Optimized receivers for faster than nyquist (FTN) transmission rates in high spectral efficiency satellite systems

Patent metadata

Field	Value
Publication number	US-9634870-B2
Application number	US-201615007149-A
Country	US
Kind code	B2
Filing date	Jan 26, 2016
Priority date	Jun 30, 2014
Publication date	Apr 25, 2017
Grant date	Apr 25, 2017

Abstract

An approach is provided for increasing transmission throughput rates for a source signal transmitted over a wireless channel, applying faster-than-Nyquist (FTN) signaling rates combined with tight frequency roll-off to the a source signal. A receiver is provided that compensates for ISI effects induced by the FTN rate and tight frequency roll-off, where the complexity of the receiver grows only linearly with the interference memory. The receiver comprises an equalizer configured to compensate for the ISI effects, and a decoder configured to decode the output of the equalizer to determine and regenerate the source signal. The receiver processes the received signal via a plurality of processing iterations. For one processing iteration, the decoder generates a set of a posteriori soft information based on the output of the equalizer, and the equalizer uses the a posteriori soft information as a priori soft information for a subsequent processing iteration.

First claim

The invention claimed is:

1. An apparatus comprising:
a receiver configured to receive a signal transmitted over a wireless channel via a high-power amplifier of a transponder,
wherein the received signal comprises a discrete carrier signal of a respective carrier phase and frequency, and wherein the carrier signal reflects a plurality of source data symbols of a respective source signal with which it was modulated, and
wherein the carrier signal includes inter-symbol interference (ISI) effects induced based on a faster-than-Nyquist (FTN) signaling rate and a tight frequency roll-off applied to the respective source signal for transmission over the wireless channel;

a sampler circuit configured to sample the carrier signal at the FTN signaling rate to generate a sequence of sampled estimates of the source data symbols of the respective source signal; and
a receive signal processor configured to process the sequence of sampled source data symbol estimates to determine original source data symbols of the respective source signal;
wherein the receive signal processor comprises:
an equalizer configured to compensate for the ISI effects induced based on the FTN signaling rate and the tight frequency roll-off applied to the source signal; and
a decoder configured to decode an output of the equalizer to determine and regenerate the respective source signal for the carrier signal.

2. The apparatus according to claim 1 , wherein the FTN signaling rate is approximately 6% and the tight frequency roll-off is approximately 5%.

3. The apparatus according to claim 1 , wherein, in compensating for the ISI effects induced by the FTN signaling rate and tight frequency roll-off, the equalizer is configured to use a priori soft information of every code bit for the carrier on which the source signal was transmitted.

4. The apparatus according to claim 3 , wherein the a priori soft information comprises log-likelihood ratios (LLRs).

5. The apparatus according to claim 3 , wherein:
the decoder is further configured to generate a set of a posteriori log-likelihood ratios (LLRs) based on the output of the equalizer; and
the a priori soft information used by the equalizer comprises the a posteriori LLRs generated by the decoder.

6. The apparatus according to claim 3 , wherein, in compensating for the ISI effects induced by the FTN signaling rate and tight frequency roll-off, the receive signal processor is configured to process the received signal via a plurality of processing iterations, and wherein:
for a one processing iteration, the decoder is further configured to generate a set of a posteriori soft information based on the output of the equalizer; and
for a processing iteration subsequent to the one processing iteration, the a priori soft information used by the equalizer comprises the a posteriori soft information generated by the decoder for the one processing iteration.

7. The apparatus according to claim 3 , wherein, in compensating for the ISI effects induced by the FTN signaling rate and tight frequency roll-off, the receive signal processor is configured to process the received signal via a plurality of processing iterations, and wherein the receive signal processor further comprises:
a log-likelihood ratio (LLR) processor configured to generate, for a one processing iteration, a set of a posteriori log-likelihood ratios (LLRs) based on the output of the equalizer; and
wherein the decoder is further configured to decode, for the one processing iteration, the a posteriori LLRs generated by the LLR processor, and to provide the decoded a posteriori LLRs back to the equalizer; and
wherein the a priori soft information used by the equalizer, for a processing iteration subsequent to the one processing iteration, comprises the decoded a posteriori LLRs provided by the decoder from the one processing iteration.

8. The apparatus according to claim 7 , further comprising:
a deinterleaver configured to deinterleave the a posteriori LLRs generated by the LLR processor before being decoded by the decoder; and
an interleaver configured to interleave the decoded a posteriori LLRs generated by the decoder prior to being provided back to the equalizer.

9. A method comprising:
receiving, by a communications terminal, a signal transmitted over a wireless channel via a high-power amplifier of a transponder, wherein the received signal comprises a discrete carrier signal of a respective carrier phase and frequency, and wherein the carrier signal reflects a plurality of source data symbols of a respective source signal with which it was modulated, and wherein the carrier signal includes inter-symbol interference (ISI) effects induced based on a faster-than-Nyquist (FTN) signaling rate and a tight frequency roll-off applied to the respective source signal for transmission over the wireless channel;
sampling the carrier signal at the FTN signaling rate to generate a sequence of sampled estimates of the source data symbols of the respective source signal; and
processing the sequence of sampled source data symbol estimates to determine original source data symbols of the respective source signal;
wherein the processing of the sequence of sampled source data symbol estimates comprises:
equalizing the sequence of sampled source data symbol estimates to compensate for the ISI effects induced based on the FTN signaling rate and the tight frequency roll-off applied to the source signal; and
decoding an output of the equalizing step to determine and regenerate the respective source signal.

10. The method according to claim 9 , wherein the FTN signaling rate is approximately 6% and the tight frequency roll-off is approximately 5%.

11. The method according to claim 9 , wherein, in compensating for the ISI effects induced by the FTN signaling rate and tight frequency roll-off, the equalizing of the received signal comprises:
utilizing a priori soft information of every code bit for the carrier on which the source signal was transmitted.

12. The method according to claim 11 , wherein the a priori soft information comprises log-likelihood ratios (LLRs).

13. The method according to claim 11 , wherein the decoding of the output of the equalizing step comprises:
generating a set of a posteriori log-likelihood ratios (LLRs) based on the output of the equalizing step, wherein the a priori soft information utilized in the equalizing step comprises the a posteriori LLRs generated by the decoding of the output of the equalizing step.

14. The method according to claim 11 , wherein, in compensating for the ISI effects induced by the FTN signaling rate and tight frequency roll-off, the processing of the received signal comprises decoding the received signal via a plurality of processing iterations, and wherein:
for a one processing iteration, the decoding of the output of the equalizing step comprises generating a set of a posteriori soft information based on the output of the equalizing step; and
for a processing iteration subsequent to the one processing iteration, the a priori soft information utilized in the equalizing step comprises the a posteriori soft information generated by the decoding of the output of the equalizing step for the one processing iteration.

15. The method according to claim 11 , wherein, in compensating for the ISI effects induced by the FTN signaling rate and tight frequency roll-off, the processing of the received signal comprises decoding the received signal via a plurality of processing iterations, and wherein the method further comprises:
for a one processing iteration, generating a set of a posteriori log-l

Assignees

• Hughes Network Systems Llc

Inventors

• Beidas Bassel
• Seshadri Rohit Iyer
• Eroz Mustafa
• Lee Lin-Nan

Classifications

• H04L2025/03611

  Iterative algorithms · CPC title

• H04L2025/03777

  characterised by the signalling · CPC title

• H04L25/03286

  with channel-decoding circuitry · CPC title

• H04L25/03318 Primary

  Provision of soft decisions · CPC title