Performance of IEEE 802.11n LDPC codes with modified reliability based hybrid ARQ and Unequal Error Protection

Abstract

Wireless communication standards such as the IEEE 802.11n Wi-Fi standard employ powerful error correcting codes such as Low Density Parity Check (LDPC) codes and Hybrid Automatic Repeat reQuest (HARQ) to achieve reliable transmission. Reliability-Based HARQ (RB-HARQ) schemes have proved to be an efficient alternative approach to incremental redundancy ARQ. This paper proposes a modified RB-HARQ scheme for IEEE 802.11n LDPC codes and combines it with an Unequal Error Protection (UEP) scheme which performs prioritized constellation mapping to exploit the inherent UEP property of the Quadrature Amplitude Modulation (QAM) constellation. With 16-QAM and a code-rate of ½, the proposed scheme provides a gain of 1.5 dB in Eb/No (ratio of energy per bit to noise power spectral density) and 2% in throughout at a Bit Error Rate (BER) close to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> over a scheme which uses conventional RB-HARQ without UEP. Moreover, with 64-QAM a maximum gain of 4.5 dB in Eb/No is obtained.