Applications are emerging that feature multiple implanted devices as part of an intra-body network. Establishing high bandwidth communications between such devices is challenging and there is a need to understand the principles of the intra-body channel. This paper presents a numerical analysis of the wave propagation between identical antennas in the MedRadio operating band (2.36-2.40 GHz) within cylindrical three layered tissue equivalent phantoms. The results presented show the effect of dielectric boundaries and different tissue properties on dominant wave propagation paths and link gain which provides essential information for efficient system design.

This paper investigates the potential improvement in signal reliability for outdoor wearable communications channels operating at 868 MHz using switched combining based macro-diversity. In this paper, a number of different macrodiversity configurations consisting of two and four base stations were considered to help mitigate the impact of body shadowing upon a wearable node, which was located on the central chest region of an adult male. During the field measurements, five different walking movements were performed, and then analyzed to investigate the efficacy of using macro-diversity. It was found that all of the considered switched combining schemes, including switch-and-stay combining, switch-and-examine combining (SEC) and SEC with post-examining selection (SECps) provided a worthwhile signal improvement when an appropriate switching threshold was adopted. The maximum diversity gain obtained in this paper was found to be 19.5 dB when using fourbase station SECps. The diversity gain, the number of path examinations, and the number of path switches between base stations for the switched combiner output varied according to the determined switching threshold, highlighting the importance of the selection of an appropriate threshold level. Furthermore, the performance/complexity tradeoff is demonstrated. Finally, the fading behavior at the output of the switched diversity combiners was then characterized using the diversity specific equations developed under the assumption of independent and non-identically distributed Nakagami-m fading channels. Over all of the measurement scenarios considered in this paper, the theoretical models provided an adequate fit to the fading observed at the output of the virtual switched combiner.

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.

A combined antennas and propagation study has been undertaken with a view to directly improving link conditions for wireless body area networks. Using tissue-equivalent numerical and experimental phantoms representative of muscle tissue at 2.45 GHz, we show that the node to node |S21| path gain performance of a new wearable integrated antenna (WIA) is up to 9 dB better than a conventional compact Printed-F antenna, both of which are suitable for integration with wireless node circuitry. Overall, the WIA performed extremely well with a measured radiation efficiency of 38% and an impedance bandwidth of 24%. Further benefits were also obtained using spatial diversity, with the WIA providing up to 7.7 dB of diversity gain for maximal ratio combining. The results also show that correlation was lower for a multipath environment leading to higher diversity gain. Furthermore, a diversity implementation with the new antenna gave up to 18 dB better performance in terms of mean power level and there was a significant improvement in level crossing rates and average fade durations when moving from a single-branch to a two-branch diversity system.

A compact higher-order mode microstrip patch antenna (HM-MPA) suitable for on-body communications at 2.45 GHz is presented. Using FDTD simulations we show that the HM-MPA had an impedance bandwidth of 150 MHz and a relatively good bodyworn efficiency of more than 60% when placed in close proximity from a lossy medium with the characteristics of muscle tissue. On-body performance was investigated by modelling S21coupling of two HM-MPAs spaced 200 mm apart on a muscle tissue layer. The HM-MPA coupling results are comparable to those achieved using a quarter wave monopole antenna on the same size of groundplane, mounted normal to the tissue surface. Considering that the HM-MPA has the benefit of being low-profile and physically more robust, it is a promising solution for over body surface applications.