An Opportunistic Error Correction Layer for OFDM Systems

In this paper, we propose a novel cross layer scheme to lower power\ud consumption of ADCs in OFDM systems, which is based on resolution\ud adaptive ADCs and Fountain codes. The key part in the new proposed\ud system is that the dynamic range of ADCs can be reduced by\ud discarding the packets which are transmitted over 'bad' sub\ud carriers. Correspondingly, the power consumption in ADCs can be\ud reduced. Also, the new system does not process all the packets but\ud only processes surviving packets. This new error correction layer\ud does not require perfect channel knowledge, so it can be used in a\ud realistic system where the channel is estimated. With this new\ud approach, more than 70% of the energy consumption in the ADC can be\ud saved compared with the conventional IEEE 802.11a WLAN system under\ud the same channel conditions and throughput. The ADC in a receiver\ud can consume up to 50% of the total baseband energy. Moreover, to\ud reduce the overhead of Fountain codes, we apply message passing and\ud Gaussian elimination in the decoder. In this way, the overhead is\ud 3% for a small block size (i.e. 500 packets). Using both methods\ud results in an efficient system with low delay

Another approach to save energy in OFDM systems

In this paper, we propose an energy-efficient error correction scheme to lower the power consumption of the ADCs in the OFDM system. The proposed opportunistic error correction scheme is based on resolution adaptive ADCs and fountain codes. The key idea is to reduce the dynamic range of the channel by discarding part of the channel in deep fading. Correspondingly, the power consumption in ADCs can be decreased. In our approach, each sub-carrier transports a fountain-encoded packet. The receiver only decodes fountain-encoded packets with high SNR. Others are discarded. To compensate for the discarded packets, a high order modulation is used. The new error correction layer does not require perfect channel knowledge, so it can be applied in a real system. With our approach and 16-QAM, the energy consumption in ADCs is reduced by around 73% with non-perfect channel estimation comparing to the traditional IEEE 802.11a system under the same channel conditions and throughput