Biomedical Engineering Reference
In-Depth Information
Table
2
shows that the lowest value of DG is obtained in the chest-to-waist link,
when there is a LOS link between Tx and Rx. This lowest value is due to the higher
imbalance with antenna spacing for different positions of Rx with respect to Tx on
the waist in an indoor environment at location 1.
Power imbalance and higher correlation, which results from dominant direct
rays, compared to multi-path components. The highest value of DG is obtained
in the back-to-waist channel, which is a NLOS channel. The higher value of
DG and low power imbalance suggest that signals are reasonably uncorrelated
and also the movements of body parts result in higher decorrelation between the
two branch signals. For all other partial LOS channels (i.e. the wrist-to-waist,
ankle-to-waist and head-to-waist cases), the DG lies between the chest-to-waist and
back-to-waist channels. This is due to the fact that the multi-path components are
slightly dominating in these cases, because of the scattering from different parts of
the human body and the rich scattering environment.
Table
3
shows the DG using different combining techniques and diversity param-
eters in an anechoic chamber, at 0.34
λ
0
spacing between diversity branch antennas.
Very low values of the DG for all cases, compared to those found in the indoor envi-
ronment, confirms the expectation that there are no reflections from the surrounding
environment and that the only source of multi-path components in the anechoic cham-
ber was the human body itself. The differences in DG observed between the different
on-body channels are due to the same causes described for the indoor environment
in the previous paragraph.
Tables
2
and
3
show that, due to the variation in Rx antenna position on the body,
the MRC-DG changes from 0.01 to 0.5 dB for the anechoic chamber case and 0.14
to 0.8 dB for the indoor environment. Results therefore show that variation of Rx
antenna position will not severely affect the measurement of DG. For the remaining
results, only position 2 of diversity antenna (shown in Fig.
2
) is used for each Rx
location.
Comparison of Diversity Gain for the Free Space and Indoor
Environments
A comparison of MRC-DG is shown in Fig.
5
for five different Rx positions (position
2 for each Rx is taken as shown in Fig.
2
), in both the anechoic chamber and three
different locations in an indoor environment, with Tx on the waist. The results
are compared with the measurement results at 2.4 GHz presented in [
1
] in an indoor
environment (this is an approximate comparison; as for both measurement results,
subject and indoor environment are different, which contributes to DG). Low values
of DG in the chamber are due to less scattering from the surrounding environment,
compared to the indoor case, where there are rich multi-path reflections. In the cham-
ber, only reflections from the moving human body parts play a role in acquiring DG;
in an indoor environment, both the human body parts and surrounding environment
contribute to DG. This shows the fact that diversity is useful only when the human
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