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Attempting to conform

With 3G network rollout predicted this year, we find out what’s involved in 3G protocol testing. By Vanessa Knivett.

The transition of mobile telecommunications to 3G has created a gap in the market for relevant protocol testing instrumentation. With time to market essential to product success, network interface designers need the test equipment fast, yet test equipment manufacturers are also battling time constraints as the fine tuning of 3G standards continues.

But business plans depend on an imminent launch and, with the need to get products to market, protocol testing is integral to the process; determining which test bed is most suitable for the design is particularly challenging.

Umts versus gsm
3G centres on the Universal Mobile Telecommunications System (umts), envisaged as the successor to gsm. As the roll out of 3G in less populated areas may take years, all 'phones must be gsm and umts compliant. Interoperability is just one reason why 3G protocol testing is more complex than for gsm.

A number of 3G protocols have been mooted. The main contenders are wideband cdma (w-cdma) and cdma2000, with cdma standing for code division multiple access. European players, including infrastructure vendors such as Nokia and Ericsson, have generally backed w-cdma; whilst North America, led by the Cdma Development Group (CDG) and infrastructure vendors such as Qualcomm and Lucent Technologies, is behind cdma2000.
Umts improves on gsm by increasing transmission speed and establishing a global roaming standard. W-cdma is set at 2Mbit/s, whilst cdma2000 is gradually moving towards 2Mbit/s. For both standards, the network interfaces are substantially more complex, increasing the complexity of protocol testing.

Previous technologies use frequencies or time slots, such as time division multiple access technology (tdma) to allow several users to use the same transmission channels. However, cdma uses mathematical codes to distinguish between multiple wireless conversations. Cdma uses a much wider bandwidth at the same data rate than simple point to point communications because it uses noise like carrier waves to spread the information contained in a signal of interest over a much greater bandwidth. However, because the conversations are distinguished by digital codes, many users can share the same bandwidth simultaneously.

A lucrative opportunity
One of the first to tackle a umts protocol test system was Racal Instruments, with its 1X-AIME system for cdma2000 phase 1 mobiles launched in April 2000. Working with cdma pioneer Qualcomm, Racal has recently released the 1xEV-DO Ats for stage 2 testing of cdma2000.

Whilst Racal is the only cdma2000 protocol test supplier to the North American market, it has competition in Europe from Agilent, Anritsu, Rohde & Schwarz and Anite, to whom it supplies hardware. Steve Gledhill, marketing manager of Racal Instruments' wireless solutions group, commented: "The US is further ahead in defining its standards, so we have committed strongly to this market. However, we have recently announced the 6401 integrated protocol and rf test solution for umts network emulation scenarios – a multistandard testing environment, which encompasses gsm, td-scdma (which combines tdma and cdma) and cdma2000."

Racal is also working with test house Radio Frequency Investigation (RFI) to create test cases for a variety of applications.

Meanwhile, Rohde & Schwarz says the CRTU-W, its protocol tester for w-cdma user equipment is in the final stages of development and will be available by mid 2002. This is also a multistandard test platform. Explains product manager Joerg Deiss: "Other standards, such as cdma2000, wcdma, or td-scdma (popular in China) can be implemented easily. We recognise that, whilst our focus is on frequency division duplex, other manufacturers are pushing tdd (time division duplex) and td-scdma (based on tdd technology). Undoubtedly, we will monitor the market and develop the product accordingly." He added: "The original goal of umts was to develop a universal telecom standard, but the real world looks very different."

Explaining the difference between the CRTU-W and other protocol test systems, Deiss said: "The requirements placed on the air interface and the complexity of layer 1 call for new technical solutions. CRTU-W implements the physical protocol layer (layer 1), media access control, the radio link control and radio resource control as a reference, meaning these protocol layers, as well as higher protocol functionality, can be fully tested."
The company terms this a 'soft radio concept': dsps and fpgas are used to implement layer 1 as a board, allowing the crtu-w to be upgraded through software.

Deiss continued: "The initial problem was that we had to think from the outset about a 2Mbit/s data rate. Calculating and transmitting the signal are two different things! Another source of complexity lies in the layer 1 functionality. Everyone is talking at the same time, so there are no time slots for special calls, which creates a problem for the coding. There are also hundreds of different channel combinations which have to be tested."
Anritsu already has available the MX785201A protocol test system (pts) and MX785101A virtual signalling test system. The systems address w-cdma standards and, used in combination, allow test cases to be reused. Among the features is an application programming interface which enables users to generate C language test scenarios.

Anritsu product manager Chris Foreman said: "The pts is based around an rf engine from Anritsu; the MD8480A. The MD8480A has been designed initially for w-cdma and currently supports DoCoMo and Third Generation Partnership Project (3GPP) systems, with gsm being added now. In the future, the pts will be enhanced by adding existing systems, future 3G systems and protocols. In our Texas facility, developments are ongoing for cdma2000 systems.

"Anritsu has invested heavily in Japan, Europe and the US to develop 3G test systems and has now sold more than 700 systems worldwide. There is much doom and gloom over 3G and stories that terminals will not be available, yet there are many companies pressuring us to get 3G terminals tested and validated as soon as possible."

What the users say
Test houses such as RFI – which has been heavily involved in gsm and gprs protocol testing – are well placed to give an opinion.. It uses a variety of test equipment, including gsm testers from Rohde & Schwarz and Anite and Bluetooth testers from Setacom and ITV. The agreement with Racal to evaluate the cdma2000 tester and to develop test cases represents its first step into 3G testing.

Richard Jacklin, operations manager for RFI's mobile communications group, said: "At present, test equipment is just coming on to the market, so we have had little chance for evaluation. A number of companies have committed to releasing cdma2000 and w-cdma equipment – which is very good news for the 3G market. Gprs test equipment was a long time coming, due to delays in agreeing a specification. This led to mobile handset manufacturers drawing up their own specifications and testing these against their own equipment. Because there was no common basis for testing, smaller companies who did not have test capabilities were lost – and consequently lots of inventiveness was lost to the gprs community."

The wireless industry has recognised the need to collaborate and, whilst the universal mobile standard is not entirely universal, there is more common ground between the various standards than for other wireless technologies. Jacklin noted: "There was a lot of variety in gsm platforms. Some were written in C, whilst later models were written in tree and tabular combined notation (ttcn). So far, all 3G test equipment manufacturers intend to use ttcn, meaning that, from the start, test systems will be more similar. With the many protocol layers, there will be differences in interpretation and timing, but there will not be as much differentiation as for gsm."

With more than 360 test cases needed in each pst, each costing an estimated £1000, 3G is a lucrative market for test equipment manufacturers. There is limited choice at present between these highly specialised pieces of equipment, but the value of this market will ensure that, in six months, it will be another story.

Author
Graham Pitcher

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