Spectrum efficient cross-layer adaptation of Raptor codes for video multicasting over mobile broadband networks

This paper explores the use of rateless application layer Forward Error Correction (AL-FEC) based on Raptor codes in a spectrally efficient way for real-time video multicasting over mobile broadband networks. The link between channel errors at the PHY, MAC and application layers and the required Raptor code parameters for quasi-error free video transmission is investigated. Low Raptor code rates are shown to place high demands on the limited bandwidth of a wireless channel. The selection of Modulation and Coding Scheme (MCS) is extended to take into account the channel resources required to accommodate the additional Raptor overheads. A cross-layer optimization approach and a novel metric are proposed to select the Raptor code parameters and the MCS mode jointly to maximize wireless transmission efficiency. Simulation results show that 166% more bandwidth is required by a non-Raptor enabled multicast WiMAX system, assuming a Mobile Station (MS) speed of 10 km/h, in comparison to the optimized Raptor AL-FEC multicast WiMAX system. Results show that more bandwidth is required at lower MS speeds. Furthermore, the optimized Raptor AL-FEC system is shown to eliminate packet loss, to enhance the link budget by up to 6 dB, which quadruples multicast coverage in LoS locations, and to increase the total goodput by 67%, in comparison to a non-Raptor enabled multicast WiMAX system.