SIMULATIVE INVESTIGATION OF TRANSMISSION PERFORMANCE FOR PROPOSED NG-PON 2 BASED ON DPQSK MODULATED DOWNSTREAM WITH TWO DIFFERENT INTENSITY MODULATED

We present a comparison between the two high data rate next generation passive optical network (NG-PON 2) which are feasible to fulfill the future demand for bandwidth hungry applications that exceeds beyond 10Gbps. This paper summarizes the best suitable network for future bandwidth hungry applications by simulating both networks through optisys simulated software considering standard values and recommendations for NG-PON 2. Both networks support 40Gbps with Differential Quadrature Phase Shift Keying (DQPSK) while at upstream one network supports 10Gbps with On Off Keying (OOK) and other support Inverted return to zero (IRZ) with 10Km fiber span. Comparison of both networks transmission performance in terms of BER with Rx power and OSNR has been investigated and results shows that NG-PON 2 support 40Gbps with DQPSK and 10Gbps IRZ is quite better than other network with higher sensitivity and OSNR.


INTRODUCTION
Evolution in PON is essential to deal with future bandwidth hungry applications.Existing PON have a capability to transmit 10Gbps and 1Gpbs downstream and upstream data rate with HDTV, multimedia and video calling simultaneously [1][2].As per the survey of CISCO in 2016 it is predicted that data rate will be increased twice compare to 2015 data rate [3].It is necessary to increase the data rate capability up to 40Gpbs in PON to deal with future bandwidth hungry applications and named as NG-PON 2 [4][5][6].
In this paper we have analyzed the performance of two high data rate NG-PON 2 having the same downstream modulation DQPSK but different upstream modulation OOK and IRZ.DQPSK modulation format is used as it has high spectrum efficiency and high transmission impairments [19] and OOK and IRZ modulation formats used as they are simple and cost effective design [20,21].Both DQPSK with OOK and DQPSK with IRZ architectures have 40Gbps data rate in downstream and 10Gpbs data rate in upstream with 10km fiber span by using FBG dispersion compensation.

DESCRIPTION OF SIMULATION
For analyzing the performance of both architectures, simulation software has been used named as Optisystem [22].Figure 1 and Figure 2 shows the simulated model of high data rate DQPSK with OOK and high data rate DQPSK with IRZ NG-PON 2 having same parameters except different modulation technique in upstream.Both networks have OLT, ONU and optical fiber length of 10Km with FBG dispersion compensator.CW LASER at 0dBm launch power is used as a carrier source which is modulated with electrical data stream generated from pseudo random generator (PRBS) having data rate 40Gbps through two series connected Lithium Niobate Mach-Zehnder modulator (LiNb MZM).Modulated signal is transmitted through optical fiber span of 10km with 0.2dB/km attenuation co-efficient as shown in Table 1.DQPSK modulation technique is used in the downstream of both networks.DQPSK transmitter modulator is shown in Figure 3. DQPSK transmitter is composed of CW Laser having 0dBm power (1mW) works at 1550nm and data is generated from psuedorandom bit squence (PRBS) generator of 40Gbps.Data is modulated after differential precoding through two LiNb Mach-Zehnder Modulators.One modulator is act as a phase modulator to create a dephasing of π/2.After modulation, signal is transmitted through optical fiber towards the reciever of the ONU where signal is splitted into two signals demodulated through coupler and followed by two photodetector PIN.There output combines with the subtractor and gives the electrical output as shown in Figure 4.The ONU transmitter remodulates the signal through OOK modulation in one network while IRZ in another network.For OOK transmitter, same signal is modulated through Mach-Zehnder modulator with data generator from psuedo-random bit squence (PRBS) generator of 10Gbps shown in Figure 5. Modulated signal transmitted through optical fiber received by photodetector which demodulates the signal gives electrical output as shown in Figure 6.Whereas IRZ transmitter for second network, same signal is modulated through Mach-Zehnder modulator with data generator from psuedo-random bit squence (PRBS) generator of 10Gbps which added with pulse generator having frequency 5GHz and phase of -π/4 shown in Figure 7. Modulated signal transmitted through optical fiber received by photodetector which demodulates the signal gives electrical output shown in Figure 8.          Figure 17 and 18 shows the simulation results obtained on 10Km and back to back (B2B) fiber span with downstream and upstream of both DQPSK with OOK and DQPSK with IRZ. Figure 17 shows the comparison of downstream of both networks at 10Km and B2B fiber length.Receiver sensitivity of DQPSK with IRZ at standard BER is much better than DQPSK with OOK on both 10Km fiber span and B2B i.e. -31dB and -33dB at 10Km fiber span and -32dB and -33.5dB at B2B.From Figure 17, it also can be seen that the transmission power penalty of both networks at 10Km fiber span and B2B is 1dB and 0.5dB.Figure 18 shows the comparison of upstream of both networks at 10Km and B2B fiber length.Receiver sensitivity of IRZ at standard BER is much better than OOK on both 10Km fiber span and B2B i.e. -38dB and -42.5dB at 10Km fiber span and -38.5dB and -45.5dB at B2B.From Figure 18, it also can be seen that the transmission power penalty of both networks at 10Km fiber span and B2B is 0.5dB and 3dB.Comparison of result is being mentioned in Table 2.      networks at 10Km and B2B fiber length.It can be seen that as the receiver sensitivity is increased so does OSNR increased.Transmission performance of DQPSK with IRZ at downstream is better compared to DQPSK with OOK as it works at higher receiver sensitivity and OSNR. Figure 20 shows the comparison of Rx power vs OSNR at upstream of both networks at 10Km and B2B fiber length.Here, it can also be seen that IRZ works at higher receiver sensitivity and high OSNR compared to OOK.From the results, it can be seen that DQPSK with IRZ network is much better than DQPSK with OOK network in terms of performance as receiver sensitivity is high and transmission power penalty is within the standard range.

CONCLUSIONS
In this paper, we have investigated two high data rate next generation passive optical network 2 (NG-PON 2) with the same modulation DQPSK at downstream but different modulation formats at upstream i.e. one is OOK and another one is IRZ at 10Km fiber span.Simulated results validate that transmission performance of DQPSK with IRZ is better than DQPSK with OOK in term of higher receiver sensitivity and better OSNR values with very low transmission power penalties in both directions under the similar simulative conditions.

Figure 13 ,
Figure 13,14,15 and 16 shows the eye diagram of both DQPSK with OOK and DQPSK with IRZ which are wide open having few transmission errors but in an acceptable range to transmit the data.The power and BER of DQPSK/OOK downstream and upstream are 3.41961x10 -046 and 4.10171x10 -018 and -8.168dB and -34.347dB whereas for DQPSK/IRZ are 1.26888x10 -034 and 3.84401x10 -020 and -8.167dB and -37.824dB.From the loss margin of both the systems i.e. -22.832dB and -8.153dB for downstream and upstream of DQPSK/OOK and -34.343dB and -7.676dB, it can be seen that both systems are feasible for High Data Rate NG-PON 2.

Figure 13 .
Figure 13.Eye Diagram of Downstream DQPSK with OOK upstream Signal.

Figure 15 .
Figure 15.Eye Diagram of Downstream DQPSK with IRZ upstream Signal.

Figure 19
Figure19and 20 shows the simulation results obtained on 10Km and back to back (B2B) fiber span with downstream and upstream of both DQPSK with OOK and DQPSK with IRZ.Figure19shows the comparison of Rx Power vs OSNR at downstream of both

Table 2 .
Transmission Performance of DQSPK modulated downstream with OOK and IRZ modulated upstreams.