Please explain the purpose of operation: |
Testing a communication link between wireless RF-ID sensors and a base station.
We have proposed a novel architecture for data extraction from a network of low-power sensors with limited communication and computation capabilities that we term an Imaging Sensor Net. Unlike in conventional multihop sensor to sensor communication, the sensors communicate directly with the collector/base
station node using a line of sight channel. Since the origin of the sensed data is critical in many applications, this architecture utilizes a radar-like round trip delay estimation to additionally locate the sensors. The collector node transmits a RF beacon, which is a long aperiodic pseudorandom noise sequence to initiate the communication using a highly directional high gain antenna. The sensors that are illuminated by the beacon electronically reflect the collector nodes beacon, modulating the return with low rate data and frequency translation to avoid backscatter or ground return. The collector proceeds to sweep the entire field with overlapping illuminations of sensors. The
received signals from these multiple illuminations are then jointly processed using techniques similar to Synthetic Aperture Radar Processing to extract the data, and locations of the corresponding sensors. The 60GHz millimeter wave band was chosen for this prototype, since there is unlicensed bandwidth available and also at this frequency, multipath effects are
at a minimum due to significant attenuation during reflections, which is desired to make the delay estimation algorithm accurate. We consider two possible architectures for the sensors - one in which the sensor reflects the beacon with no gain(similar to RF-ID sensors) at the sensor and the other, where the sensor
amplifies the signal before reflection. In the RF-ID like sensors, the collector node must provide enough power in the beacon in order to compensate for the attenuation in both the down and up links, which necessitates large transmit powers at the collector. |