Hong Yin Lam

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.

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.

Preliminary investigation of rain cells in equatorial Malaysia for propagation applications

This work investigates the physical structure and geometrical features of rain cells based on two years of meteorological observations collected by a radar located at Kluang, Johor, Malaysia. Raw radar data are duly processed and rain cells are identified to carry out a detailed investigation on some features of the rain cells such as the mean rain rate, the equivalent minor and major axis length and the orientation. Preliminary results indicate that the majority of the rain cells are characterized by an equivalent diameter lying between 1 to 6 km (threshold 5 mm/h), with the mean minor and major axis lengths being approximately equal to 0.9 and 1.5 km, respectively. Furthermore, the rain cells orientation distribution is almost uniform, which is in accordance with the results obtained from the data collected in temperate regions. Further work is necessary to provide radio engineers with useful information for the design of wireless communication system in this particular area (heavy rain region).

1-Minute Integrated Rain Rate Statistics Estimated From Tropical Rainfall Measuring Mission Data

This letter presents a new model for the prediction of the 1-min integrated complementary cumulative distribution function (CCDF) of the rain rate, <i>P</i>(<i>R</i>)₁, valid for tropical and equatorial regions (specifically, latitudes ranging from 35^°S to 35^°N). The proposed model inherits its analytical formulation from the method currently recommended by the International Telecommunication Union - Radiocommunication Sector (ITU-R) for global <i>P</i>(<i>R</i>)₁ prediction (Annex 1 of recommendation P.837-6), but it relies on Tropical Rainfall Measuring Mission (TRMM) data, in place of the ERA40 database, for the extraction of the required local meteorological inputs. With respect to the ITU-R model, the proposed model requires a lower number of inputs (two instead of three) and, in addition, it shows a better <i>P</i>(<i>R</i>)₁ prediction performance when tested against the experimental <i>P</i>(<i>R</i>)₁ curves (tropical/equatorial sites) included in the global DBSG3 database of ITU-R.

Statistical and Physical Descriptions of Raindrop Size Distributions in Equatorial Malaysia from Disdrometer Observations

This work investigates the physical characteristics of raindrop size distribution (DSD) in an equatorial heavy rain region based on three years of disdrometer observations carried out at Universiti Teknologi Malaysia’s (UTM’s) campus in Kuala Lumpur, Malaysia. The natural characteristics of DSD are deduced, and the statistical results are found to be in accordance with the findings obtained from others disdrometer measurements. Moreover, the parameters of the Gamma distribution and the normalized Gamma model are also derived by means of method of moment (MoM) and maximum likelihood estimation (MLE). Their performances are subsequently validated using the rain rate estimation accuracy: the normalized Gamma model with the MLE-generated shape parameter µ was found to provide better accuracy in terms of long-term rainfall rate statistics, which reflects the peculiarities of the local climatology in this heavy rain region. These results not only offer a better understanding of the microphysical nature of precipitation in this heavy rain region but also provide essential information that may be useful for the scientific community regarding remote sensing and radio propagation.

Application of the SC EXCELL model for rain attenuation prediction in tropical and equatorial regions

The aim of this paper is to provide additional information about the performance of the SC EXCELL model, specifically when applied to the prediction of rain attenuation in equatorial and tropical regions. The model generates a long-term rain attenuation Cumulative Distribution Functions (CDF) that separately accounts for stratiform and convective precipitation. The model assessment in estimating attenuation CDFs due to rain are carried out against experimental data for three particular South-East Asian regions, namely Kuala Lumpur, Singapore and Thailand. The overestimation outcomes of the model suggest that to correctly predict rain attenuation on satellite communication links, the concurrency between rain attenuation and rain intensity measurement should be taken into account.

Estimation of Millimeter Wave Attenuation Due to Rain Using 2D Video Distrometer Data in Malaysia

Hilbert Vibration Decomposition (HVD) is introduced to the voltage flicker analysis. When voltage flicker accompanies with high order harmonics, the instantaneous frequency of its analytic signal in principle consists of two different parts, power frequency and a rapidly varying asymmetrical oscillating part. The important property of the instantaneous frequency offers a direct way to estimate the power frequency using a low-pass filter and remove the high order harmonics without pre-treatment procedures. Corresponding voltage flicker envelope is estimated using synchronous detection. The HVD method does not involves basic functions that the wavelet transform method needs. It can also adaptively estimate the frequency and amplitude of every modulation frequency component. Simulation results prove that the proposed method could accurately detect voltage flicker with high order harmonics. It has higher calculation efficiency and detection precision than wavelet transform method. Experimental results show that the new algorithm is feasible and efficient.

The relationship between ground wind direction and seasonal variation of rain attenuation at Ku band satellite broadcasting services

This study is aimed to investigate the relationship between ground wind direction and the seasonal variation of rain attenuation based on one year of weather station data recorded in Universiti Teknologi Malaysia (UTM), Johor, Malaysia. Preliminary analysis of wind direction based on monsoon seasonal and their impact on rain field advection are carried out to clarify the characteristics of rain attenuation in monsoon season. It is found that rain attenuation is not only affected by the monsoon seasonal variation but it also depends on rain field advection which can be preliminary identified from the wind direction. Such information is useful for the system operators to apply appropriate site diversity techniques during heavy rain events to reduce the system outage in this particular equatorial region.