JPS Communications case study
Editor’s Note: This is a vendor-contributed article from JPS Communications. It is rare that MRT will publish a vendor-contributed article. In cases that we believe it will provide a service to our readers, however, we will make an exception.
In this case, we thought that this might provide ideas or alternatives to public safety readers struggling with 911 implementation.
Population growth in rural United States has forced many smaller emergency dispatch centers to seek new technology and creative methods to handle the increasing number of calls for service.
In rural Washington, growth combined with a substantial increase in recreation was leading to an overflow of emergency radio traffic that, at peak periods, began to choke the Kittitas County dispatch center. Its solution was to alleviate dispatcher intensive repeater switching. KITTCOM, the county’s 911 PSAP (public safety answering point), opted to install JPS Communications’ SNV-12 signal-to-noise voter comparators and companion simulcast broadcast equipment to enhance its dispatch radio system. The system has led to an increase in radio call throughput of about 35 percent during the peak periods, which ultimately pays for itself by eliminating the need for additional dispatchers and workstations.
According to KITTCOM Communications Engineer, Bob Johnson, “JPS Communications’ SNV-12 voters are the heart of the Kittcom simulcast system and have allowed us keep up with ever growing demands for service in Kittitas County.”
As the only 911 dispatch center in Kittitas County, Washington, KITTCOM covers emergency 911 calls for about 34,000 residents. In 2002, the civilian staffed 911 center handled 46,017 “events.” While the population is still sparse — about 15 people per square mile — the geography covers 2,300 square miles broken into five geographical areas that require emergency radio coverage. Over the years, as the requirement for services increased, KITTCOM and its predecessors had installed multiple repeaters to expand coverage for fire, police and EMS agencies. Despite the expansive area, however, the relatively low volume of calls dictated that one dispatch workstation must be able to handle the work in a timely manner.
“The trend in public safety is toward using more portable radios as opposed to mobile devices, which may be mounted in a car or vehicle. This has changed the landscape of radio communications,” said Ed O’Connor of Simulcast Solutions LLC who helped select the JPS system with KITTCOM.
He said, “portable devices provide limited transmitting power, and therefore require many more receiving towers to enable the talk-in signals to be repeated or heard back at dispatch.”
For example, a 25W mobile radio may be able to transmit approximately six miles, but a portable may only be able to transmit three miles. Signal from a 100W transmitter tower can reach out 25 miles or more.
To solve KITTCOM’s communications talk-out problem, a number of towers were required to cover the entire geography of Kittitas County. Each tower repeats the same signals at exactly the same time. This is the basis of simulcast transmissions. For simulcast to work, the frequencies and audio must be precisely matched; audio must be controlled to better than 50 microseconds and frequency to better than 3-Hz at the carrier frequency.
Initially when conventional VHF duplex repeaters were installed, operators at KITTCOM’s dispatch center were required to switch channels manually to “select” the appropriate frequency. This became work intensive for the dispatchers, as they were switching between various channels and repeaters according to emergency personnel location. At times when law enforcement traffic was high, such as holidays or weekends, this was particularly a problem. During these busy times, the dispatcher would often run into radio traffic “collisions,” choking the system and delaying assistance to personnel in the field and, ultimately, its citizens in need.
Johnson, who was named APCO International’s and Washington State APCO’s Technician of the Year in 2000, says, “Statistically, when a dispatch radio system reaches saturation, each call takes longer.”
This delay wastes valuable time in the field for police or emergency personnel and in dispatch.
KITTCOM was faced with two alternatives to deal with the increase in radio traffic. It could create another dispatch workstation requiring an additional radio channel and dispatcher during the peak workloads, or they could turn to technology. Clearly, the investment in new technology was a one-time capital expense while the costs of operating an additional workstation and dispatcher would be recurring.
Additionally, the implementation of the newer technology would reduce radio traffic collisions, provide wide area coverage along 80 miles of mountainous interstate, and allow for full duplex audio at the dispatch center. The duplex audio would allow officers to hear each other at the far ends of the county and the dispatcher, even if they were talking, to hear an officer who began to transmit in contention.
KITTCOM (Kittitas County 911) began the installation of a voted simulcast system using JPS Communications’ SNV-12 voter comparators. The first phase of KITTCOM’s simulcast system was to install JPS Communications’ voter on each of two channels (police and fire/EMS) followed by Tait transmitters, and Convex audio delay lines. Each JPS voter can accept up to 12 input (receiver tower) signals.
Voter technology works like this: A call transmitted from the public safety emergency personnel in the field is received at all remote receivers within reach. This is typically more than one tower location. The signals from each tower are then instantaneously sent to the SNV-12 voter comparator module over KITTCOM’s digital T1 microwave. Using digital signal processing (DSP), the voter compares each signal and “votes” for the best audio transmission (See figure 1). The voted and best audio then appears at their Zetron dispatch consoles through a hardwire connection. Simultaneously, this same audio is sent through a Convex audio delay subsystem and out to the transmitters at the remote sites. There, the audio is broadcast “repeated” throughout the expansive coverage area (see figure 2). Transmitters at each site are kept on frequency by Spectracom Model 8195 GPS Ageless Master Oscillators. Voting enables dispatch to hear the best available audio transmission. Voting plus simulcast allows everyone in the field to hear the best audio available. This system is ideal for a single dispatch center because no matter where the officer is, the dispatcher and field officers can hear the call without requiring manual frequency locating or switching. Using JPS’ SNV voters, the radio system now has less radio traffic collisions. This allows the dispatcher, for most calls, to interact with the field units without having to interact first with the radio system.
The flexibility of the SNV voters provided another benefit to KITTCOM. The particular configuration of features needed by KITTCOM was determined and set in the field following deployment. The multiple voted audio outputs of the SNV-12 eliminated the need for separate simulcast and distribution amplifiers. Additionally, selecting from a variety of site switching criteria, adding audio delay to a few of the incoming remote receiver audio circuits, and setting adjustable module timeouts optimized the voting system for the infrastructure and radio system used.
By adding JPS Communications’ SNV-12 voter comparators to its simulcast system, KITTCOM was able to accommodate increased emergency radio traffic with a “return on investment” that made sense from all perspectives. The voter comparator helped enable the dispatch center to fully utilize its existing radio channels and reduced the need to hire additional employees to operate another workstation. The SNV-12 voter comparators increased peak throughput by about 35 percent and paid for themselves in just a short time. As radio traffic continues to increase in Kittitas County, Washington, KITTCOM is installing a third voted channel intended for tactical use and as an alternate dispatch channel for special events.