We propose a new architecture for trust management in ubiquitous environments that deals with RBAC policy, digital signatures, and user presence in a uniform framework. The proposed architecture includes inferences about user presence from incomplete sensor signals based on the hidden Markov model. We implemented a prototype system for a connection service in an office computer network with an RFID tag sensor system. Experimental results show that the proposed architecture is effective in providing both useful and secure services in a ubiquitous environment.

Wireless sensor network systems are coming into increased use because of their potential to reduce power consumption in homes and factories. Ad-hoc multi-hop sensor networks are a key to attaining low-cost, low-power, small-size, and easy installation / maintenance. Sensor networks handle various kinds of sensed data, e.g., images, voice, temperature, and ID data, as well as various interval-lengths in intermittent communications: once per second, per minute, per day, etc.A reduced-power-consumption wireless ad-hoc multi-hop network system has been developed, the Dual-Link system, using the following two technologies: 1. Dual-Link communication, which handles two different frequency bands, achieves low-power data transmission through independent optimum settings of both operation periods and communication distances for each band. The selection of frequency bands and operation settings depends on both the data sizes and communication intervals defined for individual applications. This Dual-Link communication is applicable to various kinds of intermittent communications. 2. A vine-tree network topology that offers low addressing-bit counts and results in low packet-error rates even in low transmission-power communications. Since the topology does not require a routing table for individual nodes, hardware complexity can be kept to a minimum.A Dual-Link system, which is a combination of Dual-Link communication and the vine-tree network topology, promises to contribute significantly to various kinds of low-power sensor network systems.Almost all sensor network node operation time will be spent in stand-by, just listening for communication from neighboring nodes (listening periods). Figure 29.7.1 shows an example of a camera sensor network system and illustrates the power distribution for an individual terminal node. Almost all node-operation power is consumed in the Radio portion, within which most is consumed in the local-oscillator (LO) and LO-buffer circuits during listening periods. A reduction in the power for listening periods is key to reducing power consumption.In response to this situation, a Dual-Link communication scheme is developed, in which data transmission between nodes is made in two different frequency bands: a low frequency / power / data-rate band and a high frequency / power / data-rate band. Since each single terminal node has two transceivers, operation periods and communication power are independently controllable for each band.To verify the design, a Dual-Link system was developed for an image sensor network application which sends / receives compressed images in an ad-hoc multi-hop wireless network. A 433MHz band and a 2.4GHz band are adopted for, respectively, listening periods and image data transfer periods. In a listening period, resulting power consumption in the LO and the LO-buffers is roughly 1/6 of what it would be if all signals were at 2.4GHz. Dual-Link communication requires, however, transmission power control because of the difference in propagation between the two frequency ban...