Interference management for self-organized femtocells towards green networks
ABSTRACT The femtocell concept is an emerging technology for deploying the next generation of the wireless networks, aiming at indoor coverage enhancement, increasing capacity and offloading the overlay macrocell traffic. One of the main challenges in short range femtocell networks is how to (re)configure the Home Node Bs (HNBs) in an autonomous manner so as to manage interference and diminish the energy consumption among nearby femtocells efficiently. In this paper, we investigate the indoor femtocell deployment making use of both the Frequency Division Duplexing (FDD) and the Time Division Duplexing (TDD) methods. In the FDD case, the HNBs share both the Uplink (UL) and Downlink (DL) channels with the macrocell without any cooperation to coordinate their access to the air interface. Conversely, in the TDD underlay case, femtocells only reuse the macrocell UL spectrum and cooperate with each other in order to minimize the interference among themselves, either with or without further coordination with the Macro User Equipment (MUE). The proposed solution is evaluated by means of system-level simulations using the Monte Carlo approach. Investigations have shown that the TDD underlay approach not only reduces the perceived interference levels, but also diminishes the outage probability.
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ABSTRACT: Full-duplex (FD) radio has been introduced for bidirectional communications on the same temporal and spectral resources so as to maximize spectral efficiency. In this paper, motivated by the recent advances in FD radios, we provide a foundation for hybrid-duplex heterogeneous networks (HDHNs), composed of multi-tier networks with a mixture of access points (APs), operating either in bidirectional FD mode or downlink half-duplex (HD) mode. Specifically, we characterize the net- work interference from FD-mode cells, and derive the HDHN throughput by accounting for AP spatial density, self-interference cancellation (IC) capability, and transmission power of APs and users. By quantifying the HDHN throughput, we present the effect of network parameters and the self-IC capability on the HDHN throughput, and show the superiority of FD mode for larger AP densities (i.e., larger network interference and shorter communication distance) or higher self-IC capability. Furthermore, our results show operating all APs in FD or HD achieves higher throughput compared to the mixture of two mode APs in each tier network, and introducing hybrid-duplex for different tier networks improves the heterogenous network throughput.IEEE Transactions on Wireless Communications 11/2014; 14(5). DOI:10.1109/TWC.2015.2396066 · 2.76 Impact Factor
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ABSTRACT: The past decade has seen a vast growth in wireless communication, continuously fueled by the users' ever-increasing demand for higher data rates. Various technologies are constantly competing with each other, trying to establish supremacy over other concurrent technologies and desperately vying to make its own space in the field of telecommunication. With the advent of 4G systems, we are at a crucial juncture. The all-important question has become: how to provide ubiquitous coverage for all the users in the network in a cost-efficient manner while at the same time satisfy high data rates and the Quality of Service (QoS) requirements proposed by ITU-R for IMT-Advanced systems? One technology which can provide an answer to the above question is low-power home base stations called femtocells used for local area deployments such as residences, apartment complexes, offices, business centers and outdoor hotspot scenarios. Through this work, we propose a scalable and fully distributed solution called the Distributed Capacity Based Channel Allocation Algorithm to overcome the problem of interference management and efficient system operation in a local area environment. The proposed scheme is simple yet robust and helps Home eNodeBs select the best available radio resources which minimizes interference to the neighboring nodes. Further, the scheme is subjected to various mitigating circumstances and interference-limited scenarios. The performance evaluation of the scheme is done under such conditions to ensure that it is scalable, flexible and can be considered as a practically viable option. Through this work, we try to not just improve the throughput experienced by the average user in a cell, but also the ones at the cell-edge who suffers the most due to interference from the neighboring cells. The scheme proposed aims to be energy-efficient as well by reducing the total number of component carriers used by each HeNB without compromising the average cell throughput values.02/2011, Degree: M.Sc. (Tech), Supervisor: Prof. Olav Tirkkonen; Instructor: Dr. Klaus Doppler
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ABSTRACT: With the introduction of third generation mobile services, femtocells are considered as an economically feasible solution for combining mobile and internet technologies, thereby giving fast and reliable access to data with a better coverage. However, it is well-known that the femtocells and macrocells sharing the same licensed frequency spectrum results in heavy cross-tier interference which degrades the downlink performance considerably. In this paper, we investigate a novel frequency–division duplex allocation strategy which eliminates the downlink cross-tier interference to the femtocell network from the macrocell base station throughout its coverage area. The proposed scheme seamlessly embed the femtocells within a macrocell resource network to create a heterogeneous two-tier system. It makes use of a cross-tier complementary spectrum sharing technique known as reverse frequency allocation (RFA) where the frequency carriers used in the macrocell transmission are reversed and allocated to femtocells. As a result, it better balances the requirement of greater inter-cell orthogonality and reduced inter-cell interference since macrocell and femtocell operates on different bands in uplink and downlink. It also assures enhanced spectral efficiency and the well-known benefit of reduced outage probability, especially for cell-edge users. This work further analytically quantifies and highlights through simulation results that RFA guarantees greater overall network throughput in the downlink and reduced cross-tier interference regardless of the positioning of the femtocell with respect to the macrocell base station. Also it is to be noted that, with recent academic surveys illuminating that the benefit of femtocells is reflected more in downlink, the focus of the current work is on downlink transmission where the traffic is high and the deployment is more beneficial.Wireless Networks 12/2014; DOI:10.1007/s11276-014-0868-x · 1.06 Impact Factor