Simulation of Comparison from NRZ and RZ Pulse in Free Space Optics with Different Weather Conditions

FSO (Free Space Optic) is a form of optical technology communication by transmitting light to media free space. In the FSO system, the data transmission can be larger, namely 1-100 Gbps, and this is due to the large bandwidth width. FSO runs at a wavelength of 850 nm and 1550 nm. FSO is usually with a maximum distance of 2-4 km. This paper simulates the FSO optical transmission system using NRZ and RZ line coding in bright and rainy weather conditions. The parameters analyzed are Eye diagram, Optical Spec-trum, photocurrent, and received signal power. In the FSO line coding system, NRZ has an eye height value, received signal power and received photocurrent is greater than the RZ line coding at a distance of 1 km and 5 km in bright and rainy conditions. In the trial of this FSO communication system, it is better to use it at a distance of 1 km, because the received signal power is above 20 dBm and received photocurrent is still above 800 mA for NRZ and RZ line coding. This is due to the attenuation value of sunny weather conditions that are smaller between 0.2-3 dB/km, while in rain conditions between 4-17 dB/km.


Introduction
is an optical communication technology in which data is transmitted by light propagation in empty space that allows optical connectivity. The FSO works almost similar to the OFC (Optical Fiber Optics) network but the only difference is that the FSO is sent by free air while the OFC is sent using glass fiber using cables. FSO communication offers a wide bandwidth potential that can provide high data rates [17]. Making this type of communication system is very interesting in meeting the consumers' large demand supported by high internet.
FSO is an environmentally friendly communication system because it has low price, high-speed data transmission and is easy licensed in the building window. Using an FSO can send data over 1-100 Gbps due to the large bandwidth width. FSO runs at a wavelength of 850 nm and 1550 nm [16]. FSO data links can be fully integrated into current short and longhaul high speed optical networks. Utilizing current 1550 nm technology platforms FSO data links can fully attain current system architectures, additionally the systems can be completely scaled to higher data rates and configurations. So that the FSO system provides comfort to the user [18]. FSO is usually with a maximum distance of 2-4 km.
There are several shortcomings of the FSO (Free Space Optics) communication system in poor weather conditions, which will affect the work of the FSO, like in obstruction of rain, fog, and dew. In addition to weather factors, there are also technical factors, like the lack of precision in the installation of light between FSO, blocked by escalators.

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Simulation of Comparison from NRZ and RZ Pulse in Free Space Optics with Different Weather Conditions

FSO Communication Work System
In the FSO communication work system, network traffic becomes pulses that have binary numbers, namely numbers 1 and 0. After that, the transmitter works to send data through an air intermediary with light. Then, the receiver will receive data from the transmitter via the photodetector. In the end, the signal obtained from the receiver will be connected to fiber or copper connected to the network.

Damping Concept on Geometry
In the concept of geometric attenuation caused by deviations from beam optic transmission between the transmitter and receiver with the following equation [7]: With is geometric attenuation (dB), 1 and 2 are optical transmitters and receivers (cm), L is the distance between sender and receiver (km), and θ is the angle of divergence (mrad) [8].

Signal to Noise Ratio (SNR)
Noise in the FSO system can be divided into two parts, namely thermal noise and shot noise. The SNR value on the FSO system is as follows [9]: ℜ is the recipient's responsiveness at λ = 1550 nm, q is the large electron charge (C), B is the bandwidth (Hz), i_S the received signal current (mA), k is the Boltzman constant (J/K), T is the temperature (K) and RL is load resistance (Ω) [8].

Bit Error Rate
The FSO system BER parameter Algorithm defines the numerical method to use for the BER estimation. Assuming Gaussian noise with the standard deviations σ 0 and σ 1 , the BER is [12]: Where P 0 and P 1 are the probabilities of the symbols, M is the number of samples for the logical 0, and N is the number of samples for the logical 1. Also, P e0 and P e1 are: Where µ 0 , µ 1 , σ 0 and σ 1 are average values and standard deviations of the sampled values respectively, and S is the threshold value.
An enhancement of the simple Gaussian approximation can be achieved by averaging the separately estimated BERs for different sampled symbols [14]. For M sampled values for the logical 0 and N sampled values for the logical 1, the corresponding error rates are: The eye height is calculated by [15]

Receiver Power
In the equation to calculate the receiving power as follows [10]: At is atmospheric losses which include loss of weather and scintillation losses ( t ), while includes geometric losses ( ), and system losses ( ), are variations in signal fading un-der turbulence conditions with probability of fluctuating indices bias, ( ) is the characteristic of AWGN (Additive white Gaussian noise), and and are calculated in mW [8]. After that, it can only calculate the signal power (dBm).

NRZ and RZ Pulse
In telecommunication, NRZ and RZ systems pulse is a type of line coding. Line coding is a process of converting digital data into digital signals, assuming that data contains or takes the form of faxes, numbers, images, audio, or video stored in computer memory as bit sequences [10]. In nonre-turn to zero (NRZ) modulation is a binary code that is represented by one significant condition, usually a posi-tive voltage, while zero is represented by a negative voltage. Pulses on NRZ have more energy than return to zero (RZ). While modulation of return to zero (RZ) describes line code used where at the time the signal drops to zero between each pulse in the telecommunications signal. This will occur even if 0 or 1 consecutive numbers occur in the converted signal [4].
The NRZ Pulse component produces rectangular non-return to zero (NRZ) electrical pulses with the following edge shapes is exponential [5]: And the RZ Pulse component produces rectangular return to zero (RZ) electrical pulses with the following edge shapes is exponential [5]:

Different Weather Conditions
The bad weather conditions will affect the performance of the communication system of the FSO, such as sunny, rainy, snowy, thin fog and thick weather. The following is the weakening distance of the FSO communication system, namely:

Free Space Optics System Design
In figure 3, it can be seen that the information signal is converted into a digital signal on the NRZ and RZ coding line, and then the signal is forwarded to the Mach Zender modulator to convert digital signals converted to light and sent. The receiver is the receiver of the data signal and converts it to the data signal, and then the signal will be filtered on the low pass bessel filter and read by BER 154 Simulation of Comparison from NRZ and RZ Pulse in Free Space Optics with Different Weather Conditions analyzer (Bit Error Rate Analyzer), then the eye diagram will be obtained in this simulation.

FSO Communication System Design Specifications
The following are the design specifications of the combined FSO communication system, below this:

Results from Eye Diagram and Optical Spectrum Analyzer
The following is a comparison of the simulation results from eye diagrams with attenuation of 0.7 dB/km as well as bright weather conditions within 1 km using NRZ and RZ coding line, below this:   figure 6 (a) the highest amplitude is at eye height at 1 km, its maximum amplitude is 7.49 at 0.5 s. While in figure 7 (a) the highest amplitude is at eye height at 1 km, the maximum amplitude is 2.83 at 0.46 s. Whereas figure 6 (b) and figure 7 (b) are graphs of eye height in the RZ line coding in bright weather conditions and rain with attenuation of 0.7 and 5 dB/km. In figure 6 (b), the highest amplitude is at eye height at 1 km, the maximum amplitude is 6.3 at 0.46 s. While in figure 7 (b) the highest amplitude is at eye height at 1 km, the maximum amplitude is at 2.34 at 0.46 s. Figure 8 (a) is a graph of between received signal power with distance using NRZ and RZ line coding in bright conditions at attenuation of 0.7 dB/km. In figure 8 (a) NRZ line coding has a received signal power value greater than the RZ line coding at its highest point at 44.78 dBm and its lowest point at 16.61 dBm at a distance of 1 km and 5 km. While the RZ line coding is at its highest point at 40 dBm and its lowest point is at 11.89 dBm at a distance of 1 km and 5 km. Figure 8 (b) is a graph of between the received photocurrent with distance using line coding NRZ and RZ in bright conditions at attenuation of 0.7 dB/km. In figure  8 (b) NRZ line coding has a received photocurrent value greater than the line coding RZ at its highest point at 4367.65 mA and its lowest point at 170.49 mA at a distance of 1 km and 5 km. While the RZ line coding is at its highest point at 2187.65 mA and its lowest point is at 85.39 mA at a distance of 1 km and 5 km.  Figure 8. (a) Graph of between received signal power with distance using NRZ and RZ line coding in bright conditions at attenuation of 0.7 dB/km, (b) Graph of between received photocurrent with distance using NRZ and RZ line coding in bright conditions at attenuation of 0.7 dB/km. Figure 9 (a) is a graph of between received signal power with distance using NRZ and RZ line coding in rain conditions in attenuation 5 dB/km. In figure 9 (a) the NRZ line coding has the received signal power value greater than the RZ line coding at its highest point at 36,18 dBm and its lowest point at -26.38 dBm at a distance of 1 km and 5 km. While the RZ line coding is at its highest point at 31.47 dBm and its lowest point is -31.09 dBm at a distance of 1 km and 5 km.

Results of Data Processing Comparison of NRZ with RZ Line Coding in Rainy Weather
In rainy conditions it has a decrease in the received signal power value to distance. NRZ line coding at a distance of 4 km received signal power decreased by more than 0 dBm which is -12.9 dBm. Meanwhile, in the RZ line coding, a distance of 3 km is received signal power which is -3.24 dBm. This is because the characteristics of the physical attenuation will be different in different weather conditions too. The attenuation value of bright weather conditions is smaller between 0.2-3 dB / km, while in rain conditions between 4-17 dB / km. Figure 9 (b) is a graph of between the received photocurrent with distance using NRZ and RZ line coding in the rain conditions in attenuation 5 dB/km. In figure 9 (b) NRZ line coding has a received photocurrent value greater than the RZ line coding at its highest point at 1622.73 mA and its lowest point at 1.2 mA at a distance of 1 km and 5 km. While the RZ line coding is at its highest point at 812.79 mA and the lowest point is at 0.6 mA at a distance of 1 and 5 km. Figure 10 (a) is a graph of between received signal power and distance using NRZ line coding in bright and rainy conditions at attenuation of 0.7 and 5 dB/km. In figure 10 (a) line coding NRZ bright conditions have a received signal power value greater than the NRZ coding line rain conditions at the highest point at 44.78 dBm and the lowest point at 16.61 dBm at a distance of 1 km and 5 km. Whereas NRZ rain conditions at the highest point at 36.18 dBm and the lowest point at -26.38 dBm at a distance of 1 km and 5 km. Figure 10 (b) is a graph of between received signal power and distance using RZ line coding in bright and rainy conditions at attenuation of 0.7 and 5 dB/km. In figure 10 (b) line coding of RZ bright conditions has a received signal power value greater than the RZ coding line the condition of rain at its highest point at 40 dBm and the lowest point at 11.89 dBm at a distance of 1 km and 5 km. Whereas NRZ rain conditions at its highest point at 31.47 dBm and the lowest point at -31.09 dBm at a distance of 1 km and 5 km.  Figure 10. Graph of between received signal power with distance using NRZ line coding in bright and rainy conditions at attenuation 0.7 and 5 dB/km, (b) Graph of between received signal power with distance using RZ line coding in bright and rain conditions at attenuation 0.7 and 5 dB/km.

Conclusions
Based on the simulation results, it can be concluded that each NRZ and RZ line coding has its own characteristics, as seen from the results of different Eye Diagram and Optical Spectrum Analyzer diagrams. In the system, the FSO line coding NRZ has an eye height value, received signal power, and receives currents greater than the RZ line encoding at a distance of 1 km and 5 km in bright and rainy conditions. In the trial of this FSO communication system, it is better to use it at a distance of 1 km, because the received signal power is above 20 dBm and received photocurrent is still above 800 mA for NRZ and RZ line coding. This is because the weakening value of sunny weather conditions is smaller between 0.2-3 dB/km, while the weather conditions are between 4-17 dB/km.