Highly-spectrally-efficient reception using orthogonal frequency division multiplexing
Circuitry for use in a receiver may comprise: a front-end circuit operable to receive an orthogonal frequency division multiplexing (OFDM) symbol on a first number of physical subcarriers. The circuitry may comprise a decoding circuit operable to decode the OFDM symbol using an inter-carrier interference (ICI) model, the decoding resulting in a determination of a sequence of symbols, comprising a second number of symbols, that most-likely correspond to the received OFDM symbol, where the second number is greater than the first number. The sequence of symbols may comprise N-QAM symbols, N being an integer. The ISCI model may be based, at least in part, on non-linearity experienced by the OFDM symbol during transmission by a transmitter, propagation over a channel, and/or reception by the receiver. The ISCI model may be based, at least in part, on phase-noise introduced to the OFDM symbol during transmission by a transmitter, propagation over a channel, and/or reception by the receiver.
1. Circuitry for use in a receiver, said circuitry comprising:
a front-end circuit operable to receive an orthogonal frequency division multiplexing (OFDM) symbol on a first number, C, of physical subcarriers;
a decoding circuit operable to perform decoding of said OFDM symbol using an inter-symbol correlation and/or inter-subcarrier interference (ISCI) model, said decoding resulting in determination of a sequence of a second number, C′, of symbols that most-likely corresponds to said OFDM symbol, where C′ is greater than C; wherein:
said decoding circuit is based on iterative decoding;
said iterative decoding uses feedback from a forward error correction (FEC) decoder; and
said feedback comprises one or both of: error location information and log likelihood ratios.
2. The method of claim 1 , wherein:
said circuitry receives OFDM symbols via a channel having a significant amount of nonlinearity;
said significant amount of nonlinearity degrades a performance metric in said receiver by less than 1 dB, relative to a perfectly linear channel; and
in a full response communication system, said significant amount of nonlinearity would degrade said performance metric by 1 dB or more, relative to a perfectly linear channel.
3. The circuitry of claim 1 , wherein said sequence of symbols comprises N-QAM symbols, N being an integer.
4. The circuitry of claim 1 , wherein said decoding circuit is based on maximum likelihood (ML) or maximum a priori (MAP) sequence estimation.
5. The circuitry of claim 1 , wherein said decoding uses reduced-state sequence estimation.
6. The circuitry of claim 1 , wherein said iterative decoding comprises exchanging elements between a first symbol candidate or survivor and a second symbol candidate or survivor.
7. The circuitry of claim 1 , wherein said ISCI model is based, at least in part, on non-linearity experienced by said OFDM symbol during transmission by a transmitter, propagation over a channel, and/or reception by said receiver.
8. The circuitry of claim 1 , wherein said ISCI model is based, at least in part, on phase-noise introduced to said OFDM symbol during transmission by a transmitter, propagation over a channel, and/or reception by said receiver.
9. The circuitry of claim 1 , wherein ISCI model is a frequency domain model.
10. The circuitry of claim 1 , comprising an equalizer circuit operable to perform per-subcarrier equalization of said physical subcarriers, wherein coefficients used for said per-subcarrier equalization are adapted based on a reconstructed signal generated using said ISCI model.
11. The circuitry of claim 1 , wherein said decoding circuit is operable to:
generate a first feedback signal to be used for phase and/or frequency correction of said physical subcarriers; and
generate a second feedback signal to be used for adapting coefficients of an equalizer.
12. The circuitry of claim 1 , wherein said circuitry is operable to measure one or more performance indicators for said OFDM symbol such that said one or more performance indicators may be transmitted as feedback to a device which transmitted said OFDM symbol.
13. The circuitry of claim 1 , wherein said decoding seeks to achieve a target symbol error rate, target bit error rate, and/or target packet error rate in presence of additive white Gaussian noise and a dynamic frequency selective fading channel.
14. A method performed in an electronic receiver, the method comprising:
receiving a first orthogonal frequency division multiplexing (OFDM) symbol on a first number of physical subcarriers of a channel;
generating an inter-carrier interference (ICI) model that accounts for non-linear distortion experienced by said first OFDM symbol and phase noise experienced by said first OFDM symbol;
subsequent to receiving said first OFDM symbol, receiving a second OFDM symbol on said physical subcarriers of said channel; and
using at least part of said ISCI model in performing decoding of said second OFDM symbol to determine a sequence of a second number of symbols that most-likely correspond to said second OFDM symbol, where said second number and is greater than said first number, wherein:
said decoding is iterative decoding that uses feedback from a forward error correction (FEC) decoder; and
said feedback comprises one or both of: error location information and log likelihood ratios.
15. A receiver comprising:
a front-end circuit operable to receive an orthogonal frequency division multiplexing (OFDM) symbol on a first number, C, of physical subcarriers;
a sequence estimation circuit operable to perform a sequence estimation process on said OFDM symbol using at least part of an inter-carrier interference (ICI) model, said sequence estimation process resulting in a determination of a sequence of quadrature amplitude modulation (QAM) symbols that most-likely correspond to said received OFDM symbol, said sequence comprising a second number, C′, of symbols, where C′ is greater than C, wherein:
said sequence estimation process is an iterative process that uses feedback from a forward error correction (FEC) decoder; and
said feedback comprises one or both of: error location information and log likelihood ratios.
16. The receiver of claim 15 , wherein said ISCI model is based, at least in part, on non-linearity experienced by said OFDM symbol during transmission by a transmitter, propagation over a channel, and/or reception by said receiver.