At the moment, China currently sits at the top of the world standings when it comes to the number of 5G towers successfully installed. However, even with 600,000 5G towers and base stations installed throughout the country, it has only touched the surface of complete 5G penetration, as the country will need up to 10 million towers before it reaches true nationwide 5G coverage. 


Read on to learn how Passive Optical Networks – or PON – holds the key to the mass deployment of 5G.

The Science Behind 5G Deployment and Infrastructure

The millimeter-wave band, which can drive large throughputs, comes with a drawback of distance. The signal radius drops from 1 km in 4G radio to a mere 100m or less, depending on the terrain. This means it requires approximately 20 to 50 times more access points than 4G to achieve complete 5G penetration. However, the problem does not subside after all the mobile towers have been built. Another challenge presents itself, which is how to connect all the towers that have been built? 

When observing the network architecture of 5G’s predecessor, 4G, a base station is co-located within each tower, which requires a large physical space equipped with a backup battery and temperature control. With 5G, due to its requirement of having significantly higher numbers of mobile towers, building a complete and fully-equipped individual mobile tower may be highly costly, which is why 5G networks have uncoupled the data processing within the distributed unit (DU) from the signal-bearing radio unit (RU). By allocating a DU to several mobile towers at the edge of the access network, the size and cost of the base stations are greatly reduced. 


Fiber reliance has been common practice within network architectures. Within 5G, this is especially true due to its deployment, which is based on the cloud RAN topology where antenna-sector data will travel directly towards DUs via fiber. This kind of data will require 10-Gbps to 25-Gbps connections, sitting at the higher end of microwave technology. 

Moreover, 5G requires as much as 20 times more bandwidth than its predecessor, which must be accommodated by fiber. These fiber connections must allow for an extremely low level of latency of up to 10 times less delay than 4G LTE. 


A seemingly obvious solution is to deploy all new fiber to connect millions of radio towers, however, this will result in a huge delay, fraught with logistical complications, and added costs to operators. As long as these infrastructure hurdles are not overcome, the benefits of 5G cannot be fully realized. 


How Passive Optical Network (PON) Plays a Role 

A more efficient alternative to this is for operators to optimize the tower deployment cost and the last-mile transport to reach the base stations. To accomplish this, it is imperative that the RAN capacity is maximized by exploiting existing fiber infrastructure. Passive Optical Networks (PONs), which are already available for fiber-to-the-home (FTTH) connectivity, can allow the 5G data to be transported via fibers from the radio towers to the RAN. 


PONs come in different types, such as GPON (Gigabit Passive Optical Network), which is able to sustain a top capacity of around 2.5-Gbps downstream and 1.2-Gbps upstream. However, the fronthaul would require remarkably more capacity, such as XGS-PON, which are able to offer up to 10-Gbps upstream and downstream. 


Another alternative that is growing in support is the WDM-PON (Wavelength Division Multiplexing PON), which allows for higher network security and works by overlaying new wavelengths onto legacy PON networks without compromising the bandwidth of the existing fixed broadband service. Due to its ability to use the four wavelength colors within the fiber for GPON to serve both GPON for FTTH and XGS-PON for 5G fronthaul on the same fiber, the same existing infrastructure can be used to reach home and to connect from RU to the DU. 


The newest proposed addition is the NG-PON2, which is capable of handling up to 40 Gbps in each direction over PON by using eight wavelengths of XGS-PON. Due to its massive transport capacity, it has the potential to extend the PON network to connect mid-haul between DUs and CU even deeper into the radio access network. At its core, PON is a time-dimension multiple access (TDMA) protocol, which presents a naturally added delay between the arrival of traffic and response to permit delivery. This can result in a millisecond delay, which is substantial in 5G terms. All things considered, WDM-PON seems highly eligible for a low-latency fronthaul transport option. 


Final Words 

As more 5G networks are moving toward mass deployment, PONs are mostly recognized as parts of the blueprint of 5G transport from the antenna to RAN. Although more work needs to be done to reduce the latency to meet 5G benchmarks, PONs are able to distinguish themselves due to their availability, installation simplicity, scalability, and reliability. Above all, PONs will help to ensure operators are able to redirect their infrastructure budget to building more mobile towers, which are the backbones of 5G deployment. 


VIAVI Solutions’ industry-leading offerings deliver complete 5G solutions for validation, verification, and visibility. Learn more about 5G Validation, 5G Test & Verification, and 5G Visibility on our website, and do not hesitate to contact us with any questions. 


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Channel Marketing Manager - APAC

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