Loading...
3 results
Search Results
Now showing 1 - 3 of 3
- Performance evaluation of directional antennas in ZigBee networks under NLOS propagation conditionsPublication . Azevedo, Joaquim Amândio; Santos, FilipeMany authors suggest directional antennas to enhance the transmission performance of ZigBee networks. For line-of-sight propagation, directional antennas can extend the transmission range or reduce the transmit power. Directional antennas may also reduce interference between networks operating in the same frequency channel. However, these antennas may not perform similarly under non-line-of-sight propagation conditions. This work presents a study with ZigBee modules comparing the performance of a directional antenna with an omnidirectional one. The measurements were conducted on a university campus for different propagation outdoor environ ments. A deconvolution technique was applied to estimate the received signal as a function of the azimuth angle. The results demonstrated that the received power followed the gain difference between antennas only for paths with low attenuation. Considering the same Effective Isotropic Radiated Power (EIRP), the system with directional antennas started to lose packets at the same distance as the omnidirectional antennas. The directional antenna did not allow the increase in the link range compared to the omnidirectional antenna. The power consumption was also measured for different transmit power levels of the ZigBee radio. The study showed that the control circuits of directional antennas typically consume more power than omnidirectional antennas operating at a higher transmit power level.
- Sleeping ZigBee networks at the application layerPublication . Azevedo, Joaquim; Rodrigues, Maurício; Santos, Filipe; Aguiar, LuísZigBee/IEEE 802.15.4 is one of the most used standards for low-power applications. However, full function devices must be always active to route data in a mesh network. The objective of this work is to implement a sleeping technique at the application layer that enables sleep mode for all nodes of a ZigBee network. A time synchronisation mechanism to deal with the clock drift of the sensor nodes was developed. The technique also enables the recovery of lost messages. A large network is organised into smaller groups to reduce latency and packet collisions. The active interval of each node is dynamically adapted to the network operation to optimise the energy consumption. The proposed technique was applied to a real testbed and the increase in energy efficiency was evaluated. The results demonstrated energy savings of about 95% for networks containing up to 20 nodes per group and wake up periods longer than 2 min
- Implementation of a hydric energy harvesting system for wireless sensor networksPublication . Santos, Filipe; Azevedo, Joaquim