## 3 Description of WDM-RoF System  
The suggested system consists of four RF signals transmitted over single-mode optical fibre at different distances (5, 10, 20, 50, and 60 km) and received by four remote stations. RoF network with optical communication can be simulated and implemented using Optisystem, a powerful and inventive software design tool that allows users to design, test, and simulate virtually each optical type of link positioned in the transmission layer of the broad spectrum of the optical networks. The block diagram of the proposed WDM-RoF system is shown in Figure 2. The transmitter consists of channels, and each channel has its own operating wavelength. Channel 1 is 1552.50 nm, with a linewidth of 10 MHz, and so on. As a result, a wavelength spacing equal to 0.4 nm between subsequent channels is maintained for low and smooth transmission. Because the separation is narrow, it helps to support big client numbers and to accomplish a high rate. Each channel has an input power to be changed from \(-15\) dBm to 15 dBm with a step of 5 dBm. The WDM multiplexer that has a bandwidth of 10 GHz can combine the signal that comes from the input channel and then transmit it over the optical fibre. The optical fibre length varies from 5 km to 60 km. In optical communication links, Erbium Doped Fiber Amplifiers (EDFAs) are used for enhancing the signal power to all channels simultaneously. The proposed WDM multiplexer of 10 GHz bandwidth has a four-signal combination, each from one input channel, which it transmits over an optical fibre link that operates in the wavelength window of 1550 nm and requests for dispersion management. At the transmitter, the binary data supplied by the pseudo-random bit sequence (PRBS) is converted into non return to zero (NRZ) electrical pulses to generate a baseband signal. The information rate for the re-enactment of both the downlink and uplink signals is set to 1 Gbps. The carrier frequency of the electrical amplitude modulator is 1.7 GHz and can be used to convert the frequency of the baseband signal to the RF clock frequency. The RF signal is applied to the 90\({}^{\circ}\) hybrid coupler after the SCM carrier generator, as shown in Figure 3. Furthermore, the outputs of the hybrid coupler are connected to the dual port, dual drive, Lithium Niobate (LiNb), Mach-Zender modulator (MZM). The MZM is used for the transmission of microwave signals into optical signals. This MZM has four ports, out of which three are used as an input port and one is used as an output port. Subsequently, port 1 of MZM is driven by the amplitude modulator, and port 2 is driven by a 1 Gbps baseband signal. The optical signal obtained at the output port of MZM is further transmitted over the optical fibre link. Figure 2: The proposed WDM-radio over fibre (RoF) system. Then, the optical modulated signal is passed through an SMF channel. This optical link model utilises an SMF, which confirms a good quality level through the transport of signals. The attenuation factor value can be chosen with 0.2 dB/ km, and the distance changes from 5 km to 600 km. Figure 4 shows a receiver with a positive intrinsic negative (PIN) photodetector, low-pass Bessel electrical filter with 16 GHz cut-off frequency, and BER analyzer. The thermal noise of the PIN detector is not taken into account. In the figure, the optical modulated signal sent through the fibre is directly detected on the PIN photodiode with a suitable sensitivity. The photocurrent is a replica of the modulated RF signal applied externally by means of the MZM modulator at the transmitter. This PIN photodiode converts the optical signal to an electrical signal, which is then amplified through an electrical amplifier for making up the power loss owing to the attenuation in the fibre. A gain of 20 dB confirms that all distorted signals that are attenuated through transmission by fibre channels may be recovered at the receiver.