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Number of sensor nodes and AP differs as per user’s interest of measurement, environment
and coverage area. Deploying mesh topology one should be very careful to know the
supportability of multi-hop structure (node talking to adjacent node) by selected devices. For
example, NI-WSN 3202 and Wireless HART support internode communication whereas
nodes like NI-WLS 9163 can be configured only in star topology.
Advantages of multi-hop network topology are, it helps to increase the distance of
communication and adds redundancy feature. It is also true that use of multiple AP can also
increases distance in star network topology.
2.1 Standard Transmission Protocol
The scalar data such as temperature, humidity, pressure, vibration have low sampling rate.
Vibration data have relatively high sampling rate compared to others. However, they are
considered to be less as compared to video and picture data. WSNs mainly deal with such
data having less scan rate (sampling rate). The advantage of low scan rate data is that WSN
can be designed based on low power and low bandwidth transmission protocols. It gives clear
concept of why ISM band is deployed in WSN as transmission protocol. ISM band is license
free 2.4 GHz band used by Wi-Fi, Zig-bee, Bluetooth and Wireless HART.
2.1.1 Bluetooth
Bluetooth is a low powered, low cost and short-range protocol governed by IEEE 802.15.1
standard. Bluetooth is promoted by Bluetooth Special Interest Group (SIG) [6].There are 5
different versions of Bluetooth namely, V 1.0/b, V1.1, V1.2, V2.0 and V 3.0. First three
versions use Gaussian Frequency Shift Keying (GFSK) as a modulation scheme and fourth
version uses GFSK,
⁄
Differential Quadrature Phase Shift Keying ( DQPSK) and 8
Differential Phase Shift Keying (8DPSK) as modulation scheme. The maximum data rate
supported by V 1.0/b, V1.1, V1.2 is 1 Mbps. V2.0 supports up to 3 Mbps and latest version
V3.0 supports up to 24 Mbps. Maximum transmission range of Bluetooth is 100m. Technical
overview of Bluetooth in terms of raw data rate, version and modulations scheme is included
in Table 2.1.
Bluetooth has low latency, high throughput operation with minimum channel hopping period
of 600 microseconds [7]. Since it has very less channel hopping period, all nodes should be
synchronized very fast, this adds complication in some WSNs where nodes sends data very
slowly. Bluetooth based WSN takes 2.4 seconds for connection establishment that is its
disadvantages.
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