Characterization of bright-band in a tropical station for satellite communications

Tropical regions experience signal degradations due to hydrometeors in addition to paucity of database for slant path rain propagation estimations. The melting layer is the region where rain starts to occur; lying just below the 0oC isotherm height. Frozen hydrometeors exhibit peculiar characteristics in the form of increased radar reflectivity as they fall from the sky, morphing from solid to liquid; and manifesting itself as the popular bright-band signature. Knowledge of the formation and recognition of the bright-band is necessary to characterize the melting layer. Adequate information on diurnal, seasonal and annual variation effects on rain height can give valuable information for satellite equipment design and planning. Rain height is highly correlated with signal attenuation and co-channel interference resulting from scattering. This work involves the characterization of bright-band data for UTM Johor Bahru campus, Malaysia. Thirteen months (1 November, 2006 to 30 November, 2007) 3D RAPIC ground radar data at 500 m range bins resolution were sourced from MMS. Additionally, twenty-two months (January 2011 to May 2013) TMPA-RT radar data at 50 x 50 latitude-longitude horizontal resolution were obtained to complement the ground radar data. The reflectivity from these data was analysed to characterize the melting layer. Malaysia experiences two monsoon events yearly: The North-East monsoon and the South-West monsoon. Results from this work suggest that freezing and rain heights are highest in the months of November 2006, March and September 2007; which coincides with the end of the two monsoons. Equally, these parameters are observed to be lowest in February, April, July and October; thus suggesting seasonal and annual variability. The bright-band is thicker in the day, while freezing and rain heights are higher at night than in the day time, suggesting diurnal dependence. However, data for a longer period of time is needed to consolidate these findings. The results show good degree of agreement when compared with similar previous findings from Malaysia. But, ITU-R.P. 618 model largely underestimated the total measured attenuation. Thus, there is a need to include the melting layer effect in satellite communication attenuation prediction in the tropics for improved Quality of Service

Rain Attenuation Modelling and Mitigation in The Tropics: Brief Review

This paper is a brief review of Rain AttenuationModelling and Mitigation in the Tropics. The fast depleting availability of the lower frequency bands like the Ku-band as a result of congestion by commercial satellite operations coupled with severe rain attenuations experienced at higher frequency bands (Ka and Q/V), particularly in the tropical regions which was caused by higher rainfall rates and bigger raindrop size, amongst others; it was pertinent that deliberate effforts be geared towards research along this direction. This became even more critical owing to a dearth database along the slant path in the tropical regions for use in rain propagation studies at microwave frequencies, especially at millimeter wave bands (where most signal depolarization and fading takes place). The results presented in this work are valuable for design and planning of the satellite link, particularly in the tropical regions.DAH, ITU-R and SAM model simulations along the slant-path were investigated using local rainfall data at 0.01% of the time, while making use of TRMM data from NigComSat-1 satellite to obtain the measured data for Lagos. Terrestrial attenuation data for 0.01% of the time for UTM were obtained from the UTM wireless communication center (WCC). The attenuation data were thereafter transformed to slant path using transformation technique proposed for Ku band byA. Y. Abdulrahman. Theattenuation exceeded for other percentages of the average year was obtained using statistical interpolation extrapolation method.It was observed that the proposed model predicts creditably well for the ka down link frequency band, by producing the best performance when compared with SAM, DAH and ITU-R models.DOI:http://dx.doi.org/10.11591/ijece.v2i6.122

Seasonal and Diurnal Variability of Rain Heights at An Equatorial Station

Seasonal and diurnal rain heights variation at Universiti Teknologi Malaysia, Johor was studied. Slant path rain attenuation prediction and modeling is crucial to satellite equipment design; a major input is the rain height. One year meteorological ground-based, S-band, 3D RAPIC precipitation radar data at 500m resolution sourced from the Malaysian Meteorological Department was complemented with two-year TRMM PR data sourced from JAXA Earth Observation Research Center. After filtering, sorting, extraction and decoding of the data, vertical reflectivity profiles were constructed; from which rain height parameters were extracted. TRMM PR processed monthly (3A25) and daily (2A23) rainfall precipitation data were similarly used to obtain rain height parameters to investigate the seasonal and diurnal variations. Results from this work suggested that rain height parameters are influenced by both seasonal and diurnal variations. Higher seasonal variability was observed during south-west and pre-southwest monsoons. Rain heights were also observed to be higher in the night than in the day time

Comparative analysis of bright band data from TRMM and ground radar data in Malaysia

Good knowledge of the formation and recognition of the bright band is necessary to determine the location of the melting layer. This is partly because the melting layer is one of the major hydrometeors (others include as rain, hail, and cloud) responsible for signal degradations along the slant-path, in the tropical regions of the world. These may result in signal fading, amongst others, which may lead to errors in slant-path attenuation predictions. This paper involves the comparative analysis of radar data sourced from both ground 3D RAPIC bistatic radar and space-borne precipitation radar above the Malaysian air space. For this research work, the terrestrial meteorological radar data were sourced from the Meteorological Department of Malaysia, while the satellite radar data were obtained from the near-real-time TRMM Multi-Satellite Precipitation Analysis (TMPA-RT) version 7 products. Frozen hydrometeors are observed to exhibit peculiar characteristics in terms of increased radar reflectivity as they fall from the sky, transiting from solid to liquid, and manifesting in the popular bright band signature. The melting layer is the region where melting occur, just below the 0? isotherm height. It is a major factor responsible for the problems being encountered in characterization and modelling of microwave signal propagation along the earth-space link. , Nor Hisham Khami

Determination of Melting Layer Boundaries and Attenuation Evaluation in Equatorial Malaysia at Ku-Band

Upsurge in bandwidth demand in recent times for real-time data transmission have put serious constraints on satellite communication channels, leading to congestion of the lower frequency bands; necessitating migration to higher bands (Ku, Ka and V) with attendant problems such as signal fading, depolarization and attenuation due to presence of hydrometeors. There is need to separately account for attenuation due to the melting layer along the earth-space microwave links. One year data from ground-based S-band meteorological radar sourced from Kluang station of the Malaysian Meteorological Department was processed to build the vertical reflectivity of rain profile for UTM, Malaysia. Results from this work suggested that the effects of the melting layer on signal attenuation at Ku-band can be quite significant in the tropical and equatorial regions. It was estimated to be 13.36 dB and 15.44 dB at 0.01% of the time exceeded using Laws-parsons and Marshall-Palmer regression coefficients, respectively. Furthermore, it was observed that ITU-R. P.618-11 model largely under-estimated the attenuation along the slant-paths because of its failure to account for attenuation due to the melting layer in its formulation by its assumption of constant rain rate; thus rendering it unsuitable for rain attenuation predictions in the tropics

Rain attenuation models at ka band for selected stations in the southwestern region of Nigeria

Rain is the major factor in radio propagation analyses that is responsible for outage on terrestrial point-to-point and point-to-multipoint radio communication systems at millimeter wave bands. This hampers radio wave signal transmission in the tropics. This paper investigates the performance of ITU-R P.530-16, Silver Mello, Moupfouma and Abdulrahman rain attenuation prediction models using locally-sourced data. The aim is to determine their suitability or otherwise in tropical Nigeria. Two years daily rainfall data were sourced from the Nigerian Meteorological Services (NIMET) for six different stations in southwestern Nigeria. Southern Nigeria is predominantly influenced by the southwest monsoon wind from the Atlantic Ocean due to its proximity to the coastal belt. The data were analyzed using these prediction models by comparing with measured data. The ITU-R P.530-16 rain attenuation prediction model closely matched the measurement value for p≥0.1% of the time but over-estimated it at p<0.1% while Abdulrahman and Silver Mello proposed prediction models generally over-estimated for p<0.01 of time exceeded. Overall, Abdulrahman proposed prediction model presented the best performances; it was closely followed by Silver Mello, ITU-R and Moupfouma prediction models respectively. These results further accentuate the need for urgent review of the ITU-R P.530-16 prediction model or alternatively, the development of a separate rain attenuation prediction model specifically for the stations in the tropical region

Site Diversity Technique Application on Rain Attenuation for Lagos

This paper studied the impact of site diversity (SD) as a fade mitigation technique on rain attenuation at 12 GHz for Lagos. SD is one of the most effective methods to overcome such large fades due to rain attenuation that takes advantage of the usually localized nature of intense rainfall by receiving the satellite downlink signal at two or more earth stations to minimize the prospect of potential diversity stations being simultaneously subjected to significant rain attenuation. One year (January to December 2011) hourly rain gauge data was sourced from the Nigerian Meteorological Agency (NIMET) for three sites (Ikeja, Ikorodu and Marina) in Lagos, Nigeria. Significant improvement in both performance and availability was observed with the application of SD technique; again, separation distance was seen to be responsible for this observed performance improvements

Performance Evaluation of Rain Attenuation Models in a Tropical Station

The non-uniformity of rainfall in both the horizontal and vertical directions makes the estimation of slant path attenuation complex. At frequencies above 10 GHz, the effects of attenuation and noise induced by rain are quite significant. One year satellite attenuation data were sourced from Malaysia East Asia Satellite at Ku frequency band; using ASTRO beacon signals to monitor and measure the slant path rain rate and attenuation at Universiti Teknologi Malaysia, Skudai. Four years’ one minute rain rate ground data at 0.01% of time exceeded were collected using rain gauge. The attenuation exceeded for other percentages of the time was obtained using statistical methods. Different rain attenuation prediction models were investigated and their performances compared. The validation results clearly suggested that the Breakpoint attenuation prediction model produced better results when compared with other models of interest.DOI:http://dx.doi.org/10.11591/ijece.v4i5.658

Investigating Rain Attenuation Models for Satellite Links in Tropical Nigeria

The analyses of rain models for satellite communication links of Ku and Ka bands in Lagos, Nigeria is the focus of this paper. The choice of these frequency bands was informed by the acknowledged fact that satellite signal fading and outages are predominant at those bands. The ITU-R P. 618-12 is the globally adopted prediction model; temperate, equatorial and tropical regions, inclusive. However, there was need to review the suitability of this model especially as it concerned equatorial and tropical stations. Rainfall data spanning a period of three years were collected from Nigerian Meteorological Agency (NIMET). The ITU-R P. 618-12 model along with some renowned prediction models were analyzed and their performances with the locally recorded measurement data were compared to establish their suitability or otherwise. The results obtained suggested ITU-R P. 618-12 exhibited the overall best performance at 12 GHz while DAH showed best performance at 26 GHz, even as both models underestimated and overestimated the measurement at Ku and Ka bands respectively. Again, at both frequencies, SST presented the worst performances

Modified itu-r rain attenuation prediction model for a tropical station

Most satellite communication takes place above the 10 GHz frequency bands, a direct consequence of over-congestion of lower frequency bands. A dearth of database along the slant path in the tropical regions for use in rain propagation studies at microwave frequencies, made further studies at millimeter wave band quite attractive. Rain height data were sourced from the Tropical Rainfall Measuring Mission (TRMM) 3B43 V6 and NigComSat-1 satellite for 37 stations in Nigeria as reported in the literature. Terrestrial attenuation measurement data at 0.01% of time, sourced from the Universiti Teknologi Malaysia’s Wireless Communication Centre (WCC) were transformed to slant path attenuation values using a transformation technique. Attenuation exceeded for other percentages of time were obtained using statistical methods. The ITU-R model is modified to suit the results. Further analysis at 12 GHz suggested that the proposed modified ITU-R model show good performance when compared with other models of interest