Design and Simulation of a MAC Protocol for WBAN Communication Scenarios - Ultra Wideband Wireless Body Area Networks - page 44

3.3.1 Transmission Power Regulations of the Gated UWB
Pulse Transmission

According to the Federal Communications Commission (FCC) regulations a UWB
signal is power limited by measured Full Bandwidth (FBW) peak power of 0 dBm
(1 mW) and measured average power density of -41.25 dBm/MHz (75 nW/MHz)
[ 15 , 16 ]. These power measurements assume a resolution bandwidth of 1 MHz and
an integration time of 1 ms for the measuring equipment.
The peak emission limit of a UWB signal depends on the resolution bandwidth
of the spectrum analyzer and varies according to ( 3.4 )[ 16 ]:

dBm

B R
50

P peak ¼ 20 log ð 3 : 4 Þ

where P peak is the peak power limit and B R is the resolution bandwidth of the
spectrum analyzer. For average power measurements, a resolution bandwidth of
1 MHz and an integration time of 1 ms should be used while the resolution
bandwidth can be varied between 1 and 50 MHz according to ( 3.4 ). A data packet
is transmitted at much shorter time than the integration time of 1 ms as recom-
mended by the FCC regulations. The data transmission resembles a gated system
where a sensor node transmits a data packet within a very short time slot and
switches off the transmitter till the next transmission slot. If P peak is the measured
peak power and P avg is the measured average power, the maximum allowable
UWB transmit power for a system with much higher PRF than the resolution
bandwidth of the spectrum analyzer can be given by ( 3.5 )[ 16 ]:

P peak ¼ P peak
sR

¼ P avg
sR

ð 3 : 5 Þ

where P peak is the actual maximum transmit power of the UWB signal, s is the
UWB pulse width and R is the pulse repetitive frequency. This equation suggests
the peak emission power limit for a continuous transmission system, but not for a
gated system such as the system described in this chapter. An update to the original
FCC standards is made in 2005 allowed using higher transmit power for gated
UWB systems [ 17 ]. If d represents the duty cycle of the packet transmission based
on an integration time of 1 ms, it can be seen from ( 3.6 ) that the total allowable
transmit power is much higher for a gated system than that of a non-gated system.

P peak ¼ P avg
sRd

ð 3 : 6 Þ

The UWB based WBAN sensor node design example given in this chapter is
simulated with a PRF of 100 MHz, which is comparably high relative to a reso-
lution bandwidth of 1 MHz. Hence it is considered a high PRF system. These