WO2008052406A1

WO2008052406A1 - Method for sending sch in tdd system

Info

Publication number: WO2008052406A1
Application number: PCT/CN2007/001613
Authority: WO
Inventors: Shuqiang Xia; Chunli Liang
Original assignee: Zte Corporation
Priority date: 2006-10-31
Filing date: 2007-05-17
Publication date: 2008-05-08
Also published as: CN101175058A; CN101175058B

Abstract

This invention provides a method for sending synchronization channel (SCH) in a time division duplex (TDD) system based on orthogonal frequency division multiplexing (OFDM). It includes following steps: sending primary SCH (P-SCH) in DwPTS, sending secondary SCH (S-SCH) utilizing the last OFDM symbol in TS0, sending the cyclic suffix (CS) of the S-SCH symbol in the time interval between S-SCH and P-SCH. The time span of CS is determined according to the length of the cyclic prefix (CP) of OFDM symbols, so the time in TS0 which is not used to send CS is invariable when different CP is used.

Description

Method for transmitting synchronous channel of time division duplex system

The present invention relates to the field of digital communications, and in particular to a cell search technique for a time division duplex system based on OFDM (Orthogonal Frequency Division Multiplexing) technology, and more particularly to a synchronization channel in an orthogonal frequency division multiplexing time division duplex system. (Synchronization Channel, SCH) is sent.

Background technique

When the mobile station is powered on or loses network service, the system needs to be captured by an initial acquisition process, which means that the cell that the mobile station is to wait for and demodulate the system information in the broadcast channel is identified. The capture process is also known as the cell search process. The cell search mainly obtains the time and frequency synchronization with the target cell, and also obtains the target cell identification number and some other basic information. The cell search process is mainly based on a Synchronization Channel (SCH), that is, the time synchronization with the target cell, the cell identification number or the cell identification group number information, etc. are obtained according to the synchronization channel. When only the cell identification group number information can be obtained through the synchronization channel, the complete cell identification number information and other information related to the cell/system can be obtained through a broadcast channel (BCH) and a pilot. .

Generally speaking, the cell search process is a hierarchical process, so the corresponding synchronization channel (SCH) is divided into a primary synchronization channel (Primary SCH, P-SCH) and a secondary synchronization channel (Secondary SCH, S-SCH). The P-SCH is used to implement slot timing and frequency calibration. The S-SCH is mainly used to implement frame timing and cell identification number or cell identification group number and some cell/system related information detection.

1 is a schematic diagram of a frame structure of a time division duplex system based on orthogonal frequency division multiplexing (OFDM) technology. In the diagram, a 10 ms radio frame includes two equal length subframes, each of which has a length of 5 ms. Each subframe further includes 7 general time slots and 3 special time slots. The seven general time slots are TS0 ~ TS6, and the length of each general time slot is 0.675ms. The three special time slots are: DwPTS time slot, GP time slot and UpPTS time slot, where DwPTS time slot For the downlink time slot, the downlink synchronization signal is fixedly transmitted in the time slot, and the time length is 75 s; the GP time slot is the uplink and downlink protection time slot of the TDD (Time Division Duplex) system, and the time length is also 75 s; the UpPTS time slot is the uplink. Time slot. For TS0 in a general time slot, it includes 8 or 9 OFDM symbols and a time slot interval (TI), where the common pilot signal used for channel estimation is located at the first and third last OFDM In the symbol. When TS0 includes 8 OFDM symbols, each OFDM symbol is a long cyclic prefix (CP), wherein the long cyclic prefix length is 16.67 s, and the data portion length is 66.67 μ _δ , and the corresponding slot interval length is 8.33 s; When TS0 contains 9 OFDM symbols, each OFDM symbol is a short cyclic prefix, wherein the short cyclic prefix length is 7.29 μ _δ , and the data portion length is also 66.67 s, and the corresponding slot interval length is 9.38 μ _δ . Since TS0 includes 8 or 9 OFDM symbols, the data portion length of each OFDM symbol is 66.67 μβ, so the slot interval length of TSO is mainly determined according to the cyclic prefix length of each OFDM symbol. Usually, no data is sent in the slot interval.

In addition, the upward arrow in Fig. 1 indicates that the time slot is an uplink time slot, and the downward arrow indicates that the time slot is a downlink time slot. Except that the time slot TS0 is fixed as a downlink time slot, and the time slot TS1 is fixed as an uplink time slot, other time slots can be flexibly allocated as uplink or downlink time slots according to service requirements.

2 is a transmission method of a synchronization channel in the prior art. It can be seen that, regardless of the long cyclic prefix or the short cyclic prefix, the downlink primary synchronization signal P-SCH is fixedly transmitted in the DwPTS slot, and the secondary synchronization signal S-SCH is transmitted on the last OFDM symbol of TS0. Therefore, there is a slot interval between the time slot DwPTS and the last OFDM symbol of TS0. Since TS0 can adopt a long cyclic prefix structure or a short cyclic prefix structure, the time between P-SCH and S-SCH The gap interval is an amount that varies with the length of the cyclic prefix used by TS0.

Therefore, with the existing synchronous channel transmission method, after the mobile station obtains the time slot timing synchronization by using the P-SCH, the S-SCH signal cannot be directly extracted, and the S-SCH must be blindly detected. This undoubtedly increases the time of cell search and the complexity of the implementation of the mobile station. Therefore, it is necessary to improve the transmission method of the existing synchronous channel. Summary of the invention

The technical problem to be solved by the present invention is to provide a method for transmitting a synchronization channel in a time division duplex system based on orthogonal frequency division multiplexing technology, so as to improve the performance of cell search and reduce the complexity of device implementation. The present invention is applicable to a time division duplex system in which a primary synchronization channel P-SCH is fixedly transmitted on a DwPTS time slot. The invention provides a method for transmitting a synchronization channel of a time division duplex system. Based on the orthogonal frequency division multiplexing technology, the primary synchronization channel P-SCH is transmitted on the downlink time slot DwPTS, and the secondary synchronization channel S-SCH is at the end of the TS0 time slot. An Orthogonal Frequency Division Multiplexing (OFDM) OFDM symbol transmission, characterized in that: a cyclic suffix of an S-SCH symbol is transmitted on a slot interval between an S-SCH and a P-SCH, and a time length of the cyclic suffix is used according to the OFDM symbol. The cyclic prefix length is determined so that the constant C is different at each cycle.

When the TS0 includes 8 OFDM symbols, the slot interval between the S-SCH and the P-SCH is ^CP, and the slot interval may not transmit a cyclic suffix of the S-SCH symbol, and the TS0 includes When 9 OFDM symbols are used, the slot interval between the S-SCH and the P-SCH is ^Ζ ^, and the ^L SCP - ^L LCF portion of the slot interval may be used to transmit a cyclic suffix of the S-SCH symbol.

The slot interval between the S-SCH and the P-SCH may all be used to send a cyclic suffix of the S-SCH symbol.

Wherein, when the TS0 includes 8 OFDM symbols, if the S-SCH signal is expressed in the frequency domain as: X ( k ) , k=0, -1...N-1 , the TS0 includes 9 In the case of OFDM symbols, the S-SCH signal can be expressed in the frequency domain as:

Exp(- ^27rk ( ^L scp - L _LCP ) _{) x (kk = 0;} i, ... jv - l where ^Ζ ^ indicates that the TS0 contains 8 OFDM symbols, the S-SCH and the slot interval between said P-SCH; the ^ζ represents the time TS0 contains nine OFDM symbols, the slot spacing between the S-SCH and the P-SCH; T represents the said S - The length of time in the data portion of the SCH signal.

The data content of the cyclic suffix may be the same as the data content of the beginning portion of the S-SCH symbol. Moreover, the cyclic suffix may be placed at the end of the S-SCH symbol and connected to the S-SCH symbol.

The signal transmission method provided by the present invention has the following advantages:

1. The mobile station can directly extract the S-SCH signal after completing the slot timing synchronization by using the P-SCH, omitting the step of detecting the cyclic prefix length, reducing the processing delay and reducing the implementation complexity. 2. According to the method proposed by the present invention, when the S-SCH timing lags, the data transmitted in the last symbol of TS0 can still maintain orthogonality, effectively avoiding inter-carrier interference.

3. Since the S-SCH is transmitted close to the P-SCH, the P-SCH has higher energy and density than the common pilot, thus ensuring better demodulation performance of the S-SCH. BRIEF abstract

1 is a schematic diagram of an embodiment of a time slot structure in a TDD system;

2 is a schematic diagram of an embodiment of a method for transmitting a synchronization channel in the prior art;

3 is a schematic diagram of transmission of a synchronization channel according to an embodiment of the present invention;

4 is a schematic diagram of transmission of a synchronization channel according to Embodiment 2 of the present invention;

FIG. 5 is a schematic diagram of transmission of a third synchronization channel according to an embodiment of the present invention. - a preferred embodiment of the invention

In order to facilitate a deep understanding of the present invention, an embodiment including the present invention will be given below by taking the time slot structure shown in Fig. 1 as an example.

The main feature of the present invention is: transmitting a cyclic suffix of the S-SCH symbol at part or all of the time slot interval between the S-SCH and the P-SCH, and requiring that the time slot not used as the cyclic suffix is a time A constant that does not depend on the OFDM symbol cyclic prefix length variation.

Since the time length of the slot interval is mainly determined according to the length of time of the OFDM symbol cyclic prefix, the length of the cyclic suffix portion in the slot interval is also determined according to the length of time of the OFDM symbol cyclic prefix. As long as the time that is not used as the cyclic suffix in the slot interval is a constant that does not depend on the cyclic prefix length variation of the OFDM symbol, the mobile station can directly extract the S-SCH signal after completing the slot timing synchronization using the P-SCH.

For example, suppose the data of the S-SCH symbol is: s ( 0 ) , s ( 1 ) ....s ( N-1 ), and a piece of data is appended to the symbol, and the content and the beginning part of the data of the S-SCH symbol. The content is the same, and the new data is composed of: s ( 0 ) , s ( 1 ) ....s ( N-1 ) , s ( 0 ) , s ( 1 ) , s ( 2 ) (where N is S-SCH The number of data in the symbol); that is, the data of the beginning portion of the S-SCH symbol is placed as a cyclic suffix at the end of the S-SCH symbol, and is connected to the S-SCH symbol. The new composition The s (0), s ( 1 ), and s (2) at the end of the data are the cyclic suffixes of the symbol. The length of the cyclic suffix can be long or short. If 10 data can be placed in the slot interval, the cyclic suffix can be: s (0), s (1), s (2), ... s (9).

I set the length of the slot interval corresponding to TS0 of the OFDM symbol using the short cyclic prefix and the long cyclic prefix as ^L LCP ( ^L SCP > L _LC P ), respectively. Then, in order to ensure the two frame structures, the time that is not used as the cyclic suffix in the slot interval is a constant that does not depend on the cyclic prefix length change. If C is set, the following method can be used to insert the cyclic suffix:

(1) When TS0 uses a short cyclic prefix, the length of the insertion of the cyclic suffix is - C;

(2) When TS0 uses a long cyclic prefix, the length of the inserted cyclic suffix is ^^ - C; where c ranges from: o ≤ c ≤ z _iCP .

FIG. 3 is a schematic diagram of transmission of a synchronization channel according to an embodiment of the present invention. In this diagram, it corresponds to the C = _iCP case. For TS0 with a short cyclic prefix, the ^CT- ^z portion of the slot interval is used to transmit the cyclic suffix of the S-SCH signal; TS0 with a long cyclic prefix does not need to insert a cyclic suffix. Thus, the time that is not used as the transmission cyclic suffix in the slot interval corresponding to the TS0 slot under the two cyclic prefix structures is a constant that does not depend on the cyclic prefix length variation of the OFDM symbol, and is equal to α> (:. The method for transmitting the channel, the mobile station can directly extract the S-SCH signal after completing the slot timing synchronization by using the P-SCH, thereby avoiding the step of detecting the cyclic prefix length, which reduces the processing delay and reduces the implementation complexity. The S-SCH signal is transmitted near the P-SCH signal (the interval between the P-SCH and the S-SCH is not more than 9.38μ _δ ), and the P-SCH signal has higher energy than the common pilot. And density, thus providing better channel estimation for the S-SCH, thereby ensuring better demodulation performance of the S-SCH signal.

4 is a schematic diagram of transmission of a synchronization channel according to Embodiment 2 of the present invention. In this diagram, it corresponds to the case of 0 < C < Z _CP . For TS0, ^ slots with short cyclic prefix interval - ^ cyclic suffix portion for transmitting the S-SCH signal; cyclic postfix with long cyclic prefix TS0, C portion of slot intervals for transmitting a signal s_ _SC H . Thus, the time that is not used as the transmission cyclic suffix in the slot interval corresponding to the TS0 time slot under the two cyclic prefix structures is also an independent loop. The constant of the prefix length change, and both are C. Compared with FIG. 3, in the transmission method shown in FIG. 4, the interval between the P-SCH and the S-SCH is smaller, and thus the channel estimation provided by the P-SCH more realistically reflects the channel variation of the control signal. Moreover, the structure of two different cyclic prefix lengths adopts a cyclic suffix, and the S-SCH is more resistant to channel frequency selective fading. Therefore, the transmission method shown in FIG. 4 can provide better methods than the method shown in FIG. Performance.

FIG. 5 is a schematic diagram of transmission of a third synchronization channel according to an embodiment of the present invention. In this diagram, the slot spacing between the P-SCH and the S-SCH is used to transmit the cyclic suffix of the S-SCH, that is, the case corresponding to C = 0. Compared to the first two methods, this method increases the length used to transmit the cyclic suffix, thus making the S-SCH more effective against the frequency selective fading of the channel.

In addition, when TS0 includes 8 OFDM symbols, if the S-SCH signal is expressed in the frequency domain as: X ( k ), k=0, 1...N-1 (N is the number of data of the S-SCH signal), When the 'J TSO contains 9 OFDM symbols, the S-SCH signal can be expressed in the frequency domain as the expression (1):

= 0,1. — 1 formula (1)

Where Τ denotes the duration of the S-SCH signal (excluding the cyclic prefix, the cyclic suffix part), that is, the length of time in which the data portion.

Moreover, as long as the timing of the P-SCH is accurate, regardless of whether the TS0 contains 8 OFDM symbols or 9 OFDM symbols, the content of the S-SCH signal received by the receiver is exactly the same as that of the transmitting end, because according to the long cyclic prefix The time length τ between the S-SCH signal and the P-SCH signal (as shown in Figures 3, 4 and 5), together with the information contained in the cyclic suffix, is sufficient to receive the S-SCH. The signal is complete.

Industrial applicability

According to the signal transmission method provided by the present invention, since the mobile station can directly extract the S-SCH signal after completing the slot timing synchronization by using the P-SCH, the step of detecting the cyclic prefix length is omitted, which not only reduces the processing delay, but also reduces the processing delay. Reduced implementation complexity. With the method proposed by the present invention, when the S-SCH timing lags (the maximum range of timing lag does not exceed the time of the cyclic suffix) Degree), the data transmitted in the last symbol of TS0 still contains the complete S-SCH data information, so the orthogonality can still be maintained to avoid the inter-carrier interference; if the method proposed by the present invention is not adopted, then When the -SCH timing lags, the data transmitted at the last symbol of TS0 is incomplete, and its orthogonality cannot be guaranteed, causing severe inter-carrier interference. At the same time, the S-SCH is transmitted close to the P-SCH (the maximum interval between the S-SCH and the P-SCH is 9.38 s), and the P-SCH has higher energy and density than the common pilot, so The S-SCH signal provides better channel estimation, which in turn ensures better demodulation performance of the S-SCH.

Claims

Claim

A method for transmitting a synchronization channel of a time division duplex system, based on orthogonal frequency division multiplexing, a primary synchronization channel P-SCH is transmitted on a downlink time slot DwPTS, and a secondary synchronization channel S-SCH is in a last one of TS0 time slots. Orthogonal frequency division multiplexing OFDM symbol transmission, characterized in that: a cyclic suffix of an S-SCH symbol is transmitted on a slot interval between an S-SCH and a P-SCH, and a time length of the cyclic suffix is according to a cycle adopted by the OFDM symbol The prefix length is determined such that the time that is not used as the transmission cyclic suffix in the slot interval corresponding to the TS0 slot under different cyclic prefix structures is a constant c

2. The method according to claim 1, wherein when the TS0 includes 8 OFDM symbols, the slot interval between the S-SCH and the P-SCH is ^, and the slot interval does not send S. a cyclic suffix of the -SCH symbol, when the TS0 includes 9 OFDM symbols, the slot interval between the S-SCH and the P-SCH is £ _sep , and the _sep - part of the slot interval is used to transmit the S-SCH The cyclic suffix of the symbol.

3. The method according to claim 1, wherein the slot interval between the S-SCH and the P-SCH is used to transmit a cyclic suffix of the S-SCH symbol.

The method according to claim 1, wherein when the TS0 includes 8 OFDM symbols, if the S-SCH signal is expressed in the frequency domain as: X ( k ), k=0, 1. ..N-1, when the TS0 includes 9 OFDM symbols, the S-SCH signal is expressed in the frequency domain as:

When representing a TS0 comprises 8 OFDM symbols, said time slot interval between the S-SCH and P-SCH; when the _SCP indicates the TS0 contains nine OFDM symbols, and the S-SCH by The slot interval between P-SCHs; the T represents the length of time of the data portion of the S-SCH signal.

The method according to claim 1, wherein the data content of the cyclic suffix is the same as the data content of the beginning portion of the S-SCH symbol.

6. The method according to claim 1, wherein the cyclic suffix is placed at the end of the S-SCH symbol and is connected to the S-SCH symbol.