The picture below is a wireless enthusiast's treat. It's no illusion either! With the number of standards flooding the wireless domain, plotting them in chronology on a single chart could look no less than that. Bluetooth, WiMAX, cdma2000, ZigBee, GSM, EDGE, and RFID -- the list of wireless and communications standards continues to grow at an unprecedented pace. At the same time, viewing football highlights on V-CAST and obtaining location data from Google Earth are becoming commonplace, fueled by the likes of Microsoft, Vodafone, and Google. While chip manufacturers are working to pack as much functionality into their latest chipsets as possible, device manufacturers are scrambling to implement this new functionality into their latest products and test these devices.
Given this insatiable demand for more data bandwidth and the fact that wireless communications are now outpacing land communications in many countries, the large challenge ahead for mobile communications becomes meeting this demand effectively. In addition to the demand for multiple wireless standards, industry is driven by the ever-present pressure to quickly get new products to market, and research and design are outpacing test. Manufacturers release ZigBee and 802.11n devices before the standards are complete. Predefined standard test systems from stand-alone instrument manufacturers no longer exist. This is attributable to the fact that the traditional cycle of releasing a wireless standard, prototyping devices among lead users, and developing test equipment for mass commercial use is too time-consuming.
Traditionally, you would need a separate stand-alone instrument for every communications standard to be tested. Each instrument has vendor-defined functionality for a particular standard. The communications measurement algorithms for the standards exist as firmware running on the embedded processor in each instrument, which means they are not user-accessible or customizable. Purchasing a new standalone instrument for each standard that you need to test is not productive or cost-effective. This is pushing engineers to seek flexible, out-of-the-box solutions. To combat this accelerated product development cycle, a flexible, software-based architecture is essential to rapidly prototype, design, and test devices using current and emerging wireless and communications technologies. In a nutshell, it couldn't have been more necessary to make your communication test system "future proof"!
Flexible software-defined communications test
One way to keep stride with wireless and communications advances is through software. You can take a software-defined approach to instrumentation by using coding and modulation software to generate and measure signals through modular, general-purpose RF instrumentation. This software-defined radio (SDR) approach to test is completely application-driven and user-defined. You can use it to leverage the software modeling and simulation software used in research and design for test and measurement.
The figure above illustrates a functional block diagram of a typical communications system with National Instruments LabVIEW graphical code. The functions are for source coding, channel coding, modulation, and upconversion on the transmit side and downconversion, demodulation, channel decoding, and source decoding on the receiver side. The software is particularly suited for a PXI system, which provides the modular, general-purpose RF instrumentation required to both generate/upconvert and downconvert/acquire the communications signals.
PXI for Software-Defined Communications Test
There are many reasons why the PXI platform is ideal for software-defined communications test. Most importantly, it is PC-based. The functionality of PXI instruments is defined in software so a single PXI RF instrument can test multiple communications standards by simply changing the software running on the system controller. PXI controllers employing the latest dual-core processors can easily process the most complex communications algorithms.
As communications standards continue to scale the amount of data transferred, it is important to base a communications test platform on a high-throughput bus to transfer the data. PXI is based on the PCI and PCI Express buses, providing up to 6Gbps of system bandwidth and up to 2Gbps of bandwidth to a single instrument. With this throughput, you can use PXI to perform long-duration recording of communications signals for offline analysis and the playback of previously recorded or simulated signals.
Also, with the modular nature of PXI, you can upgrade a single component of a system. For example, you can increase the performance of all of the instruments in a PXI system by upgrading to a controller with a higher-performance processor. This type of upgrade is not possible with standalone instruments where the embedded processor is not user-accessible or upgradable. Moreover, because PXI is a multivendor platform, the modular components of a system can come from multiple vendors. You are not locked into a single vendor, and, because all PXI products must adhere to the PXI hardware and software specifications, interoperability among different vendors is guaranteed.
Most systems that test communications must also test other device functionality and include other instruments, such as digital multimeters (DMMs), programmable power supplies, and switching. The PXI platform is general-purpose and offers instruments for most applications and measurements. More than 1,000 PXI modules are available from the more than 68 members of the PXI Systems Alliance (PXISA).
Conclusion
The trend toward software-defined communications test systems will continue to grow. Organizations have embraced the movement because it helps them develop test systems in conjunction with standards development. Software-defined test offers the solution for current communications systems, but, more importantly, it provides a paradigm and platform for emerging and future communications systems.
Download the Guide to Architecting Next Generation Test Systems: http://digital.ni.com/express.nsf/bycode/ATEGuide
Author Information
Soumendra Ghosh leads the team of application engineers at National Instruments, India. His business regions also include Arabia, Australia, Russia and Singapore. He holds a degree in Telecommunication Engineering from RVCE, Bangalore.
