12 System Feature Overview
April 2011 68007024085
For an advanced, more comprehensive understanding of RF coverage prediction for the
MOTOTRBO site, the reader is encouraged to obtain the TIA Telecommunications Service Bulletin
TSB-88 – “Wireless Communications Systems-Performance in Noise and Interference-Limited
Situations, Recommended Methods for Technology-Independent Modeling, Simulation, and
Verification.”
A copy of TSB-88 can be obtained from http://www.tiaonline.org
2.1.3.3 User Expectations for Digital Audio Performance
There are a number of differences between how digital audio behaves compared to analog audio
from the end user (listener’s) perspective. Motorola has found that setting proper end user
expectations in this regard is an important aspect of system planning.
What End-Users will Experience with Digital Audio
• Consistent performance throughout coverage area with no gradual fade at the
fringes: While analog signals slowly degrade as the receiver moves away from the
transmitter, digital signals perform more consistently throughout the coverage area.
However, digital signals, more abruptly, shift from “good” to “no signal”, when crossing
the fringe of the coverage area. This means, users cannot rely on degrading audio
quality to warn them that they are approaching the fringe of coverage. On the other
hand, just prior to the fringe of the coverage area, digital audio is still crisp and clean,
whereas analog audio has excessive noise and static.
• Digital Sounds Different: The vocoding process is designed to deliver optimum audio
quality with a very small number of bits. Some listeners find the resulting tonal qualities
of digital speech somewhat different from what they have experienced with analog
speech. Because the vocoding process is highly specialized for reproducing human
speech, other sounds like music and tones are not reproduced accurately. Additionally,
digital audio can introduce end-to-end audio delays. When overwhelming errors or
dropouts are encountered, digital radios can generate some unique-sounding audio
“artifacts”.
• Background Noise Reduction: The advanced vocoding capabilities in MOTOTRBO
also include background noise reduction. Regardless of what is happening in the
environment of the transmitting radio, only voice is reconstructed at the receiving radio –
background noise, like machine noise, wind noise, and traffic noise, is not
reconstructed, and thus, not heard. This is a key advantage of the MOTOTRBO digital
voice solution over typical analog solutions, because noisy environments like factories,
stores, work sites, and windy locations do NOT significantly degrade communication
intelligibility.
What End-Users will NOT Experience with Digital Audio:
• Digital radio is not “CD Quality.” MOTOTRBO is the first radio in the industry to use
the AMBE+2
TM
low bit rate vocoder to deliver communications grade voice quality. End
users should not be misled into thinking that “communications grade” digital audio
quality in radio systems is analogous to the high fidelity audio quality of CD’s and DVD’s.
• Digital cannot solve historic problems. System issues with coverage and
interference are not necessarily eliminated by switching to digital. Adjacent or co-
channel interference may sound different to a digital user, but digital technology does
not solve interference issues. For example, analog interference will not be heard as
voice to a digital radio and vice versa, but disruption of system performance can still
occur.
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