16 Kb/s high quality voice encoding for satellite communication networks

Abstract

AbstractThis paper describes applications of adaptive predictive coding (APC) with maximum likelihood quantization (MLQ) which can cover a wide range of coding rates from 4.8 to 16 kb/s for low C/N satellite communication systems, such as maritime, aeronautical mobile and thin‐route satellite communication systems, and also for speech and data integration, including digital circuit multiplication equipment (DCME) in business communication systems, such as INTELSAT business services (IBS). A 16 kb/s APC–MLQ hardware codec has been implemented by NEC–7720 DSP chips and the performance has been confirmed in subjective quality of speech through conversational tests. The objective performance has also been evaluated for non‐voice signals, such as single and multi‐frequency tones, and 1200 and 2400 b/s voiceband data signals. The APC‐MLQ codec can transmit the voice‐band data at 1200 b/s over two asynchronous tandem links and at 2400 b/s over one link. It was noted that the APC‐MLQ codec is superior in speech performance at 16 kb/s to a narrow‐band companded FM and meets requirements for low C/N satellite communication systems. For voice and data integration into 16 kb/s for 64 kb/s links, we propose a multi‐media multiplexing for low C/N digital satellite communication systems and also a small‐scale circuit multiplication system for business use. In these systems, a variable rate coding of APC‐MLQ from 4.8 to 16 kb/s can be effectively introduced for voice and data integration.