Ocenjevanje kota prihoda signala z uporabo neusmerjenih anten in merjenja moči signala : doktorska disertacija

slovenian

doktorska dela

2013

Univerza v Mariboru, Fakulteta za elektrotehniko računalništvo in informatiko

In this thesis we deal with the problem of determining the position of sensors connected into Wireless Sensor Networks (WSN). When choosing the concept of determining the position we consider the following cost functions of these networks and their associated sensors, i.e., (i) the minimization of energy consumption and (ii) minimization of sensor cost. The cost functions are served best by using sources available in topology of WSN, and through operating of the radio sensors. Many methods of determining the position of sensors work in such way. In the thesis we limit ourselves to the method basedon the angle measurement of the RF signals (AoA) arrival. The angles are measured by specific, rotating nodes in the network, where by estimation we measure the received power of the RF signals from other sensors in the network. The received signal strength (RSSI) is measured by all radio modules sensors that communicate in accordance with IEEE 802.15.4. AoA measurement capability is limited to the reference nodes (beacons), which know their position. These beacons have more complex hardware than other sensor nodes. The reference nodes in WSN may also serve as traffic routers and as data sink for data from other sensors. Other, so called "unknown nodes , are ordinary units, with no particulars. For the experimental validation underlying research and studies for this thesis we have developed a new hardware and software for the assessment of AoA. The software is based on algorithms, for which we claim to be an original contribution of the dissertation. The algorithms exploit specifics of dipole antennas: (i) radiation characteristic of the magnetic field (H) is isotropic, (ii) radiation characteristics of the electric field (E) is anisotropic in a very narrow area of the spherical surface. The fading of the received RF signal from the sensor, which position we are searching, is used to determine the direction where it is located. This method, in comparison to other AoA techniques based on finding maximum oriented radiated power farfetched method, allows also requires simpler additional hardware and software. Since beacons use dipole antenna, they can also be used as router of the data networks. The experiments were constrained to optically visible distance, i.e. the case of LOS (line of Sight), between the beacon sensor and other sensors. Any barriers that obscure visible line cause unwanted echoes of radio signals and thus aggravates the measurement of AoA. For the experimental confirmation of the thesis we have developed and made three measurement testbays: (i) testbay with beacon having four dipole (microstrip) antennas mounted on a rotating plate, (ii) the testbay with beacon having a rotating dipole (microstrip) antenna and (iii) the testbay with beacon having twelve (microstrip) dipole antennas arranged on the circumference of a stationary circular plate. For each testbay we have adapted the algorithm to estimate AoA to the specifics of the used hardware. All options of the developed hardware and software have validated our thesis. The obtained experimental results, of course, differ from one another in the accuracy of AoA assessment.

07.08.2023