4378 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 16, NO. 7, JULY 2017 Evolutionary Channel Sharing Algorithm for Heterogeneous Unlicensed Networks M. A. Raza, Sangjun Park, and Heung-No Lee, Senior Member, IEEE Abstract— Channel sharing in TV whitespace (TVWS) is challenging because of signal propagation characteristics and diversity in network technologies employed by secondary net- works coexisting in TVWS. In this paper, the TVWS sharing problem is modeled as a multiobjective optimization problem, where each objective function tackles an important coexisting requirement, such as interference and disparity in network technologies. We propose an evolutionary algorithm that shares the TVWS among coexisting networks taking care of their channel occupancy requirements. In this paper, the channel occupancy is defined as the time duration; a network desires to radiate on a channel to achieve its desired duty cycle. Simulation results show that the proposed algorithm outperforms existing TVWS sharing algorithms regarding allocation fairness and a fraction of channel occupancy requirements of the coexisting networks. Index Terms— Coexistence set, evolutionary algorithm, indica- tor function, pareto optimal, pareto dominance, TV whitespace, whitespace object. I. I NTRODUCTION T V WHITESPACE (TVWS) refers to the TV spectrum not in use by licensed operators in a spatiotemporal region. Worldwide efforts have been initiated to permit unlicensed devices to operate in TVWS. Therefore, several standards such as IEEE 802.22-2011 [1], 802.11af [2], 802.15.4m [3], and ECMA-392 [4] have been developed to regulate access to TVWS. The MAC/PHY layer technologies in these stan- dards are incompatible. A collocated deployment of secondary devices operating on these standards may create coexistence issues, such as unresolved interference due to a disparity in MAC/PHY layer technologies, spectrum congestion due to indiscriminate spectrum usage, and spectrum scarcity in con- gested areas [5]–[7]. Such issues, if left unresolved, may result in inefficient use of TVWS. Therefore, IEEE has developed a standard namely 802.19.1 to provide coexistence among sec- ondary devices, namely whitespace objects (WSO), operating on heterogeneous network technologies [8]. The collocated Manuscript received February 11, 2016; revised July 19, 2016 and January 16, 2017; accepted April 7, 2017. Date of publication April 27, 2017; date of current version July 10, 2017. This work was supported by the National Research Foundation of Korea (NRF) funded by the Korean Government (MSIP) under Grant NRF-2015R1A2A1A05001826. The associate editor coordinating the review of this paper and approving it for publication was J.-M. Park. (Corresponding author: Heung-No Lee.) The authors are with the School of Electrical Engineering and Computer Sci- ence, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea (e-mail: raza@gist.ac.kr; sjpark1@gist.ac.kr; heungno@gist.ac.kr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TWC.2017.2697880 WSOs operating on heterogeneous network technologies are referred to as hetero-WSO throughout this paper. A set of tasks to achieve peaceful coexistence among hetero-WSOs sharing the common spectrum is referred to as coexistence decision making (CDM) procedure. A system implementing CDM procedure is referred to as a CDM system [9]. Some literature work exists that implements CDM procedure in the TVWS domain. Most of such work like in [9]–[12] implements a CDM procedure to fully satisfy the channel demands of hetero-WSOs. However, such channel allocation policy may cause some of the WSOs to get the channel while rest of them do not. This situation is intensified in a highly-congested area where a limited TV spectrum is available for secondary user activities due to the active presence of licensed operators. Considering the free-to-use status of the TVWS, we aim to define a CDM procedure that accommodates as many as hetero-WSOs on the available TVWS by relaxing their channel occupancy demands. In this paper, we propose an Evolutionary Coexistence decision making (EvCo) algorithm for an 802.19.1-complaint CDM system. The algorithm addresses the critical coexistence issues like allocation fairness, system throughput maximiza- tion, and WSO satisfaction, each of which is modeled as an objective function in the TVWS multiobjective optimization problem (MOP), as will be defined in Section IV. The main contributions of the proposed work are summarized as follows. 1) A CDM procedure is implemented as a process of shar- ing a set of TV channels of predetermined bandwidth among a set of hetero-WSOs. Unlike existing CDM formulations in the TVWS sharing domain [9]–[11], the proposed formulation accommodates as many as hetero- WSOs on the available TVWS by relaxing their channel demand satisfaction. 2) The proposed CDM system transforms the nonconvex, nonlinear multiobjective function in the TVWS shar- ing MOP (Section IV-B) into a max-min optimization formulation, using a binary epsilon indicator function (Section IV-D). Such formulation enables the CDM system to achieve a true multiobjective optimization as it does not require a priori articulation of preferences of the decision maker nor does it need to scalarize the multiobjective function in the TVWS sharing MOP. Consequently, a better approximation of global minima of the TVWS sharing MOP is achieved as compared to the existing CDM systems in [9] and [10]. 3) An evolutionary algorithm, called EvCo is proposed to obtain a feasible Pareto-optimal solution for the 1536-1276 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.