Pulse or digital communications – Synchronizers – Feedback – receiver to transmitter
Reexamination Certificate
1999-08-18
2002-08-06
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Synchronizers
Feedback, receiver to transmitter
C370S519000, C455S424000, C455S067700, C455S067700
Reexamination Certificate
active
06430241
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for the synchronization of system units which are connected to one another via an, in particular, asynchronously transmitting connection, specifically of telecommunications devices which have to be supplied with synchronous operating clock signals and are connected to one another via a high-speed LAN (Local Area Network).
Telecommunications devices are usually interconnected with the aid of synchronous networks. The clock supply of remote units is thereby effected by means of various clock generators operating as slave, and a master clock generator, which synchronizes these remote units with the aid of synchronization pulses sent to the slave clock generators. The time duration between two synchronization pulses is bridged with phase control loops which keep the clock signal in the slave clock generators constant. Particularly in the case of digital data transmission, the exact synchronization of all the system units is important in order that no data bits can be lost. However, as the propagation delay of the synchronization pulse increases, which may be caused for example by long line lengths between the master and slave clock generators, the phase angle of the slave clock signal is shifted with respect to the master clock signal as a function of the time duration required by the synchronization pulse on its way from the master clock generator to the slave clock generator. Problems arise when the propagation delay causes a phase deviation of the slave clock signal relative to the master clock signal which is greater than the permissible phase deviation for a respective communications application. Problems can arise, therefore, at very high clock rates, and/or in the case of very small permissible phase deviations.
However, there are telecommunications devices commercially available which impose very stringent requirements on the timing and phase accuracy of the operating clock signal in the entire communications system. Particularly high requirements are imposed on the quality of the clock supply in this respect by digital wireless communications links, such as, by way of example, those according to the DECT standard (DECT=Digital Enhanced Cordless Telephone) and according to the GSM standard (GSM=Global System for Mobile Communication). In those cases, call connections of base stations which serve different communications cells have to be handed over to one another if a communications subscriber moves into an adjacent communications cell in the course of an existing connection, without any impairment of the connection quality being allowed in the process.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a configuration for synchronizing two or more system units, which overcomes the above disadvantages of the heretofore-known devices and methods of this general type, that is, a method and a configuration by means of which the operating clock signals of system units which are connected to one another in particular via an asynchronously transmitting connection can be synchronized by means of this connection.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of compensating a phase angle of an operating clock signal for first and second system units connected via a time-delaying transmission connection, the method which comprises:
transmitting a test signal with a first system unit via a connection to a second system unit, receiving the test signal with the second system unit, looping the test signal through and returning the test signal to the first system unit, and measuring, with the first system unit, a loop propagation delay representing a time duration elapsed between a sending and an arrival of the test signal;
determining with the second system device an internal delay time representing a processing duration required for processing a signal arriving via the connection; and
compensating the phase angle of an operating clock signal of the first and second system units with the loop propagation delay and the internal delay time.
The method according to the invention provides not merely for measuring the propagation delay of a signal between the adjacent system units, which are connected to one another in particular via an asynchronous network, but likewise for taking account of the processing duration required by a unit for the conversion of a data frame arriving on the asynchronous connection. This advantageously ensures that account is taken of the essential time-relevant operations during the communication of the system units via the connection network, that is to say the propagation delay and the processing duration for the conversion of a communications protocol. The invention is advantageously applied both to asynchronous connections and to synchronously transmitting connections in which the propagation delay of a synchronization pulse shifts the phase angle of the operating clock signals with respect to one another beyond a permissible extent.
The requisite measurements and evaluations and also the necessary adaptations can in this case be implemented with any desired work division and technically practical combination of individual or a number of units. By way of example, the role of the master and slave units during the measurement, looping and clock matching can be interchanged as desired.
In accordance with an added feature of the invention, a permissible phase deviation of the phase angle is defined and the phase angle is compensated using the permissible phase deviation. In other words, in the course of the compensation of the phase angle it is not merely the loop propagation delay and the internal delay time that are taken into account, rather a permissible phase deviation is also included. In this way, clock fluctuations of the phase-locked loop are to an extent permissible and a synchronization pulse to be transmitted may not need to be sent as often. The clock fluctuations may even be of a statistical nature in the framework of the sampling theorem.
In accordance with an additional feature of the invention, an information item concerning an internal delay time is communicated from the second system unit, and the phase angle is compensated with the first system unit. In other words, one unit, for example the slave unit, communicates its internal delay time to the other unit, for example the master unit, and the latter corrects its clock signal, for example the master clock signal, as a function of this delay time and of the loop propagation delay. The master clock unit generally has higher computing capacities and can perform a correction more easily. In addition, the method is practicable for a plurality of system units which are connected to one another and are all connected to the same network, if it can be assumed that the transmission durations of the signals to the different units within the network are approximately constant and only the communication between two such units has to take place in order to coordinate all the operating clock signals of the communications devices present in the system with one another.
In accordance with an alternative feature of the invention, the method comprises a step of communicating from the first system unit an information item concerning the loop propagation delay to the second system unit, and wherein the compensating step comprises compensating the phase angle with the second system unit. That is, the measurement of the loop propagation delay by the slave unit can take place if the master unit loops through the connection in order to determine the delay by the master unit (P
1
→P
0
→P
1
in FIG.
2
). This advantageously enables slave units to adapt their clock signal and their phase angle automatically.
In accordance with another feature of the invention, a synchronization information item for synchronizing the operating clock signal is sent between the first and second system units, and the phase angle
Manzardo Marcel-Bruno
Rupprecht Johannes
Greenberg Laurence A.
Le Amanda T.
Mayback Gregory L.
Siemens Aktiengesellschaft
Stemer Werner H.
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