Exploiting multiple-input multiple-output in the personal sphere

An analysis of the propagation characteristics of communication links in the personal sphere is presented. The results of two wideband measurement campaigns in the 5.2 GHz band involving on-body multiple-input multiple-output (MIMO) arrays are reported. In the first measurement, transmission takes place between on-body antennas and a uniform linear array, positioned at close range and with line-of-sight (LOS) propagation conditions. Despite the LOS operation, MIMO is shown to offer a significant increase in the information theoretic capacity of the system when compared with a conventional single-input single-output (SISO) antenna system. Although this appears counter-intuitive to the well-known fact that uncorrelated scattering results in high capacity, two previously less well-known mechanisms are highlighted to explain this result. This analysis reveals the potential use of MIMO in personal area networks. The second measurement campaign uses two on-body MIMO arrays to focus on the subject of body area network propagation. Analysis of the SISO characteristics of the links highlights the influence of the user on the channel. Body shadowing and user motion are shown to lead to multiple rapid changes in the channel characteristics. Again, MIMO is shown to be able to offer performance enhancement. In the measured channels, polarisation diversity is shown to outperform spatial diversity.