Underwater acoustic communication is a technique of sending and receiving message below water. There are several ways of employing such communication but the most common is using hydrophones. Under water communication is difficult due to factors like multi-path propagation, time variations of the channel, small available bandwidth and strong signal attenuation, especially over long ranges. In underwater communication there are low data rates compared to terrestrial communication, since underwater communication uses acoustic waves instead of electromagnetic waves.
SEMINAR REPORT ON UNDERWATER WIRELESS COMMUNICATION
ELECTRONICS & COMMUNICATION ENGG. Dheeresh kumarB.TECH. 4RD YEAR ROLL NO. 110600102008
SURAJMAL LAXMIDEVI SAWARTHIA EDUCATIONAL TRUST & GROUP OF INSTITUTIONS
introductionUnderwater wireless communication is the wireless communication in which acoustic signals (waves) carry digital information through an underwater channel. Electromagnetic waves are not used as they propogate over short distances. Over the past decades, heavy cables were used to establish a high speed communication between remote end and the surface. To overcome such difficulties, underwater wireless communication has come into existence The propagation speed of acoustic signals in water is typically 1500 m/s.It cannot rely on the Global Positioning System (GPS).
NECESSITY OF UNDERWATER WIRELESS COMMUNICATION
Wired underwater is not feasible in all situations as shown below-:Temporary experimentsBreaking of wiresSignificant cost of deploymentExperiment over long distances. To cope up with above situations, we require underwater wireless communication.
FACTORS INFLUENCING ACOUSTIC COMMUNICATION
Path loss: Due to attenuation and geometric spreading.Noise: Man-made noise and ambient noise(due to hydrodynamics)Multi-path propogationHigh propogation delayDoppler frequency spread.
HARDWARE PLATFORM INTERFACES
Sensor Interface: Must develop common interface with different sensors (chemical, optical, etc.) and communication elements (transducer) .Wide (constantly changing) variety of sensors, sampling strategiesCommunication Interface:Amplifiers, TransducersSignal modulationHardware:Software Defined Acoustic Modem (SDAM)Reconfigurable hardware known to provide, flexible, high performance implementations for DSP applications
Employ advanced modulation scheme and channel equalization for improved signal to noise ratio.Employ high performance error detection and correction coding scheme which reduces bit error rate to less than 10-7Parts of an acoustic modem:DSP Board AFE(Analog Front End) BoardDC/DC Converter
DATA TRANSMISSION IN MODEM
When no data is being transmitted, the modem stays in sleep mode, it periodically wakes up to receive possible data being transmitted by far end modem. This results in low power consumption. Similarly when the data is to be transmitted , the modem receives data from its link in sleep mode and then switches to transmit mode and transmit the data.
ADVANCED MODEMS AVAILABLE
UNDERWATER ACOUSTIC SENSOR NETWORKS (UW-ASN)
Group of sensors and vehicles deployed underwater and networked via acoustic links, performing collaborative tasks.EquipmentAutonomous Underwater Vehicles (AUVs) Underwater sensors (UW-ASN)
UW-ASN COMMUNICATION ARCHITECTURE
UW-ASN COMMUNICATION ARCHITECTURE
Can be used to provide early warnings of tsunamis generated by undersea earthquakes.It avoids data spoofing.It avoids privacy leakage.Pollution monitoring.
Seismic monitoring. Pollution monitoring Ocean currents monitoring Equipment monitoring and control Autonomous Underwater Vehicles (AUV) Remotely operated vehicle(ROV) Acoustic navigation technology for multiple AUVs. Solar Powered AUVs
Search and rescue mission
Battery power is limited and usually batteries can not be recharged easily.The available bandwidth is severely limited.Underwater sensors are prone to failures because of fouling, corrosion, etc.Channel characteristics including long and variable propagation delays. Multipath and fading problems. High bit error rate.
The aim of this is to build a acoustic communication. This is not only the way for underwater communication. By using optical waves which offers higher throughput (Mbps) over short distances (up to about 100 m) .