Calling Area Coverage - Motorola iDen i850 Field Service Manual

OVERVIEW: iDEN Voice Compression Technology
(GPS) system. Each burst is numbered; the number is referred to as the slot number. All bursts
occurring at a given time carry the same slot number.
Inbound transmission bursts (sent from the unit) are offset 19 milliseconds from the outbound burst;
the inbound burst begins 4 milliseconds after the end of the outbound burst (see Figure 1-2 on
page 1-3). This offset in time allows the unit to appear capable of transmitting and receiving at the
same time (it actually is switching rapidly back and forth between receiving and transmitting).
In current iDEN systems, outbound transmissions in the 800 MHz band range from 851–870 MHz;
inbound transmissions are 45 MHz lower in frequency. For the 900 MHz band, outbound
transmissions range from 935-940 MHz; inbound transmissions are 39 MHz lower in frequency.
An iDEN channel is created by grouping bursts so that their slot numbers differ by a number referred
to as the repetition rate. The unit uses two repetition rates for interconnect voice calls: 6:1 and 3:1. A
single frequency can handle 6 calls using a 6:1 repetition rate with the 4.2 Kbps coder.
Dispatch calls always use this rate. However, the audio quality of the 3:1 repetition rate with the 8.0
Kbps coder is superior to the 6:1 rate with the 4.2 Kbps coder. Most service providers configure the
system and unit to allow only the 3:1 rate for interconnect calls.
Calls are set up on a primary control channel (PCCH) in response to a request from a unit or a
regular telephone connected to the Public Switch Telephone Network (PSTN). The PCCH is
established by the base station equipment; typically, it is a 6:1 channel.
The outbound PCCH carries system information and "pages" to specific subscriber units and asks
them to respond if they are available for a call. Inbound PCCH transmissions carry responses to the
"pages" and requests by subscriber units to set up calls. Inbound transmissions on the primary
control channel only take 7.5 milliseconds and can be timed to occur in either half of a 15-
millisecond burst.
The dual band unit will power up in the 800 MHz band and will use these channels for control
channels—Primary Control Channel (PCCH) and Broadcast Control Channel (BCCH). The 900
MHz mode will be used only during 3:1 interconnect calls. Every attempt will be made to assign the
unit to 900 MHz carriers during new 3:1 interconnect calls, handovers into a cell, and inter-cell
handovers. If no resources are available, or if available resources have insufficient channel quality
(in the case of a handover), then 800 MHz carriers will be evaluated.
Using the above techniques, the iDEN system can operate 6 voice channels simultaneously in
dispatch mode or 3 voice channels simultaneously in interconnect mode on a single RF carrier at
25 kHz bandwidth.
1.2.2

Calling Area Coverage

Area coverage is obtained by dividing the area into a mosaic of cells. Coverage is controlled so that
frequencies can be reused with less distance between sites. Each cell is covered by a base station,
which is classified as Omni or Sectored. An Omni station connects base transceivers to antennas
that have a circular pattern centered at the site. A Sectored station connects base transceivers to
directional antennas that point in particular directions. Units that operate in a multi-site system must
be able to "handoff" from one coverage area to another as the user moves about during a call.
Handoff is controlled by the iDEN system.
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