Opportunistic Error Correction: When Does It Work Best for OFDM Systems?

The water-filling algorithm enables an energy-efficient OFDM-based transmitter by maximizing the capacity of a frequency selective fading channel. However, this optimal strategy requires the perfect channel state information at the transmitter that is not realistic in wireless applications. In this paper, we propose opportunistic error correction to maximize the data rate of OFDM systems without this limit. The key point of this approach is to reduce the dynamic range of the channel by discarding a part of the channel in deep fading. Instead of decoding all the information from all the sub-channels, we only recover the data via the strong sub-channels. Just like the water-filling principle, we increase the data rate over the stronger sub-channels by sacrificing the weaker sub-channels. In such a case, the total data rate over a frequency selective fading channel can be increased. Correspondingly, the noise floor can be increased to achieve a certain data rate compared to the traditional coding scheme. This leads to an energy-efficient receiver. However, it is not clear whether this method has advantages over the joint coding scheme in the narrow-band wireless system (e.g. the channel with a low dynamic range), which will be investigated in this paper.

Opportunistic Error Correction for OFDM-Based DVB Systems

DVB-T2 (second generation terrestrial digital video broadcasting) employs LDPC (Low Density Parity Check) codes combined with BCH (Bose-Chaudhuri-Hocquengham) codes, which has a better performance in comparison to convolutional and Reed-Solomon codes used in other OFDM-based DVB systems. However, the current FEC layer in the DVB-T2standard is still not optimal. In this paper, we propose a novel error correction scheme based on fountain codes for OFDM-based DVB systems. The key element in this new scheme is that only packets are processed by the receiver which has encountered high-energy channels. Others are discarded. To achieve a data rate of 9.5 Mbits/s, this new approach has a SNR gain of at least 10 dB with perfect channel knowledge and 11 dB with non-perfect channel knowledge in comparison to the current FEC layer in the DVB-T2standard. With a low-complexity interpolation-based channel estimation algorithm, opportunistic error correction offers us a QEF (Quasi Error Free) quality with a maximum DF (Doppler Frequency) of 40 Hz but the current DVB-T2 FEC layer can only provide a BER of 10?7 quality after BCH decoding with a maximum DF of 20 Hz.