GB2387997A

GB2387997A - Synchronisation in w-cdma by combining secondary synchronisation codes from plural slots

Info

Publication number: GB2387997A
Application number: GB0209414A
Authority: GB
Inventors: Paul Howard
Original assignee: IPWireless Inc
Current assignee: IPWireless Inc
Priority date: 2002-04-25
Filing date: 2002-04-25
Publication date: 2003-10-29
Anticipated expiration: 2022-04-25
Also published as: GB0209414D0; GB2387997B

Abstract

Synchronisation information is needed by a receiver so that it can communicate with a transmitter. UMTS standards provide two alternative frame patterns for synchronisation slots, containing both primary and secondary synchronisation codes (PSC, SSC), and these alternate arrangements prevent plural synchronisation slots being directly integrated. The invention provides that the SSC of plural slots can be combined in using plural polarity patterns to produce plural SSC estimates (610, 620, 630) and these can be combined (preferably by adding) to produce a combined SSC estimate (640). In this way full integration can be achieved without any prior knowledge of the frame pattern being used.

Description

02.0026-ipw 1 - METHOD AND ARRANGEMENT FOR SYNCHRONISATION IN A WIRELESS

COMMUNICATION SYSTEM

5 Field of the Invention

This invention relates to synchronization in wireless communication systems, and particularly (though not exclusively) UTRA WCDMA (Universal Mobile Telephone 10 System Terrestrial Radio Access, Wideband CodeDivision-

_ultiple-Access) systems.

Background of the Invention

In the field of this invention it is known that in UTRA

TDD (Time Division Duplex) mode the synchronization channel (SCM) has two functions. The primary function is to provide a signal that enables a 'UK' (user equipment, 20 such as a wireless terminal) to search for and identify a Node B' (i.e. a wireless Base Station of a UMTS system).

The secondary function provides sufficient information to allow a UE to demodulate a P-CCPCH (Primary Common Control Physical CHannel) transmission and obtain the 25 system information (sent on the 'BCH' transport channel which is carried by the P-CCPCH) needed in order to be able to communicate with the network.

Two synchronization cases are provided for by the 3GPP 30 (3rd Generation Partnership Project) standard: Case l and Case 2. Case l is as described above with only one SCH

r co e e r. 02.0026-ipw - 2 - transmission per frame (slot k). Case 2 uses two SCH transmissions per frame, one in slot k and one in slot k+8. 5 The general format of the SCH includes a primary synchronization code (PSC) transmitted at power PpsC, and a secondary synchronization code (SSC) transmitted simultaneously with the PSC at power Pssc. In addition these codes, chosen from 4 code sets (see 3GPP Technical 10 Standard (TS) 25.223) are multiplied by a complex value, by 9=0,1,2,3). The code sets, s, in conjunction with the complex multiplier values, by, are used to transfer the information bits to the UK.

15 The PSC is used as a coherent phase reference in order to obtain the SSC modulation. In low signal-to-noise conditions, the PSC correlation does not provide an accurate phase reference for the SSC. Given this, and the fact that the SSC power can be scaled down (if required) 20 relative to the PSC power, it is very unlikely that every SSC received can be accurately decoded. It is therefore necessary to be able to combine successive received SSC in order to reduce the noise variance associated with these estimates.

It is beneficial, in terms of the overall system design, to be able to maximise the SSC performance, such that less system resource (e.g., transmit power) is dedicated to supporting these basic channels.

r en e r e e e e . e i. I. r 02.0026-ipw - 3 - In synchronization Case l, the SSC symbol alternates between odd and even frames. In Case 2, the SSC symbol alternates between slot k and slot k+8 as well as odd/even frames. However, the modulating data is not mapped on to 5 the SSC symbol in a manner that is independent of the code group.

As a direct consequence, the successively received SSC symbols cannot be directly combined, as the combination 10 requires a priori knowledge of the code group to identify which codes in the code set are toggling.

It is possible to use sub-optimal combining schemes that rely on combining identical SSC symbols. Such a scheme 15 would, in case l, give two averaged outputs - one for even frames and one for odd frames, which could then be hard-decoded (i.e., decisions made separately on the two outputs). A correct decoding could then be identified if both decoded outputs were consistent with the code group 20 and frame.

Such a scheme for case 2 would require that four soft-

combined outputs are generated and decoded. It would also require that a majority of the hard decisions were 25 consistent with code group, frame and slot.

Such a scheme is sub-optimal as only half (or quarter in case 2) the received energy is used to make the hard decision (i.e., each decision made independently of the 30 others).

À Àe e À À . ó( - 'be e at. 02.0026-ipw - 4 - A need therefore exists for a method and arrangement for synchronization in a wireless communication system wherein the abovementioned disadvantage(s) may be alleviated. Statement of Invention

In accordance with the present invention there is 10 provided a method and arrangement for synchronization in a wireless communication system as claimed in claim 1.

Brief Description of the Drawings

One method and arrangement for synchronization in a wireless communication system incorporating the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. l shows a block diagrammatic representation of a UTRA system in which the present invention is usedi z5 FIG. 2 shows a schematic representation illustrating the format of SCH in UTRA TDD mode; FIG. 3 shows a table illustrating Code allocation for 3GPP synchronization Case l;

so r 0 À À ,-,. t 02.0026-ipw - 5 FIG. 4 shows a table illustrating Code allocation for 3GPP synchronization Case 2; FIG. 5 shows a schematic diagram illustrating Soft 5Combining of SSC in Case 1; and FIG. 6 shows a schematic diagram illustrating Soft-

Combining of SSC in Case 2.

Description of Preferred embodiment

Referring firstly to FIG. 1, a typical, standard UMTS network (100) is conveniently considered as comprising: a 15 user equipment domain (110), made up of a user SIM (USIM) domain (120) and a mobile equipment domain (130)i and an infrastructure domain (140), made up of an access network domain (150), and a core network domain (160), which is in turn made up of a serving network domain (170) and a 20 transit network domain (180) and a home network domain (190).

In the mobile equipment domain (130), user equipment UP (130A) receives data from a user SIN (120A) in the USIM 25 domain 120 via the wired Cu interface. The UE (130A) communicates data with a Node B (150A) in the network access domain (150) via the wireless Uu interface.

Within the network access domain(150), the Node B (150A) communicates with a radio network controller or RNC 30 (150B) via the Tub interface. The RNC (150B) commmunicates with other RNC's (not shown) via the Iur

À o. r em - By-,, _ 02.0026-ipw 6 - interface. The RNC (150B) communicates with a SGSN (170A) in the serving network domain (170) via the Iu interface. Within the serving network domain (170), the SGSN (170A) communicates with a GGSN (170B) via the Gn 5 interface, and the SGSN (170A) communicates with a VLR server (170C) via the Gs interface. The SGSN (170A) communicates with an HLR server (19OA) in the home network domain (190) via the Zu interface. The GGSN (170B) communicates with public data network (180A) in 10 the transit network domain (180) via the Yu interface.

Thus, the elements RNC (150B), SGSN (170A) and GGSN (170B) are conventionally provided as discrete and separate units (on their own respective software/hardware 15 platforms) divided across the access network domain (150) and the serving network domain (170), as shown the FIG. 1.

The RNC (150B) is the UTRAN element responsible for the 20 control and allocation of resources for numerous Node B's (150A); typically 50 to 100 Node B's may be controlled by one RNC. The RNC also provides reliable delivery of user traffic over the air interfaces. RNC's communicate with each other (via the interface Iur) to support handover 25 and macrodiversity.

The SGSN (170A) is the UMTS Core Network element responsible for Session Control and interface to the Location Registers (HER and VLR). The SGSN is a large 30 centralized controller for many RNCs.

e - * e À: To iv ; 02.0026-ipw The GGSN (170B) is the UMTS Core Network element responsible for concentrating and tunnelling user data within the core packet network to the ultimate destination (e.g., interned service provider - ISP).

In UTRA TDD mode the synchronization channel (SCM) of the wireless interface Uu has two functions. The primary function is to provide a signal that enables a UE to search for and identify a Node B. The secondary function 10 provides sufficient information to allow a UE to demodulate a P-CCPCH transmission and obtain the system information (sent on the BCH transport channel which is carried by the P-CCPCH) needed in order to be able to communicate with the network.

Two synchronization cases are provided for by the 3GPP (3rd Generation Partnership Project) standard: Case 1 and Case 2. Case 1 is as described above with only one SCH transmission per frame (slot k). Case 2 uses two SCH 20 transmissions per frame, one in slot k and one in slot k+8. The general format of the SCH is shown schematically in FIG. 2. This figure shows that the PSC, Cp, is a real 25 valued sequence of length 256 chips, transmitted at power PPsc. The SSC, Cs,i (i=1,2,3), of length 256 is transmitted simultaneously with the PSC; the total power of the SSC is set to Pssc. In addition the SSC codes are multiplied by a complex value, by 9=0,1,2,3). The subscript s in Csi, 30 refers to a code set, of which there are 4 (see 3GPP Technical Standard (TS) 25.223). The code sets, s, in

'. r r. r À _ tt - r , . 02.0026-ipw - 8 conjunction with the complex multiplier values, by, are used to transfer the information bits to the UK.

The location of the SCH relative to the beginning of the 5 time slot is defined by town. It is calculated as follows: t _: nTL976-2564 n<16 outsets tarn C 976+512+(n-16 7/U-Q TC n216 which can be simplified to: n. 48.Tc n<16 tosetn l(720+n.48)Tc n 216 10 where n = 0,1,..., 31. The value of n is related to the code group and is obtained by demodulating the information on the SSC.

Encoding Informs Lion on SSC The SSC is made up of three codes that are QPSK (Quadrature Phase Shift Key) modulated and transmitted in parallel with the PSC. The QPSK modulation carries the following information: 20 À the code group that the base station belongs to (32 code groups: 5 bitsi Cases l, 2); À the position of the frame within an interleaving period of 20 msec (2 frames: l bit, Cases l, 2); À the position of the SCH slot(s) within the frame (2 25 SCH slots: l bit, Case 2).

c r e À C r 0 i' 02.0026-ipw _ 9 _ The SSCs are partitioned into two code sets for Case l and four code sets for Case 2. The set is used to provide the following information: 5 Code Set Allocation for Case l Code Set | Code Group l 0-15 2 16-31

The code group and frame position information is provided by modulating the secondary codes in the code set.

0 Code Set Allocation for Case 2 Code Set | Code Group l 1 1 0-7 7

2 8-15

3 16-23

4 24-31

The following SCH codes are allocated for each code set: Case l Code set l: Cal, C3,Cs.

5 Code set 2: Coo, Cal, Cry.

Case 2 Code set l: Cal, C3,Cs.

Code set 2: Coo, Ct3, CI4.

Code set 3: Co,C6,C2.

20 Code set 4: C4, C8, Cat.

Code allocation for Case l is shown the table of FIG. 3.

It should be noted that in this table the code construction for code groups O to 15 using only the SCH 25 codes from code set l is shown. The construction for code groups 16 to 31 using the SCH codes from code set 2 is done in the same way.

À. A..-

02.0026-ipw - 10 Code allocation for Case 2 is shown the table of FIG. 4.

It should be noted that in this table, similarly to the table of FIG. 3, the code construction for code groups 0 5 to 15 using the SCH codes from code sets 1 and 2 is shown. The construction for code groups 16 to 31 using the SCH codes from code sets 3 and 4 is done in the same way. 10 SSC Soft Combining The PSC is used as a coherent phase reference in order to obtain the SSC modulation. In low signal-to-noise conditions, the PSC correlation does not provide an 15 accurate phase reference for the SSC. Given this, and the fact that the SSC power can be scaled down (if required) relative to the PSC power, it is very unlikely that every SSC received can be accurately decoded. It is therefore necessary to be able to combine successive received SSC 20 in order to reduce the noise variance associated with these estimates.

It is beneficial, in terms of the overall system design, to be able to maximise the SSC performance, such that 25 less system resource (e.g., transmit power) is dedicated to supporting these basic channels.

In synchronization Case 1, the SSC symbol alternates between odd and even frames. In Case 2, the SSC symbol 30 alternates between slot k and slot k+ 8 as well as odd/even frames. However, the modulating data is not mapped on to

r :;.. A" ^ 6'

02.0026-ipw - 11 -

the SSC symbol in a manner that is independent of the code group.

As a direct consequence, the successively received SSC 5 symbols cannot be directly combined, as the combination requires a priori knowledge of the code group to identify which codes in the code set are toggling.

It is possible to use sub-optimal combining schemes that 10 rely on combining identical SSC symbols. Such a scheme would, in case l, give two averaged outputs - one for even frames and one for odd frames, which could then be hard-decoded (i.e., decisions made separately on the two outputs). A correct decoding could then be identified if 15 both decoded outputs were consistent with the code group and frame.

Such a scheme for case 2 would require that four soft-

combined outputs are generated and decoded. It would also 20 require that a majority of the hard decisions were consistent with code group, frame and slot.

Such a scheme is sub-optimal as only half (or quarter in case 2) the received energy is used to make the hard 25 decision (i.e., each decision made independently of the others). The present invention is based on a novel and inventive mechanism for SSC combining, which in a preferred 30 embodiment is used in a UK.

r s : -,,.. I

02.0026-ipw - 12 Combining of SSC in Synchronisation Case 1 In synchronization Case l, only one information bit toggles between successive SSC transmissions. This bit is 5 used to signal odd / even framing. As already mentioned, this bit is mapped onto different SSC codes within the code set, depending on which code group is used by the Node B. 0 In a preferred embodiment of the invention, to be able to correctly combine the SSC results from each frame, the following combining scheme is used: À Combining successive SSC correlations across n 15 frames creates two partial SSC estimates, Estl and Est2. À Estl is obtained by coherently summing the SSC correlation outputs across n frames. Any SSC 20 correlations that keep the same sign across all frames are combined, while the correlations that change sign on alternate frame will cancel out.

Correlations due to noise will also tend to cancel as they have zero mean value.

À Est2 is obtained by summing the SSC correlation with alternate signs across all frames. This estimate should coherently combine the signals that change sign on alternate frames, while other signals should 30 tend towards a zero mean value.

o À À ... r 02.0026-ipw À The overall combined SSC estimate is computed by summing Estl and Est2. It should be noted that these estimates are calculated for all the valid SSC codes. In synchronization Case 1, only code set 1 5 and code set 2 are used, restricting the SSC combining to six codes (1, 3, 5, 10, 13, 14).

However, for consistency with Case 2, which will be discussed in greater detail below, 12 elements are employed and the unused codesets generate noise 10 terms which are used to calculate the codeset SNR (Signal/Noise Ratio).

FIG. 5 illustrates the soft combining process in Case 1.

As shown, across n frames, the SSC correlation outputs 15 (these signals being obtained in known manner and their derivation not needing any further description) from each

of the frames are summed coherently (with same sign) in combiner 510 to produce a first SSC estimate Estl. Also, the SSC correlation outputs from each of the frames are 20 combined with alternate signs in combiner 520 to produce a second SSC estimate Est2. The first and second SSC estimates Estl and Est2 are then summed in combiner 530 to produce an overall combined SSC estimate so.

25 Defining the vector Psych, the elements for which rSsc(i), i=1...12 are the SSC correlation results for SSC codes 1, 3, 5, 10, 13, 14, 0, 6, 12, 4, 8, 15 (Case 1), then the vector rk)Ssc,! contains the SSC results for frame k. The soft combined estimate of the SSC code word, so, is given 30 by:

i, e o À -

r -: 02.0026-ipw - 14 s= rkC+ (-l)krk', where k=O...n-1 k k Combining of SSC in Synchronisation Case 2 5 In synchronization Case 2, it is possible for all three SSC codes to toggle sign across the length 4 sequence of SSCs transmitted in synchronization Case 2. By inspecting the modulation mappings detailed in FIG. 4, three possible sign toggle patterns are possible for each 10 single SSC code in the code set. The three patterns are defined as: CSi = [++3] C52 = [+'-,+'-]

CS3 = [+',+]

Each SSC code vector in Case 2 contains 12 possible SSC 15 codes (1, 3, 5, 10, 13, 14, 0, 6, 12, 4, 8, 15). The combining sequences csi are used to generate three soft decision estimates from SSC correlations from successive frames and slots.

20 The three estimates are designed to combine the possible bit toggling sequences on each individual SSC code within a code set whilst averaging out any zero-mean sequences such as noise. The final combined version of the SSC is obtained by summing all three estimates.

FIG. 6 illustrates the soft combining process in Case 2.

As shown, across n frames, the SSC correlation outputs (from SSC's in slot k and k+8) from each of the frames are

r, r C r it: r at, 02.0026-ipw - 15 summed with signs sequentially in the pattern cs in combiner 610 to produce a first SSC estimate Estl. The SSC correlation outputs from each of the frames are also combined with signs sequentially in the pattern CS2 in 5 combiner 620 to produce a second SSC estimate Est2. The SSC correlation outputs from each of the frames are also combined with signs sequentially in the pattern C53 in combiner 630 to produce a third SSC estimate Est2. The first, second and third SSC estimates Estl, Est2 and Est3 10 are then summed in combiner 640 to produce an overall combined SSC estimate so.

Defining the vector rSSC2 the elements for which rSSC2(i), i=1...12 are the SSC correlation results for SSC codes 1, 15 3, 5, 10, 13, 14, 0, 6, 12, 4, 8, 15 (as for case 2), then the vector r(k)ssC,2 contains the SSC results for the Ash SSC. The soft combined estimate of the SSC code word, 52, is given by: s2= (-1)rssc2+ (-1) rssc2+ (-1) rSsc2 where k = 0...n - 1 k k k The number of SSC correlations combined to give the soft estimate is indefinite. Code set power estimates are used to decide when sufficient SSC correlations have been accumulated. CodeSet Determina tion and SSC Accumula Lion The power relationship between the PSC and SSC transmissions is operator definable. This power cannot be

e À it, À À 02.0026-ipw - 16 signalled, as it is part of the initial synchronization set up. Therefore the UE secondary synchronization algorithm must be able to cope with a range of PSC/SSC power ratios.

The scheme adopted in a preferred embodiment of the present invention relies on accumulating successive SSC correlations and estimating the powers in each code set.

Accumulation continues until the power of one code group 10 exceeds the combined powers in the other code groups by at least PSSC,Thresh. The value of this threshold is chosen such that the probability of SSC decoding error is small when the condition is met.

15 Simulation results of the probability of SSC decoding error versus the code set power target for the preferred embodiment described above have shown that: (i) A PSSC,Thresh target of approx lOdB is sufficient to achieve an acceptable probability of error.

20 (ii) The number of accumulated SSC correlations to achieve varies between 10 and 100 frames depending on the PSC/SSC power ratio, more accumulations being required for lower SSC powers. 25 (iii) The overall probability of error is independent of the SSC power as the action of the algorithm compensates by increasing the averaging period where necessary.

. r - 02.0026-ipw Code Set and SSC Accumulation Algorithm The soft combined SSC correlations are grouped into their relevant code sets and the power in each code set is 5 calculated by multiplying the softcombined SSC estimate vector by its complex conjugate.

For Case 1 and Case 2, the element-wise power of the soft combined SSC estimate vector, sl, is calculated. The 10 elements of this power vector are summed across all code sets. Pl = s, À Sl Pl= ply), where petri) are the elements Of Pl, gives i=1,3.5 the power for code set 1.

15 P2= ply), where pail are the elements of Pl, gives i=1O,13,14 the power for code set 2.

P3 = pl (i), where paid are the elements of Pl, gives i=0,6,12 the power for code set 3.

P4 = Pi), where piri) are the elements of Pl, gives i=4,8,1 5 20 the power for code set 4.

The SNR is defined as follows: Pm = max(p,P2,P3,P4) SNR = 4 Pm Pj Pm i=l

: : 02.0026-ipw - 18 Every time an SSC correlation is calculated, the soft combined SSC is updated and the code set power is updated. The SNR is calculated and if it is found to be below Pssc'resh, the loop iterates again adding further SSC 5 symbols to the soft combined SSC. If the threshold has been exceeded, then the code set identified as Pm is selected and passed to the decoder.

SSC Decoding Once the code set has been identified, the phase modulation applied to the three SSC codes that make up the code set needs to be demodulated. The SSC correlations have already been rotated by the complex 15 conjugate of the PSC prior to soft-accumulation. Hard decisions of the phase of each of the three correlations will give the SSC symbol sit This is then decoded by means of a look-up table (not shown).

20 The phase, ci, of the SSC correlations is determined from the following algorithm if |Re(si)>lIm(si) then ci=sgn(Re(si)) else c=sgn(n(si)) 25 It should be noted that the resultant SSC symbol represents the first SSC symbol received. In Case l the decoded SSC will point to the code group and also indicate if the first SSC was received in an odd or an even frame. In Case 2, the decoded SSC will point to the 30 code group, odd/even frame and also either Slot k or Slot

r - dl 02.0026-ipw - 19 k+8. Note that the detection of Slot k or Slot k+ 8 is inherent in the PSC identification process. It is therefore possible to restrict the SSC soft-combining process such that it always begins in slot k.

It will be appreciated that the method described above for synchronization in a wireless communication system may be carried out in software running on a processor (not shown), and that the software may be provided as a 10 computer program element carried on any suitable data carrier (also not shown) such as a magnetic or optical computer disc.

It will be also be appreciated that the method described 15 above for synchronization in a wireless communication system may alternatively be carried out in hardware, for example in the form of an integrated circuit (not shown) such as an FPGA (Field Programmable Gate Array) or ASIC

(Application Specific Integrated Integrated Circuit).

It will be understood that the arrangement and method for synchronization in a wireless communication system described above provides the following advantages: À Improves SSC detection probability by combining all 25 energy from successively received SSC symbols.

À Is tolerant of SSC power variations, enabling 'blind detection' of SSC power.

À Minimises number of received SSCs that need to be combined to obtain a given probability of error for 30 a given SSC SNR.

r 4 5 _.' I, C

02.0026-ipw - 20 Thus, the described soft-combining scheme improves the probability of correctly decoding the secondary synchronization symbols in the user equipment unit, and is also robust to a wide spread of PSC / SSC power ratios 5 within the SCH transmission.

Claims

To À. . .

r '' _ 02.0026-ipw - 21 Clams 1. An arrangement for synchronisation in a wireless communication system, the arrangement comprising: 5 means for producing a first synchronisation code estimate by combining in a first predetermined sign pattern a plurality of signals representative of synchronisation codes in a plurality of information frames; and 10 means for producing at least a second synchronisation code estimate by combining the plurality of signals in at least a second predetermined sign pattern; and means for combining the first synchronisation 15 code estimate and the at least a second synchronisation code estimate to produce a combined synchronisation code estimate.

2. The arrangement of claim 1, wherein the plurality of 20 information frames each contain a single synchronisation indication, the first predetermined sign pattern comprises the same sign for all of the plurality of signals, and the second predetermined sign pattern comprises alternating signs.

3. The arrangement of claim 1, wherein: the plurality of information frames each contain a plurality of synchronisation code indications) 30 the means for producing at least a second synchronisation code estimate comprises:

_ 02.0026-ipw - 22 means for producing a second synchronization code estimate by combining the plurality of signals in a second predetermined sign pattern, and 5 means for producing a third synchronization code estimate by combining the plurality of signals in a third predetermined sign pattern; the first predetermined sign pattern being 10 represented by [+,+,-,-], the second predetermined sign pattern being represented by [+,-,+,-], and the third predetermined sign pattern being represented by [+,-,-,+], where "+" indicates same sign and "-"

indicates opposite sign.

4. The arrangement of claim 1, 2 or 3 wherein the arrangement further comprises means for accumulating successive synchronization code correlations and estimating the powers in each code set until the power of 20 one code group exceeds the powers in the other code groups by at least a predetermined amount.

5. The arrangement of any one of claims 1-4 further comprising phase determining means for determining the 25 phase of the combined synchronization code estimate by determining whether the real part of the combined synchronization code estimate is greater than the imaginary part of the combined synchronization code estimate.

{P À . r 02.0026-ipw - 23 6. The arrangement of any one of claims 1-5 further comprising lookup table means for looking up a synchronization code from the combined synchronization code estimate.

7. The arrangement of any one of claims 1-6 wherein the wireless communication system comprises a UTRA TED system.

: to - ' ' l; 02.0026-ipw À 24 8. A method for synchronisation in a wireless communication system, the method comprising: producing a first synchronisation code estimate by combining in a first predetermined sign pattern a 5plurality of signals representative of synchronisation codes in a plurality of information frames; and producing at least a second synchronisation code estimate by combining the plurality of signals 10 in at least a second predetermined sign pattern; and combining the first synchronisation code estimate and the at least a second synchronisation code estimate to produce a combined synchronisation code estimate.

9. The method of claim 8, wherein the plurality of information frames each contain a single synchronisation indication, the first predetermined sign pattern comprises the same sign for all of the plurality of 20 signals, and the second predetermined sign pattern comprises alternating signs.

10. The method of claim 8, wherein: the plurality of information frames each 25 contain a plurality of synchronisation code indications) the step of producing at least a second synchronisation code estimate comprises: producing a second synchronisation code 30 estimate by combining the plurality of signals in a second predetermined sign pattern, and

C À À

- i 02.0026-ipw - 25 producing a third synchronisation code estimate by combining the plurality of signals in a third predetermined sign pattern; the first predetermined sign pattern being 5 represented by [+,+,-,-], the second predetermined sign pattern being represented by [+,-,+,-], and the third predetermined sign pattern being represented by [+,-,-,+], where "+" indicates same sign and "-"

indicates opposite sign.

11. The method of claim 8, 9 or 10 wherein the method further comprises accumulating successive synchronisation code correlations and estimating the powers in each code set until the power of one code group exceeds the powers 15 in the other code groups by at least a predetermined amount. 12. The method of any one of claims 8-11 further comprising determining the phase of the combined 20 synchronisation code estimate by determining whether the real part of the combined synchronisation code estimate is greater than the imaginary part of the combined synchronisation code estimate.

25 13. The method of any one of claims 8-12 further comprising looking up in a lookup table a synchronisation code from the combined synchronisation code estimate.

15. The method of any one of claims 8-13 wherein the 30 wireless communication system comprises a UTRA TDD system.

r _ i. a - cI ' r r r 02.0026-ipw - 26 16. User equipment for use in a UTRA TDD system, the user equipment comprising the arrangement of any one of claims 1-7.

17. An integrated circuit comprising the arrangement of any one of claims 1-7.

18. A computer program element comprising computer 10 program means for the method of any one of claims 8-15.

19. An arrangement, for synchronization in a wireless communication system, substantially as hereinbefore described with reference to the accompanying drawings.

20. A method, for synchronization in a wireless communication system, substantially as hereinbefore described with reference to the accompanying drawings.