Adrian McKernan

Received signal characteristics of outdoor body-to-body communications channels at 2.45 GHz

In this paper we conduct a number of experiments to assess the impact of typical human body movements on the signal characteristics of outdoor body-to-body communications channels using flexible patch antennas. A modified log-distance path loss model which accounts for body shadowing and signal fading due to small movements is used to model the measured data. For line of sight channels, in which both ends of the body-to-body link are stationary, the path loss exponent is close to that for free space, although the received signal is noticeably affected by involuntary or physiological-related movements of both persons. When one person moves to obstruct the direct signal path between nodes, attenuation by the persons body can be as great as 40 dB, with even greater variation observed due to fading. The effects of movements such as rotation, tilt, walking in line of sight and non-line of sight on body-to-body communications channels are also investigated in this study.

Technical communique: Sampled-data gain scheduling of continuous LTV plants

This paper discusses the design of gain-scheduled sampled-data controllers for continuous-time polytopic linear parameter-varying systems. The scheduling variables are assumed to be available only at the sampling instants, and a bound on the time-variation of the scheduling parameters is also assumed to be known. The resultant gain-scheduled controllers improve the maximum achievable delay bound over previous constant-gain ones in the literature.

Characterization of inter-body interference in context aware body area networking (CABAN)

The characterization and understanding of body to body communication channels is a pivotal step in the development of emerging wireless applications such as ad-hoc personnel localisation and context aware body area networks (CABAN). The latter is a recent innovation where the inherent mobility of body area networks can be used to improve the coexistence of multiple co-located BAN users. Rather than simply accepting reductions in communication performance, sensed changes in inter-network co-channel interference levels may facilitate intelligent inter-networking; for example merging or splitting with other BANs that remain in the same domain. This paper investigates the inter-body interference using controlled measurements of the full mesh interconnectivity between two ambulatory BANs operating in the same environment at 2.45 GHz. Each of the twelve network nodes reported received signal strength to allow for the creation of carrier to interference ratio time series with an overall entire mesh sampling period of 54 ms. The results indicate that even with two mobile networks, it is possible to identify the onset of co-channel interference as the BAN users move towards each other and, similarly, the transition to more favourable physical layer channel conditions as they move apart.

Event-based sampling for wireless network control systems with QoS

Communications load in a wireless channel can saturate the network when the wireless link between stations is weak. This paper shows that, by using a state-differential event based sampling scheme with QoS, this load can be reduced such that a control loop closed over that network can remain stable for much worse wireless channel conditions. By varying the event threshold, systems with high state variance will have higher sampling rates than those without, while the overall throughput of the system is reduced to a level which does not saturate the network.

GPS-Disciplined Analog-to-Digital Converter for Phasor Measurement Applications

This paper presents a data acquisition unit which synchronously samples multiple channels in a manner such that the time of day at which each sample is taken is known. This allows measurements taken at multiple locations to be compared with confidence. The intended application is wide area electrical power system measurements, in particular phasor measurement units (PMUs). The novelty of the authors’ design is the application of an open hardware development platform to discipline a commodity analog-to-digital converter (ADC) to a broadcast time signal, usually but not exclusively GPS. The methodology used creates a driver layer for the ADC to achieve real-time sampling in a nonpreemptive Linux environment. The use of open hardware and software addresses the need for a transparent instrument for use in research and development of PMU technology. Through a choice of either a software or hardware phase-locked loop, the ADC is controlled to acquire exactly 256 samples per nominal power system cycle (i.e., 50/60 Hz), precisely time synchronized to GPS, at 16-b resolution and 94.2-dB SNR. The design of a printed circuit board expansion board featuring all necessary components is provided. The performance of the system is evaluated. Interoperability and data exchange with other systems is achieved by use of open schemas and communication protocols. This allows rapid integration with popular numerical simulation environments.

Simultaneous channel measurements of the on-body and body-to-body channels

In this paper, we characterize the simultaneous channel response of narrowband on-body and body-to-body channels at 2.48 GHz using the κ-μ fading model. The measurements considered three nodes, two of these were located on the front-chest and front-central-waist of an adult male, and the third node was located on the front-central-waist of an adult female. Multiple human mobility scenarios were considered for three different environments namely an anechoic chamber, reverberation chamber and laboratory environment. For all of the measured channels, the κ-μ probability density function (pdf) provided an excellent fit to the empirical distribution of the measured short-term fading. In addition, the channel measurements also demonstrated the channel reciprocity property for each of the on-body and body-to-body links, and scenarios considered here. Finally, we also show that the sample period of the measurement system developed for this study was well within the coherence time of the channel.

Co-design of IEEE 802.11 Based Control Systems

This chapter is concerned with wireless control using IEEE 802.11 or WiFi technology. A cart-mounted inverted pendulum was used to compare wireless control, using a packet-based DMC predictive controller against the conventional hard-wired performance. Importantly, the random delay from the 802.11 channel is modelled by an Inverse Gaussian probability distribution derived experimentally from practical measurements in a wireless reverberation chamber. The same application is also employed to expose the advantages of variable sampling for wireless control, specifically using state differential sampling. In both cases, the round trip delay constitutes a QoS measure to support the overall co-design approach to control, enabling the controller to respond to changing channel conditions to maintain the designed performance. While the chapter has a strong application focus, the results are presented in the general context of an up-to-date review of the relevant research in wireless network control. This includes alternative approaches to theoretical closed-loop stability and proposals for packet-based predictive control and sample rate adaptation.