Yuriy I. Nechayev

Measurements and Statistical Analysis of On-Body Channel Fading at 2.45 GHz

The fading of an on-body transmission channel at 2.45 GHz is investigated. For the first time a large amount of data has been gathered in practical environments, for realistic activities, and has been subject to statistical analysis. It is clear that significant variations of the path gain and fading can occur due to the movements of body. Extensive statistical analysis has shown that fading in on-body channels is a non stationary process. This letter presents results of a number of significant statistical parameters, including level crossing rate and average fade duration.

Experimental Characterization of UWB On-Body Radio Channel in Indoor Environment Considering Different Antennas

An experimental investigation to characterize the transient and spectral behavior of the ultrawideband (UWB) on-body radio propagation channel for body-centric wireless communications is presented. The measurements were performed considering over thirty on-body links in the front of human body in the anechoic chamber, and in indoor environment. Two different pairs of planar antennas have been used, namely, CPW-fed planar inverted cone antennas (PICA), and miniaturized CPW-fed tapered slot antennas (TSA). A path loss model is extracted from measured data, and a statistical study is performed on the time delay parameters. The goodness of different statistical models in fitting the root mean square (RMS) delay has been evaluated. Results demonstrate that the TSA, due to its more directive radiation behavior is less affected from the reflections from body parts and surrounding environment. The antenna shows significant size reduction and improved time delay behavior, and hence is an ideal candidate for UWB body area networks (BAN).

Performance of antennas in the on-body environment

This paper presents the performance of antenna combinations for on body communications. Several different antennas have been designed and built such as monopole antennas, patch antenna, loop antenna, patch and patch array antennas. These antennas were designed for the operation in the unlicensed ISM band, 2.45 GHz. The antennas then were tested in the on body environment. The performance of the antenna combinations is determined by measuring the path gain between two on-body paths for a range of body postures. Measurement results show that the combination of monopole antennas performs best in most of the measurement cases compared to other combinations. The comparison between calculation and measurement results, which consider the free space loss and antenna gain give results that are within 10dB of measurements for most body postures.

Simulation and Measurement of Dynamic On-Body Communication Channels

A study is presented of wireless on-body communication links, with the body in motion. This paper compares simulations and measurements of the path gain (PG) on moving male and female bodies. Simulations using avatars derived from an animation software have been performed at 2.45 GHz. Male and female avatars walking and a male rising from a chair have been simulated and the results are compared with measurements carried out in an anechoic chamber. The results show that good agreement between simulation and measurement of slow fading features can be achieved for a reasonable computational effort.

Antennas for on-body communication systems

The optimum choice of antenna for on-body communications is discussed in this paper. Several different antennas, including the monopole, the loop and patch and patch arrays have been fabricated and tested in the on-body environment. In particular, path gain measurements of two on-body paths has been performed for a range of body postures. It is clear that the monopole antenna performs best in most of the measurement cases. A first order analysis of the path loss, consisting of antenna gain deduced from link geometry and a free space loss appropriate to the path distance, give results that are within 10 dB of measurements for most body postures.

Use of Animation Software in Simulation of On-Body Communications Channels at 2.45 GHz

As wearable electronic devices become increasingly popular, there is a growing interest in the design of body area networks (BAN). The propagation characteristics of such channels are of interest to assist in proper design of BAN systems. It has been shown that body movement is a primary factor in channel fading and hence channel modelling must include the effect of movement. In this letter, results are presented for a walking phantom created using animation software. Simulations of a walking avatar for three different channels at a frequency of 2.45 GHz are shown and compared to measurements made on a human body in an anechoic chamber. It is shown that such a phantom can give good prediction of mean and standard deviation of the propagation channel of a walking subject.

Wireless channels and antennas for body-area networks

In this paper a review of recent research in characterizing on-body wireless channels is presented. Path gain random variations caused by body movements in various environments have been investigated at several frequencies, including 2.45 GHz and 5.8 GHz. In a scattering environment, such as an office, the fading of on-body channels was found to undergo a combination of two types of variation, namely, short-term and long-term variations. The short-term variation is due to multipath fading and can be described by either Rician or Nakagami distribution, and the long-term fading usually follows a log-normal, or gamma distribution. The rates of fading expressed in terms of level crossing rate and average fade duration have been also obtained. The effect of these indings on the system design parameters, such as link reliability, fade margin, and required transmitted power, is discussed. Performance of different types of antennas which can be used in WBAN devices has been evaluated as well. It is found that antenna diversity can be successfully applied in order to mitigate the effects of channel fading and interference.

On-Body Diversity Channel Characterization

Statistical analysis of the on-body diversity combined and branch signals are presented. The distribution of short-term fading envelopes of the branch and combined signals show that the fading environment for the on-body channels is Rician. The long-term fading best fits the log-normal distribution. The average best fit parameters are presented for short-term and long-term fading envelopes of the branch and combined signals. The Doppler spectra are also presented. Three different types of antennas were used and two on-body channels were characterized at 2.45, 5.8, and 10 GHz.

Short-term and long-term fading of on-body transmission channels at 2.45 GHz

Variation of the path gain in on-body transmission channels is investigated in several realistic scenarios. Short-term and long-term fading statistics are investigated and non-stationarity of both the types of fading in indoor multipath environments is demonstrated. It was found that the short-term fading is best described by a Rician distribution with the K-value log-normally distributed, and a gamma distribution is best suited for the long-term fading.

Onbody Diversity and Angle-of-Arrival Measurement Using a Pattern Switching Antenna

Diversity is one of the methods to overcome the multipath effect in the mobile environment. A pattern diversity antenna with four beams was used to investigate the diversity performance in the onbody environment. A switched diversity combining method-switch-and-stay strategy-was used to analyze the data. Finding an angle of arrival (AoA) of different multipath components is very useful since it allows optimization of the base-station antenna radiation patterns and can be used to locate and track the handsets that operate in a particular cell. Similarly, in onbody communications, knowing the AoA enables determining the position of the antennas relative to each other and supports the design of antennas with optimized radiation patterns. Diversity and AoA measurements have been performed for five randomly movements body channels. In diversity measurements, the antenna beams are switched quickly considerably faster than the body movements. The results show that significanct gains are achieved for non-line-of-sight channels and no gain is obtained for the LOS channel since the signal is received by the same beam during the measurement. During AoA measurements, the 2-D process is chosen in which the angles are in a 2-D plane around the ground plane of the antenna. The main propagation paths of the transmitted signal are limited to a limited interval of the AoA range. These AoA estimates for onbody propagation channels can be used for designing better fixed beam and pattern diversity antennas.