Post-Resource Sharing Power Allocation in Cellular Networks to Coexist with D2D Underlay Nandish P. Kuruvatti, Hans D. Schotten Institute for Wireless Communications and Navigation University of Kaiserslautern Email: {kuruvatti,schotten}@eit.uni-kl.de Abstract—Device to Device communications (D2D) is consid- ered as a key technology component in fifth generation (5G) of mobile communication, which anticipates higher user density and traffic volume than in present. D2D communication aims to offload base station from traffic routing by enabling direct link between communicating devices in proximity. D2D underlay allows a D2D pair to reuse resources with a cellular link, lead- ing to better spectrum utilization. However, D2D transmission causes significant interference to cellular link with which it reuses physical resource block (PRB), thereby hindering cellular performance. Regulating D2D transmissions to mitigate the aforementioned problem would mean sub-optimal exploitation of D2D communications. As a solution, post-resource allocation power control at cellular users is proposed in this paper. Three schemes namely interference aware power control, blind power control and threshold based power control are discussed. Simulation results show reductions in dropping of cellular users due to interference from D2D transmissions, improvement in throughput at base station (uplink) while not hindering the D2D performance. Index Terms- 5G, D2D communication, power control, resource allocation, context awareness I. I NTRODUCTION Mobile communication is one of the most ubiquitously used technologies in the world, evolving towards its fifth generation (5G). Wireless data traffic is anticipated to be in order of 1000 times more in 2020 as opposed to 2010 and the number of connected devices will be 10 to 100 times more [1]. Management of such large density of users and traffic volume are major concerns for network operators in 5G. Device to Device (D2D) communication is a concept where mobile users in close proximity can communicate over a direct link between them without routing their traffic via base station [2]. D2D is treated as an important technology in 5G, capable of managing high user density and data volume [1]. D2D communication can be carried out in two major ways, namely: 1) Overlay: D2D communication takes place over dedicated spectrum [2]. 2) Underlay: D2D links and conventional cellular links share the available spectrum in a cell for their transmissions [2]. D2D underlay allows for better spectrum utilization but, mutual interference among D2D pairs and cellular users (CUE) would hamper the SINR at receivers, there by reducing the performance. There are several resource allocation schemes in literature that discuss resource reuse between D2D pairs and CUEs that would cause minimum interference to each other [2][3]. Fur- ther, several proposals are made to regulate transmission power of D2D users to mitigate interference[3][4]. Some proposals emphasize on selection of either D2D or conventional modes of transmission based on constraints of SINR, throughput etc,[3][5], and some allow the usage of D2D only in a specified region [6] fairly away from base station. However, majority of these schemes impose restrictions on usage of D2D communications, hence maximum benefit cannot be reaped from D2D communications at all times. On the contrary, D2D links would pose high interference to cellular links with which they reuse PRBs and cause significant dropping of cellular connections due to interference. In this work, we propose post-resource allocation (RA) power control for cellular users as a solution against interfer- ence caused by D2D transmissions on shared PRBs. Three post-RA power control (PC) schemes namely: Interference aware PC, blind PC and threshold based PC are introduced. Simulation results demonstrate that proposed schemes reduce dropping of cellular connections, improve cellular throughput while not hindering D2D performance. II. POST-RESOURCE ALLOCATION POWER CONTROL A. Interference Aware Power Control This scheme is carried out on the CUEs sharing PRBs with D2D users. CUEs which have their SINR lesser than target SINR due to interference, will be boosted with power levels sufficient to overcome the interference. Equations 1 and 2 are similar to LTE open loop power control [7], but has been designed to overcome interference from D2D transmission along with pathloss compensation. The logic of the scheme is described in algorithm 1. Denotations of terms used in algorithm 1 are as below, • SINR cue ⇒ SINR of relevant CUE • SINR t ⇒ intended target SINR • α ⇒ path loss compensation factor • PN 0 ⇒ average noise power per PRB • NF ⇒ noise figure at base station • M 0 ⇒ number of PRBs • PL ⇒ pathloss of the CUE w.r.t base station • P cue ⇒ power allocated to CUE • ˜ I D2D ⇒ estimated interference from D2D pair