A Framework for Dynamic Selection of Backoff Stages during Initial Ranging Process in Wireless Networks

yesThe only available solution in the IEEE 802.22 standard for avoiding collision amongst various contending customer premises equipment (CPEs) attempting to associate with a base station (BS) is binary exponential random backoff process in which the contending CPEs retransmit their association requests. The number of attempts the CPEs send their requests to the BS are fixed in an IEEE 802.22 network. This paper presents a mathematical framework that helps the BS in determining at which attempt the majority of the CPEs become part of the wireless regional area network from a particular number of contending CPEs. Based on a particular attempt, the ranging request collision probability for any number of contending CPEs with respect to contention window size is approximated. The numerical results validate the effectiveness of the approximation. Moreover, the average ranging success delay experienced by the majority of the CPEs is also determined.The full text will be available at the end of the publisher's embargo: 7th Aug 201

Enhanced Dynamic Frequency Hopping Performance in Cognitive Radio IEEE 802.22 Standard

IEEE 802.22 is a Cognitive Radio based standard designed for Wireless Regional Area Networks (WRAN) for the purpose of providing wireless broadband access to rural and remote areas. The standard relies on the utilization of the unoccupied spectrum that became available after the TV signal was converted from analog to digital. In this thesis, we present an enhanced scheme for the operation of the Dynamic Frequency Hopping (DFH) technique in the IEEE 802.22 standard for WRANs. The performance of the DFH is analyzed thoroughly for various types of channels and for a Multiple-input Multiple-output (MIMO) systems. The core of this research is based on the coexistence of the incumbent users and the WRANs in the TV white spaces (TVWS). The proposed technique, aims at protecting the licensed users from interfering with the cognitive broadband access in the TV spectrum. In order to achieve that, spectrum sensing is performed in the intended working channel in DFH while spectrum monitoring with the energy-ratio (ER) algorithm is applied during the WRAN data transmission in the currently working channel. Hence, in the DFH-ER algorithm the reappearance of an incumbent user in a band occupied by the WRANs would be detected immediately, providing interference free performance for the licensed user as well as reliable data transmission for the unlicensed one. Simulation results of the proposed DFH-ER technique compared to the conventional DFH scenario exemplify the enhancement of the WRAN data transmission while protecting the incumbent users

Coexistence of DTT and Mobile Broadband: A Survey and Guidelines for Field Measurements

This article provides a survey and a general methodology for coexistence studies between digital terrestrial television (DTT) and mobile broadband (MBB) systems in the ultra high frequency (UHF) broadcasting band. The methodology includes characterization of relevant field measurement scenarios and gives a step-by-step guideline on how to obtain reliable field measurement results to be used in conjunction with link budget analyses, laboratory measurements, and simulations. A survey of potential European coexistence scenarios and regulatory status is given to determine feasible future use scenarios for the UHF television (TV) broadcasting band. The DTT reception system behavior and performance are also described as they greatly affect the amount of spectrum potentially available for MBB use and determine the relevant coexistence field measurement scenarios. Simulation methods used in determining broadcast protection criteria and in coexistence studies are briefly described to demonstrate how the information obtained from field measurements can be used to improve their accuracy. The presented field measurement guidelines can be applied to any DTT-MBB coexistence scenarios and to a wide range of spectrum sharing and cognitive radio system coexistence measurements.</p

Spectrum sensing algorithms and software-defined radio implementation for cognitive radio system

The scarcity of spectral resources in wireless communications, due to a fixed frequency allocation policy, is a strong limitation to the increasing demand for higher data rates. However, measurements showed that a large part of frequency channels are underutilized or almost unoccupied. The cognitive radio paradigm arises as a tempting solution to the spectral congestion problem. A cognitive radio must be able to identify transmission opportunities in unused channels and to avoid generating harmful interference with the licensed primary users. Its key enabling technology is the spectrum sensing unit, whose ultimate goal consists in providing an indication whether a primary transmission is taking place in the observed channel. Such indication is determined as the result of a binary hypothesis testing experiment wherein null hypothesis (alternate hypothesis) corresponds to the absence (presence) of the primary signal. The first parts of this thesis describes the spectrum sensing problem and presents some of the best performing detection techniques. Energy Detection and multi-antenna Eigenvalue-Based Detection algorithms are considered. Important aspects are taken into account, like the impact of noise estimation or the effect of primary user traffic. The performance of each detector is assessed in terms of false alarm probability and detection probability. In most experimental research, cognitive radio techniques are deployed in software-defined radio systems, radio transceivers that allow operating parameters (like modulation type, bandwidth, output power, etc.) to be set or altered by software.In the second part of the thesis, we introduce the software-defined radio concept. Then, we focus on the implementation of Energy Detection and Eigenvalue-Based Detection algorithms: first, the used software platform, GNU Radio, is described, secondly, the implementation of a parallel energy detector and a multi-antenna eigenbased detector is illustrated and details on the used methodologies are given. Finally, we present the deployed experimental cognitive testbeds and the used radio peripherals. The obtained algorithmic results along with the software-defined radio implementation may offer a set of tools able to create a realistic cognitive radio system with real-time spectrum sensing capabilities