Parameter interpolation to enhance the frame erasure robustness of CELP coders in packet networks

Frame erasure (FE) robustness is an important quality measure for voice over IP networks (VoIP). The recovery of the erased frames from the received information is crucial to realize this robustness. We allow the lost frames to be recovered from both the "previous" and "next" good frames. We first give quantitative distortion comparisons between predictive and interpolative frame recovery. Then we add FE-robust LSF coding modes to the popular ITU G.723.1 and G.729 CELP coders. These FE-robust modes utilize intraframe LSF VQ and invoke no bit-rate increase for the G.723.1 coder and a small increase (0.4 kb/s) for G.729. Simulations show that FE robust coding with interpolation achieves average spectral distortions 0.7-1.8 dB smaller than that of the original coders. Significant quality improvement was achieved by combined implementation of FE robust coding, LSF and pitch interpolation, and a proposed fixed codebook excitation recovery method