SIR-based uplink admission scheme for a two-tier CDMA system under mobility incorporation

Enhancing the total system performance along with supporting a large number of users is the challenge of cellular service providers. Code division multiple access (CDMA) system capacity as an interference limited capacity performance is mainly affected by the out of-cell interference. While the in-cell interference is controlled within each cell using power control algorithms, the out of -cell interference is not, and may impact network coverage and the total user capacity. One approach used to enhance users´ quality of service, increase the system capacity, and widen the system coverage is to use cells of different radii, hierarchically organized in overlapping layers, this is known as multitier system. In this paper the system capacity in the uplink direction of a certain two-tier CDMA system consisting of two cells operating at the same frequency band is examined. A fast/slow mobility profile is used to study the effect of the users´ mobility on the call blocking and call dropping probability for a Signal-to-Interference Ratio (SIR)-based uplink admission control scheme. Two schemes for uplink capacity calculation are utilized. For the first scheme, to have a non negative solution of the received powers of current active users, i.e., feasible solution, a randomly selected user(s) is(are) dropped. For the second scheme, the user with highest amount of interference is dropped regardless of the cell membership. Computer simulation results show that, for the second scheme, the system capacity increased roughly by about 8 % over the first scheme and the dropping probability is 50 % less than that of the first scheme. The dominant parameters affecting the system performance are the users´ velocity, new users´ arrival rate, and the distance between the two cells.