Technique for increasing the rain margin of a satellite communication system

In a TDMA satellite communication system comprising a satellite and a plurality of remote, spaced-apart, ground stations that communicate with one another via the satellite using message bursts in assigned time slots of a frame sequence and one of the ground stations transmits a frame marker unique word to each of the ground stations once during each frame sequence, a receiver capable of receiving one or more associated message bursts during a frame sequence where each message burst includes a preamble and a data information section, the receiver comprising:

• an input capable of receiving the associated message bursts from the satellite;
• and
• means (60) capable of generating from a portion of the preamble information and the remainder of the burst a recovered clock and carrier signal;
• a demodulating means (71) capable of demodulating the received message bursts using the carrier signal recovered by the clock and carrier recovery means;
• a bit detection means (70) capable of detecting the instantaneous value of each bit of a received burst in response to each pulse of the recovered clock signal from the clock and carrier recovery means;
• a frame synchronization circuit (74) coupled to the output of the bit detection means and capable of detecting the frame marker unique word in a received bit stream and for regenerating a frame marker signal in synchronism with the normal arrival of each frame marker unique word;
• and
• a processor (78) capable of detecting the start of a message burst associated with the receiver and for properly formatting the received message burst information for transmission to a utilization circuit
• CHARACTERIZED IN THAT
• an associated message burst can comprise either one of a first form comprising the preamble and data information section transmitted in one time slot of the frame sequence under conditions where the fade encountered by the transmitted message burst will not exceed a predetermined system power margin, and a second form comprising a preamble section including an extended field portion and a redundancy encoded portion and a redundancy encoded data information section transmitted in a plurality of time slots of the frame sequence under conditions where the transmitted message burst is expected to experience a fade exceeding a predetermined system power margin, the receiver further comprising:
• a switch controller (62) capable of both generating a first control signal during the period of a received message burst comprising said first form and generating a second control signal during the period of a received message burst comprising said second form;
• and
• a receive timing controller (73) capable of generating proper timing signals to the processor to enable the processor to operate on each associated message burst;
• and
• the carrier and clock recovery means (60) comprises means capable of selectively generating the recovered clock and carrier signals from a received message burst comprising either one of said first and second form in response to a first and second control signal, respectively, from said switch controller;
• and
• the processor (78) comprises means capable of selectively detecting the start of a message burst comprising either one of said first and second form in response to the first and second control signal, respectively, to enable the proper processing and formatting of the information contained in each received associated message burst.

In a TDMA satellite communication system comprising a satellite and a plurality of remote, spaced-apart, ground stations which communicate with one another via the satellite using message bursts comprising a preamble section and a data information section in assigned time slots of a frame sequence, a method of increasing the rain margin in transmission between two ground stations of the system when at least one of the two ground stations is experiencing a fade condition above a normal power margin of the system, the method comprising the step of:

• (a) at a transmitting ground station, transmitting the preamble and data information sections of each message burst destined for a remote receiving ground station in a normally assigned time slot of the frame sequence under conditions where no fade condition is beingexperienced at the transmitting and receiving ground station
• CHARACTERIZED IN THAT
• the method comprises the further step of:
• (b) transmitting the preamble and data information sections of each message burst destined for a remote receiving ground station over a plurality of time slots of the frame sequence where portions of the preamble section related to information for enabling the processing of each message burst at the receiving ground station are transmitted using extended fields and the remaining portion of the preamble section and the data information section are transmitted in a redundancy encoded form under conditions where a fade condition is experienced above the normal power margin of the system at at least one of the transmitting and receiving ground stations.