Motorola R2010D Operator's Manual page 7

regarding a new voice channel, it also informs the
mobile of the SAT frequency to -be expecting on the
new channel. The returned SAT signal is used at the
cell site to verify the presence of the radio-telephone
on the designated channel and to determine the signal
strength of the cellular radio's RF carrier. A separate
10 kilohertz tone is utilized by the mobile on the
reverse channel to acknowledge various commands
from the cell site.
When first turned on, the cellular radio-telephone
will scan through the nationwide set of forward con-
trol channels and measure the signal strength on each
one. It will then tune to the strongest one and receive
the overhead control message. From the overhead
message, the radio will be able to determine whether
or not
it
is in its home system, and the range of chan-
nels to scan for paging and access. Radios not in their
home system will be able to use other cellular phone
systems depending on the level of service requested
by the user. The radio next scans each paging channel
in the specified range and tunes to the strongest one.
On that channel the radio continuously receives the
overhead message information plus paging messages.
At this point the radio idles, continuously updating
the overhead message information in its memory and
monitoring the paging messages· for its phone
number. When a page match occurs, the radio scans
each of the channels designated as access channels
and tunes to the strongest one.
On the access channel the radio acknowledges the
page and thus notifies the central controller of its cell
location. The controller then assigns a voice channel
and a SAT code to the radio. Upon reception of the
voice channel command the radio tunes to the voice
channel, verifies the presence of the proper SAT fre-
quency and transponds the tone back to the cell site.
At the cell site, the reception of the SAT tone signals
the central controller that the radio is ready for the
call. An alert order is then sent to the radio which
responds with a 10 KHz signaling tone. The. sub-
scriber unit rings for 65 seconds or until the user
answers. Then the 10 KHz signaling tone is ter-
minated to alert the central controller that the user
has answered. The central controller then connects
the incoming call to the appropriate circuit leading to
the cell in contact with the radio.
2
As the call progresses, the cell site continuously
monitors the reverse channel for signal strength.
Transmitter power commands will be sent to the
cellular radio as required to maintain the received
signal level within prescribed limits. This is done to
minimize interference possibilities within the fre-
quency reuse scheme. If the mobile is at its maximum
allowed power for the cell that it is within and the
received signal at the cell is approaching the mini-
mum allowable, the cell will signal the central con-
troller. The central controller will in turn have a scan-
ning receiver at each of the surrounding cell sites
measure the receive signal strength. The site with the
strongest signal will be the site to which the call will
be handed off. The handoff and transmitter power
level changes are executed by interrupting the conver-
sation with a burst of data containing the command.
The radio acknowledges the order by a data burst in
the case of a power control order, or by a burst of 10
kilohertz signaling tone in the case of a handoff. It
should be noted that this data exchange happens very
quickly and is hardly noticed by the user.
When the call is terminated by the party calling the
cellular radio, the central controller issues a release
order to the radio which acknowledges with a 10
kilohertz signaling tone burst and the cellular radio
ceases transmission. If the call was terminated by the
user of the cellular radio, the signaling tone burst
signals the central controller which terminates the
connection. In either case after call termination, the
cellular radio goes back to rescan the nationwide set
of forward control channels and repeats the process
it performed at first turn on to re-establish itself on a
paging channel.
When the call originates at the cellular radio, the
radio scans the access channels and tunes to the
strongest one. On that channel then the radio notifies
the central controller of its identity and the number it
wants to be connected to. From that point the proc-
ess by which the cellular radio is assigned a voice
channel and the call completed is the same as pre-
viously described.
Figure 1 provides a frequency spectrum overview for
the domestic cellular system.