Chapter8.Simulation

Chapter 8. Simulation

William H. Tranter, James O. Neel, and Christopher R. Anderson

Simulation, which is the subject of this chapter, is a both a design and an analysis tool. Through the use of repeated simulations, design alternatives can be explored, parametric studies can easily be conducted, and the impact of varying critical parameters can be quickly determined. Due to the growing complexity of communications systems and the power of simulation tools and computer platforms, simulation plays an increasingly important role in understanding the performance characteristics of complex communications systems.

Simulation is a difficult subject for a variety of reasons. First, simulation development is part art and part science; second, simulation requires a detailed knowledge of a large number of fields. To see where art enters into the process, consider the steps to developing a simulation:

1. Map the system configuration under study to a simulation model. As many solutions exist and there are innumerable dependencies to consider, it is impossible to formulate definitive guidelines for choosing the most efficient model. This makes this step more art than science.

2. Partition the system to be simulated into small segments or subsystems. Again there are an innumerable number of ways in which this partitioning can be done, and the partitioning is highly dependent on the system under study and on the platform on which the simulation is being implemented. This step of partitioning is again more art than science.

3. Choose the set of modeling, simulation, and estimation tools most appropriate to the various subsystems that comprise the system under study. Fortunately, this step is more science than art, as the set of tools is limited, and well-defined criteria exists for determining the appropriateness of each tool.

4. Finally, combine the results of the subsystem simulations in a way that allows a solution to the system-level problem to be obtained. Again, an innumerable number of combinations exist, and the determination of the best combination is an art.

It can be seen that three of the four preceding steps are more art than science. Performing these steps in the best manner requires mastering the art. Mastering the art of simulation cannot be accomplished by reading a paper or a textbook, but can only be accomplished through experience. However, the literature on the subject of simulation as applied to the design and analysis of communication systems is vast, and the reader is referred to two recently published books for a basic understanding of the subject [1,2].

It should also be mentioned that one basic decision made in simulation development is whether to use a general-purpose language and build the simulation "from scratch" or to use a simulation package specifically targeted to the type of system being considered. A number of software packages targeted to the simulation of communication systems exists, and many of these have model libraries that can prove useful for UWB systems. Especially useful are packages that are "block diagram" orientated. These range from general-purpose packages, such as SIMULINK, to packages specifically targeted to communications systems, such as SPW. The choice of simulation language is again a function of many different considerations, such as language familiarity, the uniqueness of the system being simulated, and simulation runtime requirements, so this decision can also be deemed more art than science.

The second reason simulation is a difficult subject is the fact that simulation requires a broad and detailed knowledge of numerous areas. Certainly the device to be simulated must be well understood and appropriate models must be available. Additionally, the assumptions used in model development must be known, and the impact of these assumptions on the accuracy of the resulting simulation must be evaluated. Further, simulation development requires knowledge of computer languages and software management principles as well as a thorough grounding in digital signal processing.

As the material included here focuses on UWB systems, it is assumed that the reader has a basic understanding of the subject. Models for propagation, transmitters, receivers, and signals are all addressed elsewhere in this book and are not covered in this chapter except through examples. Rather, this chapter focuses on the simulation techniques and approaches that are well-suited for simulating UWB systems at the level presented in [1].

Specifically, this chapter covers the following subjects:

1. Particular challenges introduced by the simulation of UWB communication systems.

2. An overview of fundamental simulation methodologies and terminology.

3. Architectural approaches to simulating UWB communication systems.

4. Simulation models for UWB communication systems components.