We have been independent radio (wireless) communications consultants for almost 38 years.
Although we have prided ourselves on the success of each of our approximately 80 projects, the recent success of the design and implementation of a new police department mobile radio communications system once again proved the importance of adhering to an established, structured project management and system design process from concept to commissioning, and the essential buy-in and a common goal by all stakeholders.
A large part of the success can be attributed to the efforts of our client’s project manager, who worked tirelessly and with admirable devotion to the cause, to make sure that everything critical to the project success was accomplished, often in the face of political reservation and skepticism.
Of course, we also are pleased to take some credit for the success of the project.
Our extensive radio frequency (RF) system design and project management experience combined with our strong technical skills and business knowledge enabled us to create the right system design using the right technology to meet the police department’s needs and expectations.
New Radio Communications System Overview
The new police radio communications system is a P25, 7 site transmitter simulcast and voting receiver infrastructure design.
4 sites are for transmitters operating in the simulcast transmitter mode with co-located voting receivers, plus 3 additional voting receiver sites.
The area is not large, but the slightly undulating terrain and heavy tree foliage in the late spring, summer and early fall presented critical RF propagation challenges.
All RF sites are interconnected by a microwave network operating in the 4.9 GHz band. Each microwave site is a redundant microwave radio configuration.
The new system also includes 5 new dispatcher console positions. The dispatch center provides emergency dispatch and communications services for multiple fire departments throughout the area, in addition to the police department.
A new stand-alone remote location backup dispatch center was also implemented as part of the new system. The backup center includes 4 dispatch consoles, configured for the same screen displays as the primary dispatch consoles.
The primary and the backup dispatch centers also provide 911 call answering services for the area.
The infrastructure system design is intended to enable other municipal emergency services such as the fire-rescue department to share the infrastructure, including the antenna system at each site.
System Design Challenges
RF System Design
Although the service area is not large, the RF environment is challenging and required 4 transmitter sites in relatively close proximity to each other to meet the demanding RF coverage requirements for handheld and vehicle radios.
The biggest technical hurdle was the simulcast RF design. Consistently high quality voice communications in the transmitter site overlap areas combined with high reliability RF signal conditions throughout the entire service area were essential, non-negotiable police department requirements.
The relatively close proximity of all 4 transmitter sites resulted in a number of areas with extensive overlap from up to 3 sites.
The RF design required extensive RF propagation modelling to ensure sufficient RF levels throughout the entire area for consistent reliable two-way communications for handheld radios and vehicle radios under a wide variety of RF environmental conditions, and reliable, consistently high quality voice communications in the RF overlap areas.
The system acceptance tests and measurements prior to system commissioning revealed no areas of unreliable or poor coverage and all areas had clear, consistently high quality voice communications for handheld and vehicle radios.
The system was placed into operation and worked seamlessly throughout the entire service area and beyond without any RF adjustments or system design changes.
The system was commissioned in early February 2020 and has worked flawlessly since.
No RF coverage or voice quality complaints have been received from the police officers since the system was commissioned.
Microwave System Design
The 7 radio sites are interconnected with 6 microwave links operating in the 4.9 GHz band.
As mentioned above, all 7 sites are located in relatively close proximity to each other and are in a geographical pattern that limits frequency reuse among the sites.
We were fortunate to have access to the full 50 MHz of bandwidth allocated by the regulators for the 4.9 MHz frequency band, but the link digital and RF bandwidth requirements combined with the small angular differences between most of the links resulted in very tight restrictions for frequency reuse among the links.
The microwave path design required extensive microwave path interference analysis to select RF channels within the regulated 4.9 GHz allocations that would result in minimizing interference potential among the microwave links and ensure reliable microwave RF path conditions and link performance.
There have been no instances of path unreliability or interference between any of the links, and the microwave system has provided consistently reliable connections between all sites since the new radio communications system was commissioned in February 2020.
What Did We Learn?
Something we have always known, but worth repeating again:
There is no substitute for structured, experienced planning, extensive technical expertise and skills, sound cooperative project management, and buy-in by all stakeholders.