Interactive Channel Capacity Revisited

We provide the first capacity approaching coding schemes that robustly simulate any interactive protocol over an adversarial channel that corrupts any $\epsilon$ fraction of the transmitted symbols. Our coding schemes achieve a communication rate of $1 - O(\sqrt{\epsilon \log \log 1/\epsilon})$ over any adversarial channel. This can be improved to $1 - O(\sqrt{\epsilon})$ for random, oblivious, and computationally bounded channels, or if parties have shared randomness unknown to the channel. Surprisingly, these rates exceed the $1 - \Omega(\sqrt{H(\epsilon)}) = 1 - \Omega(\sqrt{\epsilon \log 1/\epsilon})$ interactive channel capacity bound which [Kol and Raz; STOC'13] recently proved for random errors. We conjecture $1 - \Theta(\sqrt{\epsilon \log \log 1/\epsilon})$ and $1 - \Theta(\sqrt{\epsilon})$ to be the optimal rates for their respective settings and therefore to capture the interactive channel capacity for random and adversarial errors. In addition to being very communication efficient, our randomized coding schemes have multiple other advantages. They are computationally efficient, extremely natural, and significantly simpler than prior (non-capacity approaching) schemes. In particular, our protocols do not employ any coding but allow the original protocol to be performed as-is, interspersed only by short exchanges of hash values. When hash values do not match, the parties backtrack. Our approach is, as we feel, by far the simplest and most natural explanation for why and how robust interactive communication in a noisy environment is possible

Programmable H.263-Based Wireless Video Tranceivers for Interference-Limited Environments

In order to exploit the non-uniformly distributed channel capacity over the cell area, the intelligent 7.3 kBaud programmable videophone transceiver of Table I is proposed, which is capable of exploiting the higher channel capacity of uninterfered, high channel-quality cell areas, while supporting more robust, but lower bitrate operation in more interfered areas. The system employed an enhanced H.263-compatible video codec. Since most existing wireless systems exhibit a constant bitrate, the video codec's bitrate fluctuation was smoothed by a novel adaptive packetisation algorithm, which is capable of supporting Automatic Repeat Request (ARQ) assisted operation in wireless distributive video transmissions, although in the proposed low-latency interactive videophone transceiver we refrained from using ARQ. Instead, corrupted packets are dropped by both the local and remote decoders, in order to prevent error propagation. The minimum required channel signal to interference-plus-noise ratio (SINR) was in the range of 8-28 dB for the various transmission scenarios of Table I, while the corresponding video peak signal-to-noise ratio (PSNR) was in the range of 32-39 dB. The main system features are summarised in Table I. Index Terms - H.263-based video communications, interactive wireless video, QAM-based video transmission, video communications in interference-limited environments, video tranceivers