Yes, increasingly complex networks, maybe. But the operators are interested in increasingly simple test solutions. How to square the circle?
The move from GSM to GPRS gave the testing community a host of different problems to deal with. The adoption and widespread roll-out of 3G networks gave several more. Instead of merely dealing with making one network technology, the test community was faced with CDMA networks interacting with GSM and GPRS networks. Not only did it have to test and validate new WCDMA networks themselves, but test the handover of calls from those networks to the GSM networks, and vice versa. The growth of protocols to be tested at handset level also grew exponentially.
WCDMA brought with it new issues to the European mobile market because, unlike GSM and GPRS, WCDMA users all occupy the same frequency channel. Power tolerances and waveform quality had to be kept very tight. Concepts such as the near-far problem, and the constant power adjustments at the rate of 1600 per second, gave network planners and their partners in the network testing community many headaches.
Gradually productised solutions to these problems began to emerge. One of the key differences in the way the test community worked was that more and more of their contact and business was and is being done with the operators, rather than the OEM community. Another was that the solutions available had to become much more holistic, addressing RF issues from the chip in the handset out to base station equipment. For example at the handset design level, Agilent’s mobile test set, the 8960, combined RF source hardware for GSM, GPRS and EGPRS technologies to create a one-box network emulator for wireless chipset, application and device designers, providing RF measurement capability, real-time phone-to-Internet connectivity, and live user data transfers for verifying real-life applications. The difference came about as testing happened in a live rollout environment, and operators realised they needed to be speaking directly to the experts, rather than merely plugging in equipment as provided by the network integrator.
One of the first companies with a test solution for the handover of calls between GSM/ GPRS/ EDGE networks and UMTS was Racal Wireless Instruments Solutions (RIWS), now a subsidiary of Aeroflex. Rhode & Schwarz, too, has been an active supplier of test cases for intersystem handover, the capability of mobile terminals to switch between 2G, 2.5G and 3G telecommunication systems without encountering problems.
With these increasing numbers of test cases, and technologies, the vendors are aware that operators, especially, and test houses, do not want to be faced with a huge number of testing products. Or if they are, they want them to be easily integrated into their existing test systems. The test solution for 2G/3G intersystem handover from Rohde & Schwarz, for example, consists of the protocol tester CRTU-W for WCDMA and the universal protocol tester CRTU-G for GSM. Once the intersystem measurements have been performed, each of these instruments is separately available to handle test scenarios within its own specific mobile radio technology. Rhode & Schwarz hopes this flexibility will mean users require fewer instruments. A good example of this is the ability to test dual transfer mode, which is the ability to use circuit and packet switched connections to a mobile simultaneously. RIWS will have DTM capability on its existing platform, and Rhode & Schwarz says its CRTU-G already supports the planned DTM.
But there are greater challenges afoot in global interoperability of handsets and networks. One of the problems facing those producing the test sets is that standards operate more as a menu of things, some of which you will defintely include, some of which you may not, not all “standards” compatible equipment is the same. The official 3GPP test specifications state that each mobile should be tested one protocol layer at a time. Interoperability between a mobile radio network and user equipment is ensured only if a parameter set is tested while all protocol layers are interacting. This is a huge burden on the number of test cases test manufacturers need to produce. Rhode & Scharz, for example, is set to produce 80 test scenarios for 3GPP compliant phones by July 2004, after working with Japanese operator NTT DoCoMo on scenarios for global roaming alone.
There is also the inescapable truth that UMTS networks themselves are not set to stand still. Most of the base station nodes being installed, or already installed now, are Release 99. But operators are already planning the implementation of 3GPP R4 and R5 equipment and the high speed downlink technology HSDPA.
Operators also know that the take-up of 3G services will disappoint unless customer expectations are met. 3G is not competing in a vaccuum, and faces challenges from alternative high-speed wireless data services based on technologies such as Wi-Fi. In order to attract customers, 3G will have to deliver compelling and reliable applications that go beyond what is currently available on 2/2.5G networks and Wi-Fi.
Improved networks will be an important part of this, and 3G equipment vendors who have lost out on many of the early contract awards for 3G networks are pinning their hopes on HSDPA.
In accord with this push Anritsu, for example, has recently launched HSDPA Signal Pattern software, using the HSDPA high-speed packet communication system for receiver tests of 3.5G user equipment. Downloading this software into Anritsu’s MG3681A Digital Modulation Signal Generator (again, stressing the importanace of integration of new applications with existing platforms) makes it possible to output the digital modulation signals for tests of HSDPA user equipment conforming to 3GPP Release 5.
As terminals move more and more to being data communication devices, higher-speed communication is required to download more data in less time. To cope with such requirements,3GPP Release 5 meeting determined the new standard to achieve high-speed data communication of a maximum of14.4 Mbps in the downlink from base station to user equipment. This not only activates research and development for testing user equipment employing the HSDPA system conforming to this standard; it also intensifies the need for a signal generator that can test HSDPA user equipment receiver.
In the face of these changing performance characteristics, test engineers need correspondingly more sophisticated measurement capabilities to handle emerging WLAN and 3G devices. Traditional radio-frequency (RF) measurement systems using low sample rates with kilohertz-wide final intermediate frequencies (IFs) just will not be able to keep up with WLAN and 3G device test demands. Suitable WLAN testers already need RF subsystems with a nominal bandwidth of 20 MHz to fully capture an 802.11 signal, and other emerging standards will double those bandwidth requirements. For reliable test data acquisition, more advanced WLAN test systems are delivering high-speed, high-precision sample rates with 50 MHz and faster converters and bit resolution exceeding 12 bits.
Besides providing increased performance and resolution, wireless test is already migrating to more effective techniques needed to handle modulated signals. Active devices such as power amplifiers behave differently under modulated stimuli. Newer methods like Modulated Vector Network Analysis (MVNA) use modulated stimuli to provide more accurate results. Along with these more sophisticated measurement methods, wireless test now requires measurements that go well beyond traditional RF tests like noise figure or third-order intercept point (IP3) measurements. To uncover defects in leading-edge wireless ICs, semiconductor manufacturers now need more involved measurements like Adjacent Channel Power Ratio (ACPR) results and even end-to-end system metrics like Bit Error Rate (BER) and Error Vector Magnitude (EVM).
Anite is another test solution provder to address HSDPDA. Its HSDPA 3.5G test platform provides the ability to undertake both Radio Frequency and protocol tests. Again, because HSDPA enables much faster data transmission via the W-CDMA network, Anite amphasises that mobile operators and manufacturers must work closely with test solution providers to ensure a smooth delivery of this advanced 3G service — especially against competing technologies.
Nigel Coxon, managing director of the telecoms division at Anite, says, “Much doubt has been cast on the success of 3G against rival technologies such as EDGE or WiFi. The development of HSDPA is key to driving 3G in both consumer and business markets. The additional bandwidth will ensure far greater network efficiency, and subsequent improved service for users. We are demonstrating our commitment to delivery of quality 3G service by being the first to market with a testing platform that will turn the 3G promise into a reality.”
As well as growing number of network technologies, there are the growing number of applications themselves — designed to take advantage of increased network capacities. Dilithium Networks, for example, has recently developed a quality of service (QoS) measurement tool for 3G operators offering advanced video services such as videotelephony, videoconferencing and real-time streaming. The probe will perform measurements on their 3G wireless networks enabling the assessment of the quality of real-time video services delivered. The probe software platform can be integrated with a test equipment vendor or system integrator’s QoS , using the 3GPP and 3GPP2 adopted 3G-324M/H.324M technology to make/receive calls at regular intervals to other probes in the network.
“Conversational video services are a key differentiator for 3G operators throughout the world,” said Paul Zuber, chief executive officer, Dilithium Networks. “As more operators offer 3G-video services, it is clearly important for them to perform network measurements and gather call statistics throughout their network, comparable to that of their existing voice networks. The VT-Probe enables operators to perform a variety of measurements that they can use to assess service level quality of their networks and make improvements to their service offerings.”
From network, to handset, to application, the increasing demands of 3G networks will continue to drive the production of such solutions. But innovation and integration must now be bedfellows for a test community facing a smaller number of operators with increased buying power.