Browsing by Author "Quazi, Tahmid Al-Mumit."

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Application of real-world modulation schemes to advanced spatial modulation systems.
(2022) Khalid, Ahmad Bin.; Quazi, Tahmid Al-Mumit.; Xu, Hongjun.
Abstract available in PDF.
Artificial intelligence based design optimization for improving diversity in wireless links.
(2021) Solwa, Shaheen.; Naidoo, Bashan.; Quazi, Tahmid Al-Mumit.
Abstract available in PDF.
Cross-layer design for the transmission of multimedia traffic over fading channels.
(2009) Quazi, Tahmid Al-Mumit.; Xu, Hongjun.
Providing guarantees in the Quality of Service (QoS) has become essential to the transmission of multimedia traffic over wireless links with fading channels. However this poses significant challenges due to the variable nature of such channels and the diverse QoS requirements of different applications including voice, video and data. The benefits of dynamic adaptation to system and channel conditions have been accepted, but the true potential of optimized adaptation is lost if the layers operate independently, ignoring possible interdependencies between them. Cross-layer design mechanisms exploit such interdependencies to provide QoS guarantees for the transmission of multimedia traffic over fading channels. Channel adaptive M-QAM schemes are examples of some of the earliest works in the area of cross-layer design. However, many of the original schemes use the assumption that thresholds designed for AWGN channels can be directly applied to slow-fading channels. The thresholds are calculated with a commonly used approximation bit error rate (BER) expression and the first objective of the thesis was to study the accuracy of this commonly used expression in fading channels. It is shown that that the inaccuracy of the expression makes it unsuitable for use in the calculation of the threshold points for an adaptive M-QAM system over fading channels. An alternative BER expression is then derived which is shown to be far more accurate than the previous one. The improved accuracy is verified through simulations of the system over Nakagami-m fading channels. Many of the cross-layer adaptation mechanisms that address the QoS provisioning problem only use the lower layers (physical and data link) and few explore the possibility of using higher layers. As a result, restrictions are placed on the system which introduces functional limitations such as the inability to insert more than one class of traffic in a physical layer frame. The second objective in this thesis was to design a physical and application layer cross-layer adaptation mechanism which overcomes this limitation. The performance results of the scheme in both AWGN and fading channels show that the cross-layer mechanism can be efficiently utilized for the purposes of providing error rate QoS guarantees for multimedia traffic transmissions over wireless links.
Design and implementation of an on-demand ad-hoc routing algorithm for a positional communication system.
(2003) Quazi, Tahmid Al-Mumit.; McDonald, Stephen A.
A mobile ad-hoc network is an autonomous network of mobile devices that are connected via wireless links. In such networks there is no pre-existing infrastructure and nodes are free to move in a random fashion. Due to this mobility mobile ad-hoc networks have dynamic topologies. A host in the network typically has limited bandwidth and energy resources. Routing is a major challenge in the development of such systems and there have been many solutions proposed in the recent past. The aim of this work is to design and implement a routing scheme for a Positional Communication System (PCS). The PCS is a network of mobile handheld pocket PCs connected via wireless interfaces. The system allows voice and data communication between nodes in the network. This dissertation addresses the process of designing a routing protocol for an ad-hoc network. There have been many proposed algorithms that solve the routing problem in a mobile ad-hoc network. It is a difficult task to compare the performance of'these protocols qualitatively as there are many parameters that affect network performance. Various simulation packages for networks of this type exist. One such package is the Network Simulator (NS-2). It is a discrete time event simulator that can be used to model wired and wireless networks. This dissertation presents NS-2 simulations that compare four recently proposed routing algorithms. From this comparison study it is shown that on-demand algorithms perform best in a mobile ad-hoc environment. The dissertation then describes the design of a novel on-demand routing algorithm. The ondemand algorithms proposed thus far use a blind flooding technique during the route discovery process. This method is inefficient and creates excessive routing overhead. The routing protocol proposed in the dissertation implements a query localization technique that significantly reduces the network traffic. The protocol also introduces a load checking metric in addition to the metric used by most on-demand schemes, namely hop count. Simulation results show that such a scheme makes the on-demand routing algorithm more efficient and scalable than existing ones. It is widely believed that prior to implementing a routing protocol in real world systems it is essential that it is tested and validated on a test-bed. The dissertation presents the implementation of an on-demand routing algorithm in a Positional Communication System test-bed, where each handheld PC in the network runs an embedded Linux operating system.
Hierarchical modulation with signal space and transmit diversity in Nakagami-m fading channel.
(2013) Saeed, Ayesha.; Xu, Hongjun.; Quazi, Tahmid Al-Mumit.
Hierarchical modulation (HM) is a promising scheme for wireless image and video transmission, exploiting the benefits of unequal error protection to ensure enhanced system performance. However, there is a limiting factor to the benefits of using only hierarchy to improve bit error rate (BER) performance of a transmission system. Diversity, namely signal space diversity (SSD) and Alamouti transmit diversity (ATD), can be introduced to improve BER performance results for HM systems. This dissertation presents the BER analysis of hierarchically modulated QAM with SSD and using maximal ratio combining (MRC) to retrieve the transmitted symbol from 𝑁 receiver antennas. In addition, the study includes the BER analysis of an identical system in an ATD scheme employing two transmit antennas and 𝑁 receiver antennas with MRC. SSD comprises of two fundamental stages: constellation rotation and component interleaving. The angle at which the constellation is rotated can affect the performance of the system. In the past, the rotation angle is determined based on a design criterion which maximizes the diversity order by minimizing the Euclidean square product or, alternatively, minimizes an SER expression. In this dissertation, a simple method for determining a rotation angle at which system performance is optimal for hierarchical constellations is presented. Previously, the BER analysis for HM involves an intricate approach where the probability of an error occurring is determined by considering the probability of a transmitted symbol exceeding past a set decision boundary. This dissertation presents the Nearest Neighbor (NN) union bound approach for determining an accurate approximation of the BER of an HM system with SSD. This method of analysis is later extended for an ATD scheme employing HM with SSD. Although introducing diversity elevates the system performance constraints on HM, it does so at the cost of detection complexity. To address this issue, a reduced complexity maximum-likelihood (ML) based detector is also proposed. While the conventional ML detector performs an exhaustive search to find the minimum Euclidean distance between the received symbol and all possible modulated symbols, the proposed detector only considers the nearest neighbors of the received symbol. By reducing the number of comparisons, a complexity reduction of 51.43% between the proposed detector and the optimal detector for 16-QAM is found.
Investigating machine and deep-learning model combinations for a two-stage IDS for IoT networks.
(2021) Van der Walt, André.; Quazi, Tahmid Al-Mumit.; Van Niekerk, Brett.
By 2025, there will be upwards of 75 billion IoT devices connected to the internet. Notable security incidents have shown that many IoT devices are insecure or misconfigured, leaving them vulnerable, often with devastating results. AI’s learning, adaptable and flexible nature can be leveraged to provide networking monitoring for IoT networks. This work proposes a novel two-stage IDS, using layered machine- and deep-learning models. The applicability of seven algorithms is investigated using the BoT-IoT dataset. After replicating four algorithms from literature, modifications to these algorithms' application are then explored along with their ability to classify in three scenarios: 1) binary attack/benign, 2) multi-class attack with benign and 3) multi-class attack only. Three additional algorithms are also considered. The modifications are shown to achieve higher F1-scores by 22.75% and shorter training times by 35.68 seconds on average than the four replicated algorithms. Potential benefits of the proposed two-stage system are examined, showing a reduction of threat detection/identification time by 0.51s on average and an increase of threat classification F1-score by 0.05 on average. In the second half of the dissertation, algorithm combinations, layered in the two-stage system, are investigated. To facilitate comparison of time metrics, the classification scenarios from the first half of the dissertation are re-evaluated on the test PC CPU. All two-stage combinations are then tested. The results show a CNN binary classifier at stage one and a KNN 4-Class model at stage two performs best, outperforming the 5-Class (attack and benign) system of either algorithm. This system's first stage improves upon the 5-Class system's classification time by 0.25 seconds. The benign class F1-score is improved by 0.23, indicating a significant improvement in false positive rate. The system achieves an overall F1-score of 0.94. This shows the two-stage system would perform well as an IDS. Additionally, investigations arising from findings during the evaluation of the two-stage system are presented, namely GPU data-transfer overhead, the effect of data scaling and the effect of benign samples on stage two, giving a better understanding of how the dataset interacts with AI models and how they may be improved in future work.
Quadrature spatial modulation aided single-input multiple-output-media based modulation: application to cooperative network and golden code orthogonal super-symbol systems.
(2022) Bamisaye, Ayodeji James.; Quazi, Tahmid Al-Mumit.
SIMO-MBM (single-input multiple-output media-based modulation) overcomes the limitations of SIMO (single-input multiple-output) systems by reducing the number of antennas required to achieve a high data rate and improved error performance. In this thesis, the quadrature dimension of the spatial constellation is used to improve the overall error performance of the conventional SIMO-MBM and to achieve a higher data rate by decomposing the amplitude/phase modulation (APM) symbol into real and imaginary components, similar to quadrature spatial modulation (QSM). The average bit error probability of the proposed technique is expressed using a lower bound approach and validated using the results of Monte Carlo simulation (MCS). The proposed system also investigates the effect of antenna correlation in combination with channel amplitude to select a sub-optimal mirror activation pattern. The results of MCS show a 3.5dB improvement at 10b/s/Hz with m 𝑚𝑟𝑓=2 and a 7dB improvement at 12b/s/Hz with 𝑚𝑟𝑓=2 over the traditional SIMO-MBM scheme. The effect of imperfect channel estimation on the proposed scheme is investigated, with a trade-off of 2dB in coding gain due to channel estimation errors. Cooperative Networking (CN) improves wireless network reliability, link quality, and spectrum efficiency by collaborating among nodes. The decode and forward relaying technique is used in this thesis to investigate the performance of QSM aided SIMO-MBM in a Cooperative Network (CN). This technique uses two source nodes that simultaneously transmit a unique message block on the same time slot to the relay node, which then decodes the received message block from both transmitting nodes before re-encoding and re-transmitting the decoded message block in the next time slot to the destinations in order to significantly improve the QSM aided SIMO-MBM’s error performance. Using network coding (NC) techniques, each Node can decode the data of the other Node. To enhance network performance, complexity, robustness, and minimize delays, data is encoded and decoded in NC; algebraic techniques are applied to the detected message to collect the various transmissions. The proposed scheme's theoretical average error probability was defined using a lower bound technique, and the results of Monte Carlo simulation (MCS) validated the result. The MCS results achieved exhibit a significant improvement of 8 dB at 6 b/s/Hz and 12 dB at 8 b/s/Hz over the conventional QSM aided SIMO-MBM scheme. The media-based modulation (MBM) technique can achieve significant throughput, increase spectrum efficiency, and improve bit-error-rate performance (BER). In this thesis, the use of MBM in single-input multiple-output systems is examined using radio frequency (RF) mirrors and Golden code (GC-SIMO). The goal is to lower the system's hardware complexity by maximizing the linear relationship between RF mirrors and spectral efficiency in MBM in order to achieve a high data rate with less hardware complexity. The GC scheme's encoder uses orthogonal pairs of the super-symbol, each transmitted via a separate RF mirror at a different time slot to achieve full rate full diversity. In the results of MCS obtained, at a BER of 10−5, the GC-SIMO-MBM exhibits a significant performance of approximately 7dB and 6.5 dB SNR gain for 4 b/s/Hz and 6 b/s/Hz, respectively, compared to GC-SIMO. The proposed scheme's derived theoretical average error probability is validated by the results of the Monte Carlo simulation.
Uncoded space-time labelling diversity : data rate & reliability enhancements and application to real-world satellite broadcasting.
(2019) Patel, Sulaiman Saleem.; Quazi, Tahmid Al-Mumit.; Xu, Hongjun.
Abstract available in PDF.