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Test companies live up to the WiMAX challenge

Posted: 29 Aug 2008 ?? ?Print Version ?Bookmark and Share

Keywords:WiMAX? wireless? network analyzer? RF designer?

In an effort to put complete WiMAX analysis in the hands of RF designers, test and measurement companies continue to develop software upgrades, spectrum analyzers, test sets and network analyzers to comply with the rapid buildout of these wireless networks.

WiMAX, the wireless digital communications system also known as IEEE 802.16, is expected to provide broadband wireless access of up to 30mi for fixed stations and from 3mi to 10mi for mobile stations. In contrast, the Wi-Fi/802.11 WLAN standard is limited. In most cases, it is from 100ft to 300ft.

Aside from allowing higher data rates over longer distances, WiMAX provides more efficient bandwidth use and less signal interference. It employs OFDM transmission, which makes the signal in RF systems less likely to be affected by fading when compared with the other CDMA employed in older technologies such as GPRS. OFDM signals fill the bandwidth with a series of subcarriers that offer smaller bandwidths.

Superior performance
WiMAX's adaptive modulation scheme increases link reliability for carrier-class operation and increases the possibility of keeping higher-order modulation at longer ranges, extending networks' total capacity.

Thanks to its performance, WiMAX's popularity is catching up worldwide. The standard, which serves all usage models from fixed to mobile with the same infrastructure, is on its way to hitting 133 million users globally by 2012, according to the WiMAX Forum in a forecast based on the results of an independent research study released in April.

Reported estimates are expected to hit around 70 percent of the predicted WiMAX users by 2012 who are mobile and portable WiMAX devices fanatics and those who access broadband Internet services.

WiMAX incorporates multiple technologies in one versatile system, including bandwidths in excess of 20MHz, configurations with more than 2,000 subcarriers, high peak-to-average power ratios and both SISO and MIMO radio configurations. But this complexity has made testing a challenge for manufacturers. As new signal standards debut and WiMAX equipment evolves to support operation in the 2.3GHz and 2.5GHz frequency bands, major vendors are developing more powerful test analyzers and tools that are more flexible in addressing signal complexity while remaining cost-effective.

Making waves
Wave 2 of the WiMAX broadband mobile networking standard, a technology that further mitigates interference, creates a big bash. Wave 2 includes several multi-antenna techniques such as MIMO and space-time coding. Keithley Instruments Inc. has introduced a set of signal creation and analysis tools that extend its RF test capabilities to include WiMAX signal testing.

"The new RF test set is built on a next-gen hardware platform that eases to have support for new signal standards, such as 802.16e mobile WiMAX Wave 2 testing with up to 4 x 4 MIMO channels, without expensive hardware upgrades or different instrumentation," Keithley said.

Based on the company's Model 2820 RF vector signal analyzers (VSA) and Model 2920 RF vector signal generators (VSG), these instruments enable users to test WiMAX in any frequency band between 400MHz and 4GHz, and up to 6GHz if WLAN measurements are needed. The VSA or VSA can be used in an automated production environment or moved easily to the bench for standalone test applications. Working in conjunction with the two RF test instrument families is ver 2.0 of Keithley's SignalMeister Waveform Creation Software, designed for creation of the entire range of signals according to WiMAX and WLAN wireless connectivity standards and 3GPP and 3GPP2 cellular standards.

A new suite of signal analyzer application firmware from Rohde & Schwarz carries WiMAX MIMO measurements compatible with IEEE 802.16e-2005. The R&S FSQ-K94 option runs on the R&S FSQ and R&S FSG signal analyzers. It also supports a combination of several analyzers for testing up to 4 x 4 MIMO systems.

Simplified testing
Many of the measurements required for testing MIMO systems can be made by means of a single VSA, but testing the interaction between individual components may sometimes require two instruments. In such cases, users can have several R&S FSQ or R&S FSG analyzers to create a flexible test solution made up of standalone signal analyzers for testing 4 x 4 MIMO systems.

Such aids reduce the time required for user training. Moreover, WiMAX MIMO measurements can easily be added to existing programs. Tried and tested R&S FSQ-K93 functions such as automatic demodulation or user-specific spectrum emission masks are also given in R&S FSQ-K94.

For designers requiring multistream signal capabilities for Wi-Fi and WiMAX MIMO development, LitePoint Corp. offers IQnxnplus test systems. This system features a modular approach to MIMO R&D testing. Each module contains its own VSA and VSG. It also includes a synchronizer subsystem to ensure that the modules work in lockstep. Developers can test programs on this system and then port them to a single IQmax tester for production testing.

The IQnxnplus systems are offered from 1x1 (one module and a synchronizer subsystem) to 4 x 4 (four modules and a synchronizer subsystem) configurations. The modules support Wi-Fi and WiMAX frequency ranges from 2.15GHz to 2.7GHz; 3.3GHz to 3.8GHz; and 4.9GHz to 6GHz. The GUIs (IQsignal for Wi-Fi and IQsignal for WiMAX) give analysis and display capabilities for single, multistream and beam-forming adaptive-antenna functionality testing.

Signal analysis tools
Agilent Technologies Inc. was eager to add MIMO and Wave 2 test support to its Mobile WiMAX instruments early on. In August 2007, the company announced that its VSA, Signal Studio and Mobile WiMAX test set measurement solutions test Wave 2 system profiles. These standardized profiles specify options such as MIMO.

Offering tools for engineers who require signal analysis, signal generation and end-to-end functional test of Mobile WiMAX, the 89601A VSA and N7615B Signal Studio measurement products started to give a range of new test capabilities supporting PHY signal generation and analysis for Wave 2 system profiles. Specific capabilities include matrix A and matrix B signals for downlink, uplink collaborative MIMO and creation of HARQ bursts and uplink sounding zones. Recently, however, Agilent started shipping the first in a series of planned software products based on the Sequans SQN1130 chipset for WiMAX mobile stations.

Powerful baseband chip
Sequans's SQN1130 system on chip is said to be the industry's lowest-power, highest-throughput chip for WiMAX mobile stations. The SQN1130 is an advanced baseband chip based on the IEEE 802.16e standard, implementing MIMO and hybrid ARQ Category 1-4, as well as all MAC and PHY features required for WiMAX Forum Wave 2 certification. Designed for Agilent N8300A wireless networking test set, the N7300 series chipset software helps control, calibrate and test WiMAX devices and modules. The N7300 series' first product, the N7302A chipset software, is geared toward mobile WiMAX chipset manufacturers, as well as manufacturing engineers and managers involved with parametric testing of WiMAX mobile stations, customer premise equipment and modules.

- Ismini Scouras

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