What type of digital radio system is right for me?

If you are choosing to invest in a radio system for the first time there are a number of key factors you need to consider. So what type of radio system is right for your needs?

The Digital Mobile Radio (DMR) standard, which operates in PMR frequency bands from 30–960 MHz, offers two main choices for professional users: DMR Tier II conventional systems; and DMR Tier III trunking systems.

The number of users and talk groups you expect the system to support and the amount of traffic likely to be generated will largely determine which one you choose. You also need to consider how often individuals and talk groups will want to use the system and if you want to use data applications you need to be aware of how much bandwidth they will consume.

A general rule of thumb is that if you are a small to medium-sized enterprise with less than 100 individual users, who are primarily looking to access voice services, then a DMR Tier II conventional system should support your requirements.

If the radio system needs to support more than 100 subscribers, or is expected to do so in the future, then a DMR Tier III trunking system should be considered, especially if you also want to access advanced data applications as well as voice services.

The key difference between the two tiers is that Tier II conventional radio systems use a dedicated channel for each individual group of users, while Tier III trunking radio systems automatically allocate a pool of channels to different groups of users. If your allocated channel in a Tier II system is busy, your call has to wait in a queue until it becomes free. In a Tier III system, the network dynamically assigns you the next available free channel from the pool of channels.

However, there is an additional option that bridges Tier II and Tier III. Hytera offers a number of ways to expand capacity and coverage on DMR Tier II conventional radio systems: simulcast; and Extended Pseudo Trunking.

Expanding your DMR Tier II systems

If you have invested in a DMR Tier II system and you find you need more capacity because your organisation has grown or you just want to put more of your existing staff onto the radio network, then you can deploy Hytera Extended Pseudo Trunking (XPT).

What the XPT solution (an exclusive Hytera development) does is offer a way to replicate a distributed trunking network, but in a simpler and more cost-effective way if you are not in a position to invest in a full Tier III trunking system. XPT enables users to double their radio capacity using their existing spectrum resource without having to deploy a centralised system controller. (See our Hytera blog on XPT for more information).

Another option if you are looking to extend coverage on your DMR Tier II system is to use a simulcast, or simultaneous broadcast system. It is really best suited for organisations who want to deliver DMR radio coverage over a wide area, but who only have access to limited radio frequency resources.

What simulcast does is simultaneously transmit the same signal with very precise timing between base station repeaters from two or multiple repeater sites on the same frequency. Just one frequency pair is needed for the whole mobile radio system, no matter how many base stations are in the network.

So, if you have limited frequency resources and need to broadcast over a wide area coverage, simulcast may be a good option (see Hytera blog on DMR Tier II for more information). However, as mentioned, if you need to support more than 100 users and have a large number of active talk groups then a DMR Tier III system may be the way forward.

Frequency considerations

DMR radios are available in VHF and UHF frequencies and which spectrum you choose will depend to a large extent on the nature of your business. For the same power, VHF will transmit over longer distances and is therefore good for wide area outdoor use, especially if the topography is not too hilly, heavily wooded, or built-up.

UHF is good for indoor use and in built-up urban areas, as it is better at penetrating metal and concrete. It might also be a better choice outdoors in woody and hilly areas with lots of obstructions. UHF radios also have shorter antennas than VHF, which can be a plus, especially if terminals are worn on the belt or inside jackets as the device is more discreet.

You also need to check what frequencies are available in the areas you wish to transmit within. Big cities like London can be very crowded and it can be difficult to find free frequencies that will not cause interference with existing neighbouring systems.

Professional radios require a licence and each country has its own licensing regimes. In the UK, licensed frequencies are available for DMR systems in UHF (400 – 470MHz) and VHF (136 – 174MHz) channels. There are different grades of licence available from the regulator Ofcom, which give an idea of the kinds of license you might need.

Simple UK Light is suitable for a small coverage area and does not cover the use of a base station. 15 frequencies spread across four business radio bands are available.

Simple Site Light covers the operation of a base station and radios over a small area (typically one kilometre or less) and is good for an industrial unit, warehouse and the like. Licensees have access to a range of frequencies and must self-coordinate with other Simple Site Light licensees.

A Suppliers Light license is for business radio suppliers who service, repair and hire out business radios. The Technically Assigned license covers a wide range of radio equipment, frequencies and coverage areas from very small areas, such as for in-building coverage, right up to very large, even countrywide systems.

An Area Defined license gives you exclusive use OF a frequency across anything from a 50km2 grid square, a county, or the whole of the UK. In practice in the UK the availability of UK-wide channels above 165 MHz is extremely limited.

Your Hytera authorised partner will advise on the available frequencies and which one(s) will suit you best in your particular location. They can also help obtain the licence for you and programme your radios to the right frequencies.