[TrunkCom] Fwd: R Dispatch on CDMA......Yes CDMA!

[thepolishdude]

--- In project25@y..., iDEN-Test Port-Marcelrf <Marcelrf@B...> wrote:
From: marcel <marcelrf@xxxxxxxxx.xxxx
Date: Sun Sep 26, 1999  10:40 pm
Subject: Dispatch on CDMA......Yes CDMA!


Motorola has been developing a Dispatch system on CDMA. This could 
change things
for iDEN. This method could be introduced as alternative to iDEN's 
full TDMA
Network.

A typical dispatch two-way radio communication system comprises 
communication
units, communication resources, communication sites, and a 
communication resource
allocator. Each of the sites have a substantially distinct coverage 
area and are
geographically located throughout the system. Each site also has a 
number of
communication resources assigned to it, where at least one of the 
communication
resources is used as a control channel, while a number of the 
remaining
communication resources are used as voice channels. Such systems are 
known to use
both frequency division multiplex access (FDMA) and time division 
multiple access
(TDMA) methods to rebroadcast transmissions.


The communication units are typically arranged into communication 
groups
(talkgroups) and may be located anywhere within the system (in any 
site). When a
communication unit of a talkgroup requests a group call, it 
transmits, via a
control channel of the site in which it is located, an inbound 
signaling message
to the communication resource allocator. (A group call typically 
allows all
members of the same talkgroup that are located within the system to 
communicate
with each other.) The inbound signaling message generally comprises 
the
requesting communication unit's individual identification number, the 
requesting
communication unit's talkgroup, and a request for a group call. Upon 
receiving
the inbound signaling message, the communication resource allocator 
will allocate
a voice channel in each site to the requesting communication unit's 
talkgroup.
Thus, in FDMA and TDMA dispatch systems a forward link is established 
(one in
each site where communication units are present) and monitored by all 
units
involved in the group call in that site, and a single reverse link 
which is used
by the group member who is currently transmitting to the other 
members.
Non-transmitting talkgroup members are typically in a listen only 
mode (i.e., not
able to transmit when another member is talking) and thus are not 
allocated a
dedicated reverse link. In a TDMA system, for example, time slots are 
allocated
to different users. A talkgroup member transmitting on an assigned 
reverse link,
is allowed to use full power transmission to support short bursts of 
signals in
allocated time slots.  Despite the discontinuous or discrete nature 
of this
approach, the listener receives what appears a continuous service.


In the last decade, in response to an ever-accelerating worldwide 
demand for
mobile and personal portable communications, spread spectrum digital 
technology,
of which one type is known as CDMA, has achieved much higher 
bandwidth efficiency
for a given wireless spectrum allocation, and hence has proved to be 
an excellent
alternative for serving large populations of multiple access users, 
than analog
or other digital technologies. CDMA relies on processing power to 
extract a coded
signal embedded across a broad frequency spectrum. The only way to 
extract the
wanted signal from among many other overlaid unwanted signals is to 
have the
right code. The use of coding allows more channels to be derived by 
the
overlaying of carriers one over another and greatly enhances 
performance in terms
of derived channels per hertz of bandwidth.
CDMA is well suited for cellular communications, but has never been 
employed in a
conventional dispatch system. Current CDMA systems employ a form of 
forward power
control. This means that, in a typical one-to-one (cellular) 
conversation, the
communication unit periodically informs the base station how well it 
is receiving
the outbound signal. If possible, the base station reduces its 
outbound power. If
necessary, the base station increases its outbound power. This 
communication
between the base station and the communication unit requires a two-way
communication link between the two. In a dispatch situation, the most 
intuitive
outbound power control scheme is for the base station to respond to 
requests to
increase the power coming from any unit which requires it. However, 
this can only
occur if all units involved in the dispatch call have an established 
two-way
communication link.


CDMA systems also use soft hand-off at cell (site) boundaries which, 
in a
dispatch setting, would require each of the listening units to signal 
the base
station when another cell is found to have sufficient (usually 
greater) signal
strength to handle the call as the communication unit migrates away 
from the base
station, and closer to another base station. In turn, the base 
station will
enable the now closer base station to both send and receive the same 
traffic to
and from the migrating communication unit. In order for this 
procedure to take
place, the communication unit must have a communication path in to 
the fixed end.

Reverse power control is another important aspect of CDMA systems. 
(In fact, this
is much more important than forward power control.) Reverse power 
control
attempts to equalize the received signal powers for all communication 
units
controlled by a particular base station. By having the base station 
monitoring
(and accordingly vary) power from listening communication units, the 
efficiency
of CDMA is realized.


In order to avoid excessive interference on the reverse link, 
communication units
accessing the channel for the first time (i.e., before reverse power 
control has
been established) use what is known as "access probes". This means 
that they
access the channel with low power, and slowly ramp up their power 
until a
response from the fixed end tells them that their signal has been 
received. For
cellular communications, the time delay caused by this access method 
is
insignificant. On the other hand, the time delay in setting up a link 
for a
follow-up call during a dispatch group call would be significant and 
must
necessarily have been established in advance. In dispatch, any one of 
the
talkgroup members may want to send an inbound message and then drop 
back to
listening status. If each access required access probes, the delay 
would be
intolerable for a quality dispatch service.
As stated above, non-CDMA systems do not have multiple reverse link 
connections
in a dispatch call because the nature of the access methodology (TDMA 
or FDMA)
does not demand it (quality dispatch functionality is possible for 
listening
units without the power control and soft hand-off required in CDMA 
systems). TDMA
and FDMA systems assemble a talkgroup by alerting the members of the 
call, and
informing them of where to tune to listen to the call.  The 
establishment of
multiple reverse (inbound) signaling links is simply not an issue. 
For CDMA
systems, there are to date only point-to-point communication protocols
established (i.e., dispatch capability has never been deployed). 
Therefore, the
establishment of multiple reverse signaling links and the conflict 
that this can
cause with the strict timing requirements of a dispatch service have 
not been
addressed.


A hybrid TDMA/CDMA system indirectly addressing the delay problem 
with CDMA
channel access was proposed in U.S. Pat. No.5,295,152, entitled "TDMA 
for mobile
access in a CDMA system". In the proposed system, a separate TDMA 
channel is
defined, either separated in frequency band or time interleaved in 
the same
frequency band as the CDMA channel. Because TDMA does not require 
stringent
inbound power control, immediate access on the TDMA channel portion 
is possible
without the access probe delays seen in CDMA. This TDMA channel could 
therefore
be used for access and control signaling (e.g., fast follow-up in a 
dispatch
call), while the CDMA portion of the system would be used for the 
traffic
channels.  Such a hybrid approach, however, would require essentially 
two
different types of radio equipment (TDMA and CDMA) at the base and 
mobiles ends,
leading to higher costs, and may present interference problems to 
nearby, pure
CDMA systems.


Providing all listening-only units on a CDMA system with a full 
traffic capable
reverse link would quickly deteriorate system performance in a heavy 
user system
due to excessive interference and would be a great waste of 
resources. CDMA
systems are interference limited, in that capacity is determined by 
the amount of
interference due to all the users on the system. An alternative might 
be to set
up non-talking group members in a listen-only mode with no reverse 
link
whatsoever. However, this latter scenario would lead to serious 
difficulties with
forward power control, soft hand-offs, and rapid channel access for 
the follow-on
calls in the dispatch conversation (group call).

It would be a great advancement in the art of dispatch communications 
to be able
to provide quality dispatch service on a CDMA based wireless 
system.Reverse links
are necessary in a CDMA dispatch system since such links provide to 
listening
group call members the means for inbound power control to enable fast 
access in
response to the dispatch call, the means for outbound power control, 
and the
means for enabling soft hand-off. The establishment of these links, 
however,
could seriously impact the call setup time, and thus service quality. 
There is
also a further need therefore for a CDMA based wireless system which 
establishes
reverse links for all talkgroup members participating in a dispatch 
call but that
does so without seriously negatively impacting the call set up time 
and thus
service quality.

Marcel


iDEN-Test Port-Marcelrf wrote:

> I'm sure you remember a few years ago I posted a excerpt from a 
white paper
> that spoke to the theory of implementing dispatch over a CDMA 
network. While
> it was rather crude I know of some scholars at Virginia Tech's 
Mobile &
> Portable Radio Research Group (MPRG ) who have tinkled in the LAB 
with this
> concept but were never able to beat the always-on-packet data 
network.
>
> While FDMA may be a steep towards their CDMA cousin I don't know if 
it robust
> enough to support the hard-core OTA (over the air) applications of 
today.
> While OTAR is a option for P-25, I suspect the data is less 
intensive and
> requires less on board memory.
>
> With today's handsets running applications on board I wonder if  
LMR will
> move towards that direction. It appears that OTA may have to be 
addressed in
> later phases of P-25.
>
> The signaling issue is mind baffling. The control channel action is
> staggering. I won't even try to address this in this forum because 
I will
> most likely trip over my feet.
>
> As far as CALEA they want it all. I think will get it too. I look 
for Over
> the air interception with the roll out of 3G.  No more re-routing 
data from
> the PSTN via a T1 to their office. I suspect the will have a 
wireless gateway
> that will route the traffic to the field and the will be able to 
manipulate
> it also.
>
> Technology is just moving too fast for the average user. I'm sure 
everyone
> has seen the "Digital Opposition" from the Scanner Guys to the 
Fireman in
> NYC. Everyone hates what they can't understand. Don't get me wrong 
I love 450
> mhz analog just like I love my HT-220 Slimline but times have 
changed time to
> move on. If we are not careful this whole "Digital" world could 
fall apart
> around us. There needs to be a balance.
>
> arclight_arclight wrote:
>
> > I have to agree that this looks like the thing that will finally
> > provide some degree (maybe a large degree) of seamlessness, but in
> > order to really do so the mechanism for packetizing the voice and
> > doing the required signalling on the wireline side has to become
> > standardized. It also occurs to me that if an entity (of any type)
> > attempts to sit on the standardization process and heavily 
manipulate
> > it, the market is large enough and there are enough players that 
the
> > market will simply take their marbles and walk.
> >
> > As far as I can see the only technology robust enough to allow for
> > streaming packetization on the RF link itself with sufficient 
error
> > correction to handle multipath is some CDMA varient.  The FDMA and
> > TDMA platforms don't have enough capacity in my mind to accomplish
> > this without an ENORMOUS amount of compression.  This is NOT to 
say
> > that TDMA / FDMA systems won't be able to interoperate VoIP with
> > their CDMA cousins...it just means that the actual RF link will
> > remain more circuit-based (as it is today) than packet-based.
> >
> > It's exciting as it can be from a technology standpoint, and as 
Rik
> > wrote on one of the other lists earlier, it's probably going to 
punch
> > large holes in existing technology deployments.
> >
> > The downside: By definition this requires an intelligent endpoint,
> > and for maximum effectiveness, one that is "always on" or at
> > least "mostly on".  It's logical enough to assume that this 
platform
> > will incorporate some form of mail (Marcel already does that).  
Let's
> > throw in voice recognition to make the call setup easier
> > (particularly mobile).  Now how hard is it to add a little more to
> > the endpoint such that it can be commanded to (a) open its 
internal
> > microphone, (b) capture all audio +/- 15 seconds around certain 
key
> > words or phrases (e.g. "president", "congress", "religion", etc.) 
and
> > (c) send that audio in packetized form to another computer for 
post-
> > processing and threat analysis.  If the commands and the results 
are
> > all packets, there's no special "connect" sequence to go
> > through...it's just packets that get transmitted at some rate
> > (possibly even as "signalling" bits in the next "regular" packet
> > stream generated by the endpoint device).  Sure makes first-level
> > surveillance easy, doesn't it?  From there, a court order to do 
more
> > intensive surveillance with more specialized tools (does the court
> > have to know that the "informant" who indicated "probable cause"
> > happens to be electronic?), and a MUCH higher probability of 
catching
> > things happening.  And the average Joe or Jane will never make the
> > connection between the innocent endpoint device and the increase 
in
> > law-enforcement actions that that device makes possible.  There's
> > probably 1,000 things wrong with what I outlined above (at least I
> > sure hope there is), but it still gives me pause.
> >
> > It may well be that the primary effect of Moore's law is to make
> > Orwell's vision (1984) realizable.  Wouldn't that be a real burner
> > for us technology-loving folks?
> >
> > Dave Maples
> >
> > --- In project25@y..., iDEN-Test Port-Marcelrf <Marcelrf@B...> 
wrote:
> > > Yes-
> > >
> > > Motorola  has already interfaced their iDEN system
> > > to several smart net systems. Just has not ben done via IP yet. 
So
> > P-25 is
> > > not far away.
> > > Did you know Qualcom has played with P-25?
> > >
> > >
> > > Ron Haraseth wrote:
> > >
> > > > I would guess since P25 systems are already using VoIP to
> > interconnect
> > > > base stations, vocoders are the only thing holding things back
> > from a
> > > > P-25 handheld talking to a Nextel unit if their respective
> > networks were
> > > > tied together & appropriate control system software 
(theoretically
> > > > speaking of course).
> > > >
> > > > Ron
> > > > -----Original Message-----
> > > > From: kloch@m... [mailto:kloch@m...] On Behalf
> > > > Of Kevin Loch
> > > > Sent: Tuesday, January 15, 2002 6:09 PM
> > > > To: project25@y...
> > > > Subject: Re: [project25] FW: [PrivateWirelessForum] Article: 
VoIP
> > > > Technology Has Potential to Turn Wireless Industry 'Upside 
Down'
> > > >
> > > > iDEN-Test Port-Marcelrf wrote:
> > > > >
> > > > > I do believe that P-25/VoIP/3G CDMA will cross paths. Looks
> > like they
> > > > > are all headed in the same direction.
> > > > >
> > > >
> > > > You mean APCO/VoIP/3G?  P25 is what it is and it definately
> > > > isn't the other things.  The convergance would show up in the
> > > > future standards, right?
> > > >
> > > > KL
> > > >
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