Carrier Phase and Clock Recovery for Continuous Phase Modulated Signals

This paper presents an analysis of a synchronization circuit to be used for carrier-phase and symbol-timing recovery in continuous phase modulation systems.M-ary modulation formats with arbitrary pulse shaping and rational modulation indexes are assumed. Circuit performance is expressed in terms of variances of phase and timing errors. Numerical results are provided for some important cases, including minimum shift keying and tamed frequency modulation. Theoretical results are found in good agreement with computer simulations.     

Chip-level differential encoding/detection of spread-spectrumsignals for CDMA radio transmission over fading channels

This paper is concerned with the design and performance evaluation of a direct-sequence spread-spectrum transmission and signal-detection technique for application to code-division multiple-access mobile radio networks. Unlike the conventional differential encoding/detection of data symbols, such a technique envisages differential encoding/detection of the spreading code chips to counteract the fast time-selective fading encountered in mobile radio transmissions. Binary PSK modulation on a Rician frequency-flat-fading channel is assumed, with Gaussian and Rayleigh channels as particular cases. The bit-error rate performance of the receiver is analytically evaluated as a function of the relevant system parameters, and the impact on the receiver performance of a carrier frequency offset is also investigated     

Simple carrier frequency rate-of-change estimators

This paper is concerned with the estimation of the rate-of-change of the instantaneous frequency of an unmodulated carrier. Such an issue arises, for instance, in satellite communication systems based on a low-Earth-orbit constellation, wherein the speed of each satellite relative to earth is rapidly time-varying, and consequently, the received carrier is affected by nonnegligible Doppler shift and Doppler rate. First, we present simple yet efficient estimators of the Doppler rate derived from maximum-likelihood estimation theory. Next, we investigate their performance in terms of bias and estimation error variance. Finally, we compare our variance results with the relevant modified Cramer-Rao bound     

Mobile and Personal Communications in the 60 GHz Band: A Survey

This paper intends to present a summary of the technical issues arising in the exploitation of the 60 GHz mm-wave band for mobile and personal communications. The most significant applications proposed so far are surveyed, with particular emphasis placed on recent experimentation about millimeter-wave propagation for road/railway transportation as well as indoor scenarios. As a case study, the capacity of a (micro-)cellular Code Division Multiple Access (CDMA) network in the 60-GHz band is also evaluated in detail.     

The modified Cramer-Rao bound in vector parameter estimation

In this paper we extend the scalar modified Cramer-Rao bound (MCRB) to the estimation of a vector of nonrandom parameters in the presence of nuisance parameters. The resulting bound is denoted with the acronym MCRVB, where “V” stands for “vector”. As with the scalar bound, the MCRVB is generally looser than the conventional CRVB, but the two bounds are shown to coincide in some situations of practical interest. The MCRVB is applied to the joint estimation of carrier frequency, phase, and symbol epoch of a linearly modulated waveform corrupted by correlated impulsive noise (encompassing white Gaussian noise as a particular case), wherein data symbols and noise power are regarded as nuisance parameters. In this situation, calculation of the conventional CRVB is infeasible, while application of the MCRVB leads to simple useful expressions with moderate analytical effort. When specialized to the case of white Gaussian noise, the MCRVB yields results already available in the literature in fragmentary form and simplified contexts     

Low-complexity blind carrier frequency recovery for OFDM signals over frequency-selective radio channels

This paper introduces a blind (i.e., data independent) algorithm for carrier frequency offset recovery in an orthogonal frequency-division multiplexing (OFDM) receiver operating over frequency-selective fading channels. The main idea behind this algorithm is to exploit the time-frequency-domain exchange inherent to the modulation scheme. Due to this feature, a carrier frequency offset has a similar impact on OFDM as a clock timing offset has in a quadrature amplitude modulation (QAM) system. The scheme we propose is a variant of Oerder-Meyr's (1988) feedforward clock recovery. Its performance is assessed by simulation, and the results are compared to those obtained from Van de Beek-Sandell-Borjesson's (1997) frequency synchronizer, which bears comparable complexity. The new scheme is shown to outperform the latter over frequency-selective fading channels, notably at medium to high signal-to-noise ratios. We also evaluated the efficiency of two different (time domain and frequency domain) offset correction strategies embedded in a particular OFDM receiver.     

Blind subcarrier frequency ambiguity resolution for OFDM signals over selective channels

Many frequency-recovery algorithms for orthogonal frequency-division multiplexing systems are geared to recover offsets up to half the distance of the subcarriers. If the error is larger, an ambiguity of an integer number of subcarrier spacings is left. This paper develops a blind algorithm for ambiguity resolution that works effectively over frequency-selective radio channels. Simulation results show a sizable improvement over existing techniques, expecially at high signal-to-noise ratios.     

A space-time discretization criterion for a stable time-marchingsolution of the electric field integral equation

Numerical techniques based on a time-domain recursive solution of the electric field integral equation (EFIE) may exhibit instability phenomena induced by the joint space-time discretization. The above problem is addressed with specific reference to the evaluation of electromagnetic scattering from perfectly conducting bodies of arbitrary shape. We analyze a particular formulation of the method of moments which relies on a triangular-patch geometrical model of the exterior surface of the scattering body and operates according to a “marching-on-in-time” scheme, whereby the surface current distribution at a given time step is recursively evaluated as a function of the current distribution at previous steps. A heuristic stability condition is devised which allows us to define a proper time step, as well as a geometrical discretization criterion, ensuring convergence of the numerical procedure and, therefore, eliminating insurgence of late-time oscillations. The stability condition is discussed and validated by means of a few working examples     

Performance analysis of an adaptive receiver structure for digital mobile communications

In this paper we investigate the performance of a combined estimation/equalization technique for the mobile radio channel, assuming a GSM-recommended transmission format (narrowband TDMA with midamble, recommendation 5.04) and MSK modulation scheme. Channel estimation is performed via correlation of the received signal with a suitably modulated replica of the transmitted midamble. Equalization is then obtained by means of a maximum likelihood sequence estimation (MLSE) scheme in the form of a so-called Viterbi equalizer. Our analysis provides theoretical results concerning the bit error rate (BER) attained by the receiver for a given stationary multipath channel model. Simulation results are also presented in order to integrate and validate the theory.     

Performance evaluation of an adaptive GSM receiver with frequency-selective fading and adjacent- and co-channel interference

This study represents the sequel and conclusion of a previous one already published in this Journal a few issues ago.¹ In that article, we tackled the problem of evaluating theoretically the performance of an adaptive MLSE receiver for MSK signals on a frequency-selective stationary radio propagation channel, and we validated the theoretical findings (in the form of upper and lower bounds to the BER of the receiver) by means of computer simulations. In the present paper, we report on the performance of the very same scheme of channel-estimator-plus-Viterbi-equalizer receiver for mobile communications in a more realistic operating environment. In particular, we completely encompass here the groupe spécial mobile (GSM) transmission format, based on the Gaussian minimum shift keying (GMSK) modulation scheme and on narrowband time-division multiple access (TDMA) transmission. Also, we remove the assumption of a time-invariant propagation channel, assuming the recommended standard GSM channels as benchmark transmission conditions. Finally, with the aid of extensive computer simulations, we analyse the sensitivity of the MLSE receiver to unwanted co-channel and adjacent-channel interference coming from other users of the mobile cellular GSM system.