When Is Joint Source-Channel Coding Worthwhile: An Information Theoretic Perspective

We study, from an information theoretic perspective, the merits of joint sourcechannel (JSC) coding versus traditional tandem coding, which consists of separately performing and concatenating source and channel coding. Specifically, we provide a systematic comparison of the JSC coding error exponent EJ (Q, W ) with the tandem coding error exponent ET (Q, W ) for communication systems with discrete memoryless source and channel pairs (Q, W ). We establish sufficient conditions under which EJ (Q, W ) > ET (Q, W ), which are satisfied for a large class of (Q, W ) pairs. We also show that EJ (Q, W ) can sometimes be twice as large as ET (Q, W ), hence illustrating the substantial gain that joint coding can achieve over tandem coding.