Antennas for Fixed WiMAX Application & Adaptive Modulation in Wimax Technology

Directional antennas enhance the fade margin by adding together extra gain. This increases the link accessibility comparisons between directional and Omni-directional antennas. Delay spread is further reduced by directional antennas at both the Base Station and Customer Premise Equipment (CPE). The antenna pattern restrains any multi-path signals that appear in the side lobes and back lobes. The efficiency of these methods has been verified and demonstrated in booming deployments, in which the service operates under considerable NLOS fading. (J,R.Sanford)

Adaptive Modulation

WiMAX system supports adaptive modulation to regulate the Signal Modulation Scheme (SMC) depending on the Signal to Noise Ratio (SNR) state of the radio link. When the radio link is soaring in quality, the peak modulation scheme is used, offering the system additional capacity. During a signal fade, the WiMAX system can move to a lower modulation scheme to keep the connection quality and link permanence.

This element allows the system to overcome time-selective fading. The key element of adaptive modulation is that it enhances the range that a higher modulation scheme can be used over, because the system can bend to the actual fading circumstances, as opposed to having a fixed scheme that is planned for the worst case situations. (Sam W. Ho, 2004)

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