The global navigation satellite system (GNSS) has been used in various areas as an infrastructure to provide precise position and timing. Furthermore, according to proliferation of the location-based services and the advent of network centric warfare, sharing of the acquired situational information became important as well as estimating the physical position of persons or objects. However, the GNSS is vulnerable to intentional or unintentional interferences and is not available in shaded areas due to weak received signal strength and well-known signal structure. Since positioning and communication systems are separately configured, an extra link is needed for sharing. For these drawbacks, the alternative positioning and the integration of communication and navigation is required.
This dissertation deals with the alternative positioning scheme for GNSS-less environments, and presents the design of multiple access scheme for combining the proposed positioning scheme with communication networks. We propose an independent positioning scheme: 1) airborne relay-based positioning scheme (ARPS) and design two schemes for improving the performance of ARPS: 2) Enhanced algorithm and 3) Self-correction scheme. We also integrate the ARPS into time division multiple access (TDMA) networks: 4) Networked ARPS (N-ARPS).
ARPS employs the relaying of navigation signals through airborne nodes to provide positioning up to non-LOS user. The user sequentially estimates the position of airborne relays and its own position using reception and propagation times of relayed signals. Enhanced algorithm re-estimates the user position by adding a virtual pseudorange measurement of reference station to improve the ARPS vertical accuracy. To prevent performance degradation, the user calculates the expected errors for the initial and re-estimation using geometrical factor and error source information, and then compares to determine whether to re-estimate. In self-correction scheme, each reference station adjusts the transmission time of navigation signals to reduce errors in pseudorange measurements. N-ARPS uses three strategies to integrate ARPS into TDMA networks: First, consecutive slot allocation for minimizing mobility effect: Second, airborne relay selection based on the distance from a master station: Third, secondary scheme against navigation signal loss.
We conduct extensive simulations to evaluate ARPS, N-ARPS, and enhanced schemes. The simulation results show that ARPS guarantees high accuracy than conventional pseudolite-based positioning scheme. Furthermore, the enhance scheme improves the accuracy of ARPS and expands service coverage. Finally, ARPS can operate in TDMA networks with relatively good performance.