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University of Glamorgan Propagation effects in WiMAX systems Sharmini Enoch Dr.Ifiok Otung.

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Presentation on theme: "University of Glamorgan Propagation effects in WiMAX systems Sharmini Enoch Dr.Ifiok Otung."— Presentation transcript:

1 University of Glamorgan Propagation effects in WiMAX systems Sharmini Enoch Dr.Ifiok Otung

2 University of Glamorgan Contents WiMAX Propagation effects in WiMAX Signal to noise ratio performance Conclusions

3 University of Glamorgan WiMAX WiMAX- Worldwide Interoperability for Microwave Access Technology based on IEEE standard Use wireless links with microwave or millimetre wave radios Use licensed spectrum (typically) Are metropolitan in scale Provide public network service to fee-paying customers (typically) Use point-to-multipoint architecture with stationary rooftop or tower-mounted antennas Provide efficient transport of heterogeneous traffic supporting quality of service (QoS)

4 University of Glamorgan Propagation effects in WiMAX 2-66 GHz frequency range affected by impairments Propagation loss in terrestrial LOS relative to free space loss is sum of different contributions such as: (1) Rain (2) Atmospheric gases (3) Fog (4) Atmospheric multi-path (5) Diffraction (6) Snow In NLOS additional attenuation introduced by: (1) Shadowing (2)Vegetation Simulation carried out using ITU-R models

5 University of Glamorgan Rain attenuation Prediction of rain attenuation in LOS and NLOS terrestrial links is essential above 2 GHz frequency band Above 10 GHz temporal variation in path loss is due to rain attenuation – the process depending on instantaneous rainfall rate ITU-R 838 predicts rain attenuation

6 University of Glamorgan Attenuation due to atmospheric gases Propagation loss has to be calculated for absorption due to water vapor and oxygen Using ITU-R 676, the calculation is performed

7 University of Glamorgan Fog and Cloud attenuation Typical particle diameter is between ten μm (fog) and several ten μm (water vapor) and number of particles per cm3, is between 100 and 500 Incidence of fog with visibility less than 200 m in UK is typically in the range of 1% to 3% of the year Attenuation due to thick fog is around 0.1 dB which is quite negligible

8 University of Glamorgan Atmospheric Multipath fading A particularly severe form of frequency selective fading occurs when beam spreading of the direct signal combines with a surface reflected signal to produce multi-path fading ITU-R 530 and ITU-R 453 are used in finding the average annual percentage distribution

9 University of Glamorgan Diffraction fading When the atmosphere is sufficiently sub-refractive (large positive values of the gradient of refractive index, low k-factor values), the ray paths will be bent in such a way that the earth appears to obstruct the direct path between transmitter and receiver, giving rise to the kind of fading called diffraction fading Diffraction fading is the factor that determines the antenna heights

10 University of Glamorgan Attenuation due to Snow and Dust Attenuation due to snow or dust is predominantly a function of the moisture content of the particles From ITU-R 839, there will be no additional attenuation due to melting layer if the following condition is satisfied: hlink < hrainm hlink -> rain height at the centre of the path link hrainm -> median rain height In our calculation the above equation is satisfied

11 University of Glamorgan Shadowing Shadowing is an important effect in wireless networks It causes the received SINR to vary dramatically over long time scales The Walfish-Ikegami (W-I) model applies to smaller cells It is recommended by WiMAX forum for modelling microcellular environments The model assumes an urban environment with a series of buildings

12 University of Glamorgan Vegetation attenuation Attenuation due to vegetation varies due to: (1) Irregular nature of medium (2) Wide range of species (3) Densities (4) Water content Specific attenuation through trees in leaf is 20% greater than for leafless trees above 1 GHz

13 University of Glamorgan Signal to noise ratio performances For all percentages of time the signal is subjected to outage. Such a link is not acceptable BER is very high in the value of 0.2 for all percentages of time

14 University of Glamorgan Improvement of BER By reducing bit rate and coverage distance No significant improvement in BER with decreasing distance and lower data rate

15 University of Glamorgan Conclusions Our study shows that availability of 99.99% is difficult to achieve under realistic propagation impairments conditions WiMAX theoretical data rates between 1 Mbps to 75 Mbps is not possible as BER is higher at high data rates Future work is aimed at reducing fading using space time block coding and increasing data rates using MIMO techniques

16 University of Glamorgan Thank you for your attention!!!


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