Jafri Din

Investigation of Rain Attenuation in Equatorial Kuala Lumpur

This letter investigates rain attenuation in Kuala Lumpur, Malaysia, by exploiting local drop size distribution (DSD) measurements. Coefficients for the well-established power-law model relating rain rate and specific attenuation are derived for frequencies in the Ku-, Ka-, and Q/V-bands based on three years of disdrometer data. We analyze the diurnal variation of rainfall rate for four time intervals and, moreover, we present statistics of rain attenuation for slant-path Earth-space links estimated by means of a new model (Stratiform-Convective SST) that combines the advantages of the Dual-Layer Synthetic Storm Technique (SST) and the SC EXCELL model. The predicted statistics are in good agreement with those obtained from beacon measurements (MEASAT-1 satellite at 12 GHz). Finally, the diurnal variation of the slant-path rain attenuation is presented to provide system operators and radio communication engineers with useful information on the quality of service (QoS) that can be achieved during a typical day on an Earth-space link.

Analysis of raindrop size distribution characteristics in Malaysia for rain attenuation prediction

The assessment of the variability of rainfall characteristics in the equatorial regions is a key problem in estimating adequate fade margin due to rain attenuation in satellite communication systems. Based on one year of disdrometer data that have been collected in Kuala Lumpur, Malaysia, this paper investigates the general characteristics of the raindrop size distribution (DSD) and the dependence of the rain attenuation on the DSD. Its diurnal variation and the role of critical diameter values on the estimation of the specific attenuation are also discussed. Preliminary results suggest that satellite links operating in the afternoon and early evening hours should be provided with an extra fade margin to compensate for rain attenuation impairments.

Low noise amplifier circuit design for 5 GHz to 6 GHz

The development of wireless portable electronics is moving towards smaller and lighter devices. Although low noise amplifier (LNA) performance is extremely good nowadays, the design engineer still has to make some complex system trades. Many LNA are large, heavy and consume a lot of power. The design of an LNA in radio frequency (RF) circuits requires the trade-off of many important characteristics, such as gain, noise figure (NF), stability, power consumption and complexity. This situation forces designers to make choices in the design of RF circuits. The designed simulation process is done using the Advance Design System (ADS), while FR4 strip board is used for fabrication purposes. A single stage LNA has successfully designed with 7.78 dB forward gain and 1.53 dB noise figure; it is stable along the UNII frequency band.

Stratiform and convective rain discrimination for equatorial region

This paper presents the application of the Lowered EXCELL model to discriminate between stratiform and convective precipitation in Kuala Lumpur, Malaysia, which is located in the equatorial region. The model generates two longterm cumulative distribution functions (CDFs) that separately account for the two different types of rain, based on the input rainfall statistics reflecting the local climatology. The aim of this paper is to present the applicability of the model in equatorial climates. The model performance in estimating stratiform and convective CDFs is carried out using 3 years of time series of rainfall intensity data collected in Kuala Lumpur by a disdrometer. The stratiform and convective rain rate CDFs are finally shown to be well predicted by the Lowered EXCELL model. Hence, the outcome of this paper seems encouraging for further application of the model to improve the prediction of rain attenuation for satellite communication, especially in equatorial region.

Analysis of Fade Dynamic at Ku-Band in Malaysia

This work investigates fade dynamics of satellite communication systems in equatorial heavy rain region based on a one year of Ku-band propagation measurement campaign carried out in Universiti Teknologi Malaysia (UTM), Johor, Malaysia. First order statistics of rain attenuation are deduced and the results are found to be in good agreement with those obtained from other beacon measurements gathered within the same area (Kuala Lumpur). Moreover, the fade duration and slope statistics of the satellite signal variations are also carefully derived and subsequently compared with the ITU-R recommendation model. Such information is useful for the system operator and radio communication engineer for the design of appropriate fade mitigation techniques as well as the quality of service that could be offered to the user (according to the time interval for a typical day). Further evaluation on the performances of several ITU-R models in the heavy rain region are needed based on the measurement database available of this climatic region.

Rain fade characteristics analyses for V-band link in tropical region

A decade ago, the operating frequencies of most available satellites in the tropics were C band, S-band and Ku-band. The V-band satellite links were initially confined mainly to temperate regions. Recently however, this new service has gradually been introduced worldwide including the tropical regions. In the future, new satellites in the tropical and equatorial will also have no alternative but to operate at V-band and higher frequencies due to spectrum limitations. Therefore, it is very critical to be able to predict accurately the likely impairment to be encountered on a given link in order to plan the services economically. The predicted value of signal loss and fading are used to determine the design parameters. This paper aimed to discuss the seasonal, diurnal and possible fade mitigation technique that can be used and the challenges to be able to use V-band frequency in tropical region in the future.

Cross Layer Design of Wireless LAN for Telemedicine Application

Telemedicine system requires an acceptable network quality of service and cost. IEEE 802.11 wireless LAN technology has been developed to provide scalable and low cost network. For telemedicine applications however, the technology does not fulfill the quality of service requirement yet. In order to overcome this problem, a new cross layer design of wireless LAN is proposed.The design is based on IEEE 802.11g standard with modification in datalink and physical layer. This has been implemented in NS2 simulation environment. The simulation has been performed to deliver the video data for telemedicine application. Simulation result shows that the new cross layer design has better network quality of service for PSNR (Peak Signal Noise Ratio) and delay values than the conventional wireless LAN. Thus, the new design has a potential to be used in telemedicine system.

Rainfall rate from meteorological radar data for microwave applications in Malaysia

This paper present the rainfall rate obtained from the analysis of a meteorological radar data in Malaysia. Rainfall rate is an important parameter for a microwave link because it enables the attenuation due to rain to be determined. An important parameter in rain attenuation studies is the rain rate for 0.01% of the time or R/sub 0.01/. Design and system engineers use this value to construct communications system such that the link is available for 99.99% of the time. This result is obtained by utilizing the radar data from the Malaysian Meteorological Department. Knowing the rainfall rate, rain attenuation can be calculated. This information is useful for microwave link applications.

Determination of rain cell size distribution for microwave link design in Malaysia

In designing or planning for a microwave link, attenuation due to rain is often a major obstacle to overcome. Sometimes, a mitigation technique such as space diversity is also considered. However, a rain event occurring in an area is not constant. Rain does not distribute evenly in a region experiencing precipitation. This is especially true in tropical regions as rain has been found to be more convective in nature rather than widespread. Tropical regions also suffer heavier rainfall rates as compared to temperate regions. Important information are rain cell size and rain distribution inside a cell. Results from this study confirmed that the rain cell in Malaysia is highly convective and a rain cell with a center rainfall rate of 120 mm/hr has a diameter of about 1.2-1.5 km.

A modified rain attenuation prediction model for tropical V-band satellite earth link

Radio wave propagation plays a very important part in the design and eventually dictates performance of space communication systems. Over time, the requirements of satellite communication have grown extensively where higher capacity communications systems are needed. Escalating demands of microwave and millimetre wave communications are causing frequency spectrum congestion. Hence, existing and future satellite system operators are planning to employ frequency bands well above 10 GHz. The challenge in operating at such high frequencies for communication purposes is that there exists stronger electromagnetic interaction between the radio signals and atmospheric hydrometeors. Such instances will degrade the performance of such high frequency satellite communication systems. The development of a revised model for a better-improved rain fade prediction of signal propagations in tropical region is considered very important. Researchers and engineers can employ the model to accurately plan the future high frequencies satellite services.