A Hybrid Statistical and Prioritised Unequal Error Protection Scheme for IEEE 802.11n LDPC Codes

Abstract

The combination of powerful error correcting codes such as (LDPC) codes and Quadrature Amplitude Modulation (QAM) has been widely deployed in wireless communication standards such as the IEEE 802.11n and DVB-T2. Recently, several Unequal Error Protection schemes which exploit non-uniform degree distribution of bit nodes in irregular LDPC codes have been proposed. In parallel, schemes that exploit the inherent UEP characteristics of the QAM constellation have also been developed. In this paper, a hybrid UEP scheme is proposed for LDPC codes with QAM. The scheme uses statistical distribution of source symbols to map the systematic bits of the LDPC encoded symbols to the QAM constellation. Essentially, systematic symbols having highest probabilities of occurrence are mapped onto the low power region of the QAM constellation and those with a low probability of occurrence are mapped onto the high power region. The decrease in overall transmission power allows for an increased spacing between the QAM constellation points. Additionally, the scheme uses the distribution of the bit node degree of the LDPC code-word to map the parity bits having the highest degree onto prioritised QAM constellation points. Simulations with the IEEE 802.11n LDPC codes revealed that the proposed scheme can provide gains of up to 0.91 dB in Eb/No compared with other UEP schemes for a range of Bit Error Rate (BER) values

An unequal error protection scheme for non-binary LDPC using statistical QAM and prioritized mapping

“…1. It is based on the transmitter proposed in [19] with the exception that NB-LDPC has been used in this case. Only one of the two optional multiplexing modes labelled as "Mode 1" and "Mode 2" is used at a time, depending on which mode is selected.…”

“…The alphabet in the stream are fitted into packets such that the number of bits obtained after performing VLC on the alphabet in each packet is equal to the number of systematic bits required for NB-LDPC encoding [19]. [19].…”

“…Consequently, the average energy needed for image transmission was much smaller and allowed for increasing the spacing between QAM constellation points for the same average energy thus improving the BER [18]. Finally, in [19], a novel hybrid UEP scheme was proposed for LDPC codes with QAM. The scheme used the statistical distribution of the source symbols to map An Unequal Error Protection Scheme for Non-Binary LDPC using Statistical QAM… 303 the systematic bits of the LDPC encoded symbols on the QAM constellation.…”

“…In this paper, the hybrid UEP scheme of [19] is extended to NB-LDPC codes. In general the hybrid UEP scheme combines the concepts of statistical QAM, prioritized constellation mapping and uneven degree distribution of variable nodes with LDPC codes.…”

“…Results showed that the proposed hybrid scheme can provide gains ranging from 0.58 dB to 1.24 dB in E b /N 0 for code rates of 1/2, 2/3 and 3/4 as compared with other UEP schemes for a range of Bit Error Rate (BER) values. Compared with LDPC codes of [19], when the proposed UEP scheme is applied to NB-LDPC codes, additional gains of up to 0.17 dB and 0.22 dB are obtained when using 16-QAM and 64-QAM respectively. This paper is structured as follows.…”