WO2006067658A2

WO2006067658A2 - Method and apparatus for time slot synchronization in wireless communication system

Info

Publication number: WO2006067658A2
Application number: PCT/IB2005/054117
Authority: WO
Inventors: Yan Li; Xia Zhu
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-12-24
Filing date: 2005-12-08
Publication date: 2006-06-29
Also published as: WO2006067658A3

Abstract

The invention provides a method of time slot synchronization in a mobile terminal and the apparatus therefor. The apparatus first acquires a coarse time parameter of a midamble in a time slot of a signal received by the mobile terminal. Then it performs correlation calculation of specific signal sequences in a sequence that conforms to the midamble and their respective corresponding specific signal sequences based on the coarse time parameter. In the end, the apparatus compares the results of said correlation calculation to determine an accurate time parameter of the midamble, thus achieving time slot synchronization. Using this method and apparatus the complexity of correlation calculation and the corresponding hardware cost can be reduced.

Description

METHOD AND APPARATUS FOR TIME SLOT SYNCHRONIZATION IN WIRELESS COMMUNICATION SYSTEM

BACKGROUND OF INVENTION

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for time slot synchronization of mobile terminal and the apparatus therefor.

Time division synchronization code division multiple access (TD-SCDMA) is one of specifications for the third generation mobile communication air interface formally released by the International Telecommunication Union (ITU). It adopts the transmission mode of time division duplex (TDD), under which the physical channel appears as a burst.

Fig. 1 shows a standard subframe structure of TD-SCDMA. The length of the subframe is 5ms, i.e. 6400 chips. Each subframe is divided into 7 main time slots (TS0-TS6) and 3 special time slots: downlink pilot time slots (DwPTS) of 96 chips, guard period (GP) of 96 chips and up link pilot time slots (UpPTS) of 160 chips. The length of each main time slot is 0.675ms, i.e. 864 chips, wherein TSO is a downlink time slot, TSl is a uplink time slot, while the remaining main time slots can be configured flexibly to be used for down/uplink according to the user need.

The burst is sent in a specific main time slot, which mainly consists of two fields, i.e. traffic and signaling data fields, totaling 704 chips with time length of 675μs, wherein each data field (data 1, data 2) is of 352 chips respectively. Besides, each main time slot further comprises a midamble (training sequence) of 144 chips located between data 1 and data 2 and a guard period (GP) of the last 16 chips, wherein midambles for different users are acquired by performing cyclic shift on a cell- specific fundamental midamble.

In a wireless communication system adopting TD-SCDMA, a mobile terminal first establishes downlink synchronization by acquiring and identifying DwPTS. After the down link synchronization is established, the mobile terminal could read the cell's common control information from a broadcast channel by calculating a basic midamble and scrambling code through current DwPTS. The downlink synchronization could also be referred to as subframe synchronization because the DwPTS appears only once in each subframe. When the subframe synchronization is established, a coarse time parameter of the midamble in the subframe could be obtained. Making use of fairly good autocorrelation of midambles, the time slot synchronization between a transmitter and a receiver could be achieved.

At present, a TD-SCDMA system usually adopts matching filter to perform time slot synchronization. Fig. 2 and Fig. 3 illustrate related operation procedure, wherein a conventional mobile terminal could obtain a coarse time parameter of a midamble through cell search first, then it selects a small range with respect to said coarse time parameter to perform sliding correlation calculation between an input data stream and an expected midamble within said range by means of the matching filter. An accurate time parameter of the midamble can be determined from the maximum value of the correlation calculation results.

Fig. 3 is a partial block diagram of time slot synchronization in a conventional mobile terminal, wherein a sliding correlation calculations between a part of the received signal x(t) that locates within the range of a coarse time parameter of a midamble and an expected midamble are performed in correlation module 10'.

The correlation module 10' performs the following algorithm: t_{r a} + ι + L_m -l

R₁ = ∑ x(t) ^• midamble '[t - (t_r0 + i) + l], -w ≤ i ≤ w ,^

I=IrO +'

Where, R₁ represents the results of correlation calculations, L_m is the length of the midamble, x(t) is the signal received by the mobile terminal, t_ro represents the time position of the midamble, while [t_ro- w, t_ro+w] represents the range taken on the basis of the coarse time parameter, and midamble [t — (t_r0 + i) + 1] is the conjugate of the expected midamble.

The maximum value of the calculation result of expression (1) is selected in accurate synchronization module 20', and thus an accurate time parameter of the midamble is determined.

Accurate synchronization module 20' comprises an integrator, and accurate synchronization module 20' performs the following algorithm:

R₁, = max(i?₍ ), -w≤ i ≤ w t_r = t_r0 + ϊ

(2) Where, R₁- represents the maximum value after correlation calculations, t_r represents the accurate time parameter of the midamble.

In the above time slot synchronization method adopted in the prior art, at least L_m multipliers (144 in TD-SCDMA) must be employed, thus resulting in rather complex calculation procedure and high hardware cost.

Therefore, a simpler and faster method of time slot synchronization for mobile terminal as well as the apparatus therefor are needed to resolve the time consuming and cost ineffective problem resulted from the complex calculation caused by the application of existing method to time slot synchronization.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method and apparatus of time slot synchronization for mobile terminal in wireless communication system. Said method and apparatus could reduce the complexity of correlation calculation and corresponding cost of hardware module in time slot synchronization.

To achieve the above object, the following method is carried out by an apparatus in accordance with an embodiment of the present invention, which comprises: first obtaining a coarse time parameter of a midamble in a time slot of a signal received by the mobile terminal, then based on the coarse time parameter, performing correlation calculation between symmetrical specific sequences of a signal sequence in said time slot which conforms to the midamble, and in the end, comparing the results of correlation calculations to determine an accurate time parameter of the midamble, thus achieving synchronization of said time slot.

Compared with the prior art, the beneficial effect of the present invention is: the correlation calculation in a method of time slot synchronization is performed between partial sequences of a midamble, without having to perform correlation calculation between the entire midamble and an expected midamble, thus effectively reducing the calculation amount and achieving time slot synchronization faster. Besides, as less multipliers are employed, an apparatus for time slot synchronization in a mobile terminal in the invention has lower hardware complexity and cost as compared with the prior art.

Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in further detail with reference to the accompanying diagrams wherein:

Fig. 1 illustrates a standard subframe structure of a TD-SCDMA system;

Fig. 2 illustrates a schematic diagram of the correlation operation of a method for time slot synchronization in a mobile terminal according to the prior art;

Fig. 3 illustrates a partial block diagram of a mobile terminal for time slot synchronization according to the prior art;

Fig. 4 illustrates a typical midamble structure of a TD-SCDMA system;

Fig. 5 illustrates a flow chart of a method for time slot synchronization in a mobile terminal according to the present invention;

Fig. 6 illustrates a schematic diagram of correlation operations of a method for time slot synchronization in a mobile terminal according to the present invention;

Fig. 7 illustrates a partial block diagram of an apparatus for time slot synchronization in a mobile terminal according to the present invention;

Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions.

DETAILED DESCRIPTION OF THE INVENTION

Following are further detailed illustrations of the present invention with reference to drawings and specific embodiments.

In a TD-SCDMA system, each cell has specific basic midamble of 128 chips, and said basic midamble is cyclically shifted to generate different midambles of 144 chips, which can be used by different users in the cell separately.

To further explain how to shift a basic midamble to obtain different midambles, now supposing that the basic midamble is m = {m_l,m₂,---,m_l2& } , the sequence obtained through periodic expansion is rri = { m_L , m₂ , • • • , m₁₂₈ , m_L , m₂ , • • • , m _} } , wherein m _} = m₇__12g for j>128. Different midambles in the same time slot come from different indexes to m'. As the lengths of midambles are all 144 chips, any one of midambles could be expressed as /w = {/w_Λ , /W₁₁₊₁,- -,/W₁₁₊₁₄₃ J C m¹. Because midamble in is a subset of m' , it also has the characteristic of periodic cycles, the sequence of its first 16 chips being completely identical with that of the last 16 chips. The symmetry of a midamble is illustrated in Fig. 4.

The present invention makes use of said symmetry of a midamble for time slot synchronization. As illustrated in Fig. 5, a method for time slot synchronization in a mobile terminal according to an embodiment of the present invention comprises: first receiving signal x(t) (step SlOO), then performing cell search on the received signal x(t) (stepSHO), obtaining subframe synchronization, and learning therefrom a coarse time parameter of a midamble in the time slot.

Next, a small range [Ww, t_r0+w] with respect to said coarse time parameter is selected, wherein t_Λ represents the time position of the midamble. Within this range, autocorrelation calculations between signal sequences that correspond to the first 16 chips and last 16 chips at the time parameter position conforming to the midamble are performed (step S 120). The operation procedure of the autocorrelation calculation is illustrated in Fig. 6. The algorithm performed by step S 120 is as below: f_r0 +1+15

R₁ = ∑ x(t)x^' (t + m τ_c ), - _w< i < _w (3)

Where, R₁ represents the results of correlation calculations, T_c is code rate, x(t) is the first 16 chips at the time parameter position that conforms to the midamble, + l28T_L ) is the last 16 chips at the time parameter position that conforms to the midamble.

In the end, an accurate time parameter t_ro of the midamble is determined from a maximum value of the correlation calculation results (step S130), thus completing the synchronization of said time slot. The algorithm performed by step S 130 is as below: R₁, = max(R_ι ), - άk i ≤ w (4) t_r = t_r0 + ϊ (5)

Where, R₁- represents the maximum value after correlation calculations, t_r represents the accurate time parameter of the midamble.

The schematic diagram of the autocorrelation calculation operation in the above step S 120 is illustrated in Fig. 6. During the implementation of step 120, no expected midamble is necessary to be used because the correlation calculation is carried out only between the first 16 chips and last 16 chips of the midamble of the received signal. Fig. 7 is a partial block diagram of an apparatus for time slot synchronization in a mobile terminal according to an embodiment in the present invention, which includes autocorrelation module 10, accurate synchronization module 20 and delay module 30.

Delay module 30 delays the last 16 chips at the time parameter position that conforms to the midamble in the received signal x(t) after subframe synchronization by a length of 128 chips, then outputs the delayed chips to autocorrelation module 10, to perform their correlation calculation with the first 16 chips at the time parameter position that conforms to the midamble in the received signal x(t). Accurate synchronization module 20 finds a maximum value of the correlation calculation results outputted from autocorrelation module 10 and determines an accurate time parameter of the midamble.

In a method for time slot synchronization in a mobile terminal according to the present invention, it only needs to perform multiplication of 16 elements for each correlation calculation, which effectively reduces the calculation amount and achieves time slot synchronization faster as compared with the multiplication of 144 elements used in the prior art. In addition, an apparatus for time slot synchronization in a mobile terminal according to the present invention has lower hardware complexity and cost as compared with the prior art because only 16 multipliers are involved.

The above embodiment illustrates the present invention mainly with respect to a TD-SCDMA system. However, the present invention could also be applied to other wireless communication systems, as long as the sequences for synchronization of the wireless communication systems possess symmetry similar to the midamble of the TD- SCDMA system.

While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.

Claims

CLAIMS:

1. A method of time slot synchronization in a mobile terminal, comprising the steps of:

(a) acquiring a coarse time parameter of a midamble in a time slot of a signal received by the mobile terminal;

(b) performing correlation calculations between specific signal sequences in a sequence conforming to the midamble and their respective corresponding specific signal sequences within a corresponding coarse time range based on the coarse time parameters; and

(c) comparing the results of said correlation calculations to determine an accurate time parameter of the midamble.

2. The method as claimed in claim 1, wherein the coarse time parameter in step (a) is obtained by performing cell search on the received signal.

3. The method as claimed in claim 1, wherein determining the accurate time parameter of the midamble in step (c) is performed based on a maximum value of said comparing results.

4. The method as claimed in claim 1, wherein the method is used in a TD-SCDMA system, and said corresponding specific sequences include signal sequences of the first 16 elements and the last 16 elements of a midamble.

5. The method as claimed in claim 4, wherein the correlation calculation in step (b) is performed between the first 16 elements and the last 16 elements of a signal sequence that conforms to the midamble.

6. An apparatus for time slot synchronization in a mobile terminal, comprising: an autocorrelation means, for performing correlation calculation between specific signal sequences in a sequence conforming to a midamble in a time slot of a signal received by the mobile terminal and their respective corresponding specific signal sequence, based on a coarse time parameter of the midamble; and an accurate synchronization means, for comparing the results of the correlation calculation to determine an accurate time parameter of the midamble.

7. The apparatus as claimed in claim 6, wherein the coarse time parameter of the midamble is obtained through performing cell search on the received signal by the mobile terminal.

8. The apparatus as claimed in claim 6, wherein the apparatus is used in a TD-SCDMA system, and said symmetrical specific sequences include signal sequences of the first 16 elements and the last 16 elements of the midamble.

9. The apparatus as claimed in claim 8, wherein the autocorrelation means performs correlation calculation between the first 16 elements and the last 16 elements in signal sequences that conform to the midamble.

10. The apparatus as claimed in claim 6, wherein the accurate synchronization means determines the accurate time parameter of the midamble based on a maximum value of said comparing results.

11. A mobile terminal, comprising: a receiving means, for receiving signals; and a time slot synchronization means, which includes: an autocorrelation means, for performing correlation calculation of specific signal sequences in a sequence that conforms to a midamble in a time slot of said received signal and their respective corresponding specific signal sequences based on a coarse time parameter of the midamble; and an accurate synchronization means, for comparing the results of the correlation calculation to determine an accurate time parameter of the midamble.

12. The mobile terminal as claimed in claim 11, wherein the mobile terminal is used in a TD-SCDMA system, and symmetrical specific sequences include signal sequences of the first 16 elements and the last 16 elements of the midamble.