Device and method for nodal multiple access into communications channels

1. A method for multiple access to a communications channel on a satellite comprising the steps of:

transmitting a first modulated signal from a first site to a transponder;

receiving, from the transponder, a composite signal, the composite signal comprising the first modulated signal and a second modulated signal transmitted from at least a second site;

modulating an information bit stream with a modulating signal according to a carrier of said received composite signal, comprising the steps of:

converting said composite signal into in-phase (I) and quadrature (Q) components of the second modulated signal to define a local I/Q coordinate space for signal processing at the first site, wherein said local I/Q coordinate space is determined with respect to a local oscillator reference and the carrier of the received composite signal;

determining an optimum location for the I and Q components of the modulated information bit stream according to a distance between the I and Q components of the second modulated signal and the I and Q components of the modulated information bit stream in the local I/Q space; and

modulating the information bit stream according to the optimum I/Q location and the carrier;

transmitting the modulated information bit stream.

2. The method of claim 1 , further comprising the step of:

locking the local oscillator reference to the carrier of the received composite signal.

3. The method of claim 1 , wherein said step of converting the composite signal into I and Q components of the second modulated signal comprises removing local modulation from said composite signal.

4. The method of claim 3 , wherein said step of removing local modulation from said composite signal further comprises applying a coarse synchronization process and applying a fine synchronization processes.

5. The method of claim 4 , wherein the coarse synchronization process comprises the steps of:

creating a replica of the first modulated signal; and

subtracting the replica of the first modulated signal from the composite signal.

6. The method of claim 5 , wherein said step of creating a replica of the first modulated signal comprises the steps of:

determining an estimated signal delay time at least in part from an estimated transponder-to-ground distance;

determining an estimated carrier frequency shift at least in part from a time-rate-of-change of the estimated transponder-to-ground distance; and

modifying the replica of the first modulated signal according to the estimated signal delay time and the estimated carrier frequency drift.

7. The method of claim 4 , wherein said fine synchronization process comprises applying an early/late delay locked loop.

8. The method of claim 1 , wherein said step of transmitting the modulated information bit stream comprises the steps of:

determining an estimated of signal delay time at least in part from an estimated transponder-to-ground distance;

determining an estimated carrier frequency shift at least in part from a time-rate-of- change of said the estimated transponder-to-ground distance; and

modifying the modulated information bit stream according to the estimated signal delay time and the estimated carrier frequency drift; and

transmitting the modified modulated information bit stream.

9. The method of claim 8 , wherein the transponder-to-ground distance is estimated at least in part from orbital parameters of the transponder.

10. The method of claim 1 , wherein the first modulated signal is modulated according to a first site carrier signal and the method further comprises the steps of:

receiving said first modulated signal at said at least a second site;

obtaining a frequency of the first site carrier signal; and

wherein the second modulated signal transmitted from the second site is generated according to a second site carrier signal generated at least in part according to the frequency of the first site carrier signal.

11. The method of claim 10 , further comprising the step of tracking carrier frequency errors between the first site carrier signal and the second site carrier signal using a phase locked loop.

12. A method for multiple access to a communications channel on a satellite comprising the steps of:

transmitting a first modulated signal from a first site to a transponder;

receiving, from the transponder, a composite signal, the composite signal comprising the first modulated signal and a second modulated signal transmitted from at least a second site;

modulating an information bit stream according to a recovered carrier of the received composite signal;

transmitting an outgoing signal having the modulated information bit stream from the first site;

wherein the step of modulating the information bit stream according to the recovered carrier of the composite signal comprises the steps of:

creating a replica of said outgoing signal, comprising the steps of:

determining an estimate of signal delay time from a distance from the transponder to the first site;

determining an estimate of a composite signal carrier frequency shift from a time-rate-of-change of the distance from the transponder to the first site; and

using said estimate of the signal delay time and the composite signal carrier frequency shift to modify an archive of the outgoing signal and define said replica of the outgoing signal; and

subtracting said replica of the outgoing signal from said composite signal to produce a difference signal;

recovering the carrier of the received composite signal using the difference signal.

13. The method of claim 12 , further comprising the step of:

using the difference signal as a local carrier reference for frequency and phase reference at the first site.

14. The method of claim 13 , wherein the modulated information bit stream comprises I components and Q components, and the step of modulating the information bit stream according to the recovered carrier of the composite signal further comprises the steps of:

converting the difference signal into in-phase (I) and quadrature (Q) components to define a local I/Q coordinate space for signal processing at the first site;

determining an optimum location for I components and Q components of the modulated information bit stream by maximizing a distance between the I and Q components of the difference signal and the I and Q components of the modulated information bit stream.

15. The method of claim 12 , wherein said step of recovering the carrier of said composite signal further comprises removing local modulation from said composite signal.

16. The method of claim 15 , wherein said step of removing local modulation from said composite signal further comprises applying coarse and fine synchronization processes.

17. The method of claim 12 , further comprising the step of applying a fine tracking loop for tracking differences between the replica signal and the composite signal.

18. The method of claim 17 , wherein said fine tracking loop further comprises an early/late delay locked loop.

19. The method of claim 12 , wherein the transmitted outgoing signal further is compensated to remove the effects of a changing geometry from the transponder and the first site.

20. The method of claim 19 , wherein the compensation uses orbital parameters of the transponder and geometric data to compensate said transmitted outgoing signal.

21. The method of claim 12 , further comprising the steps of:

receiving the first modulated signal at said at least a second site; and

obtaining a carrier frequency of the first modulated signal;

wherein the second modulated signal transmitted from the second site is generated according to a second site carrier signal generated at least in part according to the carrier frequency of the first modulated signal.

22. The method of claim 21 , further comprising the step of tracking carrier frequency errors between the carrier frequency of the first modulated signal and second site carrier signal using a phase locked loop.

23. The method of claim 1 , wherein the optimum location for the I and Q components of the modulated bit stream maximizes the distance between the I and Q components of the second modulated signal and the I and Q components of the modulated bit stream in the local I/Q space.

24. The method of claim 23 , wherein the composite signal comprises a plurality of second modulated signals, each having an I and Q component defined in the local I/Q coordinate space, and the optimum location for the I and Q components of the modulated bit stream maximizes the distance between the I and Q components of the plurality of second modulated signal and the I and Q components of the modulated bit stream in the local I/Q space.