High speed modulated wavelength division optical fiber transmission systems performance signature

This study presents modulated-wavelength division radio signals over fiber with mixed modulation techniques in the transmitter stage. Hybrid optical sources are used to achieve optimal performance and enhancement for an optical fiber communication network. The proposed modulation techniques work at a frequency of 250 GHz. Optical quadrature phase shift keying (OQPSK) and phase modulation (PM) techniques were merged to create OQPSKPM. This was in addition to the minimum shift keying (MSK) modulation scheme that was applied in the proposed model. The modulated wavelength division multiplexing design to four subscribers was examined with a single mode optical fiber at a 1550 nm wavelength. The proposed and previous simulation models were executed, investigated and measured on important operating parameter quantities that expressed the behavior of the optical fiber network in detail, like maximum quality factor, minimum bit error rate, and output power. The obtained simulation results demonstrated the priority of the proposed simulation model.


INTRODUCTION
Yunhao Z., et al. [1] have noted radio over fiber (RoF) systems that have deployed passive optical network architecture wavelength-division multiplexing (WDM) with self-interference cancellation, with the most importance results recognized at 240 Mbps with interference cancellation of 32 dB. In addition, it has applied both the orthogonal frequency division multiplexing (OFDM) modulation technique and 16-QAM (quadrature amplitude modulation) not only for an uplink at 390.63 Mbps but also for a downlink at 468.75 Mbps. However, Beilei Wu, et al. [2] have presented a RoF communication system concerned with transmitting a colorless upstream that depended on a modulation technique described correction of an orthogonal phase that can be recognized as a rotation of a polarization rotator plus a Mach-Zehnder modulator (MZM); it was used in a central office where it was applied at 800-Mbps (OFDM) downstream for a signal at 58 Gbps, and at 800 Mbps (OFDM) upstream for a signal at 1 Gbps. [3] presented a RoF communication system using different modulation techniques, such as QAM, differential phase-shift keying (DPSK), and phase-shift keying (PSK). For example, it performed modulation at 5.28 Gbps by using 16-QAM signals.
Nevertheless, the study [4,[5][6][7][8][9] presented a RoF communication system that was an experimental implementation that depended on division multiplexing for polarization to have the ability of increasing both TELKOMNIKA Telecommun Comput El Control  High speed modulated wavelength division optical fiber transmission systems... (Aadel M. Alatwi) 381 efficiency and capacity. It used a mix of both OFDM and pulse-duration modulation (PDM). The system architecture was executed with both modulation techniques at 200 Mbps to realizing an aggregation bit rate of 1.2 Gbps. However, a RoF system at 75-110 GHz, depending on an external optical modulator (EOM), for realizing several Gbps bit rates has been introduced in [5,[10][11][12][13][14][15][16][17][18]. The aim of this study was not only to enhance the transmission behavior with using two modulation techniques, QAM and OFDM, at 40 Gbps but also to achieve a higher spectral efficiency. The important recognized results were achieved with a distance of transmission reaching 50 km and a bit error rate (BER) reduction of 3.8x10 -3 . Nevertheless, they have presented a RoF communication system at 35-GHz that depends on a colorless laser diode (CLD) with an orthogonal polarization pair wavelength. Hence, the CLD provided one of a pair of wavelength modes with orthogonal polarizations, and the QAM and OFDM modulation techniques were applied. The obtained results achieved a transmission distance of 25 km at 24 Gbps (using 64-QAM and OFDM) and a BER reduction of 3.7×10 −3 [6,[19][20][21][22][23][24][25][26][27]. A bidirectional transmission and massive multi-input multi-output (MIMO) RoF communication system has also been investigated. The optical upstream was recognized from the central office to the remote antenna unit through a core (inner) for the coreless fulfillment. An advanced 2×2 MIMO-based OFDM/optical quadrature amplitude modulation (OQAM) channel estimation algorithm was optimally designed to equalize the hybrid optical and wireless MIMO channels. The study demonstrated the bidirectional transmission of 4.46 Gbps over 20 km by the 2×2 MIMO-OFDM/16-OQAM technique [7,[28][29][30][31]. J. Wang, et al., presented a digital mobile front haul (MFH) architecture with a sigmadelta (σ-ơ) pulse modulation technique interface instead of conventional common public radio interface [8]. However, 2-bit (σ) or 1-bit (ơ) technique modulations have been executed on signals then sent by 4-pulse amplitude modulation (PAM), and it realized a transmission distance of 25 km with 10 gigabaud. The most important results have been achieved in increasing capacity, a reduction of error vector magnitude (EVM) of less than 5%, and a BER reduction evaluated at 3×10 −5 .
The current work clarifies various modulation techniques that are used to enhance high-modulated RoF communication systems. Hybrid optical sources were used to achieve optimal performance and enhancement for optical fiber communication networks. These modulation schemes were mixed in the aptly named optical quadrature phase-shift keying phase modulation (OQPSKPM). In addition, a minimum shift keying (MSK) modulation scheme was applied in the proposed model. The proposed and previous simulation models were executed, investigated, and measured on important operating parameter quantities that expressed the behavior of the optical fiber network in details like the maximum quality factor, the minimum bit error rate, and the received power levels.

RESEARCH METHOD
The configuration of a modulated WDM-RoF subsystem transmitter model simulation involves several elements is shown in Figure 1. First, a serial sequence sample has to generated. Then, it is electrically modulated by one of the novel mixing techniques. These modulation schemes are OQPSK, OQPSKPM, in addition to the MSK technique. The modulated signals are combined and filtered before the optical modulation process. Then, this is carried out by a hybrid of vertical-cavity surface-emitting (VCSEL) lasers and LiNb (lithium niobate) MZM. Then, the optical signals are propagated through single-mode optical fiber. However, these optical signals are wavelength multiplexed or combined by a wavelength-division multiplexer (digital switch) that has multiple inputs and a single output [6]. The channel bandwidth is 40 Gb/s, and the channel frequency spacing is 50 GHz in the proposed simulation. Figure 2 illustrates the transmitter construction of the proposed model of the WDM-RoF communication system. The single mode fiber cable losses have been compensated by using an erbium-doped fiber amplifier (EDFA), which has been widely applied [7]. After completion of the transition process of the optical signals through an optical fiber, it is fitted by a Bessel optical filter before the conversion process. Hence, the optical signals are converted into an electrical form at the receiver end, and this is carried out by an avalanche photodiode (APD). The construction of the proposed modulated WDM-RoF receiver system simulation has been demonstrated as shown in Figure 3, where the demultiplexer (DEMUX) is the component that selects one of several input optical signals and forwards the selected signal into a multiple-line [8][9][10][11][12][13][14][15]. The essential function of the demultiplexer is to separate the combined or multiplexed optical signals, however, both a multiplexer (MUX) and DEMUX are joined here in one component. They function synchronously to realize the proper information or data transmission [16][17][18][19][20][21][22][23][24][25][26][27].

RESULTS AND ANALYSIS
The proposed simulation model was developed for a modulated wavelength division transmission system with an OQPSKPM technique at the transmitter end-stage. Performance was measured by a number of parameters. Most of the parameters express behavior that can be measured at the receiver end like the maximum quality factor. This parameter indicates the ability of the system to produce reasonable output and enhance the signal quality. In addition, the quality factor (QF) measures the quality of the transmitted signal, and the BER is the percentage of bits that have error related to the total number of received bits in a transmission. Moreover, comparisons were made between this model and the previous proposed simulation model approaches in terms of the maximum quality factor, minimum BER, and received power. These performance parameters were controlled and adapted by the performance behavior development of the WDM-RoF network, depending on the simulation parameters listed in Table 1.  Figure 4 illustrates the variations of the maximum QF regarding the extension length of the single mode (SM) cable. As the fiber length is extended, the maximum QF is reduced. The proposed model is based on OQPSKPM with MSK modulation techniques introduced at higher values of the maximum QF parameter compared to the previous model. The variation of minimum BER regarding data rates is clear from Figure 5. When the data rate increases, the minimum BER increases. However, the BER has minimal increasing values in the proposed OQPSKPM technique when compared to the previous model.  Figure 6 clarifies the description of the received power behavior related to the number of subscribers for both the proposed and previous models of the WDM-RoF communication networks. With a rising subscriber number (N), the received power decreases. However, received power reduction for the proposed WDM-RoF communication network based on the OQPSKPM with MSK technique is minimal when compared with the previous model. Figure 7 demonstrates the received power versus the data rate for both the proposed and previous WDM-ROF communication network simulation models. Increasing the bit rate decreased the received power. The proposed model was based on applying a mix of OQPSK and PM, or OQPSKPM, in the transmitter of the WDM-RoF communication network simulation model better than in the previous model. Hence, the proposed simulation model has optimized the decreasing received power. Figure 8 illustrates the maximum QF in relation to the number of subscribers (N) for the proposed and previous simulation models of the WDM-ROF communication network at data rates of 10 Gb/s and L = 20Km. The increase in subscriber number (N) causes a decrease in maximum QF. Moreover, it was noticed that the decrement in the maximum QF for the proposed simulation model was the lowest. So, the maximum QF was granted in terms of procedure priority for the proposed simulation model case. Figure 9 elucidates the minimum BER variation against the SM length with the development of the newly proposed OQPSKPM in the WDM-RoF transmitter communication system simulation model. The extension of the SM fiber length was met with an increase in the minimum BER. Moreover, it was noticed that the proposed OQPSKPM model behavior was optimized. Thus, the minimum BER parameter supports a preference for the proposed OQPSKPM simulation dependence model than others that depend on OQPSK and FM modulation techniques individually. Figure 10 clarifies the maximum QF changes regarding the bit rate with developing the novel mixed OQPSKPM in the proposed WDM-RoF communication network simulation model. The increase in data rates causes a decrease in maximum QF. Moreover, the maximum QF was observed to be best for the proposed modulation simulation model. So, the maximum QF grantee priority for the proposed simulation model depended on the novel OQPSKPM in comparison with the OQPSK and PM individually. Figure 11 demonstrates the variation of maximum QF distinction regarding the SM fiber length with using the novel mixed OQPSKPM in the proposed WDM-RoF communication system simulation model. As the SM fiber was extended, the maximum QF was reduced. Moreover, the decreasing maximum QF was noticed to still be the best for the OQPSKPM simulation model case.
So, the maximum QF parameter supports a preference for the OQPSKPM simulation model in comparison with the simulation model that depended on the OQPSK and PM, individually. Figure 12 indicates the received power variation regarding the SM cable fiber length when applying the novel hybrid OQPSKPM in the proposed WDM-RoF communication system simulation model. With an extension in the SM cable fiber length, the received power begins decaying. However, the proposed hybrid OQPSKPM technique grants higher values of received power than the original OQPSK and PM individually. Figure 13 illustrates the minimum BER variation regarding the data rates with the development of the mixed OQPSKPM in the proposed WDM-RoF communication system simulation model. Increasing the bit rate causes an increase in the minimum bit error rate. However, the increasing BER was lowest in the simulation model that depended on the OQPSKPM as observed. So, the lowest variation of the minimum BER showed a preference for the proposed model OQPSKPM dependence.  Figure 14 illustrates the maximum QF variation against the subscriber number (N) with the development of the mixed OQPSKPM in the WDM-RoF system. The increase in the subscriber number (N) resulted in a decreasing maximum QF. Moreover, the reduction in the maximum QF for the novel mixed OQPSKPM in the proposed model was the lowest. So, the maximum QF parameter permits a priority proposed simulation model to depend on the OQPSKPM in comparison with the individual OQPSK and PM dependence model. Figure 15 clarified that the received power changed regarding the bit rate with the development of the hybrid OQPSKPM in the WDM-RoF system. With the increasing of the bit rate, there was decreasing in the values of the received power. Moreover, the lowest decreasing of the received power level was the case of the OQPSKPM technique. Thus, the lowest variation of the received power level grants a preference for the proposed simulation model that depended on the novel OQPSKPM technique in comparison with the model which depended on the OQPSK and PM individually.  Figure 16, the received power variation in relation to the number of subscribers (N) while using the new mixed OQPSKPM in the WDM-RoF system was clear. The rising in subscriber number reduced the received power. While the reduction in the received power was noticed in the novel mixed OQPSKPM dependence simulation model to be lower than the ordinary modulation, OQPSK and PM, simulation model. Thus, the received power parameter allowed priority for the proposed simulation model which depended on the novel OQPSKPM technique in comparison with the model depending on OQPSK and PM individually. The optimized parameter values for the proposed modulation scheme based on the WDM-RoF system are listed in Table 2.

CONCLUSION
The modulated-wavelength division-multiplexing radio over fiber communication system was executed with single-mode optical fiber at a wavelength of 1550 nm. The merged advanced modulation (OQPSKPM) techniques granted enhanced behavior for the proposed WDM-RoF communication system simulation model more than the ordinary modulation dependence basic simulation model. In addition, the validation and verification for the operating parameters have been carried out and the optimized values have been obtained. The maximum quality factor value reached 30.2, the bit error rate parameter decayed to 43.6x10 -20 , and the received power was recognized at 886.5 μW. In addition, the optimized transmission length was extended to 130 km, and the bit rate reached 150 Gb/s.