Method and apparatus for enhancing data rates in spread spectrum communication systems
A high data transmitter and a high data receiver that uses both Walsh codes and quasi orthogonal functions in spreading and despreading transmitted and received signals.
1. A high data rate spread spectrum receiver comprising:
an RF front end for receiving a signal;
a generator for generating a set of quasi orthogonal functions (QOF) and a set of Walsh codes;
a despreader, which has a plurality of PN despreaders and a plurality of respective, parallel fast Hadamard transformers (FHT) each corresponding to one multipath, for despreading the received signal to form a plurality of despread signals corresponding to the set of quasi orthogonal functions and the set of Walsh codes;
a multi-user detection block having a plurality of multi-user detectors for subtracting interference in the plurality of despread signals resulting from use of the quasi orthogonal functions and the set of Walsh codes to form plurality of corrected signals; and
a combiner for combining the plurality of corrected signals.
2. The high data rate spread spectrum receiver of claim 1 where the multi-user detection block is configured to exploit the mini-max cross-correlation between the QOF's and the set of Walsh functions.
3. The high data rate spread spectrum receiver of claim 1 where the multi-user detection block is configured to exploit the equal cross-correlation between the QOF's and every Walsh function of the same length.
4. The high data rate spread spectrum receiver of claim 1 wherein the multi-user detection block is configured to exploit the optimal cross-correlation properties between the QOF's and Walsh functions of shorter length as would be needed with the use of shorter spreading factor Walsh functions for higher data rates.
5. The high data rate spread spectrum receiver of claim 1 wherein the multi-user detection block is configured to exploit the optimal cross-correlation properties the QOF's from different QOF sets have with each other as well as with the set of Walsh functions.
6. The high data rate spread spectrum receiver of claim 1 wherein the multi-user detection block is configured to utilize parallel interference cancellation.
7. The high data rate spread spectrum receiver of claim 1 wherein the multi-user detection block is configured to utilize successive interference cancellation.
8. The high data rate spread spectrum receiver of claim 1 wherein the combiner is a rake combiner.
9. The high data rate spread spectrum receiver of claim 1 wherein the combiner is an inter-path interference equalizer (IPI).
10. Communication apparatus for communicating over a transmission channel comprising:
a high data rate spread spectrum transmitter comprising:
an encoder for encoding an input bit stream of R bits/second to produce an output bit stream of R.sub.S bits/second;
an interleaver for scrambling the bits of the output bit stream of the encoder to produce an interleaved bit stream;
a M-ary modulator for modulating the interleaved bit stream to produce a modulated bit stream;
a serial-to-parallel converter to convert the modulated bit stream to a plurality of parallel bit streams;
a generator for generating a set of quasi orthogonal functions of a set of Walsh codes;
an array of multipliers, each multiplier receiving one of the parallel bit streams and multiplying it with a Walsh code or a quasi orthogonal function of a Walsh code to produce a spread spectrum bit stream; and
a combiner for combining the spread spectrum bit streams from the array of multipliers to form a signal to be transmitted over the transmission channel; and a high data rate spread spectrum receiver comprising:
an RF front end for receiving a signal from the transmission channel;
a generator for generating a set of quasi orthogonal functions and a set of Walsh codes;
a despreader, which has a plurality of PN despreaders and a plurality of respective, parallel fast Hadamard transformers (FHT) each corresponding to one multipath, for despreading the received signal to form a plurality of despread signals corresponding to the set of quasi orthogonal functions and the set of Walsh codes;
a multi-user detection block having a plurality of multi-user detectors for subtracting interference in the plurality of despread signals resulting from use of the quasi orthogonal functions and the set of Walsh codes to form a plurality of corrected signals; and
a combiner for combining the plurality of corrected signals.
11. The communication apparatus of claim 10 where the multi-user detection block is configured to exploit the mini-max cross-correlation between the QOF's and the set of Walsh functions.
12. The communication apparatus of claim 10 where the multi-user detection block is configured to exploit the equal cross-correlation between the QOF's and every Walsh function of the same length.
13. The communication apparatus of claim 10 wherein the multi-user detection block is configured to exploit the optimal cross-correlation properties between the QOF's and Walsh functions of shorter length as would be needed with the use of shorter spreading factor Walsh functions for higher data rates.
14. The communication apparatus of claim 10 wherein the multi-user detection block is configured to exploit the optimal cross-correlation properties the QOF's from different QOF sets have with each other as well as with the set of Walsh functions.
15. The communication apparatus of claim 10 wherein the multi-user detection block is configured to utilize parallel interference cancellation.
16. The communication apparatus of claim 10 wherein the combiner is a rake combiner.
17. The communication apparatus of claim 10 wherein the combiner is an inter-path interference equalizer (IPI).