Received: 20 December 2017 Revised: 17 March 2018 Accepted: 3 April 2018 DOI: 10.1002/ett.3422 RESEARCH ARTICLE Hierarchical decision model for throughput maximization in D2D-enabled LTE-WiFi HetNets Abiodun Gbenga-Ilori 1 Aydin Sezgin 2 1 Department of Electrical and Electronics Engineering, University of Lagos, Lagos, Nigeria 2 Institute of Digital Communication Systems, Ruhr-Universität Bochum, Bochum, Germany Correspondence Abiodun Gbenga-Ilori, Department of Electrical and Electronics Engineering, University of Lagos, Lagos, Nigeria. Email: gbengailori@unilag.edu.ng Funding information Alexander von Humboldt-Stiftung Abstract This paper proposes a hierarchical decision model for efficient and fair coex- istence of Wireless Fidelity (WiFi) and heterogeneous cellular networks with device-to-device (D2D) communications. The first submodel is an allocation game formulated to model the data rate gain possible through the deploy- ment of D2D communication in cellular networks. This is to guarantee that the Long-Term Evolution (LTE) network is optimally utilized before offload- ing traffic to WiFi small cells. The second submodel is a Markovian model proposed as an optimal spectrum sharing scheme that guarantees efficient spectrum utilization and interference reduction in LTE-WiFi heterogeneous net- works (HetNets). Simulation results verify that the proposed decision model not only provides a more spectrum efficient sharing scheme but also shows better network throughput while ensuring fairness in spectrum access for WiFi users. 1 INTRODUCTION The demand for higher data rates and congestion has put an enormous demand on the existing communication net- works. * The future fifth-generation (5G) network will emerge as an enabler to deliver services at very high data rates putting more demand on the communication network. This challenge has led to the proposal of device-to-device (D2D) communication in the fourth-generation (4G) and 5G cellular networks. The multi-radio access technology (RAT) has also been standardized to support high channel utilization, which translates to increased network data rates in heteroge- neous networks (HetNets). 1 In such HetNets, users can move seamlessly from one RAT to another. 2 Recently, there has been a development of Long-Term Evolution Unlicensed (LTE-U) by standardization bodies. LTE-U is expected to achieve spectrum integration through coexistence of multi-RAT systems in unlicensed bands. 3 In LTE-U technology, the evolved Node B (eNodeB) is expected to handle critical control signaling, mobility, and high-quality data while less critical data can be offloaded to the unlicensed band. The motivation behind this development is that LTE-U will utilize the unli- censed spectrum more efficiently since there is a central coordinating base station for resource distribution. 4 However, one important concern for operators is the issue of fair coexistence with the incumbent Wireless Fidelity (WiFi) systems and interference management in the unlicensed band. In this paper, we propose a hierarchical decision model for optimization of spectrum resource capacity in LTE-WiFi HetNet. We introduce the concept of offloading D2D communication from one RAT to another in order to maximize the overall throughput of the HetNet while protecting users in the network from harmful interference. First, we propose an LTE subband allocation game to ensure that the spectrum resource available in the primary macrocell is maximally utilized. If there is a need for more spectrum after our allocation game, then the eNodeB can offload D2D users to the *Equally contributing authors. Trans Emerging Tel Tech. 2018;e3422. wileyonlinelibrary.com/journal/ett Copyright © 2018 John Wiley & Sons, Ltd. 1 of 14 https://doi.org/10.1002/ett.3422