Motorola V186 - Cell Phone - GSM System Planner Manual page 129

Communications
Analog Trunked Radio Systems
In an analog trunked radio system, any unit that needs to send a message, requests, and is
assigned to, a channel by the trunking system controller. The ACE3600 RTUs are
typically clustered into a single trunked data group and are managed by the trunking
system controller as a single entity. Therefore, any RTU that requests a channel causes all
RTUs to switch to the assigned channel so that all units hear, decode, and may
appropriately respond to the data transmitted. Two way data transfer among many RTUs
may occur following a single channel request/assignment. Also, trunked systems provide
an infrastructure that is inherently redundant—if one base station should fail, the trunked
system automatically assigns communications to a remaining station. SCADA system
data and trunked radio systems are very compatible!
Most analog trunked radio systems are set up to optimize the performance of the many
mobile and portable voice radios in the system. This setup may not be optimal for data
users. ACE3600 operates best in the Message Trunking mode whereas many systems are
setup to use the PTT-ID Trunking mode. ACE3600 may be made compatible by
lengthening the delay-before-transmit time to allow the PTT-ID activity to be completed
before the ACE3600 data is transmitted.
Many trunked radio systems are designed with multiple transmit and receive sites. This is
advantageous for the mobile and portable users that roam over a large territory but
detrimental to ACE3600 data use. Receiver voting is present so the best quality received
audio will be used; a quality analysis will occur at regular intervals, typically 350 msec,
and a switch to the better quality signal may occur. That switch (revote) may introduce a
small hole and/or a signal phase change into the audio message. Voice users are
minimally affected by the hole/phase-change, but those artifacts may compromise the
data message so that no throughput occurs (complete destruction). When ACE3600 is
used in a multi-site system, the antenna choice and placement must be carefully selected
so that only one site will receive a strong signal — this will prevent the site switch
associated with a revote.
System engineers are encouraged to contact the ACE3600 Product Support Group during
the design phase of any trunked radio system so that these and other issues may be
discussed.
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