To anyone considering the purchase of a wireless communications system today, whether it’s cellular or personal communications services (PCS), nationwide or local, the choices can be overwhelming. For the consumer, the purchase of a simple phone requires more investigation than ever before about features (roaming, voice mail, short messages), packaging (ounces vs. grams, NiCad vs Lithium Ion, hands-free, flip), and technologies (digital, analog, broadcast).
To the wireless service providers, the challenge is to obtain customers and maintain their loyalty. This requires providing the best possible service—especially in relation to competing services—including exceptional voice quality and the capability to access the network and complete phone calls whenever and wherever necessary. So how are wireless service providers, specifically wireless PCS operators, able to achieve this quality of service?
A Highly Competitive Market
Many new PCS wireless systems are commercially operational throughout the United States, in direct competition with embedded cellular service providers. For more than a decade, cellular operators have had the time to formulate a solid business plan that optimizes their networks to minimize dropped calls, maximize RF coverage, and provide ubiquitous service over all major metropolitan areas. Additionally, the cellular web of consortiums and partnerships allows customers to roam throughout the United States almost seamlessly.
To meet and exceed the quality and features of these well-established cellular networks, PCS carriers must deliver exceptional service to their customers, many who are experienced wireless users with specific expectations and requirements in mind. Also, PCS carriers must deliver service faster and more efficiently than their cellular counterparts to compete with well-established networks and brand identities.
What does this mean to PCS operators? They must deploy their networks more efficiently, more rapidly, and more accurately to sign on new wireless users and entice existing customers away from cellular providers. And they must maintain and increase customer loyalty and confidence by providing a service that is truly better than the competition, primarily through fewer dropped calls, better coverage, easier roaming, and reduced prices.
Optimizing the Network
One way for PCS operators to provide better service, both faster and cheaper, is to ensure that their wireless networks are optimized for maximum performance. Often, the original business plan set forth by a new PCS operator may require substantial adjustments as service is launched or the network matures.
Adjustments in the profile of users, the location of heavy-use areas, and coverage requirements directly affect the network planning and testing process. An effective network optimization plan, one that accounts for changes in the business model as the network matures, can bring substantial improvements in service quality, leading to greater customer retention and higher revenues.
From a business perspective, two simple factors dictate the degree of profitability of a wireless system:
Minimizing capital expenditures and operational costs while maximizing the performance of its infrastructure equipment.
Offering service that is more reasonably priced and higher in quality than the competition to increase customer satisfaction and retention.
How does an operator maximize system operations through optimization? Operators must have in-depth knowledge of the technology they have chosen to deploy and a systematic, comprehensive approach to testing and optimizing their networks.
As new technologies enter the market, the demand for such expertise increases as in-house engineers come up the learning curve on new systems and as the number of systems multiplies. However, the implementation of a relatively new technology presents operators with a challenge to quickly hire staff with the right expertise and experience, train their existing staff, or acquire the services of competent and proven consultants to ensure that they have qualified personnel operating, maintaining, and optimizing their networks.
PCS and CDMA
In the United States, more than 50% of all cellular and PCS operators have chosen to implement the code division multiple access (CDMA) technology in their networks. CDMA offers higher capacity, greater coverage, and better voice quality.
In addressing this market, it is important to understand that the CDMA standard offers manufacturers a great amount of flexibility in implementing the technology. This means that all CDMA systems are not created equal. In addition, the discrepancy between network planning tools—those that have migrated from other technologies vs those built specifically for CDMA—can affect the quality of the network design and the system. The system performance issues related directly to the network design can include:
Voice quality.
RF coverage.
Call drop rates.
Access failure rates.
Blocked calls.
System capacity.
To ensure that an operator’s network is truly performing to the maximum potential of CDMA technology, many critical system features that affect system performance must be examined.
For example, CDMA systems achieve high capacity by employing forward (from base station to phone) and reverse (from phone to base station) link power control. Fast and accurate power control settings automatically adjust for the dynamic elements of a cellular system such as cell load, multipath fading, and proximity of mobiles to the base station.
The CDMA mobile transmits only the bare minimum power required to maintain a link. As a result, the average transmit power is low, and the subscriber’s battery power is conserved. Operators can adjust the settings associated with this parameter to affect the performance of the system.
CDMA system parameters, such as power control, can be adjusted depending on the system performance goals of the operator. This results in a system optimized for a particular market condition. The optimization process must improve system performance in specific areas without degrading performance in other areas.
System Optimization Steps
The network optimization process should follow a proven plan that successfully troubleshoots and improves the network. A sample process that supports successful optimization of the network includes seven steps:
Step 1. Review System Performance Goals
Each operator’s CDMA PCS system is designed to meet performance criteria defined by marketing needs and business projections. These criteria for core and overall network performance determine minimum performance standards to meet customer expectations. Based on daily averages and busy hour statistics, an operator may find that the system performance goals are not being met.
A detailed review of system specifications provided by the infrastructure vendor is the first step in understanding the network design. The system performance goals for most CDMA networks include specific, measurable objectives for voice quality, call success rates, and network capacity. Evaluate design criteria and definitions, analyze performance calculations and assumptions, and identify critical design specifications as they relate to meeting system performance goals.
Step 2. Review System Parameter Settings
Setting and understanding CDMA system parameters are critical to understanding and optimizing the network. These parameters and the values that are set determine the overall performance of the system. Improper settings can cause degraded performance, dropped calls, and poor call quality. The most difficult portion of optimizing system parameters is understanding the effects of individual and combined parameters interacting with each other.
An understanding of many key system parameters is necessary to customize and optimize CDMA networks. For example, CDMA systems can be configured for different rate sets. These rate sets determine the maximum amount of bandwidth allocated to each call (usually 13 kb/s or 8 kb/s) and affect the ratio between voice quality and system capacity. Operators may choose a rate set that prioritizes voice quality over capacity to meet specific system goals.
Step 3. Analyze the Existing RF Network Plan
The next step is a detailed review of the network. This analysis uses a computer-based CDMA simulation tool to evaluate the coverage and capacity of each cell in the existing network.
To conduct the RF analysis, the optimization team must utilize detailed information about the network. This includes cell site locations, cell site configuration, and switch data such as time-based traffic loading.
Through proper analysis, the radio capacity loading can be applied to the propagation calculations for each sector of each cell in the CDMA system. The CDMA analysis identifies problem areas, such as where either forward or reverse link coverage may be inadequate under a loaded condition. The recommended corrective action may be as simple as adjusting antennas or system parameters.
Location-specific problems encountered by the system operator also can be evaluated through this portion of the process. Some of the newer radio planning tools incorporate sophisticated CDMA optimization algorithms that analyze potential problems related to pseudo-noise offset planning. This involves implementing codes that determine which part of the CDMA 1.25-MHz carrier will be used for each sector and cell in the network.
These new tools also assist with neighbor list selection or, more specifically, determine which sectors the mobile can be handed off to when moving from one cell or sector to another. Both of these factors can lead to high dropped calls and related system performance issues if they are not correctly implemented.
Step 4. Perform Cell Site Audit
To ensure that the network is properly operating independently of CDMA operations, perform an independent audit of all cell sites to validate and verify proper installation and equipment commissioning. Evaluate each cell site to ensure that proper installation procedures have been followed and that the peripheral equipment is operating per the predetermined specifications. The major areas to investigate include the RF antennas and cabling, the global positioning system antennas and cabling, T1 backhauls (T1 link from base station to base station controller), alarming, and grounding.
Step 5. Collect Sample System Data and Perform Field Measurements
To effectively determine the performance of the network and measure key system metrics, sample data needs to be collected in the field. As a minimum, certain system parameters must be readily available through proven and calibrated measurement devices.
Much of the challenge of optimizing networks is coordinating the data-collection process with infrastructure vendors and correlating the data into a meaningful and usable format. Critical to the data-collection and field-measurement processes is defining controlled drive routes and repeatable conditions. This includes the proper logging of data at both the forward and reverse links.
Step 6. Post-Process and Analyze Data
Post-processing measurement data is required to better understand system performance. Typically, a group of qualified systems engineers processes forward-link data and presents the information in statistical, graphical, and other output formats necessary to evaluate system performance.
The processing of reverse link data typically is based on the ability of the infrastructure vendor to collect and analyze the data. Without post-processed and correlated reverse link data, the optimization process is very limited in terms of overall system troubleshooting and analysis.
Step 7. Taking Corrective Action
The final step is making the changes and recommendations to bring the system up to market quality levels and meet the objectives established in the first step. Often, the set of recommendations is broken into three groups.
The first group represents relatively simple changes, including system-wide parameter adjustments combined with sector-specific parameter changes to improve general performance. Such changes may include decreasing or re-ordering the neighbor lists or antenna downtilting/reorienting.
The second set of recommended modifications may require more time and expense for the operator and include site-configuration changes. These may range from a rework of the antenna model and mounting height on some structures to the removal or addition of sectors at a cell site.
Typically, these are intended to balance system loading across sectors and cells to allow more use of the existing radio equipment. Another goal may be to increase or decrease area-specific soft handoff to allow more capacity or simply improve network performance in certain areas.
Finally, virtually all wireless networks go through growth phases during the first several years of operation. Certain cell locations that provided ubiquity in coverage now may be the source of system-wide interference issues. Other cells that originally were intended to cover certain key areas may not, in practice, be meeting the original goals.
In either case, the solution may be redesigns of portions of the network through the removal or addition of cell sites. Due to their expense, such changes require executive management review and approval and normally are part of larger network expansion plans.
An additional outcome of detailed CDMA system analysis may be recommendations to the vendor of the infrastructure equipment concerning unique implementations of IS-95-based hardware. Each vendor has options on how to implement forward-channel power control, what size of high-power amplifier to deploy, and how to handle critical system messages.
Conclusion
To meet the challenges of signing on and maintaining customers, today’s wireless CDMA PCS service providers must undertake the challenge of optimizing their networks to provide the best possible service based on real field conditions. That best service of exceptional call quality is critical to survival in localities where wireless service is being provided by as many as six different companies.
About the Authors
Robert Sanchez is senior director for development in the Globalstar® division at QUALCOMM. He also has held several senior positions in the CDMA Test and Deployment Products and Services division at the company.
Mark Kelley is a senior director of network planning at QUALCOMM. He assisted in the preparation of this article.
QUALCOMM Network Optimization Services, 6455 Lusk Blvd., San Diego, CA 92121, (619) 651-3919, www.qualcomm.com.
Copyright 1998 Nelson Publishing Inc.
July 1998
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