Multidimensional OFDMA Scheduling in a Wireless Network with Relay Nodes

LTE Advanced and other 4G cellular standards allow relay nodes (RNs) to be deployed as a substitute for base stations (BSs). Unlike a BS, an RN is not directly connected to the backbone. Rather, each RN is associated with a donor BS, to which it is connected through the OFDMA wireless link. A very important task in the operation of a wireless network is packet scheduling. In a network with RNs, such scheduling decisions must be made in each cell not only for the BS, but also for the RNs. Because the scheduler in a network with RNs must take into account the transmission resources of the BS and the RNs, it needs to find a feasible schedule that does not exceed the resources of a multidimensional resource pool. This makes the scheduling problem computationally harder than in a network without RNs. In this paper, we define and study the packet-level scheduling problem for a network with RNs. This problem is not only NP-hard, but also admits no efficient polynomial-time approximation scheme. To solve it, we propose an efficient algorithm with a performance guarantee and a simple water-filling heuristic. To the best of our knowledge, our algorithm is the first packet-level scheduling algorithm that provides a performance guarantee for a network with RNs. Using simulations, we evaluate our new algorithms and show that they perform very well.