PARTIAL DISCARDING OF CYCLIC PREFIX FOR EFFICIENT TDD OR HALF-DUPLEX FDD OPERATION

• US 20090122731A1
• Filed: 09/08/2008
• Published: 05/14/2009
• Est. Priority Date: 10/01/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Montojo, Juan, Patel, Shimman, Malladi, Durga
• Granted Patent: US 8,681,666 B2
• Time in Patent Office: Days
• US Class Current: 370/280
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/1484 operating bytewise

Abstract

Techniques for performing partial cyclic prefix discarding are described. A user equipment (UE) may reduce the amount of cyclic prefix to discard for the last OFDM symbol prior to a switch from data reception to data transmission. This may allow the UE to complete data reception earlier and to switch to data transmission in a timely manner. In one design, the UE may receive a first OFDM symbol and discard a first amount of cyclic prefix for the first OFDM symbol. The UE may then receive a second OFDM symbol and discard a second amount of cyclic prefix for the second OFDM symbol. The second amount of cyclic prefix to discard may be determined based on the amount of time needed to switch from data reception to data transmission, which may be dependent on the amount of time advance between transmit timing and receive timing at the UE.

Claims

1. A method for wireless communication, comprising:

receiving a first orthogonal frequency division multiplexing (OFDM) symbol via a first link;

discarding a first amount of cyclic prefix for the first OFDM symbol;

receiving a second OFDM symbol via the first link following the first OFDM symbol;

determining a switch time to switch from data reception on the first link to data transmission on a second link;

determining a second amount of cyclic prefix to discard based on the switch time, the second amount of cyclic prefix being less than the first amount of cyclic prefix; and

discarding the second amount of cyclic prefix for the second OFDM symbol.

2. The method of claim 1, wherein the determining the switch time comprises

determining a round trip delay (RTD) between a user equipment (UE) and a Node B, and

determining the switch time based on the RTD and a setup time for switching from data reception to data transmission.

3. The method of claim 1, wherein the discarding the second amount of cyclic prefix comprises

placing a fast Fourier transform (FFT) window to start within the cyclic prefix of the second OFDM symbol, and

discarding a portion of the cyclic prefix of the second OFDM symbol outside of the FFT window.

4. The method of claim 3, wherein the placing the FFT window further comprises placing the FFT window to end at least the switch time earlier than the end of the second OFDM symbol.

5. The method of claim 1, wherein the first amount of cyclic prefix comprises an entire cyclic prefix of the first OFDM symbol, and wherein the second amount of cyclic prefix comprises a portion of the cyclic prefix of the second OFDM symbol.

6. The method of claim 1, further comprising:

transmitting a single-carrier frequency division multiplexing (SC-FDM) symbol in accordance with transmit timing for data transmission on the second link, wherein the transmit timing is advanced relative to receive timing for data reception on the first link, and wherein the switch time is determined based on amount of time advance between the transmit timing and the receive timing.

7. The method of claim 6, further comprising:

discarding a portion of a cyclic prefix of the SC-FDM symbol, the discarded portion of the cyclic prefix being determined based on the switch time.

8. The method of claim 1, wherein a guard period of zero OFDM symbols is used between data reception on the first link and data transmission on the second link.

9. The method of claim 1, wherein a guard period of an integer number of OFDM symbols is used between data reception on the first link and data transmission on the second link.

10. The method of claim 1, wherein the second OFDM symbol is a last OFDM symbol prior to a switch point from data reception on the first link to data transmission on the second link.

11. The method of claim 1, wherein data reception on the first link and data transmission on the second link are for time division duplex (TDD) operation or half-duplex frequency division duplex (FDD) operation.

12. The method of claim 1, wherein the first link is downlink and the second link is uplink.

13. An apparatus for wireless communication, comprising:

at least one processor configured to receive a first orthogonal frequency division multiplexing (OFDM) symbol via a first link, to discard a first amount of cyclic prefix for the first OFDM symbol, to receive a second OFDM symbol via the first link following the first OFDM symbol, to determine a switch time to switch from data reception on the first link to data transmission on a second link, to determine a second amount of cyclic prefix to discard based on the switch time, the second amount of cyclic prefix being less than the first amount of cyclic prefix, and to discard the second amount of cyclic prefix for the second OFDM symbol.

14. The apparatus of claim 13, wherein the at least one processor is configured to determine a round trip delay (RTD) between a user equipment (UE) and a Node B, and to determine the switch time based on the RTD and a setup time for switching from data reception to data transmission.

15. The apparatus of claim 13, wherein the at least one processor is configured to place a fast Fourier transform (FFT) window to start within the cyclic prefix of the second OFDM symbol, and to discard a portion of the cyclic prefix of the second OFDM symbol outside of the FFT window.

16. The apparatus of claim 15, wherein the at least one processor is configured to place the FFT window to end at least the switch time earlier than the end of the second OFDM symbol.

17. The apparatus of claim 13, wherein the at least one processor is configured to transmit a single-carrier frequency division multiplexing (SC-FDM) symbol in accordance with transmit timing for data transmission on the second link, wherein the transmit timing is advanced relative to receive timing for data reception on the first link, and wherein the switch time is determined based on amount of time advance between the transmit timing and the receive timing.

18. An apparatus for wireless communication, comprising:

means for receiving a first orthogonal frequency division multiplexing (OFDM) symbol via a first link;

means for discarding a first amount of cyclic prefix for the first OFDM symbol;

means for receiving a second OFDM symbol via the first link following the first OFDM symbol;

means for determining a switch time to switch from data reception on the first link to data transmission on a second link;

means for determining a second amount of cyclic prefix to discard based on the switch time, the second amount of cyclic prefix being less than the first amount of cyclic prefix; and

means for discarding the second amount of cyclic prefix for the second OFDM symbol.

19. The apparatus of claim 18, wherein the means for determining the switch time comprises

means for determining a round trip delay (RTD) between a user equipment (UE) and a Node B, and

means for determining the switch time based on the RTD and a setup time for switching from data reception to data transmission.

20. The apparatus of claim 18, wherein the means for discarding the second amount of cyclic prefix comprises

means for placing a fast Fourier transform (FFT) window to start within the cyclic prefix of the second OFDM symbol, and

means for discarding a portion of the cyclic prefix of the second OFDM symbol outside of the FFT window.

21. The apparatus of claim 20, wherein the means for placing the FFT window further comprises means for placing the FFT window to end at least the switch time earlier than the end of the second OFDM symbol.

22. The apparatus of claim 18, further comprising:

means for transmitting a single-carrier frequency division multiplexing (SC-FDM) symbol in accordance with transmit timing for data transmission on the second link, wherein the transmit timing is advanced relative to receive timing for data reception on the first link, and wherein the switch time is determined based on amount of time advance between the transmit timing and the receive timing.

23. A computer program product, comprising:

a computer-readable medium comprising;

code for causing at least one computer to receive a first orthogonal frequency division multiplexing (OFDM) symbol via a first link,

code for causing at least one computer to discard a first amount of cyclic prefix for the first OFDM symbol,

code for causing at least one computer to receive a second OFDM symbol via the first link following the first OFDM symbol,

code for causing at least one computer to determine a switch time to switch from data reception on the first link to data transmission on a second link,

code for causing at least one computer to determine a second amount of cyclic prefix to discard based on the switch time, the second amount of cyclic prefix being less than the first amount of cyclic prefix, and

code for causing at least one computer to discard the second amount of cyclic prefix for the second OFDM symbol.