CONFIGURABLE BLOCK CDMA SCHEME

Abstract

Code division multiple access (CDMA) is a popular multiple access technique that is used to support multiple users simultaneously in a network. Many variants of CDMA exist, including direct sequence (DS) CDMA, multi-carrier (MC) CDMA, cyclic prefixed (CP) CDMA, and chip interleaved block spread (CIBS) CDMA. In addition to these variations, many receiver architectures are often available for implementation in CDMA systems, such as the well-known RAKE receiver, interference cancellation receivers, and receivers that rely on channel equalisation.

Description

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which:

FIG. 1 shows a block diagram of a transmitter/receiver structure according to the invention.

FIG. 2 illustrates the spreading operation.

FIG. 3 shows an example of users' signals interfering with each other in the channel and combining at the receiver.

FIG. 4 illustrates bandwidth utilisation when DFT codes are used as spreading codes and when self-shift-orthogonal spreading codes are used.

FIG. 5 illustrates user separation and subsequent MIMO detection.

FIG. 6 shows joint user and multiple stream separation.

FIG. 7 shows the complexity of frequency-domain equalisation vs. sub-block length for distributed SC-FDMA systems with R=33.

FIG. 8 shows a block diagram of a MIMO system incorporating the invention.

Claims

1. A method of generating a signal comprising a sequence of symbols for multiple access transmission, the method comprising: spreading blocks of symbols in time or frequency by applying a user-specific spreading code; andapplying a guard interval in the form of a cyclic prefix (CP) or zero padding (ZP) to separate different spread blocks,wherein the spreading code is selected from the group comprising orthogonal, mutually shift-orthogonal, and self-shift orthogonal spreading codes.

2. The method according to claim 1, wherein the user-specific spreading codes are orthogonal and mutually shift-orthogonal.

3. The method according to claim 1, wherein the user-specific spreading codes are orthogonal but not mutually shift-orthogonal.

4. The method according to claim 1 wherein the user-specific spreading codes are mutually shift-orthogonal but not orthogonal.

5. The method according to claim 1 wherein the user-specific spreading codes are orthogonal, mutually shift-orthogonal, and self-shift-orthogonal.

6. The method according to claim 1, wherein the length of the user-specific spreading codes may change so as to change the data rate for each user.

7. The method according to claim 1, further comprising the step of applying preceding to each sub-block of data in a spread block.

8. The method according to claim 7, where the step of preceding comprises progressively rotating the phase of each sub-block identically by a user-dependent amount.

9. The method according to claim 7, wherein the step of precoding comprises first applying an inverse discrete Fourier transform (IDFT) to each sub-block and then progressively rotating the phase of each sub-block identically by a user-dependent amount.

10. The method according to claim 1 further comprising the step of utilising a plurality of antennas for transmission.

11. The method according to claim 10, wherein identical spreading codes are applied to the signals at all transmit antennas for a given user.

12. The method according to claim 10 wherein different spreading codes are applied to any combination of some or all of the signals at various transmit antennas for a given user.

13. A method of receiving a signal comprising a sequence of symbols from multiple access transmission, the method comprising: removing the guard interval in the form of a cyclic prefix (CP) or zero padding (ZP) to obtain different spread blocks;de-spreading the blocks of symbols in time or frequency by applying a user-specifics spreading code,wherein the spreading code is selected from the group comprising orthogonal, mutually shift-orthogonal, and self-shift orthogonal spreading codes.

14. The method according to claim 13 further comprising the step of decoding each sub-block of received data in a spread block.

15. The method according to claim 13, where the decoder progressively rotates the phase of each sub-block identically by a user-dependent amount.

16. The method according to claim 15 wherein the step of decoding further comprises applying a discrete Fourier transform (DFT) to each phase-rotated sub-block.

17. The method according to claim 16 wherein the step of decoding further comprises applying a single-tap frequency-domain equaliser to the de-spread data at the output of the filter.

18. The method according to claim 17, further comprising the step of transforming the equalised signal into the time domain with an IDFT for further processing.

19. The method according to claim 13 further comprising the step of utilising a plurality of receiving antennas.