3.3 TWDM-PON application

area networks (LANs), or asymmetric digital subscriber line (ADSL) broadband communication technologies. Relatively, FTTB employs more optical fiber in the connection than FTTC solution. This makes it more appropriate for broadband/

Telecommunication Systems – Principles and Applications of Wireless-Optical Technologies

Furthermore, ONU deployment can take place right inside the subscribers' homes or offices in the FTTH solution. This facilitates a fully transparent network in which the ONUs are independent of the wavelength, bandwidth, as well as transmission mode and technology. These benefits enable FTTH scheme to be very ideal

In addition, the discussed IEEE 802.3 Ethernet is a 1-Gbit/sec EPON standard. It is remarkable that there is a 10G EPON standard that is capable of supporting 10G/ 10G symmetric DS and US transmission. In another effort to attend to the system requirement, the IEEE 802.3ca task force has been working relentlessly on the development of 25G/50G/100G EPON standards. A notable feature of the entire EPON standards is that they are designed to be both backward and forward compatible. This is to ensure that legacy service, as well as innovative higher-speed

Furthermore, to address the growing traffic demands, XG-PON1 has been presented. The XG-PON1 is capable of delivering higher data transmission than the legacy GPON system. Moreover, in an effort to keep the existing investments, it is backward compatible with the GPON. Also, the GPON ODN, as well as framing and management, is inherited by the XG-PON1. This encourages the reuse of the

The WDM-PON enables multiple-wavelength transmission through the multiple operators'shared optical fiber infrastructure rather than one wavelength in the PON system. This helps in ensuring that WDM-PON meets the huge subscribers' bandwidth demands. Furthermore, it presents various merits such as high wavelength efficiency and relatively simpler network management. This encourages support for various services than the TDM-PON. Besides, all anticipated services can be deliv-

In addition, it can effectively support different access networks such as FTTB, FTTH, and FTTC. Also, both small-scale and large-scale subscribers can be concurrently supported as well. Based on the inherent huge bandwidth, different types of BS bandwidth requirements can be appropriately met. Its implementation can also help in the network reach extension and in the current EPON network transition. This will help in keeping the current network investment while enhancing the network scalability [32]. In addition, UDWDM-PON offers a wavelength grid that is relatively denser for the WDM scheme. This helps not only in supporting a huge amount of aggregated wavelengths per fiber but also in accommodating higher number of RRHs per feeder fiber. Nonetheless, with the envisaged NGN stringent transport network requirements, UDWDM will be unable to maintain the high perwavelength bit rates resourcefully. For instance, subcarriers' aggregation for highspeed services usually bring about considerable latency. Therefore, UDWDM implementation is preferred in situations where there are ultradense RRH deployments and inadequate feeder fiber accessibility. Besides, it also finds application in antenna sites which demand a low-peak but high sustainable rate [6]. As discussed in subsection 3.3, WDM-PON can be employed along with TDM-PON to achieve a

narrowband service integration [32].

for access network implementations [32].

3.1.2 GPON application

existing network elements [35].

3.2 WDM-PON application

148

service, can be effectively supported using the same ODN [34].

ered over a shared communication network infrastructure.

It is notable that TDM-PON implementation in the 4G networks offers a very cost-efficient solution for a wavelength channel sharing between the cell sites, by means of diverse time slot allocations for different cell sites. However, with the evolution of mobile networks, the major ITU-defined application scenarios such as eMBB, uRLLC, and massive machine-type communications (mMTC) could make TDM-PON solution unsuitable for the fronthaul transport network in the 5G and beyond networks. As aforementioned, a hybrid TWDM-PON scheme is a feasible solution with abundant bandwidth capable of supporting the fronthaul demands.

With the scheme, time slots, as well as wavelength resources, can be allocated dynamically between the RRHs. The offered centralized and virtualized PON BS can considerably help in the system energy savings. Likewise, the virtualized scheme presents a number of advantages such as low handover delay, excessive handover reduction, and better network reliability. This results in cost saving, celledge user throughput improvement, and enhanced mobility management [32, 36, 37]. The associated multiple wavelengths, as well as potential for wavelength tenability, give TWDM-PON unprecedented means of improving the network functionalities compared with the basic TDM-PONs [36, 37]. Likewise, orthogonal frequency-division multiplexed PON (OFDM-PON) is another promising PON solution. With OFDM, there is a comparable high potential for flexible bandwidth resource sharing as experienced in the TWDM. On the other hand, regarding the reach, the OFDM variants in which direct detection is employed usually present poor performance. Similarly, variants in which coherent detection is implemented are comparatively too expensive [6]. Furthermore, it is noteworthy that among its counterparts such as standard WDM-PON, optical code division multiplexed PON (OCDM-PON), and OFDM-PON that are capable of offering 40 Gb/s or higher (80 Gb/s) aggregated bandwidth, the full service access network (FSAN) community has chosen TWDM-PON as a major broadband solution. Apart from the inherent huge capacity with 1:64 splitting ratio, it has a long reach of 40 km. The salient features enable TWDM-PON system to meet the future broadband service requirements [37–39].

A typical TWDM-PON system architecture is depicted in Figure 5. In a conventional TWDM-PON solution, multiple wavelengths can effectively coexist in a shared ODN by means of WDM. Moreover, each of the wavelengths is capable of serving multiple ONUs through TDM access. With reference to the ITU-T recommendation, 4–8 wavelengths in L band (1590–1610 nm) and C band (1520– 1540 nm) can be employed for the downstream (DS) and upstream (US) transmissions, respectively. Also, each of the DS wavelengths can operate at 10 Gb/s, while the US can function each at 2.5 or 10 Gb/s data rate [32, 37].

In addition, the TWDM-PON ONUs employ colorless tunable transceivers for selective transmission/reception of any US/DS wavelengths (data) via a pair of US/ DS wavelengths. With this approach, the ONU inventory issue can be prevented. In essence, the transceiver features help in easing network deployment as well as inventory management. Furthermore, load balancing can be supported effectively in the TWDM-PON system. Besides, with dynamic wavelength and bandwidth allocation (DWBA) implementation, large bandwidth can be flexibly exploited. It is remarkable that TWDM-PON is a stack of four 10-gigabit PONs (XG-PONs) with

Although a TWDM-PON offers effective bandwidth resource allocation among multiple clients, meeting the low latency and jitter requirements of certain services may be challenging. Consequently, its implementation for the NGN RAN transport network depends mainly on the RAN use cases and deployment scenario requirements [6]. In Section 5, we present a number of viable means for alleviating the growing stringent requirements in the system. Furthermore, as aforementioned, the NG-PON2 system employs multiple wavelengths that demand for tunable transceivers at the ONUs. However, this requirement might hinder its implementation as the existing optical tunable transceivers are uneconomical. Based on this, a number of operators have been looking for ways around this by envisaging provisional scheme adoption before the full NG-PON2 migration. This will enable them to have a seamless transition with least possible or no disruption in the offered services. One of viable solution is the XGS-PON. It offers an improved commercial solution as a

Enabling Optical Wired and Wireless Technologies for 5G and Beyond Networks

The XGS-PON presents a novel technology that offers a generic solution for the NG-PON system. It can be viewed as an uncomplicated variant of TWDM-PON in which the wavelength tunability and mobility are eliminated for a more costeffective reason. In addition, there can be an efficient coexistence between the XGS-PON and TWDM-PON using the same fiber infrastructure, since the

employed wavelengths by each technology are different. Consequently, the operators can exploit the lower-cost XGS-PON for quick delivery of 10 Gbps services. This will also enable them to seize 10 Gbps services opportunities for immediate deployments. With XGS-PON, there can be cost-efficient, gradual upgrade, and well-controlled transition to a full TWDM-PON system, with minimum or no disruption to the offered services. It can also facilitate TWDM-PON system by enabling its deployment using the wavelength by wavelength approach. This will really help in pay-as-you-grow scheme for effective system upgrade and

Besides its capability for delivering 10 Gbps in both US and DS directions, XGS-PON has high potential for the dual rate transmission support as well [44]. Based on this, the 10/2.5G XG-PON ONUs and 10/10G XGS-PON ONUs can be coupled to the same OLT port via a native dual US rate TDMA scheme. It is remarkable that XGS-PON dual rate presents a comparable cost to XG-PON; nonetheless, it is capable of providing 4 times of the XG-PON US bandwidth. In addition, XGS-PON has been seen as a transitional scheme to NG-PON2 due to its ability for offering the associated NG-PON2 high-data rates in conjunction with the XG-PON1 CAPEX efficiency [33, 43]. Furthermore, it should be noted that the GPON employs 1490 and 1310 nm in the DS and UP, respectively. Likewise, XGS-PON utilizes 1578 and 1270 nm in the DS and UP, respectively. This implies that the XGS-PON service can be effectively overlaid on the same infrastructure as that of GPON. Similarly, the G.989 standard is employed in NG-PON2. The G.989 supports TWDM technologies

In addition, NG-PON2 is not only a state-of-the-art PON technology with the potential for intense revolution in the operational models of providers but also offers them flexible platform that is capable of enhancing their agility to the market demands as never before. Besides, it has the ability for cost-effective support for both the scale and capacity of the existing gigabit services while at the same time having more than enough room for the multi-gigabit bandwidth requirements of the future networks [38]. Consequently, based on the aforementioned advantages

and its proficiency for multiple networks converging with outstanding

result of the less costly elements being employed.

DOI: http://dx.doi.org/10.5772/intechopen.85858

and it is a multiwavelength access standard [44].

3.4 XGS-PON application

migration [33, 43].

151

Figure 5. Typical TWDM-PON architecture.

four pairs of wavelengths. In the stack, each XG-PON is operating on different wavelengths. Also, as stated earlier, the GPON and XG-PON GEM frames are compatible with and can be employed in the TWDM-PON solution. Based on this and the ability for coexistence with existing PON solutions, it is a viable scheme for optical access network swift evolution [11, 32, 37]. Consequently, TWDM-PON has been adopted for the NG-PON2. In NG-PON2, TWDM-PON can be employed with optional P2P WDM overlay extension. It is remarkable that DWDM scheme will enable NG-PON2 to deliver multiple unshared P2P connections, while TDM scheme simultaneously offers multiple P2M connections. This will enable the operators to efficiently support both fronthaul/backhaul and business services with the P2P WDM overlay technology, by using dedicated wavelengths [11, 40, 41].

In addition, based on the inherent colorless tunable transceivers of the TWDM-PON ONUs, three classes of wavelength channel tuning time have been specified for the NG-PON2 by the physical media dependent layer recommendation (ITU-T G.989.2). Table 1 illustrates the specified tuning time classes by the G.989.2 recommendation. It should be noted that different innovative technologies can be exploited by the wavelength tunable devices in order to have the capability for supporting various classes. This will enable a number of potentials for the NG-PON2 system at relatively different costs. Out of the defined three classes, Class 3 is based on the slowest tunable devices. Consequently, it is applicable in scenarios with occasional tuning operations or in applications that can tolerate short service disruption. On the other hand, Class 1 wavelength tunable devices present the shortest tuning time. This feature makes them attractive for offering DWBA feature in the network. Besides, with this class implementation, the ONU transmission wavelengths can be dynamically controlled by the OLT for wavelength hopping between the transmission periods [42].


Table 1. Tuning time classes [42].

Enabling Optical Wired and Wireless Technologies for 5G and Beyond Networks DOI: http://dx.doi.org/10.5772/intechopen.85858

Although a TWDM-PON offers effective bandwidth resource allocation among multiple clients, meeting the low latency and jitter requirements of certain services may be challenging. Consequently, its implementation for the NGN RAN transport network depends mainly on the RAN use cases and deployment scenario requirements [6]. In Section 5, we present a number of viable means for alleviating the growing stringent requirements in the system. Furthermore, as aforementioned, the NG-PON2 system employs multiple wavelengths that demand for tunable transceivers at the ONUs. However, this requirement might hinder its implementation as the existing optical tunable transceivers are uneconomical. Based on this, a number of operators have been looking for ways around this by envisaging provisional scheme adoption before the full NG-PON2 migration. This will enable them to have a seamless transition with least possible or no disruption in the offered services. One of viable solution is the XGS-PON. It offers an improved commercial solution as a result of the less costly elements being employed.

#### 3.4 XGS-PON application

four pairs of wavelengths. In the stack, each XG-PON is operating on different wavelengths. Also, as stated earlier, the GPON and XG-PON GEM frames are compatible with and can be employed in the TWDM-PON solution. Based on this and the ability for coexistence with existing PON solutions, it is a viable scheme for optical access network swift evolution [11, 32, 37]. Consequently, TWDM-PON has been adopted for the NG-PON2. In NG-PON2, TWDM-PON can be employed with optional P2P WDM overlay extension. It is remarkable that DWDM scheme will enable NG-PON2 to deliver multiple unshared P2P connections, while TDM scheme simultaneously offers multiple P2M connections. This will enable the operators to efficiently support both fronthaul/backhaul and business services with the P2P WDM overlay technology, by using dedicated wavelengths [11, 40, 41].

Telecommunication Systems – Principles and Applications of Wireless-Optical Technologies

In addition, based on the inherent colorless tunable transceivers of the TWDM-PON ONUs, three classes of wavelength channel tuning time have been specified for the NG-PON2 by the physical media dependent layer recommendation (ITU-T G.989.2). Table 1 illustrates the specified tuning time classes by the G.989.2 recommendation. It should be noted that different innovative technologies can be exploited by the wavelength tunable devices in order to have the capability for supporting various classes. This will enable a number of potentials for the NG-PON2 system at relatively different costs. Out of the defined three classes, Class 3 is based on the slowest tunable devices. Consequently, it is applicable in scenarios with occasional tuning operations or in applications that can tolerate short service disruption. On the other hand, Class 1 wavelength tunable devices present the shortest tuning time. This feature makes them attractive for offering DWBA feature in the network. Besides, with this class implementation, the ONU transmission wavelengths can be dynamically controlled by the OLT for wavelength hopping

Tuning time <10 μs 10 μs to 25 ms 25 ms to 1 s

Class 12 3

between the transmission periods [42].

Figure 5.

Table 1.

150

Tuning time classes [42].

Typical TWDM-PON architecture.

The XGS-PON presents a novel technology that offers a generic solution for the NG-PON system. It can be viewed as an uncomplicated variant of TWDM-PON in which the wavelength tunability and mobility are eliminated for a more costeffective reason. In addition, there can be an efficient coexistence between the XGS-PON and TWDM-PON using the same fiber infrastructure, since the employed wavelengths by each technology are different. Consequently, the operators can exploit the lower-cost XGS-PON for quick delivery of 10 Gbps services. This will also enable them to seize 10 Gbps services opportunities for immediate deployments. With XGS-PON, there can be cost-efficient, gradual upgrade, and well-controlled transition to a full TWDM-PON system, with minimum or no disruption to the offered services. It can also facilitate TWDM-PON system by enabling its deployment using the wavelength by wavelength approach. This will really help in pay-as-you-grow scheme for effective system upgrade and migration [33, 43].

Besides its capability for delivering 10 Gbps in both US and DS directions, XGS-PON has high potential for the dual rate transmission support as well [44]. Based on this, the 10/2.5G XG-PON ONUs and 10/10G XGS-PON ONUs can be coupled to the same OLT port via a native dual US rate TDMA scheme. It is remarkable that XGS-PON dual rate presents a comparable cost to XG-PON; nonetheless, it is capable of providing 4 times of the XG-PON US bandwidth. In addition, XGS-PON has been seen as a transitional scheme to NG-PON2 due to its ability for offering the associated NG-PON2 high-data rates in conjunction with the XG-PON1 CAPEX efficiency [33, 43]. Furthermore, it should be noted that the GPON employs 1490 and 1310 nm in the DS and UP, respectively. Likewise, XGS-PON utilizes 1578 and 1270 nm in the DS and UP, respectively. This implies that the XGS-PON service can be effectively overlaid on the same infrastructure as that of GPON. Similarly, the G.989 standard is employed in NG-PON2. The G.989 supports TWDM technologies and it is a multiwavelength access standard [44].

In addition, NG-PON2 is not only a state-of-the-art PON technology with the potential for intense revolution in the operational models of providers but also offers them flexible platform that is capable of enhancing their agility to the market demands as never before. Besides, it has the ability for cost-effective support for both the scale and capacity of the existing gigabit services while at the same time having more than enough room for the multi-gigabit bandwidth requirements of the future networks [38]. Consequently, based on the aforementioned advantages and its proficiency for multiple networks converging with outstanding

performance, in this work, we focus on the NG-PON2 system. Its PHY architecture and development are presented in Section 6.

generations can effectively coexist over a shared ODN fiber infrastructure. Besides, optical time-domain reflectometer (OTDR) and RF signals can also coexist with the PON systems. This is mainly due to the fact that there is no wavelength overlap between each of the technologies. So, this permits in-band measurement without any service interruption [34, 45]. Different ODN optical path loss classes are

Enabling Optical Wired and Wireless Technologies for 5G and Beyond Networks

It is remarkable that, apart from the fact that the existing GPON subscribers can be kept together with higher-bandwidth services, the coexistence will also give the operators the profound chance to take advantage of different approaches such as asymmetrical and symmetrical data rates. They also have deployment flexibility by operating on fixed or tunable wavelengths in order to offer appropriate operations and services at suitable costs. It will also assist the operators in the NG-PON evolution path not only by allowing them to upgrade their networks accordingly but also for gradual migration to the evolving PON technologies that are capable of offering the full optical potential. Thus, they have the liberty of adopting the cost and deployment pace that best fit their precise business requirements [43]. Moreover, this will enable the operators in making further revenue by exploiting flexible bandwidth and wavelength plans in order to support any service type as well as any business need. Figure 6 depicts a PON system coexistence for a gradual and pay-

As explained in Section 1, C-RAN is envisioned to be a promising candidate for efficient management of the access network and the associated emergent complexity. This is due in part to its cost-effectiveness and remarkable flexibility for the network element deployments. Normally, the inphase and quadrature (I/Q) component stream transmission in this architecture is via the D-RoF-based CPRI. It is remarkable that CPRI-based fronthaul demands huge bandwidth which could be a limiting factor in the 5G and beyond networks in which mm-wave and massive MIMO are anticipated to be implemented. Consequently, an advanced optical transmission technology such as analog RoF (ARoF) has to be employed for an

The RoF schemes offer efficient and economical methods for modulated RF signal transmission. For instance, it can be used for transmission from the CO, to a number of distributed RRHs, through low-loss optical fiber networks, by employing an optical carrier. In addition, as aforementioned in Section 1, optical and wireless network convergence is highly imperative for scalable and cost-effective broadband wireless networks. The envisaged convergence for the next-generation mobile communication networks can be efficiently achieved with the implementation of RoF. This is due to its simplicity and efficiency in conveying wireless signal via an optical carrier. Furthermore, the inherent low attenuation and huge bandwidth of optical link can effectively support multiple wireless services on a shared optical fronthaul network. Moreover, with RoF implementation, the CUs and DUs can be well-supported. This offers effective centralized network control that subsequently presents advantages such as easy upgrade, simple maintenance, and efficient

It should be noted that there are various RoF options that can be employed in the network. Furthermore, each of the viable options presents related distinct merits

presented in Table 2.

DOI: http://dx.doi.org/10.5772/intechopen.85858

as-you-grow expansion [33].

5.1 RoF schemes

resource sharing [11, 47, 48].

153

5. System requirement alleviation schemes

efficient fronthaul solution realization [11, 13, 14].
