Mathematical Modeling of Association Attempt with the Base Station for Maximum Number of Customer Premise Equipments in the IEEE 802.22 Network Humaira Afzal Department of Computer Science, Bahauddin Zakariya University, Multan, Pakistan humairaafzal73@yahoo.com Irfan Awan School of Electrical Engineering and Computer Science, University of Bradford, UK I.U.Awan@Bradford.ac.uk Muhammad Rafiq Mufti School of Electrical Engineering and Computer Science, University of Bradford, UK rafiq_mufti@yahoo.com Abstract— Avoiding collision among contending customer premise equipments (CPEs) attempting to associate with a base station (BS), the only available solution in IEEE 802.22 standard is binary exponential random backoff process in which the contending CPEs retransmit their association requests. The number of attempts the CPEs sends their requests to the BS are fixed in IEEE 802.22 network. This paper presents a mathematical framework for helping the BS in determining at which attempt the majority of the CPEs become the part of wireless regional area network (WRAN) from a particular number of contending CPEs at a given initial contention window size. Keywords—Collision probability; IEEE 802.22; WRAN; CPEs; BS; I. INTRODUCTION Due to the rapid growth of wireless devices and ever increasing bandwidth demands from users, more and more spectrum resources are required. Within the conventional spectrum framework, most of the spectrum bands have been exclusively allocated to specific licensed services. However, reports on spectrum usage measurements show that a lot of licensed bands, such as those for TV broadcasting, are underutilized, which results in spectrum wastage [1], [2]. The emerging cognitive radio (CR) technology has been proposed as a new solution to increase the efficiency of spectrum utilization. It is different from conventional radio devices in the sense that it can equip users with cognitive capability and reconfigurability [3], [4], [5], [6]. Exploiting these capabilities, a CR can sense and collect data about transmission frequency, bandwidth, power, modulation, etc. from its surrounding environment. After incorporating this information, it can identify the best available spectrum to meet communication requirements, and then can reconfigure its operational parameters according to the achieved information in order to attain the optimal performance. Due to this technology, the Federal Communications Commission (FCC) has allowed the licensed bands to unlicensed users. The IEEE 802.22 working group has been formed to develop the first international standard for WRAN cell. Its basic purpose was to provide broadband access in remote and rural areas by effectively utilizing the unused TV band provided no harmful interference is caused to the licensed users which may be digital TV, analog TV or wireless microphone [7], [8]. The core components of the WRAN cell consist of one BS and a number of fixed or portable CPEs having different QoS requirements. The cell follows fixed-point to multi- point topology with master/slave architecture and can facilitate up to 512 CPEs after fulfilling the requirements necessary for the protection of an incumbent. The BS controls all the communication in the cell, i.e. there is no peer-to-peer communication directly between the CPEs and no CPE is allowed to transmit without receiving an appropriate authorization from the BS. When a CPE is powered on, it first scans the TV band to determine which channels are occupied by the incumbent and which channels are free. On the basis of its observation, it builds up its spectrum usage report. The same mechanism of spectrum sensing is also carried out on a BS and it periodically broadcasts using an operating channel. The broadcast from a BS is distinguished from other TV broadcasts by the preamble transmitted at the beginning of each superframe. The CPE after receiving the particular frame tunes to that frequency and sends its association request in the uplink direction using the initial contention window. If more than one CPE attempts to associate with the BS, collision occurs. In this case, the binary exponential random backoff (BERB) process is carried out. According to this process, the CPE adjusts its internal backoff window and re-attempts to associate with the BS. If collision occurs again, the CPE involves in second backoff phase and does the same procedure before the maximum number of attempts expired as specified by IEEE 802.22 standard [9]. This paper focuses on a mathematical model that helps the BS in finding at which attempt the majority of the CPEs become the part of WRAN cell for a particular number of attempting CPEs at a given initial contention window size. The paper is organized as follows. Section-II provides a brief overview of the collision probability. Numerical results are discussed and a mathematical framework is developed based on number of contending CPEs in Section-III. Finally, the concluding remarks and some proposed future work are described in Section –IV 2015 3rd International Conference on Future Internet of Things and Cloud 978-1-4673-8103-1/15 $31.00 © 2015 IEEE DOI 10.1109/FiCloud.2015.128 289