Calling Area Coverage - Motorola i897 Detailed Service Manual

OVERVIEW: iDEN Digital Modulation Technology
An iDEN channel is created by grouping bursts so that their slot numbers differ by a number
referred to as the repetition rate. The i897 unit uses two repetition rates for interconnect voice calls:
6:1 and 3:1. A single frequency can handle six 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 six 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 "hand off" from one coverage area to another as the user moves about during a call.
Handoff is controlled by the iDEN system.
In Figure 1-3, the area is divided into several cells, each containing a cell site (base station)
operating on a given set of channels, which interfaces radio-telephone subscribers to the switching
station.
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Figure 1-3. Hypothetical iDEN Cell System
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