System capacity of a two-sector OFDMA downlink with QoS constraints

Abstract

We consider the downlink of an Orthogonal Frequency Division Multiple Access (OFDMA) network. OFDMA transmission technology will be used in the next generation of wireless networks such as the LTE (Long Term Evolution) and WiMAX wireless standards. In such a channel, multiple User Equipments (UE) may each be allocated multiple Resource Blocks (RBs) in each frame. A RB is a collection of subcarriers spanned over all symbols that are available for data transmission. For each UE we assign a utility function that depends on the UE's average throughput. Such a function can be used to achieve specified Quality of Service (QoS) guarantees of the UE. We are concerned with the optimal allocation of power and bandwidth in each sector with the objective of maximizing the sum utility over all UEs in all sectors. Note that since we are considering sector-wide performance then the influence of intersector interference is also taken into account. In general, this problem is intractable and so we focus on the two-sector case. We determine an upper bound on performance for any set of utility functions and for any strategy for scheduling, power control and interference management. This bound can therefore be used to evaluate the optimality of any particular strategy.