Small cell networks: Speed based power allocation

Small cell networks promise to boost the capacity and provide good QoS (Quality of Service) to cell edge users. However they pose serious challenges, especially in the case of high speed unidirectional (e.g., users traveling on highways or in metros) users, in the form of frequent handovers. The extent of the handover losses depend greatly upon the speed of the user and it is shown previously that optimal cell size increases with speed. Thus in scenarios with diverse users (speeds spanning over large ranges), it would be inefficient to serve all of them using common cell radius and it is practically infeasible to design different cell sizes for different speeds. We alternatively propose to allocate power to an user based on its speed. Higher power virtually increases the cell size. We obtain an expression for optimal power division, optimal for busy probability and load factor (a QoS influenced by handover losses), for any given average power constraint and cell size. We show that the optimal power depends linearly upon the speed. We reinforce the theory via numerical simulations, illustrating good improvements in the performance (upto 60% in busy probability and 30% in load factor) with optimal power law. The improvement in performance increases as either the path loss increases or as the range of speeds to be supported by the system increases.