The Utility of Hybrid Error-Erasure LDPC (HEEL) Codes for Wireless Multimedia Invited Paper

Traditional wireless communication protocols do not relay corrupted packets towards the application layer and neither do they forward such packets over multiple hops. Such an approach can lead to a significant number of packet drops and thus a severe deterioration in performance of high bandwidth applications. Cross-layer protocols which do relay and forward corrupted packets have exhibited substantial promise to mitigate the above problem and thus their utility for wireless multimedia needs to be explored further. Moreover, there is a need to identify efficient channel coding methods for the cross-layer channel. Unlike the traditional schemes, where the channel observed at the application layer is a pure erasure channel, in the cross-layer schemes the application layer channel exhibits hybrid erasure- error impairments. Thus in this paper, we use a rather abstract link-layer model on the basis of which we compare the performance of cross-layer and conventional schemes. We identify the modifications required to be made to RS and LDPC based FEC schemes in order to use them over hybrid erasure- error channels. Finally we compare the considered schemes in terms of video quality using the emerging H.264 video standard. Our video analysis is based on employing a hybrid error-erasure channel coding FEC for the cross-layer schemes versus employing erasure recovery FEC for the traditional protocols. We show that cross-layer schemes can lead to a significant improvement in video quality.