Abstract—IEEE 802.15.7 is introduced to standardize the visible light communication system for connecting devices via visible light spectrum. A slotted CSMA/CA MAC protocol defined in the standard to coordinate channel access for numbers of the optical wireless devices. In this paper, we proposed a Discrete Time Markov Chain (DTMC) model for modeling the behavior of the Contention Access Period (CAP) of the IEEE 802.15.7 to acquire valuable insightsand inner workings of the protocol. The through performance of the Contention Access Period (CAP) of the IEEE 802.15.7 is analyzed. ns-2 simulations are used to verify the accuracy of the proposed model. The results between the proposed model and ns-2 simulation are closely matched. Thus, verify the accuracy of the proposed model. Index Terms—Discrete time Markov chain, IEEE 802.15.7, medium access layer, visible light communication. I. INTRODUCTION In recent years, interest in optical wireless as a favorable complementary technology for radio frequency (RF) communication has gained momentum supported by substantial deployments in solid state lighting technology and the released of the IEEE 802.15.7 draft standard [1]. The IEEE 802.15.7 compliant networks consist of two types of nodes, namely, a coordinator which initializes and manages the network and a remote device which communicate with each other via the coordinator. The IEEE 802.15.7 standard defines three types of topologies, namely, peer-to-peer, star, and broadcast as shown in Fig. 1. The IEEE 802.15.7 defines the first two layers of ISO/OSI stack protocol that includes Physical and Medium Access Control (MAC) layers. IEEE 802.15.7 MAC is a Carrier Sense Medium Access/Collision Avoidance (CSMA/CA) based protocol. Fig. 1. IEEE 802.15.7 topologies defined in IEEE 802.15.7 draft standard. Manuscript received January 20, 2013; revised April 20, 2013. The authors are with Faculty of Electrical Engineering, UniversitiTeknologi MARA (UiTM), Shah Alam, Selangor, Malaysia (e-mail: anuarmusa@tmrnd.com.my). There are several methods based on simulations and experiments that have been proposed for performance evaluation of CSMA/CA networks for the IEEE 802.11 [2], [3], IEEE 802.15.4 [4]-[6] and IEEE 802.15.7 [7]. However, it is importance to develop analytical tools that can predict accurately the network performance without resorting to a complicated analytical model, an extensive simulation or a tough experiment. An excellent and simple model for the IEEE 802.15.4 unsaturated traffic condition is presented in [8]. Specifically, a Discrete Time Markov Chain (DTMC) based model that described both the remote devices and the channels. In this paper, we extend [8] to cater for the IEEE 802.15.7 CSMA/CA MAC and include acknowledgement mechanism to make the analysis to closely conform to the IEEE 802.15.7 standard. The accurate model is import to understand and to gain valuable insight of the protocol. The rest of this paper is organized as follows: Section II provides an overview of the IEEE 802.15.7 MAC; Section III describes the proposed MAC analytical model; simulation results are given in Section IV; and finally Section V concludes this paper. II. OVERVIEW OF THE IEEE 802.15.7 The IEEE 802.15.7 describes two mechanisms for MAC channel access: contention based and contention free. Contention-based access allows devices to access the channel in contention access period (CAP) using a random access backoff algorithm. Contention-free access is managed by the coordinator through the use of guaranteed time slot (GTS) mechanism in contention free period (CFP) as shown in Fig. 2. Fig. 2. IEEE 802.15.7 MAC in IEEE 802.15.7 draft standard. In slotted CSMA/CA of the IEEE 802.15.7 as shown in Fig. 3, first the MAC sublayer initializes two variables: NB and BE. NB is the number of backoff times which the algorithm tries to backoff when the medium is busy. BE is the backoff exponent, which is related to the number of backoff periods a device peer-to-peer coordinator star broadcast devices beacon inactive period beacon GTS GTS CFP CAP | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |11|12 |13|14|15 SD = aBaseSuperframeDuration*2 SO optial clocks (active) BI = aBaseSuperframeDuration*2 BO optial clocks Analysis of the Contention Access Period (CAP) Model for the IEEE 802.15.7 Visible Light Communication A. Musa, M. D. Baba, and M. A. Mansor International Journal of Computer and Communication Engineering, Vol. 2, No. 5, September 2013 621 DOI: 10.7763/IJCCE.2013.V2.261