This paper aims to improve the handover performance in heterogeneous networks (HetNets). Since achieving high data rates, low signaling loads, and a better coverage area are highly dependent on the number of handovers, reducing the number of unnecessary handovers is crucial for both mobile users and the whole network. In this paper, a new decision-making algorithm, based on traffic and propagation metrics, is proposed for HetNets that can reduce the number of unnecessary handovers in comparison with the traditional handover algorithms, especially when the femtocell assignment probability is relatively high. We further analyze the handover probability for the proposed scheme which is in a close agreement with simulation results. Simulation results show that a higher assignment probability is achieved for the femtocell base station in the proposed scheme. We also show that the proposed scheme reduces the number of unnecessary handovers compared to the conventional RSS-α algorithm.
Cognitive radio (CR) heterogeneous network (HetNet) is an emerging technology that aims at enhancing spectrum utilization through spectrum sharing among macro base stations and femto base stations. Similar to other CR networks, in CR HetNets, providing the desired quality of service for the licensed primary users (PUs) is of utmost importance. Due to the shared spectrum between PUs and cognitive secondary users (CSUs) as well as offloading policies, the spectrum handover (SHO) process must be carefully designed. Using the idea of reserved channels, this paper proposes 2 traffic‐aware SHO schemes for cognitive HetNets. In the proposed schemes, each CSU can adopt either a shared‐to‐reserved or a reserved‐to‐shared SHO strategy. The proposed approaches can be implemented in both distributed and centralized manners to maintain a trade‐off between performance and complexity. The performance of the proposed schemes is mathematically analyzed, and closed‐form expressions are derived for the blocking probability of the PUs and the forced termination probability of the CSUs. Numerical results show that the proposed schemes outperform the existing SHO approaches, such as always‐change, always‐stay, and proactive methods, specifically at higher arrival rates of PUs. Moreover, several evaluation metrics, such as effective throughput, energy efficiency, and a proposed combinational utility function, are investigated for both distributed and centralized schemes. The results show that the proposed centralized schemes offer higher performance compared to the distributed schemes.
Cognitive heterogeneous network is a promising technology to meet the requirements of future wireless networks in cost and energy efficiency. By using vertical handover (VHO) between different network tiers, such as macro and femto, the traffic congestion can be potentially alleviated, and the spectral efficiency is significantly increased. However, performing VHO for a cognitive handover user (CHU) and simultaneously guaranteeing the quality of service of the primary user (PU) is the most challenging issue in such a network. This paper proposes an efficient VHO strategy in a cognitive heterogeneous network, which considers both adaptive average received signal and spectrum availability, namely, average received signal and spectrum availability. To analyse the performance of the proposed average received signal and spectrum availability algorithm, several metrics are investigated. First, the assignment probability of a CHU from a macro base station to a femto base station is evaluated and simplified in a closed-form expression. Then, the outage probability of a CHU and collision probability of the PU are theoretically investigated for the proposed algorithm and are compared with 2 well-known algorithms, the modified received signal strength-α and the received signal strength and wireless transmission loss. We also introduce a new performance metric, referred to as figure of merit, which jointly considers the assignment and outage probability of a CHU, collision probability of a PU, and the number of unnecessary handovers of a CHU. Figure of merit effectively shows the superiority of the proposed handover algorithm to conventional ones. KEYWORDSARSA, cognitive handover user (CHU), cognitive HetNet, femtocell, macrocell, vertical handover (VHO)
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