Hazem H. Refai

Performance and reliability of DSRC vehicular safety communication: a formal analysis

IEEE- and ASTM-adopted dedicated short range communications (DSRC) standard toward 802.11p is a key enabling technology for the next generation of vehicular safety communication. Broadcasting of safety messages is one of the fundamental services in DSRC. There have been numerous publications addressing design and analysis of such broadcast ad hoc system based on the simulations. For the first time, an analytical model is proposed in this paper to evaluate performance and reliability of IEEE 802.11a-based vehicle-to-vehicle (V2V) safety-related broadcast services in DSRC system on highway. The proposed model takes two safety services with different priorities, nonsaturated message arrival, hidden terminal problem, fading transmission channel, transmission range, IEEE 802.11 backoff counter process, and highly mobile vehicles on highway into account. Based on the solutions to the proposed analytic model, closed-form expressions of channel throughput, transmission delay, and packet reception rates are derived. From the obtained numerical results under various offered traffic and network parameters, new insights and enhancement suggestions are given.

Minimizing HVAC Energy Consumption Using a Wireless Sensor Network

This paper presents a conceptual design of a multizone HVAC controller based on a wireless sensor network that aims to optimize energy consumption while maintaining the comfort level of users. The proposed system is capable of learning the occupancy pattern of the residents in the building. Moreover, it is transparent (requires no manual configuration). Wireless sensor network technology is used to collect the required measurements for the control system, simulation results are used to demonstrate the system performance in terms of power consumption and comfort level Additionally, a comparison between the proposed system and other HVAC control systems is presented. The results show that the proposed system is capable of providing a major energy savings.

Unsaturated Performance of IEEE 802.11 Broadcast Service in Vehicle-to-Vehicle Networks

In this paper, we propose an analytic model for performance evaluation of IEEE 802.11 ad hoc broadcast networks without the assumption of saturation condition that is not true in safety related vehicle-to-vehicle (v2v) communication. We use a discrete time M/G/l queue to model occasional occurrences of safety related message in each vehicle. By means of probability generating function (PGF) and a recursive algorithm, we obtain solution to the analytic model. Based on the solution, we derive several important performance indices for IEEE 802.11 broadcast service, such as packet delay, throughput, packet delivery ratio, and service time distribution. The proposed analytic model is validated by extensive simulations. Numerical results also reveal characteristics of the broadcast service in a typical v2v wireless network.

A Quantitative Approach to Evaluate DSRC Highway Inter-Vehicle Safety Communication

Inter-vehicle safety applications on highways rely considerably on the real-time and reliable communication in the vehicular ad hoc network. For engineers and researchers, it is greatly necessary and important to evaluate the provisions of the communication systems before they start designing them for such applications. This paper presents a quantitative approach to evaluate the quality of service that the inter-vehicle communication (using IEEE- and ASTM-adopted dedicated short range communication (DSRC)) can provide to the inter-vehicle safety application in the context of highway scenarios. Based on the proposed model, we analyze performance indices such as delay and packet delivery ratio (PDR). Outputs of the model are validated by computer simulations. On one hand, our quantitative model provides not only a convenient framework to conduct fast evaluation for the communication of the inter-vehicle safety applications but also a means to analyze the suitability of 802.11a- based DSRC for highway safety applications. On the other hand, it reveals the requirements for further improvement of the performance.

Saturation Performance of IEEE 802.11 Broadcast Scheme in Ad Hoc Wireless LANs

Broadcast communication is important in inter- vehicle communication. Vehicles broadcast safety related messages to pre-warn the vicinity vehicles. The new IEEE 802.11p is being developed based on IEEE 802.11a to address the need for vehicle-to-vehicle and vehicle-to-roadside-unit communication. In this paper, we study the saturation performance of IEEE 802.11 broadcast by developing an analytic model as well as by conducting simulation. Having investigated the literature and studied the features of the broadcast, we point out that the analytic models for IEEE 802.11 unicast cannot be simply applied for broadcast. We construct our model to characterize the operation of the backoff counter in broadcast. Based on solutions to the model, closed form expressions of performance indices including throughput, packet delay, and packet deliver ratio are derived. Numerical results reveal several characteristics of the broadcast service. Our research work provides a new means to approach analysis and enhancement of IEEE 802.11 broadcast performance and reliability in wireless ad hoc networks.

Automatic count of hepatocytes in microscopic images

This paper describes a part of current research work on counting dead and live hepatocytes (liver cells) in cultures from microscopic images. The requirement of the work is to develop an automatic cell counting process that is simple, fast, and achieves high level of count accuracy. Cells in the acquired images are difficult to identify due to low contrast, uneven illumination, gray intensity variations within a cell, irregular cell shapes. For automatic counting, our cell images undergo three-stage image processing: conditioning, segmentation, and mathematical morphology operations. Local adaptive thresholding technique is employed in the segmentation stage. At the end of the morphological process, cells are identified and counted based on size. Compared to a manual cell count, the automatic count has achieved an on average accuracy of 95% for single cell counting and 85% for total cell counting.

On the Broadcast Packet Reception Rates in One-Dimensional MANETs

In this paper, we investigate saturation performance of broadcast service in IEEE 802.11 based one-dimensional mobile ad hoc networks (MANETs) under multi-hop environment. Having analyzed the features of the multi-hop broadcast MANETs, for the first time we derive a closed form expression of broadcast packet reception rates, which is one of the important reliability metrics for broadcast communications. The analytic model takes IEEE 802.11 backoff counter process and hidden terminal problem into account. The proposed analytic model is validated by extensive simulations. From the obtained numerical results under various network parameters, new observations and potential enhancement suggestions are given.

Enlargement of Beam Coverage in FSO Mobile Network

Pointing, acquisition and tracking of a free-space optical node in a mobile network experiencing misalignment due to adverse factors including vibration, motion and atmospheric turbulence requires a different approach than traditional free-space optical transceivers. A recent fiber-bundle approach for beam steering at the transmitter was investigated to provide continuous beam coverage at the receiver without the application of mechanical devices. Utilizing multiple fibers-lenses sets at the receiver was also proposed to enhance the tolerance of optical link misalignment. This paper investigates the feasibility of applying multiple fibers with a single lens at the transmitter and multiple fiber-lenses sets at the receiver to improve the transmission performance on tolerating link misalignment. Two series of laboratorial experiments were implemented to compare the optical link robustness for different transceiver setups as the fiber-lens distance (zfl) was varied to modify the beam divergence: multi-fiber transmitter working with single-fiber-lens receiver and multi-fiber transmitter working with multi-fiber-lens receiver. The results showed that using multiple fibers in both the transmitter and the receiver reveals significant potential to maximize the up time of the link.

Free-space optical wavelength diversity scheme for fog mitigation in a ground-to-unmanned-aerial-vehicle communications link

Atmospheric weather conditions adversely affect the performance of free-space optical communications systems. Fog present in the atmosphere has the largest impact on free-space optical systems. We use simulation techniques to investigate the performance of a slant-path, wavelength-diversified free-space optical link between a ground station and an unmanned aerial vehicle in the presence of radiation fog. The free-space optical link is configured to operate using the simultaneous transmission of three wavelengths, 0.85, 1.55, and 10 µm, connecting a ground station to an unmanned aerial vehicle operating at either a 4- or 8-km altitude. The link is further analyzed by combining the multiple carrier wavelengths into either an equal-gain diversity scheme or a selective diversity scheme. The simulation results are obtained using ALTM and PcModWin simulation software from Ontar Corporation. The results obtained demonstrate that the use of either an equal-gain diversity scheme or a selective diversity scheme enables the deployment of a ground-to-air free-space optical communications link. Furthermore, a selective diversity scheme demonstrates a received power approximately three times greater than an equal-gain diversity scheme.

CSMA based Inter-Vehicle Communication Using Distributed and Polling Coordination

Intelligent transportation systems rely heavily on inter-vehicle communication (IVC) systems to support, among other things, safe driving by relaying essential information in real time. It is very important to guarantee the delivery of an imminent collision warning in real time in order to make appropriate actions to avoid it. Several existing MAC layer protocols are modified to address real-time traffic in ad hoc vehicle environment; carrier sense multiple access (CSMA) is one such protocol. This paper implements a priority in CSMA using different backoff time spacing (BTS) to allow higher priority traffic to access the medium faster than those with medium-to-low priority. The backoff time spacing is inversely proportional to the priority; the higher the priority, the lower the backoff time. The paper also proposes a new media access control (MAC) protocol implementation that combines distributed and polling coordination functions to further enhance the BTS-priority-based CSMA and to ensure the absolute delivery of traffic with the highest priority. A computer simulation was carried out to evaluate the performance of the proposed protocol. When compared with the BTS-based CSMA implementation, the simulation results indicate significant improvements in the system throughput and successful packet rate for the traffic with highest priority.