Abstract
We describe a multilayered video transport scheme for wireless channels capable of adapting to channel conditions in order to maximize end-to-end quality of service (QoS). This scheme combines a scalable H.263+ video source coder with unequal error protection (UEP) across layers. The UEP is achieved by employing different channel codes together with a multiresolution modulation approach to transport the different priority layers. Adaptivity to channel conditions is provided through a joint source-channel coding (JSCC) approach which attempts to jointly optimize the source and channel coding rates together with the modulation parameters to obtain the maximum achievable end-to-end QoS for the prevailing channel conditions. In this work, we model the wireless links as slow-fading Rician channel where the channel conditions can be described in terms of the channel signal-to-noise ratio (SNR) and the ratio of specular-to-diffuse energy . The multiresolution modulation/coding scheme consists of binary rate-compatible punctured convolutional (RCPC) codes used together with nonuniform phase-shift keyed (PSK) signaling constellations. Results indicate that this adaptive JSCC scheme employing scalable video encoding together with a multiresolution modulation/coding approach leads to significant improvements in delivered video quality for specified channel conditions. In particular, the approach results in considerably improved graceful degradation properties for decreasing channel SNR.
Highlights
The wireless channel varies over time and space and has short-term memory due to multipath
Previous work [9, 11] described joint source-channel coding (JSCC) approaches for digital video transport over wireless links employing either a single-layer source coder with FEC or a 2-layer source coder in conjunction with FEC/unequal error protection (UEP) across layers to combat channel errors
We describe and investigate an adaptive wireless video coding and delivery system which combines a scalable video codec with UEP across layers achieved through a combination of FEC and use of multiresolution modulation schemes using nonuniform MPSK signal constellations
Summary
The wireless channel varies over time and space and has short-term (or small-scale) memory due to multipath. FEC/UEP channel coding approach across layers, this leads to a more flexible and efficient JSCC procedure which is better able to exploit the differential sensitivities of the different source-encoded layers Such schemes can be used in an adaptive fashion by modifying the source coding rate as well as the channel modulation/coding strategy, based on the prevailing channel conditions, in an effort to maximize the end-to-end quality of the delivered video. When the channel conditions are good it is possible to use a higher-order signaling alphabet with less powerful FEC coding This allows larger throughput which can support the transport of additional enhancement layers to improve the quality of the reconstructed video.
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