Wireless underground sensor networks
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Wireless underground sensor networks (WUSNs) have several advantages over conventional above-ground sensor networks for monitoring underground environments, such as increased concealment and ease of deployment. However, WUSNs also face significant challenges due to the harsh underground conditions and channel properties. The document discusses these challenges at different layers of the protocol stack, including high path loss, lower bandwidth, and power constraints. It suggests that cross-layer protocol designs and optimizations across layers may help address some of these issues to better support wireless underground sensor network applications.
Wireless underground sensor networks
- 2. 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
- 3. 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.
- 4. 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
- 5. 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
- 6. 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
- 7. 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
- 8. 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
- 9. 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
- 10. • 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
- 11. 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
- 12. Border patrol and security monitoring › Home security systems › Detecting border intrusions
- 13. Power conservation Topology design Antenna design Environmental extremes
- 14. 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
- 15. 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
- 16. 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
- 17. Underground topology Hybrid topology
- 18. 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
- 19. 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
- 20. 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
- 21. Underground channel properties › Extreme path loss › Reflection/Refraction › Multi path fading › Reduced propagation velocity › Noise
- 22. 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
- 24. 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
- 25. 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
- 26. 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.
- 27. 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
- 28. › 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
- 29. 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
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