Multiplex communications – Wide area network – Packet switching
Patent
1992-08-07
1994-12-27
Chin, Wellington
Multiplex communications
Wide area network
Packet switching
3701101, 455 321, H04J 316
Patent
active
053771923
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of and a system for communicating data, in particular communicating data across a radio based communication system.
DISCLOSURE OF THE INVENTION
The present invention consists in a method of communicating data over a radio based communication system between a base station and one or more remote stations wherein the data is transmitted between the base station and each remote station in a down link comprising one or more down time-frames of fixed length, and data is transmitted between each remote station and the base station in an up link comprising one or more up time-frames of fixed length, each down frame comprising a fixed number of down slots at least one of which is a general control slot, at least one other is a down-setup slot, at least one other is a down transfer slot, and at least one other is a down acknowledgement slot, control data in the general control slot serving to identify to each remote station the down-setup slot in which the base station is to announce the transmission of data for it and identify the down-transfer slot or slots in which said data is to be transmitted, and each up frame comprising a fixed number of up sloes at least one of which is identified by control data in the general control slot as an up-setup slot, at least one other is an up transfer slot, and at least one other is an up acknowledgement slot, the up-setup slot being divided into a number of sub-slots in which each remote station can transmit a request to transmit data to the base station, and the base station serving to respond to such a request in a down acknowledgement slot by identifying the up transfer slot or slots in which the remote station is to transmit said data.
The communication of data on the down link and up link involves two phases: a setup phase and a data transfer phase, with a separate slot or group of slots, i.e. data channels, being allocated for each phase. The advantage of this technique is that the data transfer channel need not be loaded with data unless the setup phase is successful, and the setup messages can be very short and hence use very little bandwidth. This is especially advantageous for transmissions on the up link, since the remote stations, which may be a mobile fleet of users, are necessarily uncoordinated and will therefore contend for channel capacity. Contention channels, whether operating in Aloha- or CSMA- type modes, have to be operated at low utilisations to avoid instability. By ensuring that contentions take place only between short setup messages, even though the contention time-slots have to be operated at low utilisation, this has little impact on the overall efficiency of channel usage. The base station responds to a successful up-setup request by allocating capacity on a data transfer channel, which thereby may be operated in a "scheduled" manner at high utilisation. Similarly, as packets arrive at a base station to be transmitted to a particular remote station, the base station first executes a down-setup to tell the remote station to monitor the down data transfer channel, then schedules the data itself into the down data transfer channel.
Preferably, all data transmitted in the down transfer slot is labelled with a mobile group label by which it is identified by the remote station or stations to which it is addressed.
The down-setup slot contains data which identifies the mobile or group of mobiles to which a message is to be sent, i.e. the mobile group label allocated to that message. The mobile or mobiles then identify that message simply by reference to the mobile group label as attached to data in one or more down transfer slots until the complete message has been received.
In an alternative embodiment of the invention, however, the down-setup phase may be incorporated in a down acknowledgement slot which the base station transmits in response to a message from a mobile so that the mobile is more rapidly setup to receive a message or reply, thereby shortening the response time. Furthermore, where th
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Carter Leigh
Goodings Rupert Leslie A.
Mitchell Patrick
Chin Wellington
Cognito Limited
Nguyen Chau T.
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