By Darek Wieczorek, Principal Consultant, Tait Communications.
Here’s something you may not know: for smaller Public Safety organizations, there may be very little practical gain between inexpensive P25 conventional systems and high-end trunked ones.
While trunking undoubtedly has its advantages for large networks with many subscribers, unless your system is very busy, rapidly expanding or supports a large number of users, there may be very little functional difference between a trunked and conventional system for smaller systems.
Smaller agencies, however, when faced with this cost and complexity, are often tempted to stay with their conventional analog systems or, even worse, upgrade to commercial level proprietary digital technologies. In either case, they are abandoning (or at least compromising) their ability to interoperate with others.
The main contributors to the cost of any system—regardless of technology—are the repeaters, switching/control equipment, backbone infrastructure (high-grade microwave or other links), towers, shelters and services. The majority of these costs simply will not apply when you switch to a competitively priced conventional P25 system that is well designed to maximize re-use of your existing infrastructure.
But of course cost is only half the story. Is the P25 conventional architecture flexible enough to meet your needs?
Now that we have established the affordability of P25 conventional, let’s look at the possible configurations. Is the architecture flexible enough to meet your needs? Let’s look at a basic example.
Now let’s look at the ways these elements can be configured.
For digital/encrypted communications a single stand-alone repeater is sufficient, with no administrative interface or monitoring. This might mean just replacing your existing repeater while reusing your current antenna system and power supply.
Single base station
For limited coverage applications, a P25 conventional base station can operate in simplex or semi-duplex. It can connect to a remote control terminal with a variety of options.
Single base station/repeater with P25 Console Gateway
This may mean simply replacing an existing repeater connected to your existing dispatch consoles. This will require a device converting the standard analog conventional interface to P25 protocol, and analog voice to digital format. If a P25 channel is added (rather than replaced), there will be new antennae and associated RF equipment, power supply and connections to the dispatch equipment.
Cross-band or cross-mode repeater
You may need to connect your P25 conventional operation to another band or system. Depending on what you are connecting the new P25 channels to, this may be very simple (e.g. connecting to a conventional system in a different frequency band) to quite challenging (e.g. connecting to a proprietary trunked system).
Single repeater/base station with satellite receivers
Where coverage talk-out needs to be balanced with talk-in, a single P25 conventional repeater can connect to a number of geographically dispersed receivers. Such a system is relatively easy to design and implement and does not require high quality links between sites. Satellite receivers cost a little less than the repeaters.
Multi-cast with optional voting and/or scanning
Where coverage requires multiple sites and several frequencies are available, P25 conventional can broadcast the same information on multiple channels at different locations. Subscriber units can be programmed to scan the channels. Repeaters can be configured to send a control signal (allowing the radios to select the best site) and to vote the received signals from the subscribers. The subscriber units will automatically roam between sites and the repeaters will always broadcast the best signal. Link requirements between sites are more forgiving than for simulcast or trunked systems and therefore less expensive.
When a single site is insufficient and multiple frequencies are not available, a P25 conventional system can be configured as simulcast. Its great advantage is the ease of use for subscribers, but design and implementation require significantly more skill than the previous alternatives. Compared with trunked systems, P25 conventional may not require any core switching, greatly lowering your costs. However, conventional or trunked, P25 simulcast requires high quality links between sites.
This article is taken from Connection Magazine, Edition 3. Connection is a collection of educational and thought-leading articles focusing on critical communications, wireless and radio technology.
Share your views, comments and suggestions in the Tait Connection Magazine LinkedIn group.