Orthogonal code division multiple access on return link of satellite links

• US 7,633,895 B2
• Filed: 05/01/2003
• Issued: 12/15/2009
• Est. Priority Date: 06/24/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Schiff, Leonard N., Jalali, Ahmad
• Primary Examiner(s): Sheikh; Ayaz R
• Assistant Examiner(s): LEE, ANDREW CHUNG CHEUNG
• Application Number:
  US10/428,953
• Publication Number:
  US 20040037238A1
• Time in Patent Office: 2,420 Days
• Field of Search: 370/320, 370/316, 370/342, 370/204, 370/350, 370/305, 375/147, 375/1, 375/200
• US Class Current: 370/321
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04B 7/18543 for adaptation of transmission parameters, e.g. power control for detecting or preventing errors in the information received H04L1/00
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Orthogonal CDMA (OCDMA) in the return link of a satellite based communications system provides improved bandwidth efficiencies; increased ability to overcome channel degrading phenomenon; reduced transmission power; or various combinations thereof. By achieving code synchronization needed for advantageous use of OCDMA in the return link of a satellite based communication system, a plurality of terminals, each with a unique time slot/code channel assignment, may transmit concurrently, with the same, or lower, aggregate power as would be used by a single terminal using TDMA. Use of OCDMA in the return link allows one or more terminals, each in a common beam and assigned a common time slot, to transmit at a higher transmission power to overcome channel degradation effects. The ability to allow for higher transmission power for a particular terminal can increase the effective data rate for that terminal by enabling the use of a higher order modulation technique.

Claims

1. A method of operating L access terminals on a return link in a satellite communication system comprising:

transmitting a reference signal from each access terminal to a satellite gateway;

assigning a unique orthogonal Walsh code to each access terminal of the L access terminals, wherein each access terminal of the L access terminals repeats a data modulation symbol L times during the access terminal'"'"'s assigned Walsh code interval to achieve a processing gain of L;

receiving a message at an access terminal from the satellite gateway, the message assigning a time slot for the return link, a code channel for transmission for the return link, a transmit time adjustment instruction for the return link, a transmit power instruction for the return link, and a data rate instruction for the return link;

wherein the transmit power instruction is based on, at least in part, a location of the access terminal with respect to a beam center;

wherein the time slot assignment informs the access terminal of the time or times at which it is to transmit; and

wherein the transmit time adjustment instruction enables the access terminal to adjust its time slot assignment in order to maintain code synchronism for orthogonal code division multiple access (OCDMA) on the return link; and

transmitting a Walsh code modulated message from the access terminal to the satellite gateway during a time slot specified by the time slot assignment, at a transmit power specified by the transmit power instruction, and at a data rate specified by the data rate instruction.

2. The method of claim 1, further comprising:

transmitting a message to the gateway indicating an amount of data that is to be transmitted from the access terminal on the return link, wherein the transmit power instruction is further based on, at least in part, the amount of data that is to be transmitted from the access terminal on the return link.

3. The method of claim 1, further comprising, prior to transmitting at least a portion of the amount of data that is to be transmitted on the return link, adjusting the transmit time so as to substantially achieve code synchronicity on the return link, code modulating a signal on the return link in accordance with the code channel assigned to the access terminal for the return link;

transmitting at the transmit power level specified by the transmit power instruction; and

transmitting on the return link, at least a portion of the amount of data that is to be transmitted on the return link.

4. The method of claim 3, further comprising detecting a degradation in channel conditions.

5. The method of claim 4, further comprising increasing transmit power to substantially compensate for the degradation in channel conditions.

6. The method of claim 5, wherein the degradation in channel conditions is substantially due to rain fade.

7. The method of claim 1, further comprising:

assigning the transmit power of each access terminal of the plurality of L access terminals to a value that is between at least 1/L of a maximum available transmit power and at most the maximum available transmit power.

8. The method of claim 1, further comprising:

achieving frequency synchronization between the access terminal and the satellite gateway based on, at least in part, the access terminal adjusting the frequency of its oscillator in order to lock to the frequency of the signal received from the gateway.

9. A method of operating a communication system utilizing L access terminals, comprising:

a) receiving, at a satellite gateway, a message from an access terminal, and determining therefrom the channel conditions between the satellite gateway and the access terminal;

b) determining, at the satellite gateway, a received signal strength of the received message;

c) determining, at the satellite gateway, a timing offset of the received message;

d) assigning a unique orthogonal Walsh code to each access terminal of the L access terminals, wherein each access terminal of the L access terminals repeats a data modulation symbol L times during the access terminal'"'"'s assigned Walsh code interval to achieve a processing gain of L;

e) transmitting, to the access terminal, a time slot assignment for the return link, a code channel assignment for the return link, a transmit time adjustment instruction for the return link, a transmit power instruction for the return link, and a data rate instruction for the return link, wherein the transmit power instruction is based on, at least in part, a location of the access terminal with respect to a beam center;

wherein the time slot assignment informs the access terminal of the time or times at which it is to transmit; and

wherein the transmit time adjustment instruction enables the access terminal to adjust its time slot assignment in order to maintain code synchronism for orthogonal code division multiple access (OCDMA) on the return link; and

f) transmitting a Walsh code modulated message from the access terminal to the satellite gateway during a time slot specified by the time slot assignment, at a transmit power specified by the transmit power instruction, and at a data rate specified by the data rate instruction.

10. The method of claim 9, further comprising repeating steps (a) through (f) for each of the L access terminals;

wherein the time slot assignment transmitted to each of the L access terminals is the same.

11. The method of claim 10, further comprising receiving, during the time slot specified by the time slot assignment, a plurality of code modulated messages.

12. The method of claim 11, further comprising despreading, in parallel, the plurality of code modulated messages.

13. A satellite gateway, comprising:

a code source coupled to at least one code modulator, and to a plurality of despreaders, wherein each despreader of the plurality of despreaders comprises a Walsh despreader, and wherein the code source comprises a source of orthogonal Walsh codes;

an upconverter coupled to the at least one code modulator, and further coupled to an antenna;

a downconverter coupled to the antenna, and further coupled to the plurality of despreaders;

a plurality of demodulators, each demodulator coupled to a corresponding one of the despreaders;

means for transmitting the following to each access terminal of L access terminals;

a time slot assignment of the return link, a code channel assignment for the return link, a transmit time adjustment instruction for the return link, a transmit power instruction for the return link, and a data rate instruction for the return link;

wherein the transmit power instruction is based on, at least in part, a location of the access terminal with respect to a beam center;

wherein the time slot assignment informs the access terminal of the time or times at which it is to transmit; and

wherein the transmit time adjustment instruction enables the access terminal to adjust its time slot assignment in order to maintain code synchronism for orthogonal code division multiple access on the return link;

means for assigning a unique orthogonal Walsh code to each access terminal of the L access terminals, wherein each access terminal of the L access terminals repeats a data modulation symbol L times during the access terminal'"'"'s assigned Walsh code interval in order to achieve a processing gain of L; and

means for transmitting a Walsh code modulated message from the access terminal to the satellite gateway during a time slot specified by the time slot assignment, at a transmit power specified by the transmit power instruction, and at a data rate specified by the data rate instruction.

14. A wireless communications access terminal, comprising:

means for transmitting a reference signal from L access terminals to a satellite gateway;

means for receiving, at each access terminal of the L access terminals, a message assigning a time slot for a return link, a code channel for transmission for the return link, a transmit time adjustment instruction for the return link, a transmit power instruction for the return link, and a data rate instruction for the return link, wherein the transmit power instruction is based on, at least in part, a location of the access terminal with respect to a beam center;

means for receiving, at each access terminal of the L access terminals, a message assigning a time slot for a return link, a code channel for transmission for the return link, a transmit time adjustment instruction for the return link, a transmit power instruction for the return link, and a data rate instruction for the return link, wherein the transmit power instruction is based on, at least in part, a location of the access terminal with respect to a beam center;

means for assigning a unique orthogonal Walsh code to each access terminal of the L access terminals, wherein each access terminal repeats a data modulation symbol L times during the access terminal'"'"'s assigned Walsh code interval in order to achieve a processing gain of L;

means for transmitting a Walsh code modulated message from an access terminal of the L access terminals to the satellite gateway during a time slot specified by the time slot assignment, at a transmit power specified by the transmit power instruction, and at a data rate specified by the data rate instruction; and

means for informing the access terminal, via the time slot assignment, of the time or times at which the access terminal is to transmit;

wherein the transmit time adjustment instruction enables the access terminal to adjust its time slot assignment in order to maintain code synchronism for orthogonal code division multiple access on the return link.

15. The access terminal of claim 14, further comprising:

means for transmitting a message to the satellite gateway indicating an amount of data that is to be transmitted from the access terminal for the return link, wherein the transmit power instruction is further based on, at least in part, the amount of data that is to be transmitted from the access terminal for the return link.

16. The access terminal of claim 14, further comprising:

means for, prior to transmitting at least a portion of the amount of data that is to be transmitted on the return link, adjusting the transmit time so as to substantially achieve code synchronicity on the return link;

means for code modulating a signal on the return link in accordance with the code channel assigned to the access terminal;

means for transmitting on the return link, at the transmit power specified by the transmit power instruction; and

means for transmitting on the return link, at least a portion of the amount of data that is to be transmitted on the return link.

17. The access terminal of claim 16, further comprising means for detecting a degradation in channel conditions.

18. The access terminal of claim 17, further comprising means for increasing transmit power to substantially compensate for the degradation in channel conditions.

19. The access terminal of claim 18, wherein the degradation in channel conditions is substantially due to rain fade.

20. A method comprising:

transmitting a reference signal from an access terminal of L access terminals to a satellite gateway via a return link of a satellite communication system;

assigning a unique orthogonal Walsh code to each access terminal of the L access terminals, wherein each access terminal of the L access terminals repeats a data modulation symbol L times during the access terminal'"'"'s assigned Walsh code interval to achieve a processing gain of L;

receiving a message from the satellite gateway at the access terminal of the L access terminals, the message assigning a time slot for the return link, a code channel for transmission for the return link, a transmit time adjustment instruction for the return link, a transmit power instruction for the return link, and a data rate instruction for the return link;

wherein the transmit power instruction is based on, at least in part, a location of the access terminal with respect to a beam center;

wherein the data rate instruction is based on, at least in part, an energy per bit received on the code channel;

wherein the time slot assignment informs the access terminal of the time or times at which it is to transmit; and

wherein the transmit time adjustment instruction enables the access terminal to adjust its time slot assignment in order to maintain code synchronism for orthogonal code division multiple access on the return link; and

transmitting a Walsh code modulated message from the access terminal to the satellite gateway during a time slot specified by the time slot assignment, at a transmit power specified by the transmit power instruction, and at a data rate specified by the data rate instruction.

21. The method of claim 20, further comprising:

limiting total transmit power from all access terminals of the L access terminals to less than or equal to an allowable interference between the satellite communication system and an adjacent satellite.