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Test systems spell 3G LTE future

Posted: 16 Apr 2007 ?? ?Print Version ?Bookmark and Share

Keywords:3G interoperability testing? 3G HSDPA systems? mobile WiMAX networks?

Historically, the rollout of next-generation cellular networks, with interoperable handsets available at the right price/performance points, has not been a smooth operation. That was the case with GSM, which over time has nonetheless become a phenomenal success for Europe. It is currently the case with 3G and its higher-data-rate versions, high-speed packet access and high-speed downlink packet access (HSDPA).

Chip designers, network equipment vendors, makers of test-and-measurement (T&M) gear and network operators are already plotting the next stage of the W-CDMA air interface. The standards setters at the Third Generation Partnership Project (3GPP) have dubbed that follow-on Long-Term Evolution (LTE). Initial standards are expected this September, as pressure from mobile WiMAX and a parallel effort by the CDMA community called Ultra Mobile Broadband (UMB) compel the 3GPP effort to build momentum quickly.

According to a new study from ABI Research, network operators will invest almost $18 billion in LTE capital infrastructure over the period to 2014. That will yield pay-offs in reduced operating expenses and in the creation of revenue from Internet Protocol-based services.

Past pitfalls
Many believe the pitfalls associated with past rollouts can be avoided, provided that T&M suppliers help ensure a smooth migration. At 3GSM, players such as Aeroflex, Anritsu, Anite, Rohde & Schwarz and Spirent either demonstrated or discussed plans for test equipment for both the PHY and handsets that are being specified and standardized for LTE.

On the infrastructure side, equipment makers such as LM Ericsson, Alcatel-Lucent, Nortel and NEC are already demonstrating test beds for the very high-data-rate mobile broadband they suggest the industry needs: speeds of 100Mbps on the downlink, half that on the uplink, with latencies on the order of 20ms.

"The challenge is not to repeat the mistakes the industry has made in past transformations. I really believe we have raised our game this time round," said Phil Windred, business unit manager of the wireless group at Aeroflex Test Solutions.

Windred said it is crucial to act cooperatively, since this "evolution" is more complex. "This time around, we are making fundamental changes to the radio layout, as LTE will not only be an all-packet-based network, but will rely on a shift from W-CDMA to an OFDM modulation scheme, coupled with smart multiple-input, multiple-output (MIMO) antenna technology so as to deliver the really high data rates."

'Act smarter'
"We are dealing with complex technologies, and a lot of issues will need to be sorted out on prototypes," added Windred. "And if you take that into account when we come to interoperability and conformance testing, we will also need to take care of legacy 3G and HSDPA systems. Testing and ensuring synchronization will pose really tough challenges. We will need to act smarter than ever, and the standards-setting procedure will need to be more coordinated than ever."

One factor that should help is that LTE shares many RF characteristics with WiMAX, such as OFDM and MIMO, according to Jonathan Borrill, market strategy manager for Anritsu in Europe. All the major T&M players have already developed testers for mobile WiMAX networks and terminals. But while some of the measurement techniques used for WiMAX can be reused for LTE, cutting the time needed to develop test gear, Borrill is not overly optimistic about the prospects for mobile-broadband harmonization.

"I think we will continue to see multiple radio technologies, with coexistence of the 3GPP-led LTE effort, mobile WiMAX and the cdma2000-based version that is now evolving from Rev. C of the Evolution-Data Optimized specification to UMB," said Borrill.

But he noted that because of the push toward convergence and all-IP-based mobile networks by operators, notably via the Next Generation Mobile Networks (NGMN) initiative, "harmonization of a standard at that level should exist, and applications testing may become similar for the different radio bearers. This is really a positive for the mobile industry."

Interoperability testing
Echoing the plans recently laid out by the NGMN group, which includes some of the world's major carriers and communications equipment suppliers, Borrill said it is vital to avoid the issues experienced with 3G deployment, where fully functional user equipment was not available for interoperability testing and early deployment. "Interoperability testing must be nearer the top of the agenda than it has been in the past," Borrill said.

For that to happen, the standardization process and the engagements among network operators, equipment and handset suppliers and the T&M community must work smoothly, Borrill stressed.

Aeroflex's Windred added that complete visibility into the very lowest layers of the radio modem will allow users to diagnose the actual cause of a synchronization problem rather than just knowing that synchronization has failed.

Without the higher-layer protocol, it is necessary to configure the PHY completely using test scripts. As a consequence, many early test failures may not be the result of real problemsrather, they may stem from a mismatch in the setup between the prototype under test and the test equipment. Given the hundreds of parameters that must be selected, the risk of a mismatch is significant.

Test automation
A further implication of PHY testing when the higher-layer protocol is not available is that test automation is essential, Windred said.

The incorporation of test script configuration tools into test equipment would allow the easy generation of all scripts needed to select the different configurations and tests. Those various scripts could then be initiated by a test controller to synchronize control of the prototype under test and the test equipment. It would be possible to alter parameters in real-time to enable test coverage to be extended across the wide range of configurations used in a live system, in relation to testing of both the LTE network and early LTE prototype mobile devices.

That, Windred stressed, would allow the early detection of software bugs associated with particular parameter values. Such bugs would not otherwise be found until much later in the design cycle, when diagnosing and rectifying errors tends to be much more expensive.

- John Walko
EE Times

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