In this paper, we propose a low bit rate (4.0-4.8kbps) speech coding algorithm for digital mobile communication. The coding algorithm is based on a frame synchronous time domain compression (FS-TDC) of LPC residual signal which is optirnaly combined with stochastic coding algorithm. Like other TDC schemes, FS-TDC basically uses pitch periodicity of speech, but different from others, its compression and expansion process are both completed within a frame, and the compression ratio is large and fixed. In evaluation tests, the sochastic coders with FS-TDC shows better speech quality than an usual system, and shows good robustness for channel error if parameters are protected by optimized error protection scheme.