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A parallel architecture for high-bandwidth analog-to-digital conversion is presented. The proposed architecture uses frequency translation along with multi-rate signal processing to digitize a wide-band continuous-time analog signal through an array of identical narrowband analog-to-digital converters (ADCs). The basic idea behind this structure is to decompose the input signal into smaller frequency (channels). Each channel is composed of a two-path system that includes mixers, identical low-pass filters and identical baseband ADCs. The signal in each two-path channel is sampled and digitized into narrowband quadrature signals. After digitizing the signal in each channel, the low-rate subband samples are upconverted back to their respective center frequencies, then filtered and combined to reconstruct the digital representation of the original wide-band input signal. The digital filters are designed to minimize the reconstruction error. The effects of some major nonidealities are discussed. Several simulation results are also presented to demonstrate the performance of the system. Index Terms--Analog-to-digital conversion, multi-rate signal processing, parallel analog-to-digital converter (ADC) structure, wide-band.

When it comes to integratability, the zero-intermediate frequency (IF) receiver is an alternative for the heterodyne or IF receiver. In recent years, the zero-IF receiver has been introduced in several applications, but its performance cannot be compared to that of the IF receiver yet. This lower performance is closely related to its baseband operation, resulting in filter saturation and distortion, both caused by DC-offsets and selfmixing at the inputs of the mixers. The low-IF receiver has a topology which is closely related to the zero-IF receiver, but it does not operate in the base-band, only near the baseband. The consequences are that, as for the zero-IF receiver, the implementation of a low-IF receiver can be done with a high degree of integration, however, its performance can be better. In this paper, the fundamental principles of the low-IF receiver topology are introduced. Different low-IF receiver topologies are synthesized and fully analyzed in this paper. This is done by applying the complex signal technique - a technique used in digital applications to the study of analog receiver front ends.

This paper describes a method of designing even-degree lower-sideband polylithic crystal filters which have stop-band characteristic similar to even-degree elliptic-function filters. The asymmetrical filter is obtained by adding a bridge capacitor across each of the dual-resonator monolithic crystal filter elements of a symmetrical Chebyshev function polylithic crystal filters.

In this paper, we present cumulant analysis tools suitable for the study of chaos communication systems. The approach uses random process models for all signals involved. The analysis is applied to the differential chaos shift keying (DCSK) scheme and its close relative--the transmitted reference (TR) approach under additive white Gaussian noise (AWGN) channel conditions. Approximative as well as exact performance figures are derived, the latter agreeing with results recently presented in the literature. The parameter ranges for the application of either solution are specified. The noise robustness problem present in DCSK/TR is discussed and quantified. The paper extends results from works published earlier by the authors. Index Terms--AWGN performance, chaos communication, cumulant analysis, differential chaos shift keying.

Recent advances in the development of communication schemes based on chaos suggest that differential chaos shill keying (DCSK) is one of the most promising candidates tot a feasible implementation. Traditionally, the demodulation--decoding of DCSK has been achieved by means of a noncoherent approach based on a correlation detector. This approach in general works for any differential noise shift keying (DNSK) out of which DCSK is a subclass, i.e., it does not exploit the chaotic dynamics involved. In this paper, it will be shown that the simple correlation detector can be augmented by information based on the chaotic dynamics to improve the performance, yielding a statistically optimal detection. Introducing a rigorous probabilistic framework, the optimal receiver for additive white Gaussian noise (AWGN) will be derived, and it is shown that it decomposes into a part based on correlation and a part based on the chaotic dynamics. Index Terms--Communication with chaos, correlation detection, DCSK, optimal detection.

Using chaotic signals in spread-spectrum communications has a few clear advantages over traditional approaches. Chaotic signals are nonperiodic, wide-band, and more difficult to predict, reconstruct, and characterize than periodic carriers. These properties of chaotic signals make it more difficult to intercept and decode the information modulated upon them. However, many suggested chaos-based communication schemes do not provide processing gain, a feature highly desirable in spread-spectrum communication schemes. In this paper, we suggest two communication schemes that provide a processing gain. The performance of these and of the earlier proposed differential chaos shift keying is studied analytically and numerically for discrete time implementations. It is shown that, when performance is characterized by the dependence of bit error rate on [E.sub.b]/[N.sub.o], the increase of the spreading sequence length beyond a certain point degrades the performance. For a given [E.sub.b]/[N.sub.o], there is a length of the spreading sequence that minimizes the bit error rate.

Kolumban [1] has shown that, under specified conditions, the noise performance of frequency-modulated differential chaos shift keying (FM-DCSK) in a single-ray additive white Gaussian noise (AWGN) channel is independent of the shape of the underlying waveform. This paper discusses the qualitative features of the FM-DCSK system and characterizes the performance of this system in standard reference multipath channels. Index Terms--Chaotic communications, chaotic modulation, low-pass equivalent model, multipath performance.

Performance evaluation of a self-synchronizing Lorenz chaotic system is formulated as a stochastic differential equation problem. Based on stochastic calculus, we provide a rigorous formulation of the numerical evaluation and analysis of the self-synchronization capability and error probabilities of two chaotic Lorenz communication systems with additive white Gaussian noise disturbance. By using the Ito theorem, we are able to analyze the first two moments behavior of the self-synchronization error of a drive-response Lorenz chaotic system. The moment stability condition of the synchronization error dynamic is explicitly derived. These results provide further understanding on the robust self-synchronization ability of the Lorenz system to noise. Various time-scaling factors affecting the speed of system evolution are also discussed. Moreover, an approximate model of the variance of the sufficient statistic of the chaotic communication is derived, which permits a comparison of the chaotic communication system performance to the conventional binary pulse amplitude modulation communication system. Due to synchronization difficulties of chaotic systems, known synchronization-based chaotic communication system performance is quite poor. Thus, alternative synchronization-free chaotic communication systems are needed in the future. The use of a stochastic calculus approach as considered here, however, is still applicable if the considered chaotic communication system is governed by nonlinear stochastic differential equations. Index Terms--Bounded-input--bounded-output stable, error probability, Ito and Stratonovich integral, Lorenz chaotic communication system, stochastic calculus, stochastic differential equation.