Carrier tracking without pilots
View Patent ↗A carrier tracking technique includes allocating a first number of bits per symbol to a carrier tracking subcarrier of a plurality of subcarriers of an orthogonal frequency division multiplexing (OFDM) signal based on a first target performance margin. The technique includes allocating numbers of bits per symbol to other subcarriers of the plurality of subcarriers based on a second target performance margin.
1. A method comprising:
allocating a first number of bits per symbol to a carrier tracking subcarrier of a plurality of subcarriers of an orthogonal frequency division multiplexing (OFDM) signal based on a first target performance margin;
allocating numbers of bits per symbol to other subcarriers of the plurality of subcarriers based on a second target performance margin; and
communicating data using the OFDM signal, the first number of bits per symbol of data modulating the carrier tracking subcarrier and the numbers of bits per symbol of data modulating the other subcarriers of the plurality of subcarriers,
wherein allocating the first number of bits per symbol comprises determining a maximum number of data bits that provides the first target performance margin based on a performance estimate for the carrier tracking subcarrier, and
wherein allocating numbers of bits per symbol to other subcarriers comprises determining maximum numbers of data bits that provide the second target performance margin based on corresponding performance estimates for the other subcarriers.
2. The method, as recited in claim 1 , wherein the first target performance margin is substantially greater than the second performance margin.
3. The method, as recited in claim 1 , further comprising:
communicating indications of the first number of bits per symbol allocated to the carrier tracking subcarrier and the numbers of bits per symbol allocated to the other subcarriers.
4. The method, as recited in claim 1 , further comprising:
selecting the carrier tracking subcarrier from the plurality of subcarriers of the OFDM signal based on performance estimates for the plurality of subcarriers.
5. The method, as recited in claim 4 , wherein the selecting is based on a performance estimate for the carrier tracking subcarrier as compared to performance estimates corresponding to others of the plurality of subcarriers.
6. The method, as recited in claim 4 , wherein the selecting comprises:
determining as the carrier tracking subcarrier, a subcarrier of the plurality of subcarriers of the OFDM system having a maximum performance estimate.
7. The method, as recited in claim 4 , further comprising:
generating the performance estimates for the plurality of subcarriers based on known received symbols.
8. The method, as recited in claim 1 , further comprising:
selecting additional carrier tracking subcarriers from the plurality of subcarriers; and
allocating numbers of bits to the additional carrier tracking subcarriers based on the first target performance margin.
9. The method, as recited in claim 1 , further comprising:
generating a frequency offset indicator based on data received using the carrier tracking subcarrier.
10. The method, as recited in claim 9 , further comprising:
adjusting received data of an OFDM receiver based on the frequency offset indicator.
11. The method, as recited in claim 1 , wherein the first target performance margin is at least 3 dB greater than the second target performance margin.
12. An apparatus comprising:
a select module configured to select a carrier tracking subcarrier from a plurality of subcarriers of an orthogonal frequency division multiplexing (OFDM) signal based on performance estimates for the plurality of subcarriers; and
a bit allocation module configured to allocate a number of bits per symbol to the carrier tracking subcarrier frequency based on a first target performance margin and configured to allocate numbers of bits per symbol to other subcarriers of the plurality of subcarriers based on a second target performance margin,
wherein the bit allocation module allocates the number of bits per symbol to the carrier tracking subcarrier according to a maximum number of bits that provides the first target performance margin based on a performance estimate for the carrier tracking subcarrier, and
wherein the bit allocation module allocates the numbers of data bits per symbol to other subcarriers according to maximum numbers of bits that provide the second target performance margin based on corresponding performance estimates for the other subcarriers.
13. The apparatus, as recited in claim 12 , wherein the first target performance margin is substantially greater than the second target performance margin.
14. The apparatus, as recited in claim 12 , wherein the first target performance margin is at least 3dB greater than the second target performance margin.
15. The apparatus, as recited in claim 12 , further comprising:
a performance estimator configured to generate a plurality of performance estimates for the plurality of subcarriers.
16. The apparatus, as recited in claim 12 , wherein the select module comprises:
a maximum performance detector configured to identify as the carrier tracking subcarrier, a subcarrier having a maximum performance estimate of the plurality of performance estimates.
17. The apparatus, as recited in claim 12 , further comprising:
a carrier tracking circuit module configured to generate a frequency offset indicator based on data recovered from the carrier tracking subcarrier.