Practical Quantizer Design for Half-Duplex Estimate-and-Forward Relaying

• Published in: IEEE transactions on communications Vol. 59; no. 1; pp. 74 - 83
• Main Authors: Chakrabarti, A, Sabharwal, A, Aazhang, B
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.01.2011; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; AWGN; Codes; Coding, codes; compress-and-forward; Cooperative communication; Counters; Distortion; distortion minimization; Encoding; estimate-and-forward; Exact sciences and technology; Information, signal and communications theory; Links; Minimization; Modulation; Modulation, demodulation; mutual information maximization; Preserves; Protocols; Quantization; quantize-and-forward; Relay; relay protocol; Relaying; Relays; Signal and communications theory; Signal to noise ratio; Simplification; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments); Performance evaluation; Relaying; Relay; quantize-and-forward; AWGN; Cooperative communication; Bit error rate; distortion minimization; compress-and-forward; Binary phase shift keying; mutual information maximization; Duplex process; Information source; estimate-and-forward; Error correcting code; Parity check codes; Quantifier; relay protocol; Mutual information; Signal to noise ratio
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2010.110310.090102

We propose a quantizer design method for practical half-duplex estimate-and-forward (EF) relaying. First, we identify the regime in which EF relaying yields substantial gains where the SNR is low and the relay-destination link is strong. Then we discover design simplifications that reduce complexity with little loss in the above regime. For relay quantizer design, we first consider mean-squared distortion minimization. To illustrate the unsuitability of the approach, we present an example with AWGN links and a BPSK source where the quantizer with worst mean squared distortion in a given set maximizes achievable rate. A distortion-minimizing quantizer attempts to preserve the received signal at the relay. The quantizer should instead preserve source information. In information theoretical terms, the quantizer should maximize the mutual information between the source transmission and the quantizer output conditioned on the side information at the destination subject to a rate constraint. The above conclusion, derived from information theoretical principles, is then translated to a quantizer design method for the low SNR regime. Using LDPC codes of blocklength 100000, BPSK modulation, and quantizers designed using the proposed criterion, we observe performance less than a decibel away from the achievable rate at a BER of 10 -4 .