Biomedical Engineering Reference
In-Depth Information
Fig. 3.7 Variation of full
bandwidth peak power with
duty cycle
measured power limitations can
be converted to maximum allowable
FBW
transmit power limits using (
3.7
) and (
3.8
)[
16
,
18
];
2
1
d
B
p
R
P
peak
7
:
5
10
8
W
ð
3
:
7
Þ
2
2
W
B
R
50
10
6
B
p
R
P
peak
0
:
001
ð
3
:
8
Þ
where B
p
= 1/ s. The maximum allowable FBW transmit power is governed by
smaller of the two P
peak
values in (
3.7
) and (
3.8
).
For the simulated system, a pulse width of 2 ns is used. Hence B
p
in (
3.7
) and
(
3.8
) is equal to 0.5 GHz for the UWB signals used in the simulations. Figure
3.7
shows the variation of maximum allowable FBW transmit power values with the
duty cycle (d) for a sensor node that generates UWB signals with a PRF of
100 MHz and a pulse width of 2 ns. Resolution bandwidth (B
R
) is taken as 1 MHz
according to the FCC specifications. According to Fig.
3.7
, the transmit slot of the
UWB data should be kept within 187.5 ls (micro seconds) in order to transmit at
maximum allowable power of 0.01 mW that complies with the FCC limitations.
3.3.2 BER Analysis of Multiple PPB Scheme
Since the power required to transmit a data bit is equal to the summation of the
power of number of pulses sent to represent that data bit, a considerable power
saving can be achieved if allocation of the number of PPB can be dynamically
changed according to the minimum Bit Error Rate (BER) requirement at the
receiver end. The timing parameters, that are used in this MAC protocol is decided
using this calculation and are further described in this section. An energy-detecting
