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WiMAX fame births new analysis solutions

Posted: 29 Aug 2008     Print Version  Bookmark and Share

Keywords:WiMAX  wireless networks  bandwidth use  test and measurement 

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

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

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

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 this kind of performance, WiMAX's popularity is catching on worldwide. The standard, which serves all usage models from fixed to mobile with the same infrastructure, is on its way to hitting 13.3 crore (133 million) users globally by 2012, according to the WiMAX Forum in a forecast based on the results of an independent research study published in April.

Additional data from the study estimates that approximately 70 per cent of the predicted WiMAX users by 2012 will use mobile and portable WiMAX devices to 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 analysers and tools that are more flexible in addressing signal complexity while remaining cost-effective.

Wave 2 of the WiMAX broadband mobile networking standard, a technology intended to further mitigate interference, is also making a splash. Wave 2 includes several multi-antenna techniques such as MIMO and space-time coding (STC). 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-generation hardware platform that makes it easy to add 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 analysers and Model 2920 RF vector signal generators, 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 signal analysers or signal generators can be used in an automated production environment or moved easily to the bench for stand-alone test applications. Working in conjunction with the two RF test instrument families is version 2.0 of Keithley's SignalMeister Waveform Creation Software, designed for creation of the entire range of signals in accordance with WiMAX and WLAN wireless connectivity standards and 3GPP and 3GPP2 cellular standards.

A new suite of signal analyser application firmware from Rohde & Schwarz handles 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 analysers. It also supports a combination of several analysers for testing up to 4 x 4 MIMO systems.

Many of the measurements required for testing MIMO systems can be performed by means of a single vector signal analyser, but testing the interaction between individual components may sometimes require two instruments. In such instances, users can combine several R&S FSQ or R&S FSG analysers to create a flexible test solution made up of stand-alone signal analysers for testing 4 x 4 MIMO systems, for example.

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 (SEM) are also provided in R&S FSQ-K94.

For designers requiring multi-stream signal capabilities for WiFi and WiMAX MIMO development, LitePoint Corp. is offering IQnxnplus test systems. IQnxnplus features a modular approach to MIMO R&D testing. Each module contains its own vector signal analyser (VSA) and vector signal generator (VSG). The system also includes a synchroniser sub-system 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 synchroniser sub-system, for example) to 4 x 4 (four modules and a synchroniser sub-system) configurations. The modules support Wi-Fi and WiMAX frequency ranges of 2.15GHz to 2.7GHz, 3.3GHz to 3.8GHz and 4.9GHz to 6GHz. The included GUIs (IQsignal for WiFi and IQsignal for WiMAX) provide analysis and display capabilities for single, multi-stream and beam-forming adaptive-antenna functionality testing.

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 vector signal analyser, Signal Studio and Mobile WiMAX test set measurement solutions test Wave 2 system profiles. These standardised profiles specify options such as MIMO.

Providing 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 offer a range of new test capabilities supporting physical (PHY)-layer 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. More recently, however, Agilent started shipping the first in a series of planned software products based on the Sequans SQN1130 chipset for WiMAX mobile stations.

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 base band 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 use with the 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 aimed at 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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