CogMAX- A Cognitive Radio Approach for WiMAX Systems Hazem Shatila*, Mohamed Khedr** *Bradley department of electrical and computer engineering, Virginia Polytechnic Institute and State University Virginia, USA hshatila@vt.edu **Dept. Electronics and Communication, Arab Academy for Science and Tech, Egypt, khedr@aast.edu Abstract— In this paper we propose a cognitive radio approach for WiMAX systems called CogMAX. The proposed system has all the capabilities of cognitive radio from monitoring to action decision and learning. We used case-based reasoning (CBR) and fuzzy logic (FL) reasoning as the core of the reasoning engine. The reasoning engine designed is used to determine the type of channel that the WiMAX system is operating in. Evaluation is done based on the time taken for the system to determine the type of channel and the error in the decision of the reasoning engine. Numerical results reveals that the use of a FL reasoning engine decreases the error in decision and in most cases faster in the decision making of the channel type. I. INTRODUCTION W iMAX is a wireless MAN technology that provides broadband wireless connectivity to fixed and mobile users [1]. WiMAX is based on adaptive modulation with OFDM and has impressive capabilities especially in NLOS environments [2]. These technologies can potentially be used to provide backhaul in many networks such as IEEE 802.11 hotspots, cellular networks and WLANs to the Internet. The mobile standard of WiMAX means that it can provide broadband wireless access in a mobile (fast varying) environment. WiMAX base-stations can serve their subscribers without the need of LOS (Line of Sight) connection. A WiMAX base station can serve multiple numbers of users due to the large amount of available bandwidth. It can also be used as a solution for last- mile connection, especially to users who cannot get connected to broadband services through cable or DSL, WiMAX base stations can cover a large area range and can reach areas where traditional wireless broadband access is not possible. As stated in [3] "although the term WiMAX is only a few years old, 802.16 has been around since the late 1990s, first with the adoption of the 802.16 standard (10–66 GHz) and then with 802.16a (2–11 GHz). Although the work on IEEE 802.16 standard started in 1999, it was only during 2003 that the standard received wide attention when the IEEE 802.16a standard was ratified in January". WiMAX standard currently includes two versions: 802.16-2004 and 802.16e [3] as shown in Figure 1. 802.16-2004 uses OFDM to serve large number of users in a time division technique in a cyclic method, but done extremely quickly so that users have the perception that they are always transmitting/receiving [3]. In case of 802.16e, where user mobility is an important issue, WiMAX utilizes OFDMA (Orthogonal Frequency Division Multiple Access) and can serve multiple users simultaneously by allocating sets of subcarriers to each user. W I M A X (Current Standards) 802.16 Revision for 802.16, 802.16a. Fixed broadband wireless system profile, errata for 2-11GHz (formerly 802.16REVd) Combined fixed and mobile wireless broadband at vehicular speeds in licensed bands from 2-66GHz 802.16 (2001) 802.16e (2005) 802.16- (2004) 802.16a (2003) band Fixed Broadband wireless MAC, PHY (10-66GHz) Fixed Broad wireless air interface (10-66GHz) Fig.1 WiMAX Standards IEEE 802.16-2004 is a fixed wireless access technology; it is designed to provide wireless DSL technology in areas where service providers cannot extend broadband cables or DSL. IEEE 802.16e (mobile WiMAX) is similar to IEEE 802.16-2004 but with a new additional function, which is mobility. It allows user to move around while being served with broadband wireless services. The use of WiMAX offers lots of benefits. WiMAX base-stations provide higher throughput at longer ranges (up to 50 km) [3]. Scaling system capacity is easily