An iterative joint source channel decoding （ISCD） scheme for WMSN is proposed

based on a soft-input-soft-output （SISO） a posteriori probability decoding algorithm for variable-length coded sources

which leads to not only maximum likelihood （ML） sequence estimation but also the computation of bit-based reliability values which are necessary for ISCD. Another innovation is that the technique of scaling extrinsic information is brought into the field of ISCD

and the optimal constant scaling factors is obtained under the guide of extrinsic information transfer characteris- tic. This technique improves the ISCD performance with increasing neglectable complexity. The notable feature of the proposed technique is that it requires very low computational complexity and small memory space

and can be applied to WMSN nodes. Simulation results show that the proposed ISCD scheme provides a significant improvement on error pro- tection capability for the variable-length coded data in WMSN.