Abstract
Reliable interactive video transmISSIon in COMA cellular networks is difficult because residual channel errors (after error correction) cannot be completely eliminated and the available bandwidth is scarce. To improve the quality of the decoded video. this paper introduces a novel architecture for low bit rate transmission in multicode OS-CDMA (MC-COMA) cellular systems. Unlike previous protection schemes, the new architecture not only improves video quality, but it also achieves an efficient use of the available resources in the network. As an application of this concept, we propose a robust scheme for reliable video communication from wired to mobile users in slow fading environments. This scenario has been shown to be the most critical owing to long block error bursts present in the forward link of COMA systems where closed-loop power control is not used (such as IS-95B), and the inability of error resilience approaches incorporated in wired video codecs to guarantee an acceptabk video quality in wireless transmissions. Our approach consists of two main ingredients: (i) a novel closed-loop error control technique to reduce packet loss, delays, and interference, and (ii) a new scheme to stop error propagation in the decoded sequence originating from residual channel errors. Based both on theoretical analysis and numerical results, we show thaI our approach achieves important improvements in the quality of the decoded video. Furthermore, we show that the new architecture oUlperforms previous error protection schemes with low additional complexity.
Highlights
Multicode direct sequence code division multiple access (MC-COMA) has been adopted by several standards to support variable data rates [I ]-[3]
The architecture proposed in this work consists of (i) a novel closed-loop error control technique to reduce packet loss, called the non-selective variable bandwidth retransmission scheme (NSVBR), and (ii) a new scheme to stop error propagation in the decoded sequence originating from residual channel errors, which is called the centralized video quality recovery (CVQR) scheme
NSVBR achieves a good tradeoff between efficiency and complex ity, as we show
Summary
Multicode direct sequence code division multiple access (MC-COMA) has been adopted by several standards to support variable data rates [I ]-[3]. The video quality achieved at the decoder in transmission over error-prone channels depends critically on both error correction and error resilience techniques The ability of the latter to improve video quality in MC-COMA wireless transmission at low rates requires further considerations. Increasing the frequency of refresh with an intra-coded frame (i.e., a coded video frame that can be decoded by itself) to stop error propagation is not a proper solution because this frame has low compression efficiency and significant additional bandwidth is required to reduce time delays This affects the overall video quality and system capacity (it increases interference) [I2l, but it requires elaborate bandwidth allocation algorithms. The architecture proposed in this work consists of (i) a novel closed-loop error control technique to reduce packet loss, called the non-selective variable bandwidth retransmission scheme (NSVBR), and (ii) a new scheme to stop error propagation in the decoded sequence originating from residual channel errors, which is called the centralized video quality recovery (CVQR) scheme.
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