Carla Feldman, Wireless Business Unit Marketing Manager, Agilent Technologies
The wireless industry has changed dramatically over the years, and, in turn, so too has society's desire for and reliance on wireless technology. The impetus for much of the change has come from development of standards like 3GPP Long Term Evolution (LTE) and Mobile Worldwide Interoperability for Microwave Access (WiMAX). LTE provides a framework for increasing capacity, improving spectrum efficiency, improving cell-edge performance and reducing latency, while Mobile WiMAX is generally more immune to interference, allows more efficient use of bandwidth and is intended to allow higher data rates over longer distances. Change has also come from the use of Multiple-Input Multiple-Output (MIMO) technology, which plays a critical role in making wireless communication systems based on LTE and Mobile WiMAX work. In fact, MIMO, a capacity-enhancing, multi-antenna technology designed to bring about a two- to four-fold increase in throughput with no additional frequency spectrum required, will likely be employed in all upcoming 4G wireless communication systems.

While these exciting technology developments offer compelling new functionality to consumers and service providers alike, they come at the price of increased complexity and, as a result, increased measurement challenges. Addressing these challenges has led the measurement industry to make some fairly significant advances, such as developing innovative test and measurement solutions which can span the entire product development life cycle and incorporate measurements specific to LTE, Mobile WiMAX and MIMO.

Technology-Specific Challenges and Resulting Developments

Challenge: LTE and Mobile WiMAX are evolving standards and, are, therefore, open to change and interpretation until they finalized. Development: The availability of conformance and protocol tests.

The early availability of conformance tests helps alleviate interoperability issues and provides basic testing. Rigorous test solutions also now exist for protocol development. Wireless libraries with signal processing models and preconfigured simulation setups are available to create waveforms used to produce real-world physical test signals. However, a successful commercial launch of either LTE or Mobile WiMAX technology will require comprehensive functional testing and real-world verification of LTE and Mobile WiMAX products.

Challenge: The 802.16 standard on which Mobile WiMAX is based specifies a tight Error Vector Magnitude (EVM) requirement (-31 dB, based on a 1% packet error rate). Meeting this target requires that all system blocks be more linear and phase noise be considerably better than in an 802.11 design. Power amplifiers must also be more linear and boast higher efficiency. Development: The commercial realization of nonlinear network analysis.

Figure 1. Agilent's Nonlinear Vector Network Analysis software, for use with the PNA-X microwave network analyzer, provides all the power, flexibility and measurement capability of the PNA-X for linear measurements and then can easily switch into the NVNA modefor nonlinear measurements.
The key to developing linear active devices for LTE- or Mobile WiMAX-based systems is to first characterize nonlinear behaviors — those which do not have a linear input/output relation and are a major contributor to information interference and the reduction in effective bandwidth. A new nonlinear vector network analysis capability featuring a breakthrough in X-parameters (new, nonlinear scattering parameters) now allows engineers to quickly and accurately design and develop linear components and subsystems by removing the trial and error loops (see Figure 1).

Challenge: Due to the complexity of MIMO technology, ensuring its optimal operation requires the engineer to accurately test the MIMO receiver — a challenging task given the large combination of variables that must be tested in a given MIMO configuration. Development: A fully-integrated MIMO receiver test solution.

Figure 2. The Agilent Technologies PXB MIMO Receiver Tester provides up to four baseband generators, eight faders, 120-MHz bandwidth, custom MIMO correlation settings and supports testing and troubleshooting of 2x2, 2x4 and 4x2 MIMO. Signal Studio signal creation software runs in the instrument and provides the engineer with up-to-date standards-compliant signal creation.
A critical part of testing a MIMO receiver is replicating real-world conditions and channels and performing real-time fading of MIMO signals. A recent advance in MIMO receiver testing marries the signal source, noise source and fader together in a fully-integrated, solution to successfully accomplish these tasks (see Figure 2). Rather than offering signal generation only, as is the case with most current solutions, this measurement approach offers an exceptionally versatile platform for testing LTE and WiMAX receivers. It not only allows the engineer to replicate real-world MIMO conditions and channels, but also to generate realistic fading scenarios including path and channel correlations.


While the challenges mentioned only scratch the surface of the totality of issues created by LTE, WiMAX and MIMO, they do provide a glimpse of the developments today's measurement companies are making in an effort to keep pace with their customer' technology innovation. As engineers push the limits of these new technologies, measurement companies will also be driven to push the limits of test and measurement in support of their efforts. They will need to ensure that as test specifications are defined, standard-compliant test and measurement solutions are available to support them. Addressing technology challenges as they arise with appropriate measurement solutions will be crucial to the widespread proliferation of developing technologies like LTE, Mobile WiMAX and MIMO, and the success of any products based on them.

Carla Feldman joined the company in 1985 and held a variety of product marketing and management positions in her 15-year tenure within the test and measurement sector of Hewlett-Packard Company and Agilent Technologies, focused on RF/Microwave spectrum analysis, optical and digital parametric analysis. In 2000, Carla left Agilent — where she held the position of vice president of sales and marketing — for a MEMS optical switch start up. In 2002, she joined JDSU as the director of sales and marketing for the commercial laser and custom optics portion of the business. Carla rejoined Agilent Technologies in 2007 as the wireless business unit marketing manager. Carla holds a Bachelors of Science in electronic engineering from the University of Michigan.