Optimized irregular Gallager codes for OFDM transmission

LDPC code design for OFDM channel: graph connectivity and information bits positioning

“…Therefore, the position of connection degree of the variable node is an important parameter. Recently, this property has been exploited in [4]. Since the optimization of the LDPC codes is done by minimizing the probability of error, the optimized code does not have good performance in term of FER below the targeting probability of error.…”

“…In a real system, SNRs are different between the subcarriers (or equivalently for every variable node) and therefore the means m u0,i (h i ) are different for each i as well. In order to drastically reduce the number of parameters m u0,i , we use the same approximation that is proposed in [4]. The original channel spectrum shown on Fig.…”

“…However, the positioning of the information/redundancy bits can not be considered in this approach. For binary or AWGN channels, optimization of the information bits placement gives minor gains as shown in [4]. Nevertheless, for an OFDM transmission as noticed in [4], significant gain in term of Bit Error rate (BER) and FER are expected.…”

“…Much attention is being given to LDPC codes due to their excellent performance and the simplicity of iterative decoding making high throughput possible [2]. It has been shown in [4], that for an OFDM transmission, the optimization of the LDPC code accordingly with the channel spectrum provides large performance gain with no reduction of 1 This work was supported in part by Nokia Corporation, Texas Instruments Inc., and by NSF under grants ANI-9979465, EIA-0224458, and EIA-0321266. the spectral efficiency.…”

“…Irregular LDPC codes have excellent performance at moderate computational complexity: they are strong candidates for channel coding in such systems. In the context of an OFDM transmission, the authors in [Mannoni, 2002] proposed to optimize the graph connectivity of the irregular LDPC code accordingly to the channel spectrum. However, their codes did not have good performance for a FER range of 0.001 -0.0001.…”