Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
1997-10-06
2001-05-01
Urban, Edward F. (Department: 2772)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C370S316000, C370S320000
Reexamination Certificate
active
06226491
ABSTRACT:
TECHNICAL FIELD
The present invention relates to multiple access satellite communications systems, and more particularly to inhibiting unauthorized access to such systems.
BACKGROUND ART
In general, the evolution of satellite system designs which allow for use of small, low cost earth stations has significantly increased the opportunity for an unauthorized, or “pirate” operator, to gain access to a communications satellite transponder. This is particularly true for conventional “bent pipe” pseudo-linear transponders.
More specifically, as shown in
FIG. 1
, a conventional bent pipe repeater
10
receives individual carriers transmitted by authorized earth stations via antenna system
12
. The received signals are processed in a signal processing subsystem
13
, wherein the carriers are amplified by a low noise amplifier
14
and then frequency translated, as a group, to the desired down link frequency via a mixer or translator
16
. A local oscillator
18
is required for the frequency translation and is fixed in frequency and normally crystal controlled. The frequency translated spectrum is then demultiplexed in demux
20
into frequency passband channels. Each channel is applied to the appropriate channel conditioning circuits
22
, and high power amplifiers
24
. The outputs of the high power amplifiers are then recombined, using a frequency multiplexing technique in mux
26
, and applied to the transmit antenna system
28
where they are radiated to the appropriate earth terminals. In such a conventional repeater, each carrier transmitted from the satellite is an exact amplified replica of the carrier received.
Past approaches to preventing unauthorized access to such repeaters have required inclusion of specialized on-board circuitry for demodulating, remodulating, signal processing, and signal switching. However, the addition of such on-board circuitry has not proven satisfactory because of a concomitant increase in system complexity and cost, as well as undesirably increasing payload size and weight of the satellite.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide an improved method and system for restricting access to a multiple-access satellite communication transponder to prohibit unauthorized users from gaining access thereof.
It is another object of the present invention to provide an improved method and system for inhibiting unauthorized access to a multiple-access satellite communication transponder which does not significantly increase payload size and weight.
It is yet another object of the present invention to provide a method and system for inhibiting unauthorized access to a multiple-access satellite communication transponder which utilizes pseudo-random modulation in the satellite transponder to prevent proper reception by unauthorized earth terminals.
In accordance with these and other objects, the present invention provides a system for inhibiting unauthorized access to a multiple-access satellite communication transponder comprising a receiving antenna subsystem located in the satellite repeater, a first pseudo-random noise generator located in the satellite repeater, and a mixer having a local oscillator connected to the first pseudo-random noise generator. The local oscillator is frequency modulated about a nominal frequency with a waveform generated by the first pseudo-random noise generator. A second pseudo-random noise generator located in each authorized user terminal is used to frequency modulate the transmitted carrier with an inverse of the pseudo-random waveform in addition to its normal baseband modulation. A controller is provided for synchronizing the first and second pseudo-random noise generators.
In accordance with another aspect of the present invention, a method is provided for restricting access to a satellite repeater having a receiving antenna subsystem connected to a signal processing subsystem, wherein the method comprises the steps of generating a pseudo-random noise signal in the satellite signal processing subsystem, synchronizing the pseudo-random noise signal with an inverse of the generated pseudo-random signal, and modulating a carrier signal in the authorized user terminal with the inverse pseudo-random signal. All carrier signals received at the satellite repeater are modulated with the generated pseudo-random signal.
Thus, in accordance with the present invention, frequency translation by the satellite transponder automatically removes the pseudo-random frequency modulation from authorized communications carriers. The removal of this frequency modulation reduces the rf bandwidth of each carrier to that required by its respective communications modulation. An unauthorized carrier attempting to access the satellite will not have the inverse pseudo-random frequency modulation. Thus, frequency translation by the satellite transponder for unauthorized carriers will impart the pseudo-random modulation on these carriers thereby increasing their rf bandwidth.
These and other features, aspects, and embodiments of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.
REFERENCES:
patent: 5303286 (1994-04-01), Wiedeman
patent: 5748669 (1998-05-01), Yada
patent: 5793795 (1998-08-01), Li
Dixon, Robert C., Spread Spectrum Systems With Commercial Applications, p. 32, 1994.
Berman Arnold L.
Wachs Marvin R.
Duraiswamy Vijayalakshmi D.
Hughes Electronics Corporation
Sales Michael W.
Santiago Enrique L.
Urban Edward F.
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