Biomedical Engineering Reference
In-Depth Information
chest and the back (see Fig.
3
), a 2
2 grid was applied with approximate spacing of
5 mm and in the case for the ankle and the head a one dimensional grid was used with
similar spacing. Table
5
shows DG values based on different combining techniques,
envelope correlation (
ρ
e
) and power imbalance between two branches for Loc. 2
in an indoor environment (as shown in Fig.
3
) at 0.34
λ
0
spacing between diversity
branch antennas (whereas, power imbalance is calculated by using the ratio of mean
power of two branch signal envelopes).
Results show that the values of DG are lower, when Rx is placed at chest and ankle
as compared to other links, because there is a direct LOS link between Tx and Rx.
Higher power imbalance and relatively higher value of correlation are the factors that
plays a role in reducing DG. The highest value of DG is obtained in NLOS channel,
i.e. when Rx is placed at the back. Higher value of DG and low power imbalance
suggests that movements of body parts result in higher decorrelation between the
two branch signals. For other partial LOS Rx locations, i.e. wrist and head cases, DG
lies between the LOS and NLOS channels (i.e. chest and back). This is due to the
fact that for partial LOS cases, branch signals are less uncorrelated, as for the case of
NLOS scenario. From the Table
5
, it is obvious that the variations of DG with slight
changes in Rx locations for each position is very small (varies from 0.2 to 1.46 dB).
It leads to the conclusion that accidental variations in receiver locations on the body
have negligible effects on the DG for the UWB off-body diversity as well like for
the on-body case. In the rest of off-body diversity discussion, only position 2 for
each Rx location is considered(except for wrist case where position 1 is considered).
×
Ultra-Wideband Diversity Gain Variations Versus Different
Locations in an Indoor Environment
Table
6
shows the DG (using different combining techniques) and different diversity
parameters for 0.34
λ
0
spacing between the diversity branch antennas at eight differ-
ent locations in an indoor environment (marked as Loc. 1-Loc. 8, each location is at
spacing of 0.5 m from the every other location, as shown in Fig.
3
). Compared to all
other channels, highest DG is obtained as expected, for the back channel (i.e. NLOS
scenario), and due to highly uncorrelated signals and very low power imbalance.
Same reasoning can be applied for DG variation for all other links as described ear-
lier in “Reliability of Diversity Measurements Versus Small Variations in On-Body
Diversity Receiver Position”. For all channels due to the change of subject position
(from Loc. 1 to Loc. 8 as shown in Fig.
3
), there are slight variations in DG and other
diversity parameters (i.e. power imbalance and correlation). The maximum DG vari-
ations among different subject locations for Rx on chest (with respect to off-body Tx)
are only 1.58 dB. For all other Rx locations (i.e. head, wrist, ankle and back), the max-
imum DG variations with respect to subject position are below 1.5 dB. These lesser
variations in DG are due to the fact that for off-body diversity case, there is very small
change in power imbalance and correlation coefficient with respect to the change of
locations. From the results it is obvious that off-body diversity is independent of
subject location, carrying diversity branch antennas in an indoor environment.
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