COM1204 Spring 2001 -- A call originating at a cell phone

The figure below is taken from Fig. 3.15 of Wireless Personal Communication Systems by David J. Goodman (copyright 1977 by Addison Wesley Longman, Inc.) It deals specifically with a call originated at a cell phone. Note that many of the operations shown deal with the fact that transmission and reception may be so weak or noisy that they may fail. Our simulation does not deal with these RF signal strength problems, real though they are in practice.

Some of the more important parts of the figure are:

• The PAGE messages which are sent to all phones simultaneously by the Base Station over the FOCC (Forward Control Channel) are monitored constantly by the phone when it's in the IDLE state. There is only one FOCC in a cell.



• In this example the cell phone user dials a number and presses the SEND button and an ORIGINATE message is sent over the RECC (Reverse Control Channel) which is shared by all phones (only one available per cell, normally).



• The Base Station selects one of the voice channels, if any is available, and sends an INITIAL VOICE CHANNEL message over the FOCC with the identity of the voice channel that the phone is to use. (There are two voice channels, one Forward Voice Channel, FVC, from the Base and the Reverse Voice Channel, RVC, to the Base.)



• If the phone is successful in getting a basic signal over the voice channel it assumes that the call will work it then begins the conversation over the two voice channels, temporarily dedicated to this phone for the duration of the call. It is important to note that during the call, signals between the Base and phone are exchanged over this dedicated voice channel, in addition to the audio conversation that is occurring. That is, the physical voice channels, each occupying a certain radio frequency range, are each divided into two logical channels, one for voice and the other for signalling.



• The most important signal sent over the logical control channel of the RVC is the one that the phone sends when the user hangs up which tells the Base that the frequency can be reused (at which time the phone stops transmitting and goes into its IDLE state).

There are variations on the above sequence; this is only one example.

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