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Suppose that we want to send a description of a single source to two listeners through a Gaussian broadcast channel, where the channel is used once per source sample. The problem of joint source-channel coding is to design a communication system to minimize the distortion D/sub 1/ at receiver 1 and at the same time minimize the distortion D/sub 2/ at receiver 2. If the source is Gaussian, the optimal solution is well known, and it is achieved by an uncoded "analog" scheme. We consider a Gaussian mixture source. We derive inner and outer bounds for the distortion region of all (D/sub 1/, D/sub 2/) pairs that are simultaneously achievable. The outer bound is based on the entropy power inequality, while the inner bound is attained by a digital-over-analog encoding scheme, which we present. We also show that if the modes of the Gaussian mixture are highly separated, our bounds are tight, and hence, our scheme attains the entire distortion region. This optimal region exceeds the region attained by separating source and channel coding, although it does not contain the "ideal" point (D/sub 1/, D/sub 2/)=(R/sup -1/(C/sub 1/), R/sup -1/(C/sub 2/)).

In this letter, we extend results regarding the behavior of a symbol-spaced tapped-delay-line LMS-adapted equalizer in frequency domain terms to a fractionally spaced implementation. These results rely on an eigendecomposition of the autocorrelation matrix of the received signal. In fractionally spaced equalization systems, the output of the analog channel is oversampled, resulting in a cyclostationary signal. We derive its autocorrelation matrix. A symbol-spaced representation of the combined channel, equalizer and downsampling device is formed in the frequency domain, and the convergence rate of the time-domain LMS algorithm is described in the frequency domain.

We consider the problem of broadcasting a single Gaussian source to two listeners over a Gaussian broadcast channel, with rho channel uses per source sample, where rho>1. A distortion pair (D1 ,D2) is said to be achievable if one can simultaneously achieve a mean-squared error (MSE) D1 at receiver 1 and D2 at receiver 2. The main result of this correspondence is an outer bound for the set of all achievable distortion pairs. That is, we find necessary conditions under which (D1,D2) is achievable. We then apply this result to the problem of point-to-point transmission over a Gaussian channel with unknown signal-to-noise ratio (SNR) and rho>1. We show that if a system must be optimal at a certain SNRmin, then, asymptotically, the system distortion cannot decay faster than O(1/SNR). As for achievability, we show that a previously reported scheme, due to Mittal and Phamdo (2002), is optimal at high SNR. We introduce two new schemes for broadcasting with bandwidth expansion, combining digital and analog transmissions. We finally show how a system with a partial feedback, returning from the bad receiver to the transmitter and to the good receiver, achieves a distortion pair that lies on the outer bound derived here

We show that for every analog source with smooth density transmitted over an AWGN channel with unknown but high SNR, with one channel use per source sample, a single system achieves R(D) /spl ap/ C for all SNR. We also extend the results to non-Gaussian channel noise.

Advances in blind identification of fractionally-spaced models for digital communication channels and blind fractionally-spaced equalizer adaptation rely on the assumption that the time span chosen for the fractionally-spaced equalizer exceeds that of the channel. This paper considers time-domain design formulas minimizing the mean-squared symbol recovery error achieved by a finite-length FIR fractionally-spaced equalizer with a time span shorter than the channel impulse response time span for white zero-mean QAM sources in the presence of white zero-mean channel noise. For minimum mean-squared error designs the symbol error rates achievable are plotted versus the ratio of the source variance to the channel noise variance (with the channel model power normalized to achieve a received signal of unit variance) for different fractionally-spaced equalizer lengths on 64-QAM for several T/2-spaced channel models derived from experimental data. Our intent is to fuel the ongoing debate about fractionally-spaced equalizer length selection . Upprättat; 1995; Bibliografisk uppgift: Se artikeln för övriga 7 medförfattare; 20070109 (ysko)