Dino Miniutti

Challenges in body area networks for healthcare: the MAC

Body area wireless sensor networks (BANs) are a key component to the ubiquitous healthcare revolution and perhaps one of its most challenging elements from a communications standpoint. The unique characteristics of the wireless channel, coupled with the need for extreme energy efficiency in many healthcare applications, require novel solutions in medium access control protocols. We present the main characteristics and challenges associated with BANs from a healthcare perspective, and present some MAC techniques based on studies of the BAN channel that could be used to address these challenges.

Propagation Models for Body-Area Networks: A Survey and New Outlook

This article is a review of wireless body-area network (BAN) channel models, with observations about the selection of the best channel model in terms of both first- and second-order statistics. Particular insight into the dominant factors that affect propagation for body-area networks is given. Important second-order statistical measures are discussed, where coherence times and fade durations are of particular interest. The IEEE 802.15.6 standard is used as a basis for the review, with observations and insights given about body-area networks. In this context, narrowband and ultra-wideband (UWB) models are summarized for different measurement environments and carrier frequencies. On-body, in-body, and off-body propagation models are discussed where appropriate. In general, lognormal fading or gamma fading models of the body-area network channel are most applicable. A goodness-of-fit criterion that directly trades off model error and complexity is presented, which gives a new outlook for channel modeling. By this new outlook it is demonstrated that through significant simplification of individual link propagation models for body-area networks, it is possible to combine link models with only a few parameters. Common misconceptions regarding the appropriateness of applying traditional path-loss measures to these short-range networks are then exposed. Finally, the use of relays, which is an option in IEEE 802.15.6, is shown to be important for maintaining reliability in various body-area-network propagation scenarios.

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.

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.

Simple Prediction-Based Power Control for the On-Body Area Communications Channel

Methods for transmit power control based on simple long-term channel prediction for the general body-area communications channel are presented. The power control methods are based on large sets of empirical every-day activity data. Numerous transmit-receive pair (Tx-Rx) locations on the human body, i.e. on-body, for a typical body-area-network (BAN) are considered. With the use of a simple prediction method based on held samples, and an enhanced held simple prediction method that uses short term mean path loss with the held sample, optimal power allocation for long-term transmit power control is described. When tested, according to the draft IEEE 802.15.6 BAN radio standard, on empirical data, both power allocation methods are shown to be more reliable, and also more energy efficient in terms of transmit circuit power consumption, than systems that use typical set Tx power levels for BAN.

Characterization of the Body-Area Propagation Channel for Monitoring a Subject Sleeping

A dynamic characterization of the wireless body-area communication channel for monitoring a sleeping person is presented. The characterization uses measurements near the 2.4 GHz ISM band with measurements of eight adult subjects each over a period of at least 2 hours. Numerous transmit-receive pair (Tx-Rx) locations on and off the body for a typical body-area-network (BAN) are used. Three issues are addressed: 1) modeling of channel gain, 2) outage probability, and 3) outage duration. It is shown that over very large durations (far in excess of a delay requirement of 125 ms that is typical for many IEEE 802.15.6 medical BAN applications) there is not a reliable communications channel for star-topology BAN. The best case outage probability, with 0 dBm Tx power and - 100 dBm Rx sensitivity, is in excess of a packet-error-rate of 10%. Following from these issues the feasibility of using alternate on-body or off-body links as relays is demonstrated.

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.