Universiti Teknologi Malaysia - Research Data

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A millimeter wave reflectarray antenna with tilted side patch elements for fifth generation communication systems
(Universiti Teknologi Malaysia, 2019) Dahri, Muhammad Hashim
A flat surface reflectarray antenna is becoming an impending competitor for fifth generation (5G) communications among the generally known conventional antenna systems. Its narrow bandwidth and high loss performance lead to restrict its gain and effciency at millimeter wave frequencies. Additionally, high design sensitivity is also an issue at millimeter waves that can trigger the problem of imperfect fabrications. Therefore, a simple design of reflectarray patch element is required with wide reflection phase range to achieve wideband and high gain performance. Effciency of reflectarray antenna is also needed to be formulated properly to acquire polarization diversity. In this work, a new reflectarray patch element with a tilted side is recommended for a wideband dual resonance operation within 24 GHz to 28 GHz frequency range. Dual resonance of the tilted side patch element offers a reflection phase range of more than 600' and a reflection loss of 1.6 dB with a novel design. Simulated results of the patch element have been verified by the scattering parameter measurements using a waveguide simulator. Additionally, a mathematical relationship has been formulated to predict the effciency of the reflectarray antenna based on its aperture shape and feed distance. It has been found that, a circular aperture reflectarray attains 21.46% higher effciency than its equivalent square aperture reflectarray of the same feed distance. Consequently, a circular aperture reflectarray consisting of 332 variable size tilted side patch elements has been designed and tested at 26 GHz with various possible configurations. The high cross polarization issue due to the asymmetric design of the tilted side patch element has been tackled by mirroring the orientations of the elements on the surface of reflectarray. Moreover, circular ring slots with variable radius have been embedded in reflectarray ground plane for gain improvement. Experimental results show that, the slotted ground reflectarray antenna offers a 3.5 dB higher gain with 22.9% higher effciency and 3% wider bandwidth than a full grounded reflectarray antenna. A maximum of 26.1 dB gain with 41.3% effciency and 11.5% (3 GHz) bandwidth has been acquired with the slotted ground reflectarray antenna. The tilted side patch reflectarray has offered dual linear polarization when its elements are mirrored to each other and dual circular polarization when its elements are not mirrored to each other. Its main beam has been numerically steered up to +20' by a progressive phase shift of 80'. The acquired parameters of the tilted side patch reflectarray antenna fit within the requirements of the 5G communication systems.
Beamforming and non-orthogonal multiple access for rate and secrecy enhancement of fifth generation communication system
(Universiti Teknologi Malaysia, 2019) Alsaba, Yamen
The fifth-generation (5G) communication systems have many anticipated functionalities and requirements such as high data rate, massive connectivity, wide coverage area, low latency and enhanced secrecy performance. In order to meet these criteria, communication schemes that combine 5G key enabling technologies need to be investigated. In this thesis, a novel communication system that merges non-orthogonal multiple access (NOMA), energy harvesting, beamforming, and full-duplex (FD) techniques in order to enhance both capacity and secrecy of 5G system is introduced. In the capacity improving scheme, NOMA is first combined with beamforming to serve more than one user in each beamforming vector. Next, simultaneous wireless information and power transfer (SWIPT) technique is exploited to encourage the strong user (user with better channel condition) to relay the information messages of the weak user (user with poor channel condition) in FD manner. The total sum rate maximisation problem is formulated and solved by means of convex-concave procedure. The system performance is also analysed by deriving the outage probability of both users. Additionally, the model is extended to a more general case wherein the users are moving, and the outage probability of this dynamic topology is provided by means of the stochastic geometry framework. Novel secure schemes are also introduced to safeguard legitimate users’ information from internal and external eavesdroppers. In the internal eavesdropper’s case, artificial signal concept is adopted to protect NOMA’s weak user’s information from being intercepted by the strong user. The secrecy outage probability of theweak user is derived and validated. In addition, game theory discipline is exploited to provide an efficient eavesdropping avoidance algorithm. Null-steering beamforming is adopted in the external eavesdropper’s case in two different schemes namely self and nonself-cooperative jamming. In self-cooperative strategy, the base station applies the null-steering jamming to impair the eavesdropper channel, while sending the information-bearing signals to the intended legitimate users. Whereas in the nonself-cooperative jamming scheme, the base station provides the helpers with the required information and power by means of SWIPT technique in the first phase. The helpers deploy null-steering beamforming to jam the eavesdropper during the information exchange between the base station and the intended users in the second phase. The secrecy outage probability of the legitimate users is derived in both jamming schemes. Game theory is also introduced to the nonself-cooperative jamming scheme for further improvements on the secrecy outage behaviour and the economic revenue of the system. The proposed capacity enhancing scheme demonstrates about 200% higher sum rate when compared with the non-cooperative and half-duplex cooperative NOMA systems. In addition, the novel secure scheme in the internal eavesdropper case is proven to enhance the information security of the weak user without compromising the functionalities of the strong user or NOMA superiority over orthogonal multiple access systems. Null-steering based jamming system also illustrates improved secrecy performance in the external eavesdropper case when compared to the conventional jamming schemes. Numerical simulations are carried out in order to validate the derived closed-form expressions and to illustrate the performance enhancement achieved by the proposed schemes where the rate is increased by 200% and the secrecy outage probability is decreased by 33% when compared to the baseline systems.
Graphene antenna design and characterisation for fifth generation applications
(Universiti Teknologi Malaysia, 2020) Sa’don, Siti Nor Hafizah
The incoming fifth generation (5G) technology requires antennas with a greater capacity, wider wireless spectrum utilisation, high gain, and beam steering ability. This is due to the cramped spectrum utilisation in the previous generation. As a matter of fact, conventional antennas are unable to serve the new frequency due to the limitations in fabrication and installation mainly for smaller sizes. The use of graphene material promises antennas with smaller sizes and thinner dimensions, yet capable of emitting higher frequencies. Graphene is a unique material that can display tuning characteristics. This characteristic originates from its surface complex conductivity, which is controlled by a chemical potential. Most characteristics of tunable graphene antenna have been studied on terahertz frequency range, thus making it difficult to be realised practically. Besides, the standard antenna that uses switching components may have trouble during installation, and size consuming as it can be seen in the reconfigurable antenna. Due to that, another study to produce graphene with excellent properties is vital for the advancement of wireless communication system. In this thesis, graphene antennas for fifth generation applications are conducted in three parts of studies. In the first part, the graphene antenna properties are studied in different curing temperatures and times. The curing temperatures are 250°C, 300°C, and 350°C, then each temperature is set with curing times of 20 minutes, 30 minutes, 1 hour, 2 hours, and 3 hours to manufacture graphene based antenna with different properties. The proposed graphene based antenna properties are then respectively investigated using performance network analyser (PNA), vector network analyser (VNA), field-emission scanning electron microscope (FESEM), and Raman spectroscopy. From analyses on the dielectric, conductivity and characterisation on graphene’s physique, the antenna properties exhibit a tunability through its resonance frequency and main beam direction of the radiation pattern by the variation obtained in curing temperature and time. In the same time, the gain of the antennas can also be varied. The second part is the study of graphene antennas at a frequency of 15 GHz in both single and array elements. The high-frequency antenna contributes to a large bandwidth and is excited by coplanar waveguide for easy fabrication on one surface via screen printing method. The defected ground structure is applied in an array element to improve the radiation and increase the gain. The results show that the printed graphene antenna for single element produces an impedance bandwidth, gain, and efficiency of 48.63%, 2.99 dBi, and 67.44%, respectively. Meanwhile, the array element produces slightly better efficiency (72.98%), approximately the same impedance bandwidth as the single element (48.98%), but higher gain (8.41 dBi). Moreover, it provides a beam width of 21.2° with scanning beam capability from 0° up to 39.05°. The last part is a tunable antenna based on graphene operating at microwave frequency range is proposed. The antenna is designed and fabricated at 15 GHz with a gate electrode placed behind it. They are connected to external direct current (DC) bias during the measurement. The biasing is applied from 0 V to 30 V. The result shows that the resonance frequency is tuned to 20 MHz and reflection coefficient magnitude improves by 1.24 dB. Following this, an analytical calculation on chemical potential is also derived to enhance the graphene tunability. It is shown that at least 2.85 kV of the gate voltage is needed to vary the chemical potential and less than 0.29 µm of dielectric thickness is suitable for tuning purpose with a given condition. Based on the three parts of studies on antenna design and characterisation, graphene can be a good alternative material for future communication. It is due to the exhibited performances are comparable with conventional material and could act beyond the common antenna properties under the influence of tunability, which is owned by graphene.
Indoor path loss modeling for fifth generation applications
(Universiti Teknologi Malaysia, 2018) Majed, Mohammed Bahjat
The demand for high data rate transmission for the future wireless communication technology is increasing rapidly. Due to the congestion in the current bands for cellular network, it may not be able to satisfy the user requirements. For the future cellular networks, the millimeter wave (mm-wave) bands are the promising candidate bands because of the large available bandwidth. The 28 GHz and 38 GHz bands are the strongest candidate for fifth generation (5G) cellular networks. The channel needs to be characterized based on large-scale characterization to know the channel behavior in mm-wave bands in indoor environment. The narrowband channel is characterized based on the path loss model. For the development of new 5G systems to operate in bands up to 100 GHz, there is a need for accurate radio propagation models, which are not addressed by existing channel models developed for bands below 6 GHz. This attempt was conducted through extensive measurement campaigns and by using Information and Communication Solutions (ICS) Telecom simulation tool. The measurement environments were a closed-plan scenario in two buildings that included a line-of-sight (LOS) and non-line-of-sight (NLOS) corridor, a hallway, a cubicle room, and different adjacent-rooms communication links. The main limitation of the study was the limited distance range of LOS and NLOS environments because of the building structure design. Well-known single-frequency and multi-frequency directional and omnidirectional large-scale path loss models such as close-in free space reference (CI), floating intercept (FI) and alpha-beta-gamma (ABG) models and modified model are presented in this thesis. The modified model has a correction factor for different environments and it provides physically-based and efficient estimated path loss data points for the reference distance. Directional path loss model was done in co-polarized and cross-polarized antenna orientations, while omnidirectional path loss model was done in co-polarized antenna orientation only. The ICS Telecom simulation results show very high compatibility when compared with measurement campaign results. Also, it is found that the CI model is simpler, more convenient and more accurate for path loss prediction comparing with FI and ABG models. Also, the results show that the modified large-scale path loss model has the smallest path loss exponent (PLE), n and standard deviation, s values compared to the CI model. The results suggest that the modified path loss model can provide a sound estimation of path loss prediction and act as a reference analysis for developing mm-wave for wireless communication planning in indoor environments.
Microstrip patch beamforming linear antenna array with complementary split ring resonator for fifth generation applications
(Universiti Teknologi Malaysia, 2019) Selvaraju, Raghuraman
The next generation cellular standard which is called fifth generation (5G) requires high gain beamforming antenna array to provide high speed and secured communication. Therefore, the proposed research work investigates the design and development of a four-element linear microstrip patch array operating at 25 GHz for 5G beamforming application. To investigate the radiation characteristics of the proposed array, five beamforming radiation patterns (main beam at 0', +15' and +20') have been considered. The mutual coupling between array elements raise the challenge of designing the antenna array system. The coupling alters the array element input impedance and distorts the overall radiation performance. Hence, a simple complementary split ring resonator (CSRR) structure has been developed to alleviate the coupling problem. The modeled configuration is numerically analyzed, verified and implemented between the array elements. The existence of the CSRR configuration in antenna array, controls the unnecessary surface current flow between the array elements, thus the mutual coupling between array elements has been significantly reduced from -23 dB to -55 dB. The effect of coupling on the array radiation patterns has been studied in the presence and absence of CSRRs. Most importantly, the effectiveness of CSRR has been studied by steering the main beam as well as the nulls in different angles. By implementing the CSRR elements in array antenna, the distorted array patterns have been recovered and are presented. The proposed CSRR implemented in antenna array have the advantage of easy and low cost fabrication and it offers excellent coupling suppression without changing the antenna profile. Moreover, to the best of the authors knowledge, it was observed for the first time that the CSRR worked effciently in reducing the effect of mutual coupling when the beam was steered off from broadside direction from -20' to +20'. The simulation tools such as MATLAB and Ansys HFSS have been used for array weights calculation and antenna design respectively. Finally, the fabricated prototype has been experimentally verified, and it shows that the analytical and computed results agree well with the measured results.
Multibeam dielectric lens antenna for 5g mobile base station
(Universiti Teknologi Malaysia, 2022) Ansarudin, Farizah
The introduction of fifth-generation (5G) mobile communication technology has new features such as millimetre wave operation, small cell size and multibeam base station antenna to meet massive multiple-input multiple-output (MIMO) requirements. The introduction of fifth-generation (5G) mobile communication technology has new features such as millimetre wave operation, small cell size and multibeam base station antenna to meet massive multiple-input multiple-output (MIMO) requirements. At millimetre wave, the base station antenna size is expected to be less than 30 cm, and aperture antennas such as the reflector and the dielectric lens antenna can be among the alternatives to replace the present array antenna. Based on previous works, the dielectric lens antenna was designed to produce excellent multibeam radiation patterns as compared to the reflector antenna. Many lens antennas have been reported for various applications such as airborne radar and vehicle’s collision avoidance system. For base station application, the lens antennas with small thickness and curvature are required for light weight and ease of installation. The main objective of this research is to propose a new lens design method for thin and small curvature antenna and ensure its multibeam characteristics. By developing the geometrical optics algorithm for lens shaping method in MATLAB software, the conventional Aperture Distribution Condition (ADC) and the Abbe’s Sine Condition (ASC) are designed to ensure the accuracy of the developed algorithm. In order to achieve the thin lens and small curvature structure, a newly proposed design method, namely Straight-Line Condition (SLC) lens at designed frequency of 28 GHz and material with dielectric constant, εr of 4 was developed. At the lens size of 10 cm antenna with ratio focal length-to-diameter, F/D=1, the SLC lens structure provides thickness of 1.38 cm as compared to ADC and ASC with thickness of 1.7 cm and 1.48 cm, respectively. Multibeam radiation patterns of ADC, ASC and SLC were compared by using electromagnetic simulator FEKO. Good multibeam radiation patterns for SLC is ensured for scanning beam angle from 0° to 42.6°. To determine the optimum feed positions for multibeam performances, the focal region ray tracing was conducted in receiving mode by the Ray Launching-Geometrical Optics (RL-GO) solver of FEKO simulator. New feed positions locus for SLC was obtained and compared to ADC and ASC. For the practical application to install base station pole, the cylindrical structure of SLC lens antenna was designed at the F/D ratio of 0.6 and polycarbonate material with dielectric constant, εr of 2.9 was selected. The practical size of cylindrical height of lens antenna is 20 cm and the cylinder diameter is 29 cm with thickness of about 5.13 cm. New feed position locus for SLC cylindrical structure was obtained at F/D ratio of 0.6. From the near field distribution, phase constant and adequate amplitude distribution on the aperture plane is ensured. Fan beam radiation pattern was produced for the cylindrical lens. In the vertical plane, multiple beams radiation pattern was achieved. The beamwidth of fan beam is 45° and vertical beam is 3.28° with maximum antenna gain of 22.98 dBi. Good multibeam radiation patterns are obtained for wide scanning beam ranging from 0° to 47.1° in the vertical plane. Gain reduction is 6.56 dBi. As a result, the new proposed of cylindrical SLC dielectric lens antenna is suitable for the use of 5G multibeam base station application.
Non-orthogonal multiple access for cellular-connected unmanned aerial vehicles
(Universiti Teknologi Malaysia, 2022) New, Wee Kiat
Cellular-connected unmanned aerial vehicles (UAVs) have been introduced for 5th Generation (5G) and beyond cellular networks to enable various UAVs’ operations which require real-time and ubiquitous connectivity. Existing solutions are relying on orthogonal multiple access (OMA) to support existing terrestrial users (TUs) and UAVs as new aerial users (AUs). However, OMA is unable to provide an efficient network performance because each orthogonal resource block can only be utilised by a single user. To address this limitation, non-orthogonal multiple access (NOMA) can be employed. NOMA enables AUs and TUs to share the same orthogonal resource block. By leveraging their downlink asymmetry, NOMA could efficiently serve the AUs and TUs. Nevertheless, concurrently serving the AUs and TUs in cellular networks introduces new challenges. Specifically, reverse successive interference cancellation (SIC) policy and inappropriate NOMA power allocation might occur if the AUs are moving in three dimensional space and perfect channel state information (CSI) is unavailable. These issues will result in spectral inefficiency and unreliable communications. Due to high altitude, AUs also suffer strong inter-cell interference (ICI) that causes the pairing of AUs and TUs in NOMAto be inefficient. Therefore, this thesis investigates the performance of NOMA which concurrently serves a mobile AU and a TU in the absence of perfect CSI. Results show that pairing a mobile AU and a TU is more beneficial than pairing TUs only. Furthermore, NOMA provides up to 99% rate of improvement and lower outage probability as compared to OMA. Performance analysis for AUs and TUs in multi-cell networks is also carried out by using stochastic geometry. The analysis highlights the effects of different network parameters and reveals that the network performance can be affected by user association, receiving antenna configuration and ICI mitigation technique. This thesis proposes and provides an important insight about an efficient combination of user association, transmitting and receiving strategies known as aerial-terrestrial network NOMA. The proposed scheme outperforms existing schemes up to 91% in terms of sum-rate and its analytical outage probability can be as low as the order of 10-17. This thesis concludes that NOMA can efficiently serve the AUs and TUs in downlink cellular networks.

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