Browsing by Author "Van Rooyen, Gert-Jan"

Now showing 1 - 7 of 7
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    Baseband compensation principles for defects in quadrature signal conversion and processing
    (Stellenbosch : Stellenbosch University, 2004-04) Van Rooyen, Gert-Jan; Lourens, J. G.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Keywords: software-defined radio, SDR, quadrature mixing, quadrature modulation, quadrature demodulation, digital compensation, software radio, direct-digital synthesis, DDS. An often-stated goal of software-defined transceiver systems is to perform digital signal conversion as close to the antenna as possible by using high-rate converters. In this dissertation, alternative design principles are proposed, and it is shown that the signal processing techniques based on these principles improve on the prior system's accuracy, while maintaining system flexibility. Firstly, it is proposed that digital compensation can be used to reverse the effects of hardware inaccuracies in the RF front-end of a software-defined radio. Novel compensation techniques are introduced that suppress the signal artefacts introduced by typical frontend hardware. The extent to which such artefacts may be suppressed, is only limited by the accuracy by which they may be measured and digitally represented. A general compensation principle is laid down, which formalises the conditions under which optimal compensation may be achieved. Secondly, it is proposed that, in the design of such RF front-ends, a clear distinction should be drawn between signal processing complexity and frequency translation. It is demonstrated that conventional SDR systems often neglect this principle. As an alternative, quadrature mixing is shown to provide a clear separation between the frequency translation and signal processing problems. However, effective use of quadrature mixing as design approach necessitates the use of accurate compensation techniques to circumvent the hardware inaccuracies typically found in such mixers. Quadrature mixers are proposed as general-purpose front-ends for software-defined radios, and quadrature modulation and demodulation techniques are presented as alternatives to existing schemes. The inherent hardware inaccuracies are analysed and simulated, and appropriate compensation techniques are derived and tested. Finally, the theory is verified with a prototype system.
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    Impact of Neighbor Awareness at the MAC Layer in a Vehicular Ad-hoc NETwork (VANET)
    (IEEE -- Institute of Electrical and Electronics Engineers, 2013-06) Booysen, Marthinus J.; Zeadally, Sherali; Van Rooyen, Gert-Jan
    Despite various proposed Medium Access Control (MAC) approaches, efficient medium access in VANET remains a significant challenge, especially for the broadcast of safety messages. A key contributing factor to packet loss is the hidden terminal problem, which is exacerbated by the high node mobility apparent in VANET. Since the hidden terminal problem is fundamentally a problem of lack of awareness, this work evaluates the effects of increased neighbor awareness at the MAC layer. An increased awareness of neighboring nodes’ slot allocation in a TDMA-based MAC, directly impacts on the number of available slots. Therefore, the effects of TDMA frame size is also evaluated for different awareness ranges. To support the analysis, a TDMA-based MAC with configurable neighbor awareness and configurable TDMA frame size is introduced. The impact is assessed using the packet delivery ratio, receiver throughput, and end-to-end latency. The results show packet delivery ratio and receiver throughput to increase for increased awareness ranges, up to an optimal of 2 hops, after which performance worsens. An increase in TDMA frame size leads to an increase in packet delivery ratio for small awareness ranges, and an oscillating increase for large awareness ranges. The receiver throughput also initially increases for an increased TDMA frame size, but reaches an optimum,also at 2 hops.
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    Machine-to-machine (M2M) communications in vehicular networks
    (Korea Society of Internet Information (KSII), 2012-02) Booysen, Marthinus J.; Gilmore, J. S.; Zeadally, Sherali; Van Rooyen, Gert-Jan
    To address the need for autonomous control of remote and distributed mobile systems, Machine-to-Machine (M2M) communications are rapidly gaining attention from both academia and industry. M2M communications have recently been deployed in smart grid, home networking, health care, and vehicular networking environments. This paper focuses on M2M communications in the vehicular networking context and investigates areas where M2M principles can improve vehicular networking. Since connected vehicles are essentially a network of machines that are communicating, preferably autonomously, vehicular networks can benefit a lot from M2M communications support. The M2M paradigm enhances vehicular networking by supporting large-scale deployment of devices, cross-platform networking, autonomous monitoring and control, visualization of the system and measurements, and security. We also present some of the challenges that still need to be addressed to fully enable M2M support in the vehicular networking environment. Of these, component standardization and data security management are considered to be the most significant challenges.
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    A performance comparison of media access control protocols for vehicular ad-hoc networks (VANETs)
    (The Institution of Engineering and Technology (IET), 2012-04) Booysen, Marthinus J.; Zeadally, Sherali; Van Rooyen, Gert-Jan
    The emergence of computationally rich vehicles and recent advances in wireless communication technologies are fueling vehicular network research in industry and academia. A key challenge to the successful deployment of vehicular communication is the implementation and efficiency of the Medium Access Control (MAC) layer. There are mainly two types of MAC approaches, namely contention-based and contention-free. The current standard, IEEE 802.11p, is a contention-based approach, which has the severe limitation of unbounded transmission delays. An alternative contention-free approach called Dedicated Multichannel MAC (DMMAC) has been proposed in the literature. In this work we analyze these two approaches, discuss their limitations and introduce an improved approach called Medium Access with Memory Bifurcation and Administration (MAMBA). We evaluate the performance of the three approaches in highway and urban scenarios, for both low and high density traffic. Our performance evaluation results show that MAMBA improves throughput and message delivery ratio by up to 150% and 205% over IEEE 802.11p and DMMAC approaches respectively. MAMBA also improves on the latency achieved by the other methods by up to 72% and 99% respectively, compared to IEEE 802.11p and DMMAC.
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    Performance evaluation of neighbor-awareness at the Media Access Control (MAC) layer for Vehicular Ad-Hoc Networks (VANETs)
    (IEEE -- Institute of Electrical and Electronics Engineers, 2013-06) Booysen, Marthinus J.; Van Rooyen, Gert-Jan
    Efficient medium access in Vehicular Ad-hoc NETworks (VANETs) remains a significant challenge. Two types of Media Access Control (MAC) approaches have been proposed, namely contention-based and contention-free. We propose a novel MAC approach called Discretized RAndom Medium Access (DRAMA) for VANET. DRAMA is based on a contentionfree MAC, but unlike existing contention-free approaches, it is neighbor-agnostic. We evaluate the effect on performance of taking away all forms of channel coordination, thereby essentially removing neighbor awareness from an existing MAC approach. The evaluation is performed in terms of packet delivery ratio, receiver throughput, and end-to-end latency. We also present a performance evaluation of DRAMA and compare it to the IEEE 802.11p standard for various traffic scenarios. The results show that removing awareness from a MAC has a similar effect on performance to reducing awareness, in terms of number of hops used. Our performance results demonstrate performance improvements of 48%, 130%, and 73% over IEEE 802.11p in terms of packet delivery ratio, receiver throughput, and end-to-end latency, respectively.
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    Recognition of driving manoeuvres using smartphone-based inertial and GPS measurement
    (2014-12) Engelbrecht, Jarrett; Booysen, Marthinus J.; Van Rooyen, Gert-Jan
    The ubiquitous presence of smartphones provides a new platform on which to implement sensor networks for ITS applications. In this paper we show how the embedded sensors and GPS of a smartphone can be used to recognize driving manoeuvres. Smartphone-based driving behaviour monitoring has applications in the insurance industry and for law enforcement. The proposed solution is suitable for real-time applications, such as driver assistance and safety systems. An endpoint detection algorithm is used on filtered accelerometer and gyroscope data to find the start- and endpoints of driving events. The relevant sensor data is compared against different sets of manoeuvre signal templates using the dynamic time warping (DTW) algorithm. A heuristic method is then used to classify a manoeuvre as normal or aggressive based on its speed and closest matching acceleration and rotation rate templates.
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    Survey of Media Access Control (MAC) protocols for Vehicular Ad hoc NETworks (VANETs)
    (The Institution of Engineering and Technology (IET), 2011-07) Booysen, Marthinus J.; Zeadally, Sherali; Van Rooyen, Gert-Jan
    Recent advances of various wireless communication technologies and the emergence of computationally rich vehicles are pushing Vehicular Ad-hoc NETwork (VANET) research to the forefront in academia and industry. A lot of research results have been published in various areas (such as routing, broadcasting, security, and others) of VANET in the last decade covering both Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) scenarios. One specific area of VANET that still faces significant challenges is the design of reliable and robust Media Access Control (MAC) protocols for V2V communications. We present a survey of V2V MAC methods (including various VANET standards) that have been proposed for VANETs over the last few years. We focus on the benefits and limitations of the proposed MAC techniques as well as their ease of implementation in practice and future deployment. We also discuss some of the challenges that still need to be addressed to enable the implementation of highly efficient and high performance MAC protocols for V2V communications. Finally, we propose some innovative solutions that can be developed to address these challenges.