WO2001020816A1

WO2001020816A1 - Synchronisation method

Info

Publication number: WO2001020816A1
Application number: PCT/DE2000/003112
Authority: WO
Inventors: Zoran Gardijan; Jörg Dauerer; Gerhard Steib; Birgit Gruber-Waldhauser
Original assignee: Siemens Aktiengesellschaft
Priority date: 1999-09-15
Filing date: 2000-09-07
Publication date: 2001-03-22
Also published as: DE19944302A1

Abstract

The invention relates to a method for synchronising the physically separate units of a device consisting of a central unit and units which are separate from said central unit and connected thereto. Said method comprises the following steps: measuring a respective delay time between the central unit and the separate units; delaying the internal clock of each separate unit by a maximum delay; and subtracting the delay times detected respectively from the time base of each separate unit as delayed by the maximum delay time.

Description

description

Synchronization procedure

The invention relates to a method for synchronizing a device consisting of a central unit and units spaced therefrom, in particular for use in a base station of a radio communication system.

In radio communication systems, messages (for example languages, image information or other data) are transmitted with the aid of electromagnetic waves via a radio interface. The radio interface relates to a connection between a base station and mobile stations, it being possible to supply fixed radio stations instead of the mobile stations. The electromagnetic waves are emitted at carrier frequencies that lie in the frequency band provided for the respective system. In the known GSM mobile radio system (Global System for Mobile Communication), the carrier frequencies are in the range of 900, 1800 or 1900 MHz. For future radio communication systems, for example the UMTS (Universal Mobile Telecommunications System) or other third generation systems, frequencies in the frequency band of approx. 2000 MHz are provided.

Furthermore, from the older German patent application DE 197 55 379.6 a base station with a multiplicity of transmitting / receiving units is known, the transmitting / receiving units with a central unit of the base station using at least one individual line according to a point-to-point - Connection for the transmission of traffic data are connected. The central unit contains a central time base from which the local time bases of the remote transmitter / receiver units are derived. Since the length of the connection lines between the central unit and the remote transceiver units is different, the signal propagation times on these connections are different.

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System allows. The measured delay due to the transit time is subtracted from this artificial fixed delay. Then all the remote units run synchronously with one another, the accuracy being in the clock rate of the transmission clock.

It is therefore advantageously no longer necessary to have the same length of lines. Additional drivers can also be used in the line, for example to allow different transmission media. The maximum delay value, which corresponds to the maximum cable length, can be made variable so that there is no unnecessary delay if this should not be necessary.

A preferred embodiment is explained below using two drawings. Show:

Fig. 1 is a schematic representation of the communication between the central unit and remote transmitters of a base station, and

2 shows a time diagram of the individual delay due to different signal propagation times.

1 shows a base station BTS of a radio communication system consisting of a central unit CORE and a plurality of remote transmitting / receiving units CU1 ... CU3. The central unit CORE and the transceiver units CU1 ... CU3 are connected in accordance with the prior art mentioned via a star-shaped structure of individual lines CC-Link, so that a point-to-point connection for traffic data to be transmitted S results. Furthermore, each remote transmitting / receiving unit CU1 ... CU3 and the central unit CORE have an interface device SELIC (Serial Link Interface Control), whereby the data transmission on the serial link CC-Link is established. The synchronization of the base station BTS, ie the synchronization of the remote transmitter / receiver units CU1 ... CU3, has the following four main tasks:

a) Compensation of the delay due to the lines CC-Link: for example, in the known GSM mobile radio system, a time difference between two carriers of less than a quarter bit, which is slightly less than 1 μs, must be ensured.

b) In the GSM system, the exact base clock signal must be transmitted to each remote transmitter / receiver unit CU1 ... CU3, where it is used to generate the system clock (for example 26 MHz for GSM). The system clock is used to generate the RF transmission frequency and LO frequencies (Local Oscillator), which are required to receive the RF frequency. The jitter must therefore be very low in order to meet the GSM framework.

c) System-specific signals, such as the 577 μs long GSM time frame signal, must be generated on each remote transmitter / receiver unit CU1 ... CU3. Furthermore, system-specific signals and the counters from each remote transmitter / receiver unit CU1 ... CU3 must be synchronized with each other.

d) The synchronization of the various units of the base station BTS must be quick and it must be reliable, for example after new transmitter / receiver units have been introduced, for example due to maintenance work or expansion of the system.

Since the CC-Link connection is the only way to create a common time base for all remote transmission units CU, it is necessary to determine the delay time between the central unit CORE and the individual transmission units. ten CU exists to compensate in order to be able to generate correct clock signals.

The synchronization method according to the invention is illustrated below with reference to FIG. 2.

The delay time of a single connection is measured continuously as follows:

The SELIC interface of the CORE central unit transmits a burst, i.e. a digital word to the SELIC interface of the remote transmitting / receiving units CU1 ... CU3, and a counter is started in the central unit CORE. After receiving the burst of the central unit CORE, the interface SELIC of the remote unit CU1 ... CU3 sends a burst back after an internal delay time. The internal delay time is formed by the internal processing time of the remote unit CU1 ... CU3, which is required to generate the return burst and is known, or by a preset delay, which includes the internal processing time. The central unit CORE then stops the counter by receiving the returned burst signal.

The delay time dp is then calculated as follows:

dp = (tg - tp) / 2,

where tg is the total time that the burst needs to get from the central unit CORE to the corresponding remote unit CU1 ... CU3 and back again, tp the usually preset internal delay or processing time within the remote units CU1 ... CU3 is and dp then gives the delay time of the respective line. The remote transmitter units CU have defined an internal time base that is delayed by a maximum delay time dmax. This maximum delay time dmax is now reduced by the individual delay time dpl ... dp3 determined for each connection, as a result of which all remote units CU1 ... CU3 run synchronously.

The delay time dp calculated by the central unit CORE is transmitted to the corresponding remote unit CU1 ... CU3 in a synchronization field of the protocol of the CC-Link. If a transmission rate of 16,384 Mbit / s is used, the minimum compensable delay time is 61 ns, since the delay is compensated in multiples of a period of the transmission frequency. The maximum delay that can be compensated by the interface depends on the maximum length of the CC link, which can be, for example, 300 according to the catalog of requirements. Therefore, the maximum delay that can be compensated within the interface device SELIC is 2 μs, and a word length of 6 bits is sufficient in this case to transmit the delay time.

Claims

claims

1. Method for the synchronization of units (CU1 ...) of a device consisting of a central unit (CORE) and associated spatially remote units (CU1 ...), characterized in that the method comprises the following steps:

Measuring a respective delay time (dpi ...) between the central unit (CORE) and the remote units (CU1 ...)

Delaying a time base of each remote unit (CU1 ...) by a maximum delay time (dmax)

Subtract the respectively determined delay times (dpi ...) from the time base delayed by the maximum delay time (dmax) of each remote unit (CU1 ...).

2. The method according to claim 1, characterized in that the respective delay times (dpi ...) are determined by the central unit (CORE).

3. The method according to claim 2, characterized in that the central unit (CORE) for determining a runtime sends a digital word in the form of a burst to the respective remote unit (CU1 ...), starts a counter and the counter after receipt of the returned Bursts stops.

4. The method according to any one of the preceding claims, characterized in that an internal delay time within the remote units (CU1 ...) is taken into account.

5. The method according to claim 4, characterized in that the internal delay time are preset.

6. Base station (BTS) of a radio communication system with a central unit (CORE) and with the central unit (CORE) star-shaped connected units (CUl ...), the remote units (CUl ...) being synchronized according to the method of one of the preceding claims.