Katsuhiro Naito

Revisiting overlapped channels: Efficient broadcast in multi-channel wireless networks

In wireless networks, broadcasting is a fundamental communication primitive for network management and information sharing. However, in multi-channel networks, the broadcast efficiency is very poor as devices are distributed across various channels. Thus, a sender tries all channels for broadcasting a single message, which causes large overhead. In this paper, we propose a novel scheme for efficient broadcast in multichannel networks. Our scheme leverages the overlapped band, which is the frequency range that partially overlapped channels (i.e., adjacent channels) share within their channel boundaries. Specifically, a sender advertises the rendezvous channel through the overlapped band of adjacent channels; the message sharing via broadcast is done on the rendezvous channel. Our scheme employs Signaling via Overlapped Band (SOB), which defines a new signal processing mechanism for communication via the overlapped band. SOB is integrated with MAC layer mechanisms: 1) Reserve Idle Spectrum Fragment (RISF) to reduce waiting time, 2) Reinforce Switch Notification (RSN) to reduce the residing time at a wrong channel, and 3) Multi-sender Agreement on Rendezvous CHannel (MARCH) to support multisender broadcasts. We implemented our scheme on the SORA platform. Experiment results validated communication through the overlapped band. Intensive simulation studies showed that our scheme drastically outperformed previous approach.

High efficient packet aggregation scheme for multi-rate and VoIP packet transmissions in next generation MU-MIMO WLANs

In the next generation wireless local area network (WLAN), the multi-user spatial multiplexing combined with packet aggregation can increase the system performance significantly. However, the space channel time may arise due to non-uniformity in the transmission times of wireless frames on the different spatial streams during MU-MIMO transmissions. In addition, for various communication services such as voice communication, the quality of service (QoS) provision is essential in the current WLANs. In this paper, our objectives are reduction of the space channel time and QoS provision for voice communications. Then, we propose a high efficient packet aggregation scheme taking into account the multi-rate and VoIP packet transmissions. The results of computer simulations demonstrate the effectiveness of the proposed scheme under recent WLAN environments.

A Survey on the Internet-of-Things: Standards, Challenges and Future Prospects

Technological development in communications and electronics has made the growing expansion of the Internet of Things (IoT). IoT is expected to make a great impact to our society because smart devices in IoT are easily integrated into existing service. As a result, standardization of technologies to support the IoT is becoming more important to realize a smart society through different service domains. This paper presents a survey on the current state of the art of standards for IoT technologies and gives a brief introduction to related standards and recent research areas in IoT. Finally, it also proposes an idea of the future platform of scalable IoT systems. The proposed idea employs IP mobility technologies to realize inter-operability among IoT devices in different networks.

Feasible cooperative communication with IEEE 802.11a based devices for multi-hop networks

Wireless multi-hop networks are candidate communication infrastructures in developing regions because their installation cost is quite low comparing to that for conventional wired networks. Reliable and scalable dissemination mechanism is required in practical multi-hop networks. Cooperative communication is a new scheme to improve communication performance to realize a reliable dissemination mechanism. However, high mobility networks have a big issue for autonomous control for cooperative communication. Additionally, conventional cooperative schemes cannot reduce packet collisions even if packet collisions are a big degradation factor of performance in dense multi-hop networks. We have discussed a new cooperative communication scheme that employs Orthogonal Frequency-Division Multiplexing (OFDM). Our scheme can improve communication performance and reduce packet collisions based on distributed control matter. Our advance evaluation has shown a good potential of the proposed scheme to improve communication performance in multi-hop network simulations. On the contrary, the feasibility of the proposed scheme with a real hardware device was not shown. This paper evaluates the feasibility of our original cooperative communication scheme on IEEE 802.11a standard devices. Almost all conventional cooperative communication schemes require a special physical layer and a media access control mechanism. We have focused on a characteristic of OFDM, where a receiver can demodulate multiple signals within a guard interval period. The experimental evaluation has been performed with software defined radio devices (USRP B200). We have implemented multiple transmitters, a receiver and a fading simulator for each transmitter with two USRP B200 devices. The results can show that the proposed scheme works well on IEEE 802.11a standard devices and improves communication performance in practical situations. Hence, the proposed scheme will be a new candidate of cooperative communication mechanisms that can employ general consumer devices and can realize effective dissemination mechanism for multi-hop networks.

Demo: Implementation of unconscious bus location sensing system with smartphone devices and beacon devices

This paper demonstrates a new unconscious sensing system for bus location. Our system is a new type of application based on participatory sensing systems. However, it can perform sensing operation without users operation. Therefore, we can employ the mechanism to realize practical application such as bus location systems. Our sensing system consists of a beacon device, a smartphone application and a cloud service. The beacon device is installed on a bus to activate the smartphone application. The smartphone application can upload a bus location to the cloud service when the smartphone application detects the beacon device. The cloud service manages the bus location and distributes them for smartphone applications. The demonstration shows a prototype system for a bus location system based on the new participatory sensing mechanism.

Safety message dissemination in NLOS environments of intersection using TV white space

Safety message dissemination is a key mechanism for preventing intersection collisions. Normally, the dissemination is based on vehicular communications, of which the de-facto standard is Dedicated Short Range Communications (DSRC). However, due to DSRC high operation frequency, a signal suffers from serious attenuation when being propagated in Non Light-Of-Sight (NLOS) conditions. Previous works have leveraged the use of relay units (e.g., repeaters installed on traffic lights) that enabled a safety message to detour large obstacles. However, one cannot guarantee that vehicles find the relay units at every intersection. To solve this problem, in this paper we propose a novel scheme that enables reliable dissemination in NLOS conditions by exploiting a TVWS band. Specifically, the proposed scheme leverages the excellent propagation characteristics of a TVWS signal even without relays. To increase the benefit of a TVWS band, the proposed scheme employs an efficient retransmission protocol, the Repetitive Retransmission via Spatial Diversity (RRSD). The above method ensures the safe message dissemination even in very harsh NLOS conditions. Moreover, the proposed scheme reduces network congestion via a cluster approach that uses both DSRC and TVWS bands. To the best of our knowledge, this is the first attempt to propose a reliable dissemination scheme that supports intersection safety services without special relaying units in NLOS conditions. Simulation studies show that the proposed scheme outperforms the previous scheme in the delivery ratio of a safety message by 25%.

Development of Field Sensor Network System with Infrared Radiation Sensors

Information technology has been focused to estimate growth degree of plants in agriculture. This paper focuses on leaf temperature that changes according to the activity of photosynthesis. Infrared cameras are a major method to measure leaf temperature in conventional methods. However, the expensive device price causes difficulty to install many sensors in practical fields. Infrared radiation sensors are new candidate device to estimate growth state by measuring leaf temperature. Since the price of infrared radiation sensors is inexpensive, we can install a lot of sensors into fields. Additionally, the consumed power of infrared radiation sensors is relatively small comparing to Infrared cameras. These features of infrared radiation sensors are appropriate for sensor networks working with a battery. This paper proposes a field sensor network to measure growth state of plants by infrared radiation sensors. Our goal is to realize a practical and inexpensive sensor network system with typical system on chip (SoC). Therefore, we employ a reasonable price SoC supporting IEEE 802.15.4 standard to design a unique device with various sensors. In order to realize multi-hop communication with low-power consumption, we propose a routing and media access control mechanisms for the developed system. The media access control technology realizes periodic sleep operation of all devices to enable long-term operation of the system. The routing control technology can construct a multi-hop network with the minimum number of hops. The experimental results demonstrated that the development system works in the practical fields.

Reliable Safety Message Dissemination in NLOS Intersections Using TV White Spectrum

Reliable safety message dissemination is a fundamental primitive for constructing intersection safety systems. Normally, the dissemination is based on vehicular communications, of which the de-facto standard is Dedicated Short Range Communications (DSRC). However, due to high frequency operations, a DSRC signal is seriously attenuated when being propagated in Non Line-Of-Sight (NLOS) conditions. Previous schemes leveraged the use of centralized infrastructures or relay vehicles enabling a safety message to bypass large obstacles. However, implementing the infrastructures in all intersections would be very costly; one may not find proper relay vehicles in low density, and frequent rebroadcasts cause serious network congestion in high density. To address this challenge, we propose a novel scheme that exploits excellent propagation characteristics of a TV White Space (TVWS) band (in addition to a DSRC band) for reliable dissemination in NLOS intersections. To ensure reliable dissemination throughout a broad range of densities without infrastructures, our scheme employs two innovative mechanisms: a collaborative procedure and a Dynamic optimal Configuration (DoC). To our knowledge, this is the first that simultaneously satisfies two vital demands for intersection safety system: 1) lacking infrastructures and 2) working well in all densities. Simulation studies show that the proposed scheme outperforms previous infrastructure-based schemes.

Demo: Implementation of cooperative bus location system with BLE devices and smartphones

This paper demonstrates a new cooperative bus location system with BLE (Bluetooth Low Energy) devices and smartphones. Our idea has extended common participatory sensing systems to realize more practical sensing systems because common participatory sensing mechanisms require a participants operation to measure some values. Our proposed system consists of a BLE devices on a bus, smartphone applications on a participants smartphone, and a cloud service. The BLE device has a GPS (Global Positioning System) receiver and a communication function based on the BLE specification. The BLE device also activates a neighbor smartphone application by transmitting a special beacon message. Hence, the smartphone application can work and obtain the bus location from BLE device even if it was a suspended status. Additionally, it also uploads the bus location to the cloud service automatically. As a result, the proposed system can collect a bus location from BLE devices through smartphones automatically. The demonstration shows a prototype system based on the proposed idea for a bus location system.

Demo: Prototype implementation of ID card based momentum measurement system

This paper demonstrates a new ID card based momentum measurement system for office workers health managements in companies. Our system can measure office workers momentum with a new ID card that implements a microprocessor, sensors and a RFID tag because an amount of momentum has a relation with a health condition and it is an important indicator to prevent chronic diseases. RFID based ID cards are widely used in office buildings to manage a security control and to record working hours. Therefore, companies can install the proposed system by updating software for a RFID reader/writer in entrance gates, doors, etc. The demonstration shows a prototype system for health management system with ID card based measurement devices of momentum.