RCS NextGen RCS Board of Directors Regular Meeting via Microsoft Teams Meeting

MtnBiker2005

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RCS NextGen RCS Board of Directors Regular Meeting via Microsoft Teams Meeting - (Public Meeting) Everyone is welcome to join.

Join Microsoft Teams Meeting via the phone number or by using apps on your iPhone/iPad/Android and other devices running the Microsoft Teams Meeting apps.

+1 619-535-0693 United States, San Diego (Toll)

Wednesday July 8, 2020 1:00pm (Pacific Time) Board Meeting Conference ID: 294 385 434#

Although members of the public are encouraged to participate via teleconference,
RCS has designated the following physical location for public participation:
County Operations Center - 5500 Overland Ave., Room 120, San Diego, CA 92123
Members of the public planning to participate the meeting in this location are required to wear
masks and to follow social distancing protocol.

Wednesday July 8, 2020 Agenda

https://www.rcs800mhz.org/board-of-directors

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Alain

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Don, congratulations on a well deserved retirement! I'm sure that I speak for folks on this San Diego forum when I say thank you for all of the tips and input that you have given this group in the past 17 years. We wish you a very pleasant transition into retirement. Please don't be a stranger here; we've always valued your thoughts and opinions and look forward to the same---as time permits!
 

Mike_G_D

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I'll heartily second what Alain said! Congratulations on a job/career well done and enjoy your retirement! And yes, please stick around and chime in anytime!
 

musician2111

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@Don. I saw that your location avatar said VA which got me thinking. Google search didn't turn up any county of san diego news feeds about your retirement. Hell, even the RCS webpage shows you are still the Ops Manager.

As a former Deputy, I want to say thank you for all of your years of hard work, especially after the 2003 and 2007 wildfires which fundamentally changed how public safety agencies moved forward with their communication centers and radios.

Fair winds and following seas, good sir. May retirement bring about more adventures and less taxes!
 

K6CDO

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@Don. I saw that your location avatar said VA which got me thinking. Google search didn't turn up any county of san diego news feeds about your retirement. Hell, even the RCS webpage shows you are still the Ops Manager.
Thank you. Thursday was my last day. I suspect it will take a couple of days for the web team to get to the page to update it.

As I posted on social media, "man. what a ride." From VHF conventional in the 1970s to 800 MHz P25 today, and all of the other technological changes I've witnessed, it has been quite a career. Now, to go do some different fun things ...
 

MtnBiker2005

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FEB 10, 2021 NextGen RCS Meeting Agenda (PDF) - Meeting Wednesday 1:00pm. Public Meeting

(Anyone from RadioReference Forum Members or Public can talk/listen to the meeting via the Microsoft Team app/phone number.)

11. Main Agenda
11.3 DOJ encryption mandate

Join Microsoft Teams Meeting 619-535-0639 Phone Conference ID# 500 535 908#
https://teams.microsoft.com/dl/laun...rue&enableMobilePage=true&suppressPrompt=true

February 10th Agenda - (PDF)

 
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MtnBiker2005

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Wednesday May 12, 2021 1:00pm NextGen RCS Meeting.

RCS NextGen RCS Board of Directors Regular Meeting via Microsoft Teams Meeting - (Public Meeting) Everyone is welcome to join.
(Could be the last call in/online meeting)

Major Projects Update
9.1 RCS Site Projects Status
9.2 NextGen RCS Project Status

Main Agenda
11.1 Presentation on RCS system performance

10.1 Request the RCS Board approve a customer agreement with Equinox Gold Corp., Western Mesquite Mines, Inc. for up to 10 radios.

10.2 Request the RCS Board approve Metropolitan Transit System (MTS) to increase their radio limit from 170 to 245 radios.

MAY 12 2021 NextGen RCS Meeting Agenda
https://www.rcs800mhz.org/board-of-directors

———————————————————————

Join Microsoft Teams Meeting via the phone number or by using apps on your iPhone/iPad/Android and other devices running the Microsoft Teams Meeting apps.

Wednesday May 12, 2021 1:00pm (Pacific Time) Board Meeting Conference ID: {Check Agenda}
Conference ID: 740 509 540#

Microsoft Teams App for iPhone/iPad
https://apps.apple.com/us/app/microsoft-teams/id1113153706

Microsoft Teams app for Android devices
https://play.google.com/store/apps/details?id=com.microsoft.teams&hl=en_US
 

inigo88

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Looks like National City is doing some TDMA.
Correct that’s just been updated, although there’s still a mix of FDMA and TDMA on their talk groups. The way P25 Phase II systems work is the zone controller keeps track of all radios affiliated with that talkgroup, and if they are all TDMA capable then the system automatically switches the talkgroup to TDMA. If any older non-TDMA capable radios are also affiliated then that talkgroup will revert to Phase I FDMA.

National City PD must have mostly updated their radios, because the majority of their comms are now TDMA with the occasional FDMA mixed in.

Not many south zone agencies have made the switch yet. The only full time TDMA agencies on south as far as I can tell are Grossmont College PD and CALTRANS.
 

es93546

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NCPD TDMA... Is TDMA encryption?
Any P25 system, whether conventional or trunked can be encrypted. Phase 1 includes both conventional and trunked systems. The Phase 1 uses "Frequency Divided Multiple Access," so when necessary a 12.5 kHz signal is divided into two 6.25 kHz signals so that 2 simultaneous conversations can occur (different talkgroups on trunked systems) on one 12.5 frequency. Phase 2 trunking uses " Time Divided Multiple Access." The frequency is divided into time slots and 2 simultaneous conversations can be carried (2 talkgroups). The radio switches back and forth so rapidly that neither person on each talkgroup can detect the switching between the 2. So both TDMA or FDMA each can be encrypted or not.
 

inigo88

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Any P25 system, whether conventional or trunked can be encrypted. Phase 1 includes both conventional and trunked systems. The Phase 1 uses "Frequency Divided Multiple Access," so when necessary a 12.5 kHz signal is divided into two 6.25 kHz signals so that 2 simultaneous conversations can occur (different talkgroups on trunked systems) on one 12.5 frequency. Phase 2 trunking uses " Time Divided Multiple Access." The frequency is divided into time slots and 2 simultaneous conversations can be carried (2 talkgroups). The radio switches back and forth so rapidly that neither person on each talkgroup can detect the switching between the 2. So both TDMA or FDMA each can be encrypted or not.
From what I know Phase 1 isn’t advanced enough for 6.25 KHz spaced FDMA. Phase 1 channels are 12.5 KHz wide like conventional narrowband FM frequencies, but using C4FM (non-simulcast) or CQPSK (simulcast) modulation. The wiki has a great overview here:APCO Project 25 - The RadioReference Wiki

The only 6.25 KHz wide digital voice mode I’m aware of is NXDN. If you ever get a chance to play with a software defined radio this can be illustrated visually on the “waterfall display” (frequency on the x-axis, time on the y-axis). If you compare a P25 transmission (12.5 KHz wide) to an NXDN transmission (6.25 KHz wide), the NXDN is actually half as wide, because it’s taking up half the bandwidth. :)

But agreed that FDMA vs TDMA does not equal encryption.
 

Mike_G_D

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From what I know Phase 1 isn’t advanced enough for 6.25 KHz spaced FDMA. Phase 1 channels are 12.5 KHz wide like conventional narrowband FM frequencies, but using C4FM (non-simulcast) or CQPSK (simulcast) modulation. The wiki has a great overview here:APCO Project 25 - The RadioReference Wiki

The only 6.25 KHz wide digital voice mode I’m aware of is NXDN. If you ever get a chance to play with a software defined radio this can be illustrated visually on the “waterfall display” (frequency on the x-axis, time on the y-axis). If you compare a P25 transmission (12.5 KHz wide) to an NXDN transmission (6.25 KHz wide), the NXDN is actually half as wide, because it’s taking up half the bandwidth. :)

But agreed that FDMA vs TDMA does not equal encryption.
Yes, P25 P1 is ONLY 12.5 kHz (at its narrowest) and is FDMA. That is why P2 is an option - it increases the channel capacity to the equivalent of two simultaneous talk paths per one 12.5 kHz RF channel bandwidth using a TDMA multiplexing methodology (seperate time slots per voice "channel"). So the net RF channel bandwidth for both P25 P1 and P25 P2 is the same BUT P2 allows two voice paths per that bandwidth while P1 allows only one.

Likewise, DMR uses two slot TDMA in one 12.5 kHz bandwidth channel to provide 6.25 kHz "equivalent" though I think new systems can go to 12.5 kHz RF bandwidth - not

The only current 6.25 kHz RF channel bandwidth capable system that is popular in the US is NXDN which is a fully FDMA system.

-Mike
 

es93546

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From what I know Phase 1 isn’t advanced enough for 6.25 KHz spaced FDMA. Phase 1 channels are 12.5 KHz wide like conventional narrowband FM frequencies, but using C4FM (non-simulcast) or CQPSK (simulcast) modulation. The wiki has a great overview here:APCO Project 25 - The RadioReference Wiki

The only 6.25 KHz wide digital voice mode I’m aware of is NXDN. If you ever get a chance to play with a software defined radio this can be illustrated visually on the “waterfall display” (frequency on the x-axis, time on the y-axis). If you compare a P25 transmission (12.5 KHz wide) to an NXDN transmission (6.25 KHz wide), the NXDN is actually half as wide, because it’s taking up half the bandwidth. :)

But agreed that FDMA vs TDMA does not equal encryption.
Thank you for the information both you and Mike provided. I read about the 6.25 kHz splitting somewhere and it fell in line with my knowledge of what FDMA stands for, which is FREQUENCY DIVIDED Multiple Access. I looks like I'm wrong or I just looked up the wrong website a while back. Why would it be called frequency divided is it doesn't divide the frequency into two signals and why would it say "divided multiple" access? I

I guess, given Mike's information, that I might have been looking at a commercial DMR website and read out of context. Even so I'm still a bit confused as to my question above.
 

Mike_G_D

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FDMA IS Frequency Division Multiple Access.

Technically, if you wanted to, you could apply the term to any non-direct sequence spread spectrum non UWB (UWB - "Ultra Wide Band") radio boradcasts...even regular AM and FM broadcasts that are otherwise not further multiplexed in some way so as to contain more than one message path within one RF channel content. And, yes, I know stereo FM is multiplexed but trying to keep it simplified here.

USUALLY, however, FDMA is used in a "system" context. In the early days, wireline telephone ruled and when they started trying to find ways to send multiple voice streams down a trunk line one of the first technologies used was to upconvert the voice into a higher frequency band, RF, and then subdivide that into separate voice channels...all analog technology...hence "FDMA - Frequency Division Multiple Access".

Another usage was in satellite technology - again, mostly telephone driven. Here again, you would have one big "pipe" that was usually a large bandwidth that was then sub-divided into smaller channels with independent voice paths. Again, classic "FDMA".

When digital technology became cheap and widely available enough to be practical the concept of "TDMA - Time Division Multiple Access" became really practical. The concept could, in theory, be applied in a purely analog fashion but is/was problematic and not widely used. However, once the voice could be properly quantified in digital format it became relatively "simple" to apply the concept with fast processing to interleave two or more bit streams, each dedicated to a single voice or data path, using precise timing to keep each stream separated in time.

But digital signals can also just as well be handled by the old FDMA methods, of course. In fact, they usually are anyway even if they are further separated by time division methods as in the case of most LMR (Land Mobile Radio) applications.

Fast forward to today and the advanced digital trunking systems used and you once again, get the multiplexing concept re-applied.

In general, the FDMA vs. TDMA "battle", "debate", whatever, in terms of today's system architectures is how the SYSTEM handles the multiplexing - whether it be by time division or by frequency division, with the "systems" usually being trunked LMR or cellular telephone in nature. As stated earlier, even so-called TDMA systems are ALSO FDMA because each RF carrier is separated by channels BUT each carrier, in a TDMA system, then has separate "time slots" effectively becoming two (or more depending on the TDMA version used). In, however, a purely FDMA system, no further multiplexing is done outside of the finer subdivision by frequency.

TDMA, due to the usual requirement for a very precise and centralized time signal for each subscriber unit to synchronize with in order to allow them to separate the time slots effectively in both uplink and downlink paths to the repeater normally require the repeater to provide that synchronizing timing information. Newest technology by Motorola and others can allow simplex TDMA between mobile or portable units by essentially making one unit in a group the "master" and all the other units in that group time sync off that master and allow the usage of TDMA to provide more than one talk path per carrier even when no centralized repeater timing information is available. However, in most cases, TDMA is not used in simplex digital communications and the full RF bandwidth is usually used for one digital voice path whether it be a nominally TDMA or FDMA system so, effectively making the TDMA units FDMA only.

One big "neat special application" of the above, however, is the use of something called a "simplex repeater" which, in TDMA terms, can be effectively implemented by setting up a central unit in a high central location that can receive on one time slot and transmit on the other time slot. This effectively makes a "repeater" out of this station but, unlike a normal duplex RF repeater that requires the ability to transmit and receive simultaneously on two separate RF frequencies, this type of system does not require a duplexer and or separate antennas, etc. - it is all done using just one RF channel and the "repeating" is done on separate time slots. An additional advantage of this system is the ability of the subscribers to seamlessly move off the repeater into unit-to-unit simplex mode with the loss of the repeater signal without the subscribers even needing to switch to "talk-around" as in normal legacy analog or digital repeater scenarios (as I understand it - that is what I have read but have not dived deep into this so do your own research here to confirm).

Now, with regard to FDMA - that "old" multiplexing concept hasn't "stood still" with the rise of advanced digital radio systems. Now we start to get into the "battles" that spring up between different companies providing LMR products and how they embrace their "preferred" technology and produce competing products accordingly.

So we get, as a good example, Icom and Motorola. Icom (and initially, Kenwood) embraced an advanced digital FDMA systemology called "NXDN" that used very precisely controlled centralized RF carriers and extremely tight IF filtering and/or DSP (Digital Signal Processing) IF and post IF digital filtering and processing plus advanced vocoder technology to cram voice frequencies into a very narrow bit stream so as to provide extremely narrow digital RF voice paths seperated only by frequency but into, as stated, such small RF channels that could not practically be applied to analog FM channels (the deviation becoming so narrow, then, that any real advantages of the use of analog FM are pretty much negated) and THAT, grasshopper, is what most in the LMR world now mean when they bring up "FDMA" these days!

Sorry for the admittedly long run-on sentence...

Anyway, Motorola, meanwhile, embraced the tried-and-true TDMA concept and went with DMR which inherently uses a TDMA method.

When the (latest - there have been others in the past, oh yes!) FCC narrowband mandate came about, Motorola crammed the "bandwidth equivalent" concept down all throats stating that within a 25 kHz bandwidth (and later 12.5 kHz bandwidth) they could have two voice paths resulting in an "equivalent 12.5 kHz" (later "equivalent 6.25 kHz") bandwidth.
Only if you define the bandwidth solely in terms of modulated RF carriers can you call this to task. So, even though one DMR carrier may occupy the wider bandwidth it DID allow two voice paths within that wider bandwidth so was, effectively, "equivalent" to having two separate RF carriers in two narrow channels that together would equal the wider bandwidth of the DMR signal.

So, then, you have the "argument" between Motorola and Icom. Icom can claim that only they, using an advanced digital FDMA method, actually provide a true extremely narrow frequency separated methodology to provide separate voice paths per RF carrier. But Motorola, (and DMR in general) still can claim - in the final net view, "what's the real practical difference?!" DMR uses TDMA to cram two voice paths in the larger RF modulated carrier bandwidth so makes the capacity (relative to the stated RF channel used bandwidth) the "same". After this you get to the finer points of occupied bandwidth and adjacent channel power which I am not going to delve into here.

Kenwood initially went along with Icom in embracing NXDN only but later submitted to the inevitable popularity of DMR, helped significantly along by the backing of Motorola, and began producing DMR subscriber units. In fact, they now have units that can do multiple protocols, P25, DMR, and NXDN, simultaneously (well, actually, any two of those).

So back to P25. P25 has actually been around a long time now. "Phase 1" of P25 was all really just based on replacing analog FM with a digital modulation equivalent and not as any method to add capacity. It was, therefore, "FDMA" only but not really making the occupied bandwidth that much less than a typical analog FM system. I think they started with a 25 kHz bandwidth and then later went to 12.5 kHz along with the narrowband mandate; I think they can do 6.25 kHz but am not sure about that (read - do your own research here). Phase 1 could be applied to simplex, repeater conventional, as well as trunked systems. Anyway, "Phase 2", on the other hand, was defined from the start as a TDMA system and included trunking protocols that allowed two time slots per occupied RF bandwidth. In this sense, it is "like" DMR" but DMR is a newer and more advanced (in some ways) technology. But "Phase 2" P25 really is TDMA and can provide double the capacity of a FDMA only Phase 1 system. When conventional (non-trunked) or simplex, however, P25 is usually Phase 1 only but, I think, now some conventional (non-trunked) repeater systems are being used as P2 TDMA - again, do your own research on this as I am not sure about this.

Another advantage of TDMA RF systems vs. FDMA only (in its current advanced digital implementation) is "less plumbing" at the repeater end. This is because, with FDMA systems, you need speciallized tightly tuned duplexors, filters, etc., that help to make the tightly spaced ultra narrow signals practical, and you still need separate RF channels per voice path just as with old legacy FM and digital conventional repeater systems. TDMA, it can be argued, is "easier" to double the capacity of one repeater allowing two simultaneous (from a human user perspective) per one repeater in a conventional system WITHOUT making it necessary to add additional RF components. This makes it more "palatible" to many business users relying on more and more support from "IT" departments who are computer savvy but not usually "RF savvy". TDMA can be thought of in the sense that the "heavy lifting" is done more in the computer processing and programming arena and not as much in the RF arena as a fully NXDN type FDMA system. There is a LOT more to this than I am going to go into here and both system methodologies have their adherents and proponents, detractors, etc.

Sorry for the length and detail above but I hope it helps you grasp the "FDMA" vs "TDMA" "discussion" better in terms of today's modern LMR system implementation concepts.

-Mike
 
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es93546

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Mike, thank you for your knowledgeable and well written response to my question. I've learned oodles of things. You explained this better than a few others who have tried to answer my questions.

I paid particularly close attention to the subject of the simplex repeater. The Southern California Edison digital trunked system, the older one, had what SCE labeled as "Intellirepeaters" or some such. They were single frequency pair repeaters used to "fill in" areas of marginal coverage. These, I assume, somehow carried along what talkgroup the operator and a base station were using. However, when I finally go through the FCC licenses issued to SCE, whenever I get a chance (low priority given everything else in life), I will note if some licenses will list only the typical base frequency (downlink) in a location minus the mobile or uplink frequency. This, without your wonderful post, would have confused me and I might have assumed it was a tactical or simplex talk around frequency, which SCE has, but I can now take a better look and would program that frequency in for the system in the scanner that covers that area. Will the current SDS and BCD325P2 radios decipher these simplex repeaters? I assume that talkgroup information is carried by these newer repeaters and my 325 will show "District XX Ops" like the multi frequency trunked repeaters do.

Thanks again for your time. I'm not a techy, I'm someone who majored in a biology field in college and find purely techy subjects a bit challenging, mostly because techies are challenged trying to communicate what they know in a way I can (and other non techies) understand. Although I'm not a techy, I do love to understand how things work, so I thank you again for the rest of the post. It will help with this hobby.
 
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