On the Performance of Decentralized Cell Edge Coordinated Scheduling in Small Cell Clusters with Different Densities Omer Anjum, Carl Wijting, Mikko A. Uusitalo, Kimmo Valkealahti Nokia Research Center, Nokia Corp. Helsinki, Finland Email: firstname.middleinitials.surname@nokia.com Abstract—With the expected increase in data traffic by mul- tiple hundredfolds in the coming years, future networks will experience more and more deployment of small cells with or without detailed network planning to increase the network capacity. Networks populated with such dense clusters of small cells will likely encounter very high interference. Thus there is an urgent need to develop strategies that could help to avoid such high interference especially for cell edge users in small cell clusters. In this paper, a decentralized cell edge coordinated scheduling (CECS) has been investigated for the performance of users at varying inter-site distance especially in the overlapped regions. For certain cluster densities CECS brings significant increase in the per cell edge user throughput. It is also observed that for a certain guaranteed bit rate (GBR) the coordinated approach outperforms the other schemes such as Full Reuse (FR) and fractional frequency reuse (FFR) in the sense of the mean user throughput and the amount of satisfied users in all the considered scenarios. I. I NTRODUCTION 1 User data traffic in future (5G) cellular networks is expected to increase even by a factor of 1000 from 2010 until 2020 [1]. It is also widely acknowledged that an essential fac- tor in answering this demand is via cells which are smaller in size, aiming comparatively fewer connected user equipments (UE) per cell, with their locations closer to the base station in order to have good received signal strength. The 3GPP standardization body recommendation to use frequency reuse factor one for the future LTE wireless networks would bring interference within the clusters of small cells via densification, especially for the cell edge users, as will be shown later in the text. 3GPP standard documents do not define any exact method in order to avoid this interference. Rather there are recommen- dations for using coordination based approach with the help of certain parameters that the base stations could share on X2-interface [2]. Actual implementation of such coordination based scheme is now up to the vendors to develop their 1 This work has been performed in the framework of the FP7 project ICT- 317669 METIS. The authors would like to acknowledge the contributions of their colleagues. This information reflects the consortium’s view, but the consortium is not liable for any use that may be made of any of the information contained therein. own strategies for avoiding interference by sharing certain parameters among the base stations. Several different strategies such as FFR [3] have been investigated a lot for interference avoidance with or without coordination. The major drawback in FFR is the inefficient utilization of the spectrum as the frequency reuse factor increases. There is also Co-operative Multipoint (CoMP) [4] scheduling technique which has been heavily investigate in recent years, briefly discussed later in the text. However, to the best of authors knowledge most of the prior published work address the interference avoidance problem in small cells together with the higher tier network. However, there is an urgent need to investigate a simple coordinated scheduling with a special focus on the scenario when a macro cell is not transmitting and only the small cells in a cluster are transmitting. The main focus of this work is to investigate the scenarios where the achievable gains for the edge user throughput are significant. It is dynamic in the sense that the frequency reuse factor used is one. The resource scheduling follows the traffic demand and user location in the cells. The possible drawback of this approach could be the signalling overhead to share the scheduling information among the cells. However, in the future cellular networks the small cells are expected to have good back-haul connectivity either wired or wireless. Sharing the scheduling information should not be a problem even if it is done in the order of hundreds of milliseconds. However, to find a good trade-off this aspect is needed to be further investigated and is not included in the scope of this work. Results have been compared with FR and FFR for clusters with different densities in order to identify the cases where coordination based approach brings more benefits. The paper is organized as follows. Section II explains in detail the interference problem, when the frequency reuse is one. Section III presents some of the related work, which has been thoroughly investigated by the research community. In Section IV the CECS approach is presented with the comparison of results. Section V concludes the presented work.