Siti Zainun Ali’s scientific contributions

This study is aimed at evaluating the effect of Global Positioning System (GPS) antenna orientation for three Garmin GPS receivers that use built-in quad helix antennas; GPSmap 60CSx, GPSmap 62Cs and Oregon 550. The study is conducted using GPS simulation, which allows for the tests to be held with various repeatable conditions, as defined by the authors. Readings are taken for GPS antenna orientations of 0 to 345°, at increments of 15°. From the results obtained, it is found that there is degradation of accuracy for orientations of 75 to 120° and 240 to 285°. For the remaining orientations, the accuracy remains constant. This indicates that the quad helix antennas are operating in endfire and backfire modes simultaneously. While this type of design has smaller antenna gain than quad helix antennas that use only endfire or backfire modes, it allows for a more isotropic antenna performance. This study will be extended to evaluate the performance of antennas of a wider range of GPS receivers.

This study is aimed at evaluating the trade-off between Global Positioning System (GPS) accuracy and power saving from reduction of number of channels. The study is conducted for number of GPS receiver channels of 4 to 12 for two scenarios: (1) normal scenario with full range of available GPS satellites and (2) obstruction scenario with GPS satellite elevation cutoff of 20°. It is observed that increase of power saving from reducing the number of channels causes increase of probable error values. This is due to increasing position dilution of precision (PDOP) of the reducing number of GPS satellites tracked. However, reduction of number of channels to match the number of available GPS satellites does not cause degradation of accuracy, as there is no reduction in number of trackable GPS satellites. For the obstruction scenario, with significantly fewer available GPS satellites due to the GPS satellite elevation cutoff, significant power saving can be achieved without degradation of accuracy. An effective power saving system would require the management of minimum number of channels required to achieve the user’s minimum required accuracy.

In this study, Global Positioning System (GPS) simulation is employed to evaluate the accuracy of GPS speed measurements. The two methods of GPS speed measurement, trackpoints and Doppler shift, are compared for two conditions of tests: 1) Normal scenario with the full range of available GPS satellites; 2) Obstruction scenario with only six GPS satellites available. For the trackpoints method, significant errors are observed, due to positioning errors caused by the GPS receiver's user equivalent ranging error (UERE). The errors increased with increasing speed due to increasing length of zigzag lines connecting the trackpoints, which is caused by the receiver's positioning errors. The Doppler shift method generated much smaller errors for the normal scenario (maximum of 0.238 km/h for speeds of up to 1,800 km/h), as it is insensitive to the UERE of GPS receivers. Decrease of available GPS satellites in the obstruction scenario also caused increase of error for the trackpoints method due to increased position dilution of precision (PDOP) and thus, increased UERE. For the Doppler shift method, the increase of error was much smaller (maximum of 0.254 km/h for speeds of up to 1,800 km/h), indicating that change in GPS satellite geometry has limited effect on this method.

This study is aimed at evaluating the trade-off between Global Positioning System (GPS) accuracy and power saving from reduction of number of channels. The study is conducted for number of GPS receiver channels of 4 to 12 for two scenarios: 1) Normal scenario with full range of available GPS satellites; 2) Obstruction scenario with GPS satellite elevation cutoff of 20°. It is observed that increase of power saving from reducing the number of channels causes increase of probable error values, due to increasing position dilution of precision (PDOP) of the reducing number of GPS satellites tracked. However, reduction of number of channels to match the number of available GPS satellites does not cause degradation of accuracy, as there is no reduction in number of trackable GPS satellites. For the obstruction scenario, with significantly fewer available GPS satellites due to the GPS satellite elevation cutoff, significant power saving can be achieved without degradation of accuracy. An effective power saving system would require the management of minimum number of channels required to achieve the user's minimum required accuracy.

This study is aimed at addressing a mistake made in the authors' previous paper on Global Positioning System (GPS) static multipath simulation (Dinesh et al., 2013), whereby it was indicated that GPS performance is repeatable for every GPS satellite orbital pass of approximately 11 h, 58 min. GPS satellites only return to the original positions with respect to the earth at every two GPS satellite orbital passes of approximately 23 h, 56 min, and hence, GPS performance is only repeatable for that period. This study demonstrates the repeatability of GPS performance with respect to GPS satellite orbital passes. It is further extended to verify the findings in Dinesh et al. (2013) in regards to GPS performance in various static multipath conditions. Keywords: Global Positioning System (GPS) simulation; GPS satellite orbital passes; GPS performance repeatability; estimate probable error (EPE); multipath.

In a previous study, the determination of suitable RF detectors for detection of wireless spy devices was conducted via the measurement of two key parameters; operating bandwidth and power level threshold. However, this study was limited to RF detectors with maximum operating frequency of up to 3 GHz (based on provided speci cations). This paper is aimed at extending this study to RF detectors with speci ed maximum operating frequency of at least 6 GHz, which is considered as suf cient to cover standard wireless communications frequencies. Four RF detectors were considered for the study; Lanmda (model LM-DC 2), Skynet (model XB-68), Mini Gadgets (model CD-RFLD) and Comenzi (model RFS-DT1). Each of the evaluated RF detectors has a variable power level threshold. It was found that the Lanmda RF detector has the largest operating bandwidth (14 MHz -4.85 GHz), followed by the Comenzi (9 MHz -3.82 GHz) and Mini Gadgets (156 MHz -3.44 GHz) RF detectors, while the Skynet RF detector has the smallest operating bandwidth (0.3 MHz -2.91 GHz). It was observed that the evaluated RF detectors have varying power level threshold performances over frequency. The Comenzi RF detector generally has the lowest power level threshold performance over the tested frequencies. However, the Comenzi RF detector's signi cantly low power level thresholds could render it susceptible to false alarms, and make it dif cult to hone in on possible targets. The Lanmda RF detector's power level thresholds make it suitable for the user to sweep the suspected area using its lowest power level threshold, and then, hone in on the target using higher power level thresholds. Furthermore, its larger operating bandwidth allows it to detect a wider range of signal frequencies. It should be noted that while this operating bandwidth is suf cient to cover most commonly used wireless communications frequencies, it is unsuitable for detection of the increasingly popular 5 and 5.8 GHz communications frequencies.

On 28 June 2011, the Instrumentation & Electronics Technology Division (BTIE) conducted a test to compare the transmitted signals of two mobile phone jammers (MPJs) a portable MPJ (MPJ34) and a high powered MPJ (MPJ2000). Both MPJs are designed to operate in the bandwidths of Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM), Digital Cellular System (DCS) and Third Generation Mobile Telecommunications (3G). The test was conducted in BTIE's semi anechoic chamber in order to avoid unintended interference signals. It was observed that for all the tested bandwidths, the MPJ2000 jammer has signi cantly higher transmitted power levels as compared to the MPJ34 jammer. Hence, of the two jammers, the MPJ2000 jammer is able to conduct mobile phone jamming for signi cantly larger radiuses. It should be noted that in addition to transmitted power levels, other parameters can affect an MPJ's jamming radius, including proximity to base transceiver stations (BTSs), presence of buildings and landscape, and temperature and humidity.