Energy-efficient and reliable multicasting for WiMAX multi-hop relay networks

Orthogonal frequency division multiplexing (OFDM)-based wireless transmission technologies such as WiMAX are now widely deployed, and the frame check sequence (FCS) scheme is used to enhance the reliability of OFDM-based systems. As the padding overhead cannot be completely avoided in such systems when variable-length medium access control (MAC) frames are encapsulated, the authors propose a novel cyclic redundancy check (CRC)-based error-correction scheme that utilises the frame padding overhead to carry as much extra segmented FCS information as possible. In a multi-hop relay environment, a mobile station might receive a multicast frame more than once, so the error bit correction scheme could be triggered in the first transmission. In the IEEE´s work, the original CRC scheme is optional and only has limited error-detection capability in upper MAC layer. FCS requires a few bits in a frame, but in our work, CRC is compulsory and all sub-FCSs are carried by padding space without using any extra bit. For the best error-correction capability, all transmissions must be padded as many sub-FCSs are possible in cross layer. The proposed approach achieves a significant performance improvement over the legacy FCS scheme in terms of error detection and correction of multicast frames in a transparent mode multi-hop relay network, and it is redundancy-free as well as energy efficient. The authors assess the performance improvement via both mathematical analysis and simulations. The results show that the mobile stations get significant improvement of goodput and utilisation in an error-prone WiMAX multi-hop relay network.