Phase offset spatial multiplexing

• US 20050053169A1
• Filed: 09/05/2003
• Published: 03/10/2005
• Est. Priority Date: 09/05/2003
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Dubuc, Christian, Tong, Wen, Zhu, Peiying, Jia, Ming
• Granted Patent: US 7,356,089 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0682 using phase diversity (e.g. phase sweeping)
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0612 Space-time modulation
• CPC Class Codes: H04L 1/0625 Transmitter arrangements
• CPC Class Codes: H04L 1/0656 Cyclotomic systems, e.g. Bell Labs Layered Space-Time [BLAST]
• CPC Class Codes: H04L 25/0204 of multiple channels

Abstract

A rotation by a phase offset is applied to symbols to be transmitted by one antenna relative to symbols to be transmitted from another antenna in a wireless communication system employing multi-element antennas at the transmitter. Such a phase offset allows the functionality of a MIMO system to be maintained when a MIMO channel degenerates. Advantageously, a MIMO system using the new signal design may provide a level of performance in a rich-scattering environment that is equivalent to a MIMO system using a known signal design. Furthermore, a MIMO system employing embodiments of the present invention may show significantly improvements in robustness over conventional MIMO systems.

Claims

1. A method of transmitting from a transmitter having a first transmit antenna and a second transmit antenna, said method comprising:

transmitting a first symbol on said first transmit antenna, said first symbol belonging to a first modulation constellation; and

simultaneously transmitting a second symbol, independent of said first symbol, on said second transmit antenna, said second symbol belonging to a second modulation constellation, said second modulation constellation having a predetermined phase offset from said first modulation constellation.

2. The method of claim 1 wherein said modulation constellation is based on a Quadrature Phase Shift Keying modulation scheme.

3. The method of claim 2 wherein said predetermined phase offset is 45 degrees.

4. The method of claim 1 wherein said transmitting said first symbol and said transmitting said second symbol are performed for a given sub-carrier in an Orthogonal Frequency Division Multiplexing channel.

5. A transmitter comprising:

a first transmit antenna;

a second transmit antenna; and

a transmit processor adapted to;

cause transmission of a first symbol on said first transmit antenna, said first symbol belonging to a first modulation constellation; and

cause simultaneous transmission of a second symbol, independent of said first symbol, on said second transmit antenna, said second symbol belonging to a second modulation constellation, said second modulation constellation having a predetermined phase offset from said first modulation constellation.

6. A method of transmitting a stream of data, said stream of data divided into a plurality of bit sequences, said method comprising:

based on a first bit sequence of said plurality of bit sequences, selecting a first symbol from a modulation constellation;

based on a second bit sequence of said plurality of bit sequences, selecting a second symbol from said modulation constellation;

rotating said second symbol through a predetermined phase offset to give an offset second symbol;

transmitting said first symbol at a first transmit antenna; and

transmitting said offset second symbol at a second transmit antenna simultaneously with said transmitting said first symbol.

7. A transmitter comprising:

a mapper adapted to;

based on a first bit sequence in a stream of data, said stream of data divided into a plurality of bit sequences, select a first symbol from a modulation constellation;

based on a second bit sequence of said plurality of bit sequences, select a second symbol from said modulation constellation;

a phase adjuster adapted to rotate said second symbol through a predetermined phase offset to give an offset second symbol;

a first transmit antenna adapted to transmit said first symbol; and

a second transmit antenna adapted to transmit said offset second symbol.

8. A method of receiving a composite signal, where said composite signal includes contributions from a first transmit antenna and a second transmit antenna, said method comprising:

determining an estimate of a first channel experienced by a signal from said first transmit antenna;

determining an estimate of a second channel experienced by a signal from said second transmit antenna;

rotating said estimate of said second channel through a predetermined phase offset to give an offset estimate of said second channel; and

decoding said composite signal based on said estimate of said first channel and said offset estimate of said second channel.

9. A receiver comprising:

a channel estimation processor adapted to;

determine an estimate of a first channel experienced by a signal from a first transmit antenna;

determine an estimate of a second channel experienced by a signal from a second transmit antenna;

a phase adjuster adapted to rotate said estimate of said second channel through a predetermined phase offset to give an offset estimate of said second channel; and

a decoder adapted to decode a composite signal based on said estimate of said first channel and said offset estimate of said second channel, where said composite signal includes contributions from said first transmit antenna and said second transmit antenna.

10. A method of transmitting from a transmitter having a first transmit antenna and a second transmit antenna, said method comprising:

transmitting a first sequence of symbols on said first transmit antenna, each symbol of said first sequence of symbols belonging to a first modulation constellation; and

,

for each symbol of said first sequence of symbols,

simultaneously transmitting a symbol from a second sequence of symbols on said second transmit antenna, said second sequence of symbols independent of said first sequence of symbols and each symbol of said second sequence of symbols belonging to a respective modulation constellation having a respective phase offset from said first modulation constellation.

11. The method of claim 10 wherein said respective phase offset is equal for each symbol of said second sequence of symbols.

12. The method of claim 10 wherein said respective phase offset is defined by a sequential set of phase offsets.

13. The method of claim 12 wherein said sequential set of phase offsets is {45 degrees, 135 degrees, 225 degrees, 315 degrees}.

14. The method of claim 10 further comprising selecting said respective phase offset from a set of phase offsets.

15. The method of claim 14 further comprising:

receiving an indication from a receiver; and

performing said selecting said respective phase offset based on said indication.

16. A transmitter comprising:

a first transmit antenna;

a second transmit antenna;

a transmit processor adapted to;

cause transmission of a first sequence of symbols on said first transmit antenna, each symbol of said first sequence of symbols belonging to a first modulation constellation; and

for each symbol of said first sequence of symbols, cause simultaneous transmission of a symbol from a second sequence of symbols on said second transmit antenna, said second sequence of symbols independent of said first sequence of symbols and each symbol of said second sequence of symbols belonging to a respective modulation constellation having a respective phase offset from said first modulation constellation.

17. A method of transmitting from a transmitter having a first transmit antenna and a second transmit antenna, said method comprising:

transmitting a first symbol on said first transmit antenna, said first symbol belonging to a first modulation constellation; and

simultaneously transmitting a second symbol, independent of said first symbol, on said second transmit antenna, said second symbol belonging to a second modulation constellation, said second modulation constellation having a random phase offset from said first modulation constellation.

18. A transmitter comprising:

a first transmit antenna;

a second transmit antenna; and

a transmit processor adapted to;

cause transmission of a first symbol on said first transmit antenna, said first symbol belonging to a first modulation constellation; and

cause simultaneous transmission of a second symbol, independent of said first symbol, on said second transmit antenna, said second symbol belonging to a second modulation constellation, said second modulation constellation having a random phase offset from said first modulation constellation.

19. A method of transmitting a stream of data, said stream of data divided into a plurality of bit sequences, said method comprising:

based on a first bit sequence of said plurality of bit sequences, selecting a first symbol from a modulation constellation;

based on a second bit sequence of said plurality of bit sequences, selecting a second symbol from said modulation constellation;

rotating said second symbol through a random phase offset to give an offset second symbol;

transmitting said first symbol at a first transmit antenna; and

transmitting said offset second symbol at a second transmit antenna simultaneously with said transmitting said first symbol.

20. The method of claim 19 wherein a plurality of blocks of said stream of data are subject forward error correction coding.

21. The method of claim 20 wherein said random phase offset is distributed uniformly over each block of said plurality of blocks.

22. A transmitter comprising:

a mapper adapted to;

based on a first bit sequence in a stream of data, said stream of data divided into a plurality of bit sequences, select a first symbol from a modulation constellation;

based on a second bit sequence of said plurality of bit sequences, select a second symbol from said modulation constellation;

a phase adjuster adapted to rotate said second symbol through a random phase offset to give an offset second symbol;

a first transmit antenna adapted to transmit said first symbol; and

a second transmit antenna adapted to transmit said offset second symbol.

23. A transmitter comprising:

a mapper adapted to;

based on a first bit sequence in a stream of data, said stream of data divided into a plurality of bit sequences, select a first symbol from a first modulation constellation;

based on a second bit sequence of said plurality of bit sequences, select a second symbol, said second symbol belonging to a second modulation constellation, said second modulation constellation having a random phase offset from said first modulation constellation;

a first transmit antenna adapted to transmit said first symbol; and

a second transmit antenna adapted to transmit said offset second symbol.

24. A method of receiving a composite signal, where said composite signal includes contributions from a first transmit antenna and a second transmit antenna, said method comprising:

determining an estimate of a first channel experienced by a signal from said first transmit antenna;

determining an estimate of a second channel experienced by a signal from said second transmit antenna;

rotating said estimate of said second channel through a random phase offset to give an offset estimate of said second channel; and

decoding said composite signal based on said estimate of said first channel and said offset estimate of said second channel.

25. A receiver comprising:

a channel estimation processor adapted to;

determine an estimate of a first channel experienced by a signal from a first transmit antenna;

determine an estimate of a second channel experienced by a signal from a second transmit antenna;

a phase adjuster adapted to rotate said estimate of said second channel through a random phase offset to give an offset estimate of said second channel; and

a decoder adapted to decode a composite signal based on said estimate of said first channel and said offset estimate of said second channel, where said composite signal includes contributions from said first transmit antenna and said second transmit antenna.