Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Patent
1987-02-05
1988-08-09
Blum, Theodore M.
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
370104, 455 12, H04B 7185
Patent
active
047631295
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Phase application of PCT/IT86/00041 filed June 5, 1986 and based, in turn, on an Italian National Application No. 48177 filed June 6, 1985 under 35 USC 119 and the International Convention.
FIELD OF THE INVENTION
My present invention relates to satellite-switched time-division multiple-access communication systems and, more particularly to a system utilizing the RF beacon signal as a carrier for a clock-generating on-board synchronization signal and the telecommands for the switching circuitry on board the satellite.
BACKGROUND OF THE INVENTION
Within satellite telecommunication systems using simultaneously SS-TDMA (satellite-switched time-division multiple access) on-board multiple beam antennas, incoming traffic switching from each of the communication receiving beams onto each of the communications transmitting beams, is achieved through a switching matrix, whose task is to determine, in a cyclic manner, the origin-destination interconnections required by the time plan, generally synthesized at the ground station starting from the traffic requirement and its evolution, and sent to the satellite via telecommand.
In telecommunication systems which adopt SS-TDMA and multibeam antennas as well as demodulation, regeneration and demodulation techniques on board, together with digital modulation of signals, the switching matrix acts directly upon demodulated and on board regenerated binary data.
In this case, switching must be such that the significant part of the transient message through the satellite is not disturbed: in particular, state transitions within the switching matrix must take place during "guard times" between ground station emission bursts. To optimize the frame filling efficiency it is convenient to keep guard times short; therefore there must be a mutual time synchronization between the on board clock, which sets the matrix switching operation, and burst emissions toward the satellite by the ground stations.
If besides traffic switching operations on satellite, also processing of digital signals takes place, such as, for example, decoding, reformatting, change of signalling or data rate change operations, it is almost indispensable to perform these operations at the same speed for all data streams arriving to the satellite and a speed which is as close as possible to the signalling speed (symbol speed) of the digital streams arriving at the satellite.
Due to ground oscillator instability and Doppler effect induced frequency shifts in the ground to satellite path, due to satellite residual movement around its station point, data streams arriving to the satellite are asynchronous (in frequency and phase). It is therefore necessary to perform a resynchronization of these streams before proceeding with further processing.
In on board switching systems which also require fast time plan reconfiguration, or origin to destination interconnections from frame to frame, to cope with demand assignment of satellite capacity, it is necessary to send to the satellite a number of compounds for the dynamic reconfiguration of the switching matrix on the order of several thousands per second. This signalling requirement largely exceeds the satellite telecommand capability which, at the very best, is of the order of a few hundreds of bits per second. Therefore it is necessary to provide alternative systems to effect this information data transfer between ground and satellite.
Below I will discuss some of the known solutions for bit and pattern synchronization.
These two main problems (bit synchronization and pattern synchronization), arising from differing operational requirements, may be solved simultaneously if we can find a way to deliver to the satellite a very stable signal which is close (or identical) to the digital stream symbol frequencies sent to the satellite, which simultaneously: and timing circuits through successive divisions.
At least three techniques are known through which the above may be developed. However they all
REFERENCES:
patent: 4150335 (1979-04-01), Cooperman
patent: 4181886 (1980-01-01), Cooperman
patent: 4188578 (1980-02-01), Reudink et al.
National Telecommunications Conference (NTC); vol. 4, 1981, New Orleans; IEEE; Drioli et al.; "Access Technique for the ITALSAT SS-TDMA System", G2.4.1-G2.4.3.
Blum Theodore M.
Dubno Herbert
Gregory Bernarr
Ross Karl F.
Selenia Spazio Spa
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