roaming feature on gd77

Post Reply
va3ipg
Posts: 2
Joined: Sun Nov 14, 2021 11:57 pm

roaming feature on gd77

Post by va3ipg » Mon Nov 15, 2021 12:31 am

Hi, Roger.
Is it possible to add the roaming feature to the firmware on the gd 77? that would be amazing! I only use the dmr with repeaters around me, and here in Ontario, there are enough repeaters for us to drive from detroit(usa) to montreal(quebec) using the transceiver without losing the connection with a tg. thanks for all the work you and your team has been developing for all of us, hamradio operators. best 73 de va3ipg

kt4lh
Posts: 272
Joined: Sun Jan 12, 2020 4:27 am

Re: roaming feature on gd77

Post by kt4lh » Sat Dec 04, 2021 2:33 pm

ve7mdt wrote:
Sat Dec 04, 2021 8:11 am

The Anytone models have roaming feature, but it is incompatible with most repeaters in the Pacific Northwest here that it is discouraged to be used. However, The MotoTRBO ones are good for this.
Actually, the Anytone radios have GPS based Zone Roaming now :)

VK3KYY
Posts: 7437
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: roaming feature on gd77

Post by VK3KYY » Sun Dec 05, 2021 9:09 pm

The supported radios do not have hardware which is capable of this.

It either requires 2 receivers, or it requires a receiver which is capable of quickly switching frequency and sampling the RSSI quickly.

These radios only have one receiver
They also take a long time to change frequency, and around 25ms before the RSSI value can be read after the frequency has changed and at that time the RSSI value is inaccurate because the internal hardware in the RF chip is not stabilised. (The RF Tx/Rx chip in this radio is literally a $1 part)

Hence its not even possible to change frequencies on the alternate TS to the one the radio is actively receiving, and changeing freq to another repeater to get the RSSI, before swictching back to the original repeater.

UA0LMC
Posts: 53
Joined: Thu Oct 01, 2020 6:09 am
Location: Vladivostok, Russia

Re: roaming feature on gd77

Post by UA0LMC » Wed Dec 08, 2021 1:40 am

ve7mdt wrote:
Sat Dec 04, 2021 8:11 am
To put in in very simple terms, the way MotoTRBO radio does it is that it scans the repeaters in the roaming list for the best signal, and then park the active channel on that repeater until it is no longer the best, as it continues to scan. The way Anytone does it is that it "kerchunks" the repeater, and that messes up the network badly, and that's frowned upon, at least in the PNW area here.
In fact there are two roaming strategies: active and passive (see below).
In your example, Motorola uses passive roaming strategy (it can also be configured via CPS to use active strategy if required) - and Anytone uses active strategy (it probably could be configured to use a passive one - but I have no info on this matter).

VK3KYY wrote:
Sun Dec 05, 2021 9:09 pm
The supported radios do not have hardware which is capable of this.

It either requires 2 receivers, or it requires a receiver which is capable of quickly switching frequency and sampling the RSSI quickly.

These radios only have one receiver
They also take a long time to change frequency, and around 25ms before the RSSI value can be read after the frequency has changed and at that time the RSSI value is inaccurate because the internal hardware in the RF chip is not stabilised. (The RF Tx/Rx chip in this radio is literally a $1 part)

Hence its not even possible to change frequencies on the alternate TS to the one the radio is actively receiving, and changeing freq to another repeater to get the RSSI, before swictching back to the original repeater.
Don't know is it worth to implement, it's up to you to decide. As for me - I'd prefer to manually switch the channels.
But in fact the radio has all the required hardware for both active and passive roaming.

1. Active roaming strategy has no requirements on the repeater-side - but it's very abusive.
The radio periodically sends a wake-up packet and listens to the repeater. If received signal is below the roaming RSSI threshold or there is no answer - the radio checks the same way for other repeaters in the roaming list, and picks one with the strongest signal (or at least the one above the threshold).

2. The passive strategy, however, requires some support from repeaters - namely DMR beacons. The time on all repeaters should also be synchronized for beacons to be transmitted more or less simultaneously.
Default settings, AFAIR, is to send the beacon every 60 seconds for at least 3 seconds - so no super-quick scanning or dual-reception is required.

The radio waits for the beacon and measures it's RSSI. If it's below the threshold, or if there is no beacon received at a predefined time (i.e. the signal is too weak) - the radio scans for other repeaters beacon in the roaming list, then selects one with the best signal.

G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: roaming feature on gd77

Post by G4EML » Wed Dec 08, 2021 11:20 am

UA0LMC describes the functions of roaming very well. It was designed to be used in a co-ordinated system where the system designer has control over the settings of both the repeaters and the mobiles and has the ability to position repeaters with the necessary coverage overlaps. It doesn’t work well in a typical amateur radio environment where there is no control over the way the system is configured.

Even on a properly configured system roaming has some limitations.
If you start to transmit on one repeater and move out of range during the call you will not be heard. There is no hand over like there would be on a cellphone.
If you move out of range of one repeater it can be several minutes before the radio finds another repeater. As described before this is because the beacon transmissions from repeaters only occur about once per minute.
It has no knowledge of user activated talkgroups and so will only work correctly if all repeaters are on the same ‘always on’ talkgroup.

For these reasons roaming is of limited use on the amateur system. A well organised zone with just the repeaters on you route which can be scanned or manually selected would provide a better solution.

Colin.

kt4lh
Posts: 272
Joined: Sun Jan 12, 2020 4:27 am

Re: roaming feature on gd77

Post by kt4lh » Fri Dec 17, 2021 2:49 pm

ve7mdt wrote:
Fri Dec 17, 2021 9:16 am
kt4lh wrote:
Sat Dec 04, 2021 2:33 pm

Actually, the Anytone radios have GPS based Zone Roaming now :)
I just read about that, but I haven't tried it yet. Will see how well it works when I get the chance to w/ my D878UV.
It Just Works, as long as you grok what it's doing.. GPS has to be on, and GPS Roaming has to be on. You can use either to toggle the roaming functionality in case you don't need it at a given time. ie: It doesn't do any GPS Roaming if either are disabled. Which is important because...

It evaluates the GPS Roaming List from the top-down; the first match it finds it sets the current "VFO" to. Doesn't matter if you changed it manually or what zone you're in, it'll change to the first match. If you switch to the other "VFO" (top/bottom), it'll switch it too. There's no way to exclude a zone from roaming or such. That's frustrating some folks, but it's more "conflicting requirements" than "bug".

But it does work. I've tried it here, I set my hotspot with a small radius with a repeater zone that covers my city. If I am at the house, it sticks to the Hotspot zone, if I leave the house, it flips to the DMR zone. Works well.

There could be enhancements, like the ability for a zone to not be roamed from. Perhaps the ability to define which "VFO" (top/bottom/etc) allows roaming so if you flip to the bottom one it doesn't roam so you can use an arbitrary zone, etc.

kt4lh
Posts: 272
Joined: Sun Jan 12, 2020 4:27 am

Re: roaming feature on gd77

Post by kt4lh » Fri Dec 17, 2021 2:49 pm

ve7mdt wrote:
Fri Dec 17, 2021 9:16 am
kt4lh wrote:
Sat Dec 04, 2021 2:33 pm

Actually, the Anytone radios have GPS based Zone Roaming now :)
I just read about that, but I haven't tried it yet. Will see how well it works when I get the chance to w/ my D878UV.
It Just Works, as long as you grok what it's doing.. GPS has to be on, and GPS Roaming has to be on. You can use either to toggle the roaming functionality in case you don't need it at a given time. ie: It doesn't do any GPS Roaming if either are disabled. Which is important because...

It evaluates the GPS Roaming List from the top-down; the first match it finds it sets the current "VFO" to. Doesn't matter if you changed it manually or what zone you're in, it'll change to the first match. If you switch to the other "VFO" (top/bottom), it'll switch it too. There's no way to exclude a zone from roaming or such. That's frustrating some folks, but it's more "conflicting requirements" than "bug".

But it does work. I've tried it here, I set my hotspot with a small radius with a repeater zone that covers my city. If I am at the house, it sticks to the Hotspot zone, if I leave the house, it flips to the DMR zone. Works well.

There could be enhancements, like the ability for a zone to not be roamed from. Perhaps the ability to define which "VFO" (top/bottom/etc) allows roaming so if you flip to the bottom one it doesn't roam so you can use an arbitrary zone, etc.

Post Reply