1. Mathematical Modelling of Underwater channel for Optical communication

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The requirement of high data rates and low latency is becoming a basic demand with an increase in data, I.O.T applications, remote sensing, etc. Engineers and scientists are trying to fulfill these high-end demands; As with each passing communication generation we are getting high data rates, but these high data rates are achieved by getting higher frequency carriers, we have started from radio and now reached to optical spectrum for present and upcoming communication systems.  Like free space, wireless communication in water is in demand because of its tremendous application such as communication among divers, unmanned underwater vehicles (UUV), submarines, ships, and underwater sensors. Some of these UUVs and sensors are deployed to gather important data such as real-time videos and environmental and security data which may be time sensitive.

 

             Present Underwater wireless communication is done using acoustic signals because acoustic signals are less absorptive and scatter in the underwater channel, but acoustic signals fail to provide high data rates and low latency, the optical signal gets easily absorbed and scatters, but if we use blue-green spectrum light then it makes communication in underwater channel still feasible. The effective treatment of signal-transmission problems requires an analytical representation or "model" of the signal part. Hence for effective underwater optical wireless communication, we are trying to make communication links more reliable for transmitting and receiving.

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2. Development  of Advanced modulation schemes using FPGA 

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In practical Optical Wireless Communication systems currently, Intensity Modulation - Direct Detection (IM/DD) scheme is in existence. Challenges using this technique during the turbulent atmospheric channel in free space, high saline, and turbid conditions underwater will demand high power for proper transmission. It is not an optimized approach to increase the power of the transmitting signal. To encounter this issue, various modulation schemes are employed which will alter the switching period of the signal and hence contribute to power efficiency. Also, we get increased transmission reliability and seek for improved BER.

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3. Implementation of Error Correction codes in VLC/FSOC/UWOC

 

A condition when the receiver’s information does not match with the sender’s information. During transmission, digital signals suffer from noise that can introduce errors in the binary bits traveling from sender to receiver. That means a 0 bit may change to 1 or a 1 bit may change to 0. Whenever a message is transmitted, it may get scrambled by noise or data may get corrupted. To avoid this, we use error-detecting codes which are additional data added to a given digital message to help us detect if any error has occurred during the transmission of the message.

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               The error correction code works based on two methods.

• In Backward Error Correction, if an error is identified using error detection codes, the receiver sends an automatic repeat request(ARQ) to resend the information.

• In Forward Error Correction, the error detection code itself have some redundant data that is used to correct errors.

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4. Development  of Optical Test-bed

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Various Test-beds were developed in house to simulate various conditions, using which we can easily calculate the reliability of the communication under different adverse conditions. The aforementioned test-beds consists of 1 vacuum chamber, 1 wind tunnel, 1 dust chamber, 1 fog chamber. We have also developed an 8m Underwater optical setup which is bifurcated into one 4m clean water tunnel and two 2m muddy water tunnels which are mainly used in UWOC

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5. Bidirectional Underwater wireless optical communication

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In the field of Underwater Wireless Optical Communication (UWOC), modulation techniques such as Pulse Amplitude Modulation (PAM), Pulse Position Modulation (PPM), and On-Off Keying (OOK) are often implemented to encode data onto light signals. These methods enable data to be effectively transmitted through water by varying aspects like intensity or timing of the light signals.

To address the challenges of data reliability in underwater conditions, error correction codes like Reed-Solomon codes and other forward error correction codes are employed. These codes introduce redundancy into the transmitted data, enabling the system to minimize the errors caused by factors such as optical absorption, scattering, and turbulence in the underwater medium.

These modulation and error correction techniques are typically evaluated and refined within in-house test beds. These test beds serve as controlled environments for developing and testing UWOC systems. By using these in-house test beds, we can simulate and analyze the performance of modulation schemes and error correction codes under conditions that mimic real-world underwater scenarios. This iterative process helps optimize the communication system's reliability and efficiency, ultimately advancing the capabilities of Underwater Wireless Optical Communication technology.

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