Comparing application- and physical-layer approaches to diversity on wireless channels

Diversity techniques often arise as appealing means for improving performance of multimedia communication over certain types of channels with independent parallel components (e.g., multiple antennas, frequency bands, or time slots). Diversity can be obtained by channel coding across parallel components at the physical layer. Alternatively, the physical layer can present an interface to the parallel components as separate, independent links thus allowing the application layer to implement diversity in the form of multiple description source coding. We compare these two approaches in terms of average end-to-end distortion as a function of channel signal-to-noise ratio (SNR). When specialized to the case of an independent, identically distributed Gaussian source over Rayleigh fading channels, our results suggest that parallel channel coding at the physical layer is more efficient than independent channel coding combined with multiple description source coding. More generally, we provide intuitive guidelines for allowing system designers to identify which types of systems are preferable under different scenarios of practical interest.