High precision hybrid RF and ultrasonic chirp-based ranging for low-power IoT nodes

Hybrid acoustic-RF systems offer excellent ranging accuracy, yet they typically come at a power consumption that is too high to meet the energy constraints of mobile IoT nodes. We combine pulse compression and synchronized wake-ups to achieve a ranging solution that limits the active time of the nodes to 1 ms. Hence, an ultra low-power consumption of 9.015 µW for a single measurement is achieved. The operation time is estimated on 8.5 years on a CR2032 coin cell battery at a 1 Hz update rate, which is over 250 times larger than state-of-the-art RF-based positioning systems. Measurements based on a proof-of-concept hardware platform show median distance error values below 10 cm. Both simulations and measurements demonstrate that the accuracy is reduced at low signal-to-noise ratios and when reflections occur. We introduce three methods that enhance the distance measurements at a low extra processing power cost. Hence, we validate in realistic environments that the centimeter accuracy can be obtained within the energy budget of mobile devices and IoT nodes. The proposed hybrid signal ranging system can be extended to perform accurate, low-power indoor positioning

Time Delay Estimation in Mobile Sensors for Underwater Networking

The time synchronization between any two sensor nodes in an Ad-hoc Underwater Sensor Networks (UWSNs) could be destroyed due to motion of these wireless sensors which induced Doppler shift. This synchronization obstacle can be sorted out by exploiting the mobility between sensor nodes. In the proposed system, the time delay between sensor nodes in both divergence and convergence scenarios are estimated based on estimating the time scaling factor. An improvement is introduced in terms of packet structure in order to challenge the channel effect and accurate estimation over the speed up to ±2 m/s. To verify the proposed system robustness, different levels of the nodes speeds have been considered in the simulation. Obtained results show that the proposed system is robust against severs channel conditions. Keywords: UWSNs, time delay, time synchronization

GCL Based Synchronization and Time Domain Frequency Offset Correction in OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation technique that has become the technology of choice in most wireless communication networks of today. Despite the advantages the OFDM system offers, it has some disadvantages like sensitivity to synchronization and high power-to-average-power ratio (PAPR). Any time offset leads to inter-symbol interference (ISI) whereas any frequency offset results in inter-carrier interference (ICI) and, as a result, the system performance degrades. The studies of preamble based time synchronization show that, the standard PN sequence based preamble in IEEE 802.16a is less robust to frequency offset when used in Park’s method of time synchronization - a method that gives more accurate result as compared to other methods. Time domain channel estimation cannot be carried out in the presence of integer frequency offset. This thesis has three specific objectives. Firstly, to design and evaluate a new preamble by making use of a generalized chirp-like (GCL) sequence that has low PAPR and good time and also frequency correlation properties. Secondly, to design a new receiver scheme that estimates and corrects the integer-frequency offset in the time domain and evaluate its performance. And lastly, having corrected the frequency offset in time domain, to estimate the wireless channel in time domain and evaluate its performance. The results show that, the proposed GCL based preamble has better and more robust performance than the standard PN sequence (IEEE 802.16 standard) based preamble in the time and integer frequency synchronization and also in the time domain channel estimation. In the new receiver scheme, the presence of symmetrical correlation shows that received signal is frequency corrected. The results show that the new receiver scheme is able to detect the symmetrical correlation quite accurately. The receiver also works well even in low SNR environment