On improving SINR in LTE HetNets with D2D relays

Sathya, V and Ramamurthy, A and S, Sandeep Kumar and Tamma, Bheemarjuna Reddy (2016) On improving SINR in LTE HetNets with D2D relays. Computer Communications, 83. pp. 27-44. ISSN 0140-3664

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Abstract

Femtos, with frequency reuse one, can be deployed in hotspots, offices and residences alike to provide high indoor data rates and reduce traffic load on Macro. However, arbitrarily deployed Femtos could decrease SINR significantly because of inter-cell interference and obstacles present in the building. Hence, to attain a desirable SINR Femtos have to be placed efficiently. At the same time, minimizing the power leakage from indoor Femtos in order to improve the SINR of outdoor users in the high interference zone (HIZone) around building areas is also important. To guarantee minimum SINR to both indoor UEs (IUEs) and outdoor UEs in HIZone (HIZUEs), we apply the concept of device-to-device (D2D) communication wherein free/idle IUEs act like UE-relays for HIZUEs. We first formulate a D2D MILP model which establishes D2D pairs between free/idle IUEs and HIZUEs and also guarantees certain SINR threshold (SINRth) for both IUEs and HIZUEs. As D2D MILP model takes more computation time, it is not usable in real-world scenarios for establishing D2D pairs on the fly. Hence, we propose a two-step D2D heuristic algorithm for establishing D2D based relay pairs. In step one (called as hDPRA), it efficiently chooses potential D2D based relay pairs and allocates radio resources to them. In step two (called as hDPA), a Linear Programming (LP) model is formulated for power control of D2D links. We have evaluated the performance of the proposed D2D heuristic algorithm for different scenarios (i.e., 500 topologies) by varying densities of IUEs and HIZUEs. From our evaluation, we find that the proposed algorithm maintains almost the same SINR as that of Full Power Femto scheme (i.e., Femto transmits with maximum power) for IUEs and also guarantees certain minimum SINRth for HIZUEs. Our simulation results show that in comparison to the Optimal Femto Power (OptFP; Sathya et al., 2014) scheme (i.e., Femto transmits with optimal reduced power), it improves SINR of IUEs by 40%. However, the degradation in SINR of IUEs is only 1.6% when compared to the Full Power Femto scheme.

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