Quadtree-Decomposed Cordless Videophones

Arbitrarily programmable, but fixed-rate quad-tree (QT) decomposed, parametrically enhanced videophone codecs using quarter common intermediate format (QCIF) video sequences are proposed as a direct replacement for mobile radio voice codecs in second generation systems, such as the Pan-European GSM, the American IS-54 and IS-95 as well as the Japanese systems. The proposed 11.36 kbps Codec 1 and the 11 kbps Codec 2 are embedded in the adaptively re-configurable wireless videophone Systems 1-4 featured in Table 3 and their video quality, bit rate, robustness and complexity issues are investigated. Coherent re-configurable 16 or 4-level pilot symbol assisted quadrature amplitude modulation (PSAQAM) is used and the system's robustness is improved by a combination of diversity and Automatic Repeat Request (ARQ) techniques. When using a bandwidth of 200 kHz, as in the PanEuropean GSM mobile radio system, the number of videophone users supported varies between 3 and 16, while the minimum required channel Signal to Noise Ratio over Gaussian and Rayleigh channels is in excess of 6 and 8 dB, respectively. The salient system features are summarised in Table 3