An Improvement and Analysis of Horizontal Sector Offset Scheme for LTE Networks

With rapid increase of smartphone shipments and increasing popularity of wireless multimedia applications cellular networks are driven to capacity limits. How to effectively increase network capacity and improve user quality of experiences (QoE) are the subjects of a large body of research. Heterogeneous network structure, small cell deployment, massive MIMO and advance frequency resource management technologies are some example hot research topics for LTE cellular networks [1]. Due to the increasing network capacity presssue mobile service providers wish to achieve a frequency reuse of factor 1 in modern cellular networks. However frequency reuse across all the sectors of a cite and across cites will result in strong interference and low SINR for users located at sector boundaries and cell boundaries. A widely used approach to address the above problem is using fractional frequency reuse schemes, which improve the throughput of cell edge users at the cost of reduced frequency reuse. Recently an interesting alternative approach of improving frequency reuse schemes by horizontal sector offset is proposed for 3 sector multi-carrier UMTS in [3] and LTE networks in [4]. The main idea is that the two sectors which point to the same direction associated with the two carriers in UMTS networks or the two groups of subcarriers in LTE networks are now offset with the highest gain direction of one sector pointing to an original sector boundary. With this new approach the frequency reuse is not reduced compared to the traditional 3 sectors configuration. Large improvements on user throughput and handover performances have been reported in [3] and [4]. In the sector offset scheme the horizontal half-power beamwidth of sector antennas was set to 65° [3] [4]. Such setting is unnecessarily wide and may generate extra interference. In this paper we propose an approach to improve the existing sector offset scheme by setting a better horizontal half-power beamwidth, which can largely reduce network interference and user outrage probability, and improve network throughput. In parallel to the above work a statistic model is proposed to analyse the LTE network performance with and without sector offset, in terms of interference, spectrum efficiency and outrage probability. Numerical results show that with a properly configured half-power beamwidth network performances could be largely improved. The analytical model is also verified by simulations, which can be used as an effective tool for estimation of user QoE and network planning.