Biomedical Engineering Reference
In-Depth Information
1
2
Rx5
Diverstiy Rx
Antennas
Tx Antenna
1
2
Rx1
34
12
34
Rx2
1
Rx4
(At back)
Tx
2
1
3
Rx3
0.5 m to 4 m
Fig. 2
Measurement setup for ultra-wideband (UWB) on-body and off-body diversity (whereas,
for on-body case, transmitter (Tx) was placed at left side of waist instead of away from body as
shown here)
of the antennas up to 3 m/s during the movements. These give shifts of about 23.25
Hz with average speed of motion of 1 m/s and about 69.76 Hz with 3 m/s. The noise
floor for the measurement was at
−
90 dBm.
For on-body case, the position of Tx was fixed at the left side of the waist (belt). The
receiving antenna was placed at five different positions: on the right chest (Rx1), right
wrist (Rx2), right ankle (Rx3), on the centre of the back (Rx4) and on the right side of
the head (Rx5), as shown in Fig.
2
. For off-body case, the access point (AP) was fixed
at waist height (1 m above the ground). The receiving antenna was placed at same
five positions, as for on-body diversity. The distance between the subject carrying
diversity branch receivers and AP is varied from 0.5 to 4 m (Tx and Rx locations are
as shown in Fig.
2
). A number of measurements were made for each Rx position (as
shown in Fig.
2
), to check the reliability of the measurements with respect to slight
variations in the position of the antenna on the body; this was achieved by using a
small grid, so that the variation was controlled. Measurements were repeated in three
different locations in the indoor environment (denoted in Fig.
3
as Loc. 1, Loc. 4
and Loc. 7, respectively) to highlight the effects of varying multi-path environments
on the diversity measurements and results for on-body diversity. For off-body case,
measurements were repeated in eight different locations in an indoor environment,
each with a step of 0.5 m (denoted in Fig.
3
as Loc. 1 to Loc. 8 respectively).
This was done to highlight the effect of varying multi-path environments and the
distance between the off-body AP and the human body carrying diversity antennas,
on the diversity measurements and results. Measurements for uplink (from Tx on the
waist/off-body AP to diversity antenna (Rx) on different locations of the human body)
and downlink (from diversity antenna on the waist/off-body AP to Tx antenna on the
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