Using RTT Variability for Adaptive Cross-Layer Approach to Multimedia Delivery in Heterogeneous Networks

A holistic approach should be made for a wider adoption of a cross-layer approach. A cross-layer design on a wireless network assumed with a certain network condition, for instance, can have a limited usage in heterogeneous environments with diverse access network technologies and time varying network performance. The first step toward a cross-layer approach is an automatic detection of the underlying access network type, so that appropriate schemes can be applied without manual configurations. To address the issue, we investigate the characteristics of round-trip time (RTT) on wireless and wired networks. We conduct extensive experiments from diverse network environments and perform quantitative analyses on RTT variability. We show that RTT variability on a wireless network exhibits greatly larger mean, standard deviation, and min-to-high percentiles at least 10 ms bigger than those of wired networks due to the MAC layer retransmissions. We also find that the impact of packet size on wireless channel is particularly significant. Thus through a simple set of testing, one can accurately classify whether or not there has been a wireless network involved. We then propose effective adaptive cross-layer schemes for multimedia delivery over error-prone links. They include limiting the MAC layer retransmissions, controlling the application layer forward error correction (FEC) level, and selecting an optimal packet size. We conduct an analysis on the interplay of those adaptive parameters given a network condition. It enables us to find optimal cross-layer adaptive parameters when they are used concurrently.IEEE Circuits & Systems Societ

Experimental Evaluation of Techniques to Lower Spectrum Consumption in Wi-Red

Seamless redundancy layered atop Wi-Fi has been shown able to tangibly increase communication quality, hence offering industry-grade reliability. However, it also implies much higher network traffic, which is often unbearable as the wireless spectrum is a shared and scarce resource. To deal with this drawback the Wi-Red proposal includes suitable duplication avoidance mechanisms, which reduce spectrum consumption by preventing transmission on air of inessential frame duplicates. In this paper, the ability of such mechanisms to save wireless bandwidth is experimentally evaluated. To this purpose, specific post-analysis techniques have been defined, which permit to carry out such an assessment on a simple testbed that relies on plain redundancy and do not require any changes to the adapters' firmware. As results show, spectrum consumption decreases noticeably without communication quality is impaired. Further saving can be obtained if a slight worsening is tolerated for latencies.Comment: preprint, 13 page

Design, Development, and Implementation of a Wireless Local Area Network (WLAN): The Hartford Job Corps Academy Case Study

Wireless Local Area Networks (WLANs) offer flexibility, mobility, and scalability to educational institutions. Students are increasingly expecting anywhere, anytime access to online resources. Secondary school administrators, who serve a similar population as the National Job Corps Program (NJCP), realize that student success in the 21st century workplace depends upon the student\u27s ability to use new and emerging technologies, including wireless technology. Computer access anytime and anywhere is crucial to the success of students today. Wireless technology has been broadly deployed at educational institutions, such as the Hartford Job Corps Academy (HJCA), but little is known about how these networks are deployed and used, specifically at a Job Corps center. HJCA deployed a WLAN in 2005. Information about the core aspects of the design and implementation of anytime, anywhere initiatives, such as wireless solutions in education, is needed to complement the current research. The NJCP does not have a model for standardizing, organizing, and maintaining wireless networks. The goal of this investigation was to develop a model for planning, designing, and implementing a wireless solution for the Job Corps system. The case study findings from the investigation and the systems development life cycle (SDLC) provided the framework for structuring WLANs at other Job Corps centers. This framework also facilitated the investigation and a determination of the significance of the case study findings, and the analysis and development of the WLAN implementation model for the NJCP. The findings of the HJCA investigation from multiple sources are presented. Using the SDLC framework and the findings from the case study, the NJCP WLAN implementation model is presented. The NJCP WLAN implementation model may be used to facilitate the deployment of WLANs at government-operated, education and training facilities, such as the NJCP

On the long-term wireless network deployment strategies

Master'sMASTER OF ENGINEERIN

Design and optimization of QoS-based medium access control protocols for next-generation wireless LANs

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.In recent years, there have been tremendous advances in wireless & mobile communications, including wireless radio techniques, networking protocols, and mobile devices. It is expected that different broadband wireless access technologies, e.g., WiFi (IEEE 802.11) and WiMAX (IEEE 802.16) will coexist in the future. In the meantime, multimedia applications have experienced an explosive growth with increasing user demands. Nowadays, people expect to receive high-speed video, audio, voice and web services even when being mobile. The key question that needs to be answered, then, is how do we ensure that users always have the "best" network performance with the "lowest" costs in such complicated situations? The latest IEEE 802.11n standards attains rates of more than 100 Mbps by introducing innovative enhancements at the PHY and MAC layer, e.g. MIMO and Frame Aggregation, respectively. However, in this thesis we demonstrate that frame aggregation's performance adheres due to the EDCA scheduler's priority mechanism and consequently resulting in the network's poor overall performance. Short waiting times for high priority flows into the aggregation queue resolves to poor channel utilization. A Delayed Channel Access algorithm was designed to intentionally postpone the channel access procedure so that the number of packets in a formed frame can be increased and so will the network's overall performance. However, in some cases, the DCA algorithm has a negative impact on the applications that utilize the TCP protocol, especially the when small TCP window sizes are engaged. So, the TCP process starts to refrain from sending data due to delayed acknowledgements and the overall throughput drops. In this thesis, we address the above issues by firstly demonstrating the potential performance benefits of frame aggregation over the next generation wireless networks. The efficiency and behaviour of frame aggregation within a single queue, are mathematically analysed with the aid of a M=G[a;b]=1=K model. Results show that a trade-off choice has to be taken into account over minimizing the waiting time or maximizing utilization. We also point out that there isn't an optimum batch collection rule which can be assumed as generally valid but individual cases have to be considered separately. Secondly, we demonstrate through extensive simulations that by introducing a method, the DCA algorithm, which dynamically determines and adapts batch collections based upon the traffic's characteristics, QoS requirements and server's maximum capacity, also improves e ciency. Thirdly, it is important to understand the behaviour of the TCP ows over the WLAN and the influence that DCA has over the degrading performance of the TCP protocol. We investigate the cause of the problem and provide the foundations of designing and implementing possible solutions. Fourthly, we introduce two innovative proposals, one amendment and one extension to the original DCA algorithm, called Adaptive DCA and Selective DCA, respectively. Both solutions have been implemented in OPNET and extensive simulation runs over a wide set of scenarios show their effectiveness over the network's overall performance, each in its own way.This study was supported by the Engineering and Physical Sciences Research Council (EPSRC)

Your WiFi Is Leaking: Inferring Private User Information Despite Encryption

This thesis describes how wireless networks can inadvertently leak and broadcast users' personal information despite the correct use of encryption. Users would likely assume that their activities (for example, the program or app they are using) and personal information (including age, religion, sexuality and gender) would remain confidential when using an encrypted network. However, we demonstrate how the analysis of encrypted traffic patterns can allow an observer to infer potentially sensitive data remotely, passively, undetectably, and without any network credentials. Without the ability to read encrypted WiFi traffic directly, the limited side-channel data available is processed. Following an investigation to determine what information is available and how it can be represented, it was determined that the comparison of various permutations of timing and frame size information is sufficient to distinguish specific user activities. The construction of classifiers via machine learning (Random Forests) utilising this side-channel information represented as histograms allows for the detection of user activity despite WiFi encryption. Studies showed that Skype voice traffic could be identified despite being interleaved with other activities. A subsequent study then demonstrated that mobile apps could be individually detected and, concerningly, used to infer potentially sensitive information about users due to their personalised nature. Furthermore, a full prototype system is developed and used to demonstrate that this analysis can be performed in real-time using low-cost commodity hardware in real-world scenarios. Avenues for improvement and the limitations of this approach are identified, and potential applications for this work are considered. Strategies to prevent these leaks are discussed and the effort required for an observer to present a practical privacy threat to the everyday WiFi user is examined

Performance Analysis and Mitigation Techniques for I/Q-Corrupted OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) has become a widely adopted modulation technique in modern communications systems due to its multipath resilience and low implementation complexity. The direct conversion architecture is a popular candidate for low-cost, low-power, fully integrated transceiver designs. One of the inevitable problems associated with analog signal processing in direct conversion involves the mismatches in the gain and phases of In-phase (I) and Quadrature-phase (Q) branches. Ideally, the I and Q branches of the quadrature mixer will have perfectly matched gains and are orthogonal in phase. Due to imperfect implementation of the electronics, so called I/Q imbalance emerges and creates interference between subcarriers which are symmetrically apart from the central subcarrier. With practical imbalance levels, basic transceivers fail to maintain the sufficient image rejection, which in turn can cause interference with the desired transmission. Such an I/Q distortion degrades the systems performance if left uncompensated. Moreover, the coexistence of I/Q imbalance and other analog RF imperfections with digital baseband and higher layer functionalities such as multiantenna transmission and radio resource management, reduce the probability of successful transmission. Therefore, mitigation of I/Q imbalance is an essential substance in designing and implementing modern communications systems, while meeting required performance targets and quality of service. This thesis considers techniques to compensate and mitigate I/Q imbalance, when combined with channel estimation, multiantenna transmission, transmission power control, adaptive modulation and multiuser scheduling. The awareness of the quantitative relationship between transceiver parameters and system parameters is crucial in designing and dimensioning of modern communications systems. For this purpose, analytical models to evaluate the performance of an I/Q distorted system are considered