In this paper, we present a Minimum Spanning Tree (MST) based topology control algorithm, called Local Minimum Spanning Tree (LMST), for wireless multi-hop networks. In this algorithm, each node builds its local minimum spanning tree independently and only keeps on-tree nodes that are one-hop away as its neighbors in the final topology. We analytically prove several important properties of LMST: (1) the topology derived under LMST preserves the network connectivity; (2) the node degree of any node in the resulting topology is bounded by 6; and (3) the topology can be transformed into one with bi-directional links (without impairing the network connectivity) after removal of all uni-directional links. These results are corroborated in the simulation study.

Recently, some countries have begun conducting feasibility studies and R&D projects on High Altitude Platforms Systems (HAPS). Japan has been investigating the use of an airship system that will function as a stratospheric platform (altitude of about 20km) for applications such as environmental monitoring, communications and broadcasting. It is planned that such an airship network would cover all of Japan. Remote sensing from such an airship would be very effective because it floats above the same ground area, permitting continuous monitoring of the surface. However, the precise positioning of the airship is one of the most important technical challenges for such a project. If pseudolites were mounted on the airships, their GPS-like signals would be stable augmentations that would improve the accuracy, availability, and integrity of GPS-based positioning systems. The accuracy of the pseudolite positions would be a limiting factor for such a service since the PL 'ephemeris error' is more serious than GPS due to the lower height of the airship. In this paper, a conceptual design of the airship-based augmentation system is first introduced. Then some schemes for estimating the pseudolite position are described. Apreliminary experiment involving ' inverted-GPS' shows excellent positioning stability in the static mode, while a kinematic test suggests the need to mitigate multipath effects on ground receivers.

Abstract. Global navigation satellite systems have been revolutionising surveying, geodesy, navigation and other position/location sensitive disciplines. However, there are two intrinsic shortcomings in such satellite-based positioning systems: signal attenuation and dependence on the geometric distribution of the satellites. Consequently, the system performance can decrease significantly under some harsh observing conditions. To tackle this problem, some new concepts of positioning with the use of pseudo-satellites have been developed and tested. Pseudo-satellites, also called pseudolites, are ground-based transmitters that can be easily installed wherever they are needed. They therefore offer great flexibility in positioning and navigation applications. Although some initial experimental results are encouraging, there are still some challenging issues that need to be addressed. This paper reviews the historical pseudolite hardware developments and recent progress in pseudolite-based positioning, and discusses the current technical issues.

Abstract. Although existing integrated GPS/INS systems can overcome inherent drawbacks of each system, such as no result without line-of-sight for GPS and INS errors that grow with time, performance is nevertheless degraded in difficult operational circumstances. Some typical examples are when the duration of satellite signal blockage is excessive, resulting in large accumulated INS errors that are not able to be calibrated by GPS. Such a scenario is unfortunately a common occurrence at engineering-construction sites. In such a case, pseudolites (ground-based GPS-like signal transmitters) deployed at appropriate locations, can augment GPS (and INS), so that accurate position and attitude information can still be obtained. This paper presents the results of investigations into new kinematic positioning strategies, such as GPS/PL/INS and PL/GPS integration, that can maintain performance by continuously providing measurements necessary to update the system Kalman filter. The new concepts of PL/INS and GPS/PL/INS integration using a centralised Kalman filter are described. Typically, the former is applicable to indoor positioning where the GPS signal is unavailable for use. The latter would be appropriate for circumstances when the number and geometry of visible satellites is not sufficient for accurate positioning and attitude determination. Simulations are carried out in order to analyse the geometric strength with respect to the locations of the pseudolites and the user antennas. The results of integrated data processing are presented.

This paper discusses the introduction of pseudolites (ground-based GPS-like signal transmitters) into existing integrated GPS/INS systems in order to provide higher availability, integrity and accuracy in a local area. Even though integrated GPS/INS systems can overcome inherent drawbacks of each component system (line-of-sight requirement for GPS, and INS errors that grow with time), performance is nevertheless degraded under adverse operational circumstances. Some typical examples are when the duration of satellite signal blockage exceeds an INS bridging level, resulting in large accumulated INS errors that are not able to be calibrated by GPS. Such a scenario is unfortunately a common occurrence for certain kinematic applications. To address such shortcomings, both pseudolite/INS and GPS/pseudolite/INS integration schemes are proposed here. Typically the former is applicable for indoor positioning where the GPS signal is unavailable for use. The latter would be appropriate for system augmentation when the number and geometry of visible satellites is not sufficient for accurate positioning or attitude determination. In this paper, some technical issues concerned with implementing these two integration schemes are described, including the measurement model, and the appropriate integration filter for INS error estimation and correction through GPS and pseudolite (PL) carrier phase measurements. In addition, the results from the processing of simulated measurements, as well as field experiments, are presented in order to characterize the system performance. As a result, it has been established that the GPS/PL/INS and PL/INS integration schemes would make it possible to ensure centimetre level positioning accuracy even if the number of GPS signals is insufficient, or completely unavailable.

There are three general scenarios for the use of pseudolites in deformation monitoring systems; namely GPS augmented with pseudolites, pseudolite-only and pseudolite `inverted' positioning. This paper focuses on the results and analysis of experimental data collected for these three pseudolite scenarios. The results suggest that the use of helical antennas can reduce pseudolite multipath error. The performance of pseudolite-GPS and pseudolite-only systems are evaluated and shown to be suitable for precise (cm-level) positioning.

Traditionally, Inertial Navigation Systems (INS) provide positioning and attitude information for the guidance (and perhaps control) of a wide range of moving platforms in the air, at sea, or on the ground. However, the timedependent growth of systematic errors is a major concern in INS applications. Precise satellite measurements are ideally suited for the calibration of INS systematic errors. Therefore, integrated INS and GPS (and/or Glonass) systems have been developed, which can provide highrate precise positioning and attitude information.