Biomedical Engineering Reference
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obtained for UWB on-body diversity at location 1 are compared with the results of
Khan et al. at 2.4 GHz presented in [
1
] in an indoor environment (comparison plot is
shown in Fig.
5
). This is an approximate comparison; as for both measurement results,
human subject and indoor environment were different). Results approximately agree
for the chest-to-waist link (where there is direct LOS communication between Tx
and Rx). However, there is disagreement for partial LOS cases and NLOS cases
(i.e. the head-to-waist, wrist-to-waist and back-to-waist links); this is due to the
fact that, for NLOS cases, the reflections and contributions by the environment
have a large effect on the quality of the signal and the measurements were done
in different environments. In addition, the subject-specific behaviour of the UWB
on-body channel (see, for example, the work of Sani et al. [
30
]) will also play a role
in explaining the disagreement between the results.
Concluding Remarks on On-Body UWB Diversity
Spatial diversity techniques for UWB on-body radio channels have been investigated
and analysed. Various scenarios, including changes in antenna on-body positions,
the location of subject in the indoor environment and also variation in the inter-
spacing between antenna element branches, have been considered. Results showed
that, for dense multi-path environments, the benefits of applying diversity techniques
were significant for the NLOS cases, where there are low power imbalances due to
uncorrelated signals, in comparison to the LOS scenarios.
Maximum variations of 0.5 and 0.8 dB, for the anechoic chamber and the indoor
environment cases, respectively, have been observed in response to slight changes
in the on-body antenna position. This demonstrated the potentially negligible ef-
fect of accidental and inherited on-body element location shift, due to the subject's
sudden movement. The results presented here gave indications of the beneficial ap-
plications of diversity antenna techniques for potential performance enhancement
of UWB body-centric wireless communications as experienced in narrowband tech-
nologies. This will be increasingly appreciated for off-body communications, due to
the variation in the spatial and angular parameters of the multi-path components that
will contribute to enhanced DG. Hence, in the next section UWB off-body spatial
diversity is being investigated.
Ultra-Wideband Off-Body Diversity Performance Analysis
Reliability of Diversity Measurements Versus Small Variations in
On-Body Diversity Receiver Position
In order to ensure that all measurements are reliable, for each channel a small grid
incorporating in the Rx antenna was made to see how the small variation in position of
diversity antenna will affect the measurement of DG. For specific cases, such as the
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