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Primary Examiner: Brown, Thomas W.
Assistant Examiner:
Attorney: Gurey; Stephen M.

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Title: Digital satellite system and method for serving users of differing capacities

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Claims: What is claimed is:

1. A multibeam digital time-division switched satellite communications system comprising:

a plurality of ground stations each of which transmits an RF signal upon which is modulated an uplink digital bitstream containing data directed to each ground station and each of which receives an RF signal upon which is modulated a downlink digital bitstream containing information directed from each ground station; and

a remote satellite for receiving and transmitting the modulated RF signals from and to each ground station, respectively, said satellite comprising switching means for switching the data in each RF signal transmitted from each ground station to the appropriate RF signal transmitted from said satellite to the ground station to which the data is directed

Characterized in that

the capacity of each ground station is quantized into an integral unit;

the bit repetition rate of each uplink and downlink bitstream to and from each ground station is proportional to the quantized capacity of that station;

said satellite further comprises means for demodulating each received RF signal to recover the uplink bitstream transmitted by each ground station, means provided for each ground station for demultiplexing the recovered uplink bitstream to form a predetermined number of parallel bitstreams at the input to said switching means, said predetermined number of parallel bitstreams being equal to the quantized capacity associated with that ground station, said uplink bitstreams being bit interleaved so that in each set of bits that simultaneously enter said switching means from all ground stations the total number of bits directed to any particular ground station equals the quantized capacity of that particular ground station, for each ground station means for multiplexing at the output of said switching means the predetermined number of bitstreams containing information directed to that ground station to form the downlink bitstream, said predetermined number being equal to the quantized capacity associated with that ground station, and means for modulating each downlink bitstream onto an RF signal for transmission to the associated ground station.

2. A multibeam digital time-division switched satellite communications system in accordance with claim 1 further characterized in in that the integral units into which the capacities of the ground stations are quantized are related in accordance with the powers of 2.

3. A multibeam digital time-division switched satellite communications system in accordance with claim 1 further characterized in that said satellite further comprises:

clocking means for generating a plurality of clocking signals, the clock rate of each generated clocking signal being at one of the repetition rates of said uplink bitstreams, said means for demultiplexing for each ground station and said means for multiplexing for each ground station being responsive to the clocking signal at the clock rate associated with that ground station, and

controlling means responsive to said clocking means for cyclically switching the input/output interconnections of said switching means in a predetermined manner.

4. A multibeam digital time-division switched satellite communications system in accordance with claim 3 further characterized in that said satellite further comprises means provided for each ground station for comparing the phase of the recovered uplink bitstream with the phase of the associated clocking signal to produce a digital indicator of the comparison at an input to said switching means, each digital indicator produced being periodically transferred to the output of said switching means for transmission to the associated ground station.

5. A multibeam digital time-division switched satellite communications system in accordance with claim 4 further characterized in that said satellite further comprises means for periodically transmitting a preselected digital word to each ground station that indicates the end of a digital frame comprising a predetermined number of bits.

6. In a multibeam digital time-division switched satellite system including a plurality of ground stations and a remote satellite repeater, each ground station transmitting to said satellite repeater an RF signal modulated by an uplink digital bitstream which includes information directed to each ground station, and each ground station receiving from said satellite an RF signal modulated by a downlink digital bitstream which includes information directed from each ground station, the remote satellite repeater comprising switching means for switching the information in each uplink bitstream to the appropriate downlink bitstream for transmission to the ground station to which it is directed, a method for efficiently communicating digital information between ground stations through said remote satellite repeater when the quantity of information transmitted to and from a ground station is non-uniform for all ground stations, comprising the steps of:

quantizing the capacity of each ground station into an integral unit;

choosing the bit repetition rate of each uplink/downlink bitstream to and from each ground station to be proportional to the quantized capacity of that ground station;

at the remote satellite repeater demodulating each received RF signal to recover the uplink bitstream transmitted by each ground station;

for each ground station demultiplexing the recovered uplink bitstream to form a predetermined number of parallel bitstreams at the input to said switching means, said predetermined number of parallel bitstreams being equal to the quantized capacity associated with that ground station, said uplink bitstreams being bit interleaved so that in each set of bits that simultaneously enter said switching means from all ground stations the total number of bits directed to any particular ground station equals the quantized capacity of that particular ground station;

for each ground station multiplexing at the output of said switching means the predetermined number of bitstreams containing information directed to that ground station to form the downlink bitstream, said predetermined number being equal to the quantized capacity associated with that ground station; and

modulating each downlink bitstream onto an RF signal for transmission to the associated ground station.

7. The method according to claim 6 wherein the integral units into which the capacities of the ground stations are quantized are related in accordance with the powers of 2.

8. The method according to claim 6 comprising the further steps of:

at the remote satellite repeater comparing for each ground station the phase of the recovered uplink bitstream with the phase of a clock signal generated internal to the satellite and having a clock rate equal to the rate of the uplink bitstream;

generating a digital indicator of each comparison; and

periodically transmitting the generated digital indicator to the ground station to which it is associated.

9. The method according to claim 8 comprising the further step of:

periodically transmitting a preselected digital word to each ground station to indicate the end of a digital frame that comprises a predetermined number of bits.

10. In a multibeam digital time-division switched radio communication system including N ground stations and a remote satellite repeater, each ground station transmitting to said remote satellite repeater an RF signal modulated by an uplink digital bitstream which includes information directed to each of the N ground stations, and each ground station receiving from said remote satellite repeater an RF signal modulated by a downlink digital bitstream which includes information directed from each of the N ground stations, the remote satellite repeater comprising switching means for switching the information in each uplink bitstream to the appropriate downlink bitstream for transmission to the ground station to which it is directed; a method for efficiently communicating digital information between ground stations through said remote satellite repeater when the quantity of information transmitted to and from each ground station is non-uniform, comprising the steps of:

quantizing the channel capacities of the N ground stations into integral units of capacity C.sub.1, . . . C.sub.k, . . . C.sub.N where C.sub.k is the quantized capacity of the k.sup.th ground station and C.sub.1 is the quantized capacity of the lowest capacity station 1, for each k the bit repetition rate on the uplink and downlink signals from and to ground station k being chosen to be proportional to C.sub.k, for each k the digital bitstreams from and to ground station k being divided into frames which comprise a total number of information bits proportional by an integral factor to C.sub.k (C.sub.1 + . . . +C.sub.N) where in each uplink frame from ground station k the number of information bits directed to a ground station j is equal to C.sub.k C.sub.j times said integral factor, and for each k all uplink frames being bit interleaved so that during each interval of time equal to C.sub.1 times the bit repetition rate of ground station 1 the total number of bits directed to ground station k from all ground stations is equal to C.sub.k ; and

at the repeater, demodulating each received RF signal to recover the uplink bitstreams transmitted from each ground station;

for each k demultiplexing the uplink bitstream from ground station k to form C.sub.k parallel bitstreams having the same bit repetition rate;

for each k multiplexing at the output of said switchng means C.sub.k parallel bits directed to station k at said same rate to form a downlink bitstream at the bit repetition rate for station k; and

for each k modulating the downlink bitstream to station k onto an RF signal for transmission to ground station k.

11. The method according to claim 10 wherein the quantized capacities C.sub.1, . . . C.sub.k, . . . , C.sub.N are related in accordance with the powers of 2.

Other info:

Inventors: Arnold, Hamilton W. (Tinton Falls, NJ, US)

Application Number: 805711
Filing Date: 1977-06-13
Publication_date: 1979-03-20
Assignee: Bell Telephone Laboratories, Incorporated (Murray Hill, NJ)
Primary Class(es): 370/323 370/324, 455/13.2, 455/13.3
Other Classes:
US Patent Ref:

3535450	Oct, 1970	Vollmeyer	178/50.
3546386	Dec, 1970	Darcey	325/4.
3694580	Sep, 1972	Inose et al.	179/15.
3749839	Jul, 1973	Fornasiero et al.	179/15.
3789142	Jan, 1974	Shimasaki et al.	179/15.
3862373	Jan, 1975	Cohen et al.	179/15.
3958083	May, 1976	Hara et al.	179/15.
3982074	Sep, 1976	Clark	179/15.

Other Refs: Other References: "Satellite Capacity Allocation", AEIN et al., Proceedings of the IEEE, vol. 65, No. 3, Mar. 1977, pp. 332-342.