Optimal rate allocation in progressive joint source-channel coding for image transmission over CDMA networks

This paper presents an optimal rate allocation scheme in joint sourcechannel coding (JSCC) for image transmission over CDMA networks. Our scheme first uses progressive joint source-channel codes [1] to generate operational transmission rate-distortion (TRD) functions of different multiple-access channels with different BERs. The Lagrange multiplier is then employed to set the optimal rate allocation among different channels, subject to a total transmission rate constraint. Progressive JSCC offers the scalability feature that is very attractive for handling bandwidth variations in wireless communications. By extending the rate-distortion function in source coding to the TR-D function in JSCC, our work borrows the “equal slope” argument [2] to effectively solve the rate allocation problem in JSCC for multi-channel image transmission. Experiments show that our scheme runs in real time and provides competitive performance at all intermediate transmission rates.