Path Diversity and Multiple Descriptions with Rate Dependent Packet Losses

Simple path diversity, where the source packet is transmitted simultaneously over multiple paths, is an effective method to combat packet losses or link failures for communications over a wireless network. The bandwidth inefficiency inherent in a path diversity method can be reduced by using multiple description (MD) coding. We consider a scenario where two independent parallel paths/links are available for communicating delay-constrained packetized multimedia data over a wireless network. Motivated by the IEEE 802.11 protocols, often used in wireless LANs and mobile ad hoc networks, we drop a packet at the receiver if even a single bit in the packet is in error. As a result, the packet loss probability is proportional to the packet size. In typical packet-based networks, headers are added to packets and when the packet payloads are small, these headers can dominate the packet size. We compare the average distortion per symbol achieved at the receiver for simple path diversity methods against MD coding of a memoryless Gaussian source for packetized communication over additive white Gaussian noise channels. First, we compare the performance when a packet consists of source information only and next, we show the effect of packet overheads on the performance of each of the methods. With packet headers included, we see that a simple path diversity method requires only a slight increase in transmitted bits and consistently gives lower distortion than the MD method. We also demonstrate the penalty due to MD optimization if headers are neglected.