Analysis of a Cross-Layer Hybrid-ARQ Scheme: Application to Unequal Packet Protection

In order to improve the reliability of any HARQ technique at the IP level, a cross-layer strategy between the MAC and the IP levels has been recently developed in. This strategy consists in replacing a retransmisssion credit per MAC packet with a retransmission credit per IP packet. In other words, the transmission credit is shared by the MAC packets belonging to the same IP packet. Packet Error Rate, throughput, delay and jitter for this new approach have been extensively analyzed in. In this paper, we remark and theoretically prove that the first MAC packets are better protected than the last ones. This leads to a natural "unequal packet loss protection" that can be useful in many applications, such as video streaming, compressed image transmission, audio and protocols (TCP/IP). Exploiting this novel manner of protecting packets unequally may not exclude the use of the standard manners, such as different feedforward error correcting codes (FEC), modulation size, or hybrid ARQ scheme per required quality of protection. Finally, our claims are supported by numerical simulations.