Philip Balaban

Simulation of communication systems

Simulation plays an important role in the design, analysis, and implementation of communication systems. During the design of complex communication systems it is often infeasible to conduct performance analysis and design tradeoff studies using closed-form mathematical formula techniques. Quite frequently, simulation is the only tool available for addressing important issues in the design, analysis, and implementation of communication systems. Simulation can be used to verify the functionality of communication systems, evaluate the performance of proposed systems, and generate specifications to guide their design. Since the early 1980s a variety of modeling and simulation techniques and tools have been developed and used to support the design and implementation of a broad range of communication systems and products ranging from multi-million-dollar communication satellites to handsets for the next generation of personal communication systems. This article presents an overview of the fundamental principles behind modeling and simulation of communication systems. Keywords: communication systems; discrete time representation; signals; systems; modeling of functional blocks; simulation of functional blocks; Monte Carlo simulation; random-number generation; performance estimation

Optimum diversity combining and equalization in digital data transmission with applications to cellular mobile radio. I. Theoretical considerations

A comprehensive theory for Nth-order space diversity reception combined with various equalization techniques in digital data transmission over frequency-selective fading channels is developed. The channels are characterized by N arbitrary impulse responses possessing random parameters as well as N additive Gaussian noise sources. Various combiner-equalizers that minimize the mean-squared error are determined. Formulas are presented for the attainable least-mean-squared errors and upper bounds on average probabilities of error. The theory is applied to optimize system parameters and to predict performance for QAM data transmission operating over a model for the mobile radio channel. For this model, estimates of average attainable error rates and outage probabilities are provided as functions of system parameters. In the channel models the uncoded data rates as well as Shannon capacity are regarded as random variables. >

Dual diversity combining and equalization in digital cellular mobile radio

The performance of digital data transmission over frequency-selective fading channels is investigated. For statistically independent diversity paths, estimates of average attainable error rates and outage probabilities as functions of system parameters are provided. The dependences among the important system parameters are exhibited graphically for several examples, including quaternary phase-shift keying (QPSK). In the optimized uncoded QPSK with 1.5 b/s/Hz, two orders of magnitude in outage probability can be gained by diversity reception. When one compares the uncoded average probability of error for the optimized mean squared error (MSE) systems one finds at most an order-of-magnitude difference among the different equalizers investigated except for the zero-forcing equalizer, whose performance is drastically inferior to the others. Again, dual diversity can provide two orders of magnitude improvement in the average error rate or in outage probability for the uncoded optimized systems. >

Optimum diversity combining and equalization in digital data transmission with applications to cellular mobile radio II. Numerical results

For Pt.I, see ibid., vol.40, no.5, p.885-94 (1992). The probability distributions of the data rates that can be supported by optimum receiver structures as well as the distribution of the Shannon capacity are studied. The dependences among the important system parameters are exhibited graphically for several illustrative examples including QPSK. At outage probabilities >

Three Case Studies

The application of the concepts presented in the preceding chapters, especially the methodological concepts, is best clarified by example. Consequently, we present in this chapter three case studies, each of which illustrates different techniques, and collectively span many of the ideas that can be called upon in developing simulations.

Experimental results for multimode interference during dispersive fading

Multimoding is caused by mode conversions and multiple reflections in the horn antenna and the circular waveguide system and leads to an impairment in the performance of digital radio. It is shown that the effect of multimoding is that of an echo with a long delay that cannot be equalized. The multimode energy thus becomes a form of interference. In addition it is shown that the multimode interference increases as a function of angular offset in the elevation of antennas, and is larger for vertical polarization of the signal. It is further shown that present-day 64-QAM (quadrature amplitude modulation) digital radio with angle diversity will perform satisfactorily in the presence of multimode interference. However, for new technology where multimode interference may become a dominant impairment, some form of mode suppression may be required.<<ETX>>

Statistical distribution of parameters in a variable delay two-ray propagation model

Propagation data obtained from a 6-GHz channel with a 30-MHz bandwidth over a 23.3 mile path are used to obtain the statistics of parameters of propagation for two models, namely, the two-ray model and W.D. Rummlers (1979) model. Only scans with both an in-band notch and an in-band power difference greater than 1 dB are considered. It is noted that the statistics of the relative delay between rays is important because the mean of this delay is directly related to the severity of the dispersive fading and the outage time of the system. The results show that the relative delay of the second ray in the two-ray model can be best approximated by a gamma distribution.<<ETX>>

Analog computer simulation of semiconductor circuits

This paper describes new simulation techniques which are being used in the analysis and design of integrated circuits. They have also proved advantageous in the characterization of semiconductor devices. Two approaches are available; the breadboard method, a method based on retaining circuit topology, and the analog method which is based on traditional analog computer programing techniques.

Representation of Signals and Systems in Simulation

This chapter deals with the analysis of a system driven by deterministic (or test) signals. In a generally accepted definition of analysis there are three key words: the excitation, the system, and the response. System analysis and simulation are concerned with determining the response given the excitation of the system. In the system design stage the problem is to synthesize the system given the excitation and response.

Simulation and Modeling Methodology

Building simulation models and running (executing) simulations are activities that call upon a wide variety of skills and considerations which, for present purposes, we might divide into two broad categories: the “art” and the “science” of simulation. In the latter camp we include the more theoretically based and quantitative aspects which have formed the bulk of the preceding chapters. On the other hand, there is a set of considerations only partially or perhaps not at all related to theoretical or quantifiable matters, or difficult to describe in such terms, that are nevertheless fundamental in building simulations and in obtaining useful results. This set we might regard as the “art” of simulation. These latter considerations and ways of dealing with them essentially form the methodology of simulation. The dividing line between “art” and “science” is somewhat subjective, but is not critical, in any case. In this chapter we discuss several issues that we classify as methodological.