Patent GB-1299796-A (GB)
Title: Channel reallocation system and method
IPC: H04B7/212
Filed: 1970-03-20
Abstract: 1299796 Space satellite communication systems POST OFFICE 20 March 1970 [21 March 1969] 13610/70 Heading H4K In a time division multiple access satellite relay communication system each ground station transmits, in each cycle of the system, during a burst period of duration proportional to the number of channels allocated to the station, the number of channels allocated to each station being periodically reassessed and the positions and durations of the station transmission burst periods being adjusted in accordance with the reallocation. To achieve such adjustment each station computes the algebraic sum of the shift in transmission burst start times of all stations with earlier bursts back to a first or reference station. To achieve such adjustment without overlapping one burst time on another the adjustment is made for individual burst times that require delaying only if the next following burst time requires advancing or no change, and is made for individual burst times that require advancing only if the immediately preceding burst time requires delaying or no change. By recording at each station the algebraic sums of the burst shifts of preceding bursts of all other stations as well as the sum pertinent to its own station, each station decides in a step-by-step process, pursued in response to successive marking codes sent out by the reference station, which stations are the subject of readjustment at each step. When, as determined by a logic chain, Fig. 12 (not shown), the principles set out above are satisfied in respect of a station's shift requirements, the station's shift registration in all stations is erased to indicate in future steps of the process that no change is required and, at the station itself, to transfer the shift registration to a burst synchronization control circuit where the change in burst time is effected. It is suggested that channels may be reallocated at " three-hourly intervals and that "slack" channel time in the existing channel allotments be pooled and shared out to constitute the reallocation. The preferred method of sharing out the pooled "slack" is to give all stations an equal number of channels from the pool, any fraction of channels left over from such a division being held back. Channels that are deemed "slack" in respect of any station's allocation are those numbered above the number of the highest numbered channel in use, a station in seizing channels for use seizing a higher numbered channel only if no lower numbered channel is free at the time. When a reassessment of channel allocation is required the reference station, or any nominated station, broadcasts a "freeze" signal which has the effect that regardless of demand the "slack" channels in each station's allocation are withdrawn from use and each station broadcasts the number of its highest channel in use. Each station records all such channel numbers in respect of each station as well as itself and by subtracting the total of such numbers from the total of channels in the system the total "slack" is computed and divided by the number of stations in the system to obtain the equal shares from the pool. By adding this share to the highest channel number received from each station the new total allocation of channels for each station is obtained. By taking the algebraic difference between a preserved record of each station's old allocation and the new allocation a set of algebraic sums of such differences can be made for each station to register respective required shifts. This schedule of sums is constructed in each station and is operated upon as described above in order stepby-step to record and effect the repositioning of station burst times. The channel allotment scheme of the frequency division multiple access system described in Specification 1,269,555 is referred to.