Kenichi Takizawa

Channel models for wireless body area networks

Wireless patient monitoring using wearable sensors is a promising application. This paper provides stochastic channel models for wireless body area network (WBAN) on the human body. Parameters of the channel models are extracted from measured channel transfer functions (CTFs) in a hospital room. Measured frequency bands are selected so as to include permissible bands for WBAN; ultra wideband (UWB), the industry, science and medical (ISM) bands, and wireless medical telemetry system (WMTS) bands. As channel models, both a path loss model and a power delay profile (PDP) model are considered. But, even though path loss models are derived for the all frequency bands, PDP model is only for the UWB band due to the highly frequency selectiveness of UWB channels. The parameters extracted from the measurement results are summarized for each channel model.Wireless patient monitoring using wearable sensors is a promising application. This paper provides stochastic channel models for wireless body area network (WBAN) on the human body. Parameters of the channel models are extracted from measured channel transfer functions (CTFs) in a hospital room. Measured frequency bands are selected so as to include permissible bands for WBAN; ultra wideband (UWB), the industry, science and medical (ISM) bands, and wireless medical telemetry system (WMTS) bands. As channel models, both a path loss model and a power delay profile (PDP) model are considered. But, even though path loss models are derived for the all frequency bands, PDP model is only for the UWB band due to the highly frequency selectiveness of UWB channels. The parameters extracted from the measurement results are summarized for each channel model.

R&D and standardization of body area network (BAN) for medical healthcare

A new major application of UWB is medical healthcare using advantages of low power spectrum density, high capacity of transmission and accurate ranging. As a core network of medical healthcare based on ICT, i.e. medical ICT, a body area network (BAN) has been researched and developed. BAN can provide a wide range of applications in primary for medical healthcare such as tele-metering vital sign, e.g. ECG, EEG, tele-controlling medical equipment, e.g. capsule endoscope and in addition for non-medical service such as entertainment. To harmonize with the strong demands from both medical healthcare societies and ICT industries, a standardization committee referred to as IEEE 802.15.6 was formally set up in December 2007. The objective of 15.6 is to define new physical (PHY) and media access control (MAC) layers for wireless BAN (WBAN). This invited paper introduces a progress of research and development of body area network, i.e. BAN and its standardization in IEEE802.15.6 in a field of medical ICT in order to encourage global collaboration as well as planting many R&D and business seeds in academia and industry.

Statistical Channel Models for 60 GHz Radio Propagation in Hospital Environments

Radio channel models for 60 GHz very-high-speed radio systems in hospital environments are presented. Two possible applications of those systems have been considered: real-time video streaming for angiography and ultrasonic imaging. Channel modeling was performed for delay domain multipath characteristics based on extensive radio channel measurement campaigns in angiography and ultrasonic inspection rooms. The measurement results revealed that the shapes of the power delay profiles in the angiography and ultrasonic imaging rooms were significantly different from that reported in the IEEE802.15 TG3c and IEEE802.11 TGad channel models. For this reason, novel model structures were developed to model radio channels in these hospital scenarios accurately. Statistical descriptions of the channel model parameters are given based on the measurements, and, finally, implementation guidelines of the channel models are provided. The channel model validation results show a good agreement of root-mean-square delay spread between channel model outputs and channel measurements. The channel model is useful for the performance evaluation of the wireless systems in hospital environments.

Ground-to-satellite laser communication experiments

Ground-to-satellite laser communication experiments between the optical ground station located in Koganei, central Tokyo, and a low earth orbit (LEO) satellite were jointly performed by the Japan Aerospace Exploration Agency and the National Institute of Information and Communications Technology. In 18 trials during three non-consecutive months, the satellite was acquired and tracked 61 % of the time, when clear or partly-clear conditions were predominant. The optical link was maintained for about 6 minutes when the satellite was visible in spite of the high angular velocity of the satellite. In 3 of the 18 trials, the link was not interrupted due to clouds during the six-minute transit. The failures (39% of the time) occurred when cloudy or rainy conditions were predominant. Fluctuation in the uplink received signal power was minimized by using multiple laser beam transmissions. The measured uplink and downlink bit error ratios were 10-7-10-4. These results demonstrate the applicability of free-space laser communication for not only geostationary earth orbit-LEO optical links but also ground-to-LEO optical links.

Measurement Based Path Loss and Delay Spread Modeling in Hospital Environments at 60 GHz

This letter presents radio channel measurements and modeling results for the feasibility study of 60 GHz high-speed radio systems in hospital environments. Two possible applications of those systems are considered: real-time video streaming for angiography and for ultrasonic inspection. Channel modeling was performed for the path loss and multipath characteristics of the propagation channel, i.e., the delay spreads. Results revealed generally lower path loss and delay spread values compared to regular indoor office and residential environments. The results indicate that the 60 GHz radio systems operating in hospital environments can provide better signal quality and wider coverage than those operated in regular indoor environments, though increased interference with neighboring cells might be an unfortunate consequence.

Channel Modeling and Performance Evaluation on UWB-Based Wireless Body Area Networks

This paper provides channel models for wireless body area network (WBAN) in UWB frequency band, and also presents performance evaluation using the derived channel models. The channel model is given by a statistical model in which parameters are derived from actually measured channel transfer function in a hospital room environment. These models enable us to evaluate performance of UWB-based WBAN. In this paper, bit error ratio (BER) and packet error ratio (PER) are shown for UWB-based WBAN which employs a signaling scheme among OOK, BPPM, BPSK, and DPSK. The results show that both OOK and BPPM which generally uses a non-coherent receiver provide severe performance when the target PER is set to 10-2 under the packet size of 128 bytes. The other signaling schemes achieve the required performance from the viewpoint of such error ratio.

Low-complexity rake reception and equalization for MBOK DS-UWB systems

This paper describes low-complexity rake reception and Viterbi equalization techniques for M-ary bi-orthogonal keying direct sequence UWB (MBOK DS-UWB) systems, which have been considered a type of PHY suitable for high-speed WPANs in IEEE802.15.3a. In MBOK DS-UWB systems, rake reception and equalization are essential to compensate interpulse interference generated by multipath fading. For rake reception, we derive a novel technique to reduce its implementation complexity by setting a limit on the number of delay devices. For Viterbi equalization, we provide a reduced-state sequence estimation algorithm that reduces the computation complexity for MBOK DS-UWB systems. By employing the proposed rake reception and Viterbi equalization techniques, the complexity can be reduced to less than half of ordinary rake and equalization techniques. Simulation results show that our rake reception and Viterbi equalization techniques enable almost the same performance as existing techniques despite the lower complexity.

Channel model on various frequency bands for wearable Body Area Network

Body Area Network (BAN) is considered as a promising technology in supporting medical and healthcare services by combining with various biological sensors. In this paper, we look at wearable BAN, which provides communication links among sensors on body surface. In order to design a BAN that manages biologic information with high efficiency and high reliability, the propagation characteristics of BAN must be thoroughly investigated. As a preliminary effort, we measured the propagation characteristics of BAN at frequency bands of 400 MHz, 600 MHz, 900 MHz, and 2400 MHz respectively. Channel models for wearable BAN based on the measurement results were derived. Our results show that the channel models can be described by using a path loss model for all investigated frequency bands.

A cooperative transmission scheme for real-time data gathering in a Wireless Body Area Network

Wireless Body Area Network (WBAN) has drawn considerable attention as a means to gather vital data from on-body sensors. In WBAN, however, a star network topology is mainly supported, connecting a central coordinator to vital sensor nodes put on different positions of a human body, so the links between the coordinator and the sensor nodes are often blocked by parts of the human body when the man takes different postures and motions. Therefore, to support real-time vital data gathering in WBANs, a scheme for mitigating such link blockings is essential. This paper proposes a cooperative scheme for ensuring reliable data transmission in a WBAN. For each sensor node on a human body, the proposed scheme autonomously assigns a sensor node as a cooperator out of other sensor nodes and the cooperator retransmits packets from the sensor node for a coordinator instead of the sensor node when the direct link between them is blocked. After presenting the cooperator selection algorithm, using the Received Signal Strength Indication (RSSI) data obtained from the experiment in an anechoic chamber, the paper evaluates the performance of the proposed scheme in terms of average and worst outage rates.

Channel modelling and performance evaluation of UWB-based wireless body area networks

This paper provides channel models for wireless body area network (WBAN) in UWB frequency band, and also presents performance evaluation using the derived channel models. The channel model is given by a statistical model in which parameters are derived from actually measured channel transfer function in a hospital room environment. These models enable us to evaluate performance of UWB-based WBAN. In this paper, bit error ratio (BER) and packet error ratio (PER) are shown for UWB-based WBAN which employs a signalling scheme among OOK, BPPM, BPSK, and DPSK. The results show that both OOK and BPPM which generally uses a non-coherent receiver provide severe performance when the target PER is set to 10–2 under the packet size of 128 bytes. The other signalling schemes achieve the required performance from the viewpoint of such error ratio.