Design Issues for P25 Digital


P25 Digital mode radio equipment is expensive, sounds different to the ear of the user, and most of the radios have features that users are unfamiliar with… so why would you consider it for public safety?

Other than the pragmatic issue that P25 compatibility is virtually mandated if you acquire radio equipment using most sources of federal funding, since for three grant funding cycles it has been a grant-making requirement that any radios acquired on Homeland Security (and many other) grants be P25 compatible… why would you bother with it?

We have long taken that position, but we have changed our mind now that we’ve actually used it.

There are still disadvantages, but the “pro”s outweigh the “con”s. Here’s why:

 

The First Good Reason: Interoperability

First of all, with three years of funding already completed and more to come, many of the other agencies that arrive in your OA to assist on mutual aid assignments will either be operating in P25 mode, or have the ability to operate in P25 mode.

We recommend to our customers that they either use P25-capable radios in the field, or provide supervisors (and above in the hierarchy) the ability to enable a bridge [link to tactical bridges] instantly at the scene between the non-P25 radios in use by their personnel with the P25-capable radios in use by other agencies at the scene. It just makes good sense to be able to operate in P25 even if it is not your usual mode.

On a related topic, we also recommend that any new high-point repeaters and remote bases be of a mixed-mode type. Equipment such as the type made by Daniels, Tait, and others offer a mixed-mode so that incoming P25 digital signals are repeated back out as P25, and incoming analog signals are repeated back out as analog.

During an incident that benefits from interoperability, the tower equipment is changed remotely to “force” incoming P25 to be converted to analog. This way, visiting P25 users will be able to use their radios as-is, and still interoperate with the native users on the system.

 

More Good Reasons

But beyond interoperability, there are other good reasons for P25 digital mode:

  1. Easy Identification of Users. In a P25 system, the identity of each radio is provided on every PTT transmission. This can be displayed on other field radios, and at the dispatch/control point. This can reduce airtime, as dispatchers can instantly see which unit made the transmission and on-the-air clarification isn’t necessary.
  2. Safety of Users. A P25 radio carries a related feature of enabling a “man down” button on the radio requiring a single key press to both silence the audio from the radio (so that the bad guys cannot hear the radio), and also transmit an emergency message to the dispatcher. With appropriately equipped consoles, the emergency is made visible in a distinctive way and should not be missed by the dispatcher. Since unit identity is available (see above), this too is associated with the emergency. In the future GPS information will also be available, further aiding the user needing assistance.
  3. Visibility of Users. Called “presence”, a P25 radio can be interrogated by dispatch (or any other radio, if so equipped) to verify their presence “on the air” and available for messages, similar to a cell phone (a cellphone system knows when a particular cellphone is within the network, or is not, and if not sends a caller immediately to voicemail). This interrogation is in the background, and does not disturb the user. Presence is a powerful tool for dispatchers, and saves time in dispatching calls efficiently.
  4. Text Messaging. A P25 system can be programmed to accept text messages, and even allow individual field radios to send text messages (the user interface is so restricted that we generally recommend against this method, or to at least restrict it to “canned” messages such as “acknowledged”). This can either eliminate the need for pagers, or augment the existing pagers, particularly if a team of users is operating beyond any commercial paging service but has their own incident dispatcher [link to incident dispatching] and/or P25 repeater configured to send text messages.
  5. 1:1 Calling. P25 radios can be programmed to permit direct calling from one field radio to another (or from the dispatcher to a field radio), which allows a radio to be left silent until needed, similar to the operation of a cell phone. This feature can also be used with an audible alarm, to get the user’s attention, particularly if radio traffic is heavy and the desired user has missed the transmission intended for them.

This feature, like the “presence” and “identity” features, can be used with generic identity codes assigned to each radio, or each radio can be loaded with a table of all the first/last names (or agency unit designators) carrying each radio. We don’t always recommend this approach, despite the advantage of easy selection of the unit to call, the tables need to be maintained and that can become tiresome which often leads to out-of-date and inaccurate tables.

The astute reader may have noticed that all of the features above are routine on most (but not all) trunked radio systems, and in isolated cases have also been implemented via Motorola’s proprietary MDC-1200 signaling protocol. This is true, however all of the features described above are available in P25 radios with two revolutionary advantages:

  1. The features are available and usable in the field, and do not require a “system” of mountain-top repeaters and trunking controllers in order to be used. In fact, with as few as two handheld radios the users can enjoy the features.
  2. The protocol is a public standard, and not proprietary. As most agencies have experienced, if you use a Motorola trunking system you cannot use radios from any other manufacturer. The above features are available and compatible with any radios from any manufacturer.

Perfect for Strike Teams / Task Forces

These features that provide "Nextel like services" while operating away from the cellular industry's towers (and monthly fees) makes P25 radios ideal for Strike Teams, disaster teams, wildland fire applications, and just about any deployment that may occur away from a “home system” and needing interoperability with other teams.

Trunking systems are not practical for quick deployment, let alone traveling to another location (or accommodating visitors in your home location). P25 provides the essential features, and can be deployed by simply turning the radios on!

What's the Bad News?

There are two remaining quality issues for P25 digital in public safety. First, the quality of the audio as experienced by the user can be far less than wideband analog mode. Unfortunately, it isn’t as “natural” sounding as the analog radio transmissions your users have known for years (decades?). This is an unfortunate consequence of the long time it took for the P25 standard to be negotiated; it is using a digital technology (called a codec, although that doesn’t matter to your users) that is several years old now and doesn’t reflect the best that digital technology can do, but it is the technology stipulated by the standard. Although this will eventually be updated and presumably improved (the next generation of the P25 standard is nearly final) we advise our agencies to set expectations for audio quality to be low.

Despite the disadvantage of the audio sound, there are no other significant disadvantages to P25. Early rumors disputed the range of a P25 digital system compared to an analog system, but subsequent studies show that while there can be differences, the total effect is negligible.

As with all changes to a communication system, there is an initial cost associated with developing standard operating procedures for the new features (e.g. presence, 1:1 calling, messaging, etc.) and training all users to the new procedures, but this was also true for agencies converting to trunking systems so we do not consider it to be a significant cost.

Finally, there is a long-term advantage to P25 standard radios, which is that with a number of manufacturers making compliant radios, the overall cost will be driven downward. We are already able to offer rugged, submersible P25 radios at half the price of the comparable Motorola models, and expect this trend to continue..

We think P25 radios offer significant advantages to public safety users even beyond the effectively-mandated compatibility for interoperability. Talk to us about your needs, and we’ll help you evaluate whether P25 makes sense for you.


 

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Key Notables

Unfortunately, we must qualify the statement that “all P25 features are available and compatible with P25 radios sold by all manufacturers” since of course some of the manufacturers are meeting the letter of the law, but not the intent, and have eroded their compliance with the standard. We know of at least one manufacturer that has engineered their dispatch consoles so that incoming emergency messages are handled differently depending upon which manufacturer’s P25 radio sends the emergency message (a travesty and unpatriotic in our opinion). While the federal government is attempting to launch a P25 compatibility certification, it is not yet completely reliable. Please contact us before you acquire any P25 digital radio equipment so that we can verify compatibility.