Space invaders: DMR vs dPMR

Wireless reports on the battle taking place in the professional mobile radio industry that is causing a stir between vendors in different camps

Space invaders: DMR vs dPMR

Standards. People always seem to get in a pickle over them. And in the world of technology, this reigns particularly true. You may remember the battle some years back between VHS and Betamax around video or perhaps that between Blue-Ray and HD DVD in the high definition stakes. This normally boils down to one company or group of companies seeking to push a technology standard they support or have developed upon the rest of the field or its consumers.

In the professional mobile radio industry (PMR) things are no different. Technology has been moving at a pace from analogue to digital and those involved are seeking to turn a buck and bring businesses into line with the technology they are developing.

According to Kok Gee Siong, VP for RND Center, Hytera, the two-way radio market segments started migrating to digital after they saw the success of the migration from analogue to GSM in the commercial cellular phone market in the 1980s.

Among the first to change was the public safety market segment, where we saw EADS, Motorola and M/A COM hotly pushing their respective protocols for the public safety and security market, he says.

Then in recent years, there was a digital migration move towards the professional two-way radio market, in particular the PMR arena.

‘This started in 2003, when the two major analogue radio providers, Motorola and Kenwood, were in hot confrontation to table their respective technologies to the regulatory bodies,’ says Gee Siong.

Today, these are now collectively known as digital private mobile radio (dPMR) and digital mobile radio (DMR) technologies.

One company that has been at the forefront of developing the DMR and dPMR ETSI Standards since digital PMR was first proposed is Fylde Micro. Brian Seedle, chairman of Fylde Micro, explains that the main driver for both DMR and dPMR was the lack of available spectrum for users, particularly in heavily congested areas.

‘The first thing to say is that there is no panacea, no perfect system. Spectrum and bandwidth constrain just what you can do,’ he says. ‘An examination of the present players in the 6.25KHz market infers that there are two distinct competing camps, those who are allied to DMR and those to dPMR.’

As Seedle notes, this has left many playing the political game with one player pushing their preferred choice by discrediting another. However, given the fact that there is no perfect system and the market for PMR is global, there are always compromises to be met and there are now choices – DMR, dPMR, TETRA and P25 phase 2.  

‘All have their merits and are more suited to particular applications and particular markets,’ he says.

According to Gee Siong, the merit of each technology is pretty clear. He believes the true 6.25KHz dPMR is better when you consider cost and channel noise, as the narrower bandwidth for the receiver will tend to reduce the noise level for the channel when compared with the 6.25e of the 12.5KHz DMR technology.

However, he says, the dPMR technology, which was developed for low power operation, has its disadvantages when operated at high rf levels, as the tendency to interfere with each other is much higher.

‘Although Kenwood was slightly earlier to release a dPMR product to the market, it did not catch on well,’ he adds.

‘This may be attributed to the lack of an official dPMR standard,’ he says. ‘In fact, as late as March 2007, a news release by FCC was noted to mention that there was still no 6.25KHz dPMR standards release. In addition, most mature markets, in particular Europe, drag the thought of dPMR because they are frightened about the huge task needed to re-farm the 12.5KHz frequencies to 6.25KHz.’

Ian Lockyer, marketing manager at Icom, sees two technological differences between dPMR and DMR.  

‘One of the big selling points for dPMR is its spectrum efficient 6.25KHz channel spacing,’ he says. ‘dPMR doubles the channel capacity of 12.5KHz narrow band technology, meaning that users will have twice the capacity and also save up to 50% on licensing.

However, he points out that DMR can achieve the same 6.25KHz narrowband spectrum efficiency via a different method.  

‘Whereas dPMR system is always double capacity whether it is used with or without infrastructure, DMR, double capacity is only achieved when a repeater is synchronising the time slots and that two users are in the same geographical area, accessing the same repeater at the same time. As such, the dPMR system is the “true” 6.25KHz channel,’ he says.

In theory, this means that in identical conditions, the narrower channel width of the dPMR system should allow the signal to achieve better coverage than the 12.5KHz DMR system when transmitted at the same output power.

This, says Lockyer, is because the noise floor of any receiver is proportional to the filter bandwidth, therefore the smaller the bandwidth the smaller the signals that can be received.

With the dPMR group having many more manufacturers providing an alternative, according to Lockyer, he says his company enjoys a close relationship with Kenwood, which means that in some areas products are interchangeable – something which is great for the customer.

But before you begin to sway your thinking in favour of dPMR, Jamie Bishop, marketing manager at Tait, reminds us that DMR is a proven digital technology with over 450,000 radios deployed in over 100 countries.

‘No dPMR product is commercially available as yet, beyond an PMR446 radio from Icom,’ he says. ‘The NXDN manufacturers, Kenwood and Icom, claim that their Nexedge and IDAS products are dPMR, when in fact they are developed against the similar, but proprietary, NXDN standard.’

And, while it is true that dPMR and DMR are the two ETSI standards for Digital Air Interfaces, Mike Atkins, MD at Kenwood Europe, says his other protocol, Nexedge, is gaining strong sales in many markets including the UK.

This is 6.25KHz FDMA technology, like dPMR but uses the NXDN air interface jointly developed between Kenwood and Icom.

‘The fact that Nexedge is not an ETSI Standard does not of course preclude it from use in EU Countries,’ explains Atkins.

‘Users and regulators are seeing the benefit of true 6.25KHz frequency usage as more users can fit into the same channel, providing savings for the user and additional income for the regulator – potentially very important in the current economic climate.’

According to Atkins, one of the major benefits of Nexedge is its ability to provide full control channel trunking, like the Analogue MPT, so it can be viewed as a kind of Digital MPT system.

He believes its migration path is the most flexible of all of the technologies because it has a mixed mode, which allows simultaneous use of analogue and digital, giving users the ability to combine both old and new radios on the same system.

If you are confused then you are not alone. Gee Siong, attempts to offer some clarity.

‘The obvious advantage of DMR is the absence of a need to do frequencies re-farming,’ he says.

‘This ETSI & FCC approved standard had been in the market since 2007 when Motorola and Selex released their products to the market.’

Indeed, to date, the DMR MOU have more than a dozen members, which include both Icom and Kenwood. With several of these having already released their DMR products or  releasing their products soon.

‘In addition measurement from both MOTOTRBO and Hytera DMR portable confirms that there is an energy saving of 40% thus extending an otherwise 8 hours battery life for an analogue radio to 11 hours when operated in TDMA mode,’ adds Gee Siong.

For anyone that has ever owned an iPhone, you’ll know that a major challenge with hand portable devices is the battery life. 

Bishop says because of the two-slot TDMA nature of DMR, products developed to this standard provide greater power efficiency. 

‘An individual call uses only one of the two timeslots, so it requires only half of the transmitter’s capacity,’ he says. ‘The transmitter is idle for half of the time. In a typical duty cycle of 5% tx, 5% rx and 90% idle, the transmit time accounts for a high proportion of the battery current drain. By reducing the transmit time by half, DMR can enable a 40% improvement in battery life and talktime compared with analogue.’

Two-slot TDMA means that DMR can be used to simultaneously transmit voice and data on the same 12.5KHz channel. This means that when voice is utilising the first timeslot, data can be transmitted on the second. 

‘The future roadmap for DMR allows for the two timeslots to be combined to effectively double the data rate to 9.6Kbps,’ says Bishop.

Tom Mockridge, chair of the Technical Working Group at the DMR Association, agrees that the differences between DMR and dPMR stem from the fact that DMR uses two slot 12.5KHz TDMA technology and dPMR uses 6.25KHz FDMA, something which has a number of consequences.

‘DMR uses less infrastructure equipment per channel and therefore has lower costs per channel in any system that has infrastructure,’ he adds. ‘Today, pretty much all customers deploy digital use infrastructure because it’s at the high end of the market so this is a real consideration to them.’

DMR technology can also have advanced features like reverse channel signalling, full duplex calls, can double data rates compared with dPMR and run voice and data applications together by using both time slots together in innovative ways - as well as do basic voice and data at 6.25KHz efficiency. 

Mockridge says dPMR does not have this flexibility as it is limited to 6.25KHz bandwidth and it is this that makes DMR well suited to professional sophisticated systems while giving buyers room for growth and development.

At present many more manufacturers are building to the DMR standard. Motorola, Hytera, Selex Communications and Radio Activity all build DMR products today, while Vertex Standard, Tait, Sepura, Team Simoco, and specialist rail radio manufacturer Funkwerk have all declared they are launching DMR products soon.

In addition, Mockridge says there is activity among other Chinese vendors, something that gives buyers great choice and security of supply. 

‘For example, simulcast is available from two DMR infrastructure vendors today,’ he adds. ‘Also the DMR market is very attractive to the application developer community because of the wide cross industry support.’

Many believe DMR is easier to adopt in mature markets like those in Europe, the US and some parts of Asia because it’s just plug and play. At the same time others feel that the lower cost and less complicated dPMR technology is well suited for emerging markets where the frequencies are yet to be assigned or occupied in countries such as India, China, Indonesia and parts of Eastern Europe and South Africa. These are counties where there is a large population and the need for future capacities are high, and can benefit from the dPMR lower direct material cost.

As Gee Siong points out: ‘The two technologies are pretty futureproof as long as the fundamental requirement is to provide a good talk range.’ 

That said, the future can be full of surprises, and what is considered high tech and acceptable now can be obsolete in a few years. 

‘So, until some smart Alec comes up with some new technology, dPMR and DMR will be the key technologies for the PMR market for years to come,’ he says.

A question of standards
There are four digital standards, three of which originate from the European Telecommunications Standards Institute (ETSI) in Europe. These are TETRA, Digital Mobile Radio (DMR) and digital Private Mobile Radio (dPMR). 

The other, Project 25 (P25), was developed by the Telecommunications Industry Association (TIA) in the US. Kenwood and Icom have also developed another proprietary technology known as NXDN.

Written by Wireless magazine
Wireless magazine

1Comment

  1. pete hizzey
    Pete Hizzey 29th Nov 2010

    Your recent article entitled Space Invaders DMR v dPMR caught my attention but unfortunately for the wrong reasonsYou devoted virtually a quarter page...

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