Orthogonal code division multiple access on return link of satellite links

• US 20040037238A1
• Filed: 05/01/2003
• Published: 02/26/2004
• Est. Priority Date: 06/24/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Schiff, Leonard N., Jalali, Ahmad
• Granted Patent: US 7,633,895 B2
• Time in Patent Office: Days
• 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 an access terminal, comprising:

transmitting a reference signal to a gateway; and

receiving a message assigning a time slot, a code channel for transmission, a transmit time adjustment instruction, a transmit power instruction, and a date rate instruction;

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

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; and

wherein the transmit power instruction is based, at least in part, on the amount of data that is to be transmitted from the access terminal.

3. The method of claim 2, wherein the transmit time adjustment instruction is based, at least in part, on a location of the access terminal with respect to the beam center.

4. The method of claim 3, further comprising transmitting a Walsh code modulated message to the gateway via the return link 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.

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

and transmitting, at the transmit power level specified by the transmit power instruction, and at least a portion of the amount of data that is to be transmitted.

6. The method of claim 5, further comprising detecting a degradation in channel conditions.

7. The method of claim 6, further comprising increasing transmit power to compensate for the degradation in channel conditions.

8. The method of claim 7, wherein the degradation in channel conditions is due to rain fade.

9. A method of operating a communication system, comprising:

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

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

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

d) transmitting, to the access terminal, a time slot assignment, a code channel assignment, a transmit time adjustment instruction;

a transmit power instruction, and a data rate instruction.

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

wherein the time slot assignment transmitted to each of the plurality of 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 dispreading, in parallel, the plurality of code modulated messages.

13. A receiver, comprising:

a downconverter;

an A/D converter coupled to the downconverter;

a plurality of despreaders, each despreader having an input terminal coupled to the A/D converter, each despreader further having an output terminal; and

a plurality of data demodulators, each data demodulator having an input terminal coupled to a corresponding despreader output terminal.

14. The receiver of claim 13, wherein the plurality of despreaders each comprise a Walsh despreader.

15. The receiver of claim 14, wherein each of the plurality of Walsh despreaders is coupled to a Walsh code source.

16. The receiver of claim 14, further comprising a Walsh code source coupled to a bus;

and wherein each of the plurality of Walsh despreaders are coupled to the bus.

17. The receiver of claim 14, wherein each of the plurality of Walsh despreaders includes at least one stored Walsh code.

18. A gateway, comprising:

a code source coupled to at least one code modulator, and to a plurality of despreaders;

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; and

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

19. The gateway of claim 18, wherein the plurality of despreaders each comprise a Walsh despreader

20. The gateway of claim 19, wherein the code source comprises a source of orthogonal Walsh codes