Adaptive symbol mapping
The continuous demand for capacity and the limited available spectrum in wireless and wired communication has led to reliance on advanced modulation techniques to dramatically increase the number of bits per hertz per second. This demand in capacity and using the higher order constellations shorten the link range, and as a result, system gain becomes an important characteristic. The modulation techniques described here improve the system gain by, e.g., as much as 2.5 dB in high order modulations such as 4096-QAM. The modulation techniques include reducing the peak to average ratio and adding shaping gain. These techniques dramatically improve the system capacity, system gain, power consumption and system cost.
1. A method comprising:
a receiving source data to be modulated into a transmit signal;
mapping the source data to:
a nominal modulation constellation symbol for the source data; and
an alternate modulation constellation symbol for the source data;
receiving signal peak feedback with respect to the transmit signal; and
selecting, responsive to the signal peak feedback, between the nominal modulation constellation symbol and the alternate modulation constellation symbol for shaping the transmit signal.
2. The method of claim 1 , where selecting comprises:
selecting the alternate constellation symbol when the signal peak feedback exceeds a pre-determined feedback threshold.
3. The method of claim 1 , where mapping comprises:
applying a binary code to at least a portion of the source data.
4. The method of claim 1 , where:
mapping further comprises encoding a specific bit arising from the source data to obtain an encoded bit.
5. The method of claim 4 , comprising:
determining the nominal modulation constellation symbol and the alternate modulation constellation symbol according to the encoded bit.
6. The method of claim 5 , where:
encoding comprises binary encoding the specific bit.
7. The method of claim 1 , comprising:
determining a candidate version of the transmit signal; and
analyzing the candidate version of the transmit signal for a signal peak.
8. The method of claim 7 , where:
determining comprises applying a shaping filter to a candidate symbol for the transmit signal.
9. The method of claim 1 , comprising:
splitting the source data into a first layer bit stream and a second layer bit stream;
coding the first layer bit stream and the second layer bit stream in different ways to obtain different coding input streams; and
determining a candidate version of the transmit signal based on a combination of the different coding input streams.
10. The method of claim 9 , comprising:
determining the signal peak feedback based on a signal peak in the candidate version of the transmit signal.
11. A system comprising:
a receiver operable to receive source data to be modulated into a transmit signal;
a symbol mapper operable to map the source data to a nominal modulation constellation symbol and an alternate modulation constellation symbol;
a peak locator operable to receive signal peak feedback with respect to the transmit signal; and
a symbol selector operable to select, responsive to the signal peak feedback, between the nominal modulation constellation symbol and the alternate modulation constellation symbol for shaping the transmit signal.
12. The system of claim 11 , wherein the symbol selector is operable to select the alternate constellation symbol when the signal peak feedback exceeds a pre-determined feedback threshold.
13. The system of claim 11 , wherein the symbol mapper is operable to apply a binary code to at least a portion of the source data.
14. The system of claim 11 , wherein the symbol mapper is operable to encode a specific bit arising from the source data to obtain an encoded bit.
15. The system of claim 14 , wherein the symbol mapper is operable to determine the nominal modulation constellation symbol and the alternate modulation constellation symbol according to the encoded bit.
16. The system of claim 15 , wherein the symbol mapper is operable to binary encode the specific bit.
17. The system of claim 11 , wherein the peak locator is operable to determine a candidate version of the transmit signal and analyze the candidate version of the transmit signal for a signal peak.
18. The system of claim 17 , wherein the symbol selector is operable to apply a shaping filter to a candidate symbol for the transmit signal.
19. The system of claim 11 , wherein the system comprises:
a bit splitter operable to split the source data into a first layer bit stream and a second layer bit stream; and
an encoder operable to code the first layer bit stream and the second layer bit stream in different ways to obtain different coding input streams; and wherein
the symbol mapper is operable to determine a candidate version of the transmit signal based on a combination of the different coding input streams.
20. The system of claim 19 , wherein the peak locator is operable to determine the signal peak feedback based on a signal peak in the candidate version of the transmit signal.