Subject: [NEXTEL-1] RE: Poll: Is APCO-25 an appropriate technology forPublic Safety?]

From: Marcel <[email-masked]>
Date: Wed, 15 Jan 2003 15:06:41 -0500

-------- Original Message --------
From: John Powell <[email-masked]>
Subject: RE: Poll: Is APCO-25 an appropriate technology forPublic Safety?

As a member of the P25 Steering Committee, chair of the NCC's 
Interoperability Subcommittee, and a public safety professional for over 30 
years (including experience as a dispatcher), I wanted to add some comments 
to the discussion string below.

John Powell

At 10:22 AM 1/15/2003 -0600, Lindsay C. Blanton wrote:
>Glen, sorry about the delayed response, but my schedule has been fairly 
>hectic this week.  My follow-up comments are listed below:
>
> >> Greetings! Lindsay,
> >> What do you do down there in SA?
>
>Glen, my primary job here in San Antonio is as a financial planner.  I 
>manage trunkedradio.net to "stay in the game."  ;-)
>
> >- voice delay in multi-radio environments
>
> >> I am not sure what you are referring to here. There is noticeable 
> processing delay if two radios are within ear shot of on another, which
> >> can be annoying. The practical solution to is simply to conduct 
> "simplex, radio to radio operations" in analogue.
>
>Yes, this is what I was referring to.  This noticeable processing delay is 
>a real pain for public safety officials who are all congregated on a 
>scene.   Speaking into the mike, and hearing yourself 1/2 sec later around 
>the scene is somewhat disturbing to the human mind.
>
>The practical solution to conduct simplex operations really doesn't fit 
>the intention or model of the Project-25 standard, since the original 
>intention of Project-25 is to reduce usage of bandwidth for public safety 
>communications models.  Exceptions for analog will negate the reason to 
>have a digital standard in the first place.

Many public safety officers are now using earpieces (usually of the 
custom-fitted variety).  This negates the problem you are referring to and 
greatly enhances officer safety and privacy of communications.  Once a P25 
system has been fielded for a period of time, users get accustomed to this 
audio delay.  As with any new technology, these initial complaints are 
often caused because it is "different from the way it used to be" - if you 
talk to folks who have used a digital system for some time, you will 
usually find that overall they like it much better than their old analog 
system.  Additionally, one of the biggest complaints of dispatchers (and 
I've been there) is audio feedback from multiple radios in the same 
location; the digital processing delay eliminates that problem.  And yes, I 
agree that analog operation defeats spectrum efficiency; it also can not be 
encrypted as required in many applications.

> >- high intensity voice handling (structure fire responses, foot pursuits 
> etc.)  Again, I am not sure to what you are referring here.
>
>What I refer to is:
>
>1.  On Scene Fireground communications.  Ambient noise levels are 
>extremely high, and signal strengths are low inside structures.  On a 
>fireground, a crew tends to "scream" into a radio, not hold it 2 inches 
>from the face and talk gently.  IMHO, the IMBE vocoder does not do a good 
>job of "reproduction" in these environments.

On the contrary, much of the testing that has been done (in labs, by 
independent panels and in the field) shows that the IMBE vocoder does very 
well in high noise environments.  For example, tests from the cab of a fire 
engine with its sirens on showed the IMBE to be clearly understandable when 
the analog signal could not be understood.  Likewise from helicopters, army 
tanks and other similar environments.  Radios of any kind are designed to 
operate within certain parameters, and garbled input isn't usually one of 
those. Again, a lot of these complaints go away when the users get 
accustomed to the new technology.

>2.  Ever heard an officer chase a suspect 10 blocks, in touch with a 
>dispatcher, over a Project 25 network?    Ask a seasoned police dispatcher 
>who works with a Project-25 system and they'll tell you it is extremely 
>difficult to understand the pursuing officer.  Furthermore, as an officer 
>gets into a remote area (creek bed etc.) where signals are notoriously 
>low, many times signal strength is low enough that the vocoder can't 
>recover  any voice frames.  In most cases, analog will make it through 
>enough to allow the dispatcher to get required info.

I've heard some pretty horrendous field operations on digital systems and 
find the overall performance to be at least as good as the analog 
systems.  In a couple of cases, these were side-by-side operations from 
different agencies on the same incident and the general performance for 
digital was just as good as analog.

>Project-25 signals do an outstanding job in low signal strength 
>environments.  The vocoder is able to use error correction to recover 
>voice frames that otherwise would generate a minor static on an analog 
>signal.  BUT, when you get to *very* low signal strength environments, 
>Project-25 doesn't make it through at all, whereas an analog signal might 
>barely make it to the repeater, but it still makes it, and a dispatcher's 
>trained ear is able to do a MUCH better job of voice recovery than any 
>vocoder on the market today.

I disagree.  Independent testing has shown that, with the same signal 
strengths into receivers of equivalent sensitivity, the coverage is just 
about equal.  When the P25 vocoder begins to loose significant frames such 
that the message can not be understood, the analog system likewise can't be 
understood by a trained ear.

>To expand upon this further.  The IMBE vocoder does a very poor job of 
>conveying voice emotion, which is an integral part of the public safety 
>communications process.  The subtle nuances that are involved between 
>officer/dispatcher communications are huge, with dispatchers trained to 
>pickup on these and react accordingly.   In fact, ask any professional 
>scanner listeners (yes, there are some!) and they'll tell you they can 
>listen to 10 different scanners at once and "pick out" a high priority 
>distress incident in progress.  A dispatcher is no differnt.  The IMBE 
>vocoder masks these nuances.

I'll agree on this one, though the IMBE vocoder is much better than 
some.  And it is a characteristic of all digital systems except those with 
very high data rates and bandwidths (such as telephones); there is just no 
way around it.

>..and I'll go even further.  Co-channel interference.   Ever heard 2 units 
>at once transmit at the same time on a Project-25 network?  Physics 
>doesn't allow it.  Remember the days of Motorola Smartnet analog systems, 
>where admins had the choice of deploying the system in "message" or 
>"transmission" trunking formats.  Transmission trunking was always chosen 
>over message trunking, because officers complained they could not transmit 
>if someone else was on the air.   2 analog transmissions at the same time 
>might cause a "Warble" or "masking", but a  trained dispatcher can 
>typically determine who transmitted, and pick out some of the 
>details.  That can sometimes mean the difference between life and death.

Yes, this is true of all digital systems though some of the digital voting 
systems offer interesting possibilities.  There are solutions, though their 
implementation (or lack thereof) is usually a matter of management 
decisions and training.  If a field officer is in a situation where he 
needs the air immediately, use the "emergency" button - that is what it is 
for.  So often, it is reserved for an "officer needs help" situation when I 
think a better use is "I have a priority/emergency 
communication".  Granted, this applies primarily to trunked systems, but 
there are also some interesting applications now appearing on conventional 
systems for these special features.

> >- all or nothing coverage.  It is a commonly held perception among the 
> uninformed, that digital coverage ends without warning. In reality, there 
> is plenty of warning for
> >> the end of your coverage... IF... you are trained to recognize it.
>
>Yes, understood here.  In fact, Motorola's product line of Project-25 
>subscriber equipment provides features  which can indicate this to the 
>user (audibly).

My experience is that digital offers better communications across a broader 
portion of the coverage area.  That is because bit errors (eg: static in an 
analog system) are recoverable over a significant area, whereas a high 
level of static makes analog systems nearly unusable.  Yes, there are ways 
of recognizing that you are in a digital fringe area, and we have talked 
about adding a standardized audible warning option into the P25 suite.

> >Has APCO-25 *really* accomplished what the end-user (dispatcher, PD 
> officer, FF etc) needs to do his job in a *more* effective manner?
>
> >>Absolutely.
>
>If your response of "absolutely" is in regards to the above, then, I 
>respectfully disagree.  I don't believe that APCO-25 has provided to the 
>end-user any additional functionality.  The only difference your average 
>firefighter or police officer sees is, well, everything that I have 
>described above.  If you mean Project-25  provides greater 
>interoperability, then I really disagree.  Many vendors and agencies have 
>publicly snubbed the Project-25 standard.  Just look at how my home town, 
>San Antonio TX, has chosen the path of an EDACS ProVoice system.  Even the 
>state of FL has decided to dismantle a Project-25 statewide system in 
>favor of a Proprietary solution, EDACS ProVoice.  Although the MA/COM 
>solution is based on the same IMBE vocoder, it doesn't help for statwide 
>interoperability.

ANY proprietary system goes against interoperability.  That is why the FCC 
has mandated P25 Phase I conventional for interoperability channels in the 
new 700 MHz public safety band where digital modulation is required.  That 
is why Pennsylvania has a P25 mode in its OpenSky system.  All of the major 
public safety vendors now offer, or will soon offer, P25 Phase I in their 
subscriber unit products, including MA/COM.  Let's be blunt on the FL 
situation: a purely political decision by a governor who wanted to 
privatize and a provider company that had strong political ties to 
officials in state government.  The P25 system FL was using worked well; it 
was designed by engineers who know Florida and its needs.  They are sure 
having implementation problems with their new system!  Why do you think 
local agencies are not joining that system at all?

Each agency needs to make its own decision based upon local conditions.  If 
everyone in the area is using something other than P25, then it probably 
makes sense to go with whatever that technology might be.  However, 
recognize that without a P25 mode, digital interoperability from outside 
agencies will be greatly hampered, and completely eliminated if you are 
talking about interoperability with Federal agencies.

Finally, the success of P25 is based upon much more than the end-user, 
though they are the most important part in my opinion.  It includes 
spectrum efficiency (yes, a direct impact on users if you consider channel 
availability and loading), graceful migration and competitive procurement 
(do you want equipment that is 15 years old or 5 years old), 
interoperability, and user-friendly equipment.  Look at the features that 
are now available from P25.  Systems like those in Michigan, Mesa-Phoenix, 
San Diego and other areas were just not possible in the analog 
world.  Standardized feature sets and advanced features that make these 
systems workable on multiple vendors' equipment are a reality because of, 
and only with, P25.

>Side Note:  I am pretty sure that MA/Com is now providing Project-25 
>Conventional capability on their newer subscriber units, so I suppose that 
>helps.
>
> >Scanner listeners, public safety professionals, and system managers all 
> participate actively on trunkedradio.net, so I'd say we've got a very
> >enlightening cross-section of the community to take a pulse from.
>
> >> I don't so I can't comment on the "enlightenment" of the group. My 
> supposition is that the group parallels others on the net...running from
> >> the "erudite and highly capable" all the way to the "hopelessly 
> uninformed and totally ignorant".
>
>We are in total agreement here.
>
> >> As far as I know, the 6.25 KHz. FDMA part of P25 is standardized. Only 
> the TDMA implementation is still unsettled. That appears to mired in a
> >> battle between various supporters of 2 slot vs. 4 slot vs. 12.5 KHz 
> vs. 25 KHz. including, but not limited to, Tetra like and multi-channel JPM
> >> modes. Only the Power above knows when or if that will be resolved.
>
>Oh Boy, another standard.  ;-)

Phase II standards for 6.25 kHz or equivalent channels, be they FDMA or 
TDMA (and the FDMA standard for 6.25 kHz has been complete for several 
years) are all part of the P25 standards series.  We are moving quickly to 
get a 2-slot 12.5 kHz TDMA package completed.  The Steering Committee has 
made it very clear that we still want a 4-slot 25 kHz TDMA option, too, but 
none has been offered from the manufacturing community since TETRA pulled 
out of the effort.  The issues of graceful migration and interoperability 
among these technologies is very important, and a key reason for keeping 
them all within the P25 standards suite.

> >Can you share with us your thoughts and experiences?
>
> >> I think I just did.
>
>This has been a great discussion, and I enjoy the discourse.   I do want 
>to make it clear that I *do* support the Project-25 standard, and I feel 
>that it *is* needed.  Bandwidth is only going to get smaller, so there 
>isn't going to be a choice but to move to more digital mediums for public 
>safety communications.  BUT.... well, read my comments above.
>
>Warmest regards to all,
>
>Lindsay

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