Link adaptation for MIMO transmission schemes

• US 20030003863A1
• Filed: 05/03/2002
• Published: 01/02/2003
• Est. Priority Date: 05/04/2001
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Wachsmann, Udo, Thielecke, Jorn
• Granted Patent: US 7,120,199 B2
• Time in Patent Office: Days
• US Class Current: 455/39
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0443 utilizing "waterfilling" technique
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence
• CPC Class Codes: H04B 7/0632 Channel quality parameters, e.g. channel quality indicator [CQI]
• CPC Class Codes: H04B 7/0837 using pre-detection combining H04B7/0868 takes precedence
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0656 Cyclotomic systems, e.g. Bell Labs Layered Space-Time [BLAST]
• CPC Class Codes: H04L 1/12 by using return channel
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0248 Eigen-space methods
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365
• CPC Class Codes: H04W 28/18 Negotiating wireless communication parameters
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

MIMO transmission methods are applied to communicaiton systems in which a transmitter has more than one transmit antenna and a receiver has more than one receive antenna. Information to be transmitted is divided into a plurality of subsignals according to the number of used transmit antennas and each subsignal is processed separately before it is emitted by the respective transmit antenna. In the receiver the different receive signals are processed thus that subsignals are detected and decoded and the contribution of each detected and decoded subsignal is subtracted from the receive signals and whereby a feedback channel from receiver to transmitter is used to send control information to the transmitter depending on the receive situation. In order to optimize the usage of the MIMO channel the invention proposes the in the receiver the link quality of each subsignal is determined and information of each subsignal is transmitted to the receiver via the feedback channel and that in the transmitter properties of the subsignals are controlled by the link quality information.

Claims

1. A method of transmitting information in a communication between a transmitter (1) having more than one transmit antenna and a receiver (2) having more than one receive antenna, whereby information to be transmitted is divided into a plurality of subsignals (Layer 0, Layer 1, Layer 2, Layer 3), each subsignal (Layer 0, Layer 1, Layer 2, Layer 3) is processed separately before it is emitted by said transmit antennas and whereby in the receiver (2) the receive signal is processed thus that subsignals are detected and decoded and the contribution of each detected and decoded subsignal is subtracted from the receive signal and whereby a feedback channel (4) from receiver to transmitter is used to send control information to the transmitter according to the receive situation, characterized in that,

in the receiver the link quality of each subsignal is determined, information of each subsignal is transmitted to the transmitter (1) via the feedback channel (4) and that in the transmitter (1) properties of the subsignals are controlled by the feedback information.

2. A method according to claim 1 whereby in the receiver the determined link qualities are evaluated to generate control information that is send to the transmitter.

3. A method according to claim 1 whereby the determined link qualities are send to the transmitter and are evaluated in the transmitter to generate control information to control each transmit subsignal.

4. A method according to claim 1, 2 or 3 where the subsignal property that is controlled by the link quality information is the data rate of each subsignal.

5. A method according to claim 1, 2 or 3 where the subsignal property that is controlled by the link quality information is the transmit power of each subsignal.

6. A method according to claim 1, 2 or 3 where the subsignal property that is controlled by the link quality information is the modulation scheme of each subsignal.

7. A method according to claim 1, 2, 3, 4, 5 or 6 where the link quality determination is based on an error rate measurement.

8. A method according to claim 1, 2, 3, 4, 5 or 6 where the link quality determination is based on a signal to noise and interference ratio measurement.

9. A method according to claim 1, 2, 3, 4, 5 or 6 where the link quality determination is based on a capacity calculation.

10. A method according to claim 9 where the capacity calculation is takes the instantaneous calculated capacities of each subsignal.

11. A method according to claim 9 where the capacity calculation takes an average of the calculated capacities of each layer with respect to a longer time period.

12. A method according to claim 9 where the capacity calculation takes the outage of the calculated capacities of each layer with respect to a longer time period.

13. A method according to one claims 1-12 where the subsignals are mutually superimposed and diversity is added to each subsignal.

14. A method according to claim 12 where for applying diversity to the subsignals a Space-Time code is used.

15. Method according to claims 1-14 where the number of subsignals is adapted to the current channel situation.

16. Method according to claim 15 where the number of subsignals is chosen according to the number of eigenvalues in the correlation matrix being significantly greater than zero.

17. Method according to claim 15 where the number of subsignals is chosen according to the number of singular values in the instantaneous channel matrix being significantly greater than zero.

18. Method according to claim 15 where the number of subsignals is chosen thus that a certain minimum rate per subsignal is achieved;

otherwise the number of subsignals is reduced.

19. A method according to one of claims 1-18 comprising the steps of determining the link quality of each subsignal, compare the set of determined link qualities with a plurality of sets of pre-calculated link qualities in order to choose one of the pre-calculated sets as the best matching set of all pre-calculated sets and use the properties of the chosen pre-calculated set on which the chosen pre-calculated set was based as properties for the sub signals.

20. A transmitter for a MIMO transmission system having more than one transmit antenna whereby information to be transmitted is divided into a plurality of subsignals according to the number of used transmit antennas and each subsignal is processed separately before it is emitted by the respective transmit antenna and whereby on a feedback channel control information from a receiver is received, characterized in that,

information of the link quality of each subsignal is received via the feedback channel and that the transmitter controls properties of the subsignals based on the link quality information.

21. A receiver for a MIMO communication system having more than one receive antenna, whereby receive signals of a respective receive antenna are processed thus that subsignals are detected and decoded and the contribution of each detected and decoded subsignal is subtracted from the receive signals and whereby a feedback channel from the receiver to a transmitter is used to send control information to the transmitterer depending on the receive situation, characterized in that,

in the receiver the link quality of each subsignal is determined, information of each subsignal is transmitted to the receiver via the feedback channel for adapting the properties of the subsignals in a respective transmitter.