Intergovernmental planning creates public safety ‘radio utility’
Spotsylvania County, VA, applies infrastructure planning to create an 800MHz radio system with long-term benefits
In 1995, the need was first identified for a new county radio system to serve Spotsylvania County, VA, and other interested entities. There was the “traditional” need within public safety (fire, law enforcement and EMS) and public services (inspectors, administrators and utilities). The broader view indicated a potential need from schools and neighboring jurisdictions as well. The future radio system could, in some sense, be viewed as a “radio utility in the sky,” serving users on a prorated, cost-share basis. The decision was made to establish an 800MHz trunked radio system because of available frequencies.
The locale Spotsylvania County, comprising 407 square miles in eastern Virginia, is midway along a 100-mile line between Washington and the Virginia state capitol at Richmond. About 65% of the county lies in Virginia’s Piedmont physiographic province, and about 35% lies in the Coastal Plain. Elevations range from sea level to 540 feet.
Spotsylvania is a growing place, therefore it needed to plan ahead to continue to provide service to its residents. According to Virginia Town and Country magazine (April 1996), the county experienced a 98% growth rate from 1990 to 1994.
Intergovernmental liaison In August 1996, the county hosted an informal workshop for all of the contiguous governmental bodies, namely the counties of Louisa, Stafford, King George, Caroline, Orange and the city of Fredericksburg, VA. The result was a pooling of the previously assigned National Public Safety Planning Advisory Committee’s (NPSPAC) frequencies for Spotsylvania County and Fredericksburg. These would be added to the five channels already licensed to the county. Mutual-aid interconnections would be established for the other counties.
Coverage requirements The area design of a radio system can, in some cases, lead to confusion or unrealistic expectations. Because of the priority nature of hardware and early commitments to infrastructure suppliers, mistakes are easily made in the planning process. To avoid this, Spotsylvania County created a user committee to define the vision and expectations of the system over the life cycle of the embedded investment. The committee also addressed the coverage requirements by agreeing on a future land use map to envision public safety needs for in-building portable radio use.
System architecture As a result of the coordination meeting and the coverage requirements, a two-site, simulcast, trunked system was specified. The design of any trunked radio system has to address system failure scenarios. In this case, two scenarios were thoroughly discussed:
*Antenna failure or tower failure -The user committee members agreed that in this unlikely event, they could operate countywide service from one site using mobiles. They would take whatever a single site would provide for portable coverage. Neither site alone will provide satisfactory portable radio, in-building coverage for the entire county.
*Fiber failure – The communications center, midway between the two sites, is connected to the microwave hub via a fiber-optic cable. Loss of this cable was the second failure scenario. A two-hop microwave system was required to connect the sites to the hub and then to the communications center. To guard against fiber-optic cable failure, all of the simulcast common equipment was placed in the microwave hub shelter. In the unlikely event of a fiber failure, countywide services would be maintained. The communications center would continue to provide dispatch services using control stations installed for that purpose. Figure 2 on page 61 depicts the system architecture.
Other communications needs Spotsylvania County also lies within the Lake Anna Nuclear Power Generation Plant evacuation area. The evacuation plan calls for the use of the county school buses. This required a communications link with the school bus system. (In the Commonwealth of Virginia, school systems are independent from the county administration.) At the time of the system inception and design, the school system was using commercial SMR service for communications with school buses. As time has passed, SMR costs have escalated. This triggered the plan to migrate the school system’s bus communications to the radio utility, thus providing another cost sharer.
RF channel usage The pooled spectrum was assigned as shown in Table 1, below. By the system mapping, countywide mobile-only talk groups will first pick channel group 2 and overflow into the high-power channels of channel group 1. The control channels are restricted to use only channel group 1. For countywide public safety portable radio use, channel group 1 will be selected first. This would overflow to channel group 2. All use for Fredericksburg or the northern county service area will have channel group 3 is the first choice, overflowing to group 1 and then to group 2.
Coverage criteria This is a mixed-spectrum system. The total system uses both the old high-power spectrum and the NPSPAC spectrum. The old band is limited only by height/power regulations. The NPSPAC spectrum is controlled by a power limitation based on service area. The system was designed and specified for the portable coverage provided by the high-power channels. The NPSPAC channels were contracted for the equipment specifications. The lesser requirements for mobile coverage were preferred to the NPSPAC channels by the system map.
Adding a new user As the system was being built, a regional jail was being built in Stafford County, to the north. The regional jail has two off-premise communications needs: work release and liaison. It was desired that on-premises officers use the 450MHz band because the Stafford County sheriff’s department uses it. In case of jail disturbances, all officers wanted to be in the same band. Off-premise activity required communications into the counties of Stafford, King George, Spotsylvania and into Fredericksburg. A cost-value determination had to be made by the regional jail on how to cover such a large area for light, but critical, use. Because of the in-building coverage requirements of Spotsylvania County, there is an extended mobile coverage beyond the county boundaries. The result was to use the radio utility, which provided mobile coverage for its service areas. The regional jail benefitted from this mobile coverage and the use of crossband repeaters.
The system configuration is shown in Figure 3 above. Two trunked control stations were installed for reliability and for direct communications to the communications center, in case of a regional event.
Implementation cost savings Most complex systems of this type are purchased on a turnkey basis. Using county employees for some of the work (if the county is willing to accept the responsibility), can save money. (Contractors pass through mark-up.) In this case, site work and grading was performed by the public works department. Shelters were accepted at the factory, then transported and installed by the county.
Site acquisition is always an independent cost. In this case, towers were constructed on county-owned property (two landfills). The benefit was threefold. First, there was minimum visual clutter. Second, costs were lower. Third, the towers were oversized to accept additional tenants for a future revenue stream. The county has elected to construct its own tenant shelters, therefore becoming the site manager and thus developing an enterprise activity.
Benefits to all This system is a benchmark of intergovernmental cooperative planning and resource use among several different entities. The administration and elected officials of Spotsylvania County have taken the long view to benefit all. n