Radio resource management in heterogeneous wireless networks
Date of Issue2014
School of Computer Engineering
Centre for Multimedia and Network Technology
Mobile traffic data has seen a growing demand from the consumers such that the wireless cellular network operators are finding it hard to meet this demand using conventional techniques of network enhancement. The typical network enhancement methods, which consist of increasing the radio spectrum or installing new base stations, are no longer scalable with the data demand. Hence, these traditional methods are neither technically viable nor economically feasible in the long term. This increase in demand has been forecasted to grow further in subsequent years, and the network operators need innovative paradigms to tackle this problem. smallcells (e.g., picocell, microcell, and femtocell) have been proposed as one of the solutions to address this issue. The basic aim of smallcells is to increase the areal spectral efficiency of the network by aggressive spectrum re-utilization and network densification using low power, short range base stations. The introduction of smallcells creates a heterogeneity where the available spectrum is shared by different base stations that have different characteristics. Thus, the deployment of smallcells themselves creates new technical challenges regarding its co-existence with the extant macrocells. In this regard, the heterogeneity in the network can be a cause for both conflict as well as cooperation. The smallcell's policy of aggressive spectrum reuse results in co-channel interference to both the macrocell as well as the smallcells themselves. This is likened to a social situation where each base station can make independent decisions to optimize their own performance parameters. Such social situations can be formally investigated by the methods of game theory. This thesis addresses some of the important issues that the co-channel interference tends to raise in a heterogeneous network. The first part of our thesis considers the problem of downlink power control. The contrast in the transmit powers of macrocell and smallcell gives rise to a natural hierarchy, which we formalize using a non-cooperative game model called the Stackelberg game. The smallcells and the macrocells in the network are assumed to compete with each other to maximize their capacity under transmit power constraints. The behavior of smallcells and macrocells is analyzed and power allocation algorithms are proposed to obtain an equilibrium solution. As a special case of this solution, it is shown that under the high interference condition, the macrocells and smallcells tend to allocate their power in mutually orthogonal channels. The performance of the system is compared to the case when such hierarchy is not considered. In the second part of our thesis, we apply the concepts of a network multiple-input-multiple-output (MIMO) system to smallcell networks. We propose a coalition formation game model to cluster the smallcell base stations so that they can perform cluster-wise joint beamforming. We take the recursive core as the solution concept of the coalition formation game. Three algorithms have been proposed and analyzed to obtain the solution, however only one of them is shown to have both a low complexity and a guaranteed stability. Analytical formulas are given to compute the average number of coalitions and the average size of coalitions that can form during such a coalition formation process. Finally, the last part of our thesis considers the problem of admission control in the uplink transmission of a smallcell network. An underlying non-cooperative power game is devised, based on which a coalition game is formulated by taking a suitable value function and payoff division function. A Markov model is constructed to obtain a stable coalition structure as the required solution of our access control problem. In summary, our work investigates the three different issues arising from co-channel interference using game theory: power allocation, beamforming, and admission control. Some possible future investigations can be directed towards joint resource allocation (e.g., power, beamforming, and scheduling) and coalition formation for the smallcell network.
DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems