Spatial diversity and correlation for off-body communications in indoor environments at 868 MHz

For the first time, cross-correlation values for the fading experienced for antennas mounted at different locations on the upper human torso are reported. Time-synchronized narrowband measurements at 868 MHz have demonstrated that when the human body is mobile, signal branches on the upper limbs, anterior chest, abdomen and back shoulders are adequately de-correlated with cross-correlation coefficients no greater than 0.6. Selection, maximal ratio and equal gain diversity combining techniques were used to combine spatially separated branches, with up to 9.6 dB diversity gain for a system operating with left chest and back right positioned antennas. When six bodyworn diversity branches are available, maximal ratio and equal gain combining eradicate all fades beyond 3 dB below the local mean signal level.