Fairness and resource allocation in device-to-device wireless regional area network

Abstract

With the rapid development in wireless devices, applications and networks, radio frequencies have become scarce resources. Therefore, it is critical to make efficient use of the radio frequencies. A promising way to solve this problem is the use of cognitive radio (CR). In CR, radio frequencies are allocated to licensed users, also called primary users (PUs) and these frequencies can be reused by unlicensed users, also called secondary users (SUs) without affecting the PUs. This way, the spectrum utilization can be increased significantly. Cognitive radio networks (CRNs) are the networks using CR technology, based on which the IEEE 802.22 working group has developed three standards and there are several other on-going projects. IEEE 802.22 aims at wireless regional area networks (WRANs) and broadband services in rural areas. TV channels are employed due to their underutilization in rural areas and good performance for long distance communication. A cellular architecture is adopted with large cells (up to a radius of 100\,km). Each cell has a base station (BS) and multiple customer premises equipment (CPE). IEEE 802.22 is a significant milestone in CRN standardization. However, WRANs have severely limited capacity due to their single operating channel, point-to-multipoint topology and the requirement for regular quiet periods (QPs) to do spectrum sensing. Moreover, the spectrum sharing amongst CPEs is not addressed by IEEE 802.22, and this influences the channel utilization directly. This thesis explores ways to enhance the network capacity by spectrum allocation. Another critical issue is also identified and addressed regarding resource allocation problems, which is the fairness issue. Many resources can be found in wireless networks, e.g., bandwidth, frequencies and energy, and their use influences the performance of the network significantly. For example, unfair spectrum allocation may lead to starvation in access opportunities of some CPEs and inefficient spectrum usage. Fairness has a different connotation depending on the context; consequently, it is difficult to answer questions such as what is fairness, how to measure it and how to achieve it. Hence, before addressing the WRAN capacity constraints, the fairness issues applicable to wireless networks in general are addressed in this thesis. This has resulted in two main research topics in this thesis. The first part deals with fairness in wireless networks. Within this part, definitions and different perspectives of fairness are discussed. To achieve fairness, an Observe-Plan-Do-Check-Act (OPDCA) based fairness process is proposed. Then, the existing fairness indices in resource allocations are examined. From this analysis we conclude that these indices are not sufficient and advanced indices are needed in the domain of wireless networks. Hence, based on the OPDCA framework, a general model of fairness indices is proposed and analyzed. The network capacity limitation of WRANs is addressed in the second part of this thesis. Device-to-device (D2D) communication is a promising method to increase the capacity of the cellular architecture, leading to the concept of device-to-device WRAN (D2DWRAN). There are three main ideas in D2DWRANs: D2D communication, channel reuse and the use of multiple operating channels. D2D communication enables intra-cell CPE-to-CPE communication and makes channel reuse possible. For links that are far from each other, the same channel can be used simultaneously, if there is transmission power control. With channel reuse, the utilization of radio frequencies can be increased significantly. One step further, to maximize the use of available channels, multiple operating channels are envisaged in D2DWRANs both in the downstream (BS to CPE) and upstream (CPE to BS) directions. These three ideas require new protocols and strategies. Hence, based on the existing standards of IEEE 802.22, relevant issues and proposed solutions in this thesis are: the D2DWRAN OFDMA system, the channel management of multiple channels, the spectrum sharing problem, the self-coexistence amongst cells and the QP scheduling. These proposals provide the basis for designing D2DWRANs that have a significantly higher capacity compared to the existing IEEE 802.22 network proposals, which is also confirmed by simulation results.