Biomedical Engineering Reference
In-Depth Information
(a)
Sensor
address
Stop
bit
Sync
Preamble
Data
140 pulses
12 bits
5 bits
80 bits
1 bit
(b)
Sensor
address
5 bits
Stop
bit
1 bit
Sync
Preamble
Data
140 pulses
12 bits
30 bits
(c)
Sensor
address
5 bits
Sync
Preamble
140 pulses
12 bits
(d)
Sensor
Address
Msg.
type
Control
message
5 bits
1 bit
5 bits
(e)
Beacon
4 bits
Fig. 6.1 a Transmit data packet for continuous sensors on the IR-UWB link, b transmit data
packet for periodic sensors on the IR-UWB link, c initialization request packet, d receive control
packet on the narrowband link, e beacon
Transmit data packet structure is modified from the one used in
Chap. 3
con-
sidering the data generation capabilities of the dual-band sensor nodes. The
micro-controller used in the dual-band sensor nodes is capable of generating data
bits that can be modulated with a minimum of 20 Pulses Per Bit (PPB) when the
IR-UWB pulse generator module is operating at a Pulse Repetitive Frequency
(PRF) of 100 MHz. This results in a maximum achievable instantaneous data rate
of 5 Mbps. Hence, 20 PPB is chosen as the minimum allowable PPB for the UWB
transmission. Maximum allowable PPB value is chosen to be 100 PPB considering
the lower bounds of data rate requirements. 140 IR-UWB pulses are sent during
the Sync portion of transmit packet by all the sensor nodes irrespective of the
number of PPB allocated for the data transmission. This is used for synchroni-
zation of the Analog to Digital Converter (ADC) sampling as discussed in a
following section. Initialization packets are used during the first two time slots of
the super frame structure for the purpose of contention based sensor initialization.
Control packets on the narrowband channel are mainly used for sensor initiali-
zation and dynamically assigning PPB value for each sensor node during changing
channel conditions. Beacon packets are used for the super frame synchronization.
They are sent on the narrowband channel that operates at a data rate of 19.2 kbps.
All the bit lengths used in packet structures are calculated based on factors, such as
the amount of data that should be transmitted using a particular packet, maximum
allowable PPB value that is to be used in each packet transmitted on the UWB
channel, and maximum allowable duty cycle for data transmission using each
packet.
