Communication channel

About: Communication channel is a research topic. Over the lifetime, 137411 publications have been published within this topic receiving 1715077 citations. The topic is also known as: communication channel & communications channel.

Channel assignment for cellular radio using neural networks

Abstract: The channel assignment problem, i.e. the task of assigning channels to radio cells in a spectrum-efficient way, is solved by a neural network algorithm. This algorithm is inherently parallel and does not rely on a particular structure of the interference graph. The results obtained so far indicate that the algorithm can be used to obtain an optimum solution. It was applied successfully for inhomogeneous interference conditions and channel demand. Cochannel and cosite constraints were taken into account, and the extension to any other technical restrictions will be possible in an obvious way. The examples studied to date are of a relatively small size; the question remains of how the algorithm behaves when applied to larger and more complex examples. The disadvantages of the algorithm are its long calculation time compared to graph coloring algorithms and the difficulty of finding appropriate parameters. However, the algorithm was not optimized for speed, and the parameter search may be a question of experience. >

Progressive image coding on noisy channels

Abstract: Numerous sophisticated techniques have been developed over the last several decades to efficiently transmit images across noisy channels. Here, we cascade an existing image coder with carefully chosen error control coding, and thus produce a progressive image compression scheme whose performance on a noisy channel is significantly better than that of previously known image compression techniques. The main idea is to trade off the available transmission rate between source coding and channel coding in an efficient manner. This coding system is easy to implement and has acceptably low complexity. Furthermore, effectively no degradation due to channel noise can be detected; instead, the penalty paid due to channel noise is a reduction in source coding resolution. As an example, for the 512/spl times/512 Lena image, at an overall transmission rate of 1 bit per pixel, and for binary symmetric channels with bit error probabilities 10/sup -3/, 10/sup -2/, and 10/sup -1/, the proposed system typically outperforms other existing systems by at least 2.6 dB, 2.8 dB, and 8.9 dB, respectively.

Toward an improvement of H.264 video transmission over IEEE 802.11e through a cross-layer architecture

Abstract: The recently developed H.264 video standard achieves efficient encoding over a bandwidth ranging from a few kilobits per second to several megabits per second. Hence, transporting H.264 video is expected to be an important component of many wireless multimedia services, such as video conferencing, real-time network gaming, and TV broadcasting. However, due to wireless channel characteristics and lack of QoS support, the basic 802.11-based channel access procedure is merely sufficient to deliver non-real-time traffic. The delivery should be augmented by appropriate mechanisms to better consider different QoS requirements and ultimately adjust the medium access parameters to the video data content characteristics. In this article we address H.264 wireless video transmission over IEEE 802.11 WLAN by proposing a robust cross-layer architecture that leverages the inherent H.264 error resilience tools (i.e., data partitioning); and the existing QoS-based IEEE 802.11e MAC protocol possibilities. The performances of the proposed architecture are extensively investigated by simulations. Results obtained indicate that compared to 802.11 and 802.11e, our cross-layer architecture allows graceful video degradation while minimizing the mean packet loss and end-to-end delays.

An exploration of L2 cache covert channels in virtualized environments

Abstract: Recent exploration into the unique security challenges of cloud computing have shown that when virtual machines belonging to different customers share the same physical machine, new forms of cross-VM covert channel communication arise. In this paper, we explore one of these threats, L2 cache covert channels, and demonstrate the limits of these this threat by providing a quantification of the channel bit rates and an assessment of its ability to do harm. Through progressively refining models of cross-VM covert channels from the derived maximums, to implementable channels in the lab, and finally in Amazon EC2 itself we show how a variety of factors impact our ability to create effective channels. While we demonstrate a covert channel with considerably higher bit rate than previously reported, we assess that even at such improved rates, the harm of data exfiltration from these channels is still limited to the sharing of small, if important, secrets such as private keys.