WO2000049723A1

WO2000049723A1 - Method and device for synchronizing a receiver with a transmitter

Info

Publication number: WO2000049723A1
Application number: PCT/DE2000/000309
Authority: WO
Inventors: Bernhard Raaf; Jürgen MICHEL
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-02-19
Filing date: 2000-02-01
Publication date: 2000-08-24
Also published as: AU3271400A; CN1340250A; EP1151548A1

Abstract

The invention relates to a method and a device for temporally synchronizing a receiver with a transmitter in a telecommunication system, especially a mobile radio system. Synchronization takes place if a predetermined requirement is met, using at least two physical channels of the telecommunication system in parallel by making separate correlation evaluations in said channels.

Description

description

Method and device for synchronizing a receiver with a transmitter

The invention relates to a method for synchronizing a receiver with a transmitter / transmit signal in a digital message transmission system, in particular a mobile radio system, the method comprising a step of time synchronization using at least one filter device matched to a predetermined synchronization code, and a device for carrying it out Procedure.

It is known to use physical channels in communication systems to transmit communication information and synchronization data. By using these physical channels, on the one hand, the digitized message and, on the other hand, a synchronization signal are transmitted from a transmitting station to a receiving station, in particular wirelessly from a first radio station to a second radio station.

In transmission or communication systems which operate according to the DS-CDMA principle (Direct Sequence Coding Spread Spectrum Principle), a digital information signal of low bandwidth is modulated with a high-frequency bit stream of high bandwidth. This is generated by a spreading code generator. A code sequence which is identical to the spread code sequence, as used for modulation in the transmitter, is generated in the receiver. To ensure correct functioning of the receiver, this code sequence on the receiver side must be synchronized with the transmitter. Then the "despread" information signal is obtained by demodulation and integration. The most important task of synchronization during the signal acquisition phase is to detect the timing and phase of a synchronization signal. Besides Depending on the mode of operation and protocol of the digital message transmission system, there are other important synchronization tasks, for which, in a system operated using time division multiple access or TDMA (Time Division Multiple Access) aspects, in particular the time slot

(Slot) synchronization and the frame (frame) synchronization belong.

With the future-oriented system UMTS / WCDMA-FDD (Universal Mobile Telecommunication System / Wide Band Code Division Multiple Access-Frequency Division Duplex), a three-stage process for synchronization during the acquisition phase is proposed at the current state of standardization. During the initial cell search, the mobile station searches for the base station to which the transmission loss is lowest. For this purpose, a primary synchronization channel (PSCH = primary synchronization channel) and a secondary synchronization channel (SSCH = secondary synchronization channel) are defined. During the first step, the time synchronization to the strongest base station of the PSCH is used. Using a single filter which is matched to a primary synchronization code c _p , which is common to all base stations, peaks are determined for each base station within the range of the mobile station. The detection of the position of the strongest peak provides the timing of the strongest base station modulo of the time slot length. To increase reliability, the output of the tuned filter is incoherently accumulated over a number of time slots.

The second step of the synchronization process is frame synchronization and code group identification for the base station found in the first step, which are carried out using the SSCH. For this purpose, the received signal at the positions of a secondary synchronization code c _{s is} correlated with all possible secondary synchronization codes (here: 17) according to the system protocol. The single Units of this step are of secondary importance in the given context, as are those of the third step, which consists in the identification of the so-called "scrambling code" which is used by the determined base station. Details of these steps are given for the system mentioned as an example in the system document "ETSI STC SMG2 UMTS-Ll 163/98, UTRA / FED Physical Layer Description".

It follows that a special physical channel, namely the PSCH, is provided for the time synchronization.

The invention is based on the object of specifying a method of the generic type in which the received signal energy is better utilized for the time synchronization process, thereby reducing measurement time and power consumption for the synchronization process, and an apparatus for carrying out this method.

This object is achieved with regard to the method aspect by a method with the features of claim 1 and with regard to its device aspect by a device with the features of claim 11.

The invention includes the basic technical teaching of using at least one additional physical channel of the message transmission system for time synchronization. This improves the utilization of the received signal energy, reduces the time required and reduces the power consumption in the receiver. Under a physical

Channel is understood to be one that is characterized by its frequency, a spreading code, the time window position or a space division state.

A time synchronization includes, in particular, the slot or time slot synchronization, but also a frame (frame) or a symbol synchronization. According to a preferred embodiment of the invention, a synchronization channel provided according to the transmission protocol of the message transmission system is used for a purpose other than that of time synchronization. In the system outlined above, this is the secondary synchronization channel (SSCH). In this case, one implementation possibility that requires comparatively little computational effort is that the code words of the second synchronization channel are obtained from the code of the primary synchronization channel or another known code by modulation with so-called Hadamard sequences. Then the evaluation of the correlations in the secondary synchronization channel for the purpose of time synchronization can be carried out via a so-called "Fast Hadamard" transformation.

In principle, however, it is also possible to use at least one control or data channel of the system in addition to time synchronization. This requires the definition of certain channel specifications.

The proposed method includes a separate correlation evaluation in the channels used for time synchronization and the subsequent linking of the evaluation results to a time synchronization indicator. This link is incoherent, provided the system protocol does not provide a fixed phase relationship between the channels used for time synchronization. However, it is particularly advantageous to provide a fixed and / or defined phase reference, in particular of +/- 90 ° and, if possible, the same antenna when transmitting the two channels in the system protocol, which is linked by coherent accumulation and thus improved detection compared to incoherent accumulation makes possible.

The proposed procedure also offers the possibility that intermediate data obtained in the step of time synchronization results are saved and used for further steps, e.g. identifying the scrambling code.

The proposed method is used either permanently or as a function of the fulfillment of a predetermined condition, in particular as a function of the evaluability of the signals in the channels that can generally be used for time synchronization - expressed, for example, by exceeding a threshold value of the signal amplitude, or falling below one Threshold in the bit error rate or the like.

The device for carrying out the method according to the invention is particularly suitable and intended for use in the mobile station of a mobile radio network. It includes several correlator stages for evaluation and a calculation unit for calculating the time synchronization indicator from the outputs of the individual correlator stages in accordance with an algorithm of incoherent or coherent accumulation chosen depending on the system protocol. The output signals of the correlator stages are linked by a linear combination. The following methods of incoherent accumulation result:

• Balanced combination • Square combination

• Selection method or coherent accumulation.

Advantages and expediencies of the solution according to the invention result from the subclaims and the following description of a preferred embodiment with reference to the figure.

The figure is a schematic diagram which serves to explain both an embodiment of the method and a preferred device for carrying out the method. The figure shows a device 1 for time synchronization, the ^~~ as a component of operating according to the UMTS / FDD standard WCDM mobile station (not illustrated in total) one is settable. A received signal x (k) is subjected to a synchronization evaluation in a primary synchronization channel PSCH and a secondary synchronization channel SSCH. A correlator stage 3 is provided in the primary synchronization channel PSCH.

Correlator level 3 computes according to the relationship

VO ⁼ 7T ∑x * (k + κ) -c _p (k) (1)

"fc = 1..2560

where:

N Constant for standardization (here 2560) x * (k) conjugates complex input signal c _p Primary synchronization code according to UMTS / WCDMA-FDD specification 256 chips (here 2560

Chips with c _p = 0 outside the 256 specified

Crisps)

the correlation function (correlation) for the primary synchronization channel PSCH.

In the secondary synchronization channel SSCH, the input signal (in accordance with the protocol specifications drawn up at the time of registration) is fed to 17 correlators, which are denoted in the figure by the reference number 5. These determine according to the relationship

ys' i *) = (2),

N i = 1..2560 the correlations y _s (κ) 17,> Ys (K),

where the above explanation of the symbols N and x * (k and also applies:

One of 17 secondary synchronization codes according to UMTS / WCDMA-FDD specification 256 chips (here 2560 chips with c _s ² = 0 outside the 256 specified chips), i = 1 ... 17 depending on the synchronization code.

The output signals of the correlators 3 and 5 are fed to an evaluation or calculation unit 9, which either according to the relationship

z (κ) = max | y _p (κ) + k (y κ)) [3)

coherent or according to the relationship

or

where k is a real constant

the overall correlation z (K) is calculated incoherently as a time synchronization indicator. In a subsequent evaluation stage 9, this is subjected to an accumulation modulo of the time slot length and then to a maximum detection in a maximum detector 11, as a result of which time synchronization with the "best" base station of the mobile radio system is established. With regard to the calculation, the correlation evaluation in the secondary synchronization channel SSCH is particularly simple in the UMTS / WCDMA-FDD system explained as an example, if the code words of the secondary synchronization channel are derived from the code of the primary synchronization channel PSCH or another known code by modulation with so-called Hadamard Consequences are formed as suggested in the conference paper Ericsson, ETSI SMG2 UMTS Ll Export Group, Meeting # 6, Helsinki, FI, September 8-11, 1998. In this case, a Fast Hadamard transformation is used, which is also described as such in the publication mentioned.

The embodiment of the invention is not limited to this example, but - in a form adapted to the respective system protocol - is also possible with other digital message transmission systems in which time synchronization of a received signal is relevant.

Claims

claims

1. A method for synchronizing a receiver with a transmitter or a transmission signal in a message transmission system, in particular a mobile radio system, the method comprising a step of time synchronization, characterized in that for synchronization, at least two physical channels of the message transmission system are parallel to one another - are used and a separate correlation evaluation is carried out and the evaluation results of the channels (y _p (κ), y _s (κ) ... y _s (K)) are then linked to form a time synchronization indicator.

2. The method according to claim 1, characterized in that at least one channel provided for another purpose with at least partially known transmission signal sequence is used for time synchronization.

3. The method according to claim 1 or 2, characterized in that the channel with an at least partially known transmission signal sequence is a control or data channel of the message transmission system.

4. The method according to claim 2, characterized in that the channel with at least partially known transmission signal sequence is a synchronization channel, in particular for a higher-level frame structure.

5. The method according to any one of the preceding claims, characterized in that known code words of a second channel are formed by modulation with Hadamard sequences and the correlation evaluation in the second channel is carried out via a Fast Hadamard transformation.

6. The method according to any one of the preceding claims, characterized in that the protocol of the message transmission system does not provide a fixed phase relationship between the channels used for time synchronization and the evaluation results of the channels are linked by incoherent accumulation.

7. The method according to any one of the preceding claims, characterized in that the protocol of the message transmission system provides a fixed or defined phase relationship between the channels used for time synchronization and in particular also the transmission of these channels via the same antenna and the linking of the evaluation results of the channels by coherent Accumulation takes place.

8. The method according to any one of the preceding claims, characterized in that results obtained in the time synchronization step are stored and used for a further synchronization step, in particular for a frame synchronization.

9. The method according to any one of the preceding claims, characterized in that the exceeding or falling below a threshold value of a parameter characterizing the evaluability of the signals of the corresponding channel, in particular the signal amplitude or the bit error rate, is defined as a predetermined condition.

10. The method according to any one of the preceding claims, characterized in that ^~~ the evaluation results of the channels before the linkage are weighted as a function of a parameter characterizing the evaluability of the signals of the corresponding channel, in particular the signal amplitude or the bit error rate.

11. Device for performing the method according to one of the preceding claims, in particular for use in the

Mobile station of a mobile radio network, with a receiving part for the channels used for time synchronization, characterized by at least one correlator stage (3, 5) assigned to the channels used (PSCH, SSCH) for channel-by-channel determination of the

Received signal correlation (y _p (κ), y _s 1 17 (K) ... y _s (K)) and a calculation unit (7) downstream of the correlator stages for calculating the time synchronization indicator (z (κ)).

12. The apparatus according to claim 11, characterized by the training for determining and evaluating the correlation in a primary synchronization channel for frame or symbol synchronization and a secondary synchronization channel for synchronization to a higher-level frame structure and / or for identifying further parameters, such as a scrambling code group, which consists of one or more different but known code word or code words.

13. The apparatus according to claim 12, characterized by an evaluation stage (9) downstream of the calculation unit (7) for accumulation and a maximum detector (11) connected to its output.

14. Device according to one of claims 11 to 13, characterized by the formation of the calculation unit (7) for coherent or

_ incoherent accumulation of the output signals (y _p (κ), y _s (K)

... y _s ¹⁷ (K)) of the correlator stages (3, 5).