Wireless underground sensor networks

Akshay Pandita Arnav Soni

Guide-K A Netravathi

Introduction

Sensor networks are highly distributed networks of small, lightweight wireless nodes, deployed in large numbers to monitor the environment or system by the measurement of physical parameters such as temperature, pressure, or relative humidity.

Sensor nodes have limited computational power, limited memory,limited power in form of battery,limited communication capability

The applications of sensor networks are endless, limited only by the human imagination

Wireless Underground Sensor Networks

WUSN is defined as a group of nodes whose means of data transmission and reception is completely subterranean

In WUSN the node is completely underground

It may be in open space like a cave or completely embedded in dense soil or rock

WUSN have many applications like infrastructure,security,environmental monitoring etc.

Current technology for underground sensing

The current system consists of a buried sensor and a data logger on the surface

Very useful for a variety of applications Suffer from several shortcomings when compared to

wireless underground sensor networks Concealment Ease of deployment Timeliness of data Reliability Coverage density

Concealment

› In current systems the dataloggers are deployed on surface

› Communication is easier as no underground communication is involved

› Above ground equipment is vulnerable to agricultural and landscaping equipment or unacceptable for asthetic reasons

› In WUSN the equipment is underground secure from any theft and protected from damage

Ease of deployment

› Current technology uses wired systems› Tough to add new sensors or data loggers› No scalability issues with WUSN as its fully

wireless

Timeliness of data

Due to wireless nature the data from sensors is forwarded in real time to sink

In data loggers the data may be stored for later retrieval

Reliability

› Current systems are fully dependent on data loggers

› Data logger failure means whole network failure

› WUSN eliminate the need of datalogger› Each sensor can forward sensor readings

independently› WUSN’s are self healing

Coverage density

› Current systems require the sensor to be deployed close to the data logger

› It results in less coverage› WUSN eliminate the need of data logger› Sensors can be deployed anywhere,hence

increasing the coverage area

Applications

Environmental monitoring› Monitor soil water and mineral content for

irrigation› Monitor soil conditions for sports field

monitoring› Monitor soil movement for landslide

prediction› Coal mine monitoring› Monitor glacier movement› Earthquake monitoring

• A WUSN deployed for monitoring a golf course.• Underground sensors can be used to monitor soil salinity, water

content, and temperature.• Surface relays and sinks, which can be placed away from playing

areas, are used to forward WUSN sensor data to a central receiving point

Infrastructure monitoring

› Underground infrastructure like pipes,wiring etc.› Monitoring underground components of bridges,

dams etc.› Minefield monitoring

Location determination of objects

Driver alert Autonomous fertilizer unit Locating people in case of building collapse

Border patrol and security monitoring

› Home security systems› Detecting border intrusions

WUSN design challenges

Power conservation Topology design Antenna design Environmental extremes

Power conservation

Underground sensor nodes require more power as attenuation is more

Difficult to recharge or replace batteries Solar or any alternate energy form also

can’t be used Power conservation is the key Should be implemented by using power

efficient hardware and communication protocols

Topology design

Considerations

› Application-The density of sensor deployment is dictated by the application.Security application require dense whereas soil monitoring less dense deployment

› Power usage minimization-Power usage can be minimized by designing a topology with a large number of short-distance hops rather than a smaller number of long-distance hops.

› Cost-Deeper and Denser deployments result in more costs.Establish trade offs

Underground topology

› All sensor devices underground› Sink may be underground or above it› Can be single depth or multi depth› Provides maximum concealment of network› Ground air ground path can be used

Underground topology Hybrid topology

Hybrid topology

› Mixture of underground and aboveground sensor devices

› Power intensive underground hops can be traded for less expensive hops in a terrestrial network.

› Terrestrial devices can be easily recharger or replaced

› Network is not fully concealed

Antenna design

Issues to be considered› Variable requirements-Devices near the

surface air interface have different requirements from those deeper inside as they suffer from reflection

› Size-Lower frequencies require larger antennas, this is a challenge as sensor device size should be small

› Directionality-The antennas should be oriented for both horizontal and vertical communication

Environmental extremes

Underground environment is not ideal for electronic devices

Protection from water,animals,insects etc. is needed.

Devices should be resistant to pressure of people or objects moving overhead

Underground wireless channel

Underground channel properties› Extreme path loss› Reflection/Refraction› Multi path fading› Reduced propagation velocity› Noise

Effect of soil properties on channel› Water content› Particle size› Density› Temperature

Alternative physical layer technologies

› EM waves not optimal for underground› Magnetic induction can be a possible alternative as it

does not get affected by soil and water› Multi path fading not an issue for MI as its near

field,non propagating› Antenna design is simpler › Antenna strength is proportional to no of turns

Communication architecture

Physical layer

› Lower frequencies are ideal for WUSN› They face less attenuation but the antenna

size becomes large› Lower frequencies result in lesser bandwidth› Due to this the data rate in WUSN is very less

Data link layer

› In WUSN the focus should be on less retransmissions

› Traditional link layer protocols are contention based or TDMA based

› These may not be applicable for WUSN› Collision avoidance using CTS/RTS involves too

much overhead› In TDMA based scheme the synchronization

may be lost between nodes

Network layer

› Ad hoc routing protocols may be proactive,reactive or geographical

› Both proactive and reactive are not applicable to WUSN due to signalling overhead and syncronization issues

› Geographical routing can be helpful for WUSN only in some cases

› Routing protocols should be dynamic as link costs change due to soil conditions,water etc.

Transport layer

› Performs function of flow control and congestion control

› Congestion control can be done by routing data to terrestrial relays which are capable of a higher data rate

› Window based mechanism for flow control may not be applicable to WUSN as retransmissions are more

› In WUSN retransmission should be less to save energy

Cross layering

› Utilizing sensor data for channel prediction › Utilizing channel data for soil property

prediction› Physical-layer based routing › Opportunistic MAC scheduling › Cross-layer between link and transport layers

Conclusion

Deploying wireless sensor networks for underground applications have many advantages like ease of deployment,concelment etc. over conventional sensor networks

Several challenges like underground wirless channel, less bandwidth, power conservation etc. arise when WSN are implemented for underground networks

Several changes need to be made at different layers of the protocol architecture for WUSN

A cross layer protocol solution may be used to solve some of the issues with the present protocols

References

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E.P Stuntebeck. D Pompili, T Melodia, " Wireless underground sensor networks using commodity terrestrial motes", in proceedings of the 2nd IEEE workshop on wireless mesh networks, pp.111-116, September 2006. 

Kumarsagar. M. Dange, Kumarsagar. M. Dange, Design of Monitoring System for Coal Mine Safety Based on MSP430 , International Journal of Engineering Science Invention, Volume 2 Issue 7 ǁ July. 2013

Mo Li , Yunhao Liu, Underground structure monitoring with wireless sensor networks, Proceedings of the 6th international conference on Information processing in sensor networks, April 25-27, 2007, Cambridge, Massachusetts, USA

T. Zia and A.Y. Zomaya, "Security Issues in Wireless Sensor Networks," Proc. Int',l Conf. Systems and Networks Comm. (ICSNC ',06), p. 40, Oct. 2006. 

Kalpana Sharma, M K Ghose,Wireless Sensor Networks: An Overview on its Security Threats, IJCA Special Issue on “Mobile Ad-hoc Networks”MANETs, 2010