Takahiro Aoyagi

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.

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.

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.

Simulation-Based Scenario-Specific Channel Modeling for WBAN Cooperative Transmission Schemes

Wireless body area networks (WBANs) are an emerging technology for realizing efficient healthcare and remote medicine for the aging society of the future. In order to improve the reliability of WBAN systems and support its various applications, channel modeling and performance evaluation are important. This paper proposes a simulation-based channel modeling for evaluating the performance of WBAN cooperative transmission schemes. The time series of path losses among seven on-body nodes are generated by the finite-difference time-domain method for seven body motions. The statistical parameters of the path loss for all the motions are also obtained. The generated path loss is then applied to the evaluation of the two-hop decode-and-forward relaying scheme, yielding an improvement in transmit power. From the evaluation of body motion, useful insights are obtained such as which relay links are more robust than others. Finally, the proposed approach is validated through comparison with a measurement-based approach.

Analysis of Dynamic On-Body Communication Channels for Various Movements and Polarization Schemes at 2.45 GHz

On-body wireless communication channels are studied by using the finite-difference time-domain (FDTD) method and moving human models. An anechoic environment is assumed. Three movements having a different dynamical characteristic each, walking, weakly walking and running, are considered. Essentially, the results are obtained for nine different polarization schemes regarding the dipole transmitter and receiver orientations and for six receiver locations. The results include the reception level curves, mean levels and standard deviation of reception (STD); dynamic path gain (PG) of a specific antenna can be obtained, too, by, e.g., using the presented “offset method.” The results, best applicable for electrically small dipole-like antennas, can be utilized in link budget calculations, channel model development and usability evaluations of different polarization schemes with different on-body links. The effect of the polarization scheme on the mean level is much understood by the theory of radiowave propagation over a lossy ground. Based on this theory, a rough method to estimate the mean reception level (and PG) is introduced and found usable for small dipole antennas under suitable conditions. Finally, reception changes due to uncertain receiver location are studied. A body-normally polarized small dipole receiver is less sensitive to its location than a body-tangential one.

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.

Numerical Analysis of Ultrasonic Beam of Variable-Line-Focus-Beam Film Transducer

In this study, the characteristics of an ultrasonic beam radiated by a variable-line-focus-beam transducer were numerically calculated by finite-difference time domain (FDTD) method and liquid-elastic wave reflection theory. The interference ripple caused by a leaky surface acoustic wave (SAW) was observed in the lens width vs received intensity curve. Reasonable results, the true-circle-arc-lens in the literature, were obtained. As in the conventional V(z) curve, the ripple changed according to the attenuation parameter α and the leaky SAW velocity. Unlike for the conventional true-circle-arc-lens, the ripples caused by the leaky SAWs are observed at both sides of the focal point.

Numerical simulations for dynamic WBAN propagation channel during various human movements

In this report, we performed six human movement simulation by a commercial software (Poser7). We performed FDTD simulations for body area network propagation with one transmitter and six receivers. Received amplitudes were calculated for every time frame of 1/30 s interval. We also demonstrated a polarization diversity effectiveness for dynamic wearable body area network propagation.

A Body Surface Coordinator for Implanted Biosensor Networks

Biomedical sensors can be implanted and networked in the human body for health monitor, diagnosis, treatment or as a prosthetic device. Life time and heat generated by implant due to communication and circuitry power consumption are big concerns. This paper presents a new network architecture for long range communications in the implanted sensor networks. We measured the on-body propagation around body surface and in-body propagation through tissue in the frequency ranges of 403MHz and 2.45GHz. We have found that the in-body path loss is more than that of on-body. To exploit the path loss difference, we propose to introduce a body surface coordinator which has more resources to the implanted sensor networks. Instead of only routing data among implants, the coordinator on the body surface can forward data from one implant to another over long distance more safely and efficiently.

Antenna De-embedding in FDTD-Based Radio Propagation Prediction by Using Spherical Wave Function

Finite-difference time-domain (FDTD) method is one of the promising approaches for the propagation prediction. However, since the computational domain includes both the antennas and the propagation environment, their coupling prevents evaluating individual contributions to the channel response. As a result, the simulation becomes always specific to the given antenna type or orientation and cannot be reused for other configurations. The simulation also requires the internal structure of the antenna which is often unavailable and/or difficult to be modeled. These problems can be addressed by antenna de-embeddeding which separately models the antenna and the propagation environment, hence the purpose of this paper. In particular, this paper proposes the implementation of spherical-wave-function (SWF) channel modeling using the FDTD method. Instead of modeling the real antenna structures inside the computational domain, the single-mode spherical wave source and the observation points are utilized. The spherical wave source is achieved by a cubical dipole array. The spherical wave source is first validated, including the investigation of the effects of cell and array size. The narrowband channel response synthesized by the proposed approach is then validated numerically through comparison with the transmission formula in free space and the conventional antenna-embedded simulation in the human shadowing environment as well.