Apr 15, 2001 12:00 PM,

BEYOND SPEED

Steve Roberts

Gauging the quality of wireless data service may come down to speed. But to correct deficiencies and optimize their networks, carriers will need more detailed performance data.

New Performance Metrics

From the perspective of today's wireless phone user, service quality is based largely on access reliability (or blockage rate), completeness of coverage and audio quality. Customer-focused cellular and PCS carriers therefore monitor network performance by measuring parameters that directly affect these characteristics. Although it's likely that 3G networks also will provide at least the equivalent of circuit-switched, direct-dial telephone service, their primary feature will be high-speed packet-data connectivity, most likely involving the Internet. Many of the factors that determine customer perceptions of quality in wireless phone systems have no direct parallels in data networks. Blockage rate, for example, really is not relevant in a packet-data system — at least not in the same context as applied to telephone networks. Expectations for high-speed data services introduce a different set of quality factors. This means new performance metrics and new ways in which performance data can be applied to help optimize 3G-network functionality.

In one respect, gauging the quality of wireless data service will be simple: It's all a matter of speed. Data rates available to the individual user will largely determine his perception of performance, and composite channel throughput will likely be a good indicator of network efficiency. Even RF signal coverage generally becomes part of the speed characteristic, as the primary effect of low RF signal levels will be reduced data throughput. Furthermore, because revenues for wireless data carriers are likely to be tied in one way or another to the quantity of data transported, it's a good bet that data-rate statistics will be a prime focus of enterprise-management attention. But measurements of data rates, both for the individual user and for the network as a whole, belie the complexity of the tasks involved in 3G-service assurance. For identifying and correcting deficiencies, to say nothing of optimizing their networks, 3G system engineers and operations managers will need more help, largely in the form of more detailed performance data.

Two key factors set wireless data networks apart from systems using wire, fiber-optic, or cable transmission. The first is the reliance on radio channels for local connectivity. Mobile radio channels are more prone to variability in performance than fixed media, so it's reasonable to conclude that 3G-network performance will be dominantly governed by the quality and efficiency of the radio-system design. It then follows that identifying and correcting the most likely problems with 3G-network performance will require specific data on the operation of the radio system.

A second difference between wireless and most wireline data networks is that in the case of wireless, the distribution medium — the radio channel — is a shared resource. That means that the data capacity of an available channel must be shared among all devices operating simultaneously on that channel. In a wireline network, more users in a given location can be served at constant speed by adding more wires. Adding more radio channels in a limited area and within limits of available RF spectrum is more difficult. Assuring adequate radio-channel capacity to meet localized (as opposed to network-wide) demand will therefore be crucial to successful maintenance of 3G networks.

Uncertainty of Application

Virtually all planned 3G systems will use one of two CDMA air-interface technologies, and experience with service-assurance requirements for mature 2G CDMA systems is helpful in developing the tools necessary for their 3G counterparts. Common CDMA problems such as pilot pollution and reduced channel capacity due to excessive coverage overlap are well understood now and will certainly be factors in the optimization of 3G systems. However, the migration from largely circuit-switched to packet-data formats undoubtedly will introduce new factors that affect the performance of CDMA channels.

Operational data supporting radio-system optimization will be particularly crucial as 3G networks grow with more users and higher per-user data volumes. As with existing mobile systems, expansion of the radio-channel capacity in 3G networks will likely pose many challenges. (By comparison, increasing the capacity of such fixed network elements as switches and routers should be relatively straightforward.) But the element of uncertainty, particularly as to new applications, may lead to even bigger growth problems for networks dedicated primarily to packet-data transmission.

With wireless phone service, at least the average per-user capacity requirement is fairly predictable. In the relatively nascent wireless data world, roll-out of new applications or features may cause rapid and substantial changes in usage patterns, leaving carriers scrambling to add network capacity. As with any spectrum-limited mobile system, 3G-network growth will ultimately be handled by deploying new radio base stations in areas where additional capacity is required. Unfortunately, there is nothing to suggest that this process will be any quicker or easier in 3G networks than in today's 2G systems. By focusing on management of radio-system capacity, service-assurance tools for 3G networks will help engineers maximize data throughput in existing infrastructure and simplify the process of adding new infrastructure as networks mature.

Support for Network Optimization

To provide 3G operations managers and system engineers the support they need to maintain top network performance and capacity, service-assurance systems will need to monitor and report more than just statistics on data-throughput rates. But specifically, what types of information will be important? The needs regarding performance metrics will become clearer with operational experience, but here are some prime examples:

Distribution of per-mobile data speeds. A high percentage of users being served at lower-than-anticipated speeds may point to problems such as poor coverage or pilot pollution.
Distribution of uplink-received signal levels. A requirement for high-received power level (relative to data rate) may point to excessive interference levels.
Trends in composite per-channel throughput by sector. When usage goes up, so does interference. Sectors affected by more than their share of interference will suffer reduced peak throughput.
Trends in per-user data rates. Generally speaking, the number of simultaneous users on a packet-data channel will not be subject to a hard limit. Instead, when total channel-throughput capacity is exhausted, the per-user data speed will decline.

The wireless industry obviously believes 3G networks will be popular. Would-be operators are bidding fortunes in spectrum auctions, and winners are investing even more to deploy networks that provide at least minimally acceptable service coverage.

But after nearly two decades of operation, mature wireless networks have raised the bar of customer expectations for wireless-service reliability and performance. Quickly meeting those expectations upon service launch will be paramount to the success of 3G enterprises, and with success will come additional burdens of maintaining service quality while accommodating growth. Properly conceived and configured, advanced service-assurance tools will help 3G network operators meet these challenges.

Roberts is WatchMark chairman & founding president (www.watchmark.com).