**2. Technology evolution over the years**

In today's telecommunication world, user access the services through different transmission media (copper, wireless, and fiber), however, backbone are predominantly optical. Most of the time, the access network is wireless, as the number of devices increases over the years due invent of IoT). In this work, users use the wireless networks for access purposes with the backbone network as optical. **Figure 2** gives an idea of how the evolution of optical networks makes an impact on the wireless network. As the requirements of high data rate and low latency are increasing, the availability of optical networks (fronthaul) is coming closer to the home and access distance through wireless is decreasing. In the following, the development of technologies will be discussed in both domains.

### **2.1 Development of wireless network**

Over the years, wireless communication evolved generation-wise, started from 1G analog to 5G digital and moving towards 6G communication. The focus of 5G and 6G technologies is to connect people, society seamlessly along with applications, services, data, and geographical area in a smart networked environment. The present wireless network is heterogeneous in terms of infrastructure (Macrocell to femtocell), spectrum usage (licensed and unlicensed, sub-GHz to THz), coverage (multi-tier), antenna (single to the massive number of antennas), cooperation (user to eNB), and power usage (mW to 100 W).

**Figure 2.** *Impact of the evolution of technologies.*

The technologies developed for supporting these heterogeneous characteristics are co-existing together. These technologies are used to serve their purpose and produce interference on other services while in use, due to this their performance is somehow limited. To enhance performance by increasing awareness and cooperation, 5G technologies proposed several new solutions. These include technologies (as shown in **Figure 3**) like massive multiple-input multiple-output (MIMO) for higher data rate and better coverage, coordinated multipoint transmission (CoMP) for a lower outage, distributed antenna system (DAS) for better connectivity, software-defined radio (SDR) for reconfigurability, cognitive radio (CR) for better spectrum utilization, cloud computing for better usage, software-defined network (SDN) for an optimized network, and mmWave communication for high bandwidth. These technologies differ in channel characteristics, usage specification, operational requirement, application supports, etc. The 5G communication stipulates to support a data rate of more than 5 Gbps, less than 1 ms latency for high mobility users [5]. Several important developments in 5G wireless networks are.

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*Convergence of Wireless and Optical Network in Future Communication Network*

ranges: FR1 (below 6 GHz) and FR2 (above 24 GHz) [7, 8].

resource. This can eventually lead to large capacity gains [9].

**5G New Radio**: Even the existence of various radio technologies, 5G communications proposed a completely new radio interface, named 5G new radio (5G NR). The 5G NR interface is a flexible air interface that supports the mainly three ITU defined categories: uRLLC, mMTC, and eMBB. It can also support various other 5G applications such as automotive and health care. 3GPP defined two frequency

**Massive MIMO**: The 5G communication uses massive MIMO as a promising multi-user MIMO technology, where the number of antennas (more than 100) at eNB is much more compared to traditional systems. This massive number of antennas allows substantial gains in system capacity and energy efficiency of both users and the system. Due to the increasing number of antennas, which guides to a more spatial resolution; subsequently, several users can use the same time-frequency

**Non Orthogonal Multiple Access (NOMA)**: Over the year, orthogonal frequency division multiplexing (OFDM) is the most preferred transmission technique. However, a non-orthogonal scheme (NOMA) has been proposed for efficient 5G communication. In NOMA, each user are distinguished by their power levels while operating in the same band and at the same time. It works with successive interference cancelation (SIC) at the receiver uses and with the help of superposition coding at the transmitter, all users can utilize the same and entire spectrum band. The transmitter site superimposed all the individual signals into a single waveform, while the receiver finds the desired signal with the help of SIC decodes

**mmWave Communication**: Availability of large bandwidth in the millimeter range, 5G & beyond wireless systems proposed to use mmWave communications. The mmWave cites a very short wavelength of the radio frequency spectrum between 24GHz and 100GHz. Due to the much shorter wavelength at millimeter band, it allows the deployment of massive antennas at the transceiver. Thus, the large propagating attenuation due to high frequency will be compensated by using a large antenna array, which provides high gains and finally, provides faster data speeds. In dense deployments scenario, it is also suitable for efficient and flexible wireless backhauling, in addition to supporting ultra-high-speed radio

**Internet of Things (IoT)**: In the present day, IoT is used almost every possible scenario and application. IoT interconnects different types of devices for various applications and enables machine-to-machine (M2M) communication. BY doing so, it enables data communication between heterogeneous devices automatically without human monitoring and control intervention. Several wireless technologies along with few open standards (Vodafon's Cellular IoT and the NB-IoT by 3GPP) have been used for the deployment of IoT. The 5G will be able to provide a connection to a massive IoT network, where billions of smart devices can be connected to the Internet. Since the 5G networks provide flexible and faster networks, IoT can be easily integrated with the wireless software define network-

**Coordinated Multipoint (CoMP)**: 5G communication supports small cell and the availability of numerous devices in the environment, makes the network very dense. In the dense environment, intercell interference will be more severe for edge users, which is one of the main reasons for the repeated outage. CoMP transmission technique exploits this interference scenario to enhance the users' performances. CoMP mechanism utilizes the resources more effectively and efficiently by dynamic coordination or transmission and reception with multiple eNBs, which eventually improves the service quality of geographically separated UE and enhances the

*DOI: http://dx.doi.org/10.5772/intechopen.97293*

mechanism [10, 11].

access [12].

ing (WSDN) paradigm [13].

overall system performance [12].

**Figure 3.** *A typical scenario of a heterogeneous wireless network.*

*Convergence of Wireless and Optical Network in Future Communication Network DOI: http://dx.doi.org/10.5772/intechopen.97293*

**5G New Radio**: Even the existence of various radio technologies, 5G communications proposed a completely new radio interface, named 5G new radio (5G NR). The 5G NR interface is a flexible air interface that supports the mainly three ITU defined categories: uRLLC, mMTC, and eMBB. It can also support various other 5G applications such as automotive and health care. 3GPP defined two frequency ranges: FR1 (below 6 GHz) and FR2 (above 24 GHz) [7, 8].

**Massive MIMO**: The 5G communication uses massive MIMO as a promising multi-user MIMO technology, where the number of antennas (more than 100) at eNB is much more compared to traditional systems. This massive number of antennas allows substantial gains in system capacity and energy efficiency of both users and the system. Due to the increasing number of antennas, which guides to a more spatial resolution; subsequently, several users can use the same time-frequency resource. This can eventually lead to large capacity gains [9].

**Non Orthogonal Multiple Access (NOMA)**: Over the year, orthogonal frequency division multiplexing (OFDM) is the most preferred transmission technique. However, a non-orthogonal scheme (NOMA) has been proposed for efficient 5G communication. In NOMA, each user are distinguished by their power levels while operating in the same band and at the same time. It works with successive interference cancelation (SIC) at the receiver uses and with the help of superposition coding at the transmitter, all users can utilize the same and entire spectrum band. The transmitter site superimposed all the individual signals into a single waveform, while the receiver finds the desired signal with the help of SIC decodes mechanism [10, 11].

**mmWave Communication**: Availability of large bandwidth in the millimeter range, 5G & beyond wireless systems proposed to use mmWave communications. The mmWave cites a very short wavelength of the radio frequency spectrum between 24GHz and 100GHz. Due to the much shorter wavelength at millimeter band, it allows the deployment of massive antennas at the transceiver. Thus, the large propagating attenuation due to high frequency will be compensated by using a large antenna array, which provides high gains and finally, provides faster data speeds. In dense deployments scenario, it is also suitable for efficient and flexible wireless backhauling, in addition to supporting ultra-high-speed radio access [12].

**Internet of Things (IoT)**: In the present day, IoT is used almost every possible scenario and application. IoT interconnects different types of devices for various applications and enables machine-to-machine (M2M) communication. BY doing so, it enables data communication between heterogeneous devices automatically without human monitoring and control intervention. Several wireless technologies along with few open standards (Vodafon's Cellular IoT and the NB-IoT by 3GPP) have been used for the deployment of IoT. The 5G will be able to provide a connection to a massive IoT network, where billions of smart devices can be connected to the Internet. Since the 5G networks provide flexible and faster networks, IoT can be easily integrated with the wireless software define networking (WSDN) paradigm [13].

**Coordinated Multipoint (CoMP)**: 5G communication supports small cell and the availability of numerous devices in the environment, makes the network very dense. In the dense environment, intercell interference will be more severe for edge users, which is one of the main reasons for the repeated outage. CoMP transmission technique exploits this interference scenario to enhance the users' performances. CoMP mechanism utilizes the resources more effectively and efficiently by dynamic coordination or transmission and reception with multiple eNBs, which eventually improves the service quality of geographically separated UE and enhances the overall system performance [12].

*Wireless Power Transfer – Recent Development, Applications and New Perspectives*

The technologies developed for supporting these heterogeneous characteristics are co-existing together. These technologies are used to serve their purpose and produce interference on other services while in use, due to this their performance is somehow limited. To enhance performance by increasing awareness and cooperation, 5G technologies proposed several new solutions. These include technologies (as shown in **Figure 3**) like massive multiple-input multiple-output (MIMO) for higher data rate and better coverage, coordinated multipoint transmission (CoMP) for a lower outage, distributed antenna system (DAS) for better connectivity, software-defined radio (SDR) for reconfigurability, cognitive radio (CR) for better spectrum utilization, cloud computing for better usage, software-defined network (SDN) for an optimized network, and mmWave communication for high bandwidth. These technologies differ in channel characteristics, usage specification, operational requirement, application supports, etc. The 5G communication stipulates to support a data rate of more than 5 Gbps, less than 1 ms latency for high mobility users [5]. Several important developments in 5G wireless networks are.

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**Figure 3.**

*A typical scenario of a heterogeneous wireless network.*

**Figure 2.**

*Impact of the evolution of technologies.*

**Cognitive Radio**: Over the spectrum has been allocated for several usages and the allocated resources are very much under-utilized, To reduce spectrum scarcity and utilize the underutilized spectrum, cognitive radio technology has been proposed. It is an intelligent radio, that can be sense, learn, aware and adapt according to the environment. With the help of software-defined radio (SDR), cognitive radio can be programmed and configured dynamically. SDR is a radio transceiver where radio components (modulators/demodulators, filters, amplifiers, mixers, detectors, etc.) are implemented by software on a personal computer or embedded system [12].

Having understood these technologies of 5G wireless communication, FCN is planning to have the communication system that can achieve data rates of about 100 Tb/s high speed, low latency, and reliable communications are essential for supporting ML/AI at the edge; giving rise to the research field entitled Communication over machine learning. Incorporation of holographic telepresence, holographic communication, virtual reality, and augmented reality in future communication, boost the requirement of wireless communication [14].

## **2.2 Development of optical network**

In the present network scenario, the data generated by the wireless devices are transported through an optical network. In general, optical fiber is connected between wireless base stations (BSs/eNB), and their controlling, switching, and monitoring centers. Due to the enormous available bandwidth, the optical fiber can carry data up to 100 Tbps for networking in the optical network. By using appropriate technology, the capacity can be increased further. Similar to the evolution of the wireless network, the optical networks also evolved generation-wise. During the process of evolution, the optical network incorporated optical cross-connect (OXC), a synchronous digital hierarchy (SDH) /synchronous optical network (SONET) rings, optical add-drop multiplexers (OADMs), Software-defined network/network function virtualization (SDN/NFV). Today's long-haul backbone networks of 10/40 Gbps wavelength channels use wavelength-division multiplexing (WDM) transmission systems. Further increase in capacity, the optical network uses a dense WDM (DWDM) frequency grid (12.5, 25, 50, and 100 GHz by G.694.1). Further development of WDM transmission systems makes the system an adaptable DWDM grid.

**Optical Transport Network (OTN)**: ITU-T G.709 defined OTN, which transport digital/optical signal across the core network is a flexible way. Each optical channel carries a separate signal using optical channels multiplexing and uses optical data as a unit. OTN supports the different functions for transporting data, such as multiplexing, routing, management, supervision, and survivability.

**Automatically Switched Optical Network (ASON)**: To accommodate dynamic traffic and their requirements, optical networks need to manage to signal and routing automatically and intelligently. It provides auto-discovery and dynamic connection set-up with the help of dynamic signaling-based over OTN and SDH networks. This is done through a distributed (or partially distributed) control plane, which enables improved support for current end-to-end provisioning, re-routing, and restoration. ASON uses the generalized MPLS (GMPLS) signaling protocol to set up and monitor edge-to-edge transport connections. It also uses single fiber switching to wavelength switching and optical packet switching. The other components, like OXCs, wavelength converters, and OADMs are required for ASON.

**Different variant of wavelength-division multiplexing (WDM)**: WDM is the main transmission technology. Over the year several of its variant has been

**85**

*Convergence of Wireless and Optical Network in Future Communication Network*

proposed and used, which are Dense WDM, Coarse WDM, and Time WDM. DWDM uses frequency grids of 12.5, 25, 50, and 100 GHz for transmission. IN the present scenario, many-core networks deployed 1.6 Tbps ( 40Gbps 40 × wavelengths) DWDM system. To support the capabilities for 5G and beyond 5G system, the core network will need to transport 10 Tbps or more per fiber which will be

CWDM combines multiple optical signals at various wavelengths for transmission in optical fiber cables. Up to 18 channels are allowed to be connected over a dark fiber pair. Unlike 0.4 nm spacing for DWDM, CWDM systems have channels at wavelengths spaced 20 nanometers (nm) apart. CWDM works well in two

TWDM is a WDM technique, where TDMA is applied to a set of wavelengths instead of just one wavelength. It requires strict coordination with the radio equipment to guarantee low latency, as with TDMA and provides more bandwidth than TDMA. In a passive optical network (PON), TWDM can be used as an alternative

**Enhanced Common Public Radio Interface (eCPRI) fronthaul**: CPRI is the key internal interface of Radio Equipment (RE), or remote radio head (RRH) and base station unit (BBU) or radio equipment controller (REC) via fronthaul transport network. For fronthaul between RRH and BBU, the overall delay must be limited to less than 100 μs over the multi-hop paths in 5G communication. Due to this stringent latency requirement, eCPRI is becoming an important technology for 5G. Its specification supports more flexibility in the positioning in eNBs, where BBU contains part of the PHY layer and higher layer functions of the air interface, whereas the RRH contains the remaining part of the PHY layer functions and the

**Software-Defined Optical Network**: The SDN paradigm separates the control

**Reconfigurable Optical Add/Drop Multiplexers (ROADM)**: OADM drops the desired wavelengths to local terminals from an incoming multi-wavelength signal by using a wavelength demultiplexer and adds a locally generated wavelength with the remaining pass-through wavelengths to generate the new outgoing multiwavelength signal. In general, the mux/demux characteristics are fixed. However, to accommodate dynamic behavior and requirements of an optical network, it is almost necessary to have a reconfigurable OADM (ROADM). A ROADM can switch traffic remotely from a WDM system at the wavelength layer and enables the flexibility and reconfigurability of an optical transport network. Having the properties of being colorless (not wavelength selective), directionless (not nodal degree selective), and contentionless (not different wavelength) improves significantly the

**Software-Defined Optics (SDO)**: Due to dynamic and variable requirements of data traffic, it is almost necessary to do cross-layer interactions. To enables this

plane from the data plane and uses an SDN controller for centralizes network control. SDN facilitates NFV for the network virtualization over the physical infrastructure so that multiple virtual networks can operate within. Due to high optical transmission capacities and the specific characteristics of optical components, software-defined optical networks (SDONs) has been proposed. With an underlying optical network infrastructure, SDONs seek to leverage the flexibility of SDN control for supporting networking applications. NFV allows for the flexible operation of multiple virtual optical networks over a given physical optical network infrastructure. SDONs are highly promising for low-latency and high-bandwidth backhauling for 5G eNBs. SDON application layer studies have developed mechanisms for achieving Quality of Service (QoS), access control and security, as well as

*DOI: http://dx.doi.org/10.5772/intechopen.97293*

prominent wavelength regions, 1310 nm, and 1550 nm.

pushed further for future FCN.

for transmitting 5G traffic [14].

analog radio frequency functions [15].

energy efficiency and failure recovery [16].

capacity of add/drop ports in a ROADM [17].

### *Convergence of Wireless and Optical Network in Future Communication Network DOI: http://dx.doi.org/10.5772/intechopen.97293*

proposed and used, which are Dense WDM, Coarse WDM, and Time WDM. DWDM uses frequency grids of 12.5, 25, 50, and 100 GHz for transmission. IN the present scenario, many-core networks deployed 1.6 Tbps ( 40Gbps 40 × wavelengths) DWDM system. To support the capabilities for 5G and beyond 5G system, the core network will need to transport 10 Tbps or more per fiber which will be pushed further for future FCN.

CWDM combines multiple optical signals at various wavelengths for transmission in optical fiber cables. Up to 18 channels are allowed to be connected over a dark fiber pair. Unlike 0.4 nm spacing for DWDM, CWDM systems have channels at wavelengths spaced 20 nanometers (nm) apart. CWDM works well in two prominent wavelength regions, 1310 nm, and 1550 nm.

TWDM is a WDM technique, where TDMA is applied to a set of wavelengths instead of just one wavelength. It requires strict coordination with the radio equipment to guarantee low latency, as with TDMA and provides more bandwidth than TDMA. In a passive optical network (PON), TWDM can be used as an alternative for transmitting 5G traffic [14].

**Enhanced Common Public Radio Interface (eCPRI) fronthaul**: CPRI is the key internal interface of Radio Equipment (RE), or remote radio head (RRH) and base station unit (BBU) or radio equipment controller (REC) via fronthaul transport network. For fronthaul between RRH and BBU, the overall delay must be limited to less than 100 μs over the multi-hop paths in 5G communication. Due to this stringent latency requirement, eCPRI is becoming an important technology for 5G. Its specification supports more flexibility in the positioning in eNBs, where BBU contains part of the PHY layer and higher layer functions of the air interface, whereas the RRH contains the remaining part of the PHY layer functions and the analog radio frequency functions [15].

**Software-Defined Optical Network**: The SDN paradigm separates the control plane from the data plane and uses an SDN controller for centralizes network control. SDN facilitates NFV for the network virtualization over the physical infrastructure so that multiple virtual networks can operate within. Due to high optical transmission capacities and the specific characteristics of optical components, software-defined optical networks (SDONs) has been proposed. With an underlying optical network infrastructure, SDONs seek to leverage the flexibility of SDN control for supporting networking applications. NFV allows for the flexible operation of multiple virtual optical networks over a given physical optical network infrastructure. SDONs are highly promising for low-latency and high-bandwidth backhauling for 5G eNBs. SDON application layer studies have developed mechanisms for achieving Quality of Service (QoS), access control and security, as well as energy efficiency and failure recovery [16].

**Reconfigurable Optical Add/Drop Multiplexers (ROADM)**: OADM drops the desired wavelengths to local terminals from an incoming multi-wavelength signal by using a wavelength demultiplexer and adds a locally generated wavelength with the remaining pass-through wavelengths to generate the new outgoing multiwavelength signal. In general, the mux/demux characteristics are fixed. However, to accommodate dynamic behavior and requirements of an optical network, it is almost necessary to have a reconfigurable OADM (ROADM). A ROADM can switch traffic remotely from a WDM system at the wavelength layer and enables the flexibility and reconfigurability of an optical transport network. Having the properties of being colorless (not wavelength selective), directionless (not nodal degree selective), and contentionless (not different wavelength) improves significantly the capacity of add/drop ports in a ROADM [17].

**Software-Defined Optics (SDO)**: Due to dynamic and variable requirements of data traffic, it is almost necessary to do cross-layer interactions. To enables this

*Wireless Power Transfer – Recent Development, Applications and New Perspectives*

munication, boost the requirement of wireless communication [14].

**2.2 Development of optical network**

adaptable DWDM grid.

required for ASON.

**Cognitive Radio**: Over the spectrum has been allocated for several usages and the allocated resources are very much under-utilized, To reduce spectrum scarcity and utilize the underutilized spectrum, cognitive radio technology has been proposed. It is an intelligent radio, that can be sense, learn, aware and adapt according to the environment. With the help of software-defined radio (SDR), cognitive radio can be programmed and configured dynamically. SDR is a radio transceiver where radio components (modulators/demodulators, filters, amplifiers, mixers, detectors, etc.) are implemented by software on a personal computer or embedded

Having understood these technologies of 5G wireless communication, FCN is planning to have the communication system that can achieve data rates of about 100 Tb/s high speed, low latency, and reliable communications are essential for supporting ML/AI at the edge; giving rise to the research field entitled Communication over machine learning. Incorporation of holographic telepresence, holographic communication, virtual reality, and augmented reality in future com-

In the present network scenario, the data generated by the wireless devices are transported through an optical network. In general, optical fiber is connected between wireless base stations (BSs/eNB), and their controlling, switching, and monitoring centers. Due to the enormous available bandwidth, the optical fiber can carry data up to 100 Tbps for networking in the optical network. By using appropriate technology, the capacity can be increased further. Similar to the evolution of the wireless network, the optical networks also evolved generation-wise. During the process of evolution, the optical network incorporated optical cross-connect (OXC), a synchronous digital hierarchy (SDH) /synchronous optical network (SONET) rings, optical add-drop multiplexers (OADMs), Software-defined network/network function virtualization (SDN/NFV). Today's long-haul backbone networks of 10/40 Gbps wavelength channels use wavelength-division multiplexing (WDM) transmission systems. Further increase in capacity, the optical network uses a dense WDM (DWDM) frequency grid (12.5, 25, 50, and 100 GHz by G.694.1). Further development of WDM transmission systems makes the system an

**Optical Transport Network (OTN)**: ITU-T G.709 defined OTN, which transport digital/optical signal across the core network is a flexible way. Each optical channel carries a separate signal using optical channels multiplexing and uses optical data as a unit. OTN supports the different functions for transporting data, such

**Different variant of wavelength-division multiplexing (WDM)**: WDM is the

main transmission technology. Over the year several of its variant has been

as multiplexing, routing, management, supervision, and survivability.

**Automatically Switched Optical Network (ASON)**: To accommodate dynamic traffic and their requirements, optical networks need to manage to signal and routing automatically and intelligently. It provides auto-discovery and dynamic connection set-up with the help of dynamic signaling-based over OTN and SDH networks. This is done through a distributed (or partially distributed) control plane, which enables improved support for current end-to-end provisioning, re-routing, and restoration. ASON uses the generalized MPLS (GMPLS) signaling protocol to set up and monitor edge-to-edge transport connections. It also uses single fiber switching to wavelength switching and optical packet switching. The other components, like OXCs, wavelength converters, and OADMs are

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system [12].
