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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