Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Patent
1996-10-17
1998-05-05
Chin, Wellington
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
455426, H04B 7212
Patent
active
057486220
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention refers to a burst alignment procedure between a cordless terminal and its base station. This procedure is of particular application in digital cordless communications systems with time division multiple access, to ensure the correct reception of bursts received with different delays due to propagation effects.
BACKGROUND OF THE INVENTION
Many communications systems, formed by a set of cordless terminals and a number of base stations, were developed with reduced range (picocells) for indoor use, the separation between the cordless terminals and the base stations being very small. Presently, the initial application of these systems is being reconsidered with a view to employing them in larger spaces, where there is an increased distance between the base stations and the cordless terminals, for their use as an alternative to systems based on cellular technology. In these communications systems, the cordless terminals obtain their timebase reference from the base stations, so that the transmitting instants of the base stations coincide with those of reception in the cordless terminals, and vice versa.
Due to the configuration that the cordless systems were originally going to have, the standards developed for this technology do not lay down guidelines for overcoming the problems resulting from propagation delays due to the distance between the base stations and the cordless terminals, such as the problems of overlapping caused by the delay with which the messages are received with respect to the instant when they should have been received, resulting in the total or partial loss of information channels. This is particularly critical in systems with time division multiple access TDMA, and with a high bit rate, where such problems can arise but which were practically of no consequence for the distances between base stations and cordless terminals that existed in the original configuration intended for these systems.
The European standard ETS 300 175-3 "Digital European Cordless Telecommunication (DECT), Common Interface Part 3: Medium Access Control Layer", October 1992, developed by the RES (Radio Equipment and System) Technical Committee, in Annex D "Synchronization", page 186, references, for this DECT system, the three types of synchronization between the cordless terminals and base stations for correct transmission and reception of the bursts interchanged: burst synchronization, frame synchronization and multiframe synchronization.
This European standard does not incorporate any procedure for compensating the delay due to propagation (which impedes the correct synchronization between the base stations and the cordless terminals, and which causes overlapping problems), since this is not a critical problem in the applications for which the system was intended. Consequently this European standard does not establish solutions for the problem that arises in base stations when the bursts coming from the different cordless terminals associated with the base stations are received with different delays due to the variation in distances existing between these cordless terminals and the base stations, which can result in interference between the two equipments that frequently produces the total or partial loss of information channels.
As a consequence of the foregoing, the technical problem to be resolved lies in achieving a correct synchronization between cordless terminals and their base stations when the distance between them is increased, so that the bursts coming from these cordless terminals are correctly received in the base stations, without the propagation delay due to distance preventing correct synchronization between the base station and the cordless terminals, avoiding burst overlapping problems with total or partial loss of information or channels.
SUMMARY OF THE INVENTION
This invention presents a burts alignment procedure between cordless terminals and their base stations, when these cordless terminals are located at some distance from their base stations, this proc
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Alcatel NV
Chin Wellington
Hyun Soon-Dong
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