Biomedical Engineering Reference
In-Depth Information
1
0
1
(a)
TS1 TS2
TS1 TS2
(b)
1
1
0
TS1 TS2
TS1 TS2
Fig. 3.6
Pulse train for '1' '0' '1' bit pattern using a two PPB and b three PPB in BPPM
outside the body, in-body propagation model is used for the distance up to the
surface of the skin, and indoor model is used for rest of the distance.
Amplitude Shift Keying (ASK) scheme is used for the narrow band commu-
nication, which operates based on the 433 MHz ISM band. The power level for the
narrowband signal is kept at -25 dBm, which is a reasonable value for operation
with less interference. Ricean fading channel for indoor propagation [
14
] is used to
simulate the propagation in the narrowband channel. The narrow band signal for
in-body communication is assumed to follow the free space channel model.
3.3 Cross Layer Design
The MAC protocol described in this chapter incorporates unique physical layer
properties of UWB transmission in its design. Hence, it forms a cross layer
architecture. A simple Binary Pulse Position Modulation (BPPM) technique is
used as the modulation scheme for the UWB transmission. This eliminates the
complexities introduced by the use of complex modulation schemes for low power
WBAN applications. The sensor nodes in the simulations use two mechanisms to
ensure that the transmit power is managed effectively. The first mechanism is to
use a gated pulse transmission scheme, where a sensor node transmits the UWB
data for a given time period and go into low power mode till the next transmission
slot. A dynamically varying multiple pulses per bit (PPB) scheme is used as the
second scheme in order to optimize the transmit power consumption by controlling
the bit transmission time. These two mechanisms are discussed in detail under this
section. Figure
3.6
depicts the use of 2 and 3 PPB schemes for sending data bits.
