Huaizhou Shi

Fairness in Wireless Networks:Issues, Measures and Challenges

The pervasiveness of wireless technology has indeed created massive opportunity to integrate almost everything into the Internet fabric. This can be seen with the advent of Internet of Things and Cyber Physical Systems, which involves cooperation of massive number of intelligent devices to provide intelligent services. Fairness amongst these devices is an important issue that can be analysed from several dimensions, e.g., energy usage, achieving required quality of services, spectrum sharing, and so on. This article focusses on these viewpoints while looking at fairness research. To generalize, mainly wireless networks are considered. First, we present a general view of fairness studies, and pose three core questions that help us delineate the nuances in defining fairness. Then, the existing fairness models are summarized and compared. We also look into the major fairness research domains in wireless networks such as fair energy consumption control, power control, topology control, link and flow scheduling, channel assignment, rate allocation, congestion control and routing protocols. We make a distinction amongst fairness, utility and resource allocation to begin with. Later, we present their inter-relation. At the end of this article, we list the common properties of fairness and give an example of fairness management. Several open research challenges that point to further work on fairness in wireless networks are also discussed. Indeed, the research on fairness is entangled with many other aspects such as performance, utility, optimization and throughput at the network and node levels. While consolidating the contributions in the literature, this article tries to explain the niceties of all these aspects in the domain of wireless networking.

An intra-cell peer to peer protocol in IEEE 802.22 networks

IEEE 802.22 mostly considers a typical cellular network with centralized control. Therefore, all intra-cell communications have to be via base stations. It not only leads to extra power consumption for intra-cell communications, but also only one channel can be used per time slot in the whole cell. This may lead to decrease in the network performance. Therefore, we propose a protocol called intra-cell peer to peer communication protocol (ICP2P) based on IEEE 802.22 protocol. The main accomplishments of ICP2P are to support direct intra-cell peer to peer communications between Customer Premises Equipments (CPEs), to allocate multiple channels per time slot in a cell, and to re-allocate same channels in one time slot. The network performance, such as capacity, channel usage and energy consumption, are significantly improved by ICP2P. Additionally, a weighed demand queue algorithm (WDQA) is proposed to guarantee the fairness in channel access opportunities for CPEs.

Self-coexistence and spectrum sharing in device-to-device WRANs

IEEE 802.22 wireless regional area network (WRAN) standard employing cognitive radios is gaining much attention recently. The WRAN standard targets reuse of unused TV channels. We propose a device-to-device wireless regional area network (D2DWRAN) to extend the capacity of IEEE 802.22. Network capacity can be increased by supporting direct intra-cell device to device (D2D) communication through channel reuse and also with aggregation of nonadjacent multiple operating channels. Self-coexistence of neighboring IEEE 802.22 cells is a major challenge in WRANs, since the availability of channels varies frequently and channels are reused by every cell as much as possible. Currently, IEEE 802.22 does not consider D2D communication. We propose a two-tier spectrum sharing mechanism for channel allocation in D2DWRANs - both at intra-cell and inter-cell levels. Algorithms and a thorough analysis are presented. We examine our proposal through simulations. Results show significant performance improvement compared to IEEE 802.22. However, there are many hurdles to cross, such as, coexistence with other cognitive radio networks (CRNs), the intra-cell routing, allocation of other network resources, etc. We believe that further work in this domain can lead to increase in capacity not only in WRANs but also in other cellular networks.

Procedure to build interference map in peer to peer IEEE 802.22 networks

Peer to peer wireless regional area network (P2PWRAN) is proposed as an extension to support peer to peer communication based on IEEE 802.22 [1]. Multiple channel allocation and reuse of channels in the same time slot in P2PWRAN significantly increase the network capacity compared to standard IEEE 802.22 networks. One of the key issues in bringing P2PWRAN into reality is building the interference map. The concept of interference map/mapping has been mentioned in literature however, how to build an interference map is still an open issue. Therefore, we propose a simple and self-adapting interference map building protocol (SIMBP) for P2PWRAN, which can also be used in other multi-channel wireless networks with minor modifications. The simulation results show that SIMBP converges under the P2PWRAN setting, and with number of available channels and growing number of nodes, the capacity of the network is reached eventually.

Spectrum- and energy-efficient D2DWRAN

IEEE 802.22 is the first world-wide standard for wireless regional area networks using cognitive radio technologies. Major drawbacks of these networks are limited network capacity and low energy efficiency. One potential solution for these drawbacks is device-to-device communication, which can be incorporated as D2DWRAN. D2DWRAN features direct intracell communication, reuse of channels, and use of multiple operating channels. In this article, we mainly discuss energy-efficient spectrum sharing in D2DWRAN. We explicate a mechanism to increase energy efficiency for long distance links using relays. Along with energy, channel utilization and fairness are also considered while choosing relays. Thus, significant improvement in both network capacity and energy efficiency can be achieved. The schemes discussed here can also be used in other D2D communication settings.

Adapting IEEE 802.22 OFDMA system for P2PWRANs

IEEE 802.22 is the first standard to utilize cognitive radio technology for wireless regional area networks (WRANs). It has adopted a cellular topology containing one base station (BS) and multiple customer premises equipments (CPEs) in a cell. It covers a very large area with radius ranging up to 100 km. Orthogonal frequency-division multiple access (OFDMA) system is employed and it is further slotted in time-domain. In one slot only one CPE can be allocated, and every intra-cell packet needs to be routed through the BS. This point-to-multi-point structure significantly limits the network capacity in the case of CPE-CPE communication, which is predicted to happen, and even the use of OFDMA does not help much. Therefore, peer-to-peer WRAN (P2PWRAN) has been proposed to support direct intra-cell communication in order to extend the network capacity. In this paper, the IEEE 802.22 OFDMA system is adapted to P2PWRAN to support direct CPE-CPE communications. The downstream burst allocation in P2PWRAN is similar to the OFDMA system of IEEE 802.16, which has been widely studied in the literature. Therefore, in this paper we look at the unexplored upstream burst allocation where slots can be reused among CPEs and the BS with power control mechanisms. We propose a burst allocation algorithm that maximizes the network capacity greedily. The algorithm is examined under various conditions such as, number of CPEs, size of requests, length of US subframes and type of requests (CPE-BS or CPE-BS). We also show that our algorithm performs better than the existing solutions.

A fairness model for resource allocation in wireless networks

In wireless networks many nodes contend for available resources creating a challenge in resource allocation. With shared resources, fairness in allocation is a serious issue. Fairness metrics have been defined to measure the fairness level of resource decisions in allocations. Therefore, fairness metrics significantly influence network and node performances emphasizing the need for due diligence to fairness metrics. It can be seen that fairness metrics in many of the allocation strategies and algorithms in the literature are not analyzed in depth to show the overall fairness of allocations from different perspectives. Hence, we propose a series of fairness metrics for resource allocation in wireless networks, which evaluate individual, system, short and long term fairness. Our metrics are general enough to be adapted in either multiple or single resource sharing scenarios. Algorithms using these metrics for channel allocation problem in peer-to-peer wireless regional area network is proposed and simulated, and the results show that our metrics in conjunction with smart channel allocation strategies guarantee both the fairness and performances.

Channel allocation in peer to peer IEEE 802.22 networks

IEEE 802.22 is the first protocol that proposes the use of TV whitespaces [1] for WRAN. It proposes a typical cellular network. However, it also has limited performance. If it were to support direct communication between CPEs in a cell, not only the network capacity could be enhanced, but also the channel usage could be increased. Therefore, we propose a peer to peer communication method in IEEE 802.22 networks and three collision area based channel allocation algorithms. The first algorithm aims to maximize the channel reuse the second one employs an algorithm for fair channel allocation. The third algorithm finds a trade-off between channel reuse and fairness. In all three algorithms, multiple channels can be allocated in one time slot to different CPEs, and same channel can also be allocated more than once in one time slot via power control techniques without causing interference or collision. Maximizing network performance in every time slot may cause unfairness in allocation. Therefore, we proposed to consider fairness in channel allocation. This leads to a trade-off between network performance and fairness. The simulation results show that our algorithms can improve network performance significantly, compared to standard IEEE 802.22 networks.

Multi-channel management for D2D communications in IEEE 802.22 WRANs

IEEE 802.22 standard is the first worldwide standard using cognitive radio (CR) technology for wireless regional area networks (WRANs). Orthogonal frequency-division multiple access (OFDMA) is employed for point-to-multi-point (P2M) communication between base stations (BS) and customer premises equipments (CPEs) in WRANs. The large coverage of a single cell (up to 100 km of radius) is the unique feature of WRANs. However, channel reuse is not considered, i.e., in one slot the channel can be allocated to only one CPE, and every intra-cell packet needs to be routed through the BS. Therefore, device-to-device WRAN (D2DWRAN) has been proposed to support direct intra-cell CPE-CPE communication. Power control strategies are used to achieve higher reuse of OFDMA slots. In this paper, we take one step further to enhance the network capacity by adopting multichannel management (MCM) with infrastructure support. This enables multiple operating channels to be used simultaneously in D2DWRANs. New channel switching strategies are also studied. We implement a MCM scheme in an OFDMA setting for D2DWRANs, and examine it in the upstream (US). For downstream (DS), there are already many proposals in the literature, which can be adopted directly by D2DWRAN. The simulation results show that MCM scheme significantly improves the network performance compared to single-channel D2DWRANs and WRANs.

Fairness and network capacity trade-off in P2P IEEE 802.22 networks

Wireless Regional Area Networks(WRAN), IEEE 802.22 standard, adopts a centralized cellular topology including base station (BS) and customer-premise equipments (CPEs). However this may lead to limited network capacity, since every CPE needs to communicate to the BS and only one channel can be used to communicate in the whole cell per time slot with one BS antenna. Peer to Peer WRAN (P2PWRAN) was proposed [3] to circumvent this, where CPEs can communicate with each other directly. P2PWRAN increases network capacity compared to the standard WRAN because of spatial reuse. Multiple communication channels can be simultaneously allocated and reused in one time slot by the BS and multiple CPEs. In IEEE 802.22b [4], a standard in progress, peer to peer communication plays an important role for enabling smart grids. Channel allocation influences the network performance significantly, therefore, we formulate the spectrum allocation problem in P2PWRAN as a quadratically constrained programming (QCP) problem. It is also proved as a computationally hard problem. The Greedy Coloring Algorithm (GCA) is examined in P2PWRAN channel allocation, and the results show that it may cause severe unfairness in allocation of channels. Thus a Fair Greedy Coloring Algorithm (FGCA) is proposed to guarantee a fair allocation by queuing flows considering previous allocations. However, FGCA guarantees fairness but leads to decrease in performance of P2PWRAN. Therefore, a Trade-off FGCA (TFGCA) is proposed considering fairness and network performance at the same time during allocation. Simulation results show that with the adjustment of two factors in TFGCA, network performance and fairness can be balanced.