Enhanced Time and Wavelength Division Multiplexed Passive Optical Network (TWDM-PON) for Triple-play Broadband Service Delivery in FTTx

Networks Samy Ghoniemy

Faculty of Informatics and Computer Science The British University in Egypt (BUE)

El-Sherouk, Cairo, Egypt samy.ghoniemy@bue.edu.eg

Abstract— Nowadays service providers are facing serious competition and are looking for new ways to address their customers' very high-bandwidth demands and emerging trends as immersive video communications and ubiquitous cloud computing. Optical access successfully proved that it is a crucial broadband technology that is proposed to meet these challenges. In this paper, the wavelength division multiplexed (WDM) PON together with TDMA as a hybrid PON technology will be proposed and investigated for enhancing the system reachability, capability, and accommodation of users. For this purpose, fiber to the home (FTTH) networks using PONs, Gigabit-capable Passive Optical Networks (GPONs) and 10G-PONs that are designed using generic architectures and implemented using OptiSystem. Simulation results based on a broad set of performance measures such as bit rate, power losses, transmission distance and number of users showed that the proposed generic transmission architecture is suitable for up- and down-stream transmission of triple play traffic over optical links of up to 10 Gbps and the ability to accommodate 32 ONUs. The second part of this paper presents the development of a wavelength division multiplexing PON (WDM-PON) model in which array waveguide gratings (AWGs) are used to MUX and DEMUX wavelengths to or from Optical Network Units (ONUs). The proposed design addresses the real-time consistency between the wavelengths of optical transceivers and the connecting AWG port; and between the wavelengths of the port on the AWG that is located in the central office and the port on the remote AWG. The experimental tests using 100 or 200 GHz channel spacing and several tens of nm between up- and down-stream channel clusters showed the ability of multiplexing up- and downstream of 40-channels based on the commercially available AWG, providing the ability to accommodate 40 ONUs. The last part in this paper discusses the designs of a symmetric 4x40Gbps TWDM-PON network for the next generation passive optical networks to improve the network capacity. In this design a distributed feedback (DFB) laser diode is used for downstream transmission and a tunable intensity modulated grating laser is used for upstream transmission. The experimental results of this design showed that TWDM-PON achieved successfully 4×40Gbps along 20km fiber at 1:128 splitting providing the ability to accommodate up 128 ONUs. To the best of my knowledge, the proposed system

provides two times larger number of ONUs than currently available systems.

Keywords— TWDM-PON; Triple-play Broadband Service Delivery; FTTx Networks; NG-PON2; Broadband optical access networks.

I. INTRODUCTION In a recent Cisco forecast projects (2014-2019), an 18 GB

of the global internet traffic will be reached by 2019 with an increase of approximately 12 GB in 2014 [1], and the internet video traffic will be approximately 80% of whole internet traffic in 2019 with an increase of 16% from that in 2014. Surprisingly, it was estimated that in 2019 that the IPTV will be 17% of the internet video traffic with estimated fourfold continuous growth, whereas the video on demand (VoD) traffic is estimated to be doubled and the high definition TV (HDTV) is estimated to be 70% of the IPVoD traffic with an increase of approximately 11% in 2014 [1]. Also, it was estimated that the mobile data traffic will be 14% of the overall IP traffic compared with 4 percent in 2014 [1]. It was also mentioned that the IP traffic in the Middle East and Africa will grow at a compound annual growth rate (CAGR) of 44% between 2014 and 2019 [1]. This exponential growth of real-time and bandwidth intensive applications as immersive video communications and ubiquitous cloud computing exploded the last segment capacity limitation problem of the access technologies and is continuing to increase the diffusion of high-capacity, low-latency fiber networks into the Fiber-To-The-x (FTTx)-based broadband access networks. Most of the FTTx models such as fiber to the node (FTTN) that serves several hundred customers, fiber to the cabinet (FTTC) that serves several customers, and fiber to the premises (FTTP) that is further categorized as fiber to the home (FTTH) for one living or working space and fiber to the building (FTTB) for those properties that contain multiple living or working spaces, are able to deliver multiple (triple- and quad-play (voice, video, data, and mobile)) services over fiber-based point-to-point access networks. One of the remarkable solutions for access networks that will meet the above mentioned requests is

deployment of the Point-to-Multipoint (P2MP) architecture using PON technologies as one of the FTTx models.

An FTTx-based PON constitutes three major parts as shown in Figure 1. The first part which is housed in the central office of the service provider is the Optical Line Terminal (OLT). The second part which is installed in or near to the client site is the Optical Network Unit (ONU). The third part is the Optical Distribution Network (ODN) in which a single distribution fiber is used as a communication channel to connect the OLT to different ONUs by employing one or more passive optical distribution elements such as optical splitters and/or wavelength filters [2].

Fig. 1. Passive Optical Network architecture.

The OLT is the location at which the backbone network meets the access networks and it contains the devices that are able to control/select and deliver the incoming triple- and quad-play traffic from the backbone network to the consumers’ ONUs in the downstream path, while in the upstream path it receives and hand out the incoming traffic from the consumers’ ONUs. A full-duplex transmission of different services over a singles fiber is facilitated by employing different wavelengths such as using a 1.49 μm wavelength in the downstream path for carrying both the voice and data traffic and using a 1.55μm wavelength for carrying the video traffic. While in the upstream path, the voice and data traffic are carried by a 1.31 μm wavelength [3]. According to the standards, the ONT normally supports different digital and analog-based services such as 1.544 and 2.048 Mbps Ethernet, telephone connections at rates from 44.736-to-34.368Mbps, 155Mbps ATM traffic, and different video formats [3].

This paper aims to present a proposed solution for the triple play transmission to the ONU side using PON architectures as a recommended approach to the NG-PON2 requests. In the subsequent sections the PON concepts are discussed. The discussion starts by introducing the major needed components, and is followed by introducing the main advantages and the limitations; then, an overview of the latest research results available in the literature will be presented. This paper is organized as follows. Section 2 introduces the current PON-based FTTH solutions. Section 3 presents the GPON to NG-PON2 transition and the needed

technologies. The proposed system architecture, simulation setup and simulation results of FTTH-based GPON for triple play services is described in Section 4. In Section 5, system architecture, simulation design, simulation results and performance evaluation for a hybrid TDM/WDM-PON (TWDM)-PON system are reported. Finally, the main conclusion are presented in Section 6.

II. OVERVIEW OF CURRENT PON-BASED FTTH SOLUTIONS

Many TDM-PON standards have been established such as broadband PON (BPON), Ethernet PON (EPON), and Gigabit PON (GPON). Also, in 2004 IEEE established the IEEE 802.3ah standard including EPON, and in 2009 they established the IEEE 802.3av for 10G-EPON [4]. In these standards both asymmetric and symmetric traffic are described as follow; a 10 Gbps traffic from the service provider to the client in the downstream direction and a 1 Gbps from the client to the service provider; on the other hand, a 10 Gbps is guaranteed in both directions in the symmetric [4]. Meanwhile, in 2006 the special interest group Full Service Access Network (FSAN) and the ITU Telecom Standardization Sector (ITU-T) recommended a refined GPON with the ability avoid receiving non-GPON wavelengths as an easy enabled migration technology to the current and future systems [4]. As PON topology is becoming more popular the need for higher bandwidth PON technologies was recommended in 2010. The NG-PON1 which was designed to provide 10 Gbps and 2.5 Gbps asymmetric traffic in the downstream and upstream, respectively and is able to support up to 256 ONUs/ONTs has been standardized [5, 6].

A. Asymmetric 10G-PON (NG-PON1) ITU-T G.987 standard recommended NG-PON1 as a

compatible technology with the existing GPON equipment, framing structure and management protocols, but with higher data rate and larger physical splitting ratio as shown in Figure 2.

Fig. 2. . Physical split reduction.

Furthermore, FSAN recommended the 1575 and 1270nm wavelengths for the downstream and upstream, respectively [3]. ITU-T G.984.5 recommended a wavelength coupler in the CO, as illustrated in Figure 3, for full compatibility between GPON and NG-PON1 systems and called it “Stacked G-PON”.

Fig. 3. Stacked GPON scheme.

Adding the WDM combiner slightly increased the power loss budget, thus it was specified that NG-PON1 could operate at 31, 33, and 35 dB power budgets. Practically, existence of the WDM filter/combiner is the major limiting factor for such deployment. Thus, to enable both the GPON and NG-PON1 using the old infrastructure at the service provider site, ITU-T G.988 [2, 3] recommended to upgrade the ONTs by installing such WDM filters.

B. Next Generation Optical Access Technologies (NG-PON2) The next-generation technology for passive optical

networks (NG-PON2) is still in the standardization process and it aims to increase the asymmetric capacity to at least 40 Gbps in the downstream path and at least 10 Gbps in the upstream path by the end of 2015 [6, 7]. A number of options have been considered for next generation broadband access standard (NG-PON2), this includes WDM-PON, ultra-dense WDM-PON, orthogonal frequency division multiplexing PON, and TWDM-PON (TDM/WDM-PON), a hybrid system that stacks four 10GPONs onto a single fiber to deliver 40 Gbps capacity that will be adequate for the future needs [4, 8, 9].

C. Wavelength Division Multiplexed Passive Optical Network (WDM-PON) A PON that employ Wavelength Division Multiplexing

(WDM) offers a distinct wavelength for each ONU based on incoherent injection seeding as illustrated in Fig. 4 [10].

Fig. 4. Basic block diagram of the WDM-PON based on incoherent injection seeding.

In this scheme, back reflection induced penalty was diminished due to incoherent nature of seed light. In addition the F-P LD provides optical gain and direct modulation advantage. Since the WDM-PON is logical point-to-point connection, although it has point-to-multipoint physical

connection, it is not easy to provide broadcasting services. There had been some demonstration in broadcasting services in WDM-PON [10]. An optical power splitter can be used in conjunction with AWG. Some cases, this scheme, can provide an evolution scenario from TDM-PON to WDM-PON [10, 11]. It is also possible to provide broadcasting service in WDM-PON by using an array of multi-wavelength transceivers as shown in Figure 5. However, this will increase the overall cost of the system, this could be alleviated by sharing the WDM-PON OLT among the subscribers, and by using tunable receivers at the WDM-PON ONUs. Another solution is to use Arrayed Wave Guide (AWG) passive router, as shown in Figure 6, at the remote node (RN) to separate the wavelengths for different ONUs [11]. Table 1 summarizes the two most common options to design such networks. The major advantages of using Arrayed Wave Guide (AWG) passive router are their low power losses the ability to statically allocate the wavelengths, that make it very suitable for metro/access integration. While, the advantage of using the power-splitter-based WDM-PON is the possibility of dynamic wavelength allocation, since these splitters are transparent to wavelengths, which make it suitable to be integrate with the current PON systems [12].

The major constraints of adopting such WDM-filter-based PON approach and leaded to NG-PON2 standard are; 1) the cost of replacing all passive splitters by AWG filters and inability to share wavelengths; 2) compatibility limit with the existent standards.

Fig. 5. Basic building block of the multiplexed GPON scheme.

Fig. 6. Architecture of a WDM-PON Arrayed Wave Guide (AWG) passive router.

TABLE I. APPLICATIONS AND TECHNICAL ISSUES FOR TWO TYPES OF WDM-PON.

D. Broadband TWDM-PON TWDM-PON was recommended in 2012 by many

organizations specially FSAN to be a remarkable solution for NG-PON2 with its basic architecture shown in Figure 7. In these standards, the maximum allowed number ONUs is 64 (16/wavelength), a maximum of 35 dBm power budget is required, and the maximum allowable transmission distance is 40km. Also, they focused on the use of 4-to-8 pairs of wavelengths, namely 1595-1605 nm for the downstream path at 40Gbps aggregated data rate (10Gbps/wavelength) and 1535-1545 nm for upstream path at aggregated data rate 10Gbps (2.5 Gbps/wavelength) [13].

Fig. 7. TWDM-PON system diagram.

In these systems, all active elements are equipped either in OLT or ONU such that each ONU is equipped with a tunable transceiver (Tx/Rx) that could be tuned over the wavelength plan and the OLT is equipped WDM Mux/DeMux and optical amplifiers to deliver an amplified downstream signals and to pre-amplify the upstream signals. One of the most architectures of NG-PON2 that allows operators to deploy simultaneously different technologies on the same ODN is based on the use of coexistence element (CE) which associates a suitable wavelength for their corresponding technology, as shown in Figure 8 [8, draft ITU-T G.989].

Fig. 8. NG-PON2 using coexistence element.

E. Migration from GPON to NG-PON2 Figure 9 shows the typical components of a GPON.

Fig. 9.Current GPON deployment.

To upgrade this network to NG-PON2, the main precaution is to preserve the infrastructure of the ODN. As described in ITU-T G.984.5, this necessitates to enclose the CE and route the fiber to it in the OLT, and to enclose the WDM filters in the ONUs as shown in Figure 10.

Fig. 10. Coexistence of GPON and NG-PON2

III. SYSTEM ARCHITECTURE AND SIMULATION SETUP OF FTTH-BASED GPON FOR TRIPLE PLAY SERVICES

This section presents the proposed system and its main parts and their effect on the estimated results. The simulation model consists of three sections: 1) optical line terminal OLT, 2) optical network unit ONU, and 3) optical Distribution network ODN. In this model a Triple-Play-64 users in which video (Broadcast CATV) is multiplexed and transmitted over 1550-nm wavelength while VoIP and data link are transmitted over a wavelength 1490-nm. The ODN fiber span is 20-km.

OLT system contains; transmitter, receiver, fiber, some optical components. The transmitter part consists of Pseudo random bit sequence generator, a NRZ encoding, CW laser, and finally the merging system. To conform the GPON transmission to the existing FTTH technology, data and voice are transmitted over 1490-1550nm wavelength range. The high-speed internet is implemented by a data link of 1.25 GBps, 2 GBps, 2.5 GBps, 5 GBps and 10 GBps bandwidth. Voice service is implemented using VoIP protocol. The architecture for such network consists of an OLT that is equipped in the CO, and an ONU mounted in or near each user site as shown in Figure 11. Only one fiber is used to connect the OLT and could be split to 64 segments that are connected to ONTs to implement a typical GPON FTTH network of up to 64 subscribers and 20km reach.

In the proposed system, voice and internet data are simulated using Pseudo random binary sequence (PRBS) generator at bit rate of 622 Mbps (PON), 2.5 Gbps (GPON), and 10Gbps (XG-PON). These data rates will be transmitted over different distances. The wavelengths assigned to downlink and uplink signal are 1550 nm and 1310 nm, respectively. Mach Zehnder modulator is used to externally modulate the laser source intensity by the incoming NRZ data encoded signals. The proposed optical splitter is a 1:64 balanced splitter with the same attenuation on each output and without any insertion loss. To enhance the signal, an amplifier is added before the fiber to decrease the BER and to accommodate more users.

Fig. 11. Simulation setup of the proposed FTTH GPON OLT transmitter.

On the other hand, the receiver part contains a photodiode, low pass filter, 3R generator, and optical filters. The received light signal is filtered with the help of Gaussian filter and then converted back to its original form using an Avalanche photodiode (APD) as shown in Figure 12. The same phenomena is repeated simultaneously for different users.

Fig. 12. Simulation setup of the proposed FTTH GPON ONU receiver.

Also, a Gaussian filter with -3dB bandwidth of 100GHz and Positive-Intrinsic-Negative (PIN) photodiodes are used for audio reception then the signal is filtered by low pass Bessel filter with a cutoff frequency of three quarters the bit rate (3/4 BR). The architecture of the proposed PON, GPON and XGPON generic model is designed using OptiSystem 13.0 simulator [14] and the experimental setup is shown in Figures 11 and 12.

A. Results and Discussions A triple-play network is one in which voice; video and

data are all provided in a single access subscription. The availability of prioritization of streams in a triple play environment must be measured. Internet traffic is given the lowest priority, since data services are not drastically affected by packet delays. Video traffic has the next highest priority, since the minimum loss of video packets does not negatively affect the perceived appearance, as long as the streaming audio track is not broken. Finally, voice over IP will have the highest priority, since voice services are very sensitive to latency and loss of packets. In this study, two techniques have been provided; the first which measure triple play BER Versus the length or distance at specific bit rate, signal power levels and number of users starting from 16 users to 64. A group of scenarios have been provided to test the system response. Table 2 shows the simulation parameters of these scenarios.

TABLE II. SIMULATION PARAMETERS IN DIFFERENT SCENARIOS.

Scenario Power Bit Rate Length

scenario 1 Sweep 622 Mbps Sweep

scenario 2 Sweep 2.5 Gbps Sweep

scenario 3 Sweep 5 Gbps Sweep

scenario 4 Sweep 10 Gbps Sweep

scenario 5 Sweep 15 Gbps Sweep

The network described above went through a barrage of tests that could not have being economically efficient without the vast array of simulation software analysis tools, namely the Optical Time Domain Visualizer (OTDV), an eye diagram analyzer, and an optical spectrum analyzer (OSA).

The performance criterion for digital receivers is governed by the bit-error rate (BER). In order to evaluate the performance of the proposed system, the BER values are measured at different distances under different bit rates, signal power levels and number of users. The experimental results are illustrate in Figures 13 (a) and (b), respectively.

Fig. 13. Experimental results of the BER vs. (a) power under different distances, (b) distance under different data rates.

This figure showed that for users at distance equal or less than 20 Km to get accepted performance, the power levels should exceeds 21.5 dBm, while high levels of BER are observed for users at distances exceeds 20km. Also it has been noted that the triple play service at rate of 1.25Gbps may be received at good quality until 30km, while at rate of 2.5Gbps will not cross 27km. Finally at rates of 5-10Gbps a good service quality is only limited to 20 km or less distance.

Tacking all together, these Figures show that with 10GBps of data rate, a nearly error-free transmission can be achieved over a bidirectional 20 km feeder for 64 users, which is sufficient for high data rate PON applications.

IV. SYSTEM ARCHITECTURE AND SIMULATION DESIGN FOR HYBRID TDM/WDM-PON (TWDM)-PON SYSTEM

To support triple play applications and converged services, future broadband services should provide higher bandwidth, larger splitting ratio and longer reach. Future optical access networks provides at least 40 Gbps aggregated capacity in a single optical distribution network, and sustainable 1 Gbps bandwidth for each ONU. Large splitting ratio with 64 to 256 ONUs per feeder ber and long reach over 40 km are highly desired. As it was discussed in Section 1, the proposed optical access networks must be backward compatible with legacy PON systems [16]. Furthermore, future broadband services will provide better resiliency, enhanced security, low power consumption and high port density [16]. To meet all these requirements, there are different technology options for future broadband services. Currently, operators have 10G PONs with an aggregated bandwidth of 10 Gbps. This could meet the customer bandwidth demands in the near future. In the longer term, there exist a few different approaches to upgrade broadband optical access networks to satisfy the limitless bandwidth demands. One obvious option is to continue to use the pure TDM scheme, as in GPON/EPON and 10G PONs, to provide an aggregated 40 Gbps bandwidth. However, transmission at 40 Gbps line rate is very dif cult and costly, as burst-mode transceiver and ber dispersion penalty at 40 Gb/s are very challenging. Alternatively, more wavelengths could be added by stacking multiple 10G PONs in the same optical distribution networks (ODN). For example, we could have a hybrid TDM/WDM PON with 4-8 wavelengths [17]. In addition to TDM and WDM, we could also use FDM (frequency division multiplexing) or CDM (code division multiplexing). FDM/OFDM

(orthogonal frequency division multiplexed) PON and ECDMA/OCDMA (electronic/optical CDMA) PON systems have been demonstrated. However, complexity, cost and power budget are the major concerns for these systems. As the technology continue to evolve, the evolution path from GPON, 10G PON to TWDM PON is the main-stream approach. Therefore, FSAN (Full Service Access Network) group and ITU-T (International Telecommunication Union Telecommunication Standardization Sector) have chosen TWDM PON as the solution for future broadband optical access.

TWDM-PON is determined as the best technical candidate among NG-PON2 technologies because it offers large split ratio which helps in achieving lower cost and power consumption per user, and it inherently supports the high flexibility of resource allocation which allows it to efficiently adapt to the varied traffic demands from the end user [18-20]. TWDM-PON mainly consists of 4 or 8 individual XG-PON subsystems stacked into a common (ODN) using a pair of wavelengths [21]. In TWDM PONs, TDM and WDM components coexist in the same ODN such that some customers are served by the TDM infrastructure and others by the WDM infrastructure. The reason for this type of coexistence is that it may be desirable to make use of the same infrastructure deployed for TDM-PON to provide WDM-PON capabilities.

In this paper, the conceptual diagram of a TWDM-PON system is shown in Figure 14 [21] is adopted, in which four TDM-PONs are stacked to share the same ODN by using four pairs of wavelengths. At the OLT, a conventional WDM de-multiplexer, is used to de-multiplex the four uplink signal wavelengths. The tunable transmitters at ONUs can work at any uplink wavelength. Each wavelength serves multiple ONUs with time division multiple access. As all the downstream wavelengths are broadcasted to all the ONUs, each ONU selectively receives a single downstream wavelength using a tunable receiver. For upstream, each ONU transmits on one of the upstream wavelengths using a tunable transmitter. Essentially, there exist multiple 10G PONs stacked in the same ODN, and each 10G PON is running on different wavelength pairs. Such system provides a total capacity of at least 40 Gbps.

Fig. 14. Conceptual diagram of a TWDM-PON.

For the purpose of this paper, the demonstrated conceptual design of the TWDM-PON is further modified, where four TDM-based PONs are stacked by a AWG to achieve 40-Gb/s symmetric aggregate rates and accommodates 4λ×8 users. At the OLT side, each transceiver (TX/RX) unit consists of a directly modulated tunable distributed feedback (DM-DFB) laser diodes and is driven by 10-Gb/s pseudorandom bit sequence (PRBS) data, these signals are then multiplexed by a WDM and are injected into the delay interferometer (DI), which is used to mitigate the chirp-induced distortions for multiple bi-directional channels. To achieve power budget higher than that of XG-PON, signals are amplified to 13 dBm per wavelength by optical amplifiers to boost the downstream

signals and to pre-amplify the upstream signals. The signals after passing through a single mode fiber (SMF) they are then distributed to each ONU by a splitter at the remote node (RN), and an optical attenuator is used to emulate the loss of optical splitter. Each ONU contains a tunable transceiver (Laser Diode (LD) and Avalanche Photo Diode (APD)) and a tunable filter with 0.8-nm bandwidth to select any of the four downstream wavelengths. The modified TWDM-PON is designed and developed using OptiSystem 13 simulator and a set of experiments have been carried out to evaluate the performance of the TWDM system using the ITU standard specifications shown in Table 3.

A. Results and Discussions The performance of the TWDM-PON system is

evaluated for down- and up-streams. In the first experiment, there are 4–8 wavelengths from 1596 to

1603 nm on ITU grid with 50-to-100 GHz channel spacing for downstream, each downstream wavelength carries 10 Gbps data. On the other hand, there are also 4–8 wavelengths from 1524-1544 (wide band), 1528-1540 (reduced band), 1532-1540 (narrow band) for upstream.

TABLE III. SPECIFCATIONS FOR TWDM PON PHYSICAL LAYER

(a) downstream, (b) upstreamOLT transmitter ONU transmitter Nominal line rate (Gbps) 10 Nominal line rate (Gb/s) 2.5

Operating wavelength band (nm) 1596-1603 Operating wavelength band (nm) 1524-1544 (wide band), 1528-

1540 (reduced band), 1532-1540(narrow band)

Operating channel spacing (GHz) 100 Minimum Operating channel spacing (GHz) 50

ODN Class N1 N2 E1 E2 Maximum Operating channel spacing (GHz) 100

Mean launched power MIN (dBm) +3.0 +5.0 +7.0 +9.0 ODN Class N1 N2 E1 E2

Mean launched power MAX (dBm) +7.0 +9.0 +11.0 +11.0 Mean launched power MIN (dBm)

ONU receiver Type A link without optical ampli er at OLT Rx +4 +4 +4 +4

ODN Class N1 N2 E1 E2 Type B link with optical ampli er at OLT Rx 0 0 0 0

Minimum sens. at 10-3 BER (dBm) -28.0 -28.0 -28.0 -28.0 Mean launched power MAX (dBm)

Minimum overload at 10-3 BER (dBm) -7.0 -7.0 -7.0 -9.0 Type A link without optical ampli er at OLT +9 +9 +9 +9

Type B link with optical ampli er at OLT +5 +5 +5 +5

OLT receiver

Minimum sensitivity at 10-4 BER (dBm)

Type A link without optical ampli er at OLT -26 -28 -30.5 -32.5

Type B link with optical ampli er at OLT -30 -32 -34.5 -36.5

Maximum overload at 10-4 BER (dBm) Type A link without optical ampli er at OLT -5 -7 -9 -11

Type B link with optical ampli er at OLT -9 -11 -13 -15

Each wavelength carries 2.5 Gaps data stream, and 10 Gbps upstream is optional.

Figure 15(a) and (b) show the measured BER curves for downstream and upstream channels with the received optical power after 40 km SMF transmission respectively.

Fig. 15. BER performance for (a) downstream signals, (b) upstream signals.

V. CONCLUSION In this paper, the comparison of the different FTTH

architectures and the proposed solutions for the design and utilization problems of passive optical networks have been presented. The major BER results illustrate that the maximum possible number of users with good quality is 64, beyond this the BER becomes unacceptable and a severe increase in BER appears when the data rate exceeds 5 Gbps. Also it was observed that the BER increases as the transmission distance increases until it become unacceptable after 120 km distance which is a problem. The BER results show that the performance of proposed 10 Gbps systems is acceptable for downstream transmission to up to 64 ONUs while it is tolerable at 15 Gbps but for less number of ONUs. This paper also demonstrated experimental results of symmetric 4×40 Gbps TWDM-PON which showed that the power difference between downstream signals after transmission over 20 km fiber and splitting ratio 1: 128 is more than 2 dB at BER of 10-9, while the difference is more than 1 dB for the upstream at BER of 10-9 after transmission over 20 km fiber and splitting ratio 1: 128. These results showed that the proposed systems are remarkably provide a huge number of available HDTV channels and over exceeds the other access technologies such as ADSL or Cable networks.

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