Ben Gilbert

Characterization of the Dynamic Narrowband On-Body to Off-Body Area Channel

A characterization of the dynamic narrowband on-body to off-body area channel is presented based on real-time measurements of the time domain channel response at carrier frequencies near the 900MHz and 2400MHz Industrial, Scientific and Medical (ISM) bands. A statistical characterization is presented of received signal amplitude when the subjects body is standing and walking, transmitted from the body to a receiver, Rx, off the body, with various orientations of the subjects body with respect to the receiver, and various distances from the receiver. Two locations of the transmitter, Tx, on the human body are considered. The Lognormal distribution provides a good fitting model with and without movement. Further, the stability is characterized based on a measure of channel response variance, which is called here the channel variation factor and can characterize the channel coherence time. The on-body to off-body area channel is determined to be generally stable over a period of 25ms, but the amount of stability is found to be dependent both on movement, Tx location on-body, and carrier frequency.

First- and second-order statistical characterizations of the dynamic body area propagation channel of various bandwidths

Comprehensive statistical characterizations of the dynamic narrowband on-body area and on-body to off-body area channels are presented. These characterizations are based on real-time measurements of the time domain channel response at carrier frequencies near the 900- and 2,400-MHz industrial, scientific, and medical bands and at a carrier frequency near the 402-MHz medical implant communications band. We consider varying amounts of body movement, numerous transmit–receive pair locations on the human body, and various bandwidths. We also consider long periods, i.e., hours of everyday activity (predominantly indoor scenarios), for on-body channel characterization. Various adult human test subjects are used. It is shown, by applying the Akaike information criterion, that the Weibull and Gamma distributions generally fit agglomerates of received signal amplitude data and that in various individual cases the Lognormal distribution provides a good fit. We also characterize fade duration and fade depth with direct matching to second-order temporal statistics. These first- and second-order characterizations have important utility in the design and evaluation of body area communications systems.

Open-source testbed for Body Area Networks: 200 sample/sec, 12 hrs continuous measurement

We present the design criteria and specifications of a novel Open-Source hardware channel sounder and Open-Source data sets for measurements of the Body Area Channel at the 2400MHz ISM band and 2360MHz band. We outline a need for open hardware and measurement data to facilitate robust standardization of the new Body Area Networks. We demonstrate typical analyses on a public data set, with reference to previous works, and show how complex network topologies may be simulated through simple real measurements using reciprocity.

Statistical characterization of the dynamic narrowband body area channel

A statistical characterization of the narrowband dynamic human on-body area channel, with application to biomedical/health information monitoring, is presented based on measured received signal amplitude. We consider varying amounts of body movement, and a variety of transmit-receive pair (Tx-Rx) locations on the human body. The characterization is presented for two different frequencies, near the 900 MHz and 2400 MHz Industrial, Scientific and Medical (ISM) bands. Common distributions used to describe fading statistics are compared to the received signal component for nine different Tx-Rx pair locations for the subjectpsilas body standing, walking and running. The Lognormal distribution provides a good fitting model, particularly when the subjectpsilas body is moving. The fit is independent of Tx-Rx pair locations. The Rayleigh distribution is a very poor fit to the received signal amplitude statistics.

Stability of Narrowband Dynamic Body Area Channel

The stability of a dynamic narrowband on-body area channel is characterized based on real-time measurements of the time domain channel impulse response (CIR) at frequencies near the 900- and 2400-MHz industrial, scientific, and medical (ISM) bands. A new parameter, channel variation factor, characterizes channel coherence time. Body movement is considered at various transmit-receive pair locations on the human body. Movement has considerable impact on the stability of the channel, a reasonable assumption for coherence time is approximately 10 ms, and there is greater temporal stability at the lower frequency.

Performance of Piconet Co-Existence Schemes in Wireless Body Area Networks

Coexistence of multiple wireless body area networks (WBAN) is a very challenging problem because each piconet can have a large number of sensors and their movement is unpredictable. Moreover, suitable global coordination schemes do not exist as there is no natural choice of coordinator between piconets. Adaptive schemes that work well with low-occupancy channels, such as listen before transmit, are not a wise global solution because of the potential for high levels of traffic in any one area [1]. In this paper we investigate the performance of three classic multiple-access schemes - namely TDMA, FDMA and CDMA - for (inter-network) piconet coexistence. We first consider a theoretical analysis of these schemes and then simulate each scheme using real-world interference measurements. It is found that co-channel interference could significantly degrade system performance if left unchecked, and that TDMA and FDMA are better choices than CDMA in terms of co-channel interference mitigation.

Interference in body area networks: Distance does not dominate

Inter-network interference is a significant source of difficulty for wireless body area networks. Movement, proximity and the lack of central coordination all contribute to this problem. We compare the interference power of multiple Body Area Network (BAN) devices when a group of people move randomly within an office area. We find that the path loss trend is dominated by local variations in the signal, and not free-space path loss exponent.

Dynamic Narrowband Body Area Communications: Link-Margin Based Performance Analysis and Second-Order Temporal Statistics

A dynamic narrowband on-body area communications scenario is characterized with respect to link margin as a difference between system operating point, in terms of receive power, and receiver sensitivity. The characterization is based on an extensive measurement campaign near the 900 MHz ISM bands, with a number of different human subjects moving at a range of speeds in an indoor-office scenario. Key implications for operating reliability in terms of outages, meeting latency requirements, infeasibility of interleaving and limits upon packet duration are drawn from this link margin analysis pertinent to body-area-communications system design. The need for receive hardware with good receiver sensitivity is highlighted. Further to this context important second-order statistics are given, such as fade duration, as well as a novel measure: average fade magnitude. Distributions are given to accurately characterize these second order statistics. Along with link margin analysis, this modeling can be used to verify possible implementations, and help in system design.

Interference in body area networks: Are signal-links and interference-links independent?

Network-to-network interference is a challenging problem in wireless body area networks which move frequently and operate in a non-coordinated way. In this paper, we characterize interference based on field measurements. We examine the correlation and independence between the desired (signal) and interference channels. The results show that over long periods, the two channels are statistically un-correlated. Over a short periods, the channels may become correlated, particularly when the channel variation is small.

A simulator for the dynamic on-body area propagation channel

A Weibull fading channel simulator appropriate to the dynamic (very) narrowband on-body area propagation radio channel has been presented. The match of second order statistics with theoretical expressions, and the approximate match to measured second order statistics, confirms both its theoretical and practical value.