Method and Arrangement For Self Interference Cancellation

• US 20120224610A1
• Filed: 11/02/2009
• Published: 09/06/2012
• Est. Priority Date: 11/02/2009
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Baldemair, Robert
• Granted Patent: US 8,837,615 B2
• Time in Patent Office: Days
• US Class Current: 375/211
• CPC Class Codes: H04B 7/15585 by interference cancellation
• CPC Class Codes: H04L 25/03146 with a recursive structure H04L25/03127 takes precedence
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

The present invention relates to a method and arrangement for receiving an OFDM signal and forwarding the received OFDM signal comprising OFDM symbols of a wireless OFDM communication network. The wireless OFDM communication network includes self-interference cancelling functionality and each received OFDM symbol to be forwarded is prefixed with a cyclic prefix (CP) which is a copy of the last part of the OFDM symbol. In the method a delay for delaying an interference generating feedback signal is determined such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with an OFDM symbol of the received OFDM signal, and interference generating feedback signal is delayed with the determined delay. Furthermore may the duration of the impulse be shortened as well.

Claims

1. A method in a relay for receiving an OFDM signal and forwarding the received OFDM signal comprising OFDM symbols of a wireless OFDM communication network including self-interference cancelling functionality, wherein each received OFDM symbol to be forwarded is prefixed with a cyclic prefix, CP, being a copy of a part of the OFDM symbol, comprising the steps of:

determining a delay for delaying an interference generating feedback signal such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with an OFDM symbol of the received OFDM signal, and

delaying the interference generating feedback signal with the determined delay.

2. The method according to claim 1, wherein the determining step further comprises:

determining the delay for delaying the interference generating feedback signal such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with the corresponding OFDM symbol of the received OFDM signal by restricting the loop delay of the interference generating feedback signal to a fraction of the length of the CP.

3. The method according to claim 1, wherein the delaying step further comprises:

determining the delay for delaying the interference generating feedback signal such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with a subsequent OFDM symbol of the received OFDM signal by introducing an additional loop delay of the interference generating feedback signal.

4. The method according to claim 1, wherein the OFDM symbol of the interference generating feedback signal completely overlaps with an OFDM symbol of the received OFDM signal.

5. The method according to claim 1, wherein the delay is introduced by a delayer integrated with a unit for other signal processing.

6. The method according to claim 1, wherein the delay is introduced by a delayer in a separate unit.

7. The method according to claim 1, wherein an impulse response experienced by the interference generating feedback signal is shortened by a shortening function.

8. The method according to claim 7, wherein the shortening function is integrated with a unit for other signal processing.

9. The method according to claim 7, wherein the shortening function is introduced by a signal processing function in a separate unit.

10. The method according to claim 1, wherein the self-interference cancellation is performed in frequency-domain.

11. The method according to claim 1, wherein the relay is a frequency-translating relay.

12. The method according to claim 1, wherein the OFDM communication network is a precoded OFDM communication network.

13. A relay for receiving an OFDM signal and forwarding the received OFDM signal comprising OFDM symbols of a wireless OFDM communication network including self-interference cancelling functionality, wherein each received OFDM symbol is prefixed with a cyclic prefix, CP, being a copy of a part of the OFDM symbol, the relay comprising:

a processing unit configured to determine a delay for delaying an interference generating feedback signal such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with an OFDM symbol of the received OFDM signal; and

a delayer configured to delay the interference generating feedback signal with the determined delay.

14. The relay according to claim 13, wherein the processing unit is further configured to determine the delay for delaying the interference generating feedback signal such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with the corresponding OFDM symbol of the received OFDM signal by restricting the loop delay of the interference generating feedback signal to a fraction of the length of the CP.

15. The relay according to claim 13, wherein the processing unit is further configured to determine the delay for delaying the interference generating feedback signal such that an OFDM symbol of the interference generating feedback signal overlaps within a margin of a length of the CP with a subsequent OFDM symbol of the received OFDM signal by introducing an additional loop delay of the interference generating feedback signal.

16. The relay according to claim 13, wherein the OFDM symbol of the interference generating feedback signal completely overlaps with an OFDM symbol of the received OFDM signal.

17. The relay according to claim 13, wherein the delayer is integrated with a unit for other signal processing.

18. The relay according to claim 13, wherein the delayer is a separate unit.

19. The relay according to claim 13, wherein the relay is configured to implement a shortening function that shortens an impulse response experienced by the interference generating feedback signal.

20. The relay according to claim 19, wherein the shortening function is integrated with a unit for other signal processing.

21. The relay according to claim 19, wherein the shortening function is introduced by a signal processing function in a separate unit.

22. The relay according to claim 13, wherein the relay is configured to perform self-interference cancellation in a frequency-domain.

23. The relay according to claim 13, wherein the relay is a frequency-translating relay.

24. The relay according to claim 13, wherein the OFDM communication network is a precoded OFDM communication network.