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Many—if not most—RF systems incorporate multi-domain designs. To effectively model such a system, the different domains could be handled within the same platform. This could prevent time-intensive and potentially error-prone interfacing caused by multiple tool use and custom generation. Ditore shares, “The best way to solve this is by providing different methods of computation that are well integrated. So you could take a fixed-point model, floating model, time-domain RF model, and frequency-domain RF model and combine them all together into one simulation.”

System-level-modeling tools, such as SystemVue, provide different methods of computation to allow different computation models to run efficiently. The ability to neatly interface the different computation methods enables simulations of an entire system to be performed more rapidly than single methods of computation. This class of tools offers frequency- and time-domain computation for both analog and RF. It also provides floating- and fixed-point methods for the digital domain.

With this approach, the method of computation can be tailored to the type of model that is optimal for each individual block within the system. Ditore shares an analog/RF example: To model an amplifier that has a gain and noise figure as well as input and output impedance matching, a frequency-domain simulation would be adequate in terms of speed. Yet a time-domain envelope simulator could be a viable option—if it was not critical to model the impedance matching  and only the gain and noise figures. The time-domain simulation would run faster with the tradeoff of losing the impedance-matching resolution.

For another example, Ditore pointed to a digital representation using a digital-signal-processing (DSP) finite-impulse-response (FIR) filter. A floating-point simulation would produce the FIR filter coefficients. If finite precision is desired, a set number of bits of resolution could be determined for each coefficient. Using a floating-point simulation with 10 bits of resolution for the coefficients—and using 2’s complement format for numeric precision—it may not be possible to run such a system in a reasonable amount of time. A fixed-point simulation could potentially run the same DSP FIR-filter model at a higher rate.

System-Level Modelers Race The Design Cycle, Fig. 3

Beyond the system-level-modeling tools that enhance the design flow from the block level, the design of robust devices can be aided by tools that account for environmental factors and other RF systems. For example, RF co-site analysis predicts the interactions between various antenna and radio systems (Fig. 3). This step is critical in ensuring that the behavior of antenna and radio systems do not interact and create interference. Shawn Carpenter, director of sales and marketing for Delcross Technologies, states,  “Co-site analysis is important anywhere you have collocated RF systems that have the potential to talk to one another in a destructive way. There are several things you have to worry about when you are trying to determine how multiple RF systems work and play together.”

Software offerings like Delcross’s EMIT use asymptotic electromagnetic (EM) analysis to acquire a superposition of currents stimulated across a multi-radio platform. This analysis involves the combining of physical-optics and EM-analysis techniques. First, rays are shot at the geometries of the platform. The circulation currents that were created are analyzed. An observer is then created spatially. It integrates the generated currents, which are transformed into an approximation of far-field contributions at some combination of angles.

Next, the software integrates the antenna, radio, cable, and filter models to define the interaction of these different radios. This can be done channel by channel, component by component, or in complete simulation mode, which Carpenter refers to as a “shooting match.” The goal of the software is to follow the design of a radio system that is intended to operate in a multi-radio platform—from early conception to final design. Such a process could indicate whether certain design decisions will produce interference and compromise the functionality of the various radio systems.

From antenna interference to chip-level component analysis, advanced system-level-modeling and analysis tools can provide valuable insight throughout the design process. If a system model is well defined and iteratively improved throughout the cycle, costly redesigns can be avoided. The test/verification process can be minimized as well. Thanks to the development of multi-domain tools and the improvements in those tools’ computational efficiency, more refined simulations of complex systems are now possible.

Of course, cost and return-on-investment (ROI) always must be considered when evaluating these often-high-priced tools. In addition, some designs would benefit from having access to multiple modeling tools so that designers could compare and contrast performance. So far, there are no complete start-to-finish tools that account for every aspect of a design. As a result, much weight is still placed on the experience and diligent planning of system architects.

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