Pulse or digital communications – Synchronizers
Patent
1995-10-06
1998-01-06
Chin, Stephen
Pulse or digital communications
Synchronizers
455 342, 4551841, H04L 700
Patent
active
057063176
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a synchronization device for a terminal of a radio communication system.
2. Description of the Related Art
In radio communication systems such as the pan-European digital cellular mobile radio system known as the GSM system, for example, calls between a terminal and a base transceiver station are conveyed by radio signals in communication channels. These systems comprise a plurality of channels for transmission from the terminals to the base transceiver stations or for transmission from the base transceiver stations to the terminals.
The latter channels include a control channel transmitted continuously to enable a terminal to access the system via the base transceiver station transmitting that channel in order to be able to set up calls. The terminal must therefore identify this control channel in order to acquire the information it needs to log onto the system. This information includes synchronization information and for this reason this procedure is usually referred to as the synchronization procedure.
The solution most widely adopted is a two-stage synchronization procedure. In the first stage the terminal measures the power of all received channels. The terminal then attempts to synchronize to the channel received at the highest power and, if it fails to synchronize to this channel, it attempts to synchronize to the other channels in order of decreasing receive power until it is able to synchronize. This solution is that set out in GSM Recommendations 4.08 version 3.11.0 and 5.08 version 3.7.0.
The synchronization procedure is systematically executed when the terminal is switched on and also, more generally, after loss of synchronization, i.e. if the radio link on the control channel between the base transceiver station and the terminal is interrupted. This interruption may be intentional, for example if the terminal is switched off, or unintentional. The terminal may be temporarily unable to synchronize because radio reception conditions are unsatisfactory. This occurs if the terminal is in a tunnel, for example, or more generally when it is in a shadow area in the radio sense of this term.
In this case the terminal will attempt to synchronize to each receive channel in succession during a synchronization period without succeeding and will resume the attempt in repetitive synchronization periods until such time as reception conditions are again adequate. The synchronization period can be of long duration, depending on the number of receive channels and the time allotted to the terminal to attempt to synchronize to a channel. This period can be in the order of 14 seconds in the GSM system, for example. During a synchronization period, the duration of which is predetermined in this case, the terminal is unable to set up any call and is therefore unavailable.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce the synchronization period.
This object is achieved by providing in the terminal a synchronization device adapted to identify a control channel constituting one of a plurality of receive channels by means of a receiver, comprising means to measure the power of the receive channels and means for attempting synchronization to at least some of the channels identified in a list. The device is characterized in that, the system being such that a reference channel, its ith predecessor and its ith successor have an ith attenuation when the receiver is tuned to said reference channel, it comprises selection means whereby the ith predecessor or the ith successor do not appear in the list if its power is less than the nominal power of the reference channel reduced by the ith attenuation.
Accordingly, the list that could initially include all of the receive channels is shortened by eliminating channels with a power substantially lower than that of the adjacent channel or channels. The effect of this is to reduce the synchronization period.
The invention will emerge more clearly from the following des
REFERENCES:
patent: 5093927 (1992-03-01), Shanley
patent: 5418839 (1995-05-01), Knuth et al.
patent: 5594944 (1997-01-01), Ogata et al.
Alcatel Mobile Phones
Chin Stephen
Le Amanda T.
LandOfFree
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