub-district with this subcode 2 will be judged as nearest sub-district.
Fig. 2 shows base station and the travelling carriage schematic diagram that uses in one embodiment of the invention.As shown in Figure 2, in base station side (Node B), multiplier multiplies each other subcode 1 and subcode 2, produces hierarchical sequence, i.e. a synchronous code.In this embodiment, subcode 1 all sub-districts in whole network are general, and each subcode 2 is special-purpose to each sub-district.
After producing synchronous code, synchronous code is launched at the every frame in DwPTS position by a reflector (not shown) in base station (Node B).
In this embodiment, travelling carriage comprises a receiver (not shown), is used to receive the signal from base station; One first correlator is carried out relevant with subcode 1 in frame; With one second correlator, in a search window that dwindles, carry out relevant with the full SYNC sign indicating number that comprises all subcodes 2; With a judgment device, be used for determining which sub-district travelling carriage is at present.
When travelling carriage was carried out search of initial zone, it received the frame of base station.In step 1, first correlator makes each frame only relevant with subcode 1 then, and this subcode 1 is a short code, and the relevant peaks in finding each continuous sub-district.Fig. 3 A shows an example using serial correlation peak, subcode 1 relevant back in first correlator.As shown in Figure 3A, there are 8 serial correlation peak values the DwPTS position in a frame.Because BS does not use subcode 1 in the remainder of frame, is other signals in this zone.In this way, can determine the position of SYNC sign indicating number.
Search window is reduced then arrives around the relevant peaks of finding, in step 2, second correlator makes the signal of reception relevant with all full SYNC sign indicating numbers in little search window, and these full SYNC sign indicating numbers comprise all subcodes 2, in order to search the relevant peaks of each sub-district.These relevant can walking abreast or the serial execution.Fig. 3 B shows an example of the relevant peaks of relevant back with the full SYNC sign indicating number that comprises subcode 2 in second correlator.Shown in Fig. 3 B, in little search window, if the SYNC sign indicating number of a sub-district is complementary with the SYNC sign indicating number that uses, a relevant peaks of this sub-district appears then in second correlator.Judge to have the sub-district of high relevant peaks near determining in each sub-district then.This sub-district is confirmed as travelling carriage present located sub-district.
In order to discern more sub-district, even need more synchronous code.Therefore in a favourable expansion example of the present invention, can use a more than subcode 1.These subcodes 1 can be quadratures.That is to say, still in step 1, try out a more than subcode, but because subcode 1 is short, so complexity is little.
In a single day travelling carriage has obtained synchronous code, and it can be proceeded other and obtain operation, then the communication linkage of foundation and the base station in determined sub-district.
Consider the TD-SCDMA system, above-mentioned synchronous code of the present invention can be used as SYNC and adopt, and other structures of TD-SCDMA can be not influenced.Therefore as shown in Figure 1, the length of synchronous code is 64, and frame (or in the TD-SCDMA system alleged subframe) has duration and 6771 chips of 5ms.The task of search of initial zone, promptly a unknown synchronous code of search 64 chip lengths in 6771 chips is identical to the original method among the TD-SCDMA with said method according to the present invention.Be a specific example of SYNC sign indicating number design according to an embodiment of the invention below.
Two sign indicating numbers that form hierarchical sequence can be referred to as X
1(I), subcode 1, and X
2(j), subcode 2, and all elements before BPSK mapping, belong to collection 0,1}.The length of sign indicating number is 8.
The element of the hierarchical sequence SYNC of definition length 64 is:
SYNC (i)=X
1(i mod 8)
*X
2(i div 8), wherein i=0 ... 63
Note, be equal to for this formation and use spreading code X
1Spread data streams X
2
Fig. 4 shows the example of carrying out search of initial zone in this embodiment of the present invention at UE (travelling carriage).All full SYNC sign indicating numbers comprise subcode 1 and all subcodes 2, are stored in advance in the memory (not shown) of mobile device.As shown in Figure 4, in first correlator, multiplier is X with subcode 1
1The signal that spread spectrum receives; An integrator is at 8T
cDuring this time signal is carried out integration; The mould of signal is calculated then, produces a relevant output.The output of first correlator is the serial correlation peak value, shown in Fig. 3 a-signal A.
The relevant output of first correlator is handled by 8 second correlators in the search window that dwindles.In each second correlator, a multiplier comprises a corresponding subcode 2, X with one
2Corresponding full SYNC sign indicating number spread spectrum input signal.Behind the spread spectrum, because whole SYNC sign indicating number is that 64 chips are long, an integrator is at 64T
cSignal to spread spectrum during week carries out integration.Calculate its mould then, export a relevant peaks, this relevant peaks is corresponding to the subcode of using in this correlator 2, shown in the signal B of Fig. 3 B.In Fig. 4, the associative operation of each second correlator is implemented by parallel, and still, as selection, they also can implement in serial.
Relevant peaks from each second correlator output, through a judgment device relatively, to determine the highest correlation peak of which second correlator output, the SYNC sign indicating number of this correlator is confirmed as the SYNC sign indicating number that use nearest sub-district then, thereby which sub-district determines that travelling carriage is current is in.
Table 1 shows X
1The constituted mode of an example of some sequences of=E8 (hexadecimal).
The constituted mode of table 1 hierarchical sequence
SYNC | X
1=E8( X
1=17)
|
Sub-district 0, X
2=00
| E8 | E8 | E8 | E8 | E8 | E8 | E8 | E8 |
Sub-district 1, X
2=55
| E8 | 17 | E8 | 17 | E8 | 17 | E8 | 17 |
Sub-district 2, X
2=33
| E8 | E8 | 17 | 17 | E8 | E8 | 17 | 17 |
Sub-district 3, X
2=66
| E8 | 17 | 17 | E8 | E8 | 17 | 17 | E8 |
Sub-district 4, X
2=0F
| E8 | E8 | E8 | E8 | 17 | 17 | 17 | 17 |
Sub-district 5, X
2=5A
| E8 | 17 | E8 | 17 | 17 | E8 | 17 | E8 |
Sub-district 6, X
2=3C
| E8 | E8 | 17 | 17 | 17 | 17 | E8 | E8 |
Sub-district 7, X
2=69
| E8 | 17 | 17 | E8 | 17 | E8 | E8 | 17 |
Therefore, if Walsh (Walsh) sign indicating number is used as X2, length is that 3 m-sequences (a kind of PN sequence) of 8 are used as X
1, have 24 different SYNC sign indicating numbers (in TD-SCDMA, only defining 19 sign indicating numbers).
As a UE (subscriber equipment) when being energized, by with the signal that receives and length be 3 X of 8 in a subframe
1Sign indicating number is relevant, the SYNC sign indicating number that search is unknown.In this first step, each is relevant to be that length on a subframe (6771 chip) is 7 add, and will carry out 3 times.In this embodiment, in Fig. 4, should be carried out 3 times by parallel or serial with the relevant of subcode 1.But, in the TD-SCDMA system, in a subframe, be that 19 sign indicating numbers of 64 are correlated with length, then each relevant be that length on 6771 chips is 63 add, and to carry out 19 times.Be about 19 so improve coefficient
*63/ (7
*3)=57.
No matter which SYNC sign indicating number is nearest Node B (base station) adopt, around the position of SYNC sign indicating number, with regard to an X
1Sign indicating number will produce 8 continuous boy peaks.Thereby X
1The general location of sign indicating number and SYCN sign indicating number can be determined.Then, because each X
2The zero cross-correlation of sign indicating number, 8 different X
2The detection of sign indicating number can easily be carried out in this position.In this second step, each is relevant to be that length on 64 chips or more more chip is 63 add, and will carry out 8 times.If correlated results is re-used in step 1, complexity can be further reduced.Thereby compare with the first step, the complexity in this step can be left in the basket.After these two steps, finished and obtained the SYNC sign indicating number.
From above description to embodiments of the invention, obviously the invention provides the favorable method of a search of initial zone when travelling carriage is energized, make travelling carriage before setting up communication linkage, can search it efficiently and be in which sub-district with the base station of nearest sub-district.The invention provides a kind of favourable classification synchronous code design, as a result of, improved the complexity that detects synchronous code, shortened the search of initial zone time greatly.
Though used the TD-SCDMA system in the above-described embodiments, but also can be used in other communication systems based on CDMA according to classification synchronous code design of the present invention and initial cell searching method, as UTRA TDD/FDD system, and CDMA2000 (IS-95) system.
The preferred embodiments of the present invention have been described in the front.Should be noted that without departing from the present invention according to of the present invention open, those of ordinary skill in the art can make amendment and modification.