**4. Access networks and 5G networks**

The primary determination of all technologies for xPON is evident from their name, a passive optical (access) network. This trend continues from the original asynchronous transfer mode PON (APON), broadband PON (BPON), GPON, XG-PON, and the latest approved next-generation PON stage 2 (NG-PON2) recommendations. The latest recommendation has become the pioneer of extending the passive optical network to mobile customers as well. However, residential customers with a fixed connection (flat or house) still remain the priority. With the onset of 5G technology in mobile communications, it will be necessary to reduce the area of cells to ensure coverage of the entire territory by radio signals. This is mainly due to the increasing permeability and diminishing cell size, so it is necessary to build more cells that cover the same area. It is possible to divide the area according to its antenna density into low density (<20 small cells/km2 ), medium density (<75 small cells/km2 ), dense (<200 small cell/km2 ), and ultrahigh density (>200 small cells/km2 ). Current long-term evolution (LTE) technology has been providing broadband data services; however, these technologies seem to be inadequate for certain services (virtual reality or generally the most sensitive services for low latency, such as access to data networks of the Internet of things devices). Current customer needs may include gigabit transmissions per second, smart home/buildings, self-driving car, working and playing in the cloud, and 3D or UHD video. Minimal latency requirements will be determined mainly based on data transmission within the national network (10–200 km). The transmission delay in the current networks ranges from 5 to 41 ms, and the delay for the access part of the network (1–10 km) is approx. 7–12 ms. Another key factor that affects the delay is the time it takes to process incoming requests from a data center (approximately 8 ms). The round-trip time (RTT) of current networks is approximately 106 + 8 ms. 5G networks aim to limit this value to 14 + 8 ms. The major merit of RTT depreciation will be to move cloud services closer to the user. Then, the RTT will be reduced to 14 ms, which will primarily generate a delay (7 ms) on the access technology. However, the question remains how the operators will move the data centers closer to the customer, since until now, a distance of 200 km a data center from the customer has been enough. Such a distance is not sufficient for 5G networks.

Among the available technologies covering the 5G signal area, there are technologies for access networks: G.fast, data over cable service interface specification (DOCSIS) and NG-PON2. G.fast technology offers symmetric transmission speeds of up to 500 Mb/s over a short distance (up to 100 m). This speed can be increased to 10 Gb/s, but the overall system reach will be shortened. In theory, G.fast can only be deployed in special cases, such as brownfield scenarios, to ensure connectivity of very small cells in buildings. The basic prerequisite is the combination of functions within the baseband unit (BBU) and remote radio unit (RRU). DOCSIS 3.1 offers bandwidth of 10/1–2 Gb/s share per coaxial segment (192 MHz orthogonal frequency-division multiplexing (OFDM) channels). Full-duplex communication (current downstream and upstream) can take up to 10 Gb/s per coaxial segment. However, neither of these methods is capable of fully serving the 5G network because the available bandwidth is shared and the common public radio interface (CPRI) does not support the lowest possible latency for transmission.

The basic idea behind the NG-PON2 network is to provide all end stations with sufficient bandwidth. The station shares the total bandwidth that the associated OLT unit is able to handle properly. NG-PON2 network parameters such as distribution ratios, power levels, transfer rates, etc. are described in [22–25]. In 5G network areas, there is ultradense deployment of basic radio stations required,

**73**

connectors.

end customers.

**Figure 5.**

more information, see **Figure 6**.

*Deployment of PON in Europe and Deep Data Analysis of GPON*

and their radiations are constrained to prevent intra- and inter-cell interference. In general, the reach of NG-PON2 (up to 20 km from the OLT) is sufficient for covering an acceptable number of end users and for effective usage of its coverage (the division of covered territory into several smaller sectors/cells). The use of access technologies for data transfers or generally for triple play has already been noted out by ITU in [26]. **Figure 5** defines a possible scheme of the NG-PON2 network for its connection to the 5G network. The connection can be realized by dedicated wavelengths (λ). By using a coexistence element (CE), such a coexistence scheme for older PON standards under the ITU recommendations can be established. Regarding the aforementioned dedicated wavelengths, up to 4λ with a 10 Gbit/s transfer rate is considered. One disadvantage of this radio tower connection method is the custom lock method that is publicly available but is much more complex than in the case of the IEEE network. As a result, it will be necessary to use the conversion station to transmit the signal from the radio station toward the

*Coexistence NG-PON2 and GPON scheme with dedicated lambdas for 5G networks.*

**5. GPON frame structure and activation process analysis**

At present, GPON is one of the most promising solutions for modern access networks. Among other useful and important features, it provides us with triple play services on a single optical fiber, good scalability, DBA, simple topology management, etc. In comparison with the previous standards that only supported transmission over asynchronous transfer mode (ATM), GPON is the first standard that supports transmission over both ATM and ethernet technologies. In the ethernet mode, the ethernet frames are encapsulated using GPON encapsulation mode (GEM) and transferred inside GEM frames. As a result, some ethernet structures, such as interpacket gap, preamble, or start of frame delimiter, are not available. For

The basic GPON topology comprises the following three components: OLT, ONU, and optical distribution network (ODN). Typically, there is/are a single/ more OLT/s in the network (depending on the preferences of the associated Internet service provider) performing encapsulation and de-encapsulation of downstream and upstream network traffic, respectively, for multiple end users (up to 128 end users per port). The ONU is located at the end user's premises and converts the signals from the optical to the electrical domain. Finally, an ODN is composed of the elements placed between OLTs and ONUs such as optical fibers, splitters, and

*DOI: http://dx.doi.org/10.5772/intechopen.82679*

The primary determination of all technologies for xPON is evident from their name, a passive optical (access) network. This trend continues from the original asynchronous transfer mode PON (APON), broadband PON (BPON), GPON, XG-PON, and the latest approved next-generation PON stage 2 (NG-PON2) recommendations. The latest recommendation has become the pioneer of extending the passive optical network to mobile customers as well. However, residential customers with a fixed connection (flat or house) still remain the priority. With the onset of 5G technology in mobile communications, it will be necessary to reduce the area of cells to ensure coverage of the entire territory by radio signals. This is mainly due to the increasing permeability and diminishing cell size, so it is necessary to build more cells that cover the same area. It is possible to divide the area according to its

Current long-term evolution (LTE) technology has been providing broadband data services; however, these technologies seem to be inadequate for certain services (virtual reality or generally the most sensitive services for low latency, such as access to data networks of the Internet of things devices). Current customer needs may include gigabit transmissions per second, smart home/buildings, self-driving car, working and playing in the cloud, and 3D or UHD video. Minimal latency requirements will be determined mainly based on data transmission within the national network (10–200 km). The transmission delay in the current networks ranges from 5 to 41 ms, and the delay for the access part of the network (1–10 km) is approx. 7–12 ms. Another key factor that affects the delay is the time it takes to process incoming requests from a data center (approximately 8 ms). The round-trip time (RTT) of current networks is approximately 106 + 8 ms. 5G networks aim to limit this value to 14 + 8 ms. The major merit of RTT depreciation will be to move cloud services closer to the user. Then, the RTT will be reduced to 14 ms, which will primarily generate a delay (7 ms) on the access technology. However, the question remains how the operators will move the data centers closer to the customer, since until now, a distance of 200 km a data center from the customer has been enough.

Among the available technologies covering the 5G signal area, there are technologies for access networks: G.fast, data over cable service interface specification (DOCSIS) and NG-PON2. G.fast technology offers symmetric transmission speeds of up to 500 Mb/s over a short distance (up to 100 m). This speed can be increased to 10 Gb/s, but the overall system reach will be shortened. In theory, G.fast can only be deployed in special cases, such as brownfield scenarios, to ensure connectivity of very small cells in buildings. The basic prerequisite is the combination of functions within the baseband unit (BBU) and remote radio unit (RRU). DOCSIS 3.1 offers bandwidth of 10/1–2 Gb/s share per coaxial segment (192 MHz orthogonal frequency-division multiplexing (OFDM) channels). Full-duplex communication (current downstream and upstream) can take up to 10 Gb/s per coaxial segment. However, neither of these methods is capable of fully serving the 5G network because the available bandwidth is shared and the common public radio interface (CPRI) does not support the lowest possible latency for

The basic idea behind the NG-PON2 network is to provide all end stations with

sufficient bandwidth. The station shares the total bandwidth that the associated OLT unit is able to handle properly. NG-PON2 network parameters such as distribution ratios, power levels, transfer rates, etc. are described in [22–25]. In 5G network areas, there is ultradense deployment of basic radio stations required,

), medium density (<75 small

).

), and ultrahigh density (>200 small cells/km2

**4. Access networks and 5G networks**

antenna density into low density (<20 small cells/km2

), dense (<200 small cell/km2

Such a distance is not sufficient for 5G networks.

cells/km2

**72**

transmission.

**Figure 5.** *Coexistence NG-PON2 and GPON scheme with dedicated lambdas for 5G networks.*

and their radiations are constrained to prevent intra- and inter-cell interference. In general, the reach of NG-PON2 (up to 20 km from the OLT) is sufficient for covering an acceptable number of end users and for effective usage of its coverage (the division of covered territory into several smaller sectors/cells). The use of access technologies for data transfers or generally for triple play has already been noted out by ITU in [26]. **Figure 5** defines a possible scheme of the NG-PON2 network for its connection to the 5G network. The connection can be realized by dedicated wavelengths (λ). By using a coexistence element (CE), such a coexistence scheme for older PON standards under the ITU recommendations can be established. Regarding the aforementioned dedicated wavelengths, up to 4λ with a 10 Gbit/s transfer rate is considered. One disadvantage of this radio tower connection method is the custom lock method that is publicly available but is much more complex than in the case of the IEEE network. As a result, it will be necessary to use the conversion station to transmit the signal from the radio station toward the end customers.
