Microwave Journal

MWJ T&M Survey 2009: Keithley Instruments

Keithley responds to questions from Microwave Journal editors about the state of RF testing and measurement equipment today.

March 11, 2009

Responses by Mark Elo Keithley Marketing Director of RF Products

MWJ - What’s your most significant new product/technology and how is it impacting how engineers work?

Keithley - The SignalMeister™ RF Communications Test Toolkit is a next-generation software tool that allows engineers to create and analyze the complex signals used in the most advanced wireless transmission protocols. It generates and analyzes both single-input, single output (SISO) signals and multiple-input, multiple-output (MIMO) signals used in the latest versions of the WLAN and WiMAX protocol standards. In addition to creating high quality signals, the SignalMeister RF Communications Test Toolkit can create impairments to model non-ideal transmitter conditions and real channel conditions such as fading and noise.

The SignalMeister software has the unique ability to analyze the transmitted signals, acquiring and demodulating the signals, then computing and displaying a wide range of parametric data. In addition, the SignalMeister toolkit can perform simulation studies without the need to use the actual hardware, which allows researchers and designers to study the impacts of transmitter impairments and channel effects on signal transmissions easily. This powerful software platform integrates the signal creation libraries of multiple wireless communication standards into a single package. It provides a common look and feel, allowing engineers to create and analyze reference signals from one or more standards easily in a single development environment. The built-in toolset can be used to modify all signal types, including non-encrypted waveform files produced by other software packages, to support extensive product testing. The PC-based software tool has an intuitive, object-oriented graphical user interface that’s easy to learn and use, substantially increasing productivity over the use of traditional software tools.

MWJ - What new technologies such as MIMO, LTE or DigRF are impacting the requirements for test equipment and how?

Keithley -LTE and WiMAX both use the same underlying technology -- OFDM and MIMO. While this has some advantages, in terms of similar radio architectures and the ability to interchange product development engineers easily between the two types of technology, a number of differences must be considered. Base stations offer the highest opportunity for a common platform, since the cost, size, and power requirements are far different from the handset, or “user equipment.” A common 20MHz IF can be employed, combined with the multiple RF systems required for the different transmission bands specified for WiMAX and LTE and the multiple streams required for a MIMO transmission. A handset presents a number of challenges because cost, size, and power performance are critical for market acceptance. LTE has been optimized for power amplifier efficiency transmitting SC-TDMA; while a WiMAX UE transmits OFDM, which requires a higher cost and more power-hungry amplifier, it has a smaller signal processing footprint.

With respect to test, two approaches could be used. It’s possible to measure the products to the documented specifications. The software-defined radio architecture in instruments such as the Keithley Model 2820 RF Vector Signal Analyzer and Model 2920 Vector Signal Generator fully support standards-based test for both LTE and WiMAX, using a single hardware platform. Or, one can take advantage of the power of this type of test equipment architecture and characterize the RF performance in terms of magnitude and phase quality. This would provide a generic way to derive specifications such as WiMAX or LTE modulation quality. When MIMO comes into play, one will need a generic indication of the isolation between each RF module or unit as well. The test equipment needs to cover the required frequency range and transmission bandwidth, such as a frequency range of 400MHz to 6GHz with a bandwidth of 20MHz. If it’s necessary to add WLAN (802.11n) into the architecture, 40MHz of bandwidth would be required. This approach may provide very fast test times and a higher utilization of test equipment, but it requires an investment in time and resources to be able to verify that the product meets both its regulatory and interoperability requirements.

MWJ - How is technology improving the capabilities of test equipment?

Keithley -The rapid development of new wireless communication standards requires an almost constant re-evaluation of the sourcing and measurement capabilities needed for wireless device research and production testing. One way in which test equipment vendors have risen to address this customer need is to design instruments that are more flexible. New technologies like software-defined radio (SDR) architectures let vendors design instruments that are flexible and adaptable to the changing needs of the industry.

The essence of an SDR implementation is that the modulation and demodulation functions performed on RF signals are done by digitizing the signals and using software and processing techniques, rather than dedicated hardware. This approach allows transmitting or receiving a wide variety of signals more economically than with dedicated, modulation-specific hardware.

The basic principle of software-defined radio is to replace analog circuitry with digital circuitry that can be programmed via software. Functions that were traditionally done in analog hardware, such as frequency generation and conversion, modulation and demodulation, and filtering, are performed with digital hardware. SDR designs also include unique digital functions that can improve the performance of the radio. These functions include decimation and interpolation, which can extend the dynamic range of the radio, and waveform pre-distortion, which can improve the modulation accuracy. In the case of waveform pre-distortion, the modulating signals are modified from the ideal signal to counteract known analog distortion characteristics.

MWJ - What are some of the issues facing production and field testing?

Keithley -As in many fields, wireless devices manufacturers need high accuracy production and field test solutions that are intuitive to operate and simple to integrate into the work environment. For example, Keithley’s Model 3500 Portable RF Power Meter is a compact, handheld instrument that makes lab-quality RF power measurements in both field and R&D laboratory environments. With an absolute accuracy as good as ±0.21dB, a wide frequency range of 10MHz to 6GHz, and a measurement range of –63dBM to +20dBM, the Model 3500 is suitable for a wide variety of RF measurement applications. Its built-in power sensor eliminates the need for users to carry both an instrument and a separate sensor module, and the same sensor is used when duplicating tests or measurements for better repeatability. Truly portable, the Model 3500 fits easily into a user’s hand or a toolkit; an optional belt loop holster or carrying case with shoulder strap is also available. To optimize flexibility, it’s capable of drawing operating power from batteries, an AC-DC converter module, or a computer via the USB interface.

MWJ - How frequently should a company consider updating test equipment and how are they addressing aging test solutions?

Keithley -Given the speed at which new wireless communication standards have been created, wireless device manufacturers need to re-evaluate their sourcing and measurement capabilities for wireless device research and production testing on a continuous basis. Obviously, no device manufacturer can afford to repeatedly scrap its test equipment and start over with new hardware when new communication standards emerge. A growing number of device manufacturers are looking to their vendors for test solutions that offer the flexibility needed to adapt readily and economically to new standards.

Test instruments employing software-defined radio (SDR) techniques, such as Keithley’s Model 2820 Vector Signal Analyzer and Model 2920 Vector Signal Generator, offer both equipment manufacturers and their customers important technical and economic advantages:
• Easy upgradeability to new communication standards. Signal generation and analysis are largely performed by routines programmed into the digital signal processor. When new standards emerge, it’s easy to create new DSP programs for the new functions and distribute them to the owners of existing instruments via firmware upgrades.
• Improved throughput due to faster frequency switching and signal analysis. Wide bandwidth A/D converters and fast DSP devices can process large FFTs very efficiently. For example, a DSP-based analyzer can provide measurement times several orders of magnitude faster than traditional spectrum analyzers, under conditions of wide spans and narrow resolution bandwidths. Direct digital synthesis provides significantly faster frequency switching than traditional approaches allow. Fast frequency switching will improve the throughput of both signal generators and signal analyzers.
• Faster time to market for test instruments. Test equipment manufacturers can leverage the capability of leading-edge, commercially available signal processing devices and achieve instrument-level performance from them. This reduces the amount of development required for test instruments dramatically, so vendors can deliver the new test solutions their customers need much faster and more economically.