Underwater communications using magnetic induction
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The majority of the work on underwater communication has mainly been based on acoustic communication. Acoustic communication faces many known problems, such as high propagation delays, very low data rates, and highly environment-dependent channel behavior. In this presentation, to address these shortcomings, magnetic induction is introduced as a possible communication paradigm for underwater applications. Accordingly, all research challenges in this regard are explained. Fundamentally different from the conventional underwater communication paradigm, which relies on EM, acoustic, or optical waves, the underwater MI communications rely on the time varying magnetic field to covey information between the transmitting and receiving parties. MI-based underwater communications exhibit several unique and promising features such as negligible signal propagation delay, predictable and constant channel behavior, sufficiently long communication range with high bandwidth, as well as silent and stealth underwater operations.
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Underwater communications using magnetic induction
- 1. Institute of Communications Presenter: Sabrina Chowdhury Under Water Communications Using Magnetic Induction
- 2. Structure of Presentation 2 Introduction • Working principle of MI communications • Comparison of different UWC technologies Basic MI communications using Single-Hop mode • System modelling • Path loss Basic MI communications using Multi-Hop- Relay mode • System modelling Numerical analysis of different UWC technologies • Path loss • Bit Error Rate (BER) *UWC=Under Water Communications *MI= Magnetic Induction
- 3. Working Principle of MI Based Communications 3 Coil Distance, r Transmitter coil Receiver coil Coil radius, a I Induced emf Magnetic FieldTransmitter coil
- 4. Working Principle of MI Based Communications 4 Antenna Antenna Antenna Antenna Receiver ReceiverTransmitter Transmitter Processor Processor r Near Field Propagation Communication Transceiver Communication Transceiver
- 5. Under Water Communications Challenges 5 Example of long path Ocean Floor Ambient noise Biological noise Transmitter Receiver Direct path Bottom reflection Surface reflection Ocean surface
- 6. Comparison of Different UWC Technologies 6 Communications paradigm Propagation speed Data rates Communications ranges Stealth operation Channel dependency Magnetic Induction Electromagnetic Acoustic Optical ~Mb/s 1500 m/s 3.33 ×107 m/s 3.33 ×107 m/s 3.33 ×107 m/s ~Mb/s ~Mb/s ~kb/s 10-100 m ≤ 10 m 10-500 m ~ km Conductivity Conductivity, multipath Light scattering, line of sight communications, ambient light noise Multipath, doppler effect, temperature, pressure, salinity, environmental sound noise Visible Audible
- 7. Promising features of Under Water MI Communications 77 Negligible signal propagation delay Frequency offsets due to the Doppler effects are negligible Predictable and constant channel response Reduced path loss due to Multi-Hop-Relay mode Sufficiently large communications range with high data rates Cost effective, easily-deployable and flexible antenna structures
- 8. Applications of Under Water MI Communications 8 Collaborative sensing and tracking with under water swarming robots Stealth and real time under water surveillance and patrol Disaster assessment, search, and rescue in a cluttered under water environment Telemetry and remote control from under water or surface equipment Diver to diver, diver to shore or diver to vessel communications
- 9. Different UWC Technologies 9 Optical Link RF Link Acoustic Link Off-Shore Infrastructure Anchor
- 10. Structure of Presentation 10 Introduction • Working principle of MI communications • Comparison of different UWC technologies Basic MI communications using Single-Hop mode • System modelling • Path loss Basic MI communications using Multi-Hop- Relay mode • System modelling Numerical analysis of different UWC technologies • Path loss • Bit Error Rate (BER)
- 11. Basic MI Communications Using Single-Hop Mode 11 Received signal Inductive link Transmitted signal Receiver coilTransmitter coil
- 12. System Modelling-MI Single-Hop Mode 12 M = μ ∙ NTX ∙ aTX 2 ∙ NRX ∙ aRX 2 ∙ π 2 (aTX 2 + r2)3 L = μ ∙ N2 ∙ A l R = N ∙ 2π ∙ a ∙ ρ A μ= Magnetic permeability in Hm-1 = μr. μ0 NTX, NRX= Number of turns of the transmitter and receiver coils ρ = Electrical resistivity in Ω⋅m A= Cross sectional area of the copper wire = π ∙ (d/2) 2 d= Diameter of the copper wire in m aTX aRX r
- 13. System Modelling-MI Single-Hop Mode 13 Z11=RTX + jωLTX Z22=RRX + jωLRX Z12= Z21 = jωM Z12, Z12= Mutual impedances Z11, Z22 = Self-impedances PTX(r)= Re V1 ∙ I1 ∗ = Re Z11 − Z12 2 ZL+Z22 |I1 |2 PTX(r0)=Re Z11 |I1 |2 Over very small distance, r0 PRX(r)=|I2 |2 Re ZL = Re ZL |𝑍12|2 |𝑍 𝐿+𝑍22 |2 |I1 |2 PL = −10log )PRX(r )PTX(r0 = −10log RL R12 2 + X12 2 R11 RL + R22 2 + XL + X22 2 XL =Inductive reactance=ω ∙ L Antenna Antenna Transmitter V2 r I2I1 ZL ZTX V1 + + - - Receiver ZL ZTX I1 - - + + V1 V2 I2 Z11 Z12 Z21 Z22 Zin (1) Zin (2)
- 14. Path Loss-MI Single-Hop Mode To maximize PRX Assuming ZTX = 0 Zin 2 = Complex conjugate of the input impedance at port 2 Zin (2) = V2 I2 = Z22 − Z12 2 ZTX +Z11 Angular frequency, ω = 2 ∙ π ∙ f Path loss of magnetic induction in fresh water ZL = Zin 2 ZL = RRX + ω2∙M2∙RTX RTX 2 +ω2∙LTX 2 + j( ω3∙M2∙LTX RTX 2 +ω2∙LTX 2 − ωLRX) PLMI = −10 log RL ∙ ω2 ∙ M2 RTX RL + RRX 2 + RTX XL + ω ∙ LRX 2 Attenuation (inverse of skin depth) α = 1 δ = π ∙ f ∙ μ ∙ σ σ = Electrical conductivity of sea Attenuation in sea water Total path loss in sea water PLα = 20 log eα∙r = 8.69α ∙ r PLSW = PLMI + PLα14
- 15. Structure of Presentation 15 Introduction • Working principle of MI communications • Comparison of different UWC technologies Basic MI communications using Single-Hop mode • System modelling • Path loss Basic MI communications using Multi-Hop- Relay mode • System modelling Numerical analysis of different UWC technologies • Path loss • Bit Error Rate (BER)
- 16. System Modelling-Multi-Hop Relay Mode 16 r r r Transmitter Coil Receiver CoilRelay Coil Relay Coil Relay Coil Antenna Antenna Antenna Antenna Antenna Transmitter ReceiverRelay node Relay node Relay node r rr V1 V2 ZTX ZL I1 I2
- 17. Structure of Presentation 17 Introduction • Working principle of MI communications • Comparison of different UWC technologies Basic MI communications using Single-Hop mode • System modelling • Path loss Basic MI communications using Multi-Hop- Relay mode • System modelling Numerical analysis of different UWC technologies • Path loss • Bit Error Rate (BER)
- 18. Numerical Analysis-Different UWC Technologies 18 MI system EM wave system Acoustic system 500 Hz 1.5 m 1.5 m 6 m 90 m 4000 m 8 kHz 1000 1000 0.01724 ohm∙mm2/m 1.45 mm (AWG 15) 1.65 mm2 400 MHz 4 S/m 0.01 S/m 716∙85×10-12 F/m Operating frequency: f (both fresh and sea water) Operating frequency: f Operating frequency: f Radius of transmitter coil: aTX Cross-sectional area for a copper wire of 1.45 mm: A Length(solenoid): l Number of turns (receiver Coil): NRX Radius of receiver coil: aRX Number of turns (transmitter Coil): NTX Electrical resistivity of copper: ρ Sea water conductivity, Ϭ Diameter of the copper wire: d Fresh water conductivity, Ϭ Dielectric permittivity, ε Deep water depth Shallow water depth
- 19. Path Loss-MI Single-Hop Mode 19 Distance in m PathLossindB
- 20. Link Budget and Bit Error Rate Signal-to-Noise Ratio (SNR) at the receiver: (general) Signal-to-Noise Ratio (SNR) at the Receiver: (Acoustic) SNR=SL−PL−NL+DI≥DT SNR=PT – PL −PN PT = Transmission power (dBm) PL = Path loss for different transmission media PN = Noise power (dBm) SL= Source level (dB) = 10 log ( 𝐼𝑡 0.67∙10−8) NL= Noise level (dB) DI = Directive index DT= Detection threshold pb 16QAM = 3 8 erfc ( 4 10 ∙ Eb N0 ) The BER for the modulation scheme 16-QAM Eb N0 = SNR ∙ BN R BN= Noise bandwidth R= Data rate 20 0
- 21. Bit Error Rate-MI Single-Hop Mode 21 BitErrorRate Distance in m
- 22. Path Loss-MI Multi-Hop Relay Mode 22 Distance in m PathLossindB
- 23. Bit Error Rate-MI Multi-Hop Relay Mode 23 BitErrorRate Distance in m
- 24. Conclusion on MI Communications System 24 Lower path loss and BER for short transmission ranges (up to 10 m) Path loss is higher in sea water due to electrical conductivity Multi-Hop-Relay mode reduces path loss and extends communications ranges Superior BER performance and potential for enormous applications
- 25. 25 Thanks !
- 26. Path Loss-Multi-Hop Relay Mode 26 PTX(r0) = Re(Z11a) |I1|2 Transmitted Power for a Small Distance, r0 Received Power PRX=Re(ZL) ∙ g=a k=b g=n−1 k=n |λgk|2 ∙ |Z21n|2 |ZL+Z22n|2 ∙ | I1|2 λgk = Z21G γgkPath Loss= −10 log PRX(r) PTX(r)
- 27. Numerical Analysis-Different UWC Technologies 27 MI system-Single-Hop mode EM wave system Acoustic system 1.6 m 1.6 m 6 m 90 m 4000 m 8 kHz 950 950 0.01724 ohm∙mm2/m 1.45 mm (AWG 15) 1.65 mm2 400 MHz 4 S/m 0.01 S/m 716∙85×10-12 F/m Operating frequency: f (both fresh and sea water) Operating frequency: f Operating frequency: f Radius of transmitter coil: aTX Cross-sectional area for a copper wire of 1.45 mm: A Length(solenoid): l Number of turns (receiver Coil): NRX Radius of receiver coil: aRX Number of turns (transmitter Coil): NTX Electrical resistivity of copper: ρ Sea water conductivity, Ϭ Diameter of the copper wire: d Fresh water conductivity, Ϭ Dielectric permittivity, ε Deep water depth Shallow water depth 2.3 kHz (fresh water), 500 Hz (sea water)
- 28. Bit Error Rate-Single-Hop Mode 28 BitErrorRate Distance in m PT= -60.01 dBm, PN=-74.81 dBm and R=7 kbps (assumption)
- 29. Under Water Communications Challenges 29 Harsh Under water environment Limited Bandwidth Extended Multipath Rapid time variation Severe Fading Noise Ambient Physical Processes Human Activities Biological Aquatic Animal Activities
- 30. Applications-Vessel to AUV Communications 30 AUV Vessel Communication Links Ocean Surface Ocean Floor
- 31. Applications-Under Water Monitoring System 31 Receiving Tower Sink Monitoring System Electromagnetic Wave Acoustic Wave AUV
Editor's Notes
- In magneto inductive communications system, the distance of coils is usually larger, and transferred power drops off sharply to a very small fraction, so the coils should be asymmetric, which the transmitter coil being heavy and large, and the receiver coils being light and small. We are working in conductive media such as water, where the electrical conductivity sigma leads to energy dissipation of the material because of the eddy current which generates strong secondary field. Electrical conductivity gives a measure of a material’s ability to conduct an electric current. 1. The principle of magnetic induction is the current in the primary coil (transmitter) generates magnetic field then the magnetic field induces current in to secondary coil (receiver). Magnetic flux is a general term associated with a field that is bound by a certain area. So, magnetic flux is any area that has a magnetic field passing through it. Electron has a magnetic dipole moment. It's close to an electric dipole moment because it generates a magnetic field that behaves similarly to an electric dipole field (falls off like 1 /r3). The lowest order moment possible in magnetism that obeys Maxwell's equations is the dipole moment.
- Magnetic induction (MI) is a promising physical layer technique for UWCNs that is not affected by multipath propagation and fading. 1. Important applications for shallow water such as diver-to-diver voice and text communications can be developed using this technique. Real-time data transfer between AUVs, or AUVs and underwater sensors, Stealth and real-time underwater surveillance and patrol Telemetry and remote control from underwater or surface equipment is also possible, since the water to air boundary is crossed by the magnetic component of an electromagnetic signal with relatively low attenuation. Communication between AUVs and docking stations, or control of AUVs from surface vessels and shore is helpful in environmental and military applications such as mine countermeasures during coastal reconnaissance missions. Diver to shore or vessel communication are other interesting applications. Collaborative sensing and tracking with underwater swarming robots. (A) Collaborative sensing and tracking with underwater swarming robots: Fish behavior shows an astonishing ability to efficiently find food sources and favorable habitat regions through schooling behavior, that is, rapid orienting and synchronized moving of a group of fish with respect to environmental gradients, such as local variations in chemical stimuli such as odorant plumes or other environmental properties such as phytoplankton density. Underwater MI communications can enable a swarm of underwater robots (e.g., agile robotic fish) to mimic this collective and synchronized intelligence of fish by exchanging control and environmental gradient information with guaranteed delay bounds. In such a way, swarming robots can collaboratively track sources of pollution, toxicity, and biohazard with high convergence speed and accuracy. (B) Stealth and real-time underwater surveillance and patrol: The high bandwidth along with the constant and reliable channel conditions achieved by underwater MI communications can enable real-time underwater surveillance, which demands high-speed delivery of a large volume of multimedia contents (e.g., audio, video, and scalar data). In addition, the stealth and silent features of underwater MI communications allow underwater surveillance to be carried out in stealth mode.
- Shortcomings of Acoustic communication: -High propagation delay as because the sound speed equals 1500 m/s -Very low data rates, low bandwidth -highly environment dependent channel behavior (salinity, pressure, temperature gradient) -prevalent Doppler effect -refraction in deep water -reflection in shallow water (water depth<100m) -High Bit Error Rate -In extreme cases, the sound speed variations with depth cause refraction of signals and result in a spatially-variant channel. As a result, shadow zones are formed, which cause significant bit error rates and loss of connectivity . Shortcomings of Optical communication: In underwater optical channels, the source and destination nodes should form a directional link in a close proximity with high precision in pointing the narrow laser beams . Furthermore, the multiple scattering of light results in dispersion and creates the inter symbol interference(ISI) -Multiple scattering ,limiting the application of optical signals to short-range distances. -the transmission of optical signals requires a direct line of sight, which is another challenge for mobile underwater vehicles and robots. For fibre optic systems, bit errors mainly result from imperfections in the components used to make the link. These include the optical driver, receiver, connectors and the fibre itself. Bit errors may also be introduced as a result of optical dispersion and attenuation that may be present. Also noise may be introduced in the optical receiver itself. Typically these may be photodiodes and amplifiers which need to respond to very small changes and as a result there may be high noise levels present. Shortcomings of Electromagnetic Signal: In underwater RF communication, electromagnetic waves propagate over very short distances due to high levels of attenuation increasing with conductivity and frequency. Large antenna size, low operation frequencies and high transmission power are necessary. -suffer from high path loss, which limits their communication range. -To increase the EM range, a large antenna is used for low frequencies, but this is unsuitable for small underwater vehicles.
- Due to the high velocity of MI propagation, frequency offsets due to the Doppler effect are negligible. -This extremely high propagation speed of MI waves can significantly improve the delay performance of underwater communications, while providing facilities to design and implement underwater networking protocols, such as medium access control (MAC) and routing, and the underwater networking services (e.g., localization). Moreover, physical layer synchronization among wireless devices becomes simple and reliable due to the negligible delay and stable channel. Comparison between MI and Acoustic : Another very promising low-cost, robust and efficient method is the magneto-inductive (MI) wireless communication Unlike acoustic channel, MI channel does not have high latency and it mitigates the challenges of dynamical conditions and high power consumptions by using simple, low cost and low power coils. The channel conditions depend on the permeability of the communication medium and a uniform channel is created in air, seawater and most types of soil and rock due to almost the same permeability. Furthermore, the feasible communication distance dramatically increases with waveguides . Negligible signal propagation delay: Different from acoustic waves that propagate at a speed of 1500 m/s under water, MI waves propagate at a speed of 3.33 × 107 m/s under water. This extremely high propagation speed of MI waves can significantly improve the delay performance of underwater communications, while facilitating the design and implementation of the underwater networking protocols, such as medium access control (MAC) and routing, and the underwater networking services (e.g., localization). Moreover, physical layer synchronization among wireless devices becomes simple and reliable due to the negligible delay and stable channel. Predictable and constant channel response: Since the radiation resistance of a coil is much smaller than that of an electric dipole, only a very small portion of energy is radiated to the far field by the coil. Hence, compared to acoustic communication, multi-path fading is not an issue for MI-based underwater communication. Moreover, because of the high propagation speed of MI waves, the frequency offsets caused by Doppler effect can be greatly mitigated. Without suffering from multi-path fading and Doppler effect, the MI channel conditions (e.g., data rate and packet loss rate over a given transmission range) are highly constant and predictable. Moreover, without suffering from light scattering as in optical communications, the transmission range and channel quality of MI communications are independent of water quality factors such as water turbidity. In addition, both acoustic and optical communications have to deal with a high level of acoustic and ambient light noises. The EM noise experienced by MI channels is limited under water because the high-frequency noise is absorbed by the water medium. Sufficiently large communication range with high data rate: In MI-based communications, the transmission and reception are accomplished through the use of a pair of small-size wire coils, that is, coil antennas. Different from the dipole antenna used in most EM wave-based communications, there is no minimum frequency below which the antenna cannot work. On the one hand, the time varying magnetic field can be generated no matter how small the coil is at the MI transmitter. On the other hand, as long as there is magnetic flux going through the coil, the MI receiver can capture the signal even if the frequency is as low as the Megahertz band. This property means that each small coil antenna can be utilized to emit low-frequency MI signals, which allow small underwater robots and vehicles to communicate over sufficiently long distances. Moreover, the operating frequency of MI coils can reach Megahertz bands while maintaining predictable and constant channel quality, which leads to much higher data rates than in the acoustic communications. Multi hop relay mode: The experiments carried out in [7] demonstrate the validity of using magnetic fields for communication in shallow water. An underwater communication system that uses the magnetic field as a carrier at a frequency of 12 kHz and has a range of 30 m was successfully designed for surface air to diver voice transmission [8]. In addition, data rates of 100 to 300 bps have been achieved in several MI communication tests carried out in coastal areas over mixed-media (air-water) ranges of 250–400 m [7]. However, the authors [7] point out that the high path loss limits the transmission distance. The s a trade off between QOS (quality of service) and distance. For this reason, they suggest using a system of MI transceivers operating in multi-hop relay-mode. We propose to reduce costs and energy using relay points (just a simple coil without any energy source or processing device). Those relay coils form a MI waveguide that guides the magneto-inductive waves.
- Magnetic induction (MI) is a promising physical layer technique for UWCNs that is not affected by multipath propagation and fading. 1. Important applications for shallow water such as diver-to-diver voice and text communications can be developed using this technique. Real-time data transfer between AUVs, or AUVs and underwater sensors, Stealth and real-time underwater surveillance and patrol Telemetry and remote control from underwater or surface equipment is also possible, since the water to air boundary is crossed by the magnetic component of an electromagnetic signal with relatively low attenuation. Communication between AUVs and docking stations, or control of AUVs from surface vessels and shore is helpful in environmental and military applications such as mine countermeasures during coastal reconnaissance missions. Diver to shore or vessel communication are other interesting applications. Collaborative sensing and tracking with underwater swarming robots. (A) Collaborative sensing and tracking with underwater swarming robots: Fish behavior shows an astonishing ability to efficiently find food sources and favorable habitat regions through schooling behavior, that is, rapid orienting and synchronized moving of a group of fish with respect to environmental gradients, such as local variations in chemical stimuli such as odorant plumes or other environmental properties such as phytoplankton density. Underwater MI communications can enable a swarm of underwater robots (e.g., agile robotic fish) to mimic this collective and synchronized intelligence of fish by exchanging control and environmental gradient information with guaranteed delay bounds. In such a way, swarming robots can collaboratively track sources of pollution, toxicity, and biohazard with high convergence speed and accuracy. (B) Stealth and real-time underwater surveillance and patrol: The high bandwidth along with the constant and reliable channel conditions achieved by underwater MI communications can enable real-time underwater surveillance, which demands high-speed delivery of a large volume of multimedia contents (e.g., audio, video, and scalar data). In addition, the stealth and silent features of underwater MI communications allow underwater surveillance to be carried out in stealth mode.
- In magneto inductive communications system, the distance of coils is usually larger, and transferred power drops off sharply to a very small fraction, so the coils should be asymmetric, which the transmitter coil being heavy and large, and the receiver coils being light and small. We are working in conductive media such as water, where the electrical conductivity sigma leads to energy dissipation of the material because of the eddy current which generates strong secondary field. Electrical conductivity gives a measure of a material’s ability to conduct an electric current. 1. The principle of magnetic induction is the current in the primary coil (transmitter) generates magnetic field then the magnetic field induces current in to secondary coil (receiver). Magnetic flux is a general term associated with a field that is bound by a certain area. So, magnetic flux is any area that has a magnetic field passing through it. Electron has a magnetic dipole moment. It's close to an electric dipole moment because it generates a magnetic field that behaves similarly to an electric dipole field (falls off like 1 /r3). The lowest order moment possible in magnetism that obeys Maxwell's equations is the dipole moment.
- When data is transmitted over a data link, there is a possibility of errors being introduced into the system. If errors are introduced into the data, then the integrity of the system may be compromised. As a result, it is necessary to assess the performance of the system, and bit error rate, BER, provides an ideal way in which this can be achieved. If the medium between the transmitter and receiver is good and the signal to noise ratio is high, then the bit error rate will be very small - possibly insignificant and having no noticeable effect on the overall system However if noise can be detected, then there is chance that the bit error rate will need to be considered. The main reasons for the degradation of a data channel and the corresponding bit error rate, BER is noise and changes to the propagation path (where radio signal paths are used). Both effects have a random element to them, the noise following a Gaussian probability function while the propagation model follows a Rayleigh model. This means that analysis of the channel characteristics are normally undertaken using statistical analysis techniques.
- Convergence Zone: In the ocean, zones where the surface waters of the ocean come together. They develop owing to unevenness in the wind field above the ocean and in the distribution of water density. They usually form at the junction of warm and cold waters and consequently are characterized by sharp horizontal gradients of temperature, salinity, density, and chemical and biological indicators (in certain cases the horizontal temperature gradient may be as much as 6°-7°C for several dozen meters). Owing to the uneven distribution of density, anticyclonic and cyclonic circulations of surface waters develop in convergence zones. In anticyclonic circulation there is intensive mixing and submergence of waters; in cyclonic circulation ascending streams of water develop and bring nutritional salts from the depths to the surface of the ocean. This creates conditions for high biological productivity in these zones.
- For Short Transmission Ranges (up to 9 m), the Path Loss and BER are Lower with the MI System for Fresh Water Compared to the Electromagnetic and Acoustic Communication Systems. The Performance of the MI System in Sea Water is Good, although the Path Loss Values are Higher than in Fresh Water Due to the Electrical Conductivity of Sea Water. The Multi-Hop Relay Technique Reduces Path Loss and Extends Communication Ranges. For Fresh Water. It Achieves Better Results than the Ordinary MI and the EM Wave Systems, and Outperforms the Acoustic System under All Propagation Phenomena. Because of it’s Superior BER Performance, the Transmission Ranges Have Been Improved Moderately in Sea Water and Have Been Extended Considerably to Hundreds of Meters in Fresh Water. This Opens the Potential for a Number of Applications to Emerge.
- harsh underwater environments. These environments include areas with a high concentration of conductive elements, through highly reflective barriers such as the surface of water and communicating through the earth. (A) Ambient Noise : Mainly 2 types: Physical activities and Human activities. Physical activities: Rainfall,, Seismic activities, Surface motion, caused by wind-driven waves is the major factor resulting in the noise in the frequency region 100 Hz – 100 kHz (which is the operating region used mostly by the acoustic systems) Human activities: Distant Shipping (Noise caused by distant shipping is more in the frequency region 10 Hz -100 Hz), Oil exploration, Construction work, Turbulence(low frequency region, (f < 10 Hz)thermal noise becomes dominant for high frequencies i.e., f>100 kHz. (B) Biological Noise: Aquatic animal made noise for communication, Prey manipulation, echolocation. 2. limited bandwidth (Limited throughput-Limited Data rates)-Bandwidth is the range of allowed or possible frequencies in which information passes. High data rates require high frequency contents ..hence high bandwidth channel to transmit them. 3. Extended multipath : Underwater channel is a time varying multipath channel causing ISI, ICI (Inter Channel Interference) and fading. Due to the effect of time and frequency spreading, achieving high data rates in underwater wireless communication is challenging. 4. Rapid time variation and severe fading: (Doppler Effect) The Doppler Effect is much more severe, because of the following reasons: the speed of sound is low, the system is inherently a wideband system, the Doppler frequencies can be relatively large compared to the carrier frequency, and the Doppler shifts are dependent on the sub-carriers. The frequency of the transmitted signal is significantly distorted by the Doppler Effect and multipath propagation. The motion induced distortion has far-reaching implications on the design of the synchronization unit and the channel estimation algorithm. Generally, Doppler effect is caused by, (i)Doppler shift caused by tx / rx motion. (ii)Doppler shift caused by the moving sea surface. SIR(Signal to Interference Ratio) not only depends on Doppler shift but also depends on bandwidth and the transmit power and all these factors are related as follows: As Doppler frequency increases then ICI (Inter Channel Interference) power (or) transmit power increases (ii) As bandwidth increases ICI power decreases but the ambient noise power increases. –fD ∞ PICI ∞ 1/BW ∞Ptx BW ∞ Pambient noise ∞1/ PICI
- Magnetic induction (MI) is a promising physical layer technique for UWCNs that is not affected by multipath propagation and fading. 1. Important applications for shallow water such as diver-to-diver voice and text communications can be developed using this technique. Real-time data transfer between AUVs, or AUVs and underwater sensors, Stealth and real-time underwater surveillance and patrol Telemetry and remote control from underwater or surface equipment is also possible, since the water to air boundary is crossed by the magnetic component of an electromagnetic signal with relatively low attenuation. Communication between AUVs and docking stations, or control of AUVs from surface vessels and shore is helpful in environmental and military applications such as mine countermeasures during coastal reconnaissance missions. Diver to shore or vessel communication are other interesting applications. Collaborative sensing and tracking with underwater swarming robots. (A) Collaborative sensing and tracking with underwater swarming robots: Fish behavior shows an astonishing ability to efficiently find food sources and favorable habitat regions through schooling behavior, that is, rapid orienting and synchronized moving of a group of fish with respect to environmental gradients, such as local variations in chemical stimuli such as odorant plumes or other environmental properties such as phytoplankton density. Underwater MI communications can enable a swarm of underwater robots (e.g., agile robotic fish) to mimic this collective and synchronized intelligence of fish by exchanging control and environmental gradient information with guaranteed delay bounds. In such a way, swarming robots can collaboratively track sources of pollution, toxicity, and biohazard with high convergence speed and accuracy. (B) Stealth and real-time underwater surveillance and patrol: The high bandwidth along with the constant and reliable channel conditions achieved by underwater MI communications can enable real-time underwater surveillance, which demands high-speed delivery of a large volume of multimedia contents (e.g., audio, video, and scalar data). In addition, the stealth and silent features of underwater MI communications allow underwater surveillance to be carried out in stealth mode.
- Magnetic induction (MI) is a promising physical layer technique for UWCNs that is not affected by multipath propagation and fading. 1. Important applications for shallow water such as diver-to-diver voice and text communications can be developed using this technique. Real-time data transfer between AUVs, or AUVs and underwater sensors, Stealth and real-time underwater surveillance and patrol Telemetry and remote control from underwater or surface equipment is also possible, since the water to air boundary is crossed by the magnetic component of an electromagnetic signal with relatively low attenuation. Communication between AUVs and docking stations, or control of AUVs from surface vessels and shore is helpful in environmental and military applications such as mine countermeasures during coastal reconnaissance missions. Diver to shore or vessel communication are other interesting applications. Collaborative sensing and tracking with underwater swarming robots. (A) Collaborative sensing and tracking with underwater swarming robots: Fish behavior shows an astonishing ability to efficiently find food sources and favorable habitat regions through schooling behavior, that is, rapid orienting and synchronized moving of a group of fish with respect to environmental gradients, such as local variations in chemical stimuli such as odorant plumes or other environmental properties such as phytoplankton density. Underwater MI communications can enable a swarm of underwater robots (e.g., agile robotic fish) to mimic this collective and synchronized intelligence of fish by exchanging control and environmental gradient information with guaranteed delay bounds. In such a way, swarming robots can collaboratively track sources of pollution, toxicity, and biohazard with high convergence speed and accuracy. (B) Stealth and real-time underwater surveillance and patrol: The high bandwidth along with the constant and reliable channel conditions achieved by underwater MI communications can enable real-time underwater surveillance, which demands high-speed delivery of a large volume of multimedia contents (e.g., audio, video, and scalar data). In addition, the stealth and silent features of underwater MI communications allow underwater surveillance to be carried out in stealth mode.