Subcarrier and Power Allocation in WiMAX

Worldwide Interoperability for Microwave Access (WiMAX) is one of the latest technologies for providing Broadband Wireless Access (BWA) in a metropolitan area. The use of orthogonal frequency division multiplexing (OFDM) transmissions has been proposed in WiMAX to mitigate the complications which are associated with frequency selective channels. In addition, the multiple access is achieved by using orthogonal frequency division multiple access (OFDMA) scheme which has several advantages such as flexible resource allocation, relatively simple transceivers, and high spectrum efficient. In OFDMA the controllable resources are the subcarriers and the allocated power per subband. Moreover, adaptive subcarrier and power allocation techniques have been selected to exploit the natural multiuser diversity. This leads to an improvement of the performance by assigning the proper subcarriers to the user according to their channel quality and the power is allocated based on water-filling algorithm. One simple method is to allocate subcarriers and powers equally likely between all users. It is well known that this method reduces the spectral efficiency of the system, hence, it is not preferred unless in some applications. In order to handle the spectral efficiency problem, in this thesis we discuss three novel resources allocation algorithms for the downlink of a multiuser OFDM system and analyze the algorithm performances based on capacity and fairness measurement. Our intensive simulations validate the algorithm performances.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

New Cryptanalysis and Modelling for Wireless Networking

High data rates and interoperability of vender devices have made WiMAX a prime desire for use worldwide. WiMAX is based on the IEEE 802.16 standard. IEEE 802.16a, b, c & d versions were updated within three years of the first launch of WiMAX. However, during those early years reports were published that highlighted the security weaknesses of the standard. These weaknesses prompted the IEEE to issue a new version, 802.16e to tackle the security issues. Despite this security enhancement, WiMAX remains vulnerable. This research project looks at the vulnerability of WiMAX 802.16e Subscriber Station/Mobile Station authentication at the initial entry and proposes approaches to the prevention of Denial of Service (DoS) attacks at this point in order to secure the Media Access Control (MAC) layer from such threats. A new protocol has been designed and developed to provide confidentiality, authentication and integrity to WiMAX users. This new protocol is integrated with Z algorithm (an algorithm described later in this paper) to provide: Confidentiality of management messages Message Authentication code ID to provide for message integrity and user authentication. A simulation package was also required, to prove that a linear load of DoS attack would disable or exhaust the capacity of the base station of a WiMAX network, as well as providing other simulation functions. The freely available simulation tool NIST (NIST IPSec (Internet Protocol Security) and IKE (Internet Key Exchange) Simulation) is oriented towards fixed network communications (NIIST, 2003). There are no other relevant simulation tools; hence the purpose of this research project is to develop a new tool to simulate WiMAX security vulnerabilities and test the new protocol

Reverse Engineering: WiMAX and IEEE 802.16e

Wireless communications is part of everyday life. As it is incorporated into new products and services, it brings additional security risks and requirements. A thorough understanding of wireless protocols is necessary for network administrators and manufacturers. Though most wireless protocols have strict standards, many parts of the hardware implementation may deviate from the standard and be proprietary. In these situations reverse engineering must be conducted to fully understand the strengths and vulnerabilities of the communication medium. New 4G broadband wireless access protocols, including IEEE 802.16e and WiMAX, offer higher data rates and wider coverage than earlier 3G technologies. Many security vulnerabilities, including various Denial of Service (DoS) attacks, have been discovered in 3G protocols and the original IEEE 802.16 standard. Many of these vulnerabilities and new security flaws exist in the revised standard IEEE 802.16e. Most of the vulnerabilities already discovered allow for DoS attacks to be carried out on WiMAX networks. This study examines and analyzes a new DoS attack on IEEE 802.16e standard. We investigate how system parameters for the WiMAX Bandwidth Contention Resolution (BCR) process affect network vulnerability to DoS attacks. As this investigation developed and transitioned into analyzing hardware implementations, reverse engineering was needed to locate and modify the BCR system parameters. Controlling the BCR system parameters in hardware is not a normal task. The protocol allows only the BS to set the system parameters. The BS gives one setting of the BCR system parameters to all WiMAX clients on the network and everyone is suppose to follow these settings. Our study looks at what happens if a set of users, attackers, do not follow the BS\u27s settings and set their BCR system parameters independently. We hypothesize and analyze different techniques to do this in hardware with the goal being to replicate previous software simulations that looked at this behavior. This document details our approaches to reverse engineer IEEE 802.16e and WiMAX. Additionally, we look at network security analysis and how to design experiments to reduce time and cost. Factorial experiment design and ANOVA analysis is the solution. In using these approaches, one can test multiple factors in parallel, producing robust, repeatable and statistically significant results. By treating all other parameters as noise when testing first order effects, second and third order effects can be analyzed with less significance. The details of this type of experimental design is given along with NS-2 simulations and hardware experiments that analyze the BCR system parameters. This purpose of this paper is to serve as guide for reverse engineering network protocols and conducting network experiments. As wireless communication and network security become ubiquitous, the methods and techniques detailed in this study become increasingly important. This document can serve as a guide to reduce time and effort when reverse engineering other communication protocols and conducting network experiments

Radio Communications

In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks