The biggest challenge for any wireless broadband network is the unpredictable nature of the fast changing channel conditions that can have a severe impact on the user's broadband experience. This impact stems from the fact that the data rate correlates directly to the signal quality, and signal quality itself is impacted by a variety of factors as summarized below:

• Data rate depends on signal quality
• Signal quality impacted by many factors
• Propagation loss over distance
• Delay spread (frequency selective tracing)
• Doppler shift (time selective fading)
• Angle spread (space selective fading)
• Interference (users in same/other sectors)

Given the unpredictable and quickly changing nature of the wireless channel, the challenge now becomes to successfully deal with these ever changing signal conditions in a wireless network so the data rates are maximized under any condition.

IEEE 802.16e or mobile WiMAX is ideally suited for applications involving fixed indoor and outdoor devices as well as fully mobile devices since it uses advanced techniques to maximize signal quality. The following features are critical in achieving high performance in the above application scenarios and thereby enable better ROI for carriers and equipment vendors:

• Scalable OFDMA
• MIMO - Space Time Coding / Spatial Multiplexing
• Beamforming
• Diversity / opportunities scheduling