In a time division multiple-access communications system using a satellite transponder and a plurality of earth stations, each earth station periodically transmits bursts of data which are timed so that the bursts from the earth stations in the system interleave and do not overlap in time when received at the satellite. The total time for transmitting one burst from all stations is the frame time of the system. Each burst is subdivided into numerous time slots or channels during which digital information, such as digitally coded voice communications, is transmitted. All slots or channels which are allocated at any given time to a particular station may be occupied (i.e. the station actually transmits information during the time slot) or only some of the slots may be occupied, depending upon the traffic from the station. Periodically, or in response to actual traffic conditions, each station transmits an indication of its highest numbered channel then in use. The remaining or slack channels for all stations are totaled and divided up equally among all of the operating stations in the frame. Burst movement to accommodate the reallocation of channels is accomplished serially, one burst at a time. Since the slack channels are at the end of the bursts, the nonuse of the slack channels effectively shortens each burst. Burst B moves forward to bunch up against burst A, burst C then moves forward to bunch up against burst B, etc. After the calculations with respect to total slack time have been performed and each station calculates its burst position relative to the reference station to accommodate its new allocation of channels, serial movement of the bursts takes place in a direction away from the reference burst, i.e., the last burst in the frame moves back to the proper position followed by the second to last burst, etc.
A control system for diversity transmission from a terrestrial station which performs time-division multiple access to a satellite communication repeater through a selected one of a plurality of transmission paths established between the satellite and the terrestrial station, in which the transmission paths are alternately selected in synchronism with a signal received over a selected one of the transmission paths when the error rate of all the transmission paths is lower than a reference threshold value, and in which a selected one of the transmission paths having the lowest error rate is continuously used when the error rates of the transmission paths are not all lower than the reference threshold value.
A time division multiple access (TDMA) communication system has a plurality of geographically separated stations including a first group of stations, each of which can communicate with any other station in the first group through a first transponder in a predetermined portion of a TDMA frame (intra-group traffic), and a second group of stations, each of which can communicate with any other station in the second group through a second transponder in a predetermined portion of a TDMA frame associated with the second transponder (intra-group traffic). The TDMA frames of the first and second transponders are synchronized and inter-group traffic, i.e., communications between a station in the first group and a station in the second group, takes place in another predetermined portion of each of the frames which is exclusive of the predetermined portion of both frames used for intra-group traffic. Transponder hopping is employed without requiring needless duplication of terminal equipment and, at the same time, assuring non-overlapping transmissions through the same transponder. The stations transmit in a multiple channel per burst format with fully variable demand assignment. The invention is a control method and apparatus for providing a control channel for (1) ascertaining the per-station intra-group and inter-group traffic requirements, (2) allotting each station the necessary burst position and duration (capacity), and (3) synchronizing burst length changes and movement of a station's bursts to insure non-interference with transmission of other stations.
In a time division multiple access satellite communication system, a reference station which allocates channel capacity also regulates demand by the ground stations for that capacity. The regulation is accomplished by means in the reference station for transmitting limiting, blocking and revocation messages to the ground stations and means in the ground stations responsive to these messages to regulate the processing of input service requests. The limiting messages notify the ground stations to limit their channel usage to the channels required in the last demand message transmitted but not to exceed their last channel assignment. The blocking messages instruct the ground stations to unconditionally block any new requests for service on their input ports, rather than counting such calls as increments of demand, and thereby effectively reduce the aggregate demand in the system. When the reference station observes that a sufficient decrease in channel requirements occurs, resulting in an increasing spare capacity, it revokes the previously communicated blocking messages by a revocation message.
In a time division multiple access communication system utilizing a satellite for communicating signals between a plurality of ground stations, at spaced times a reference ground station reallocates the total channel capacity of the system among the several ground stations to minimize system blocking and to thereby utilize the available system channel capacity more effectively. To increase the time between successive reallocations, channels are reallocated only when a ground station makes a channel capacity request that is greater than or equal to its corresponding present channel allocation. System blocking is minimized by using a table look-up scheme to generate excess capacity allocation factors for the stations and to thereby determine each station's proportionate share of excess system capacity. An appropriate portion of excess capacity is then added to each station's channel capacity request to provide a new channel allocation for each station. The new channel allocations are transmitted to appropriate ground stations and each station thereafter adjusts its burst duration to correspond to its new channel capacity allocation.
A frame (T) is sub-divided into identical time slots (61, 62, . . . , 6N) of fixed duration, each of which is capable of containing at least one lowest data rate telephone channel. These time slots are assigned on demand so that a new call is spread over one or more bursts (81, 82, 83, 84) which are located in available ones of said time slots, or else in space which may be left available in time slots which are already partially occupied by other, low data rate calls.
