Browsing by Author "Md Rafiqul Islam, Ph.D"

Fifth generation cellular technology (5G) forums in ASEAN countries has been proposed lower frequency bands for 5G applications at 4.5 – 5.5 GHz and also the fixed-satellite service (FSS) is using 3.3 – 3.8 GHz for C-band. In this project, a single band notched (SBN), a double band notched (DBN) and two variable band notched (VBN) antennas are designed, simulated, fabricated and tested to create notched bands for 5G lower band from 4.5 GHz to 5.5 GHz (1 GHz), C-band 3.3 GHz to 4.2 GHz, (0.9 GHz) and Wi-MAX 3.2 GHz to 3.8 GHz (0.6 GHz) applications in UWB spectrum. Two types of UWB antenna have been designed and proposed by using low cost substrate FR-4 with partial grounding on rectangular patch and tuning fork shaped patch antenna. A single band and dual band notched UWB antennas were designed for 5G lower band by using a slot at the top of the radiating patch and by adding an arc shape open loop (ASOL) on UWB antenna. Two variable band notched UWB antennas were also designed by introducing a semi-circular slot (SCS) on the upper part and by inserting ring shape slits (RSS) in ground plane of UWB respectively. Simulated return losses, patterns, radiation efficiencies, directivities and gains are correlation and compared with available similar antennas and found good agreement. The peak radiation efficiency of 90% and maximum gain of 8.0 dBi are achieved with as low as 28% efficiency and -2.0 dBi gain in rejection bands. All antennas are fabricated using FR-4 substrate and tested using Vector Network Analyzer (VNA). The voltage standing wave ratio (VSWR) and return loss of test results prove that all antennas have excellent performance in notched band and UWB band frequencies by showing good agreement with simulation results, except the measured return loss is slightly different from the simulated result in the notched bandwidth in dual band notched and poor performance from 6 GHz – 8 GHz of UWB in variable band notch antenna. Therefore, designed single notch, dual notch and variable notch ultra-wideband antennas are proposed as a good candidate for 5G lower bands, C-bands and Wi-MAX bands notched applications environment.

The demand for radio frequency spectrum is rapid since the most desirable frequency spectrum is congested; hence 5G and satellite communications are moving forward to the frequency band utilization above 10 GHz. Frequency higher than 10 GHz is subjected to impairment by rain. ITU-R has established rain attenuation prediction methods deduced from the measured rainfall rate with an integration time of 1-minute or less. However, recently, significant discrepancies in ITU-R prediction are found in the measurements of rain attenuation at mmWave bands for short-length propagation links. All researchers used rain intensity from 1- min integration time measurement, as not less than 1-minute data are unavailable. Therefore, this project aims to consider rain rate less than 1-minute integration time, investigate the effects of less than 1-minute integration time on rain rate distribution, and compare rain attenuation predictions using measured rain intensities with different integration times. A real-time rain gauge with a resolution of 10-secs integration time is installed in the International Islamic University Malaysia (IIUM) Gombak. A one-year measured rain rate data with integration times of 10-secs, 20-secs, 30-secs, 1- minute, and 2-minutes are utilized to analyze the effects of integration times on rain intensity distributions and rain attenuation predictions. From the analysis, it is found that at 0.01% probability, rain rates are 123 mm/hr and 191 mm/hr with 1-min and 10-secs integration times, respectively. At 0.1% and 0.001% probabilities, the differences increase to 80% and above. The rain attenuation measured at 26 GHz, 38 GHz, and 73 GHz terrestrial links with 300 m lengths and 12 GHz earth-to-satellite links in Malaysia are compared with those predicted by data from 5 integration times. Predicted attenuation with 10-secs is closer to measurement than 1-min integration time for all three terrestrial links and two satellite links. However, 30-sec integration time data was found close to the measurement for one satellite link. Hence mm-wave short paths in 5G, lower integration time-based rain rate measurement will provide more accurate prediction for path loss and high reliability in the tropical climate.

Internet of Things (IoT) is a pillar technology for the next coming industrial revolution by enabling connections between deployed small devices wherever and whenever. However, these devices are often constrained in processor, memory, and energy. Usually known as sensor nodes, these devices are connected with each other to form a network of different nodes. As a matter of fact, routing the data in such environment is a challenge because of constrained sources of power. Therefore, Routing Protocol for Low-Power and Lossy Network (RPL) was formed by Internet Engineering Task Force (IETF) to develop an adapted routing solution for such networks, made up of large number of constrained nodes with limited processing power, memory, and energy. However, the overhead exchanged, to facilitate the routing process and maintain connectivity, drains these battery-operated nodes. This research examines a solar energy harvesting module to power such constrained network devices and quantifies the effect of using harvested energy on prolonging the network lifetime when RPL routing protocol is used. Simulation is conducted in three different scales (25 nodes, 50 nodes, 100 nodes) using Contiki Cooja simulator sporting Zolertia Z1 motes. Furthermore, the harvested energy was fed from an experimental power trace. All battery levels were set to 1% of their total capacity for all nodes in the network to expedite the process of observing the energy harvesting effect. The performance evaluation results showed that the network with no-energy harvesting operated for time duration of 4:08:04 time units (e.g., hour:minute:second) with a dramatic decrease in connection between nodes in the network. However, the same network, when using the harvested energy to back up the battery operation, lasted for 6:40:01 in time units with improved connectivity, a total extended network lifetime of 2:31:97-time units. Furthermore, for the RPL routing metrics, OF0 outperformed ETX in term of throughput, packet delivery ratio, energy consumption, and network connectivity.