Once upon a time, RF testing was relatively simple. You would measure power output in a transmitter and look for spurious signals with a spectrum analyzer. At the receiver, you measured noise and sensitivity. Unfortunately, those halcyon days are gone forever.
Radio complexity has intensified dramatically with advanced digital modulation schemes, softwaredefined radio architectures featuring digital signal processing, I/Q signal chains, multiple-input/multiple-output (MIMO), and other advanced techniques. And let’s not forget the complex protocols that must be tested for regulatory compliance and interoperability requirements. On top of that, the frequencies of operation continue to skyrocket, stretching the limits of current equipment as well as budgets.
Thankfully, test instrument manufacturers aren’t sitting on their hands. The leading vendors all offer instruments with higher frequency capability. Moreover, their software and hardware automates many of the tests, whether you’re testing MIMO on a new Wi-Fi 802.11n router or WiMAX basestation or evaluating your new chip for compliance with the new 4G Long Term Evolution (LTE) cell-phone standard. Most of the latest announcements feature products for testing LTE and the newer HSDPA 3G technology, as well as WiMAX with MIMO.
NEW STANDARDS PUSH THE BOUNDARIES
Nowadays, everybody seems to be focusing on LTE and WiMAX. LTE is the 4G cell-phone technology being developed by the Third Generation Partnership Project (3GPP). Though not completed (final approval is expected later this year), it’s far enough along that both chip and equipment manufacturers are hard at work testing and evaluating products.
The LTE standard is the next step beyond the 3G WCDMA and HSPA technologies used by AT&T and T-Mobile, as well as most European carriers. Also, Verizon adopted LTE as its 4G path rather than the ultra-mobile broadband (UMB) solution developed by Qualcomm.
WiMAX, of course, is the broadband wireless technology standardized by the IEEE. Fixed (802.16d-2004) and mobile (802.16e-2005) versions are available. Its primary application is broadband wireless service to compete with cable TV and DSL for Internet access. But other applications such as cellular and other back-haul systems are becoming popular.
Some experts say WiMAX mobile is also a great contender for 4G cell-phone service. With Voice over Internet Protocol (VoIP), it could compete with LTE. The jury is still out, though. Most insiders say LTE will dominate, with WiMAX filling other niches. In any case, both technologies are complex.
Each standard uses orthogonal frequency-division multiplexing (OFDM) and orthogonal frequency-division multiple access (OFDMA). Also, each offers MIMO as an option for increasing range, data speed, and reliability. MIMO is a multiradio multi-antenna technology that transmits coded parallel data streams on the bandwidth to boost data rate and help mitigate the problems of multipath interference. Testing these technologies has become a major challenge.
INSTRUMENTS TACKLE TEST TRIBULATIONS
Instrument powerhouse Agilent introduced a whole slew of wireless test products at the Mobile World Congress show in Barcelona in February and at the CTIA show in Las Vegas in April. For example, its latest software for WiMAX Wave 2 testing works with Agilent’s Infiniium scopes and its MXG signal generators.
Also, Agilent’s one-box, fully automated E6651A WiMAX Wave 2 MIMO tester performs conformance testing, radiated performance test, end-to-end data transfer, and network entry/data connection (Fig. 1). The N8300A wireless networking test set provides fast and accurate measurements for WiMAX Wave 2 manufacturing test.
Then, there’s the J7910 A signaling analyzer for WiMAX troubleshooting. Agilent is also cooperating with WiMAX chipset manufacturers Beceem and Sequans to provide test solutions that work for conformance and interoperability verification.
LTE efforts include some LTE protocol development solutions based on the Agilent E6620A wireless communications test set (Fig. 2). It features Anite’s SAT LTE protocol development toolset. This solution targets engineers working in the early protocol design stage of LTE handsets.
Another LTE product, the J7910A real-time signaling analyzer platform, is the only integrated high-density solution for Gigabit Ethernet analysis. Agilent also offers LTE vector signalanalysis software for its MXA signal analyzer and MXG vector signal generator.
Finally, the company has a line of receivers for wireless testing and evaluation. The six models in the W1314A family cover all relevant RF bands and all wireless technologies, such as GSM, WCDMA, cdma2000, EV-DO, iDEN, and WiMAX, including the mobile version.
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