3. Passive optical network (PON)

The existing fiber-based methods as well as active P2P Ethernet might unable to meet the envisaged bandwidth-intensive traffic requirements by the 5G and beyond networks. For instance, ultradense network deployments with the associated huge network resources are envisaged in the 5G network. As illustrated in Figure 3, PON system can make better use of the current fiber infrastructures than the existing P2P system such as CPRI. This helps considerably in reducing the required number of interfaces in the network. As a result, it aids not only in reducing the site space, but also substantial amount of system power can be saved [30]. As explained in Section 2, PON technology has been deemed as an attractive access network solution owing to the presented advantages such as low-operation cost, high bandwidth, and lowmaintenance cost [11, 31, 32].

It should be noted that the PON architectures have been experiencing continuous and gradual evolution, so as to considerably enhance the service availability and the related data rates. The offered technological options and the intrinsic benefits have been attracting the operators in deploying a number of PON systems. It has been observed that the most widely deployed one is the gigabit PON (GPON) system. Moreover, the first standard 10 Gbps PON technology, the next-generation PON (NG-PON) system, known as 10-gigabit PON (XG-PON1) has also been gaining considerable attention. With continuous demand for further capacity, there are innovative PON generations such as 10-gigabit symmetric PON (XGS-PON)

service level agreement (SLA) management and network demarcation. Furthermore, this solution presents attractive features regarding low latency and high bandwidth. It is also a good approach for attending to the required colored optical interface at BBU and RRU by the passive WDM. Since colored optical interface is not demanded, wireless equipment deployment challenges are alleviated drastically by the WDM/OTN solution. Another significant advantage of the approach is the offered easy scalability. This is due to the fact that there is no need for replacing the wireless equipment optical interfaces while upgrading from non-C-RAN to the C-RAN architecture. Notwithstanding, the major drawback of the solution is the relatively higher cost of the equipment. Although power supply is not required for WDM transport in the approach, it is essential for wavelength translation and active

Telecommunication Systems – Principles and Applications of Wireless-Optical Technologies

In addition, the WDM-based systems such as coarse WDM (CWDM) and dense WDM (DWDM) exhibit promising features for the fronthaul transport applications. For instance, apart from the offered high throughput and low latency, CWDM is very cost-effective regarding fiber resource usage and equipment expenses. Also, DWDM is widely known for the higher channel counts that can be efficiently supported. This can help further in increasing the number of small cells and the associated RRHs that can be deployed effectively. Furthermore, it helps in

Potential 5G fronthaul solutions: (a) microwave, (b) point-to-point, (c) WDM-PON, (d) OTN, and

management [11, 23, 29].

Figure 2.

144

(e) Ethernet.

improving the fiber resource efficiency.

Moreover, it is remarkable that advantages of both WDM-PON and TDM-PON can be effectively exploited though joint application of the schemes. This results in the TWDM-PON architecture. The potential PON architectures and their applications in telecommunication systems are presented in the subsequent subsections.

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

The TDM-PON can be grouped into broadband PON (BPON), asynchronous transfer mode (ATM) PON (APON), Ethernet PON (EPON), and GPON. In the existing telecommunication networks, GPON and EPON are the widely adopted

The data traffic being encapsulated in the Ethernet frames as defined by the IEEE 802.3 standard is transported by the EPON solution. Different network elements such as optical network unit (ONU), optical line terminal (OLT), and optical distribution network (ODN) are the building blocks of a standard EPON system and other PON architectures. In the EPON solution, PON topology is exploited for getting the Ethernet access. Based on the joint schemes, EPON solution is capable of offering high bandwidth and good network scalability. Besides, due to the fact that it is highly compatible with Ethernet, network management can be supported in cost-effective manners. Likewise, as illustrated in Figure 4, FTTB, FTTC, and FTTH network architectures can be supported depending on the ONU deployments and demarcation point between the copper cable and optical fiber termination [32]. Typically, ONUs can be deployed beside the telegraph pole junction boxes, or else, at roadside when FTTC system is employed. Also, different types of twisted pair cables can be utilized for connecting the ONUs and the respective customer. It has been observed that FTTC technology offers a cost-effective and practical solution for delivering narrowband services. However, FTTC solution is not an ideal scheme, when broadband and narrowband services are to be incorporated [32]. Moreover, the ONU deployment can be made closer to the users in the FTTB solution. So, it can be located inside the buildings through further optical fiber penetration into customer homes. This can be achieved by means of cables, local

schemes. Therefore, in the following, we focus on both schemes.

3.1 TDM-PON application

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

3.1.1 EPON application

Figure 4. FTTX architectures.

147

Figure 3. Potential fronthaul solutions (a) CPRI-based and (b) PON-based schemes.

and the second standard of NG-PON (NG-PON2) that are now becoming the target of various providers [33]. In PON system, WDM and TDM techniques are normally employed to further enhance the capacity and fiber efficiency. Based on these techniques, the PON system can be broadly grouped into WDM-PON and TDM-PON.

Moreover, it is noteworthy that the TDM-PON is capable of giving considerable greater bandwidth for various data applications; however, availability of the resources that can be delivered to the end users is limited. In contrast, the issue can be effectively addressed with the WDM-PON scheme. This can be done by assigning a peculiar wavelength per subscriber. As a result of this, a distinct, highdata rate, as well as secure P2P channel, can be delivered over a high-capacity and longer optical reach, between each of the subscriber and the CU. Consequently, a WDM-PON scheme is suitable for partitioning the ONUs into a number of distinctive virtual P2P links over the shared physical optical infrastructure by multiple operators. This attribute facilitates fiber efficiency compared to P2P Ethernet. Similarly, in relation to TDM-based systems, it gives lower latency. These features make WDM-PON a disruptive solution that is very appropriate for FTTX as well as mobile backhaul and fronthaul applications. This will eventually aid the operators not only in developing converged networks but also in enhancing the current access networks. As a consequence of this, some redundant COs can be eliminated in an attempt to enhance the network performance in cost-effective ways [11, 31, 32].

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

Moreover, it is remarkable that advantages of both WDM-PON and TDM-PON can be effectively exploited though joint application of the schemes. This results in the TWDM-PON architecture. The potential PON architectures and their applications in telecommunication systems are presented in the subsequent subsections.

#### 3.1 TDM-PON application

The TDM-PON can be grouped into broadband PON (BPON), asynchronous transfer mode (ATM) PON (APON), Ethernet PON (EPON), and GPON. In the existing telecommunication networks, GPON and EPON are the widely adopted schemes. Therefore, in the following, we focus on both schemes.

#### 3.1.1 EPON application

The data traffic being encapsulated in the Ethernet frames as defined by the IEEE 802.3 standard is transported by the EPON solution. Different network elements such as optical network unit (ONU), optical line terminal (OLT), and optical distribution network (ODN) are the building blocks of a standard EPON system and other PON architectures. In the EPON solution, PON topology is exploited for getting the Ethernet access. Based on the joint schemes, EPON solution is capable of offering high bandwidth and good network scalability. Besides, due to the fact that it is highly compatible with Ethernet, network management can be supported in cost-effective manners. Likewise, as illustrated in Figure 4, FTTB, FTTC, and FTTH network architectures can be supported depending on the ONU deployments and demarcation point between the copper cable and optical fiber termination [32].

Typically, ONUs can be deployed beside the telegraph pole junction boxes, or else, at roadside when FTTC system is employed. Also, different types of twisted pair cables can be utilized for connecting the ONUs and the respective customer. It has been observed that FTTC technology offers a cost-effective and practical solution for delivering narrowband services. However, FTTC solution is not an ideal scheme, when broadband and narrowband services are to be incorporated [32].

Moreover, the ONU deployment can be made closer to the users in the FTTB solution. So, it can be located inside the buildings through further optical fiber penetration into customer homes. This can be achieved by means of cables, local

Figure 4. FTTX architectures.

and the second standard of NG-PON (NG-PON2) that are now becoming the target of various providers [33]. In PON system, WDM and TDM techniques are normally employed to further enhance the capacity and fiber efficiency. Based on these techniques, the PON system can be broadly grouped into WDM-PON and

Telecommunication Systems – Principles and Applications of Wireless-Optical Technologies

Moreover, it is noteworthy that the TDM-PON is capable of giving considerable

greater bandwidth for various data applications; however, availability of the resources that can be delivered to the end users is limited. In contrast, the issue can

Potential fronthaul solutions (a) CPRI-based and (b) PON-based schemes.

be effectively addressed with the WDM-PON scheme. This can be done by assigning a peculiar wavelength per subscriber. As a result of this, a distinct, highdata rate, as well as secure P2P channel, can be delivered over a high-capacity and longer optical reach, between each of the subscriber and the CU. Consequently, a WDM-PON scheme is suitable for partitioning the ONUs into a number of distinctive virtual P2P links over the shared physical optical infrastructure by multiple operators. This attribute facilitates fiber efficiency compared to P2P Ethernet. Similarly, in relation to TDM-based systems, it gives lower latency. These features make WDM-PON a disruptive solution that is very appropriate for FTTX as well as mobile backhaul and fronthaul applications. This will eventually aid the operators not only in developing converged networks but also in enhancing the current access networks. As a consequence of this, some redundant COs can be eliminated in an attempt to enhance the network performance in cost-effective ways [11, 31, 32].

TDM-PON.

146

Figure 3.

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/ narrowband service integration [32].

hybrid WDM-TDM-PON solution known as time and wavelength division

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

applications in telecommunication environment.

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

3.3 TWDM-PON application

ments [37–39].

149

multiplexed (TWDM-PON) scheme. Apart from being efficient for both small-scale and large-scale subscribers, the hybrid scheme offers a promising solution for

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 require-

A typical TWDM-PON system architecture is depicted in Figure 5. In a conven-

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

tional 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].

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 for access network implementations [32].

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

#### 3.1.2 GPON application

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 existing network elements [35].

#### 3.2 WDM-PON application

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 delivered over a shared communication network infrastructure.

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

hybrid WDM-TDM-PON solution known as time and wavelength division multiplexed (TWDM-PON) scheme. Apart from being efficient for both small-scale and large-scale subscribers, the hybrid scheme offers a promising solution for applications in telecommunication environment.
