Backwards Compatible Wideband Telephony in Mobile Networks: CELP Watermarking and Bandwidth Extension
Bernd Geiser, Peter Vary · 2007
We consider the problem of transmitting a wideband speech signal with a cut-off frequency of fc= 7 kHz over a standardized narrowband (fc= 3.4 kHz) communication link in a backwards compatible manner. In a previous contribution we have shown that backwards compatibility can be achieved by using digital watermarking: we embedded compact side information about the missing high frequency band (3.4 - 7 kHz) into the narrowband speech signal. Here, we present a related system which is especially tailored to state-of-the-art narrowband speech communication networks such as GSM or UMTS. Therefore, we propose an improved low bit rate bandwidth extension algorithm along with a robust watermarking scheme for CELP-type speech codecs. The practical relevance of our system is shown by speech quality evaluations and by link-level simulations for the "enhanced full rate traffic channel" (TCH/EFS) of the GSM cellular communication system.