Wireless Sensor Networks

Running Head: WIRELESS SENSOR NETWORKS 1
Wireless Sensor Networks
Name
Institution

Wireless Sensor Networks 2
In WSN applications, the quality of the Radio Frequency channel is vital. The noise fading
measurements are estimated through learning or probe-based methods. The result is high overhead.
(a) Select a suitable frequency band for WSN and give reasons for your selection.
Many protocols can be used creating a wireless network. 802.15.4 was built for Wirelesses
LAN. The network requirements include coverage of 9Km2 area containing 2500 animals to be
connected through wireless sensor tags. Each animal will be connected through point-to-point
WSN nodes that can transmit up to 250 Kbps. With GB of data per minute, the WSN will use a
frequency band of 2.4 GHz band built on 802.15.4 protocol having the 5HGHZ channel.
(b) Calculate the channel capacity (minimum data rate) required for:
The important considerations in data communication are the speed at which data is
transmitted. Data transmission is affected by the following:
 The available bandwidth, the available levels of digital and the quality of the
channel. There are two methods used in calculating the data rate.
 BitRate = 2* Bandwidth * Log2 (L)
 The equation shows that the data rate is proportional to the number of signal levels.
 L is the number of signal levels used in data representation.
I. One sensing device to control centre channel
For this network the data rate would be calculated as follows:

Wireless Sensor Networks 3
Bitrate = 2* 2400* log2 (2) = 6000bps.
Capacity is therefore calculated as follows:
Capacity = bandwidth * log2(1 + Signal to Noise Ratio)
Signal to noise ratio is given as 10 * log 10 (S/N) and is expressed in decibels. The S/R ratio
for this channel is given as 63DB. Therefore, the capacity is finally calculated as follows:
C= 2400Hz * log2 (1+ 63) = 24000* 5.97727992.
C=143454.71 bps. This the control centre channel capacity.
Channel capacity for one sensing device
= 143454.71/2500
=57.3bps.
II. Control center to ISP channel
Using the Shanon’s equation of calculating the channel capacity:
C= W log2 (1 +SNR)
C= 2400Hz * log2 (1+ 63) = 24000* 5.97727992.
C=143454.71 bps.
(c) For both the channel types calculate the following noise levels experienced:
I. Thermal noise

Wireless Sensor Networks 4
Calculating thermal noise at room temperature between 200C is possible. The most
commonly calculated as follows assuming that power proportional to the bandwidth/ WSN
uses impedance of 50 ohms (Horng, Chen, Chung, Shieh & Pan, 2012).
V=√4 kT B R, Where B is the bandwidth.
Using the above formulae, noise power is independent of the resistance, and it is only
on the bandwidth. From the thermal noise calculator and the following formulae, the result
is as follows:
Bandwidth = 2400Hz
Temperature = 293.15K
The figure below gives the formulae for calculating Noise:
When the formulae are applied, Noise for the WSN is -140.12 dBm
II. Total noise experienced