70 Int. J. Wireless and Mobile Computing, Vol. 9, No. 1, 2015 Copyright © 2015 Inderscience Enterprises Ltd. Modelling of IEEE 802.11 DCF in the presence of hidden nodes Rakhi Joon* and Rishi Pal Singh Department of Computer Science and Engineering, Guru Jambheshwar University of Science & Technology, Hisar 125001, Haryana, India Email: rjoon30@gmail.com Email: pal_rishi@yahoo.com *Corresponding author Abstract: Today, the most commonly used technology for wireless networks is IEEE 802.11. The performance of the Medium Access Control (MAC) layer, which consists of Distributed Coordination Function (DCF) and Point Coordination Function (PCF), has been examined over a long time period. The DCF is the random access scheme that uses CSMA/CA in IEEE 802.11 MAC layer protocol. There are various issues related to the performance evaluation of IEEE 802.11 DCF and one of the important issues is the problem of hidden terminals which exists in practice in any wireless network. In this paper, a two-dimensional analytical model is proposed for the analysis of IEEE 802.11 DCF in the presence of hidden terminals for both basic access and RTS/CTS modes by making use of the Markov chain. Keywords: IEEE 802.11; MAC; CSMA/CA; DCF; hidden terminals; Markov chain. Reference to this paper should be made as follows: Joon, R. and Singh, R.P. (2015) ‘Modelling of IEEE 802.11 DCF in the presence of hidden nodes’, Int J. Wireless and Mobile Computing, Vol. 9, No. 1, pp.70–77. Biographical notes: Rakhi Joon is currently pursuing her PhD from the Department of Computer Science, Delhi University. She has completed her degree of MTech from the Department of CSE, GJU S&T, Hisar. She has done her graduation in Information Technology from MDU, Rohtak. Her areas of interest are wireless networks and natural language processing. Rishi Pal Singh is an Associate Professor in Department of Computer Science & Engineering, Guru Jambheshwar University of Science & Technology, Hisar, India. He has done his MTech from BITS Pilani, India and PhD from JNU, New Delhi, India. He has ten papers in international journals and 12 papers in international conferences to his credit. His areas of interest are ad hoc networks, sensor networks and wireless communication. 1 Introduction The IEEE 802.11 is a standard used for wireless LANs (WLANs) (IEEE Standard, 1999) with the specification of two medium access control mechanisms which are known as DCF and PCF. Mostly, WLAN devices use only DCF owing to its efficiency and simplicity for the data transmission. In addition, DCF mechanism also supports to the ad-hoc networking environment and has been extensively adopted for wireless communication networks (Bianchi, 2000). The DCF is a random access scheme that mainly employs a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol with binary exponential back off. The data frames in DCF are transmitted by two mechanisms – Basic Access and Request-to-send/Clear-to-send (RTS/CTS) mechanism. The main purpose of this paper is to model the DCF in the presence of hidden terminals. A hidden node is one which is out of the transmission range of sender but within the range of receiver and results in the degradation of throughput significantly. Extensive work has been carried out to address the performance degradation of DCF in presence of hidden terminals, which shows the relevance of hidden terminals and factors affecting DCF. A lot of work has been done to evaluate the impact of hidden terminal on CSMA, but the protocol behaviour such as CW (Contention Window) and exponential back-off of DCF are not considered. None of the previous work accounts for modelling of DCF with Hidden terminals, i.e. by considering hidden terminals in Markov Chain model. The study aims to discuss the various aspects of DCF with respect to modelling using revised and extended Markov chain model including the hidden terminals. The rest of the paper is organised as follows. In Section 2, a brief overview of the work done by different authors is given. Section 3 presents an introduction to DCF and its access mechanisms i.e. Basic access and RTS/CTS access methods in association with the presence hidden terminals problem. In order to find out the throughput and transmission probability an analysis based on Markov chain model has been done