Volume 25, Issue 1, May 2014

Design and Realisation of Planar Star Micro-strip Diplexer for Wireless Applications [Full Text]

A. Zakriti, N. Amar Touhami, and M. Lamsalli

Abstract—In this paper, a high performance diplexer is designed and fabricated for wireless applications. The diplexer mainly comprises two dual-mode Star Bandpass Filters (BPFs), operated at 1.8GHz and 2.3GHz, respectively. Several transmission zeros are located at the passband edges, thus improving the passband selectivity. Due to the impedance matching between two BPFs, a high isolation greater than 30dB between two channels is obtained. 

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Rainfall Variability and Impact on Communication Infrastructure in Nigeria [Full Text]

O.O. Obiyemi, T.S. Ibiyemi, and S.O. Akande

Abstract— Communication satellites remain a prominent backhaul communication infrastructure. It also provides a wide coverage across the rural, sub-urban and urban areas. However, rainfall invokes a number impairments on satellite communication links, particularly for operations within the microwave and millimeter wave bands. The resultant effect of its variability has been evaluated on the viability of maintaining availability objectives, especially over long periods within which satellites might be due for replacement and re-planning. 1-min rainfall rates has been deduced from 30 years daily rainfall data, sourced from the Nigerian Meteorological Agency (NIMET) for 19 stations across Nigeria. The equivalent decadal point rainfall rates (mm/hr) were estimated from the mean rainfall accumulations over three decades using the procedure proposed by Chebil, while the rain attenuation (dB) was subsequently predicted using the ITU-R P.618-10 model for direct to home (DTH) reception at 12 GHz. Results indicate that the slight variation observed on the point rain rate statistics only accounts for little variation in the rain induced attenuation over the link, through the years and across the decades. Hence the variation is negligible at higher percentages of the time (typically between 0.1 and 1% of the time) as is the case across the climatic regions ranging from Arid to the Coastal areas. Results indicate that effects at 99 and 99.9% availability is negligible across the selected sites. It also reveals a slight variation at 99.99% of the time, which indicates a variation of about 1 dB at Calabar (Forest belt) and Ibadan (Wooded Savannah), while variation remains negligible at Maiduguri (Sahel), Jos (Sudan-Sahel) and Ilorin (Guinea Sudan) over the decades. The variation of about 1.4 dB was recorded at Calabar, 0.8 dB at Maiduguri, 1.3 dB at Ibadan, while variation remain negligible at 99.999% in Jos and Ilorin across the decades. Although it is apparent that the variation observed in rainfall intensity produces corresponding variation in the rain attenuation across the decades and over the years, this has no significant effect on communication link design, particularly over any particular location and over the years. Hence due to the short lifespan of satellite vehicles in the geostationary orbit, availability objectives can be maintained, provided no technical parameter is altered when satellites are being replaced. 

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DiffStart: An Algorithm to Improve the Start-up Behaviour of TCP for High Bandwidth-delay Networks [Full Text]

Aniruddha A. Agharkar, Gregory MacDonald, and Pramode K. Verma

Abstract—In this paper, we propose a novel algorithm “DiffStart” to improve the start-up behaviour of TCP for high bandwidth- delay networks. The standard slow start algorithm is not suitable to operate over high bandwidth-delay networks because of the aggressive doubling of the congestion window without an efficient congestion detection mechanism. Consequently, the connection undergoes a timeout that leads to a slow ramping-up to full network capacity, which adversely affects the overall performance of TCP. The proposed DiffStart algorithm anticipates the onset of congestion in the network and proactively transitions the growth rate of the congestion window from exponential to linear. Based on the simulation results, we show that DiffStart in conjunction with TCP Reno overcomes the limitations of the standard slow start algorithm, and provides an improvement over other TCP protocols namely, TCP Compound, and TCP CUBIC in the case of high bandwidth-delay networks. 

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Design of STBC- Multiband Ultra-Wideband (UWB) System by Using DWT with Three Transmit Antennas [Full Text]

Morad Abeed Helo

Abstract - This paper provides the detail about the two main applications of Multiband ultra-wideband systems MB-UWB which are fixed MB- UWB and Mobile MB-UWB. Fixed MB-UWB 802.15a delivers point to multipoint broadband wireless access to our home and offices. Whereas Mobile MB-UWB gives full mobility of cellular networks at higher broadband speeds than other networks like Wi-Fi. Both applications of MB- UWB are designed in a proper network planning which is helpful to offer better throughput broadband wireless connectivity at a much lower cost. The design of the STBC-MB-UWB systems based on DWT, simulations results, and evaluation tests of these proposed systems. The Bit Error Rate (BERs) and the operating range of these systems are obtained using frequency domain baseband simulations as well as more realistic full-system simulations, and are compared to other system types designed using FFT and Discrete Wavelets transform DWT. The results of both systems in the four types of channels will be examined and compared. The effects of several parameters of wireless channels on the systems will be investigated. In the STBC-MB-UWB system the two types of the transform FFT and DWT (Wavelet Transform) are considered. The new proposed structures for the STBC-MB-UWB system based on wavelet transform (DWT) will be studied. These STBC- MB-UWB systems were modeled using MATLAB V7.10 to allow various parameters of the system to be varied and tested. The aim of doing that simulation is to measure the performance of STBC-MB-UWB under different channel conditions.