Abstract :  Indoor localization systems are getting a significant attention because its ease of development and cost effective but with recent advancement in context and location aware technologies, the solutions for indoor tracking and localization had become more critical and difficult. In indoor environment, the GPS signal cannot be received,and the positioning service requires the aid of indoor wireless technologies,such as wireless LAN, Bluetooth,Infrared and RFID. Receive Signal Strength (RSS) paid more attention in indoor positioning system based from wireless access equipment in recent years. This system is very useful in many applications such as healthcare, loyalty management system, automatic parking allotment system, tracking service for older people or customer inside living communities, mobile robot localization, logistics systems etc. While outdoor environment and cellular network work well and are widespread used for navigation. However, there is a problem with signal propagation from satellites or cell site. They cannot be used effectively inside complex building areas or even in an urban environment. In general, the widely used method for indoor environment positioning based on Wi-Fi consists with two main categories, which are trilateration technique and location fingerprint technique (LF). It is already known that the explicit positioning performance of trilateration technique is more sensitive to noise effect than LF technique. Nevertheless, the accuracy of LF technique depends on training data set and it does not work well when environment changes. In this article, we propose an adaptive smoother based location and tracking algorithm for indoor positioning using RSS algorithm and directional antenna which able to improve the accuracy, stability and robustness.

Abstract :  The increasing demand for mobile communication services in Namibia has seen an increase in the installation of mobile base transceiver stations (MBS’s) in and around residential areas, schools and hospitals. Mobile service providers usually increase the number of MBS in an area for better signal reception, thus catering for the high demand. This situation has caused a growing health concern from the general public, especially those living in close proximity to the base stations. In Namibia, MBS radiation exposure levels are not readily available to the general public to promote consumer safety information. In this study, an EMF-839 field meter equipped with a 3-axis high frequency probe was used to measure EMF levels around the GSM 900 MHz mobile base stations located at the vicinity of the Faculty of Engineering and IT. Measurements were taken for a period of over 2 months at predefined locations in the faculty of Engineering and IT vicinity. The measured values are time averaged over 6 minute samples, to obtain the average electric field strength value for each point of interest. An Augmented Dickey Fuller (ADF) statistical test is used to determine the stability of the measured time series at each measurement point. The results showed that all the data time series were stationary. The measurement results are analysed on a daily, weekly and monthly basis. The highest estimated average value was found to be 1.86 V/m, which is well below the 41.25V/m at 900MHz exposure limit set by the ICNIRP for the general public.

Abstract :  Users in a wireless system are suffering from unequal distribution of signals caused by propagation loss and interference. Multi-hop systems are considered to be a costeffective way to overcome such problems and improve the quality of service in a wireless system. The main limitations in using multi-hop systems are the number of relays and their location over the studied area. As a result, in this paper we provide a method to solve this problem and find the optimal number of relays and their optimal placement in the studied area based on the evaluated outage probability. We evaluate the probability density function (PDF) for the signal-to-noise ratio (SNR) in a circular cell with uniformly distributed users around a BS located at the center of the cell. Then, we assess PDF for outage probability, based on the evaluated SNR. Moreover, we find the minimum number of relays and their placement over the studied area, to achieve a desirable performance in the wireless system. Finally, simulations are performed based on Long-Term Evolution (LTE) parameters to validate the derived analytical solution.

Abstract :  The IEEE 802.15.4 standard defines a new wireless personal area network (WPAN) used for applications of wireless monitoring and control. In this article, a study of the backoff exponent (BE) management in CSMA/CA in the MAC layer is conducted. Where BE determines the number of backoff periods the device must wait before access to the channel. In this paper, we aim to prolong maximum possible the life time of sensor nodes by optimizing the energy consumption. We propose an algorithm in which we can adjust dynamically the MAC parameters based on the queue length of each sensor node. We have then defined a parameter to obtain instantaneously information about the queue size. We use network simulator ns-2 to implement the network. The performance metrics of the comparison are energy consumption, average delay and throughput.

Abstract :  With the growing development of digital communication systems, it has became necessary to ensure the quality of service for real-time transmission of video applications and give users more powerful and efficient services by using better techniques. Digital modulation techniques have various performance characteristics power efficiency, Bandwidth efficiency, Error rate, cost etc. The M-ary Phase Shift Keying and M-ary Quadrature Amplitude Modulation are used in wireless communication to check test the performance of fading channels. In this paper, evaluation of BER is performed under AWGN, Rayleigh and Rician fading channels. Among these channels, Rician has showing better performances a compared to AWGN and Rayleigh channels.

Abstract :  This paper reveals a patch antenna with a large bandwidth of 34% and a high gain of 8 dBi in the frequency range from 10.1 to 14.2 GHz. The patch antenna is a four layer design comprising of a superstrate dielectric layer of ?r 10.2 on top of a metal layer with six small simply designed parasitic H-shaped elements, which are optimized using CST Microwave Studio. The six Hshaped parasitic elements are centrally located on the metal layer. On the same layer, the antenna is fed through a coupled feedline so as to reduce mutual coupling and the antenna is thus a perfect candidate to preserve its wideband feature in an antenna array. Right underneath the metal layer is the substrate dielectric layer of ?r 2.2 with two strategically placed slots underneath the metal layer in order to decrease the back radiation of the Hshaped parasitic elements. The whole design is terminated with a final metal layer to act as a conductor backed antenna to push most radiation out. The final antenna occupies a volume of 25 mm x 25 mm x 2.56 mm. The design has a high gain of 8 dBi in both the ? = 0° plane and the ? = 90° plane with a large beamwidth of 77° in the ? = 0° plane and 83° in the ? = 90° plane in the farfield.

Abstract :  This paper reveals a novel stacked slotted bow-tie antenna element with a large bandwidth resonating at 11.7 GHz for satellite TV broadcasts. The simple, cost effective antenna is built on common dielectrics and is a layered version of the popular patch antenna. It is shaped in a bow-tie and converted into the slotted version in order to increase the antenna radiating surface. The dual polarized antenna element offers a large directivity of 7.2 dBi in the farfield direction. It is terminated with a coplanar waveguide feedline which is ideal to preserve its large bandwidth in an antenna array configuration. In order to appreciate its results and its design simplicity, a comparison of its S-parameters, radiation patterns, E-fields and H-fields are made with five other popular elements at the center frequency of 11.7 GHz.

Abstract :  An ultra-broadband bow-tie with a VSWR < 2 from 5 to 60 GHz is revealed. The bow-tie antenna shows frequency independence properties and resonates periodically at multiples of its resonance frequency of 7.7 GHz with the return loss always less than -10 dB. The antenna is linearly polarized and has a maximum directivity of 6 dBi in both the elevation and azimuth planes in the farfield. The antenna is a symmetrical design with straight ends and a flare angle of 90°. It is a simple metal layer on top of a substrate layer which is fed on the metal layer right at the center with closely spaced coplanar striplines. The flare angle and the straight-end of the bow-tie antenna are varied and the 90° straight-end bow-tie antenna is compared with three other bow-tie antennas with flare angle of 60° and round-ends. All four bow-tie antennas have a low VSWR. The E-fields, H-fields and impedance plots of the ultra-broadband bow-tie antenna are shown. The impedance plot is in fact the impedance of frequency independent antennas of 189 or 60 across all frequencies.