An Approach for Downlink VoIP Capacity Estimation in OFDM-Based FDD Networks

The paper presents a methodology for estimating downlink VoIP capacity in OFDM-based FDD networks that do or do not allow for adaptive transmit power. The underlying idea is to formulate an optimization problem for a user snapshot and utilize the developed system model to enable statistical capacity estimation by adopting the results of the central limit theorem. The approach is applied to numerically study VoIP capacity in networks with LTE-like parameter settings and various inter- site distances, frequency reuse of one and three, and SISO and MIMO antennas. The study demonstrates that adjustable transmit power in downlink may improve VoIP capacity by up to 30% in interference-limited environments. In networks with frequency reuse of three and MIMO antennas, however, the effect may be lower unless a larger bandwidth is available. The paper also addresses a trade-off between the cell coverage degree and capacity by showing a marginal coverage cost in terms of VoIP capacity.