Tat Meng Chiam

Performance benchmarking for wireless body area networks at 2.4 GHz

This paper investigates wireless body area network (WBAN) performance to capture packet reception ratio (PRR) and its correlation with received signal strength indicator (RSSI), and the minimum transmission powers required for the targeted performance. We design and carry out experiments on IEEE 802.15.4 based WBAN prototype to measure the performance metrics in different activities and environments. It is observed that RSSI values for a given on-body link has radical variation in a minute-scale period in a realistic environment. This observation implies that a few of RSSI samples cannot be used as an estimate of the average RSSI over many packets transmitted over an on-body link. In postural mobility, the periodicity pattern of link property is more obviously observed at links with clearer line-of-sight and at higher transmission powers. The objective of the performance benchmarking is to provide insights and guidelines for the design of resource management schemes for WBANs.

Experimental Study on the Dependence of Antenna Type and Polarization on the Link Reliability in On-Body UWB Systems

An experimental study on the use of ultra-wideband antenna systems (3.5–4.5 GHz) on the human body for wireless body area network (WBAN) applications is conducted. It has been found that the link reliability can be improved and transmit power can be reduced by properly selecting the transmit and receive antennas with different radiation properties (omni-directional, directional, pattern diversity) and polarizations (vertical and horizontal) at each location on the body. Moreover, when there is blockage by the body, it may be possible to achieve better transmission when the antennas are horizontally polarized. Also, antennas with pattern diversity can be used to enhance the overall reliability of the communication system. In order to eliminate the use of cables in the measurements, an on-body UWB system has been developed and the reliability can be assessed more practically in terms of the peak amplitude of the received waveform and the bit error rate. It has been observed that when the link quality is improved, the transmit power can be reduced by more than 20 dB without compromising on the reliability, which will conserve the battery power.

On-body evaluation of UWB receiver position for wireless body area network

In a wireless body area network, the position of the sensor nodes are fixed, while the receiver position can be changed. In this paper, we evaluate three popular receiver positions based on the bit error rate obtained from ultra wideband (UWB) based sensor nodes and a UWB receiver hardware. The three receiver positions evaluated are waist, chest and arm. It is shown that by selecting the optimum receiver position, it is possible to transmit up to 20 dB less power, while maintaining the required bit error rate of 10−3. Evaluation of different combination of sensor nodes shows that chest position is preferred location for the receiver.

Channel Characterization of Walking Passerby's Effects on 2.48-GHz Wireless Body Area Network

A statistical analysis of walking passerbys effects on narrowband wireless body area network (WBAN) in outdoor and indoor environments at 2.48 GHz is presented. Experiments were conducted to measure the dynamic channel responses of various on-body links with four sets of pre-defined passerby movements while the user remains stationary in a standing posture. On-body links that experienced fades greater than 20 dB from the static path gain were identified. The effects of passerby movement types, in both outdoor and indoor environments, were analyzed and compared to the effects of users motions such as walking and running. Parameters for the Ricean distribution, which was found to be a good fit for channel gain variation, are presented to model the channel up to the second-order statistics, such as level crossing rate and average fade duration. The parameters allow the use of fading channel simulators to reproduce the passerbys effects in the on-body channels.

RF transmission in/through the human body at 915 MHz

The Medical Implant Communication Service (MICS), which was allocated by the Federal Communication Committee (FCC) on a shared, secondary basis in 1999, refers to a specification for using a frequency band between 402 to 405 MHz in communication with medical implants [1, 2]. It allows bi-directional radio communication with a pacemaker or other electronic implants. The maximum transmit power is limited to 25 µW, or −16 dBm, in order to reduce the risk of interfering with other users within the same band. The maximum usable bandwidth at any instant is 300 kHz, which makes it a low data rate system compared with WiFi (5.8GHz) or Bluetooth (2.4GHz). Other frequencies considered for implant communication include 915 MHz, 1.5 GHz, and 3.1–10.6 GHz ultra-wideband (UWB). The frequency band of 902–928 MHz is one of the Industrial, Scientific, and Medical (ISM) bands, commonly abbreviated as the 915 MHz ISM band. In this band, there are no restrictions to the application or the duty cycle. Furthermore, the allowed power output is considerably higher. Due to the lack of restrictions and higher allowed power, this band is very popular for unlicensed short range applications including audio and video transmissions. The FCC section 15.249 allows 50 mV/m of electrical field strength at a distance of 3 meters within the frequency band of 902–928 MHz. This corresponds to an EIRP of −1.23 dBm. A higher output power of up to 30 dBm is permitted if the system employs some form of spread spectrum such as frequency hopping or direct sequence spread spectrum since they are less likely to interfere with other systems and are also immune to interference from other systems.

Experimental correlation of path loss with system performance in WBAN for healthcare applications

This paper presents the experimental characterization of the static on-body channel for healthcare applications at 2.48 GHz. The measurements are conducted in the anechoic chamber and laboratory. The link quality is measured by either using a vector network analyzer, where the path loss is averaged over a period of time or calculated from the received signal strength indicator (RSSI), which can be calculated from the receive sensor module. A correlation between the path loss and the packet delivery ratio (PDR) will be made via the probability distribution of the RSSI for a given transmit power. In addition, the optimal transmit power at the different body locations can be obtained, which will be useful to conserve the battery energy.

RF transmission characteristics in/through the human body

In this paper, the RF transmission characteristics in/through human body are investigated experimentally and numerically. An experimental methodology to characterize the RF transmission of human body is presented. The proposed method addresses the challenge to characterize the RF transmission accurately and reliably without the body tissue effect on the antennas under test. The proposed methodology of using tissue-embedded antennas is validated at 403 MHz band (Medical Implant Communication Service, MICS).

Study of dynamic on-body link reliability for WBAN systems

In this paper, the dynamic on-body link reliability of an IEEE 802.15.4 wireless body area network (WBAN) enabling on-body communications at 2.48 GHz is studied. By having the transmitter node placed on various locations on the hands and the receiver node fixed on the waist, the link reliability can be evaluated from the received signal strength indicator (RSSI) readings when the user is stationary, walking, and jogging. From the RSSI readings, the reliability of the WBAN can be quantified by the performance metric of packet delivery ratio (PDR).

Reliability enhancement and performance visualization system for Wireless Body Area Network

Existing applications leveraging on Wireless Body Area Network (WBAN) technologies face several technical challenges and difficulties to support desirable data reliability and real-time performance visualization. So we designed and developed a testbed with integrated hardware and software solution aiming to enhance data reliability and provide performance visualization of WBAN. In this demo, we showcase our current works of improved hardware platform design and development, on-body wireless channel modeling and empirical network profiling, energy-efficient and reliable routing protocol, motion-aware reliability enhancement scheme and visualization of real-time WBAN operations. We will demonstrate the proposed reliability control, dynamic routing protocol and real-time visualization implementations using indoor fitness monitoring scenario.

Experimental study of optimal UWB antenna location for ECG application

In this paper, the RF transmission performance on the human body for ultra-wideband wireless body area network (UWB WBAN) applications will be evaluated. The UWB pulse that is generated by the transmitter sensor node has a bandwidth of 500 MHz and centered at 4 GHz. The received signal passes through a receiver frontend circuitry before entering the high speed oscilloscope. In this study, the transmission performance measurement will involve placing the printed omni-directional monopole antenna at various receiver locations near/on human body. An identical transmitter antenna will be positioned on the left chest area which corresponds to the electrocardiography (ECG) location. The peak-to-peak amplitude and waveform from the oscilloscope were recorded. From the study, it was found that the optimal receiver location to receive the strongest signal is at the waist area of the human body when the transmit antenna is vertically polarized and receive antenna is horizontally polarized.