Code division multiple access employing orthogonal filter banks
Wavelet filters computed from a wavelet transform are used for encoding, transmitting, receiving, and decoding spread spectrum signals on multiple parallel frequency channels. The transmitter encodes the data stream via a mapping to a basis set of wavelets which are orthogonal across the time domain. The spread spectrum data is parsed from a serial bit stream to several parallel streams. The number of bits per symbol need not remain constant. Signals are created from each symbol by first up sampling by inserting zeros between successive symbols. These signals are passed through a bank of low-pass and high-pass filters derived from a wavelet packet transform. The resulting signal is transmitted in the base band of the transmission system, or transmitted by modulating the carrier of the transmission system. At the receiver, the steps are reversed to recover the symbols. Symbol decisions are made through any one of a number of methods.
1. A method of transmitting a spread spectrum signal from a transmitter comprising:
(a) parsing a spread spectrum serial bit stream into a plurality of parallel streams;
(b) within each of said plurality of parallel streams, forming a plurality of successive symbols;
(c) generating a signal from said plurality of successive symbols, wherein said signal is generated by the steps of:
(c1) up sampling by inserting zeros between said plurality of successive symbols;
(c2) selecting a low-pass filter and a high-pass filter pair derived from a wavelet packet transform for encoding said plurality of successive symbols; and
(c3) alternating an ordering of said low-pass and high-pass filters within each pair to preserve a natural frequency ordering of said filter encoded plurality of successive symbols;
(d) repeating steps (c1) through (c3) recursively log 2 N times for a signal of length N yielding the spread spectrum signal; and
(e) transmitting the spread spectrum signal from the transmitter.
2. The method according to claim 1 further comprising the step of:
utilizing a spread spectrum technique to create said spread spectrum serial bit stream.
3. The method according to claim 1 further comprising the step of:
utilizing a chipping frequency f c and a data frequency f i to create said spread spectrum serial bit stream wherein a ratio of f c to f i is greater than or equal to 1.
4. The method according to claim 1 wherein in step (b) a number of bits per symbol does not need to remain constant.
5. The method according to claim 1 wherein each of said plurality of symbols are formed from the set {0, 1, . . . 2 k −1} where k is the number of bits per symbol.
6. The method according to claim 1 wherein step (b) further comprises the step of:
pre-coding said plurality of symbols to decrease a probability of bit errors.
7. The method according to claim 6 wherein said pre-coding utilizes a Gray code.
8. The method according to claim 1 wherein step (e) further comprises transmitting the spread spectrum signal in a base band of the transmitter.
9. The method according to claim 1 wherein step (e) further comprises transmitting the spread spectrum signal by modulating a carrier of the transmitter.
10. The method according to claim 1 further comprising the step of:
receiving the spread spectrum signal in a receiver; and
performing in said receiver steps (a), (b), and (c) in reverse order to recover said plurality of symbols.
11. A method for encoding a source signal in a transmitter comprising:
(a) obtaining a wavelet filter bank name and a number of filter taps for encoding the source signal;
(b) generating a plurality of low-pass and high-pass filters corresponding to said wavelet filter bank name;
(c) setting up a working array to encode the source signal;
(d) obtaining the source signal;
(e) forming a binary data of the source signal into a plurality of symbols;
(f) up sampling said plurality of symbols by inserting zeros between successive symbols;
(g) encoding said up sampled plurality of symbols with said plurality of low-pass and high-pass filters, wherein an ordering of said low-pass and high-pass filters within each pair is switched to preserve a natural frequency ordering in said encoded plurality of symbols;
(h) repeating steps (f) and (g) recursively log 2 N times for N number of symbols producing an encoded signal; and
(i) transmitting said encoded signal.
12. The method according to claim 11 further comprising the step of:
applying a spread spectrum technique to a serial bit stream of the source signal, wherein said serial bit stream is parsed into several parallel bit streams.
13. The method according to claim 11 wherein step (e) further comprises;
pre-coding a binary data of the source signal to decrease a probability of bit errors.
14. The method according to claim 13 wherein said pre-coding utilizes a Gray code.
15. The method according to claim 11 wherein in step (e) a number of bits per symbol does not need to remain constant.
16. The method according to claim 11 wherein each of said plurality of symbols are formed from the set {0, 1, . . . 2 k −1} where k is the number of bits per symbol.
17. The method according to claim 11 wherein step (i) further comprises transmitting said encoded signal in a base band of the transmitter.
18. The method according to claim 11 wherein step (i) further comprises transmitting said encoded signal by modulating a carrier of the transmitter.
19. The method according to claim 11 further comprising the step of:
receiving said encoded signal in a receiver;
obtaining said wavelet filter bank name and said number of filter taps used for said encoded signal;
generating a plurality of reconstruction filters corresponding to said wavelet filter bank name;
decoding a plurality of symbols in said encoded signal with said plurality of reconstruction filters;
reordering said decoded plurality of symbols; and
down-sampling said reordered and decoded plurality of symbols to recover the source