Subject: [NEXTEL-1] Interference To Nextel, need information

From: Marcel <[email-masked]>
Date: Mon, 04 Nov 2002 17:09:39 -0500

------- Original Message --------
   From: Jack Daniel <[email-masked]>
Subject: Interference To Nextel, need information

Robert Schwaninger wrote:
Group Members:

I need to know whether a conventional SMR signal would result in dropped
calls on a Nextel system, or whether iDen's interference rejection
methodology would compensate.

>>>> Yes, sooner or later. but it's not really rejecting interference, it's rejecting the
bad channel.

For example, if a Nextel cell is capable of operating on 860.1275 as one
of its many channels, and the channel is occupied by a conventional SMR
system's use, would the system simply direct the mobile to another
channel for communications?

>>>> Yes. chances are it's a handset and mot a mobile though.

Second, if the Nextel mobile is already occupying the subject channel
and THEN the SMR system comes on the channel, would the iDen system
compensate or would the conventional SMR system cause the Nextel mobile
user's call to be dropped??

>>>> Yes, that one call only.

Assume that the Nextel cell and the SMR station are located less than
five miles from each other.

>>>> Damned poor coordination !!

But……… There's a lot of different actions taking place in your scenario.

You need to know that what happens at one geographic location of the
portable/handset will  be different in another geographic location.

This is the near-far effect you hear about and it's all based upon the
signal levels the receiver sees from the two sites. In the most simplest
terms, if you are much closer to desired site, chances are you won't
know the other station exists.

But as you move from the vicinity of the desired signal site toward the
undesired signal site and the desired signal becomes more equal to (or
less than) the undesired signal, you will  have more and more problems.

Assuming you are on the same channel frequency, the primary effect will
be  blocking the desired channel due to a higher RF level.  Add to that
the act that blocking will usually have more effect on a digital signal
(Nextel) than on an analog signal.

This means you cannot predict the area where the near -far effect will
occur without considering the ERP of both sites, the signal-to-noise
radio the receivers need to operate properly, plus obstacles in the
radio path that may attenuate the signals.

The portable/handset transmitter is not directly affected by the
near-far effect.

For the SMR trunking system, you have to consider if the blocked channel
is a "control" channel (Motorola) or the last of the "home channels"
(LTR) because if that is the case, the SMR system cannot trunk the
portable anywhere and all connections are lost.

The difference in terminology between a SMR engineer and an iDEN
engineer can be confusing and unintentionally misleading .  In iDEN
terminology, be aware that a 'channel' may be a voice channel which is
not the same as a frequency channel.  There are multiple voice channels
(i.e. TDMA slots) on one frequency channel. An iDEN frequency channel is
the same thing as a SMR channel.  One iDEN slot can be used for the
trunking control channel while the other slots in that frequency channel
can be used for voice channels.

Also keep in mind that Nextel sites transmit continuously, so whatever
bad happens to a SMR radio is pretty constant as long as it is in that
area.

For the iDEN (Nextel system) there is usually one 'data' slot on one
channel frequency maintaining connections for several other frequency
channels, so it is similar to a SMR's control channel and you loose all
the associated channels at the same time.

But most Nextel Sites have multiple control channels on different groups
of frequency channels and the iDEN system is designed to accommodate
frequency channel outages.  In the event of a long term frequency
channel malfunction, the network controller may even change the
operating frequency remotely.

If the SMR radio blocks an iDEN channel, that specific call will
probably be dropped. As far as the iDEN system knows, their handset unit
just went south.

Maybe someone else can jump in and add more clarification to this.

It Is not a simple yes/no situation.

But I may be wrong.
Jack Daniel

---

From: Rick Parrish <[email-masked]>
Date: Mon, 04 Nov 2002 23:47:20 -0600

> user's call to be dropped??
Could be one, two, three or six calls - remember iDEN's time-division 
scheme of three duplex or six dispatch calls on the same frequency?

-rick

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