A cross layer framework for WLANs: joint radio propagation and MAC protocol

This paper proposes a cross-layer design (CLD) framework called channel-aware buffer unit multiple access (C-BUMA) for improving wireless local area network (WLAN) performance. In the framework, the radio propagation (i.e. PHY layer) is combined with the medium access control (MAC) protocol for packet transmissions. By sharing channel information with the MAC protocol, the approach reduced unnecessary packet transmissions and hence improved system performance. Through performance evaluation, we demonstrate that our CLD can significantly improve network throughput and packet delay. The proposed C-BUMA is simple and can easily be implemented in 802.11 networks without changing hardware infrastructure and no additional costs. In this paper we describe C-BUMA and present two algorithms for the implementation of the framework

The impact of transmission overheads on IEEE 802.11 throughput: analysis and simulation

While various factors affecting the performance of a typical IEEE 802.11 DCF (“DCF”) medium access control (MAC) protocol, transmission overhead is one of the main causes of DCF MAC inefficiency. This paper provides an analysis of DCF overhead to show that the network throughput degrades significantly due to its high transmission overhead for a singleuser scenario. Simulation modeling is used to demonstrate the performance degradation of DCF for a multi-user network scenario. To reduce DCF’s high transmission overheads and to improve the system performance, this paper introduces a simple packet scheduling mechanism called buffer unit multiple access (BUMA). The BUMA improves the system performance because it requires less overhead to send the same amount of payload than the DCF. Results obtained show that if BUMA is used in place of DCF, the network performance is improved significantly especially under medium-to-high loads

Quantifying the performance degradation of IPv6 for TCP in Windows and Linux Networking

Implementing IPv6 in modern client/server operating systems (OS) will have drawbacks of lower throughput as a result of its larger address space. In this paper we quantify the performance degradation of IPv6 for TCP when implementing in modern MS Windows and Linux operating systems (OSs). We consider Windows Server 2008 and Red Hat Enterprise Server 5.5 in the study. We measure TCP throughput and round trip time (RTT) using a customized testbed setting and record the results by observing OS kernel reactions. Our findings reported in this paper provide some insights into IPv6 performance with respect to the impact of modern Windows and Linux OS on system performance. This study may help network researchers and engineers in selecting better OS in the deployment of IPv6 on corporate networks

Teaching computer hardware and organization using PIC-based projects

Until recently, it has been difficult to motivate students to learn about computer hardware because students find the subject rather dry and theoretical. We have prepared a series of interesting projects that give students a hands-on introduction to computer hardware and organisation. Our projects are designed around the PIC16F84, a powerful 8-bit microcontroller chip that sells for less than $10. The projects are suitable for classroom use in introductory-level courses about computer hardware. The effectiveness of these projects has been evaluated both formally by students (student-evaluation forms) and informally through discussion within the teaching team. The feedback from students indicates that the development and the implementation of the projects were successful. This paper describes the details of the projects completed to date, their overall effectiveness and our plans for further projects

Finding a closest match between wi-fi propagation measurements and models

In a series of papers by Sarkar and his team conducted radio propagation measurements to study the performance of Wi-Fi in terms of received signal strengths (RSS) in an obstructed office block. The goal of this paper is to find a closest match between the results obtained from propagation measurements and the theoretical models. The RSS measurement results are compared with the four selected propagation models (Free-space, Two-ray ground reflection, Shadowing path loss, and the overall Shadowing models). These models were selected based on their popularity and relevance to our study. Results obtained show that the overall shadowing model is the best-fit followed by the path loss Shadowing. We found about 94% and 99% matching with RSS measurement results for non-LOS and NLOS conditions, respectively. The analysis and research findings reported in this paper provide some insights into the deployment of indoor wireless systems

The effect of people movement on Wi-Fi link throughput in indoor propagation environments

While various key performance limiting factors of IEEE 802.11-based Wi-Fi networks such as wireless protocols, radio propagation environment and signal interference have been studied by many network researchers, the effect of the movement of people (human) on Wi-Fi link throughput in indoor propagation environments has not been fully explored yet. This paper investigates the effect of people movement on Wi-Fi link throughput in six different indoor environments (i.e. lounge, bedroom, garage, common room, laboratory, and office space) using radio propagation measurements. Using a pair of wireless laptops we conducted various trials by considering both the straight line and random human movement in the above mentioned environments. Results obtained show that Wi-Fi link throughput degrades up to 20.4% as a result of people movement. The difference between the impact of straight line and random movement on Wi-Fi throughput is found to have insignificant. The research findings reported in this paper provide some insight into the impact of people movement on Wi-Fi link throughput in indoor environments

A study of MANET routing protocols: joint node density, packet length and mobility

The dynamic topology of a mobile ad hoc network (MANET) poses a real challenge in the design of a MANET routing protocol. Over the last 10 years, a variety of routing protocols have been developed and their performance simulations are made by network researchers. Most of the previous research on MANET routing protocols have focused on simulation study by varying network parameters, such as network size (node density), pause times, or node mobility independently. This paper considers the problem from a different perspective, using a simulation model the combined effect of node density and packet length; node density and mobility on the performance of a typical 802.11 MANET is investigated. This is a common and realistic scenario in MANETs where nodes move around, join and leave the network at any time. Based on the QoS (end-to-end delay, throughput), routing load and packet retransmissions, this paper systematically analyzes the performance of four diverse MANET routing protocols with the different simulation model and configurations, and drew more complete conclusions

Improving the Performance of MANET Gateway Selection Scheme for Disaster Recovery

In this paper, we propose an improved MANET gateway selection scheme suitable for disaster recovery applications. Having an infrastructure less and decentralize features, MANET is well suited to bring the network back that has been collapse after a disaster. We focus on improving throughput performance of MANET by designing a better gateway selection scheme. The key idea is to eliminate the congestion at each MANET gateway for improved performance. Simulation results show that the proposed gateway selection scheme can efficiently manage the traffic distribution at each gateway to maximize the network performance

Multiple preemptive EDCA for emergency medium access control in distributed WLANs

The increasingly use of wireless local area networks (WLANs) in public safety and emergency network services demands for a strict quality of service (QoS) guarantee especially a large number of users report an emergency for immediate channel access. Unfortunately, the traditional IEEE 802.11e-based enhanced distributed channel access (EDCA) does not support a strict QoS guarantee for life saving emergency traffic under high loads. Previous studies have attempted to enhance the performance of EDCA called the Channel Preemtive EDCA (CP-EDCA) which is a promising idea to support emergency traffic in WLANs. However, CP-EDCA supports a single emergency traffic only (i.e. no emergency service differentiation) with high delays for increased traffic loads. To overcome this problem, we propose a class of EDCA protocol called Multiple Preemption EDCA (MPEDCA) as a candidate to support multiple emergency traffics under high loads. Each MP-EDCA node can support up to four emergency traffics (life, health, property and environment) with different priorities in addition to support background (non-emergency) traffic. The proposed protocol privileged the high priority life-saving emergency traffic to preempt the services of low priority ones without much starvation in the network to maintain a strict QoS guarantee. The paper evaluates the performance of MPEDCA through an extensive analysis of simulation outcome. The results obtained show that MP-EDCA outperforms CP-EDCA in achieving lower medium access control and emergency node delays

Performance Study of Block ACK and Reverse Direction in IEEE 802.11n Using a Markov Chain Model

IEEE 802.11n networks are widely used in home and corporate network environments because they offer high-speed wireless Internet access at relatively low-cost. The 802.11n standard introduced several key features including Block acknowledgement (ACK) and reverse direction (RD) data transmission for enhanced system performance. An in-depth study of 802.11n system capacity for Block ACK mechanisms (both protected and unprotected) and RD data flows is required to assist optimum planning and design of such systems in view of the limited wireless channel capacity. In this paper we study the interdependencies of Block ACK and RD mechanisms using a discrete bi-directional Markov chain model under non-saturated traffic loads. We present a mathematical model to derive throughput, delay, and packet loss probability for both protected and unprotected Block ACKs under varying loads. We validate the model using MATLAB based numerical studies. Results obtained show that the combined effect of protected Block ACK and RD flows has a positive impact on system performance. However, unprotected Block ACK wastes transmission opportunity (TXOP) especially in collisions and therefore degrades the system performance. Our findings reported in this paper provide some insights into the performance of 802.11n with respect to Block ACK and RD methods. This study may help network researchers and engineers in their contribution to the development of next generation wireless LANs such as IEEE 802.11ac