Call Blocking Probability and Effective Throughput for Call Admission Control of CoMP Joint Transmission

Coordinated multipoint transmission (CoMP) with the joint transmission (JT) scheme is employed in cellular networks to improve data rate and cell-edge throughput and/or to increase system throughput. In CoMP-JT, since the user equipment (UE) is capable of receiving the desired signal from an adjacent cell, as well as from its serving cell, it can achieve an improved signal-to-interference ratio (SIR). However, this scheme entails exhaustion of resources in serving base stations. In this paper, we propose a call admission control scheme (CAC) to improve the performance of CoMP-JT-based cellular systems. In this CAC scheme, the CoMP-JT technique is applied to UEs located near the edge of a cell. To establish an analytical model for CoMP-JT-based cellular systems, we introduce a model for traffic analysis using a 2-D Markov chain and approximate the computation of the power sum of multiple lognormal random components in a multicell environment. Performances of CoMP-JT-based cellular systems are evaluated with respect to two quality-of-service (QoS) constraints pertaining to call-blocking and outage probabilities, respectively, from the network-layer and the physical-layer perspectives. We first measure the resource utilization and call blocking probability for the downlink resources for various offered loads in the cell. Based on that, we obtain the outage probability and effective throughput of the system. The analytical results are compared with computer simulations. Finally, we consider the dynamic point selection (DPS) scheme that is a modified version of the JT scheme, in which some resources of adjacent cells are muted.