Adaptive Beamforming Raises WiMAX Capacity

Compared to third-generation (3G) networks, mobile WiMAX has garnered attention for being a more affordable technology for transferring large amounts of data with high throughput. This advantage can be further magnified by adaptive beamforming. This technology vows to improve both the range and capacity of a WiMAX network. At the same time, it reduces capital and operating expenses by minimizing the number of base stations that are needed in a network. The operation and advantages of adaptive-beamforming technology are detailed in a white paper by Fujitsu and Cisco titled, "Beamforming Boosts the Range and Capacity of WiMAX Networks."

In a multiple-input multiple-output (MIMO) system, two antennas receive different data streams via different spatial paths in the physical environment. By increasing the number of inputs and outputs (within limits), it is possible to raise the MIMO system's efficiency when working with multiple spatial paths. Beamforming, which can be used in conjunction with MIMO, sends data on the best available path between the transmitter and receiver. To target this path, the transmitter drives multiple antennas with a phase-shifting algorithm. That algorithm focuses most of the radio power toward the intended receiver.

Adaptive beamforming results in a much higher signal-to-noise ratio, which enables the use of higher- order modulation. An adaptive-beamforming system measures the characteristics of signals that are arriving by multiple paths from subscriber devices. Next, the system creates a map of the best downlink paths to the device. The downlink signal is sent using all available multipaths. As a result, the reflected signals arrive at the subscriber device both together and in phase. The paper closes with a look at beamforming today.

Fujitsu Microelectronics America, 1250 E. Arques Ave., M/S 333, Sunnyvale, CA 94085-5401; (800) 866-8608, Internet:

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