GPS World, May 2012

INNOVATION Signal Processing E FIGURE 1 Toolbox Simulating GPS Signals It Doesnt Have to Be Expensive Alison Brown Jarrett Redd and Mark Anthony Hutton WHY DO WE SIMULATE REALITY in mathematics science engineering and other pursuits even in our recreational activities Well we do it for a variety of reasons In mathematics and science we try to comprehend reality which is complicated and variable and often has some degree of randomness We build mathematical models of physical chemical or biological processes to better understand them or to predict a particular outcome given some initial conditions The model may contain a stochastic component to reflect a degree of uncertainty associated with the processes Weather forecasting is a prime example Typically the models are run on a computer where the model parameters and initial conditions can be readily adjusted and the varying outcomes analyzed Simulations of reality are often used in teaching where students can more easily grasp the behavior of complicated systems whether they be in the natural sciences or in economics or the social sciences In medical education simulated human patients are used initially because it is safer than having students operate on real patients Similarly flight simulators are used for the training of pilots because it is cheaper and safer than using real aircraft and a wide variety of what if scenarios can be experienced Simulation is used for a range of engineering activities to see how an existing system behaves under different conditions because it is faster or cheaper than performing tests in the real world It INNOVATION INSIGHTS with Richard Langley Simulation faster cheaper safer can also be used to estimate how a proposed new system might behave before it becomes a reality looking at traffic flow in road networks for example We also use simulation for recreation whether it is playing with the latest computer game or improving our swing with a golf simulator And simulation is a mainstay of the movie industry But getting back to engineering and the main interest of this magazine simulation is a useful technique in the design and operation of equipment used with global navigation satellite systems With a radio frequency simulator we can mimic the radio signals generated by the satellites These devices allow us to define scenarios including receiver trajectories and to replay them while varying the operating parameters of the receiver Some simulators allow us to record live signals and then to play them back under different assumed conditions However such GNSS signal simulators can be expensive and beyond the limited budgets of many researchers In this months column we look at one companys approach to providing GNSS signal simulation at a low cost one that virtually any researcher can afford As the noted French sociologist and philosopher Jean Baudrillard pessimistically once said We live in a world where there is more and more information and less and less meaning In the field of GNSS engineering at least simulation is helping to stem the tide and give us a better understanding of reality GPS World May 2012 www gpsworld com 44