Spread spectrum with doppler optimization
A method of compensating for doppler phase errors includes receiving a signal at a receiver wherein the signal is spread using a pseudo-noise code, dividing the signal into a plurality of smaller coherent units and then compensating for induced doppler phase errors by analyzing the plurality of smaller coherent units. Analysis may include producing a plurality of coherent sums by summing across the smaller coherent units and then summing non-coherently the plurality of coherent sums. Analysis may also include demodulating a symbol from the smaller coherent units. A modulation technique may be selected from a plurality of modulation techniques and then be used to encode and transmit a symbol stream.
1. A method of compensating for induced doppler phase errors while communicating through a multiple access spread spectrum communication interface, the method comprising:
receiving a first signal at a receiver, wherein the first signal is spread using a predetermined pseudo-noise (PN) code;
dividing the first signal into a plurality of first smaller coherent units;
summing across each of the plurality of first smaller coherent units to produce a plurality of first coherent sums;
summing non-coherently the plurality of first coherent sums to detect a magnitude of the first signal;
selecting a coherent integration length based on the magnitude of the first signal to configure a demodulation;
receiving a second signal at the receiver, wherein the second signal is spread using the predetermined pseudo-noise (PN) code;
dividing the second signal into a plurality of second smaller coherent units; and
demodulating a first symbol from the plurality of first smaller coherent units and the plurality of second smaller coherent units comprises cross multiplying the complex conjugate of a unit of the first smaller coherent units with a unit of the second smaller coherent units.
2. The method of claim 1 , wherein the demodulation of the first symbol relies on a first unit of the plurality of first smaller coherent units and a last unit of the plurality of second smaller coherent units.
3. The method of claim 1 , wherein the first signal neighbors the second signal in a sequence of signals.
4. The method of claim 1 , wherein the first signal has a first random timing offset.
5. The method of claim 1 , wherein the second signal has a second random timing offset.
6. The method of claim 1 , further comprising:
detecting an induced doppler phase error in the first signal;
selecting a modulation technique from a plurality of modulation techniques from among the following modulation techniques: differential binary phase shift keyed modulation or 2-ary modulation;
encoding a symbol stream using the selected modulation technique; and
transmitting the encoded symbol stream.
7. The method of claim 6 , further wherein the selected modulation technique is based on the detected induced doppler phase error.
8. The method of claim 6 , further comprising:
selecting a second modulation technique from the plurality of modulation techniques; and
encoding a second symbol stream using the selected second modulation technique.
9. A device for communicating in a spread spectrum system comprising:
a receiver in communication with a processor and configured to receive a first signal and a second signal, wherein the first signal is spread using a predetermined pseudo-noise (PN) code and the second signal is spread using the predetermined pseudo-noise (PN) code; and
a processor operatively coupled to the receiver and configured to:
divide the first signal into a plurality of first smaller coherent units,
sum across each of the plurality of first smaller coherent units to produce a plurality of first coherent sums;
sum non-coherently the plurality of first coherent sums to detect a magnitude of the first signal;
select a coherent integration length based on the magnitude of the first signal to configure a demodulation;
divide the second signal into a plurality of second smaller coherent units; and
demodulate a first symbol from the plurality of first smaller coherent units and the plurality of second smaller coherent units comprises cross multiplying the complex conjugate of a unit of the first smaller coherent units with a unit of the second smaller coherent units.
10. The device of claim 9 , wherein the first signal has a first random timing offset.
11. A spread spectrum communication system comprising:
a device having a receiver configured to receive a first signal and a second signal, wherein the first signal is spread using a predetermined pseudo-noise (PN) code and the second signal is spread using the predetermined pseudo-noise (PN) code; and a processor operatively coupled to the receiver and configured to:
divide the first signal into a plurality of first smaller coherent units;
sum across each of the plurality of first smaller coherent units to produce a plurality of first coherent sums;
sum non-coherently the plurality of first coherent sums to detect a magnitude of the first signal;
select a coherent integration length based on the magnitude of the first signal to configure a demodulation;
divide the second signal into a plurality of second smaller coherent units; and
demodulate a first symbol from the plurality of first smaller coherent units and the plurality of second smaller coherent units comprises cross multiplying the complex conjugate of a unit of the first smaller coherent units with a unit of the second smaller coherent units; and
an access point in communication with the device, wherein the access point comprises a transmitter configured to transmit the first signal.
12. The system of claim 11 , wherein the first signal has a first random timing offset.