Advantages of DMR versus dPMR / NXDN / NEXEDGE

dmr-vs-dpmr-nxdn-nexedgeWhat is dPMR?

  • dPMR is an ETSI standardised minimal cost digital radio solution.
  • dPMR standards (TS102 490 and TS102 658) were published in 2007 – after DMR. There are 2 tiers specified – Tier 2, modes 2 & 3 are relevant to professional users.
  • dPMR operates in 6.25kHz channels. Tier2, Mode2 is conventional; Tier2, Mode3 is trunked.
  • NXDN is based on dPMR but is incompatible with it. NexEdge is also derived from dPMR.

What is DMR ?

  • DMR is an ETSI standardized low cost, low complexity, professional digital radio solution designed to migrate analog FM radio users to digital.
  • DMR standards (ETSI TS102 361) were published in 2005. There are 3 ‘Tiers’ specified – Tier II and Tier III are of interest to professional users.
  • DMR operates in 12.5kHz channels and uses 2 slot TDMA (Time Division Multiple Access) to achieve 6.25kHz equivalence. Tier II is conventional, Tier III is trunked.
  • Provides a simple path to migrate analog FM LMR users to 6.25kHz digital radio technology.

Key Differentiators

Spectral Efficiency

Both DMR and dPMR / NXDN / NexEdge appear to achieve 1 communication path per 6.25kHz of spectrum, but:

  • In the case of an event (emergency), when you need the radio system the most, dPMR / NXDN / NexEdge will suffer increased interference meaning a user can only reliably use every other 6.25kHz channel.
  • DMR will achieve 1 communication path per 6.25kHz of spectrum irrespective of loading; twice the capacity of Analog narrowband FM.

Ease / cost of Migration from Analogue FM

  • An analog FM user migrating to DMR can replace every analog FM base station / repeater with one DMR base station / repeater and achieve double the capacity.
    • One DMR base station / repeater ‘operates’ two communication paths in 12.5kHz of spectrum.
    • This means an analog FM user migrating to DMR can re-use existing infrastructure, existing sites, and existing frequencies.
    • It is a very simple migration.
  • An analog FM user migrating to dPMR / NXDN / NexEdge will need to replace every analog FM base station / repeater with two dPMR / NXDN / NexEdge base station / repeaters and an extra combiner to achieve double the capacity.
  • dPMR / NXDN / NexEdge Terminals are cheaper than DMR terminals, but for the reasons above you need twice as many repeaters, so dPMR / NXDN / NexEdge infrastructure costs are much greater and wipe out the terminal cost benefit.

Portable Battery Shift Life

  • A DMR Portable achieves 40% longer battery shift life than an analogue FM portable.
  • A DMR portable achieves 20% greater battery shift life than a dPMR / NXDN / NexEdge portable.

Important Takeaways

  • DMR is a professional solution designed for higher volumes of radio traffic over wide coverage area.
    • DMR will achieve twice the capacity of Analog narrowband FM systems, and provide reliable communications regardless of loading.
    • DMR is an excellent fit for low cost, mission critical applications. GridLink (many small data messages coming from throughout a large area) is a perfect application for DMR.
  • dPMR / NXDN / NexEdge is designed as a minimum cost digital radio solution.
    • When heavily loaded, dPMR / NXDN / NexEdge may only achieve the same capacity as analog narrowband FM before communication becomes unreliable. This makes it a poor fit for mission critical applications.
  • dPMR / NXDN / NexEdge infrastructure costs may be up to double those of DMR.

Questions to Think About

  • Do you have an existing analog FM LMR radio system you are looking to replace? If so, what type of system is it (conventional, trunked eg: MPT1327)?
  • How many sites does your system use? How far apart are they? Do you have good coverage now, or are there dead spots you need to fill?
  • What frequencies / channels do you have licenced? Do you want to re-use these?
  • How many users will there be on the system? How are they distributed throughout the covered area? Is the main use voice or data? If voice – how long is a typical conversation? If data, how long is a typical message?
  • Is system reliability and low cost important to you?
  • Do you maintain your own radio system? Would you consider it being managed?

If you are considering migrating from an analog system and need help with working through the above questions or with a deeper dive into your system design, please feel free to contact us.

Over the coming weeks, we will go into this topic in much more detail. To ensure that you don’t miss out, please follow our blog via email.


megan-cta-images-white-papers2-1Be sure to download our complimentary whitepaper, Digital Radio Standards Uncovered, where you’ll learn more about the differences in performance of DMR compared with dPMR, and get further information on currently available open standard, digital technologies.

You can also download Digital Radio Standards: Advantages and Disadvantages of Current Digital Radio Standards for a summarized comparison.megan-cta-images-white-papers3

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Comments

  1. Jack says:

    At low signal levels (when on an analogue system, the squelch gate intermittently closes), which system performs better, DMR or NXDN? Does the longer frame length of DMR cause it to drop out more frequently and take longer to recover than NXDN?

    • Christine Gooding says:

      Hi Jack. Thank you for your question. Assuming you’re talking about delivered audio quality at edge of coverage, there will be very little difference between DMR & NXDN. The coverage of both these systems is about the same as analogue was.

  2. Jack says:

    I guess with DMR you can’t use the adjacent 12.5kHz channel either in which case you will only use alternate 12.5kHz channels, so in the big picture, the same as NXDN: “In the case of an event (emergency), when you need the radio system the most, dPMR / NXDN / NexEdge will suffer increased interference meaning a user can only reliably use every other 6.25kHz channel.”

    Battery life may seem an issue to some sales people but with the advent on Li-ion batteries it is not a real issue. If one wanted to make it an issue, consider this: With customer doing GPS tracking of portables, most of the data transmitted is the GPS data, not the encoded voice (situation dependant but noticeable on solar powered repeater sites when customers with GPS tracking come aboard). With this in mind the extra bits in a DMR frame, compared with a NXDN frame, would make the battery life on a DMR portable less than with NXDN. “A DMR portable achieves 20% greater battery shift life than a dPMR / NXDN / NexEdge portable”

    With the same noise figures on front ends and optimised modulation index I fail to see how a narrower bandwidth is not more sensitive. “The noise bandwidth is less, but that doesn’t mean the Rx sensitivity is 3dB better”

  3. JJ says:

    How do you justify the following statement: “In the case of an event (emergency), when you need the radio system the most, dPMR / NXDN / NexEdge will suffer increased interference meaning a user can only reliably use every other 6.25kHz channel.”?

    Why can a dPMR/ NXDN / NexEdge/ IDAS system not reliably use all configured 6.25KHz channels at the same time?

    With regard to battery life. A TDMA radio transmits 1/2 of the time, resulting in a reduction of battery capacity used. On the other hand a FDMA radio receiver with 6.25Khz channel band width will see half the noise compared to a 12.5KHz radio. This means that the transmit power of the radio can be halved, meaning that a TDMA radio and a FDMA radio should have a similar battery life.

    • Hi JJ,

      The answer to your first question – it is because the adjacent channel noise is 10dB worse for a 6.25kHz dPMR system than it would be for a 12.5kHz DMR system.

      The answer to the second question is that even if you turn the dPMR Tx power down to half that of the DMR transmitter, the current drawn from the battery won’t decrease by a half. So, you don’t get the same battery life as DMR TDMA. Additionally, the Tx power needed for dPMR can only be half that for DMR if you accept a coverage reduction (The noise bandwidth is less, but that doesn’t mean the Rx sensitivity is 3dB better).

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