Abstract: A communications system (100) has at least one TDD platform pair (130, 200) operating synchronously using a Time Division Duplex (TDD) frame structure. A TDD platform pair (130, 200) has first communications platform (124) and second communications platform (126) that are coupled (135) together. First communications platform (124) transmits first data during a first frame and receives second data during a second frame. Second communications platform (126) receives third data during the first frame and transmits fourth data during the second frame. At least one TDDSU (110) receives the first data, transmits the second data, transmits the third data, and receive the fourth data. First communications platform (124) has a first coverage area, and the second communications platform (126) has a second coverage area. A dual coverage area exists where the first coverage region overlaps the second coverage region. At least one TDDSU (110) is located within the dual coverage region.

Abstract: In a communications system, an earth-based subscriber unit (40, FIG. 1) receives at least one communications beam (50, 60, FIG. 1) transmitted from one or more moving satellite communications nodes (10, 20). The earthbased subscriber unit evaluates which communications beam should be selected based on the power received (FIG. 2, 210), Doppler frequency shift (270), link quality, (290), interference level (300), and satellite and network specific parameters (310). By considering these factors, the earth-based subscriber unit selects the communications beam (50, 60) that will provide the optimum service and reduce the likelihood that an inter-satellite hand over of the call will be required while the call is in progress.

Abstract: In a code division multiplexed system, a subscriber unit (260, FIG. 1), which includes a pseudonoise code generator (70), is synchronized with the pseudonoise code generator (220) of a communications node (200). Synchronization between the pseudonoise code generators (70, 220) is achieved through measuring the time delay of a signal transmitted from the communications node (200) to the subscriber unit (260) and advancing the code generator of the subscriber unit in accordance with the time delay. This permits transmissions from the subscriber unit (260) to be received synchronously at the satellite. The synchronization is maintained through the periodic transmission from the communications node (200) to the subscriber unit (260) of a message which commands the subscriber unit (260) to adjust the timing of its pseudonoise code generator. The resulting synchronous code division multiplexed system offers increased capacity over conventional systems.

Abstract: A communications network is capable of using time division multiple access (TDMA) techniques, code division multiple access (CDMA) techniques, or a combination of both. A subscriber unit (30) makes a request for a traffic channel over a CDMA pilot channel or a TDMA broadcast channel. A satellite (20) or a base station (40) receives the request and determines whether to assign a TDMA or CDMA traffic channel. The downlink and uplink can have the same access scheme (e.g., TDMA) or different access schemes (e.g., TDMA on the uplink and CDMA on the downlink).

Abstract: In a satellite communications system (100), system capacity is improved using a satellite (110 and 120) that includes a main mission antenna (MMA) (310 FIG. 3), antenna subsystem (320), and controller (350). Antenna subsystem (320) comprises a beamformer and associated software to optimize the beam shape and cell position with respect to the satellite's location. In one example, beam optimization is performed using a location based on latitude. Satellite (110 and 120) determines its spatial position and determines its latitudinal location based on this position information. The satellite determines the number of cells, the cell sizes, and the beam steering angles required at this latitudinal location. In other cases, beam optimization is performed using a location based on latitude and longitude, system loading, and satellite health and status.

Abstract: With a constellation of low-earth orbiting satellites, instantaneous photographs of all large cities can be made available in real-time or near real-time. Those photographs can be downloaded to ground stations, and there photographically interpreted to determine traffic conditions. The use of high and low photographic resolution permit making distinctions between different causes of traffic conditions. A color-coded map may be generated showing all major roads and their current status, showing such conditions as light traffic, medium traffic, heavy traffic and traffic accidents or jams, for example. These color-coded maps or color-coded alphabetized lists of streets may be broadcast to subscribers (broadcast stations, companies or individuals). From the color-coded traffic report, the subscribers are updated about which routes to avoid and what the best detours are around the more congested areas.