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—Recent theoretical results describing the sum capacity when using multiple antennas to communicate with multiple users in a known rich scattering environment have not yet been followed with practical transmission schemes that achieve this capacity. We introduce a simple encoding algorithm that achieves near-capacity at sum rates of tens of bits/channel(More)
—Recent theoretical results describing the sum-capacity when using multiple antennas to communicate with multiple users in a known rich scattering environment have not yet been followed with practical transmission schemes that achieve this capacity. We introduce a simple encoding algorithm that achieves near-capacity at sum-rates of tens of bits/channel(More)
The fading channel is a significant problem in many communications environments. In this paper, we examine the performance of unitary space-time modulation in a time-varying channel. We use a Gauss-Markov model of the continuously varying channel to characterize performance of differential and trained modulation. We find a performance ceiling at high SNR(More)
Rapid temporal variations in wireless channels pose a significant challenge for space-time modulation and coding algorithms. This paper examines the performance degradation that results when time-varying flat fading is encountered during space-time modulation. Performance is characterized for a channel having a constant specular component plus a(More)
—We analyze the performance of trained and differential space-time modulation for channels with a constant specular component and time-varying diffuse fading. We examine the case where the channel varies from sample to sample within a space-time symbol matrix according to a first-order time-varying model. We show that the effect of the time-varying diffuse(More)
We describe a method of using a Lagrange multiplier to make a locally optimal trade off between rate and distortion in the motion search for video sequences, while maintaining a constant bit rate channel. Simulation of this method shows that it gives up to 3.5 dB PSNR improvement in a high motion sequence. A locally rate-distortion (R-D) optimal mode(More)
— A lower bound on the capacity of trained space-time modulation is presented for the case of a time-varying channel. We consider the case where the channel consists of two components of variable strength: a specular component from line-of-sight or strong coherent multipath, and a time-varying diffuse component due to a mobile receiver or scatterers. The(More)
Recent results on the throughput achievable with wireless networks have not fully considered multiple antennas and multiuser links. We introduce these topics by giving the transport capacity of the multiple-antenna multiple-access and broadcast channels. We use these topologies at the physical layer of an ad-hoc network to obtain achievable(More)
A lossy image compression algorithm designed for high-speed, high quality data applications is described. The algorithm consists of a vector quantizer followed by a modified Huffman entropy encoder. The quantizer is a mean-removed, adaptive-search, residual vector quantizer. A few details of a high-speed hardware implementation for reconnaissance are given,(More)
During the past decade, the research community and wireless practitioners have provided overwhelming evidence that the strictly layered ISO/OSI architecture can lead to largely suboptimal operation of wireless networks. The reasons for such operation are rooted in the defining features of wireless communication: the variable link quality and the fact that(More)