Bong Dae Choi

Performance analysis of opportunistic spectrum access protocol for multi-channel cognitive radio networks

Cognitive radio (CR) has emerged as one of effective methods to enhance the utilization of existing radio spectrum. Main principle of CR is that secondary users (SUs) are allowed to use the spectrum unused by primary users (PUs) without interfering PUs transmissions. In this paper, PUs operate on a slot-by-slot basis and SUs try to exploit the slots unused by PUs. We propose OSA protocols in the single channel and we propose an opportunistic spectrum access (OSA) protocols in the multi-channel cognitive radio networks with one control channel and several licensed channels where a slot is divided into contention phase and transmission phase. A slot is divided into reporting phase, contention phase and transmission phase. The reporting phase plays a role of finding idle channels unused by PUs and the contention phase plays a role of selecting a SU who will send packets in the data transmission phase. One SU is selected by carrier sense multiple access / collision avoidance (CSMA/CA) with request to send / clear to send (RTS/CTS) mechanism on control channel and the SU is allowed to occupy all remaining part of all idle channels during the current slot. For mathematical analysis, first we deal with the single-channel case and we model the proposed OSA media access control (MAC) protocol by three-dimensional discrete time Markov chain (DTMC) whose one-step transition probability matrix has a special structure so as to apply the censored Markov chain method to obtain the steady state distribution. We obtain the throughput and the distribution of access delay. Next we deal with the multi-channel case and obtain the throughput and the distribution of access delay by using results of single-channel case. In numerical results, our mathematical analysis is verified by simulations and we give numerical results on throughput and access delay of the proposed MAC protocol. Finally, we find the maximum allowable number of SUs satisfying the requirements on throughput and access delay.

Mathematical analysis of burst transmission scheme for IEEE 802.3az energy efficient Ethernet

The IEEE P802.3az Energy Efficient Ethernet (EEE) protocol specifies a Low Power Idle (LPI) mode in which Ethernet device can save energy by turning off components when its queue is empty, and defines a scheme for coordinating the transitions between the LPI and active modes. Depending on when Ethernet devices enter and exit the LPI mode, two schemes have been proposed: the frame transmission scheme and the burst transmission scheme. P. Reviriego et al. proposed the burst transmission scheme (the same as the packet coalescing scheme by Christensen et al.) where the link becomes active when either a fixed number of packets have arrived or a fixed time is passed from the epoch that the first packet has arrived. They showed by simulation that the burst transmission scheme has significantly lower energy consumption than the frame transmission scheme of EEE. In this paper, we provide an analytic model of the burst transmission scheme and obtain its energy consumption and packet delay. Our analytic results match the simulation results. In numerical results, we find the maximal timer which minimizes the energy consumption while satisfying the maximal packet delay within a pre-determined level.

An application of Riordan arrays to the transient analysis of M/M/1 queues

Abstract Riordan arrays are used extensively in many contexts as a combinatorial tool for solving enumeration problems such as lattice path counting problems. In this paper, we first show how Riordan array method can be applied to the transient analysis of M / M / 1 queue with zero customer at the initial point. Second, we extend this method to the generalized Riordan array with multiple support functions in order to deal with the transient analysis of M / M / 1 queue with non-zero customers at the initial point. Numerical examples are also given to show how easy and quick the transient probability obtained from the Riordan method can be computed.

Performance Analysis of MAC with DCF on CCH and Reservation for Multi-Channel for IEEE 802.11p/1609.4 WAVE Networks

Abstract We propose and analyze a MAC Protocol for multiple service channels (SCHs) based on reservation by distributed coordination function (DCF) on control channel (CCH) for IEEE 802.11p and IEEE 1609.4 wireless access in vehicular environments (WAVE) networks. Specifically each user sends a request for service (RFS) packet to the Road-Side Unit (RSU) on the CCH by DCF method in order to reserve one SCH over which a data file is transmitted at a once. We construct a Markov Chain to find collision probability of RFS packet. We obtain probability of successful delivery and head-of-line (HOL) delay of RFS packet, and service time of data file.