Subject: [NEXTEL-1] RE: 800 MHz interference - Testing the performance of digital technologies

From: [email-masked]
Date: Mon, 19 Apr 2004 06:03:31 -0400

-------- Original Message --------
   From: [email-masked]
Subject: RE: 800 MHz interference - Testing the performance of digital
         technologies

Ok,

Before we go any further let me ask this:

1) Have you every "Optimized" a Cellular or PCS  network?
(Please don't take this the wrong way. I think we may have a disconnect
here.)

Optimization involves manipulating system parameters to obtain maximum
performance and minimum INTERFERENCE. Minimizing transmitter OOBE and
other unwanted emissions (i.e. Adjacent Channel, Co-Channel
interference, etc.)  is one of the benefits of optimization. One of the
tools now available in the optimization process is Motorola's
"Interference Management Tool". This only ONE technique available to
iDEN engineers, there are many others.

As I said before:

Motorola's iDEN  interference management tools in S.R. 11 uses  power
control and numerous other techniques to manage interference. To Reduce
Co-channel / Adjacent Interference  (and OOBE) the duty cycle for some
of the BR’s is decreased, therefore reducing the amount of
interference.  In the Power Reduction Process the selection of UCH slots
for attenuation is performed by the BR. 25-30% Power Reduction can be
achieved.

On the Quad BR there will not be separate spikes for each active
carrier.  Instead, there will be a single carrier feed through spike at
the center frequency. When the power reduction mode is enabled, the
modulated power is decreased for UCH time slots on non-PCCH carriers. A
carrier with SCCH enabled will follow the same dekeying procedure as the
non-PCCH carriers. The ACG will monitor for periods of PCH inactivity
and these idle periods will be used as opportunities for power
reductions. When the ACG recognizes a long interval of channel
inactivity (both Inbound and Outbound), the PCH is reduced to its seed
channel on the next DCAP frame boundary.

The picture below will help you understand the process. 25-30% Power
Reduction can be achieved and seen below. The OOBE is significantly
reduced by this process.  This is not a "piece meal" Nextel will roll
this software out NATIONWIDE with minimum cost and NO disruption to
public safety. As the signal rolls off into OOBE land you will see Trace
1 (original signal)  is great than Trace 2  (signal with power
reduction). This solution combined with other optimization techniques
will significantly reduce interference.

"Buchanan, David" wrote:

> So what does all that have to do with receiver inter-modulation from
> cellular transmitters to an analog receiver?
> See above:
>
> The interference is in the front end of the receiver.Or the
> interference is from OOBE which is an on channel interferer.Either way
> you can measure the interference all day long however you want to but
> that doesn’t do anything to fix the problem.The officer still can’t
> hear dispatch and worse if the interference is on the control channel
> of a trunked system the radio won’t TX a message back to dispatch.
>
>
> See above:
>
>
> So how long to we piece meal trying to fix every new location the pops
> up with interference.What is wrong with wanting to separate public
> safety channels from cellular channels?
>
>
> This is not a "piece meal" Nextel will roll this software out
> NATIONWIDE winth minimum cost and NO disruptuion to public safety.
>
>
> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> Sent: Wednesday, April 14, 2004 12:49 AM
> To: [email-masked]
> Subject: Re: [WFHSG] RE: 800 MHz interference - Testing the
> performance of digital technologies
>
> Example #1
>
> Testing the performance of digital technologies
>
> By Doug Mach, M.S.E.E.
>
> <SNIP>
>
> The new digital systems are changing
> the way radio performance is specified
> and measured. Ensuring the best
> system operation and user satisfaction
> requires that new tests and
> measurements be made to properly
> maintain the equipment. Here are some
> of the similarities and differences in
> performance measurement between
> existing FM radios and some of the new
> digital systems.
>
> Digital radio standards differences
> Anyone who has serviced two-way
> radios is familiar with the tests and
> measurements used to confirm proper
> operation of analog FM radios. The most
> basic measurements commonly made
> in the field are likely to be power output
> and receiver sensitivity. Simple
> talk-and-listen tests verify that the radio
> is ready to be put back into service.
>
> The new digital standards have
> changed things quite a bit. Different
> digital standards result in different test
> methods and specifications, which
> further complicates the issue. The
> method of specifying and measuring the
> two basic parameters of power output
> and receiver sensitivity varies from
> system to system.
>
> A digital radio or system is one in which
> the desired intelligence (either voice or
> data) is transported by digital, rather
> than analog, means. Systems using
> digital signaling_such as trunking
> control channels or those transmitting
> low-speed digital data_have been
> around for years. Voice systems using a
> 12kbps data rate have been in operation
> on the land mobile bands since at least
> 1976. In this case, some audio quality is
> sacrificed for security and simplicity.
>
> Two trends have resulted in the
> development of new radio technology:
>
> * The increasing ability to pack higher
> and higher data rates into existing radio
> channels using improved modulation
> techniques. * New voice compression
> technology allowing increasingly lower
> data rates without sacrificing good audio
> quality.
>
> Low-power-consumption
> microprocessors make it possible to
> use both of these computation-intensive
> trends.
>
> Understanding the basic layers of a
> digital system helps in understanding
> the issues raised in measuring
> performance. The most basic layer is
> the over-the-air connection. This layer
> establishes a stream of data between
> two radios: The type of RF modulation is
> specified, and the means for
> establishing synchronization and data
> framing is determined. (See Figure 1
> below.) At this point, the traditional radio
> begins to evolve into a digital device.
> Once the radio-to-radio data connection
> is established, data are then passed on
> to be processed for signaling
> information, user verification, error
> correction and other radio control
> functions. Channels of data, including
> voice data, are prepared to be passed
> on to their appropriate applications. In
> the case of voice operation, data pass
> on to the vocoder.
>
> For voice transmissions, the vocoder
> converts analog voice information into a
> stream of digital data that can then be
> transmitted on the established data
> channels. On the receiving end, the
> reverse process is carried out. Many
> types of vocoders are available today,
> each with good and bad attributes. For
> two-way land mobile communications,
> some of the desirable characteristics
> are:
>
> * Good audio quality under noisy
> conditions. * Good data compression. *
> Immunity to degradation of voice quality
> caused by received bit errors.
>
> On a voice channel, the resulting
> intelligibility is of key importance.
>
> As in analog systems, power output and
> receiver sensitivity are important
> measurements of digital radio
> performance. How power output is
> measured depends on the type of digital
> system being measured. For an FM
> system such as an APCO Project
> 25-compliant system using C4FM
> modulation, the measurement is
> identical to that for an analog FM
> system. In the case of TDMA systems
> such as iDEN*, where the transmitter is
> pulsed on and off, a more complicated
> method that takes into account the duty
> cycle must be used.
>
> Measuring receiver sensitivity is more
> difficult. A common method of
> measuring sensitivity in a digital data
> system is the bit-error rate (BER). This
> measurement compares a known
> transmitted pattern with the received
> data stream and expresses the result
> as a percentage of the bits in error.
>
> The problem with using BER to indicate
> receiver sensitivity is that its effect on
> radio voice performance depends, to a
> great extent, on where in the radio layers
> the measurement was taken. For
> instance, a single bit error that results in
> the loss of synchronization could result
> in a series of incorrect bits being sent to
> the vocoder. How well the vocoder
> reacts to this series of incorrect bits
> determines the effect of this single bit
> error on intelligibility. On the other hand,
> various levels of error correction may be
> used before data are sent to the
> vocoder. This would correct for a single
> over-the-air bit error and, therefore,
> would have absolutely no effect on voice
> quality. Measuring only the over-the-air
> BER before framing, error correction and
> vocoding may not always be the best
> indication of actual voice performance.
>
> "Buchanan, David" wrote:
>
> As to this question of iDEN expertise being a prerequisite to
> determining a solution, that a smokescreen and you know it. The
> problem is basic physics.
>