An Experimental Evaluation of Switched Combining Based Macro-Diversity for Wearable Communications Operating in an Outdoor Environment

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 macro-diversity 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 four-base 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.