Making wireless magic a reality
Today’s wireless communications needs are complex, as, in turn, are the networks designed to support them. Variables such as coverage requirements, environment, topography, efficient use of available spectrum, and user needs and expectations must all be weighed carefully to ensure optimal system performance today and in the future.
But even the most straightforward RF system designs require not just science but the art of engineering to make them a reality — art and comprehensive testing, which is a critical benchmark for system integrity. Comprehensive performance and analysis tools for wireless networks become even more important as new technologies enabling the use of higher frequencies continue to change the wireless landscape. System designs must accommodate the resulting changes in frequency-dependent characteristics.
As a rule, equipment vendors or consultants that design wireless networks should guarantee them. Users should demand it. In addition, system design coverage and performance descriptions should be tied to an Acceptance Test Plan (ATP) that demonstrates delivered network performance. The contract terms should take into account potential deficiencies and resolutions. To avoid future coverage issues, all stakeholders must understand the level of coverage being contracted for and its limitations to avoid future coverage issues.
Why is testing important in wireless network design? Simply, to ensure the integrity of the system configuration and that it delivers necessary coverage and system capacity to meet specified existing and future communications needs. Motorola and other suppliers invest significant resources in proprietary coverage prediction and analysis tools and standards to ensure accurate, efficient and cost-effective system designs.
These tools assist engineers in accurately determining coverage and traffic for radio system architectures and protocols. Specifically, Motorola uses proprietary products to do the following:
Model coverage, and traffic, for wireless packet networks
Model coverage of, and interference to, voice radio systems (digital and analog; simulcast, voting
Verify coverage of digital and analog voice, packet data systems
Model traffic for trunked voice radio systems
Design wireless systems to specific coverage standards.
RF systems design tools historically have been created and implemented by wireless system manufacturers. However, as spectrum and standards have evolved, third parties are entering into the marketplace with their own performance-analysis tools. It’s important that users understand that off-the-shelf options may be less suitable than proprietary tools because they are frequently intended to work over a wide gamut of applications. While manufacturers remain the best sources for these system tools, users who wish to encourage competition should request that the performance of the system, the system design and evaluation tools, testing procedures and fault remedies become part of a delivery contract.
While design and system analysis tools are valuable components of the system procurement process, ongoing system performance and maintenance tools are growing in availability and importance. These tools assist in system problem identification and repair, as well as planning for system expansions as a result of increased capacity requirements or changes in areas of jurisdiction.
Despite the amount of planning that goes into RF system design, changes in signal coverage cannot always be avoided. Changes to the landscape (i.e., the construction of a building in the coverage area) or migration to new technologies can often create the need to move or add sites. However, moving and developing new sites can add millions to the cost of system infrastructure.
As more vendors adopt Project 25 standards and incorporate new 4-level digital modulation, implementing simulcast systems will create new challenges, and traditional techniques will need to be retooled. Synchronizing 4-level digital modulation is more difficult than 2-level modulation or analog FM, thus launch time and frequency precision are even more critical.
Moving to the 6.25 kHz channel spacing — and/or other system modulations with different characteristics/bit rates — will require existing sites to be modified to accommodate differences in the coverage footprint. This is of particular concern to the mission-critical user community, because it will significantly impact existing coverage.
RF system design is a complex process that requires numerous checks and balances. Performance-analysis data is critical to ensure that the network performance delivered meets user expectations and that system integrity parallels identified standards. As spectrum continues to be mined for expanded communications applications, testing techniques and analysis tools will continue to be a critical component to optimizing wireless system performance today and in the future.
TSB-88-B: The Newly Revised Spectrum Planning Standard
As wireless communications systems technology evolves, the complexity in determining compatibility between different types of modulation, separate or concurrent operational geographic areas and applications usage increases. There is a need to support the development of “best practices” in wireless system design, and TIA TSB-88-B provides a baseline metric.
To provide system managers with guidelines in determining compatibility between system types and even within single systems, TIA commissioned TSB-88-B (“the Bulletin”) to help address interference and frequency management issues between different types of technologies across different bands. It was prepared in part as a response to requests from user organizations and is intended to assist system designers as they work to design and implement new systems based on narrowband technologies and potentially incompatible types of system deployments. Some of the key issues that the document covers are the following:
Design and frequency coordination of bandwidth-efficient narrowband technologies to be deployed as a result of the FCC “Spectrum Refarming” efforts;
Quantification of the impact of new narrowband/bandwidth-efficient digital and analog technologies on current technologies;
Migration and spectrum-management issues regarding the transition to narrowband/bandwidth-efficient digital and analog technologies. Including channel-spacing issues from 30 and 25 kHz to 15, 12.5, 7.5, and 6.25 kHz.
Additionally, the Bulletin provides preliminary information regarding narrowband and wideband data coverage issues in 25, 50, 100 and 150 kHz channel bandwidths for use in the 700-MHz band.
The overall focus of the standard is on methods of modeling, simulating and verifying Noise- and Interference-Limited Systems. This is important, because system managers have more choices than ever in terms of modulation techniques, and the number of entities involved in wireless communications systems continues to climb.
This Bulletin gives guidance on modeling and simulating narrowband/bandwidth-efficient technologies in a “post-Refarming” environment and provides performance guidelines for the same. It summarizes these in a “Spectrum Management Tool Kit” for use by frequency coordinators, systems engineers and system operators. In addition, there are guidelines for acceptance testing of completed systems to provide a comprehensive list of issues and techniques to determine acceptable coverage and performance for shipped systems.
For those interested in discussing TSB-88 in its various versions, a Yahoo Group has been created. The group name is TSB-88.