**5. Simulation**

channel of CWDM to 16, number of wavelength could be increased by using 1310 nm win‐ dow. One of the advantages of CWDM is that the cost of the optics is 1/3 of the cost of same DWDM optic. This makes that the CDWM is preferable than DWDM. CWDM is able to match the basic capabilities of DWDM but with lower cost and capacity. Typically, CWDM is used for short‐range communications. In addition, CWDM equipment is more compact and cost‐

DWDM network systems provide up to 96 wavelengths, which normally has less than 0.4 nm spacing. DWDM is used for long‐haul transmission where wavelengths are compacted tightly together. Erbium‐doped fiber amplifiers (EDFA) can help the system of DWDM to work over thousands of kilometers. CWDM is not implemented in long haul transmission, where the distance reaches up to thousands of kilometers, causing simpler overall sytem components requirement. This leads to lesser cost implementation, despite of having some limita‐tions

The methodology used in designing RoF system consists of familiarization with Optisystem software, designing system, generate component and simulation object, running the simula‐ tion and analyze the data. Optisystem software is used to design, construct and simulate the

Optisystem software is a comprehensive software that provides a platform to plan, test, and simulate optical links in the transmission layer of modern optical networks. Optisystem is also an optical communication system simulation package for the design, testing, and optimi‐ zation of virtually any type of optical link in the physical layer of a broad spectrum of optical

networks, from analog video broadcasting systems to intercontinental backbones.

effective if compared to DWDM designs.

**Figure 6.** Wavelength division multiplexing.

168 Optical Fiber and Wireless Communications

especially in propagation distance.

**4. Methodology**

RoF topology.

#### **5.1. System design**

To send two signals, two continuous wave lasers are used in order to resonate 193.1 and 193.2 THz, respectively, as shown in **Figures 7** and **8**, respectively. To obtain an electrical network that simple and low in speed, a pulse generator is needed. A pseudo‐random bit (PRBS) generator is used to operate a Gaussian pulse generator so that baseband signal can be generated. 1 Gbps was set as the bit rate. The PRBS generator indicates the random source of data. To simulate the signal, 1 Gbps per channel was set as the data rate for the simulation.

As the carrier frequency is 2.7 GHz for transmitter 1 and 1.7 GHz for transmitter 2, an ampli‐ tude modulator is operated by the 1 Gbps baseband signal. After that, the amplitude modu‐ lator will operate the LiNb Mach‐Zehnder modulator (MZM)'s port 1. The main function of the amplitude modulator is to translate the baseband signal onto the RF clock. At a fre‐ quency of 49.25 MHz for both transmitter, the SCM carrier generator will mix with the RF signal. A 90° hybrid coupler is applied to the signal where it is utilized to separate that the input signal becomes 2 outputs that having 90° phase shift difference between each other. The separated signals are sent to the two arm of M‐Z Modulator. At the both transmitter sides, to allow the signal being transmitted along the fiber, the signals change from digital to analog form.

Wavelength digital multiplexer (WDM) is used to multiplex all signals from the transmitter. The bandwidth of the multiplexer was set to 10 GHz. EDFA amplifier with power 10 dBm is used to boost up the power of the optical signal. Then, through an optical fiber, the signals are transmitted. This process can be seen in **Figure 9**.

**Figure 7.** Transmitter 1.

As soon as the signal reaches the receiver side, demultiplexer is used to demultiplex the sig‐ nals before the signals being distributed to its own receivers. 16 GHz is chosen as the band‐ width of the demultiplexer. At the receiver 1 as shown in **Figure 10**, the signal is once again amplified by using EDFA amplifier with power of 20 dBm. After that, photodetector is used to convert the optical signal into electrical form. Then, bandpass Bessel filter received the sig‐ nal and filtered the signal. The received signal is amplified by using electrical amplifier with 15 dB gain before demodulated by using demodulator. 3R regenerator technique is applied to the signal before the BER analyzer analyses the received.

Same concept is applied at the second receiver. The EDFA amplifier is used to boost the power of the optical signal after the signal is demultiplexed. Photodetector will transform the signal into electrical form. The converted signal will be amplified by electrical amplifier, and the signal will be passed to the Bessel filter. After the signal has been filtered, demodulator is used to demodulate the signal before the 3R regenerator amplification is applied to the signal. Lastly, BER analyzer will analyze the signal. The configuration of the second receiver can be seen in **Figure 11**.

Receiver Performance Improvement in Radio over Fiber Network Transmission http://dx.doi.org/10.5772/intechopen.68583 171

**Figure 8.** Transmitter 2.

As soon as the signal reaches the receiver side, demultiplexer is used to demultiplex the sig‐ nals before the signals being distributed to its own receivers. 16 GHz is chosen as the band‐ width of the demultiplexer. At the receiver 1 as shown in **Figure 10**, the signal is once again amplified by using EDFA amplifier with power of 20 dBm. After that, photodetector is used to convert the optical signal into electrical form. Then, bandpass Bessel filter received the sig‐ nal and filtered the signal. The received signal is amplified by using electrical amplifier with 15 dB gain before demodulated by using demodulator. 3R regenerator technique is applied to

Same concept is applied at the second receiver. The EDFA amplifier is used to boost the power of the optical signal after the signal is demultiplexed. Photodetector will transform the signal into electrical form. The converted signal will be amplified by electrical amplifier, and the signal will be passed to the Bessel filter. After the signal has been filtered, demodulator is used to demodulate the signal before the 3R regenerator amplification is applied to the signal. Lastly, BER analyzer will analyze the signal. The configuration of the second receiver can be

the signal before the BER analyzer analyses the received.

seen in **Figure 11**.

**Figure 7.** Transmitter 1.

170 Optical Fiber and Wireless Communications

**Figure 9.** Transmission of data through optical fiber.

**Figure 10.** Receiver 1.

**Figure 11.** Receiver 2.

#### **5.2. Single parameter optimization (SPO)**

SPO can benefit a lot in the simulation. It helps to optimize parameters so we could set a target for the simulation's result. With optimization tools, the software can optimize the fiber length of the EDFA so that a maximum gain could be obtained. It can also calculate the attenuation or the gain in order to get a desired Q factor and minimize the BER by optimizing the fiber length of the system.

After all components had been connected and SPO had been inserted to the topology, the simulation is run to see the result. After the run button is clicked, it will calculate all the cal‐ culation of the system. To measure the BER and the Q factor, just simply double click at the BER analyzer component. It will give an eye diagram showing eye opening, BER value and Q factor value. The example of the result is shown as in **Figure 12**.

Receiver Performance Improvement in Radio over Fiber Network Transmission http://dx.doi.org/10.5772/intechopen.68583 173

**Figure 12.** Example of BER analyzer's result.

As shown in the example above, the result tells us that the BER is 4.560 <sup>−</sup>10 and the Q factor is 6.124. There is an eye opening in the result of the example which is 2.585 −5 . The example is a quite good result since the BER is less than 10 <sup>−</sup><sup>9</sup> and the Q factor is more than 6. If all the receiv‐ ers receive an output just like the example above, all objectives had been achieved.

#### **6. Results**

**5.2. Single parameter optimization (SPO)**

length of the system.

**Figure 11.** Receiver 2.

**Figure 10.** Receiver 1.

172 Optical Fiber and Wireless Communications

SPO can benefit a lot in the simulation. It helps to optimize parameters so we could set a target for the simulation's result. With optimization tools, the software can optimize the fiber length of the EDFA so that a maximum gain could be obtained. It can also calculate the attenuation or the gain in order to get a desired Q factor and minimize the BER by optimizing the fiber

After all components had been connected and SPO had been inserted to the topology, the simulation is run to see the result. After the run button is clicked, it will calculate all the cal‐ culation of the system. To measure the BER and the Q factor, just simply double click at the BER analyzer component. It will give an eye diagram showing eye opening, BER value and Q

factor value. The example of the result is shown as in **Figure 12**.

After the simulation is done, the performance of the receiver is analyzed by referring the BER analyzer and the eye diagram at the two receivers. All the results can be seen in **Figures 13**–**16**.

For receiver 1, the BER analyzer shows that the BER for the received signal is 3.54 × 10<sup>−</sup>20. The Q factor for this receiver is 9.13. This shows that this receiver has a very good performance since the number of BER is above 10−<sup>9</sup> and the Q factor is more than 6.

As mentioned before, the height of the eye diagram defines the immunity of the received sig‐ nal to the noise. The eye diagram for receiver 1 shows an eye opening of 0.0004.

**Figure 13.** BER result for receiver 1.

**Figure 14.** Eye diagram for receiver 1.

Receiver Performance Improvement in Radio over Fiber Network Transmission http://dx.doi.org/10.5772/intechopen.68583 175

**Figure 15.** BER result for receiver 2.

**Figure 13.** BER result for receiver 1.

174 Optical Fiber and Wireless Communications

**Figure 14.** Eye diagram for receiver 1.

**Figure 16.** Eye diagram for receiver 2.

For receiver 2, the received signal has BER of 3 × 10<sup>−</sup>24. The Q factor for the received signal is 10.09. Thus, the BER analyser shows that this receiver also received a good quality of signal.

The eye opening of the eye diagram is 0.0371. It shows that received signal in receiver 2 has more immunity to noise compared to the received signal in receiver 1.
