Biomedical Engineering Reference
In-Depth Information
Comparison Between Off-Body and On-Body Diversity
Off-body diversity results obtained here are compared with the on-body diversity
results presented earlier in this chapter. In both measurements, the same subject, Rx
locations and the NLOS cases where there is low power imbalance due to highly un-
correlated signals in comparison to the LOS scenarios. Maximum variation of 1 dB
has been observed due to slight changes in the on-body antenna position. This demon-
strates the potentially negligible effect of accidental and inherited on-body element
location shift due to sudden movement of the subject. Higher DG were obtained as
inter-spacing between diversity antenna branches increased with a few exceptions
where either the power imbalance or the correlation is high. Small variations in DG
due to changes in subject location within the indoor environment and orientation be-
tween AP and on-body diversity receiver shows that off-body diversity is independent
of subject location and orientation in an indoor environment. Results also demonstrate
that off-body diversity is almost 50 % more efficient than on-body diversity and off-
body diversity is more useful when it is considered as an uplink (i.e. diversity branch
antennas are on-body with respect to off-body Tx) as compared to downlink diversity.
Summary
Diversity for UWB body area networks is analysed, using various measurements
scenarios. The DG is calculated for five different on/off-body channels by plotting
cumulative distribution functions and it is found that DG value is very low for chamber
due to no reflections from surroundings as compared to indoor environment. Also, in
indoor environment and chamber, DG is lowest for LOS cases. There are significant
benefits of diversity techniques for NLOS cases as compared to LOS cases due to
low power imbalance and low correlation coefficient between the branch signals.
Comparison of on-body and off-body diversity shows a significant improvement for
the off-body case. It also reveals that the on-body diversity has almost similar impact
for both uplink and downlink diversity, whereas uplink is preferable over downlink
diversity for the off-body diversity case.
Analysis also shows that DG is independent of subject-specific behaviour. The
results presented in this chapter give indications of the beneficial applications of
diversity antenna techniques for potential performance enhancement of the ultra-
wideband body-centric wireless communications.
References
1. I. Khan, P.S. Hall, A.A. Serra, A.R. Guraliuc, P. Nepa, Diversity performance analysis for
on-body communication channels at 2.45 GHz. IEEE Trans. Antenna Propag.
57
(4), 956-963
(April 2009)
2. W.C. Jakes,
Microwave Mobile Communications
. (Wiley, New York, 1974)
3. I. Khan, P.S. Hall, Multiple antenna reception at 5.8 and 10 GHz for body-centric wireless
communication channels. IEEE Transac. Antenna Propag.
57
(1), 248-255 (Jan 2009)
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