Browsing by Author "Abdalla, Abdi T"

Now showing 1 - 13 of 13
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    Appropriate Media Access Control Protocol for Broadband Power-Line Access Network of Developing Countries: A Case of Tanzania
    (2012-06) Abdalla, Abdi T
    This paper investigates and compares the performances of different MAC protocols including ALOHA, slotted ALOHA and Carrier Sense Multiple Access with Collision Avoidance with the application to broadband powerline networks of Dar es Salaam and suggesting the appropriate one. In this investigation, the powerline network of Kariakoo was used as case study. During investigation, wireshark network protocol analyzer was used to analyze data traffic of similar existing network for projection and the data were simulated using MATLAB. From the results, pure ALOHA protocol gives the maximum throughput of 15.99%, slotted-ALOHA protocol gives 21.16% and CSMA/CA gives the maximum throughput of 30.6% under the same traffic load of 0.28Erlang keeping arrival rates and packet lengths constant.
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    Aspect dependent efficient multipath ghost suppression in TWRI with compressive sensing
    (Cambridge University Press and the European Microwave Association, 2017) Muqaibel, Ali; Abdalla, Abdi T; Alkhodary, Mohammad; AlDharrab, Suhail
    In through-the-wall radar imaging, multipath propagation can create ghost targets, which can adversely affect the image reconstruction process. However, unlike genuine targets, ghost positions are aspect-dependent, which means their position changes with the transceiver location. This paper proposes efficient ghost suppression methods exploiting aspect dependence feature under compressive sensing framework. This paper proposes a generalized signal model that accommodates for the reflections of the front-wall and target-to-target interactions, making the scheme more practical, yet the knowledge of the location of reflecting geometry is not a requirement as in most of the recent literatures. In addition, the sensing matrix is greatly reduced making the methods more attractive. Moreover, this paper investigates the influence of array configurations by examining two antenna array configurations: multimonostatic, and single-view bistatic configurations. Results based on synthesized data and real experiment show that the proposed method can greatly suppress multipath ghosts and hence increase signal-to-clutter ratio.
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    Aspect Dependent Multipath Ghost Suppression in TWRI Under Compressive Sensing Framework
    (2015) Abdalla, Abdi T; Muqaibel, Ali H.; Al-Dharrab, Suhail
    In through-the-wall radar imaging, multipath propagation can create ghost targets which can adversely affect the image reconstruction process. The fact that the ghost positions changes with the radar locations which is referred to as aspect dependence has been reported as among the features distinguishing ghost from true target. This paper proposes ghost suppression method which exploit the aspect dependence feature under compressive sensing framework. The existing signal model is modified so that the location of reflecting geometry is no longer a constraint. Also the sensing matrix is greatly reduced making the methods more attractive. Simulation results demonstrate the effectiveness of the proposed methods.
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    Extended Targets Modelling and Block Agnostic Sparse Reconstruction in Through-the-Wall Radar Imaging: A Different Perspective
    (Academic Publication Council-Kuwait University, 2019) Abdalla, Abdi T; Alkhodary, Mohammad; Muqaibel, Ali
    A common target model in through-the-wall radar (TWRI) imaging literature obeys the point target (PT) assumption in which a target is hypothesized to occupy a single pixel. Unlike PTs, the received signal reflected from extended target (ET) is an integration of the scattered signals from various parts of the same target. For high resolution images, a generalized model is needed to encompass the ETs. In this paper, we suggest a different but realistic ET reconstruction approach based on agnostic block sparsity. The algorithm does not impose any assumption on the length, number, or the distribution of the blocks. Results based on MATLAB simulation and experimental data show the effectiveness of the proposed reconstruction approach. The applications of the suggested approach are found in civil, rescue, surveillance, and security enforcement sectors, where an accurate tracking of large targets behind walls is vital.
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    HAPs Communication in Saudi Arabia under Dusty Weather Conditions
    (IEEE, 2013) Harb, Kamal; Abdalla, Abdi T; Mohamed, Muhidin A.; Abdul-Jauwad, Samir H.
    Technology is improving rapidly. One of the most revolutionary communication technologies that appears to be convincing and efficient is called High Altitude Platform (HAP). As any other wireless communication system, a main degrading factor of HAP Station (HAPS) propagation channel in desert and semi-desert areas is the dust storm attenuation. This attenuation increases with an increasing operational frequency and is prominent in the frequency bands above 10 GHz which is used for HAPS communications. This paper investigates the effect of dust attenuation on the reliability of the HAPs system. Also, based on a close scrutiny of the existing dust attenuation models, this paper proposes some modifications to an existing dust attenuation model to comply with the real dust phenomenon. In this paper, a platform altitude of 22 km with a minimum elevation angle of 20 were considered. The analysis showed that the dust attenuation degraded the signal to noise ratio by around 20 dB at Ka frequency band. As a result, an appropriate intelligent attenuation mitigation technique was then suggested.
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    Indoor target localization using marginal antenna with virtual radars support
    (2017) Muqaibel, Ali; Abdalla, Abdi T; Alkhodary, Mohammad
    In urban target localization, the presence of walls creates virtual radars (VRs), which can be exploited to aid in localization process. The fact that multipath changes with the radar locations, which are referred to as aspect dependence property, enable us to find a radar location, which reduces wall uncertainties. This paper proposes single-antenna target localization in an enclosed structure taking advantage of VRs. Using ultra-wideband signals, we can resolve the target returns and estimate the correct location by solving monostatic loci at real and VR locations. Simulation results show that the method can precisely and accurately localize the target for a wide range of timing errors
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    Mixed Mode Device-to-Device Communication Scheme for Congestion Reduction and Channel Usage Optimization in 5G Cellular Networks
    (University of Dar es Salaam, 2019) Chiza, Christophe; Hamad, Omar; Massawe, Libe; Abdalla, Abdi T
    Device-to-Device (D2D) communication schemes have gained more attention in cellular networks particularly in normalization process of the upcoming 5G networks. They have been investigated in core network offloading, congestion reduction and channel usage optimization. The two last cases are among the major constraints in current cellular networks and are the main concerns of this paper. The paper presents a mixed mode D2D communication scheme to decentralize data collection between devices and the base station in order to reduce the number of direct connections at the base station of ultra-dense cells characterized by different levels of channel utilizations or target data rates, as expected for 5G networks. The attachment utility is derived as the overall gain of a device for a target data rate and is used as a metric for D2D association’s decision. Results show that the attachment utility and D2D pairs increase by either increasing the D2D communication range or decreasing devices’ target data rates. A further important consideration is that the proposed mixed mode D2D communication scheme improves the throughput expectation in the cell by 14.2% compared to the regular cellular communication
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    Multipath Ghost in Through the Wall Radar Imaging: Challenges and Solutions
    (Wiley Online Library, 2018) Abdalla, Abdi T; Alkhodary, Mohammad; Muqaibel, Ali
    In through-the-wall radar imaging (TWRI), the presence of front and side walls causes multipath propagation, which creates fake targets called multipath ghosts. They populate the scene and reduce the probability of correct target detection, classification, and localization. In modern TWRI, specular multipath exploitation has received considerable attention for reducing the effects of multipath ghosts. However, this exploitation is challenged by the requirements of the reflecting geometry, which is not always available. Currently, the demand for a high radar image resolution dictates the use of a large aperture and wide bandwidth. This results in a large amount of data. To tackle this problem, compressive sensing (CS) is applied to TWRI. With CS, only a fraction of the data are used to produce a high-quality image, provided that the scene is sparse. However, owing to multipath ghosts, the scene sparsity is highly deteriorated; hence, the performance of the CS algorithms is compromised. This paper presents and discusses the adverse effects of multipath ghosts in TWRI. It describes the physical formation of ghosts, their challenges, and existing suppression techniques.
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    Path-loss Compensation in Through-the-wall Radar Imaging
    (IEEE, 2016) Alahmed, Ahmed; Alafif, Omar; Abdalla, Abdi T; Muqaibel, Ali
    In through-the-wall radar imaging (TWRI), pathloss can result in misleading targets. The fact that distant targets experience more path-Ioss than near targets is an essential feature of propagating signals. This paper proposes a path-Ioss compensator, which reverts the unavoidable loss in power by using different path-Ioss models. This will be effectively done by developing and incorporating the path-Ioss compensator matrix. The signal model is generalized so that it includes the front wall reflections. Many research papers in the field do not account for the differences in the propagation losses of the paths due to its complexity and mutable behavior, wh ich can bring great difficulties to establish distance path-Ioss model. Simulation and experimental results are presented to show how the proposed approach can efficiently compensate for far targets and thus enhancing the signal-to-c1utter ratio and reducing the normalized mean square error
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    Performance Improvement of MAC Protocols for Broadband Power-Line Access Networks of Developing Countries: A Case of Tanzania
    (2013) Abdalla, Abdi T; Anatory, Justinian
    This paper investigates the possibility of improving throughputs of some Media Access Controls protocols such as ALOHA, slotted ALOHA and Carrier Sense Multiple Access with Collision Avoidance with the aim of increasing the performance of Powerline access networks. In this investigation, the real Powerline network topology in Tanzania located in Dar es Salaam City, Kariakoo area was used as a case study. During this investigation, Wireshark Network Protocol Analyzer was used to analyze data traffic of similar existing network for projection purpose and then the data were simulated using MATLAB. This paper proposed and analyzed three improvement techniques based on collision domain, packet length and combination of the two. From the results, it was found that the throughput of Carrier Sense Multiple Access with Collision Avoidance protocol improved noticeably while ALOHA and slotted ALOHA showed insignificant changes especially when the hybrid techniques were employed. .
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    Targets Interaction in Through-The-Wall Radars under Path-Loss Compensated Multipath Exploitation-Based Model for Sparse Image Reconstruction
    (University of Dar es Salaam, 2019) Kokumo, Emmanuel; Maiseli, Baraka; Abdalla, Abdi T
    Multipath caused by reflections from interior walls of buildings has been a long-standing challenge that affects through-the-wall radar imaging. Multipath creates ghost images that introduce confusion when detecting desired targets. Traditionally, multipath exploitation techniques under the compressive sensing framework have widely been applied to address the challenge. However, the multipath component emanating from target-to-target interactions has not been considered–a consequence that may, under multiple target scenarios, lead to incorrect image interpretation. Besides, far targets experience more attenuation due to free space path loss, hence resulting into target undetectability. This study proposes a signal model, based on multipath exploitation techniques, by designing a sensing matrix that incorporates multipath returns due to target-to-target interaction and path loss compensation. The study, in addition, proposes the path loss compensator that, if integrated into the proposed signal model, reduces path loss effects. Simulation results show that the Signal to Clutter Ratio and the Relative Clutter Peak improved by 4.9 dB and 1.9 dB, respectively, compared with the existing model
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    Through-the-Wall Radar Imaging Exploiting Pythagorean Coprime-Based Synthetic Apertures with Sparse Reconstruction
    (2017) Muqaibel, Ali; Abdalla, Abdi T; Alkhodary, Mohammad; Alawsh, Saleh
    Through-the-wall radar imaging (TWRI) is receiving a considerable attention recently due to its diverse applications. One of the impinging challenges is the multipath propagation from the surrounding environment and even targets themselves. Multipath propagation produces ghost targets which populate the scene and not only create confusion with genuine targets but deteriorate the performance of compressive sensing (CS) algorithms. Unlike genuine targets, ghost locations are aspect dependent. Successful exploitation of this feature is dictated by the subarray selection modality. Up to this far, random multiple subarrays selection is the practice in exploiting aspect dependence. This paper suggests new subarray configurations based on Pythagorean triple which is made of pairwise coprime numbers that can enhance ghost suppression process and improve image resolution. The sensing matrices of the proposed subarrays are developed and analyzed. The paper investigates the effectiveness of generating the images from all the elements in the array as opposed to generating the images by processing designed subarrays individually and then combining the results. This comparison is done in view of multipath ghost suppression exploiting aspect dependence feature. Results based on synthesized data and electromagnetic propagation simulator show the effectiveness of the proposed arrays.
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    Through-The-Wall Radar Imaging with Compressive Sensing: Theory, Practice and Future Trend-A Review
    (University of Dar es Salaam, 2018) Abdalla, Abdi T
    Through-the-Wall Radar Imaging (TWRI) is an emerging technology which enables us to detect behind the wall targets using electromagnetic signals. TWRI has received considerable attention recently due to its diverse applications. This paper presents fundamentals, mathematical foundations and emerging applications of TWRI with special emphasis on Compressive Sensing (CS) and sparse image reconstruction.Multipath propagation stemming from the surrounding walls and nearby targets are among the impinging challenges.Multipath components produce replicas of the genuine target, ghosts, during image reconstruction which may significantly increase the probability of false alarm. The resulting ghost not only creates confusion with genuine targets but may deteriorate the performance of (CS) algorithms as described in this article. The results from a practical scenario show a promising future of the technology which can be adopted in real-life problems including rescue missions and military purposes