Recently, multiplication-free digital filters have been proposed for different applications to digital radio systems and signal processing. The absence of multiplication is obtained by constraining each coefficient to be sum of powers of two. In this way, multipliers are substituted by shift registers and, if appropriate, some adders. The optimal power-of-two coefficients must be computed through a nonlinear optimization procedure. Until now the problem of adapting the power-of-two coefficients of base band transversal equalizers in the case of time-varying channels had not been considered. In this paper two algorithms are proposed to cope with this problem and are compared from the viewpoint of complexity, accuracy, and convergence speed. As an application example, transmission of a biphase PSK digital radio system over a multipath fading channel is considered.

Recently, attention has been paid to the problem of transmitting audio signals whose bandwidth is wider than 3.4 kHz, tipycally 7 kHz. In this paper, three techniques are examined which allow the transmission rate of 64 kbit/s to be met. Comparisons are carried out in terms of both objective measurements and informal listening tests. Possible application fields are tele- and video-conferencing, commentary channels and broadcasting, and high quality speech and music in the future Integrated Service Digital Network.

A new approach to the jitter accumulation problem in a chain of regenerative repeaters for pulse amplitude modulation systems is described. In each regeneration section the timing circuit consists of a square-law device followed by a bandpass filter with center frequency close to the transmission rate. It is shown that, from the standpoint of jitter generation and propagation, the timing circuit is equivalent to a low-pass filter driven by the sum of the jitter generated in the previous regenerator plus a noise term. This is actually the jitter propagation mechanism suggested in [6] and referred to as Chapman's model. What makes a difference with the results published in [6] is that in our analysis an expression is given for the spectral density of the noise in the equivalent model in terms of system parameters such as pulse shape, bandpass filter mistuning, offset in the triggering level of the pulse generator, etc. In this way the various jitter sources can be qualified and their effects evaluated.

A method for evaluating the average error probability in digital fiber optic transmission systems is described. It takes into account the statistical properties of the main impairments that affect the information signal, i.e., shot noise (dark current included), thermal noise, and intersymbol interference. Unlike other methods, the analysis of shot-noise statistics does not entail the second-moment characterization alone, but uses a number of moments sufficient to evaluate the error probability with a high degree of accuracy. For this purpose it is shown how the cumulants of shot noise and intersymbol interference of any order can be computed. The baseband pulse response and the statistical distribution of the avalanche-photodetector gain are assumed to be available. Moreover, techniques for exploiting the cumulants are given; knowledge of the cumulants allows one to compute the probability of error by means of Gaussian numerical integration rules. Finally, some results and comparisons are reported.

Sequence estimation in the presence of additive Gaussian noise and intersymbol interference can be performed by means of discrete Kalman filters. In adaptive receivers for data transmission, the optimal Kalman gains must be computed on-line. A recursive algorithm is presented for this purpose and its performance, i.e., accuracy and computational requirements, is discussed briefly.