Unified and Distributed QoS-Driven Cell Association Algorithms in Heterogeneous Networks

This paper addresses the cell association problem in the downlink of a multi-tier heterogeneous network (HetNet), where base stations (BSs) have finite number of resource blocks (RBs) available to distribute among their associated users. Two problems are defined and treated in this paper: sum utility of long term rate maximization with long term rate quality of service (QoS) constraints, and global outage probability minimization with outage QoS constraints. The first problem is well-suited for low mobility environments, while the second problem provides a framework to deal with environments with fast fading. The defined optimization problems in this paper are solved in two phases: cell association phase followed by the optional RB distribution phase. We show that the cell association phase of both problems have the same structure. Based on this similarity, we propose a unified distributed algorithm with low levels of message passing to for the cell association phase. This distributed algorithm is derived by relaxing the association constraints and using Lagrange dual decomposition method. In the RB distribution phase, the remaining RBs after the cell association phase are distributed among the users. Simulation results show the superiority of our distributed cell association scheme compared to schemes that are based on maximum signal to interference plus noise ratio (SINR)

Green Cellular Networks: A Survey, Some Research Issues and Challenges

Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogeneous network deployment based on micro, pico and femto-cells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technologyComment: 16 pages, 5 figures, 2 table

Resource allocation and performance evaluation in heterogeneous and relay-based wireless networks

In the last decade, mobile data demand has been exponentially growing. Telecommunication industry finds it increasingly difficult to cope with this exponential growth through conventional cellular networks with carefully planned high power macro base stations (BSs). Therefore, the densification of BSs through introduction of low power BSs has been considered for implementation. The combination of macro BSs and low power BSs such as pico and femto BSs as well as relay nodes is referred to as heterogeneous networks (HetNets). HetNets impose major technical challenges in implementation such as severe interference cases and imbalance of load among macro BSs and low power BSs. One problem that needs to be re-addressed in the context of HetNets is the cell association problem. Although centralized cell association schemes are important in realizing the potentials of HetNets, mobile operators are interested in distributed schemes in which network elements decide based on their local information. In this thesis, we consider distributed cell association algorithms with quality of service provisioning. First, we propose a unified cell association algorithm that is particularly designed for downlink. Next, we consider uplink to have a downlink and uplink aware cell association scheme. The performances of the proposed schemes are examined through numerical simulations. Cooperative relay-based communication combined with orthogonal frequency division multiplexing (OFDM) and its multi access variant, orthogonal frequency division multiple access (OFDMA) has gained an immense interest in the last decade. Among all the research topics in OFDM relay-based communication, analyzing the outage behavior has been an invariable concern to researchers. To analyze the outage behavior, most of the researchers ignore the correlation between OFDM subchannels, and also assume equal bit allocation on all the subchannels. In this thesis, we analyze the outage behavior of a three-node OFDM relay-based network when these two assumptions are relaxed. Next, we characterize the global outage probability of a multi-user single-relay OFDMA network. Finally, a network consisting of a cluster of source-destination pairs and a cluster of relays is considered where we propose a low complexity relay allocation scheme. The outage analyses and the relay allocation scheme are examined through numerical simulations.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Selective subcarrier pairing and power allocation for decode-and-forward OFDM relay systems with perfect and partial CSI

This thesis investigates a decode-and-forward two-hop relaying system consisting of one source, one relay and one destination, in which orthogonal frequency division multiplexing is used. The relay forwards the message received from the source on a subset of available subcarriers in the second time slot. Firstly, a subcarrier pairing and selection algorithm is proposed, assuming that perfect channel state information (CSI) is available at all nodes, then, power is allocated to both the source and relay stations under individual power constraints in order to maximize the capacity. Secondly, subcarrier selection and pairing, and power allocation (PA) under partial CSI assumption along with individual power constraints are addressed. The result is a novel distributed algorithm with low complexity maximizing the expected value of capacity at the source and relay nodes. Finally, the simulation results show that selective relaying combined with subcarrier pairing and PA improves the system capacity to a considerable extent in both perfect and partial CSI cases.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Green Cellular Networks: A Survey, Some Research Issues and Challenges

Abstract—Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or “green ” cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogenous network deployment based on micro, pico and femtocells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a “green ” cellular network technology. Index Terms—Green communication, energy efficient networks, efficiency metrics, microcells, picocells, femtocells, cognitive radio, cooperative relaying. I