Case study

Wireless sensor network (WSN) can be defined as a group of spatially dispersed and dedicated sensors for monitoring and recording the physical conditions of the environment and organizing the collected data at a central location. WSNs measure environmental conditions like temperature, sound, pollution levels, humidity, wind, and so on.

There has been tremendous research on how to use WSN technology in Agriculture and Livestock industry - one of the key sectors of Australian exports.

Sense-T is one such initiative based in Tasmania and the network has proven it could help farmers by providing useful information in decisions making. Observing these positive results, recently a livestock giant VicStock came up with an idea to use a WSN in their farms to monitor the animals' health and behaviour.

The proposed pilot project will be implemented in one of their farms located in Gippsland area called MaffraStock. This farm is a 3 km x 3 km square shaped land and has got various types of animals including cattle, sheep and camel. The total number of animals is 2500.

The plan is to tag each animal with a device equipped with sensors, a GPS tracker and an accelerometer that monitors the motion.

One device generates 5 kB data per minute and there is a central node at the middle of the farm to collect data from all the sensors. This central node multiplexes data from all the sensors and uploads to a cloud based loT platform through a wireless ISP link so that VicStock can analyse trends and detect anomalies.

Planning to avoid licensing costs, the WSN uses ISM frequency bands for signal transmission. The ambient temperature around the farm is 20°C which causes a small amount of thermal noise. However, it is found that thermal noise is only 5% of the total noise experienced by WSN channels.

a) Select a suitable frequency band for WSN and give reasons for your selection.

b) Calculate the channel capacity (minimum data rate) required for:

I. One sensing device to control centre channel

II. Control centre to ISP channel

c) For both the channel types calculate the following noise levels experienced:

I. Thermal noise

II. Total noise experienced

d) It is expected to maintain SNR of 63 at the control centre for sensor signals.

I. Calculate the signal power received at control centre from one sensing device.

II. Calculate the bandwidth of the sensing device to control centre channel.

III. What will be the bandwidth of the multiplexed channel if FDM scheme is used?

e) Calculate the maximum free space loss experienced by the signals sent from sensors. (Assume control centre is located exactly at the centre of the landscape)

f) Determine the required transmission signal strength if other impairments such as attenuation and fading causes loss of 30% in signal power during the propagation from sensors to the control centre.

g) With your general knowledge in agriculture sector and business suggest  functionalities for the cloud application to effectively use sensor data.

h) Suggest how loT platforms can help the implementation of WSN. (Research in google to find answer for this)