Note - The technical feature by ETS-Lindgren’s Dr. Michael Foegelle in the March issue of Microwave Journal contains additional technical information on WiMAX RPT measurements.
MWJ: ETS-Lindgren is a leading innovator of systems and components designed to detect, measure and manage electromagnetic energy. The company has solutions ranging from RF/microwave (absorbers, chambers and high performance antennas) to wireless device air performance tests to MRI shielding. Could you elaborate on the principle ETS-Lindgren products and services that would be of concern to RF/microwave and wireless engineers?
BS: ETS-Lindgren is well known for RF shielded enclosures, anechoic chambers and precision measurement antennas. RF/microwave and wireless engineers should also be aware that we have a broad range of RF Sensors for use in precision measurement applications, field survey and tower safety applications. We also provide portable test enclosures, which incorporate many of our key technologies and are often customized to specific customer applications for test bench R&D and production line quality assurance of wireless devices.
We operate an A2LA accredited wireless test lab, which can provide radiated performance measurements in accordance with CTIA, 3GPP and WiMAX RPT standards. We provide calibration of antennas and RF sensors as well as field certification testing of wireless and EMC facilities.
One product range that we are less known for is acoustic testing. We have a world-class acoustic lab in Texas and have developed products designed to provide test engineers with the ability to measure sound pressure and quality of end user devices. For more information on our entire line of products and services, please refer to .
MWJ: The acquisition of Lindgren RF Enclosures in 2000 doubled your company’s size while giving you a presence in Asia (Singapore). Since then you’ve added facilities in Japan, China and Taiwan. Are these facilities mostly focused on design, manufacturing or customer sales and support?
BS: ETS-Lindgren’s strategy is to provide local service and support where our customers are doing business. Many of our customers have made significant investments in Asia and we have responded accordingly. We currently have over 150 employees in Asia providing customer support. We have a factory in Beijing, China, and sales/project engineering offices in Tokyo, Shenzen, Shanghai, Singapore and Taipei. As we see continued customer investments in specific regions, we will continue to invest in the local offices and personnel required to meet our customer’s needs.
MWJ: ETS-Lindgren is a member of the WiMAX Forum tasked with developing specifications for Radiated Performance Testing (RPT). What has been your participation in this Forum to date? Is it ongoing?
BS: ETS-Lindgren has been a member of the WiMAX Forum since 2006. Our principle contribution has been working with member companies to develop the Radiated Performance Testing standards, which represent the final stage of WiMAX device certification testing. We intend to remain engaged with the Forum indefinitely.
MWJ: Is the RPT specification locked down or are some aspects of it still evolving?
BS: The RPT specification has been formally approved for use in certification of WiMAX devices, although continuing comment resolution will result in minor modifications over the next few months. Testing has begun at AT4 Wireless and we understand that by mid 2008 all WiMAX Forum Designated Certification Labs (WFDCL) will be performing RPT. ETS-Lindgren is able to perform RPT measurements as an engineering service for developers who would like to understand the radiated performance of their devices prior to submission for certification.
MWJ: Are RPT measurements specifically used for the wireless device or are they used to characterize components in a wireless device such as the antenna?
BS: This is the essential point about RPT measurements. Rather than measure any individual component, RPT measures the entire device in its final configuration using a radiated RF link. WiMAX enabled devices such as laptops are complex, dynamic devices with many components, which may interfere with the RF performance of the device once the antenna is attached. RPT allows the WiMAX Forum to characterize the RF performance of the entire system to ensure that the end-user configuration meets minimum standards of performance.
MWJ: WiMAX technology uses Orthogonal Frequency-Division Multiplexing (OFDM) over Edge, GPRS, HSPA to deliver higher bandwidth efficiency and therefore higher data throughput. Is OFDM used in the RPT?
BS: Yes, 802.16d uses OFDM, but Mobile WiMAX is based on 802.16e and uses scalable Orthogonal Frequency Division Multiple Access (OFDMA) technology. RPT is intended to test subscriber and mobile stations based on the 802.16e requirements and thus those devices will use OFDMA instead of OFDM.
MWJ: Could you give us a little detail about an actual RPT? How are they performed? What kind of data is produced? How long might it take to adequately characterize a device?
BS: There are two primary metrics within the RPT. If you think of this in terms of verbal communication, Total Radiated Power (TRP) is the “talk” metric, which measures how loud the device can speak. Total Isotropic Sensitivity (TIS) measures how well the device can “hear”.
Dr. Foegelle’s article provides a block diagram of the test setup and measurement process. Additional detailed information including time lapse video of actual tests and three-dimensional radiated pattern measurement data are available at .
Measurement time is a function of the pattern density that the user desires. ETS-Lindgren’s systems allow the user full control over the number of data points. TRP measurements made at a 15 degree surface resolution generally require 10-20 minutes per channel while TIS requires more time as the search algorithm must perform packet error rate (PER) measurements across a range of power levels to determine the power level at which the PER exceeds the specification. Thus, the RPT allows reducing the angular resolution for TIS tests. Assuming 15 degree steps for TRP and 30 degree steps for TIS, full certification measurements are currently estimated to require approximately 8-10 hours of test time for a single band device. However, tests will take longer as the angular resolution and/or number of bands increases.
MWJ: Are there specific global hotspots for WiMAX device development with an increased need for RPT? If so where are they?:
BS: WiMAX is a global technology and product development is occurring all over the world. Having said that, there appears to be a very high level of activity in the Pacific Rim, particularly in Taiwan, Korea and China. The WiMAX Forum has named four WFDCL within these three countries.
MWJ: By attempting to provide mobile Internet anywhere - anytime, WiMAX devices will need to be very robust in some challenging environments. How does this reflect in the WiMAX RPT spec?
BS: The TRP and TIS metrics provide reliable device metrics, which are one component of the RF link budget used by RF network designers to determine the required network design to properly address a given geography. Networks are designed based upon assumptions about the mobile device performance. Without TRP and TIS standards for mobile devices, users might experience substandard performance when using devices, which transmit or receive at levels, which do not meet the network designer’s assumptions. The importance of consistent end-user experience was a major factor in the WiMAX Forum’s decision to implement RPT as part of the certification of mobile devices.
MWJ: Does the mobile WiMAX RPT spec reflect the worse case operating conditions, average conditions or does it reflect different expected use models?
BS: WiMAX RPT measures the “edge of link” performance and as such measures performance of the device under worst-case conditions from an RF perspective.
MWJ: How does WiMAX RPT specifications compare to other recent wireless standards?
BS: WiMAX RPT is compatible with Over The Air (OTA) measurements currently performed on 2G and 3G devices, but includes a number of innovations. One of the objectives of the WiMAX Forum was to ensure that the wireless industry would be able to utilize OTA facilities and equipment already in use. For example, the anechoic chambers, positioning systems etc. used in existing OTA measurements will be useful for RPT. The distinctions come in the implementation of site validation, range calibration and sampling methods,which are designed to optimize test time and measurement uncertainty.
MWJ: Last October Agilent Technologies and ETS-Lindgren demonstrated the industry's first solution for WiMAX radiated performance testing at the WiMAX Forum Showcase and Conference in Taipei. What product did you demonstrate? What type of device did you measure?
BS In October, 2007 we demonstrated RPT measurements of a laptop with a PCMCIA based WiMAX device utilizing profile 3A-10, which is the expected initial deployment in the US. Initial measurements were performed in ETS-Lindgren’s AMS-8800 and AMS-8500 measurement facilities at our wireless lab in Texas using an Agilent E6651A Mobile WiMAX Test Set. Measurements were subsequently demonstrated at the WiMAX Forum in Taipei in ETS-Lindgren’s portable AMS-8050 system. For detailed information including pictures, video and measurement data, please go to .
MWJ: Is this test system now available for test houses and design facilities?
BS: Yes, each of the test systems described are available for installation worldwide. The portable AMS-8050 system is available for shipment within a few weeks. Typical lead times for construction and system implementation of full-scale systems are 12-16 weeks. ETS-Lindgren’s lab in Texas is available now for pre-certification testing to the RPT standard.
MWJ: Can this system be used for certification or is it more of a diagnostic tool?
BS: Yes, the AMS-8500 and AMS-8800 systems are both capable of performing full certification testing. The portable AMS-8050 is a pre-compliance system which provides excellent correlation to the full size systems.
MWJ: Can only certified test labs certify devices? How does a test lab or facility go about getting certification?
BS: WiMAX Forum Certification can only be granted through a WiMAX Forum Designated Certification Laboratory (WFDCL). There are currently six designated laboratories world-wide. Please refer to for detailed information on obtaining WiMAX Forum certification.
MWJ: How did ETS-Lindgren and Agilent end up working together? Are you a channel partner with Agilent? Is ETS-Lindgren a reseller of the Agilent equipment that is used in this system?
BS: ETS-Lindgren works with many instrumentation providers and is an Agilent channel partner. As the WiMAX RPT standard was being developed in 2007, Agilent was the first instrumentation provider to market a fully functional tester capable of generating the signaling traffic required for WiMAX RPT. Agilent immediately recognized the importance of WiMAX RPT to the WiMAX ecosystem and provided significant support throughout the standards development process.
MWJ: ETS-Lindgren is itself a CTIA authorized test lab. Do you receive a lot of devices for accreditation? Are test result simply pass/fail or is their data generated that would help a company address issues that led to compliance failure?
BS: ETS-Lindgren was the first CTIA Authorized Test Lab (CATL) and continues to operate a fully compliant lab. We have tested many devices both for certification and for research and development. The test data provided by OTA and RPT systems are more than pass fail and are rich with information that can be used by device designers to improve the radiated performance of their devices.
In particular, these measurements provide detailed radiated pattern data, which reveals the interaction between the antenna, other components within the mobile device and near-field phantoms such as the users head or hands. This data substantially improves the designer’s insight into these factors and allows them to make design improvements.
MWJ: Will ETS-Lindgren also offer WiMAX certification testing or are you more focused on designing and manufacturing WiMAX RPT test systems?
BS: ETS-Lindgren currently offers WiMAX RPT testing as an engineering service on a pre-certification basis. Please contact our service department at (512) 531-6498 for more information.
MWJ: Do you know what percentage of companies in wireless device design and manufacture has in-house RPT measurement capability versus those that use test labs?
BS: We do not have a precise estimate on the breakdown between in-house testing and out-sourced testing. We increasingly see device manufacturers investing in antenna measurement systems specifically for R&D. Our customers tell us that these systems have become essential to their device development process and that there is a direct correlation between radiated performance testing and the performance of wireless devices on service provider networks.
MWJ: Does ETS-Lindgren offer design consulting on how to address an EMC problem or design a more robust antenna?
BS: ETS-Lindgren does offer consulting services; however, our focus is on how to make precise measurements of radiated energy including both electrical and acoustic. We have partnered with many companies to provide solutions to complex measurement problems. Often this includes custom design of a specific product to perform measurements in the lab, the field or on a factory floor.
MWJ: Thanks for taking the time to talk with us today, Bryan. As WiMAX and other next generation wireless devices proliferate and operate in the same space, I expect more and more focus will need to be paid to RPT measurements. Thanks for giving us a better understanding of what is involved.