Multi-carrier spread spectrum using non-linear modification of sub-carrier bands
A multi-carrier spread spectrum (MC-SS) technique is disclosed which includes non-linearly modifying the sub-carriers in the receiver. A method ( 600 ) and receiver ( 200, 300 ) for processing an MC-SS signal, a transceiver for MC-SS communications ( 700 ), and an MC-SS radar ( 800 ) are describe.
1. A method for processing a spread spectrum signal having a plurality of sub-carrier bands, with each of the plurality of sub-carrier bands having substantially similar information encoded therein, comprising:
receiving the spread spectrum signal at a receiver;
demodulating the spread spectrum signal to obtain the plurality of sub-carrier bands from the spread spectrum signal;
modifying at least one of the plurality of sub-carrier bands with a predetermined non-linear function to form a plurality of modified sub-carrier bands; and
summing the plurality of modified sub-carrier bands to obtain a combined signal.
2. A method as in claim 1 , further comprising modifying each of the sub-carrier bands with a predetermined non-linear function to form a plurality of modified sub-carrier bands.
3. A method as in claim 1 , further comprising despreading the plurality of modified sub-carrier bands.
4. A method as in claim 1 , further comprising despreading the spread spectrum signal before demodulating the spread spectrum signal.
5. A method as in claim 1 , further comprising phase-demodulating the combined signal with a phase detector configured to demodulate an M-ary phase shift key modulated spread spectrum signal to obtain an estimate of the information.
6. A method as in claim 1 , wherein wherein the plurality of modified sub-carrier bands are substantially normalized, to produce a soft symbol signal.
7. A method as in claim 1 , wherein modifying further comprises modifying at least one of the plurality of sub-carrier bands with an amplitude normalization function.
8. A method as in claim 1 , wherein modifying further comprises modifying at least one of the plurality of sub-carrier bands with an amplitude limiting function.
9. A method as in claim 1 , wherein modifying further comprises modifying at least one of the plurality of sub-carrier bands with an amplitude logarithmic scaling function.
10. A method as in claim 1 , wherein modifying further comprises modifying at least one of the plurality of sub-carrier bands with an nth root amplitude scaling function, wherein n is greater than 1.
11. A method as in claim 10 , further comprising modifying at least one of the plurality of sub-carrier bands with an nth root amplitude scaling function, wherein n is less than 20.
12. A method as in claim 1 , further comprising estimating a plurality of channel gains corresponding to the plurality of modified sub-carrier bands to obtain estimated channel gains.
13. A method as in claim 12 , further comprising adjusting a parameter of the predetermined non-linear function based on the estimated channel gains.
14. A method as in claim 12 , further comprising:
estimating a channel frequency response from the estimated channel gains; and
inverting the channel frequency response to obtain an estimated channel delay.
15. A method as in claim 14 , further comprising determining a distance between a transmitter and the receiver from the estimated channel delay.
16. A method as in claim 15 , further comprising:
placing the transmitter and receiver in a substantially similar location to form a spread spectrum multi-carrier radar;
determining a time difference between a transmitted spread spectrum signal and receiving a reflected spread spectrum signal; and
calculating a distance to an object from the time difference between the transmitted signal and the received signal.
17. A receiver configured to process a spread spectrum signal having a plurality of sub-carrier bands, with each of the sub-carrier bands having substantially similar information encoded therein, comprising:
a demodulator configured to demodulate the spread spectrum signal and obtain the plurality of sub-carrier bands;
a modifying module coupled to the demodulator and configured to modify at least one of the plurality of sub-carrier bands with a predetermined non-linear function to form a plurality of modified sub-carrier bands;
a despreader coupled to the modifying module configured to despread the plurality of modified sub-carrier bands; and
a summer coupled to the despreader and configured to sum the plurality of modified sub-carrier bands.
18. The receiver of claim 17 wherein the modifying module is further configured to modify each of the plurality of sub-carrier bands with a predetermined non-linear function.
19. A receiver configured to process a spread spectrum signal having a plurality of sub-carrier bands, with each of the sub-carrier bands having substantially similar information encoded therein, comprising:
a despreader configured to despread the spread spectrum signal to obtain a despread spread spectrum signal;
a demodulator coupled to the despreader and configured to demodulate the despread spread spectrum signal and obtain the plurality of sub-carrier bands;
a modifying module coupled to the demodulator and configured to modify each of the plurality of sub-carrier bands with a predetermined non-linear function to form, a plurality of modified sub-carrier bands; and
a summer coupled to the modifying module and configured to sum the plurality of modified sub-carrier bands.
20. The receiver of claim 19 wherein the modifying module is further configured to modify each of the plurality of sub-carrier bands with a predetermined non-linear function.
21. A transceiver system configured to process a spread spectrum signal, comprising:
a transmitter configured to transmit a spread spectrum signal having a plurality of sub-carrier bands, with each of the sub carrier bands having substantially similar information encoded therein;
a receiver in communication with the transmitter and configured to receive the spread spectrum signal sent by the transmitter;
a demodulator coupled to the receiver and configured to demodulate the spread spectrum signal received by the receiver and obtain the plurality of sub-carrier bands; and
a modifying module coupled to the demodulator and configured to modify each of the plurality of sub-carrier bands with a predetermined non-linear function.
22. A method for processing a spread spectrum signal having a plurality of sub-carrier bands, with each of the plurality of sub-carrier bands having substantially similar information encoded therein, comprising:
receiving the spread spectrum signal at a receiver;
demodulating the spread spectrum signal to obtain the plurality of sub-carrier bands from the spread spectrum signal;
modifying at least one of the plurality of sub-carrier bands with a predetermined non-linear function to form a plurality of modified sub-carrier bands;
summing the plurality of modified sub-carrier bands to obtain a combined signal; and
phase-demodulating the combined signal with a phase detector configured to demodulate an M-ary phase shift key modulated spread spectrum signal to obtain an estimate of the information.
23. A method for processing a spread spectrum signal having a plurality of sub-carrier bands, with each of the plurality of sub-carrier bands having substantially similar information encoded therein, comprising:
receiving the spread spectrum signal at a receiver;
demodulating the spread spectrum signal to obtain the plurality of sub-carrier bands from the spread spectrum signal;
modifying at least one of the plurality of sub-carrier bands with a predetermined non-linear function to form a plurality of modified sub-carrier bands; and
estimating a plurality of channel gains corresponding to the plurality of modified sub-carrier bands to obtain estimated channel gains.
24. A method as in claim 23 , further comprising adjusting a parameter of the predetermined non-linear function based on the estimated channel gains.
25. A method as in claim 23 , further comprising:
estimating a channel frequency response from the estimated channel gains; and
inverting the channel frequency response to obtain an estimated channel delay.
26. A method as in claim 25 , further comprising determining a distance between a transmitter and the receiver from the estimated channel delay.
27. A method as in claim 26 , further comprising:
placing the transmitter and receiver in a substantially similar location to form a spread spectrum multi-carrier radar;
determining a time difference between a transmitted spread spectrum signal and receiving a reflected spread spectrum signal; and
calculating a distance to an object from the time difference between the transmitted signal and the received signal.