Contents I. Introduction
Queueing theory is useful in solving problems in capacity planning and performance evaluation for various communication systems and networks. In particular, queueing theory can be applied to analyze cell operations in a mobile communications network. A base station (BS) of the cell provides service to multiple users. In modern mobile networks, there is a possibility of varying the service rate of a user due to a change in the signal strength. Such a possibility takes place, e.g., in LTE networks, where the cell can be divided into zones according to the quality of the signal: Excellent for zone 1, Good for zone 2, Mid-Cell for zone 3, and Cell Edge for zone 4. These zones are defined by a combination of indicators such as the Received Signal Strength Indication, the Reference Signal Received Power, the Reference Signal Received Quality, the Signal Interference + Noise Ratio and the Channel Quality Indicator. A user may activate the connection with a BS when he/she is located in various zones and then he/she can move inside the cell and depart from the cell. The modulation and coding scheme and, consequently, the rate of service for the user depends on the zone where the user is located and the number of other active users in the cell. The bandwidth of the BS is restricted. Therefore, if the total bandwidth required by all active users exceeds the bandwidth of the BS, then the discipline of bandwidth sharing, i.e., proportionally reducing the service rate, is applied.
