Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1998-07-30
2001-06-19
Patel, Ajit (Department: 2138)
Multiplex communications
Communication over free space
Repeater
C370S319000, C370S486000, C348S086000, C455S003010, C455S012100
Reexamination Certificate
active
06249514
ABSTRACT:
BACKGROUND
The invention relates to the field of satellite direct radio broadcast, and in particular to a satellite-based broadcast communication system employing frequency division multiplex uplinks and time division multiplex downlinks and for broadcasting and audio (voice and music) programming.
Early satellite communication systems used space-based radio frequency transponders which acted as simple repeaters. In one typical scheme, multiple sources each transmit at a separate uplink carrier center frequency (uplink FDMA), and the satellite transponder repeated each signal at a separate downlink carrier frequency (downlink FDMA). In another typical scheme, multiple sources each transmit bursts at the same carrier frequency in a coordinated fashion so that bursts from different transmitters do not collide (TDMA), and the transponder repeated all signals in a single downlink carrier. Still other schemes utilize multiple antenna beams and on-board-the-satellite switching so that signals in one uplink beam could be controllably switched to a selected downlink beam.
Many prior systems require substantial transmit and/or receive equipment. Furthermore, despite the various types of system architectures, there has not been implemented a system suitable for direct broadcast of audio radio programming to low-cost consumer radio receivers.
SUMMARY
There presently exists a population of over 4 billion people that are generally dissatisfied and undeserved by the poor sound quality of short-wave radio or the coverage limitations of amplitude modulation (“AM”) band and frequency modulation (“FM”) band terrestrial radio broadcast system. This population is primarily located in Africa, Central and South America, and Asia. The satellite Direct Audio Broadcast (“DAB”) system of the present invention is intended to provide high quality radio channels accessible to people worldwide who currently receive, with various kinds of limitations, terrestrial radio programming.
An object of the present invention is to provide a satellite direct radio audio broadcast system suitable for transmitting audio signals, such as voice and music programming, to low-cost consumer radio receivers.
A further object of the present invention is to provide a satellite direct audio broadcast system suitable for transmitting multiple audio signals from a variety of sources and signal qualities, such as “AM” band quality monaural, “FM” band quality stereo, and “CD” quality stereo to low-cost consumer radio receivers.
A further object of the present invention is to provide a satellite direct audio broadcast system capable of providing individual uplink broadcasters with direct access to the satellite, yet also capable of preventing unauthorized broadcasts from being received by consumer radios.
A further object of the invention is to provide a satellite direct audio broadcast system capable of providing subscription (paid reception) service by low-cost consumer radio receivers yet also capable of limiting service to non-subscription receivers in the same service area.
These and other objects of the invention are achieved by providing a satellite direct audio broadcasting system having frequency division multiple access uplinks (FDMA) and time division multiplexed (TDM) downlinks. Broadcast stations transmit one or more “prime rate” channels, each having a source signal data rate of sixteen (16) kilobit-per-second (kbps) data rates. Each prime rate channel is transmitted on a separate carrier. At the satellite, prime rate uplink channels are multiplexed into a single TDM channel. Radio receivers demultiplex the TDM downlink and recombine one or more prime rate channels to provide the selected quality of service. A system control center provides centralized command over the satellite.
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Patel Ajit
Roylance Abrams Berdo & Goodman L.L.P.
WorldSpace International Network, Inc.
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