By making wireless sensors more energy efficient, an attractive solution is to use cooperative beamforming in wireless sensor networks. The evolution of microfabrication has allowed silicon chips to become very small (on the micron scale) with a lot of intelligence capabilities. One of the applications of these small chips has been for wireless sensor networks and smart dust. The limitations of these devices is that they have small batteries with limited amounts of available power; thus reducing the operation time of the sensors.

Cooperative beamforming applies the concept from smart antennas that when using an array of antennas, the radiation pattern can focus its transmission energy in a desired direction.  This reduces the required transmission power and propagation loss. In wireless sensor networks, the array of antennas are not organized in a known structure. The sensors first must share their received data with other nearby sensors. Then each participating sensor determines the complex weight needed to allow transmitted packets to add coherently to the same destination.

Implementing cooperative beamforming clearly comes with power and time overhead for the data sharing among the collaborative sensors. In addition, mitigating synchronization issues and determining precise position locations of the collaborating sensors creates further overhead. Despite the extra overhead, using cooperative beamforming offers significant energy savings. The amount of energy saved is dependent on the size of the network, the data rate, and the design of transmitter and receiver circuits.

For a given transceiver design and data rate, as the number of collaborating sensors increase so does the energy savings over single sensor transmission, but there becomes a point where the beamforming directivity gain saturates while the energy related to the overhead continues to grow linearly. Clearly, designing a cooperative beamformer is a multi-variable optimization problem, but when optimized can achieve 90% energy savings over single sensor transmission.

More Information