Meejoung Kim

Priority-Based Service-Differentiation Scheme for IEEE 802.15.4 Sensor Networks in Nonsaturation Environments

In this paper, we propose two mechanisms, i.e., 1) backoff exponent differentiation (BED) and 2) contention window differentiation (CWD), to provide multilevel differentiated services for IEEE 802.15.4 sensor networks. The beacon-enabled mode with the slotted carrier-sense multiple-access mechanism with collision avoidance (CSMA/CA) algorithm is considered for nonsaturation. A mathematical model based on a discrete-time Markov chain is presented and analyzed to measure the performance of the proposed mechanisms. Numerical results show the effects of varying parameters. It shows that BED is better for service differentiation and channel utilization, regardless of the number of devices and the packet-arrival rate. It also shows that the throughput depends on the backoff exponent (BE), contention window (CW), and packet size and that the relative delay for successfully transmitted packets for BED is longer than that for CWD, which enables a higher relative gain for CWD. In addition, we obtain the number of unit backoff periods required to process all of the head packets of devices. Based on the numerical results, we obtain a criterion that provides guidelines for choosing a mechanism that is suitable for the objective function and determining the optimal length of the superframe to process the packets in the system.

Analysis of Directional Communication via Relaying Devices in mmWave WPANs

This letter analyzes the communication success probability of two randomly selected devices in mmWave wireless personal area networks (WPANs). Devices are randomly distributed in a piconet, each device is equipped with a directional antenna, and the antenna direction of each device is randomly chosen and fixed during the communication. The communication of the selected pair can be performed either directly or via relaying devices. In the analysis, the probability density function of the distance for devices is used and transmissions with ideal antenna and practical antenna are considered. Numerical results show an optimal beamwidth enables efficient spatial reuse to maximize the successful communication probability of a pair of devices. It also shows that the communication of a pair of devices is difficult when the directions of antennas of devices are fixed and the transmission through sidelobe of a transmitter gives a good effect in some circumstances. The obtained results will provide a criterion for the practical design of mmWave network systems, for implementing appliances using high data rate, and for developing the technology of mmWave band.

Analysis of directional neighbour discovery process in millimetre wave wireless personal area networks

The millimetre wave (mmWave) band offers the potential for multi-gigabit indoor wireless personal area networks (WPANs). However, it has problems such as a short wavelength. To compensate, utilisation of directional antennas at the physical layer is recommended. For communications using this band, neighbour discovery using directional antennas (D-ND) is one of the crucial steps. In this study, the D-ND process is analysed mathematically for mmWave WPANs based on the concept of an exclusive region, and the values that are derived from the effect of using directional antennas. Maximising the neighbour discovery probability for a given amount of time is considered as an objective function. Performance measures are derived in closed forms, such as the probability of discovering a device for one self-advertising packet and the power-efficient sojourn time of a device in one direction. Numerical results are obtained using parameters based on the IEEE 802.15.3c standard. The results show that the efficiency of the D-ND depends not only on how often devices transmit a self-advertising packet, but also on antenna properties such as beamwidth. The mathematical analysis provides a theoretical basis for the D-ND process, and the obtained results illustrate the physical layer impact on neighbour discovery.

Analysis of eavesdropping attack in mmWave-based WPANs with directional antennas

AbstractThis paper explores the benefits of using directional antennas in an eavesdropping attack in millimeter-wave (mmWave)-based wireless personal area networks (WPANs) and the security enhancement of mmWaves. The detection and protection probabilities are analyzed for the eavesdropper’s and transmitter’s perspectives, respectively. The analysis is based on the probability density function of distance between devices (DEVs), the exposure region, and the interference free (limited) exposure region of a DEV. Four cases, in which all target DEVs and an eavesdropper are equipped with either a directional antenna or an omni-directional antenna, are considered in a single-hop and a multi-hop communications. The expected lower bound of an eavesdropper’s detection probability and the relative detection rate are presented. Numerical results show that there exists a number of DEVs such that an eavesdropper can detect DEVs maximally. The detection probability tends to zero in a single-hop case, while it is saturated in a multi-hop case, as the number of DEVs increases. A DEV can communicate safely in one hop, while the communication is not secure anymore after several hops. Based on these results, we can conclude that the use of a directional antenna enables the better protection from an eavesdropping attack in mmWave-band communication and mmWave band can improve the security in communication.

Saturation performance analysis of directional CSMA/CA in mmWave WPANs†

The millimeter-wave (mmWave) band offers the potential for multi-gigabit indoor wireless personal area networks (WPANs). However, there are problems such as the short wavelength and high propagation losses. In order to compensate for these, it is highly recommended to use directional antennas at the physical layer. In this paper, directional carrier sense multiple access/collision avoidance (CSMA/CA) is analyzed in IEEE 802.15.3c, a standard for mmWave WPANs, under a saturated environment. A Markov chain model is presented and analyzed for the no-acknowledgment (No-ACK) mode. For the analysis, the device interaction is considered using directional antennas over a shared channel. A Markov chain model is presented in which the features of IEEE 802.15.3c such as backoff counter freezing and the effects of using directional antennas are incorporated. The maximal number of frames that can be transmitted concurrently and successfully is derived by an algorithm, and the system throughput and the average transmission delay are obtained in the closed forms. Numerical results show that the effects of using directional antennas in CSMA/CA and the overall analysis are verified by the simulation. The obtained results illustrate the physical layer impact on the CSMA/CA medium access control protocol, and these insights can be helpful in developing a medium access control protocol for enhancing the performance of mmWave WPANs. Copyright

Multi-level service differentiation scheme for the IEEE 802.15.4 sensor networks

In the sensor networks, the data packets transmitted by the different devices in the home networking and the industrial application maintain the different levels of importance. In this paper, we propose two mechanisms for the IEEE 802.15.4 sensor networks to provide the multi-level differentiated services which are required by each and every device. The mathematical model based on the discrete-time Markov chain is presented and is analyzed to measure the performances of the proposed mechanisms. The numerical results show the effect of the variation of the contention window size and the backoff exponent for the service differentiation on the 802.15.4 sensor networks. From the results, we derive that the contention window size is more affective than the backoff exponent on the service differentiation while the backoff exponent is more affective than the contention window size on the average delay of every device. Simulation results are also given to verify the accuracy of the numerical model.

Design and Analysis of a Wireless Switched Digital Video Scheme for Mobile TV Services Over WiMAX Networks

Mobile WiMAX is emerging as one of the most promising systems for 4th generation mobile wireless networks in which it is foreseen that mobile TV services will proliferate. In general, TV applications are bandwidth hogs that cause a challenging capacity problem in wireless networks. To address this challenge, a novel scheme for mobile TV services over WiMAX network, called the wireless switched digital video (WSDV) scheme, is proposed in this paper. Compared with the conventional broadcast or unicast schemes, the hybrid approach introduced in our proposed WSDV approach exploits the merits of two conventional schemes and mitigates their demerits, which enables it to increase wireless capacity for mobile TV services. In addition, we present a WiMAX design tool, based on an analytical model, which facilitates analysis of the influence of some system parameters on wireless capacity. The analytical model can capture the details of WiMAX resource allocation and take into consideration the popularity of the mobile TV contents being viewed by users-enabling it to provide an accurate estimate of the amount of bandwidth required for WiMAX TV services and also enabling a designer to optimally select the number of channels via the WSDV service while meeting a desired level of blocking probability. In addition, we demonstrate that our proposed optimized scheme outperforms the conventional schemes with respect to blocking probability. Finally, an end-to-end solution to the WSDV scheme is also presented.

Analysis of Neighbor Discovery Process with Directional Antenna for IEEE 802.15.3c

The neighbor discovery using directional antennas in mmWave band is a prerequisite for communications and this issue is crucial and urgent. In this paper, the synchronized, direct, two-way directional neighbor discovery process is analyzed mathematically for mmWave WPANs. The analysis is based on the values which are derived from the effect of using directional antennas. The neighbor discovery probability for a given amount of time is considered and several performance measures such as the optimal sojourn time are derived in closed forms. Numerical results are obtained using parameters based on the IEEE 802.15.3c. The mathematical analysis provides the theoretical basis for the directional neighbor discovery process.

Multi-hop communications in directional CSMA/CA over mmWave WPANs

In this paper, we consider the multi-hop communications in contention period of medium access control protocol over millimeter-wave band. A relaying devices selection policy and a grouping algorithm are proposed, and the directional carrier sense multiple access/collision avoidance protocol in the immediate acknowledgement mode for IEEE 802.15.3c is considered under saturation environments. The purpose of this paper is to analyze the effect of using directional antennas and relaying devices in contention period. A sensing region and an exclusive region are computed probabilistically and used in the grouping algorithm. Numerical results show that the narrower radiation beamwidth allows to use a channel more spatially, and the effect of using relaying devices increases as the beamwidth and number of devices increase. Those effects are presented in the throughput and average delay. The obtained results will be used as performance criterion for the multi-hop communications in millimeter-wave wireless personal area networks. Copyright

Optimal contention window size for IEEE 802.15.3c mmWave WPANs

The millimeter-wave (mmWave) band offers the potential for multi-gigabit indoor Wireless Personal Area Networks (WPANs). However, it has problems such as short communication coverage due to high propagation losses. In order to compensate for this drawback, utilization of directional antennas at the physical layer is highly recommended. In this paper, we consider the adequate contention window (CW) size for directional carrier sense multiple access with collision avoidance (CSMA/CA). To find the optimal CW size that enhances the performance of conventional directional CSMA/CA, we propose an enhanced directional CSMA/CA algorithm. The algorithm is considered in IEEE 802.15.3c, a standard for mmWave WPANs, under saturation environments. For the algorithm, we present a Markov chain model and analyze it for the no-ACK mode. The effects of directional antennas and the features of IEEE 802.15.3c Medium Access Control (MAC) such as backoff counter freezing are considered in the model. The optimal CW sizes for the two different objective functions are derived from the numerical results. The numerical results also show that the system throughput and average transmission delay of the proposed algorithm outperform those of conventional one and the overall analysis is verified by simulation. The obtained results provide the criterion for selecting the optimal parameters and developing a MAC protocol that enhances the performance of mmWave WPANs.