Abstract
Radio resources must be wisely managed, in wireless communication systems, when implementing different multiple access techniques. This perspective is pivotal since the variations in propagation channel are very fast and the system is highly complex due to random and unpredictable movement of mobile users continuously. The complexity in the cellular system periodically contributes to different interference levels, high or low, resulting in the degradation of the system capacity. Transmitter power control is an efficient technique to mitigate the effect of interference under fading conditions, combat the Near-Far problem and conserve the battery life. Several remedial measures—like space diversity, frequency diversity, route diversity, increase in antenna height, antenna tilting, etc.—have been tried by many operators to overcome the debilitating effect of multipath fading in fixed line-of-sight microwave and mobile communication links. Among these remedial measures, diversity techniques have been extensively studied in terms of improvement factor, whereas the concept of antenna tilting is relatively less explored compared with other remedial measures. In this study, the effect of antenna tilting on fixed and mobile communication links is investigated to find out the optimum tilting angles in terms of design parameters, as well as on quality of service (QoS). The paper established that a deviation of more than 1.5o in antenna elevation angle would impact on QoS requirements and seriously affect the quality of signal to be received by the mobile systems.
Highlights
IntroductionDownward tilting cannot be effectively used without each other
Antenna beam tilting effects have been effectively employed in the past to overcome multipath fading induced by super refractive or ducting layers in microwave fixed line-of-sight (LOS) links
Downward tilting decreases the probability of occurrence of unacceptable inter symbol interference (ISI) due to multipath propagation by diminishing the power level of echoes with long delay times
Summary
Downward tilting cannot be effectively used without each other. Improvement in raising base-station antenna is offset by long-distance reflectors, if downward tilting is not used. In the case of a low-site, downward tilting is ineffective because the edge of a cell cannot be discriminated from the horizon. High antenna with downward tilting will be able to discriminate the edge of the intended coverage area and significantly reduce system interference. Upward tilting is useful if radio energy has to be reached in the upper floors of high-rising towers.
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