Method and system for soft decision propagation

• US 6,343,210 B1
• Filed: 03/22/1999
• Issued: 01/29/2002
• Est. Priority Date: 03/22/1999
• Status: Expired due to Term

• Current Assignee: CDC Propriete Intellectuelle
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Emmons, Thomas Peter Jr., Peters, Robert Anthony, Startup, James W.
• Primary Examiner(s): Chang, Vivian
• Assistant Examiner(s): RAMOS FELICIANO, ELISEO
• Application Number:
  US09/274,023
• Time in Patent Office: 1,044 Days
• Field of Search: 455/12.1, 455/13-- 1, 455/226.3, 455/226.2, 455/427, 455/430, 455/504, 455/506, 455/134, 455/137, 455/67.1, 455/101, 455/522, 375/227, 375/261-262, 375/341, 375/347, 375/267, 370/206, 370/316-318
• US Class Current: 455/226.3
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04L 1/0001 Systems modifying transmission characteristics according to link quality, e.g. power backoff adaptive data allocation for multicarrier modulation H04L5/0044; controlling transmission power for radio systems H04W52/04
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/02 by diversity reception
• CPC Class Codes: H04L 2001/0097 Relays
• CPC Class Codes: H04L 25/20 Repeater circuits; Relay circuits

Abstract

A method and apparatus for soft decision propagation trades off system bandwidth in return for link margin. When signal quality on an uplink is low, a satellite (20) sends soft decision data, rather than hard decision data, to a gateway (40). When path diversity exists on the uplinks, and multiple satellites (20) receive the uplink, multiple versions of soft decision data are sent to the gateway (40). The gateway combines the soft decision data resulting from multiple uplink paths, thereby increasing the effective uplink signal to noise ratio.

Claims

1. A method of operating a communications node, said method comprising the steps of:

receiving a signal having a signal to noise ratio;

comparing the signal to noise ratio to a first threshold; and

when the signal to noise ratio is above the first threshold, quantizing the signal to generate soft decisions, decoding the soft decisions to generate hard decisions, and transmitting the hard decisions, the step of quantizing comprising quantizing an in-phase component of the signal; and

quantizing a quadrature component of the signal.

2. A method of operating a communications node, the method comprising the steps of:

receiving a signal having a signal to noise ratio;

comparing the signal to noise ratio to a first threshold;

when the signal to noise ratio is above the first threshold, quantizing the signal to generate soft decisions, decoding the soft decisions to generate hard decisions, and transmitting the hard decisions;

when the signal to noise ratio is below the first threshold, quantizing the signal to generate soft decisions, and transmitting the soft decisions;

receiving a communication from a second communications node which has also received the signal; and

responsive to the communication, refraining from transmitting either hard or soft decisions.

3. The method of claim 2 wherein the first communications node and the second communications node are satellites.

4. The method of claim 2 wherein the first communications node and the second communications node are terrestrial transceivers.

5. A method of operating a communications node, the method comprising the steps of:

receiving a signal having a signal to noise ratio;

comparing the signal to noise ratio to a first threshold;

when the signal to noise ratio is above the first threshold, quantizing the signal to generate soft decisions, decoding the soft decisions to generate hard decisions, and transmitting the hard decisions;

comparing the signal to noise ratio to a second threshold, wherein said first threshold is greater than said second threshold;

when the signal to noise ratio is less than the second threshold, refraining from transmitting either hard or soft decisions;

when the signal to noise ratio is between the first threshold and the second threshold, quantizing the signal to generate soft decisions, and transmitting the soft decisions;

receiving a communication from a second communications node which has also received the signal; and

responsive to the communication, refraining from transmitting either hard or soft decisions.

6. The method of claim 5 wherein the step of quantizing comprises the steps of:

quantizing an in-phase component of the signal; and

quantizing a quadrature component of the signal.

7. The method of claim 5 wherein the first communications node and the second communications node are satellites.

8. The method of claim 5 wherein the first communications node and the second communications node are terrestrial transceivers.

9. A method of operating a gateway in a satellite communications system, said method comprising the steps of:

receiving a first signal transmitted from a first satellite;

receiving a second signal transmitted from a second satellite;

when the first signal and the second signal include soft decision data, combining the first and second signals, thereby generating a combined signal with an increased signal to noise ratio; and

when the first signal and the second signal include hard decisions data, notifying tie second satellite that the second signal need not be transmitted, thereby reducing the use of bandwidth.

10. A method of operating a gateway in a satellite communications system, said method comprising the step of:

receiving a first signal transmitted from a first satellite;

receiving a second signal transmitted from a second satellite;

when the first signal and the second signal include soft decision data, combining the first and second signals, thereby generating a combined signal with an increased signal to noise ratio;

when the first signal and the second signal include hard decision data, comparing a signal quality of the first signal and a signal quality of the second signal; and

discarding one of the first signal and the second signal, said one having the lesser signal quality.

11. A method of operating a gateway in a satellite communications system, said method comprising the steps of:

receiving a first signal transmitted from a first satellite;

receiving a second signal transmitted from a second satellite;

when the first signal and the second signal include soft decision data, combining the first and second signals, thereby generating a combined signal with an increased signal to noise ratio; and

wherein the first and second signals are each comprised of an in-phase component and a quadrature component, and the step of combining comprises the steps of;

summing the in-phase component of the first signal with the in-phase component of the second signal; and

summing the quadrature component of the first signal with the quadrature component of the second signal.

12. The method of claim 11 futher comprising the step of:

decoding the combined signal to generate hard decisions.

13. A satellite communications system comprising:

a first satellite which receives a user transmission having a first signal quality, performs symbol decisions, and transmits either hard decision data or soft decision data as a function of the first signal quality;

a gateway which receives the soft decision data or the hard decision data from the first satellite; and

a second satellite which also receives the user transmission having a second signal quality, performs symbol decisions, and transmits either hard decision data or soft decision data as a function of the second signal quality, wherein the gateway receives the soft decision data or the hard decision data from the second satellite.

14. The satellite communications system of claim 13 wherein the gateway sums soft decision data from the first satellite with soft decision data from the second satellite.

15. The satellite communications system of claim 13 wherein the gateway compares the hard decision data from the first satellite against the hard decision data from the second satellite.