3G Design Tools

What are the critical issues driving 3G propagation models?

There's an ancient Chinese proverb that says a journey of a thousand miles begins with one step. The results of recent 3G trials by Lucent and Qualcomm have given the industry a peek at 3G's destination, namely data rates of up to 153kb/s, and helped better define the first step on 3G's journey. In order to build a successful 3G network, providers and vendors say a 3G design tool must be able to leverage the existing network and increase capacity effectively.

According to Mark Poulman, Belenos Wireless Practice director, capacity is the No. 1 priority when it comes to 3G-network design because of the increase in network traffic that data will cause. Poulman pointed out that data-packet delivery will not tolerate the same bit error rates as voice. Dropping a voice call is one thing, but losing a packet is quite another. For example, if a stockbroker makes a trade using his wireless phone, a system that is not properly designed to handle higher traffic patterns may drop the data connection, leaving the stockbroker empty-handed.

The convergence of wireless data will cause many providers to re-evaluate their network traffic models and turn coverage-focused configurations into more capacity-rich ones.

Making the Switch
One way to get more capacity in a 3G network is to use a MCPA system design. MCPA systems can stretch service providers over a wider distance and carry more traffic than a single-provider system. Clearing service providers for the migration to 3G becomes much easier using this technology because of its ability to manipulate the system non-linearly. Providers then can transmit the entire spectrum instead of just pieces of it, and no guard band is required.

According to Kris Rinne, SBC vice president of technology strategies, the "carving out the spectrum" stage is probably the longest part of any 3G design process. Rinne said tried-and-true techniques such as cell splitting and overlay/underlay engineering, which were first used to get the best out of the spectrum during the analog to digital switch, will be used again for 3G.

Tom Sawanobori, Verizon executive director of network planning, said it's a planning tool's job to take the guesswork out of system performance. 3G modeling must tell providers specifically how much data will slow a network and how much capacity must be added to maintain acceptable data rates.

"What we really want to know is how much throughput you are going to get depending on how many users you have," Sawanobori said.

Where, When, Why?
Adding capacity can be tricky. Knowing where, when and how many users will want data- or voice-only services versus how many want a combination of services is key to meeting your network specs. That's where market research comes in. According to a Vodafone spokesperson, the leading concern for 3G design is whether a tool will deliver the appropriate flexibility to incorporate market research and create scaleable propagation models based on predicted customer usage patterns.

Sawanobori agreed, saying comprehensive market research is a part of the design process that often can be undervalued. Incorporating market data allows providers to map their systems more effectively and understand their capacity growth issues better.

In some design tools, customers can be geocoded and added to modulation schemes.

"You have to look at how many people are doing e-mail versus Web browsing versus calendar scheduling," Sawanobori said. "We have to model that, and we have to run simulations according to that information."

Keeping the customer in mind, providers also are concerned about the effect 3G will have on their customers not yet ready to upgrade. SBC's Rinne said many providers will want to keep their legacy networks running in tandem with 3G technologies in order to offer service to their non-3G subscribers.

Likewise, optimizing the existing network will keep costs down and reduce time to market.

Harry Anderson, EDX Engineering president & CEO, said 3G design tools will be able to design 3G systems that share cell-site locations with 1G and 2G equipment. In most cases, that means providers will have to build and maintain a circuit-switch/packet hybrid network for a while.

For many U.S. providers, having this type of network will require adding a radio network controller (RNC) instead of just relying on BSCs. An RNC-managed network allows reliable access to your circuit-switched base stations through microwave transmission, as well as real-time IP and ATM packet switching.

A design that uses RNCs can better manage call establishment and release, handoffs, radio resource management, power control, diversity combining and soft handoffs for traditional, intermediary and 3G networks. Creating a handful of managers, RNCs deliver a clearer picture of a hybrid network than single base stations can.

Rinne said SBC's recent work on its GPRS system used a design tool that similarly leveraged the existing network, saving the company time and money.

Interference
According to design engineers, front-end interference may increase slightly due to the additional equipment used in 3G designs, but mitigation techniques will not change drastically.

"Interference-mitigation techniques are fairly well-known, using the experience gained from deploying 1G and 2G systems," Anderson said.

3G design tools, like traditional tools, will continue to offer interference-rejection algorithms and automatic channel location as a way to mitigate interference and improve system performance.

"Engineers understand the interference issues, but I don't think there is a lot of information on the capacity requirements for data traffic such as WAP, so we are more focused on that aspect of 3G system design," Anderson said.

Sawanobori said the challenges for 3G in order of priority are performance or capacity, accuracy, scaleability and then interference.

Changing Standards
Because 3G standards constantly are changing, design software vendors have the challenge of keeping up. Until the standards boards finalize the specifications on 3G standards, however, providers will have to accept some design limitations. Most vendors do a number of things to stay on top of the fluctuating standards. Taking into account what providers need the tool to do and closely watching the International Telecommunication Union and TIA are all ways vendors try to ensure that their tools are current. In addition, many vendors offer frequent and expedited upgrades as well as 24/7 technical support.

"(Design manufacturers) have to look at responding to the requirements of the wireless industry," Anderson said. "The standards bodies are just the first part of that process. We really listen to what our customers tell us about the kind of features they need to support their system-design objectives, and we respond to that."

Anderson said much of what was learned about system design from doing 1G and 2G systems can be used for 3G systems so it is not necessary for design-tool manufacturers to start from scratch for 3G. Planning tools need to be flexible and easily customizable to respond to evolving 3G-system-design methodology.

"There is still work for tool developers to do to accommodate 3G," Anderson said. "The design tools used in 1985 for 1G systems were very primitive compared to what is being used today for 2G systems. A similar design-tool evolution will occur as 3G systems are deployed and optimized."

SBC's Rinne and Vodafone officials said they were confident designers would be able to uphold 3G's changing standard.

"Most of the changes being made right now are having more to do with different flow patterns," Rinne said. "I think being able to replicate the packet-data networks into circuit-switched ones is being done by (design manufacturers) expertly."

Neils Fache, Agilent communications product line manager, added that most 3G planning tools offered training and frequent upgrades as a way to keep their products concurrent with standards.

Trial & Error
It is estimated that it takes a dozen iterations to design a traditional network. Although design manufacturers have little experience with 3G designing, they feel modulation schemes for the new technology will resemble today's rates closely and require about the same number of prototypes.

However, Fache said if a design tool can eliminate just one prototype, it can save a provider 10% to 20% on the overall design phase.