Transmitter for a wireless communications system using multiple codes and multiple antennas

• US 20030081539A1
• Filed: 04/05/2002
• Published: 05/01/2003
• Est. Priority Date: 04/05/2001
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Chloma, Alexandre M., Bakouline, Mikhail G., Tong, Wen, Shinakov, Yuri S., Kreindeline, Vitali B.
• Granted Patent: US 7,280,466 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 7/0678 using different spreading codes between antennas code allocation H04J13/16
• CPC Class Codes: H04J 13/0048 Walsh

Abstract

In a transmitter of a wireless communications system having M transmit antennas (10), each transmit antenna is supplied with a respective combined signal comprising a respective one of M groups each of N data sub-streams, orthogonally spread by N Walsh code sequences (W1 to WN). The N orthogonal code sequences used for each of the M groups comprise a respective one of M different combinations of N from N_w orthogonal code sequences, where N_w>N. M and N are integers greater than one. The combined signals can also include orthogonally spread pilot signals (WP) for channel estimation at a receiver. Orthogonality of the signals transmitted from the transmit antennas is increased, so that transmit signal power can be decreased and/or the receiver can have fewer than M receive antennas.

Claims

1. A transmitter for a wireless communications system, comprising:

a demultiplexer arranged to produce M groups each of N data sub-streams from data to be transmitted, where N and M are integers greater than one;

M orthogonal code spreaders each arranged to spread the N data sub-streams of a respective one of the M groups using N orthogonal code sequences; and

M signal combiners each arranged to combine the N orthogonally spread data sub-streams of a respective one of the M groups to produce a respective combined signal for transmission via a respective one of M transmit antennas;

wherein the N orthogonal code sequences used for each of the M groups comprise a respective one of M different combinations of N from N_w orthogonal code sequences, where N_w>

N.

2. A transmitter as claimed in claim 1 wherein the orthogonal code sequences comprise Walsh functions of length L, where L=2^k and k is an integer greater than one.

3. A transmitter as claimed in claim 2 wherein N_w<

L.

4. A transmitter as claimed in claim 1 wherein each signal combiner is also arranged to combine with the respective N orthogonally spread data sub-streams a pilot signal which is orthogonally spread relative to the data sub-streams of the respective group and relative to the pilot signal of each other group.

5. A transmitter as claimed in claim 3 wherein each signal combiner is also arranged to combine with the respective N orthogonally spread data sub-streams a pilot signal which is orthogonally spread relative to the data sub-streams of the respective group and relative to the pilot signal of each other group.

6. A transmitter as claimed in claim 1 wherein the data to be transmitted comprises encoded modulated data, and the transmitter includes an encoder for producing encoded data from a source of data and a modulator arranged to modulate the encoded data to produce the data to be transmitted, a code rate of the encoder, a number of bits per modulation symbol produced by the modulator, and the integers M and N being selected to provide a desired data transmission rate of the transmitter.

7. A transmitter as claimed in claim 2 wherein the data to be transmitted comprises encoded modulated data, and the transmitter includes an encoder for producing encoded data from a source of data and a modulator arranged to modulate the encoded data to produce the data to be transmitted, a code rate of the encoder, a number of bits per modulation symbol produced by the modulator, and the integers M and N being selected to provide a desired data transmission rate of the transmitter.

8. A transmitter as claimed in claim 3 wherein the data to be transmitted comprises encoded modulated data, and the transmitter includes an encoder for producing encoded data from a source of data and a modulator arranged to modulate the encoded data to produce the data to be transmitted, a code rate of the encoder, a number of bits per modulation symbol produced by the modulator, and the integers M and N being selected to provide a desired data transmission rate of the transmitter.

9. A transmitter as claimed in claim 4 wherein the data to be transmitted comprises encoded modulated data, and the transmitter includes an encoder for producing encoded data from a source of data and a modulator arranged to modulate the encoded data to produce the data to be transmitted, a code rate of the encoder, a number of bits per modulation symbol produced by the modulator, and the integers M and N belong selected to provide a desired data transmission rate of the transmitter.

10. A transmitter as claimed in claim 1 and including, for each of the M groups, a respective code spreader arranged to spread the respective combined signal in accordance with a PN code, and a respective linear power amplifier arranged to amplify a respective resulting PN code spread signal for transmission via the respective transmit antenna.

11. A transmitter as claimed in claim 2 and including, for each of the M groups, a respective code spreader arranged to spread the respective combined signal in accordance with a PN code, and a respective linear power amplifier arranged to amplify a respective resulting PN code spread signal for transmission via the respective transmit antenna.

12. A transmitter as claimed in claim 6 and including, for each of the M groups, a respective code spreader arranged to spread the respective combined signal in accordance with a PN code, and a respective linear power amplifier arranged to amplify a respective resulting PN code spread signal for transmission via the respective transmit antenna.

13. A wireless communications system comprising a transmitter as claimed in claim 1 with M transmit antennas via which the respective combined signals are transmitted, and a receiver with P receive antennas via which signals transmitted from the transmit antennas are received, where P is an integer greater than one.

14. A wireless communications system comprising a transmitter as claimed in claim 10 with M transmit antennas via which the respective combined signals are transmitted, and a receiver with P receive antennas via which signals transmitted from the transmit antennas are received, where P is an integer greater than one.

15. A system as claimed in claim 13 wherein M>

P.

16. A system as claimed in claim 13 wherein M=4 and P=2.

17. A method of increasing orthogonality of signals transmitted from M transmit antennas in a wireless communications system, comprising the steps of:

producing signals to be transmitted from each transmit antenna by combining N data sub-streams orthogonalized by N orthogonal code sequences, M and N being integers greater than one; and

selecting the N orthogonal code sequences used for each of the M transmit antennas as a respective one of M different combinations of N from N_w orthogonal code sequences, where N_w>

N.

18. A method as claimed in claim 17 wherein the orthogonal code sequences comprise Walsh functions of length L, where L=2^k and k is an integer greater than one.

19. A method as claimed in claim 18 wherein N_w<

L.

20. A method as claimed in claim 17 and further comprising the step of combining with the signals to be transmitted from each transmit antenna a pilot signal which is orthogonally spread relative to the data sub-streams for the respective transmit antenna and relative to the pilot signal for each other transmit antenna.

21. A method as claimed in claim 19 and further comprising the step of combining with the signals to be transmitted from each transmit antenna a pilot signal which is orthogonally spread relative to the data sub-streams for the respective transmit antenna and relative to the pilot signal for each other transmit antenna.