Biomedical Engineering Reference
In-Depth Information
antennas a promising technique to enhance the performance of UWB BCWNs [
3
].
There has been an increasing interest in diversity and multiple-input, multiple-output
(MIMO) techniques for enhanced mobile and wireless communications in recent
years [
4
-
8
]. There are some studies presented in the open literature where the bene-
fits of diversity techniques for body-centric communications in narrow-band systems
have been investigated [
1
,
3
,
9
-
17
]. The effect of human body, especially the head
and the hand, on the performance of diversity antenna at the mobile handset was dis-
cussed in [
9
] by presenting the change in diversity gain (DG) and envelope correlation
with angle of inclination of the antenna and its distance from the head. Introductory
studies for on-body diversity measurements at 2.45 GHz were presented in [
10
].
The diversity performances were evaluated in terms of DG, power imbalance and
envelope correlation coefficients between the two receiving channels. A compre-
hensive study of diversity for an on-body channel at 2.45 GHz was presented in
[
1
], using different antennas and diversity types. A significant gain was observed
for non-line of sight (NLOS) channels and dynamic channels involving large body
movements. The uplink and downlink diversities were also calculated and found to
be similar. A comparison of spatial and pattern diversity was presented in [
11
]. It
was observed that spatial diversity gave a greater improvement than pattern diversity,
in terms of DG. Cotton and Scanlon [
13
,
14
] have presented first- and second-order
statistics and some diversity results for off-body and on-body channels, at 2.45 GHz
and 868 MHz, respectively. On-body diversity at 868 MHz has been thoroughly
investigated in [
14
], with application to medical implants. Off-body spatial diversity
and correlation coefficient evaluation was performed in [
15
,
16
] at 868 MHz and 5.8
GHz respectively. Diversity performance using textile antennas for fire-fighters was
presented in [
17
].
Other studies on UWB-MIMO and UWB diversity were presented in [
18
-
27
].
Antenna diversity results for the UWB indoor channel are presented in [
21
], with an
emphasis on differences between virtual and real compact arrays, including mutual
coupling effects. UWB-MIMO for on-body has been investigated in [
19
], using
frequency space polarisation. The key findings in [
19
] were that, in BCWN, the
MIMO channel capacity is mainly determined by the power imbalance for both spatial
arrays and polar arrays. It was also found that the MIMO capacity decreases with
the frequency. Roy et al. presented an innovative space-time spatial model for UWB
multi-sensor, multi-antenna body area networks (BANs) in [
27
]. However, to the
authors' knowledge, UWB spatial diversity for on/off-body communications has not
yet been investigated systematically and thoroughly. In this study, the spatial diversity
is investigated for UWB on/off-body communication channels. The improvement
due to diversity is often measured in terms of DG; this is basically an improvement
in signal strength (or, equivalently, signal-to-noise ratio or bit-error rate) compared
with that observed with a single antenna at a certain outage probability [
1
,
2
,
4
,
7
,
8
].
The outage probability is the probability that the system performance falls below a
minimum performance threshold (typically defined in terms of signal-to-noise ratio)
within a specified time period.
Search WWH ::
Custom Search