MXPA99011249A - Time synchronisation method for a mobile station in a mobile communications system - Google Patents

Abstract

Un sistema de radiocomunicación proporciona canales de frecuencia formados por segmentos de tiempo a intervalos de frecuencia de banda ancha, en los cuales se transmiten simultáneamente informaciones de una o varias conexiones entre las estaciones móviles y una estación base, pudiéndose diferencias las informaciones de diversas conexiones conforme a una estructura fina individual de cada conexión. De conformidad con la invención, para las estaciones móviles se proporcionan para la compensación de tiempo canales de frecuencia recurrentes en dirección descendente, en los cuales, además de informaciones de otras conexiones, se transmite una forma de señal. La estación móvil por sincronizar, a partir de señales recibidas, determina cuando menos un punto en el tiempo sobre la llegada de la forma de señal, el cual, a continuación, es aprovechado por la estación móvil para la sincronización de tiempo. La invención encuentra una aplicación ventajosa, por ejemplo, en el modo TDD de la 3a generación de radio móvil, que combina con procedimiento de separación de participantes TDMA y CDMA.

Description

PROCEDURE, MOBILE STATION AND BASE STATION FOR THE SYNCHRONIZATION OF TIME OF A MOBILE STATION IN A RADIOCOMMUNICATION SYSTEM FIELD OF THE INVENTION The invention relates to a method for synchronizing the time of a mobile station of a radio communication system, as well as to a mobile station and a base station configured in this way.

BACKGROUND OF THE INVENTION The configuration of digital radiocommunication systems is shown in J. Oudelaar "Evolu ion towards UMTS", PIM C 94, 5th IEEE International Symp. on Personal, Indoor and Mobile Radio Communications, The Hague, NL, September 18-22, 1994, p. 852 and M. Lenti, H. Hageman "Paging in UMTS" RACE Mobile Telecommunications Workshop, Vol. 1, Amsterdam, NL, May 17-19, 1994, p. 405-410. The GSM mobile radio system (Global System for Mobile Communications) that currently exists is a radio communication system with a TDMA component for the separation of participants (time division multiple access). According to a frame structure, the useful information of the calls of the participants are passed to time segments. The transmission is effected in blocks. By the mobile radio system GSM, in descending direction, it is also known the frequency channels (SCH synchronization channel) adjusted to the time grid of the frame structure, for the synchronization of time of the mobile stations. In this frequency channel, a mobile station can evaluate the transmitted data for self-synchronization. A self-synchronization of this type is known from European Patent EP 0 551 803 Al. European Patent EP 0 767 557 Al, a method for synchronizing time of a mobile station is known. Calls are separated in a purely TDMA system, by time segments and frequency bands. The base station emits in a fixed manner, at regular intervals, a frequency signal for time synchronization (SCH). This frequency channel for time synchronization is always arranged in the same place of a multiple frame, for example, respectively in the first time segment of each tenth TDMA frame. The mobile station knows a 64-bit conditioning sequence, contained in the frequency channel for time synchronization, and the place where it is arranged within the TDMA frame and the time segments. German Patent DE 195 49 148.3 discloses a mobile communication system, which takes advantage of a TDMA / CDMA (CDMA code division multiple access) separation and uses a JD (joint decrement) procedure on the receiver side, for , knowing the expansion code of several participants, make a better detection of the useful information transmitted. In a frequency channel (TCH traffic channel), information of several useful data calls are transmitted simultaneously, which are differentiated by their expansion code. However, when using certain frequency channels for synchronization purposes, a large loss of capacity occurs with respect to the GSM system, since the frequency range used for a frequency channel is wider band.

OBJECTIVES AND ADVANTAGES OF THE INVENTION The invention is based on the objective of providing a procedure and devices, which in a TDMA radiocommunication system, allow the synchronization of time with a reduced consumption of the resources of the radiotechnology. This objective is achieved by the method with the features of claim 1, the mobile station with the features of claim 10 and the base station with the features of claim 11. The developments of the invention can be found in the sub-claims. . A radio communication system, for example, a TDMA / CDMA radio communication system, prepares frequency channels formed by time segments and broadband frequency intervals., in which information of one or several calls between mobile stations and base stations is transmitted simultaneously, it being possible to differentiate the information of different calls according to an individual fine structure of each call. However, several different fine structures can also be assigned to a call, which, on the receiver's side, are reassembled. According to the invention, for the mobile station, in the downward direction, recurrent frequency channels are arranged in time for compensation thereof, in which, in addition to the information of other calls, a known signal form is transmitted. This is issued by a first base station, while the other calls are provided by other base stations. Alternatively, it is also possible for a single base station to transmit in a frequency channel the known signal form for synchronization and information of the other calls. The mobile station to be synchronized, from received signals, emits at least one point in time on the arrival of the signal form, which the mobile station subsequently takes advantage of for time synchronization. By transmitting the signal form, in addition to information, other calls, the resources of the radio interface of the radio interface between the base station and the mobile stations can be better exploited. By means of the possibility of differentiating the information according to a fine structure attached, a time segment is not blocked only by synchronization, but can be exploited in various ways. The other calls can be useful data or signaling calls. In a common wave network, ie the contiguous base stations use the same frequency range, the other calls are offered, for example, by the contiguous base station. In accordance with one embodiment of the invention, the signal form is configured as a conditioning sequence of a radio block with data to be transmitted. In this way, radio blocks that transmit information for various purposes, by configuring a special conditioning sequence, can be used for time synchronization. Thus, the capacity of the radio interface is further increased. The conditioning sequence can also be used for the evaluation of channels. Advantageously, the signal form is expanded with an individual expansion code, and information about the existence of a signal form for time synchronization may be contained therein. The signal form can also be performed as a chip sequence, which generates a bandwidth that fills the frequency range. As the radioblock can be processed by expansion with the data for time synchronization together with the other radioblocks, the additional processing work on the receiver is eliminated. According to one embodiment of the invention, the at least point in time is established by determining the correlation of a received signal with a known comparative sequence by the receiver. The correlation peak obtained in this way indicates, for example, half the time of a time segment and, thus, can serve for a greater orientation with respect to the frame structure of the radio interface. Alternatively, the at least one point in time can be determined by the filtering adjusted to the signal of a received signal. To increase the accuracy of the time synchronization, advantageously the moment of reception of the signal form is determined several times and, for frequency synchronization, an average of the moments is performed. This reduces the influence of errors that happen only once.

For frame synchronization of the mobile station, the signal form, which is embodied, for example, as a digital sequence of symbols, contains in certain time segments data on a frame structure of the frequency channels. Therefore, the signal form can also be used for the transmission of this information, without having to suffer greater losses of capacity. Advantageously, the sequence of symbols at certain moments of hyper- and / or super-frames, differ from the sequence of symbols in the other time segments of the frequency channel for time synchronization. However, for the characterization of the frame, alternatively, additional symbols may also complete the sequence of symbols at certain times, such as at the start of hyper- and / or super-frames.

BRIEF DESCRIPTION OF THE DRAWINGS Next, the invention is illustrated in more detail with the help of an exemplary embodiment, with reference to the drawing. They show: Figure 1, a modular scheme of a mobile radio network. Figure 2, a schematic representation of the frame structure of the radio transmission.

Figure 3, a schematic representation of the structure of a frequency channel for time synchronization. And Figure 4, modular schemes of the mobile station and the base station and of the radio transmission in the downward direction.

DETAILED DESCRIPTION OF THE INVENTION The radiocommunication system shown in Figure 1 corresponds in its structure to a known GSM mobile radio network, which consists of a plurality of mobile communication points MSC, which are networked with each other, or well, they constitute access to a fixed PSTN network. In addition, these mobile communication points MSC are linked respectively with at least one base station controller BSC. Each base station controller BSC allows, in turn, the connection to at least one base station BS. A base station BS like this is a radio station, which, through a radio interface, can establish an informative connection with the mobile stations MS. In Figure 1, three connections for the transmission of useful information and signaling information between three mobile stations MS and a base station BS are shown by way of example. A OMC operation and maintenance center performs control and maintenance functions for the mobile radio network, or for parts of it. The functionality of this structure can be applied in other radiocommunication systems, in which the invention is used. The frame structure of the radio transmission can be seen in Figure 2. According to a TDMA component, a division of a broadband frequency range is foreseen, for example, of the bandwidth B = 1.6 MHz or B = 5 MHz , in various time segments ts, such as, for example, 8 time segments tsl to ts8 or (not shown) 16 time segments. Each of them, within the frequency range B, forms a frequency channel FK. Within the TCH frequency channels, which are provided exclusively for the transmission of useful data, the information of several calls is transmitted in radioblocks. These radioblocks for the transmission of useful data consist of segments with data d, in which segments with conditioning sequences tseql to tseqK, known by the receiver, are incorporated. The data d is individually expanded for each call with a fine structure, a participant code c, so that, on the receiver side, for example, K calls can be separated by this CDMA component. The expansion of certain symbols of the data d has the consequence that Q chips of the duration Tcj: j_p are transmitted within the duration of the symbol Ts. The Q chips constitute the individual c participant code of each call. Also, within the ts time segment, a protection time gp is provided for the compensation of various signal times of the connections. Within a wideband frequency range B, the consecutive time segments ts are divided according to a frame structure. Thus, eight time segments ts are combined in a frame, for example forming a time segment ts4 of the frame, a frequency channel TCH for the transmission of useful data and being used in its return by a group of connections. An SCH frequency channel is not introduced for the time synchronization of the mobile stations MS, but at a predetermined time within a multi-frame. The distance between the SCH frequency channels for time synchronization determines the capacity that the mobile radio network makes available for it. With the help of Figure 3 the structure of an SCH frequency channel for time synchronization is shown. The broadband frequency range B, in the frequency band of an organization channel of the corresponding cell of the mobile radio network, is part of a frame RO, which contains an SCH frequency channel for time synchronization (in which, however, other signaling connections and useful data can also be developed), and in the following time segments, exclusively TCH frequency channels for the transmission of useful data, or signaling. This frame RO is, in turn, part of a super-frame SO, which, in addition to the RO box, includes a frame R1 with frequency channels FK with other information related to the cell and a frame R2 with useful data. A_hyper-frame contains, in turn, several super-frames SO, SI, of which at least one contains an SCH frequency channel for time synchronization. In a time segment ts of the frequency channel SCH for time synchronization, a synchronization block sb is transmitted in downward direction, which contains as a conditioning sequence a signal form fl, which is known in the mobile stations MS . The signal form fl is integrated into other information of useful data or signaling to be transmitted. The synchronization block sb is expanded with an individual code cl. The other calls with the useful or signaling information are made by other base stations BS in the same frequency interval B, which synchronizes frames with the base station BS, which emits the signal form fl. Alternatively or additionally, the base station BS that issues the signal form fl can also take advantage of the time segment ts for other connections. Even so, this overlap of several signals, which can be differentiated by the participant code c that constitutes the individual fine structure for each connection, can be resolved as illustrated below. An alternative embodiment for the synchronization block sb, in addition to the signal form configured as a symbol sequence, provides fia symbols, which are used for frame synchronization. By means of these additional symbols fia, which are transmitted in the first frame RO of a super-frame SO, a receiving mobile station MS can realize an identification of the current position of the time segment ts in the frame structure. The synchronization block sb is emitted by the base station BS with an emission power which, in the sense of a power regulation, is adjusted to the reception powers of the other connections. On the receiver side, for time synchronization a point in time ti is determined, through the evaluation of the signal form fl. The point in time ti indicates approximately half of the signal form. Since the emission of the synchronization block sb also takes place, for example, in the middle of the corresponding time segment ts, by correctly evaluating the receiver side, you can determine half of a time segment ts. For this, the mobile station MS, in the corresponding frequency channel SCH, constantly tries by correlating the received signal with a comparative sequence f2, which corresponds to the signal form fl, determining the point in time ti of the arrival of signal form f1. A correlation peak then indicates the point in time ti which will be considered in the following half of the time segment ts. Figure 4 shows the downlink radio transmission of the base station BS to the mobile stations MSI to MSK. The mobile stations MS first determine one or more frequency ranges B with a sufficiently high or maximum reception power. These are the frequency ranges B of the nearest base station BS, in which cell the mobile station MS is momentarily located. The mobile stations MSI to MSK evaluate the received signals in these frequency ranges B and carry out a permanent correlation of the values of the received signal with the comparative sequence f2. In the case of a sufficiently large correlation peak, the determined time point ti of the arrival of the signal form fl is chosen as the reference point for the time synchronization and is adjusted to an internal time reference of the mobile station MS. Simultaneously, the corresponding SCH frequency channel can be used for a subsequent frequency synchronization. The base station BS contains a transmitter / receiver device SE / EE, which performs the digital / analog conversion of the data signals to be transmitted, passes from the base band to the frequency range B of the emission and modulates and amplifies the signals emitted . Previously, a signal generating device SA gathered the signals to be emitted, for example, synchronization blocks sb, and assigned them to the corresponding frequency channels SCH, TCH. The mobile station MS contains an operation field T, an SP signal processing device, a SE control device and a SE / EE emission / reception device. In the field of operation T, the participant can enter information, among other things, enter the activation of the mobile station MS, which, then, must first perform a synchronization with the mobile radio network that surrounds it. The control device SE receives this requirement and makes the signal processing device SP, through the transmission / reception device SE / EE, evaluates the signals received for, as already described, choosing the corresponding frequency interval B and perform a correlation until finding the signal form fl. For the processing of a signal, the received signals are converted into symbols with discrete values, for example, they are digitized. The signal processing device SP, which contains as a signal processor a JD processor for detecting useful information and signaling information, according to the JD-CDMA (joint detection) method, also evaluates the synchronization blocks. The evaluation is performed by determining the correlation between the received signals and the known comparative sequence f2 in the mobile station MS. In this, the point in time ti of the highest correlation is also determined, which, in the following, will serve for time synchronization. Alternatively, a filtering adjusted to the signal or other linear algorithm can also be used (for example, according to the zero forcing criterion or the minimum square error). To increase the accuracy of the time synchronization, the mobile station MS repeats the determination of the point in time ti of the arrival of the synchronization block sb and averages its values. In addition, instead of a single correlation or filter fitted to the signal, an evaluation can also be carried out in a filter bank for various frequency levels and Doppler shifts.

Claims (11)

NOVELTY OF THE INVENTION Having described the above invention, it is considered as a novelty, and therefore, the content of the following is claimed as property: CLAIMS

1. A method for synchronizing the time of a mobile station (MS) of a radio communication system, providing this frequency channels

(FK) formed by time segments (ts) and broadband frequency intervals (B), in which information of one or several connections between the mobile stations (MS) and a base station (BS) is simultaneously transmitted, and the information of different connections can be differentiated by means of an expansion code, characterized in that: - for mobile stations (MS), recurrent in downward direction, a frequency channel is provided

(SCH) for time synchronization, - within the frequency channel (SCH), in addition to the information of other connections, several known different signal forms are transmitted (fl, fia), - the synchronizing mobile station (MS), from the received signals, it determines points in time (ti) of the arrival of the signal forms (fl, fia), and - the mobile station (MS) takes advantage of the points in time (ti) and the type of the signal forms (fly fia), for the synchronization of time in regard to time segment (ts) and frame. 2. A method according to claim 1, characterized in that the signal form (fl) is configured as a conditioning sequence of a radioblock with data to be transmitted. 3. A method according to claim as claimed in any of the preceding claims, characterized in that the signal form (fl) is expanded with an individual expansion code (cl).

4. A method according to claim 1, characterized in that the at least one point in time (ti) is established by determining the correlation of a received signal with a known comparative sequence (f2) in the receiver.

5. A method according to claim 1 in any of claims 1 to 3, characterized in that the at least one point in time (ti) is determined by the filtering adjusted to the signal of a received signal.

6. A method according to claim as claimed in any of the preceding claims, characterized in that several points are determined in time (ti, t2) of the arrival and for the synchronization of time an average of the points in time is made (ti, t2).

7. A method according to claim 1, characterized in that the signal form (flj, in certain time segments (ts), contains data on a frame structure of the frequency channels (FK).

8. A method according to claim 7, characterized in that the signal form (fia), at certain points in time of the hyper- and / or super-frames, differs from the signal form (fl). ) in the other time segments (ts) of the frequency channel (SCH) for time synchronization

9. A method according to claim 7, characterized in that at the start of hyper- and / or super-frames , additional symbols complement the signal form (fl)

10. A mobile station (MS) for performing the method according to claim 1, with a signal processing device (SP) - for determine the points in time (ti) of the arrival of the signal forms (fl, fia), with a control device (SE) - for the synchronization of time considering the points in time (ti) determined.

11. A base station (BS) for performing the method according to claim 1, with a signal generating device (SA) for generating predetermined signal forms (fl, fia), and with an emitting device ( EE) to output the signal forms (fl, fia) on the frequency channel (SCH) for time synchronization.