Biomedical Engineering Reference
In-Depth Information
reliable and power efficient multi sensor communication between dual-band sensor
nodes and coordinator node [
6
,
7
]. This chapter describes the implementation and
evaluation of this dual-band MAC protocol in a hardware based system [
7
,
8
]. The
MAC protocol is adjusted to suit the implementation using available hardware
platforms. Differences between the simulations described in
Chap. 3
and system
implementation of the MAC protocol that is discussed in this chapter are listed
below;
1. On-Off-Keying (OOK) modulation is used instead of Binary Pulse Position
Modulation (BPPM) considering the ease of hardware implementation of OOK
modulation, and its similar performance to BPPM.
2. A direct conversion receiver that down-converts the received IR-UWB pulses
using a mixer and apply low pass filtering to broaden the down-converted
pulses is used instead of an energy detection based receiver architecture used
the direct conversion receiver using off-the-shelf components, ability to operate
without the use of any control signals as compared to energy detection receiver,
and small power consumption.
3. Data packet lengths and time slot durations of the super frame are adjusted
according to the communication scenarios presented in this chapter.
Apart from these differences, implementation of the MAC protocol is similar to
the MAC protocol discussed in
Chap. 3
. A full system implementation, including a
FPGA based firmware implementation is presented in this chapter. Important
algorithms used in the MAC protocol are described in terms of flow diagrams and
Very High Speed Integrated Circuit Hardware Description Language (VHDL)
code implementation examples. This chapter also presents the experimental
evaluation of the dual-band MAC protocol in terms of Bit Error Rate (BER),
initialization delay and power consumption.
6.2 Development of Packet Structure
Data communication between dual-band sensor nodes and the coordinator node
occurs using the beacon enabled super frame structure described in
Chap. 3
. Data
and control packets are sent within an allocated super frame time slot in order to
realize a reliable communication link. A maximum super frame time slot duration
of 100 ls is used for data transmission of continuous sensor nodes and that of
periodic sensor nodes is chosen as 50 ls. These timing parameters ensure that
sensor nodes transmit at a duty cycle that is less than 18.75 % based on a super
frame duration of 1 ms, enabling sensor nodes to utilize the maximum full
implementation of the MAC protocol is shown in Fig.
6.1
.
