Software Sculpts Complex Waveforms

Working with a vector signal generator, this advanced software can generate complex waveforms of virtually any size for stimulating wireless, radar, and EW systems.

Waveform generation can be complex and time-consuming. Most engineers resort to a mathematical software program to generate a complex waveform. They must then port the math files to a signal generator capable of accurately responding to the translated files. Fortunately, there is now a simpler way to create and generate long and complex waveforms, using the N5110A Baseband Studio for Waveform streaming software from Agilent Technologies (Santa Rosa, CA) on a personal computer (PC) along with one of the company's model E4438C ESG or E8267C PSG vector signal generators. The software supports virtually any waveform file size, limited only by the size of the PC's hard drive.

The N5110A waveform streaming solution (see figure) is part of Baseband Studio, a new family of products for improving the efficiency of the baseband design process when creating wireless and military products. Design verification at baseband has become increasingly important as a greater portion of the intelligence in wireless systems resides at the baseband level. By verifying the performance of baseband components and algorithms at early stages of design, engineers can save the time and cost of debugging algorithms and redesigning circuits after hardware has been built.

The more accurately that the simulated signal environment portrays its "real-world" counterpart, the more likely the system will perform well in the field. For example, receivers sent into service after being subjected to conservative approximations of signal conditions have the potential to fail when highly stressed, resulting in system performance degradation and reduction in quality of service. In the wireless industry, the downtime this could create would be unacceptable. A similar situation exists for radar and EW systems, both of which are expected to perform under varying propagation conditions as well threat scenarios. Once again, the likelihood of acceptable performance depends in large measure on how well the stimulus signals reflect these conditions.

In many cases, this level of verification can only be obtained with signal scenarios that range in length from a few minutes to several hours. In wireless applications, this is because complicated processes such as paging, acquisition, and channel assignment include large amounts of non-repetitive data. In radar applications, designers often capture live signals off the air over long periods to use as a stimulus. In both cases, the files containing these signals are invariably larger than any baseband generator can store in memory, so engineers are faced with two basic choices: They can partition the signal stream into segments small enough to fit in this memory and play back the entire file segment by segment. They can also build their own system to store, play back, and upconvert their waveforms. Both of these solutions are time-consuming, and creating a "homebrew" solution can be costly.

Agilent's N5110A Baseband Studio for Waveform Streaming software eliminates the need to resort to either of these processes by allowing the entire signal, regardless of length, to be stored on a PC hard drive and streamed out continuously through a PC-resident Baseband Studio PCI card (Agilent's N5101A) at high data rates to an ESG or PSG vector signal generator equipped with a baseband generator. (The company's E4438C series of vector signal generators includes models operating from 250 kHz to 1, 2, 3, 4, and 6 GHz, while the model E8267C microwave vector signal generator operates from 250 kHz to 20 GHz.) The instrument then converts the waveform into analog in-phase/quadrature (I/Q) or RF signals that are output as a stimulus signal to the device under test. The data rate of the streaming signal can be as high as 40 MSamples/s, which translates into a 16-MHz bandwidth for each of the I and Q channels and a total RF modulation bandwidth of 32 MHz. The bandwidth is sufficient to allow simulation of multiple modulated communications channels or generation of pulsed waveforms.

The N5101A PCI card is an essential element of the solution, because it performs operations on the baseband signals and controls I/O functions. It employs an advanced field-programmable gate array (FPGA) from Xilinx (San Jose, CA,, which enables the card to be reprogrammed to accommodate the signals that are processed by the streaming software. As many as four markers are available for creating output signals synchronized with the waveform, and waveform control functions while streaming include start/stop, looping, and an application programming interface (API) for developing custom levels of automation. P&A: $15,000 to $65,000 (N5110A Baseband Studio for Waveform Streaming software) and $4,500 (N5101A PCI card); stock. Agilent Technologies, Test and Measurement Organization, 5301 Stevens Creek Blvd., MS 54LAK, Santa Clara, CA 95052;

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