Wen-Bin Yang

A statistical path loss model for medical implant communication channels

Knowledge of the propagation media is a key step toward a successful transceiver design. Such information is typically gathered by conducting physical experiments, measuring and processing the corresponding data to obtain channel characteristics. In case of medical implants, this could be extremely difficult, if not impossible. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe RF propagation from medical implants inside a human body. This virtual environment allows for more natural interaction between experts with different backgrounds, such as engineering and medical sciences. Here, we show how this platform has been used to determine a statistical path loss model for medical implant communication systems.

Channel Models for Medical Implant Communication

Information regarding the propagation media is typically gathered by conducting physical experiments, measuring and processing the corresponding data to obtain channel characteristics. When this propagation media is human body, for example in case of medical implants, then this approach might not be practical. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe RF propagation from medical implants inside a human body. This virtual environment allows for more natural interaction between experts with different backgrounds, such as engineering and medical sciences. Here, we show how this platform has been used to determine channel models for medical implant communication systems.

Interference mitigation for body area networks

Due to very low power communication, wireless body area networks are potentially susceptible to interference from other coexisting wireless systems including other BANs that might exist in their vicinity. Using power control to combat this interference might not be efficient. It could also lead to situations with higher levels of interference in the system. On the other hand, interference mitigation can help to not only preserve link quality but also allow more nodes to simultaneously operate. This paper proposes several interference mitigation schemes such as adaptive modulation as well as adaptive data rate and duty cycle for body area networks. Interference Mitigation Factor (IMF) is introduced as a measure to quantify the effectiveness of the proposed schemes.

Interference Mitigation Using Adaptive Schemes in Body Area Networks

Considering the medical nature of the information carried in body area networks (BANs), interference from coexisting wireless networks or even other nearby BANs could create serious problems on their operational reliability. As practical implementation of power control mechanisms could be very challenging, link adaptation schemes can be an efficient alternative to preserve link quality while allowing more number of nodes to operate simultaneously. This paper proposes several interference mitigation schemes such as adaptive modulation as well as adaptive data rate and duty cycle for BANs. Interference mitigation factor is introduced as a measure to quantify the effectiveness of the proposed schemes. These schemes are relatively simple and well-suited for low power nodes in BANs that might be operating in environments with high level of interference.

Simulation study of body surface RF propagation for UWB wearable medical sensors

Ultra Wide-Band (UWB) is a favorable technology for wearable medical sensors that monitor vital signs and other health-related information. Efficient transceiver design requires in-depth understanding of the propagation media which in this case is the human body surface. The results of the few measurement experiments in recent publications point to varying conclusions in the derived parameters of the channel model. As obtaining large amount of data for many scenarios and use-cases is difficult for this channel, a detailed simulation platform can be extremely beneficial in highlighting the propagation behavior of the body surface and determining the best scenarios for limited physical measurements. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe three-dimensional RF propagation from wearable medical sensors around a human body. We have used this virtual environment to further study UWB channels over the surface of a human body. Parameters of a simple statistical path-loss model and their sensitivity to frequency and the location of the sensors on the body are discussed.

Impact of an aortic valve implant on body surface UWB propagation: A preliminary study

Efficient transceiver design in body area networks requires in-depth understanding of the propagation channel which in this case involves the human body. Several studies have been done to characterize RF propagation on the body surface and determine the parameters of an appropriate model. However, the possible effect of an already existing medical implant on body surface propagation has not been considered until during a recent measurement experiment. There it was discovered that an aortic implant may have an impact on Ultra Wide-Band (UWB) propagation between wearable nodes that are in the vicinity of the implant location. In this paper, we use a 3D immersive visualization environment to study and observe the impact of an aortic implant on body surface propagation. Specifically, we focus on the UWB impulse response of the channel between nodes located around the upper body. The difference in the obtained impulse responses (for scenarios with and without the implant) both in measurement and simulation points to the possible impact that such medical implants could have on body surface RF propagation.

Theoretical Analysis and Modeling of Link Adaptation Schemes in Body Area Networks

Considering the medical nature of the information carried in Body Area Networks (BAN), interference from coexisting wireless networks or even other nearby BANs could create serious problems on their operational reliability. As practical implementation of power control mechanisms could be very challenging, link adaptation schemes can be an efficient alternative to preserve link quality while allowing more number of nodes to operate simultaneously. This paper provides theoretical analysis and Markov chain modeling of interference mitigation schemes such as adaptive modulation and adaptive data rate for body area networks. These schemes are relatively simple and well-suited for low power nodes in body area networks that might be operating in environments with high level of interference.

A DS-CDMA Interference Cancellation technique for body area networks

A low complexity Parallel Interference Cancellation (PIC) technique that is applicable to body area networks (BANs) is presented. Using Direct-Sequence Code Division Multiple Access (DS-CDMA), the technique aims at suppressing interference caused by rapid changes in relative sensors position due to body parts motion as well as interference from adjacent BANs. Interference signal is estimated using a relationship between cyclic correlation of the received signal and interferer code without requiring any knowledge of the channel condition. The codes for the multi-sensor DS-CDMA communication are constructed by using a set of m-sequences. The cyclic correlation is performed using Fast Walsh-Hadamard Transform (FWHT) which exhibits low computational complexity. In addition to low complexity, the proposed technique does not require complicated channel condition estimation and has no convergence issues. The uncoded Bit Error Rate (BER) performance of the proposed interference cancellation over a body-surface channel is calculated and compared with the conventional scheme.

A Low Complexity Interference Cancellation Technique for Multi-User DS-CDMA Communications

A low complexity Parallel Interference Cancellation (PIC) technique is proposed to suppress Multi-Access Interference (MAI) and minimize near-far effect for multi-user communication using Direct-Sequence Code Division Multiple Access (DS-CDMA). Interference signal is estimated using a relationship between cyclic correlation of the received signal and users code of the interferer without requiring any knowledge of the channel condition. The users codes for the multi-user DS-CDMA communication are constructed by using a set of m-sequences. The cyclic correlation is performed using Fast Walsh-Hadamard Transform (FWHT) which exhibits low computational complexity, i.e., it does not require any multiplication/division operations. In addition to low complexity, the proposed technique does not require complicated channel condition estimation and has no convergence issues. The uncoded Bit Error Rate (BER) performance of the proposed interference cancellation is calculated and compared with the conventional one over three different types of channels: AWGN, slow Rayleigh fading, and multipath channels.