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Saturday, May 19, 2018

A National DMR Location Services Proposal


On the way back today from the Southern Berkshire Amateur Radio Club’s hamfest at the Goshen Fairgrounds of Connecticut proved a good opportunity to try out mobile location enablement via DMR.




Here is what was involved to make this work:
  • TYT MD-380G radio
  • JumboSpot Hotspot device
  • Mobile hotspot for internet via smartphone
  • Correctly programmed radio and Brandmeister account setup.
Some Lessons Learned

Compared to using APRS, which uses 144.39 MHz as a common national US frequency and a network of stations to ingest users packet transmissions directly or via digipeaters and igateways that can route data from "over the air" and onto the internet. Using DMR and “APRS like” functionality is different in how that same function is accomplished since it does not use AX.25 1200 baud packet..

The only way to get user reported location or messages to the aprs.fi website and back to other radios  is via your own DMR hotspot or a local repeater that is set up to allow private data calls to be passed through to the internet.

Smart Beaconing & Power Savings

APRS and much of the equipment available today supports a feature called “smart beaconing” which allows a user’s radio to transmit location data more often while traveling at higher speed compared to sitting stationary. The number of "beacon transmissions" are reduced thanks to smart beaconing to create less congestion on the dedicated national APRS frequency. More about smart beaconing can be found here and its other benefits.

The current implementation of location services on GPS enabled DMR radios such as the TYT MD-380G do not support smart beaconing, but can be user programmed to always beacon at preset intervals.  Smart beaconing provides the major benefit of better battery life and better route accuracy for APRS. 

Wish List Item #1: Location enabled DMR needs this same capability, especially for portable/handheld radios.

GPS location is only sent at a present interval or during PTT on a DMR radio, so there is no "smart" capability at present time.  Accurate travel routes can thus only be created based on how frequent the user transmits which explains the rather strange route shown on aprs.fi for this experiment. Not having smart beaconing makes DMR location enablement to be less accurate for route tracking and efficient spectrum management.

Routing & Prediction

The second lesson learned is that the APRS.fi website does not fill in better predicted routes if DMR location enabled transmissions are missed. In the case of the route 199 in New York, there is horrible mobile phone connectivity and my mobile phone did not have internet access the whole time, which prevented any GPS transmissions sent from the MD-380 to the JumboSpot from being reported.  Since there are no repeaters that cover this particular area or offer private data calls, the only way to use location enabled DMR is via a mobile hotspot. 

Wish List Item #2:  More capable repeaters are needed to fully realize DMR benefits.
Even when entering back into better mobile coverage areas on parts of routes 199 and 308, it was not safe and appropriate to continue pressing the PTT to send location packets to better report accurate “breadcrumbs” on the route since it would congest the frequency I was using with my hotspot.

Even during a discussion with another DMR user via TG 310, my  DMR radio only transmits the location data at the start of transmission. Having 30-45 seconds of my own transmit speech and then listening to a reply for as long a period spreads out the rate of GPS transmissions, which inhibits quicker location reporting via TG 310999.

National Proposal on using DMR and GPS

Some ideas to aid in adoption of using GPS via DMR  includes:
  • Add functions at the radio level that support smart beaconing rather than just setting a high rate of transmission or just via PTT. 
  • Have the radio acknowledge when its transmissions are not confirmed as being sent to the internet and to “buffer” them for later transmission to fill in gaps on possible routing.  This involves saving GPS locations with speed of travel and altitude which is available on the radio. This solves the gap issue and is not far different how many automotive GPS's work when loss of sky coverage happens. 
  • Create a network of receive only gateways on VHF or UHF to listen for data packets on common frequencies for the purpose of location messaging that will only pass traffic on a certain time slot (TS2) and destination talk group (TG 262993). 
  • Adding on transmit capability for a repeater that will broadcast private data calls to users that will not impact voice users at the same time.
  • Challenge repeater owners to add an additional equipment to support this function and make use of great siting available at repeater sites. Many repeater sites already host APRS digipeaters and have internet access so this should be easy to add and expand value offered by DMR.
  • Decide on two national frequencies for GPS messaging and reporting use for VHF and UHF.
Why do this with DMR rather than just use APRS?

APRS does many things well and is fairly simple which makes it appealing, but its age is starting to  show.

A shortcoming of APRS is the inability to easily deliver an actual street address level of resolution to a radio. All APRS radios can only show coordinates, bearing and distance to another user which is limiting at times.

Location enabled DMR provides the ability to match coordinates to a physical street address and see that on the screen of the radio.  This works simply by addressing a private message to TG 262993 by sending "gps" as a message.  The reply message takes your radio GPS coordinates, matches it against mapping API's via Google Maps or Open Street Mapping project where it finds the street address and then sends that back to your radio.



Other commands summarized in a previous article also allows you to see distance, bearing and street address closest to another location enabled DMR user.

Location enabled DMR also lets the user request weather conditions the same way by messaging to "wx gps". The resulting reply matches up the GPS enabled DMR radio with closest weather conditions found on the internet. Temperature, humidity and barometric pressure is than easily viewed on relatively inexpensive DMR radios. 



If using an APRS radio, the user needs to spend much more money to see this level of detail or sacrifice some level of portability if not using some of the advanced APRS handhelds currently available. 

Weather and location are just two easy examples of how to use location data as a source for value added information.  Sending email, local frequency information for voice communication and other data are easily routed or sent from a DMR radio.

These are some modern ways in which ham radio can remain relevant in a world of smart phone dominated but mobile network dependent messaging.

Wish List Item #3: Adding functions like this are what ham radio is all about, so perhaps more DMR repeater owners will start considering adding a simple weather station, offline mapping database and secondary receivers to support some of this functionality. 

Here is some further related reading on HVDN if this sounds of interest:








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