Shigeru Fukunaga

Error resilient video coding by dynamic replacing of reference pictures

We show the performance of the proposed error resilient video coding system, which dynamically replaces reference pictures in inter-frame coding according to the acknowledgement signals from the decoder. Scalability to the quality of the network is a feature of the system. A poor network condition in its way results in a certain picture quality and a good network condition enhances the picture quality. Two types of signaling, ACK and NACK, are evaluated. The evaluation includes the influences of the backward channel errors as well as those of the forward channel errors. ACK signaling outperforms NACK signaling especially under the existence of the backward channel errors which are highly correlated with the forward channel errors.

EACLE: Energy-Aware Clustering Scheme with Transmission Power Control for Sensor Networks

In this paper, we propose a new energy efficient clustering scheme with transmission power control named “EACLE” (Energy-Aware CLustering scheme with transmission power control for sEnsor networks) for wireless sensor networks, which are composed of the following three components; “EACLE clustering” is a distributed clustering method by means of transmission power control, “EACLE routing” builds a tree rooted at a sink node and sets the paths from sensor nodes taking energy saving into consideration, and “EACLE transmission timing control” changes the transmission timing with different levels of transmission power to avoid packet collisions and facilitates packet binding.With an indoor wireless channel model which we obtained from channel measurement campaigns in rooms and corridors and an energy consumption model which we obtained from a measurement of a chipset, we performed computer simulations to investigate the performance of EACLE in a realistic environment. Our simulation results indicate that EACLE outperforms a conventional scheme such as EAD (Energy-Aware Data-centric routing) in terms of communication success rate and energy consumption. Furthermore, we fully discuss the impact of transmission power and timing control on the performance of EACLE.

An Effect of Anchor Nodes Placement on a Target Location Estimation Performance

Many indoor localisation and tracking techniques in wireless sensor networks assume placing anchor nodes on a ceiling. However, placing the nodes on the ground can improve target localisation estimation accuracy based on received signal strength indicator as we show in this work. The presented results are based on an experiment conducted in a hall under two sets of conditions. In one case, people were present in the hall and in the other one, the hall was empty. For the case when people were present in the hall, the location estimation performance improved from 3.7 meters root-mean square error (RMSE) when using only the anchor nodes fixed to the ceiling to 2.2 meters RMSE when using only the anchor nodes placed on the ground. For the case when the hall was empty, the location estimation performance improved from 4.1 meters RMSE when using only the anchor nodes fixed to the ceiling to 2.4 meters RMSE when using only the anchor nodes placed on the ground. The target location estimation accuracy improved by 40% for both conditions

A Sensor Network Protocol for Automatic Meter Reading in an Apartment Building

A wireless sensor network for automatic meter reading needs to satisfy two contradicting requirements, i.e., long lifetime and prompt detection and notification of emergency. We propose a sensor network protocol for this purpose, in which sensor nodes operate on a low duty cycle while the latency of transmission is guaranteed to be less than a certain bound. In this protocol, each node is assigned a time slot in which it receives messages from other nodes. To accomplish slot assignment where nodes further from a BS are assigned earlier time slots for a packet to be transmitted to the BS in one cycle, we propose a slot assignment function with which a node can determine its own slot in a distributed way. We explore several slot assignment functions to find one which gives low and homogeneous contention over a grid network. The simulation results show that our protocol performs well close to the optimal case.

Distributed Time Division Pattern Formation for Wireless Communication Networks

This paper proposes a novel communication timing control for wireless sensor networks, named Phase Diffusion Time Division method. This is based on the mutual synchronization of coupled phase oscillatory dynamics with a stochastic adaptation, according to the history of collision frequency in communication nodes. Through local and fully distributed interactions in the communication network, the coupled phase dynamics self-organizes an efficient time division pattern of the communication so that the network reduces the collision frequency by diffusion of the phase pattern, while it sustains sufficient throughput of the communications. We introduce the built-in virtual node dynamics model for sensor device, to implement impulse signal based interactions. This method is designed for applications in a regular grid model of the wireless network, but it can be extended to an irregular grid model as simulation results illustrate, where the proposed method outperforms CSMA method in the efficiency.

Error resilient video coding controlled by backward channel signaling

We have proposed an error resilient video coding system, which dynamically replaces reference pictures in inter-frame coding according to the backward channel signaling. This system can prevent the temporal error propagation, because the encoder would not use the erred picture as the reference picture. This system has two modes, one is ACK mode and the other is NACK mode. ACK mode is effective in more erroneous condition, and NACK mode is effective in less erroneous condition. In this paper, we explain both modes and focus on the mode switching mechanism according to the error condition on the network so that the optimal performance can be achieved in any error conditions by the proposed system. We show the performance of our proposed system compared with the previous version of ITU-T H.263, which did not have a reference picture selection mode, by a computer simulation as well.

Reliable broadcast message authentication in wireless sensor networks

Due to the low-cost nature of sensor network nodes, we cannot generally assume the availability of a high-performance CPU and tamper-resistant hardware. Firstly, we propose a reliable broadcast message authentication working under the above-mentioned circumstances. The proposed scheme, although based on symmetric cryptographic primitives, is secure against anyone who knew the message authentication key as well as the malicious router nodes in multi-hop networks. The proposed scheme consists of three steps; (i) reliable broadcast of a message, (ii) legitimate acknowledgments from all the nodes in the network, and (iii) disclosure of the message authentication key. Secondly, we propose a way to reduce the amount of the stored information until the disclosure of the key, in which the server transmits the message integrity code of a message before transmitting the message. Finally, we consider the characteristic and the security issues of the proposed schemes.

Phase diffusion time division method for wireless communication network

This paper proposes a novel communication timing control for a wireless sensor network, named phase diffusion time division method. This is based on the mutual synchronization of coupled phase oscillatory dynamics with a stochastic adaptation, according to the history of collision frequency in the communication node. Through local and fully distributed interactions in the communication network, the dynamics self-organizes an efficient communication pattern, such that the network reduces the collision frequency by diffusion of the phase pattern, but also it sustains the sufficient throughput of communications by the stochastic adaptation. This method is designed for applications in a regular grid model of the wireless network, but it is also extended to the irregular grid model as simulation results exemplify the efficiency.

Effect of Walking People on Target Location Estimation Performance in an IEEE 802.15.4 Wireless Sensor Network

Target location estimation is one of many promising applications of wireless sensor networks. However, until now only few studies have examined location estimation performances in real environments. In this paper, we analyze the effect of walking people on target location estimation performance in three experimental locations. The location estimation is based on received signal strength indicator (RSSI) and maximum likelihood (ML) estimation, and the experimental locations are a corridor of a shopping center, a foyer of a conference center and a laboratory room. The results show that walking people have a positive effect on the location estimation performance if the number of RSSI measurements used in the ML estimation is equal or greater than 3, 2 and 2 in the case of the experiments conducted in the corridor, foyer and laboratory room, respectively. The target location estimation accuracy ranged between 2.8 and 2.3 meters, 2.5 and 2.1 meters, and 1.5 and 1.4 meters in the case of the corridor, foyer and laboratory room, respectively.

Autonomous synchronization scheme access control for sensor network

This paper describes a novel distributed communication timing control for wireless sensor networks. For collision avoidance among sensor nodes, communication slots are allocated with a centralized controller in TDMA, however, we propose Phase Diffusion Synch-Alliance model as a fully distributed communication timing control. This model is based on the coupled phase-oscillator dynamics to dynamically adjust communication timing where phase synchronization and repulsion are coordinated depending on the network topology.