GB2183128A

GB2183128A - Method for synchronising a receiver in digital data transmission

Info

Publication number: GB2183128A
Application number: GB08627298A
Authority: GB
Inventors: Ziaedin Chahabadi
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1985-11-15
Filing date: 1986-11-14
Publication date: 1987-05-28
Also published as: DE3540572C2; SE8604874D0; DK536086D0; FI864638A0; GB8627298D0; FI864638A; DK536086A; DE3540572A1; SE8604874L

Abstract

A method for synchronising the receiver to the transmitter of a digital data section is specified. In the receiver, a synchronising pulse is first detected. In accordance with the determination of the clock rate of the data stream, "windows" are then opened at time intervals, in which the synchronising pulse is sampled. The windows are narrowed down step by step. The narrowest window approximately corresponds to the width of the edge of the synchronising pulse.

Description

SPECIFICATION Method for Synchronising a Receiver in Digital Data Transmission The invention relates to a method for synchronising a receiver to a transmitter of a transmission section for digital data, using a data stream going out from the transmitter and coming in at the receiver, in which the incoming data stream is inspected in segments in the receiver in timelimited windows which are opened in accordance with the determination of the clock rate of the data system at intervals corresponding to this clock rates, and in which the receiver is adjusted until in each case a pulse of the data stream is detected in the windows which is present as synchronising pulse at constant intervals in the data stream.

In the transmission of digital data it is necessary that the receiver runs in sychronism with the transmitter if a distortion of the information items transmitted is to be prevented. The receiver must therefore be synchronised to the transmitter. This applies both with line-conducted and with wireless transmission.

A phase control circuit named "PLU'-Phase- locked loop-is known which can be used for such synchronisation. In this circuit, or the corresponding method, the clock generator of the receiver which is, for example, a quartz generator, is followed by an adjustable divider. The divider is used for dividing the high frequency of the clock generator down to the frequency of the data stream. The receiver is synchronised to the transmitter by using the incoming data stream. A pulse recurring at constant intervals in accordance with the clock rate of the data stream is used as synchronising pulse which is detected in a so-called "window". This window means a time-limited sampling of the data stream which is thus detected only from time to time, this being when a window is opened.The first window is opened in the receiver when the synchronising pulse is expected to arrive. The time is known per se since the clock frequency of the incoming data stream is known. If during this operation a pulse is detected quite accidentally in the first window, further windows are opened in each case at intervals of the clock rate of the data stream. If the pulse appears in all windows, the synchronising pulse has really been detected and the receiver is running in synchronism with the transmitter. If the pulse no longer appears in the second window, which will always be the case at the beginning, the pulse detected in the first window was either a noise pulse or the receiver is not running synchronously.

The divider of the clock generator is then adjusted until the synchronising pulse finally appears in all windows. This known synchronising method is very time consuming. It can last some minutes until synchronisation is achieved. Since the actual data transmission cannot be carried out until that time, this method is unsatisfactory.

The invention is based on the object of specifying a method which, compared with the known method, enables the receiver to achieve very rapid synchronisation to the transmitter of a digital transmission section.

This object is achieved by a method of the type initially described, in accordance with the invention, in that in a first step, the data stream is inspected in the receiver without window until the synchronising pulse has been found, that in a second step, a window which is wide in time is opened at the time interval of the clock rate of the data stream and that when the synchronising pulse is located in this window, further windows whose spacing in time from each other corresponds in each case to the clock rate of the data stream are opened in further steps and are progressively narrowed down in time from window to window until a time slot is produced as window which, taking into consideration the inaccuracy of the clock generator, is slightly wider than the possible deviation of the edge of the synchronising pulse in the period.

In this method, finding the synch ronising pulse is not left to the random detection in a first window but initially the total incoming data stream is inspected from which the synchronising pulse is picked out.

The receiver is then very rapidly synchronised by the window subsequently opened and in each case narrowed down step by step. Synchronisation is not only rapid but also accurate since the last window, called a time slot, results in accurate adjustment to the edge of the synchronising pulse.

This method is very rapid and accurate even if it is not the synchronising pulse but a noise pulse which was detected as first pulse. Since this noise pulse no longer appears in the first window, the synchronising pulse is found immediately thereafter.

The method is of advantage even when a disturbance due to a trace shift at the transmitter occurs during the transmission of data. The resynchronisation of the receiver required in that case occurs just as rapidly as initial synchronisation. To detect the synchronising pulse, the window can either be widened step by step in this case and narrowed down again after the synchronising pulse is detected or the window is completely deleted and narrowed down again step by step after the first window has been formed.

The time needed to achieve synchronisation depends on the frequency of the data stream transmitted. At a frequency of, for example, 1 kHz, the synchronising pulses follow each other at intervals of 1 msec. Synchronisation can be achieved in a few milliseconds. At higher frequencies, the synchronisation time is significantly shorter.

In the text which follows, the method according to the invention is explained as an illustrative embodiment.

In digital signal transmission, the data are transmitted from a transmitter to a receiver as bits in known codes. In this arrangement, an arbitrary number of the bits is combined in frames. At a frequency of 1 kHz, for example, 32 bits are combined in a frame. The edges of the first bits or pulses of the successive frames then occur at intervals of 1 msec from each other.

The first pulse of each frame is to be used as synchronising pulse. Strictly speaking, the synchronising method then relates only to the edge of this pulse. As soon as the synchronising pulse has been found, a still relatively wide window is opened after 1 msec. If the width of the narrowest window, that is to say of the time slot, is designated by "B", the first window can have a width of, for example, 31 B. This can correspond, for example, to a value of 31 lisec.

The windows following at intervals of 1 msec can then be narrowed down step by step by 2 B in each case so that the time slot is reached after 15 steps which corresponds to a time of 15 msec.

The windows are implemented, for example, by a counter which follows the clock generator of the receiver and which initially counts up to 15 and then counts back down to zero.

The width of the windows and the number of steps until the time slot is reached are arbitrarily chosen.

The specified data change in accordance with higher transmission rates at other clock frequencies.

Claims

1. Method for synchronising a receiver to a transmitter of a transmission section for digital data, using a data stream going outfrom the transmitter and coming in at the receiver, in which the incoming data stream is inspected in segments in the receiver in time-limited windows which are opened in accordance with the determination of the clock rate of the data stream at intervals corresponding to this clock rate, and in which the receiver is adjusted until in each case a pulse of the data stream is detected in the windows which is present as synchronising pulse at constant intervals in the data stream, characterized in that in a first step, the data stream is inspected in the receiver without window until the synchronising pulse has been found, that in a second step, a window, which is wide in time is opened at the time interval of the clock rate of the data stream and that when the synchronising pulse is located in this window, further windows whose spacing in time from each other corresponds in each case to the clock rate of the data stream are opened in further steps and are progressively narrowed down in time from window to window until a time slot is produced as window which, taking into consideration the inaccuracy of the clock generator, is slightly wider than the possible deviation of the edge of the synchronising pulse in the period.

2. Method according to Claim 1, characterized in that, in the case of a phase shift occurring during the data transmission, the window is widened step by step, starting from the time slot, until the synchronising pulse has been detected and that the window is then narrowed down again step by step until the time slot is reached.

3. Method according to Claim 1, characterized in that, in the case of a phase shift occurring during the data transmission, the window is completely deleted and is then narrowed down again step by step until the time slot is reached.

4. Method according to Claim 1, substantially as described in respect of the illustrative embodiment disclosed herein.