IV. CHALLENGES IN FSO COMMUNICATION
FSO communication is facing serious challenges because of its transmitting medium. Open space air communication has lot of obstacles and degrades the signal performance gradually.
(a). Fog
The primary challenge to FSO-based communication is dense fog. Rain and snow have little effect on FSO technology, but fog is quite different. Fog is vapor composed of water droplets, which are only a few hundred microns in diameter and can modify the light characteristics[15].
(b). Absorption Absorption occurs when the suspended water molecules in the terrestrial atmosphere extinguish photons. This causes a decrease in the power density (attenuation) of the FSO beam and directly affects the availability of a system[15]. …show more content…
CODING TECHNIQUES
When the digital information in the binary form is transmitted from one point to another point in FSO communication an error may occur. This means a signal corresponding to 0 may change to 1 or vice –versa due to presence of noise. Figure 5. shows the basic coding block diagram of FSO communication system.
Fig.5. FSO communication system with coding
It is possible to improve the reliability of FSO communications system and achieve predetermined Bit Error rate (BER) by utilizing coding schemes. Forward error correcting codes (FEC) are leading an important role to get back the original message. The biggest challenge in FSO communication is how to retrieve original message without loss of data in turbulence condition.
Error Correcting Codes can be classified in two categories: (i) block codes, and (ii) convolution codes.
(a). Block codes
To generate an (n,k) block code, the channel encoder accepts information in successive k-bit blocks; for each block, it adds n-k redundant bits that are algebraically related to the k message bits, thereby producing an overall encoded block of n bits, where n>k. The n-bit block is called block code word, and n is called the block length of the code [16] (b). Convolutional …show more content…
These codes operated by continuously adapting the information rate to accommodate the varying channel conditions. The evaluation of the codes was performed offline.[18] The temporal characteristics of the experimental channels were analyzed and the performance of the codes for different bit rates to assess the effect of temporal correlation and imperfect channel state information were compared
FSO communication is facing serious challenges because of its transmitting medium. Open space air communication has lot of obstacles and degrades the signal performance gradually.
(a). Fog
The primary challenge to FSO-based communication is dense fog. Rain and snow have little effect on FSO technology, but fog is quite different. Fog is vapor composed of water droplets, which are only a few hundred microns in diameter and can modify the light characteristics[15].
(b). Absorption Absorption occurs when the suspended water molecules in the terrestrial atmosphere extinguish photons. This causes a decrease in the power density (attenuation) of the FSO beam and directly affects the availability of a system[15]. …show more content…
CODING TECHNIQUES
When the digital information in the binary form is transmitted from one point to another point in FSO communication an error may occur. This means a signal corresponding to 0 may change to 1 or vice –versa due to presence of noise. Figure 5. shows the basic coding block diagram of FSO communication system.
Fig.5. FSO communication system with coding
It is possible to improve the reliability of FSO communications system and achieve predetermined Bit Error rate (BER) by utilizing coding schemes. Forward error correcting codes (FEC) are leading an important role to get back the original message. The biggest challenge in FSO communication is how to retrieve original message without loss of data in turbulence condition.
Error Correcting Codes can be classified in two categories: (i) block codes, and (ii) convolution codes.
(a). Block codes
To generate an (n,k) block code, the channel encoder accepts information in successive k-bit blocks; for each block, it adds n-k redundant bits that are algebraically related to the k message bits, thereby producing an overall encoded block of n bits, where n>k. The n-bit block is called block code word, and n is called the block length of the code [16] (b). Convolutional …show more content…
These codes operated by continuously adapting the information rate to accommodate the varying channel conditions. The evaluation of the codes was performed offline.[18] The temporal characteristics of the experimental channels were analyzed and the performance of the codes for different bit rates to assess the effect of temporal correlation and imperfect channel state information were compared