Chirp communications

1. A method for receiving a chirp signal at a receiver, the chirp signal communicated over a link from a transmitter, the chirp signal comprising at least one symbol, each symbol comprising a plurality of identical chirps, each chirp encoding a symbol value, the method comprising:

determining a quality of the link;

determining the number of coherent integrations and non-coherent integrations to apply per symbol in dependence on the quality of the link, such that the number of chirps per coherent integration increases if the link quality is below a threshold;

for each symbol, coherently and non-coherently integrating the plurality of chirps in accordance with the determined numbers so as to form an integrated symbol; and

for each symbol, decoding the symbol value from the integrated symbol.

2. A method for receiving a chirp signal at a receiver, the chirp signal communicated over a link from a transmitter, the chirp signal comprising at least one symbol, each symbol comprising a plurality of identical chirps, each chirp encoding a symbol value, the method comprising:

determining a drift between the receiver and transmitter;

determining the number of coherent integrations and non-coherent integrations to apply per symbol in dependence on the drift between the receiver and transmitter, such that the number of non-coherent integrations increases if the drift is above a threshold;

for each symbol, coherently and non-coherently integrating the plurality of chirps in accordance with the determined numbers so as to form an integrated symbol; and

for each symbol, decoding the symbol value from the integrated symbol.

3. A method as claimed in claim 1 , further comprising:

determining a drift between the receiver and transmitter; and

only determining the number of coherent integrations and non-coherent integrations to apply per symbol in dependence on the link quality if the drift is below a threshold.

4. A method as claimed in claim 2 , further comprising:

determining a quality of the link between the receiver and transmitter; and

only determining the number of coherent integrations and non-coherent integrations to apply per symbol in dependence on the drift if the link quality is above a threshold.

5. A method as claimed in claim 2 , wherein determining the drift comprises determining a frequency drift between the receiver and the transmitter.

6. A method as claimed in claim 5 , comprising determining the frequency drift by multiplying each received chirp with a plurality of generated chirps, each generated chirp occupying a frequency band offset from the other generated chirps, and analysing the correlation peaks so as to determine the frequency band occupied by the received chirp.

7. A method as claimed in claim 2 , wherein determining the drift comprises determining a timing drift between the receiver and the transmitter.

8. A method as claimed in claim 7 , comprising determining the timing drift by sampling each received chirp at a plurality of time periods offset from each other, and correlating each sampled chirp with a generated chirp, and analysing the correlation peaks so as to determine the time period occupied by the received chirp.

9. A receiver for receiving a chirp signal communicated over a link from a transmitter, the chirp signal comprising at least one symbol, each symbol comprising a plurality of identical chirps, each chirp encoding a symbol value, the receiver comprising:

a processor configured to determine a quality of the link, the processor further configured to determine the number of coherent integration and non-coherent integrations to apply per symbol in dependence on the quality of the link, such that the number of chirps per coherent integration increases if the link quality is below a threshold;

an integrator configured to, for each symbol, coherently and non-coherently integrate the plurality of chirps in accordance with the determined numbers so as to form an integrated symbol; and

a decoder configured to, for each symbol, decode the symbol value from the integrated symbol.

10. A receiver for receiving a chirp signal communicated over a link from a transmitter, the chirp signal comprising at least one symbol, each symbol comprising a plurality of identical chirps, each chirp encoding a symbol value, the receiver comprising:

a processor configured to determine a drift between the receiver and transmitter, the processor further configured to determine the number of coherent integration and non-coherent integrations to apply per symbol in dependence on the drift between the receiver and transmitter, such that the number of non-coherent integrations increases if the drift is above a threshold;

an integrator configured to, for each symbol, coherently and non-coherently integrate the plurality of chirps in accordance with the determined numbers so as to form an integrated symbol; and

a decoder configured to, for each symbol, decode the symbol value from the integrated symbol.

11. A receiver as claimed in claim 9 , wherein the processor is further configured to determine a drift between the receiver and transmitter, and only determine the number of coherent integrations and non-coherent integrations to apply per symbol in dependence on the link quality if the drift is below a threshold.

12. A receiver as claimed in claim 10 , wherein the processor is further configured to determine a quality of the link between the receiver and transmitter, and only determine the number of coherent integrations and non-coherent integrations to apply per symbol in dependence on the drift if the link quality is above a threshold.

13. A receiver as claimed in claim 10 , wherein the processor is configured to determine the drift by determining a frequency drift between the receiver and the transmitter.

14. A receiver as claimed in claim 13 , wherein the processor is configured to determine the frequency drift by multiplying each received chirp with a plurality of generated chirps, each generated chirp occupying a frequency band offset from the other generated chirps, and analyse the correlation peaks so as to determine the frequency band occupied by the received chirp.