Control Channels in Mobile Communication Systems

To ensure proper functioning of mobile communication systems the following transactions must be supported by the employed protocol:

• (mobile originating/terminating) Call establishment and release
• Handover
• Periodic reporting of signal quality and strength measurements
• Location updating

1. Explain under what conditions each of these transactions has to be performed. Estimate how many control messages are necessary in both the up-link and down-link direction to complete each transaction. Justify your answers.
2. For the remainder of the problem, the following assumptions regarding the traffic to be supported by the mobile network are made:
   • There is an equal number of users from two classes: the first moves at a speed of 50 km/h and the second is moving at a speed of 3 km/h.
   • Each cell has 10 traffic channels which are in continuous use¹.
   • The average call duration is 2 minutes.
   • A location area comprises 10 cells.
   • Measurements are reported every 10 seconds for every active call.
   • The cell radius is 1 km for all cells.
   Estimate the total number of control messages which have to be exchanged in support of the transactions above in one hour in a location area (10 cells).
3. Assuming each message contains 100 bits, how much channel capacity is required to carry the control traffic for the location area.
4. How do your answers change if the cell radius were reduced to 100 m? Would a measurement reporting interval of 10 seconds still be sufficient? Explain.