Abstract
AbstractAn adaptive fixed‐length differential chain coding (FL‐DCC) scheme is proposed for the transmission of line graphics, which canbe re‐configured as a lower rate, lower resolution or higher rate, higher resolution source codec. Compared to Differential Chain Coding (DCC), the proposed FL‐DCC codec has a lower coding rate in both of its lower‐ and higher‐rate operating modes, while maintaining a similar subjective graphical quality. The dual‐rate re‐configurable FL‐DCC codec is embedded in a voice, video multimedia communicator system, which allocates the FL‐DCC graphics packets to idle speech packets with the aid of the Packet Reservation Multiple Access (PRMA) multiplexer. In a bandwidth of 200 kHz, which is characteristic of the Pan‐European GSM system, nine speech, video and graphics multimedia users can be accommodated using bandwidth efficient 16‐level Quadrature Amplitude Modulation (16QAM) over benign microcellular channels. Under less favourable propagation conditions the more robust, but less bandwidth efficient 4QAM mode of operation can be invoked. In the diversity‐aided and automatic repeat request (ARQ) assisted 16QAM mode of operation the multimedia user bandwidth becomes 22.2 kHz and the minimum required channel signal to noise ratio (SNR) over AWGN and Rayleigh channels is about 11 and 15 dB, respectively. The most salient system features are summarised in Table 2.
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