Patent EA-001820-B1 (EA)
Title: Direct satellite direct broadcast system
Inventor: CAMPANELLA S JOSEPH
IPC: H04B/
Filed: 1997-10-31
Abstract: 1. A receiver unit for receiving a time division multiplexed downlink data stream from a satellite comprising: a phase shift keying demodulator for demodulating said downlink data stream into a stream of symbols, said downlink data stream comprising time slots and being provided with a predetermined number of prime rate channels in respective ones of said slots by said satellite; a correlator connected to said demodulator for locating and synchronizing to a master frame preamble inserted in said stream of symbols by said satellite, said correlator being configured to store a master frame correlation pattern corresponding to said master frame preamble and programmable to operate in one of a search mode and a synchronized operation mode; a demultiplexer connected to said correlator for locating a time slot control channel in said stream of symbols, said time slot control channel being inserted into said stream of symbols by said satellite to identify which of said slots comprises said prime rate channels corresponding to each of a plurality of broadcast service providers; and an input device configured to allow an operator to select one of said broadcast service providers and operable to provide an output signal to said demultiplexer, said demultiplexer being operable to extract selected ones of said prime rate channels using said time slot control channel and output signal; wherein said correlator is configured to operate in a predictive mode employing one of a time gate and an aperture limitation corresponding to a predicted time interval for the next correlation event at an output of said correlator when said correlator detects said master frame correlation pattern, and to operate in a search mode without employing either of said time gate and said aperture limitation when said master frame correlation pattern is not detected. 2. A receiver unit as claimed in claim 1, wherein said correlator is configured to operate in a synchronization mode when said master frame correlation pattern is detected for a predetermined minimum number of consecutive time frames of said downlink data stream, and to operate in a predictive mode when said master frame correlation pattern is not detected while operating in said synchronization mode, said correlator maintaining operation in said synchronization mode using a predicted time interval for determining another said master frame correlation pattern. 3. A receiver unit as claimed in claim, wherein said correlator is configured to return to operating in said search mode when said master frame correlation pattern is not detected for a predetermined minimum number of consecutive time frames of said downlink data stream during said predictive mode. 4. A receiver unit for receiving a time division multiplexed downlink data stream from a satellite comprising: a demodulator for demodulating said downlink data stream into a stream of symbols, said downlink data stream comprising time slots having a plurality of time slot locations and being provided with a predetermined number of prime rate channels by said satellite, said prime rate channels each comprising a plurality of symbols, each of said plurality of symbols being assigned, respectively, to said time slots to spread said plurality of symbols corresponding to each of said prime rate channels over said downlink data stream, said plurality of symbols for each of said prime rate channels being assigned to the corresponding one of said plurality of time slot locations in each of said time slots; a demultiplexer connected to said demodulator for locating a time slot control channel inserted into said stream of symbols by said satellite to identify which of said plurality of time slot locations comprises said plurality of symbols of at least one of said prime rate channels corresponding to a selected broadcast service provider; an extraction device for extracting said plurality of symbols corresponding to said at least one prime rate channel of said selected broadcast service provider from said stream of symbols in accordance with said time slot control channel; and a multiplexer for multiplexing said plurality of symbols corresponding to said selected broadcast service provider into a serial broadcast channel data stream. 5. A receiver unit as claimed in claim 4, wherein said broadcast service provider uses a plurality of said prime rate channels, and further comprising a realignment device connected to said extraction device and configured to align said plurality of said prime rate channels with respect to each other. 6. A receiver circuit as claimed in claim 5, wherein each of said prime rate channels comprises a header and said realignment device comprises: a buffer for each of said plurality of said prime rate channels; and a correlator connected to said buffer and configured to determine the instant of arrival of said header of a corresponding one of said prime rate channels and to commence writing of said prime rate channel into said buffer, said buffer for each of said plurality of said prime rate channels being read from after the instant of arrival of said header corresponding to the last of said prime rate channels is detected to generate said serial broadcast channel data stream. 7. A method of recovering at least one prime rate channel from among several prime rate channels transmitted in a time division multiplexed downlink data stream from a satellite comprising the steps of: demodulating said downlink data stream into a stream of symbols, said downlink data stream comprising time slots having a plurality of time slot locations and being provided with a predetermined number of prime rate channels by said satellite, said prime rate channels each comprising a plurality of symbols, each of said plurality of symbols being assigned, respectively, to said time slots to spread said plurality of symbols corresponding to each of said prime rate channels over said downlink data stream, said plurality of symbols for each of said prime rate channels being assigned to the corresponding one of said plurality of time slot locations in each of said time slots; demultiplexing said stream of symbols to locate a time slot control channel inserted therein by said satellite to identify which of said plurality of time slot locations comprises said plurality of symbols of at least one of said prime rate channels corresponding to a selected broadcast service provider; extracting said plurality of symbols corresponding to said at least one prime rate channel of said selected broadcast service provider from said stream of symbols in accordance with said time slot control channel; and multiplexing said plurality of symbols corresponding to said selected broadcast service provider into a serial broadcast channel data stream. 8. A method as claimed in claim 7, wherein said broadcast service provider uses a plurality of said prime rate channels, and further comprising the step of aligning said plurality of said prime rate channels with respect to each other prior to multiplexing said plurality of symbols corresponding to said plurality of prime rate channels. 9. A method as claimed in claim 8, wherein each of said prime rate channels comprises a header and said aligning step comprises the steps of: writing each of said plurality of said prime rate channels into respective buffers upon determination of the respective instances of arrival of said headers; and reading from said buffers upon determination of the last of said instances of arrival. 10. A method of receiving one of a plurality of broadcast channels transmitted via downlink signals comprising prime rate channels from a satellite comprising the steps of: demodulating said downlink signals into a baseband time division multiplexed bit stream comprising frames generated by said satellite, each of said frames comprising a plurality of time slots, each of said time slots comprising a set of symbols, each symbol in said set of symbols corresponding to a respective one of said prime rate channels occupying a similar symbol position in each of said time slots; locating said frames in said bit stream using a master frame preamble inserted in said bit stream by said satellite; retrieving from said set of symbols in each of said time slots of at least one of said frames the symbols that correspond to at least one of said prime rate channels; remultiplexing said symbols corresponding to said at least one of said prime rate channels to recover a broadcast channel corresponding thereto and as originally transmitted to said satellite; and extracting a service control header from said broadcast channel. 11. A method as claimed in claim 10, wherein said retrieving step comprises the steps of: locating a time slot control channel inserted in said bit stream by said satellite, said control channel  indicating which of said time slots contain said symbols corresponding to each of said prime rate channels; and extracting said symbols corresponding to one of said prime rate channels selected by using said control channel. 12. The method as claimed in claim 10, further comprising the step of determining if said service control header comprises an identification code inserted in said broadcast channel by a broadcast station prior to transmission to said satellite for uniquely addressing a radio receiver. 13. The method as claimed in claim 10, further comprising the steps of: determining if said service control header comprises control data; and operating a radio receiver to perform at least one of a plurality of functions depending on said control data, said plurality of functions comprising operating said radio receiver in a selected reception mode to provide a selected multimedia service, to display data, to display an image, and to decrypt data using a decryption key provided in said service control header. 14. A receiver unit for receiving a time division multiplexed downlink data stream from a satellite comp