CDMA Technology
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More Than A Day's Work

By Doug McGregor

Network engineering is no easy task. Among the challenges faced by companies are short lead times, constant shortages of staff and difficult environments. And with CDMA technology developing all the time, it’s more than a one-off assignment.

Build a wireless network and they will come. Build it incorrectly and they will leave. How well a network is constructed is often the difference between a satisfied subscriber and one who churns to the competition. Even the best marketing efforts are in vain if an operator’s wireless network performance is mediocre.

To this end, vendors often go to extremes when helping operators bring a network from the drawing board to reality. At Nortel we’ve gone as far as attaching cell site equipment to a helicopter to emulate coverage from a yet-to be constructed tower to braving 40 below zero temperatures — all to get a network deployed on time.

Ultimately, it’s voice quality, coverage and capacity that determine whether a wireless service is a winner or a loser. All three depend on well-executed network engineering and behind-the-scenes planning, the bricks and mortar of a wireless system. The ability to design and deploy an efficient wireless network in the allotted time may be the difference between a first-rate system and a cut-rate system. Engineering and planning decisions made early on are often the best predictors of success. And since network performance often determines whether or not a subscriber remains a subscriber, careful consideration must be given to the issues surrounding network deployment.
The tens of thousands of hours dedicated to designing and engineering a network in a given market are really just the beginning of what should be a long relationship between a vendor and an operator. Beyond the planning, installation and optimization related to launching a CDMA network, post deployment issues are also a consideration. There is ongoing maintenance as well as planning for system expansion.

When building a wireless network, one of the first issues to address is link budgets. This is of foremost importance when initially rolling out a CDMA system or overlaying it on top of an existing analog network. Without properly calculating RF link budgets, an operator will not have the coverage or voice quality expected or promised. The RF link budget defines the size, power and location of the cell sites, taking into account in-building penetration, interference, traffic and other market-specific variables.
This is not to say link budgets are set in stone. Network engineering is sometimes a work in process. As the network is designed, the number of base stations to deploy can be changed. If the number of base stations is reduced, the operator must carefully consider whether a smaller coverage area — resulting from corresponding reductions in network coverage, capacity or quality — will make its service less attractive to would-be subscribers.

To ensure that Sprint PCS could offer the coverage promised, Nortel resorted to some unorthodox methods during the network design phase of this operator’s roll-out. Cell site equipment was raised by helicopter to the height the equipment would eventually be installed on towers, and drive tests were done around the coverage area of these future cell sites. Similar tests were made by attaching cell site equipment to cranes, and by mounting equipment on water towers. By completing these simulations, a vendor can make sure the network is living up to expectations.

While preparation may be the watchword for a network roll-out, vendors have learned to anticipate change and adapt quickly to new situations. An operator needs to plan the network with capacity and coverage in mind. Adding capacity later, which may need the installation of additional equipment, should not create a requirement for additional, difficult-to-procure cell sites. Capacity expansion must also be achieved without affecting equipment within the network that’s already in place.
The process involves defining how to tackle this task as well as pre-testing and integration testing, all of which are used to make sure the cell sites that are added to the network will function properly. A vendor and operator must also work together to forecast any future coverage needs.
In planning for capacity, it’s also important for a vendor to be tied to the operator’s sales and marketing plan. By considering subscriber enrollment, rate plans and corresponding network minutes, a vendor is better able to determine an operator’s future needs. Special events such as trade shows must also be considered when identifying capacity needs. This can define where a cell site may be needed.

When integrating new cells into an existing system, Nortel has a set plan that defines how to achieve integration, complete related testing, confirm that new cells work well in this environment and actually bring the cells up as rapidly as possible.

For PCS operators, time to market is a major issue. In turn, many cellular operators need to make the transition from analog to digital quickly in order remain competitive and address capacity issues. These time to market requirements result in aggressive build-outs that require vendors such as Nortel to work 24 hours a day, seven days a week so as to meet operator needs.

Zoning issues, which are beyond the control of the operator, sometimes delay build-outs, shorten lead times and require engineering teams to work faster to keep an operator’s roll-out schedule on time. Situations like these can present a logistical challenge and often mean 16-hour days for engineers.
Tight timing also means that working on a network deployment in Minneapolis in 40 below zero weather becomes a fact of life. And it’s facts of life like this that make an engineering assignment to deploy a system in Miami highly desirable. Mother Nature can be far from cooperative in other situations as well. In order to protect CDMA base stations from the floods that devastated many Midwest towns last year, Nortel had to use cranes to hoist equipment above ground to keep it dry.

Even with technical and weather-related problems, staffing issues sometimes present the most daunting challenge to network deployment. The shortage of engineers with installation, database, RF, optimization and technical support skills continues to be an industry-wide challenge. Vendors, many of whom compete with each other to obtain additional manpower, need a large, experienced work force in the field that can meet the deadlines set by operators hoping to get to market quickly.

On top of staffing issues, the fact that CDMA technology is still relatively new presents challenges. Sometimes it is necessary to provide on-the-job training to get staff up to speed on the issues and characteristics associated with CDMA.

With CDMA, there are unique challenges not associated with other digital technologies. The design objectives and performance criteria of a CDMA system are different from other digital networks. CDMA, for instance, has propagation characteristics that are very different from other air interfaces. This means the cell size, signal strength and overlap of cells for coverage require a number of processes to be rethought.

Perhaps the area that is most challenging for engineers is network optimization. An AMPS or TDMA system begins with good coverage and capacity, but voice quality needs to be optimized. With CDMA, good voice quality is a given with a well-designed system, but coverage and capacity need to be optimized.

CDMA digital network deployment also requires clearing of additional channels to accommodate 1.25MHz channels, versus the 30KHz channels used for AMPS and TDMA. This can be challenging in the short term, but rewarding in the long run, given the performance and capacity advantages of CDMA.

One particularly interesting challenge Nortel encountered when deploying AirTouch’s Great Lakes network in the Detroit, Mich. MSA was overlaying a CDMA system over another vendor’s AMPS network. Nortel was required to use existing AMPS sites, and to minimize the impact on the incumbent (Ericsson) analog infrastructure. This meant no adjustments to antennas or power levels at any of the existing cell sites. Interference from neighboring systems also had to be addressed.

AirTouch had to convince its cellular neighbors to change their frequency plans in order to accommodate the CDMA network. While CDMA tolerates interference from neighboring networks, such interference can reduce the capacity benefits of the technology if not properly managed.

Although operations, administration and maintenance (OA&M) issues are present with any type of network, the type of operational data that is available from a network varies with each air interface. With CDMA, for instance, soft hand-off issues are unique to this technology. Again, because CDMA is the new air interface on the block, there is little or no experience that can be used as a point of reference. This is, of course, changing as vendors roll out more and more CDMA systems and gain insight into how this technology behaves.

OA&M is a crucial part of network deployment, providing a critically important set of tools to the vendor. These tools include a wide range of information such as whether an RF path is tuned and operating according to plan. Initially, diagnostics within the infrastructure equipment indicate whether it is operational as well as whether the T-1 connection between a cell site and the switch is working correctly. There are also end-to-end diagnostic tests that determine if a call is being completed. Tests can further reveal if the network is configured correctly.

Essentially, operational measures are used to show if the network was deployed the way it was meant to be from RF and call completion aspects. This data demonstrates if the system’s performance is meeting expectations.
As equipment is added to the network, diagnostics are run again to insure that the administrative and provisioning aspects of the network are operating correctly. There are also system alerts that notify engineers of any mistakes that have been made while provisioning equipment. After a network is up and running, performance data is used to monitor system capacity and understand how usage is increasing and whether there is a need to reallocate resources. This allows the operator’s network to grow as needed.
But in the end, it is project management that is the key function to making system deployment a smooth effort. Keeping tabs on a project may involve conference calls between RF engineers and a support team who together define priorities of the day. Additionally, integration of the teams working on a given project is crucial. With one team installing equipment in the field, another optimizing it and a third handling the switching equipment at the central office, coordination is essential in guaranteeing all players are working to tackle the same issues.

Once a system is in service, a vendor’s commitment to the operator is really just beginning. There is a need to continually analyze a system’s performance. Automated data collection and data analysis tools are in place to constantly monitor the network’s performance and provide data for preventative maintenance. If there are dropped or blocked calls, this data helps an engineer determine what to address before the operator needs to report a particular problem to the vendor. This is an ongoing process for the life of the system.

There is also a need to forecast capacity trends to accurately measure where to add equipment. Proactive capacity planning is important because of the lead time required to properly engineer additions to a system, order the equipment and install it.

Challenges associated with deploying a CDMA network are continually addressed, enabling vendors and operators to build on the experience gained from previous network roll-outs. It was just a few short years ago that CDMA technology raised eyebrows and planted doubts in the minds of many operators, investors and even consumers. The successful roll-out of dozens of networks has erased those doubts.

The art of engineering a CDMA network has been a learning experience as it is with any new technology. Vendors and operators can be proud of their accomplishments, but cannot rest on their laurels. Network engineering is a job that continues long after cell site equipment has been installed on towers.