Radio data communication system having means for reducing collisions between contending remote stations

A radio based communication system comprising a base station and one or more remote stations each incorporating a radio transmitter and receiver to support communication between the base station and each remote station on a down link and between each remote station and the base station on an up link, each link comprising a plurality of frames of fixed length divided into a fixed number of slots wherein the base station (1) includes base control means which transmits control data in a general control (GC) slot in each frame of the down link so as to identify to each remote station a down-setup slot (DSU) in each frame of the down link in which the base station (1) is to announce the transmission of data for each remote station to identify at least one down-transfer slot (DTR) in the frame of the down link in which said data for said remote station is to be transmitted to said remote station, the control data further identifying an acknowledgement slot (ACK) in each frame of the down link and an up-setup slot (USU) divided into sub-slots (1/4) in each frame of the up link, each remote station (2) including remote control means which transmits a reservation request to transmit data to the base station in any sub-slot (1/4) of the up-setup slot (USU) and receives corresponding data in the acknowledgement slot (ACK) of the down link to identify an up-transfer slot (UTR) in the up link in which it is to transmit data to the base station (1).

A method of communicating data over a radio based communication system between a base station and one or more remote stations comprising the steps of transmitting data between the base station and each remote station in a down link comprising one or more down frames of fixed duration;

• transmitting data between each remote station and the base station in an up link comprising one or more up frames of fixed duration;
• dividing each down frame into a fixed number of down slots at least one of which is a general control slot, and at least one other is a down-setup slot;
• providing control data in said general control slot to identify for each remote station the down-setup slot in which the base station is to announce the transmission of data for each remote station;
• dividing each up frame into a fixed number of up slots at least one of which is an up-setup slot;
• providing control data in said general control slot to identify for each remote station said up-setup slot;
• dividing said up-setup slot into a number of sub-slots;
• each remote station wishing to transmit data to the base station transmitting a reservation request in one of said sub-slots;
• each remote station receiving said control data in said general control slot to identify said down-setup slot and said up-setup slot, and thereafter receiving data in said down-setup slot only, at least, until directed by the base station to again receive control data in said general control slot.