5G-PON: SK Telecom’s unified distribution network
SK Telecom has detailed a networking architecture based on wavelength division multiplexing-passive optical network (WDM-PON) technology that it says will simplify the rollout of 5G while delivering significant cost savings.
The telecom operator has already deployed the networking architecture, dubbed 5G-PON, for its LTE network and is offering the design to the 5G network standards of the ITU-T.
“SK Telecom is already witnessing a great amount of cost reductions from the deployment of 5G-PON,” says Seungjoo Hong, manager of the Broadband Technology Lab at SK Telecom (pictured).
5G-PON
5G-PON provides a single distribution network for both cellular - LTE and 5G - and high-speed wireline broadband (see diagram).
Source: SK Telecom
The architecture reduces networking costs by reusing existing fibre and optical filters while expanding capacity to support different and growing traffic streams. The architecture also uses passive nodes that do not require electrical power.
The 5G-PON network comprises three main elements: a central office terminal, the remote node and a tunable SFP pluggable module.
The central office terminal is located at the cellular base band unit (BBU) and performs such functions as wavelength conversion for WDM transmission, the monitoring of the optical link, and the management and configuration - location and order - of the remote nodes. The central office terminal also collects and analyses digital diagnostic monitoring information sent over an auxiliary management and control channel.
SK Telecom is already witnessing a great amount of cost reductions from the deployment of 5G-PON
The second element, the remote node, is a passive optical wavelength router, says Hong, and can be placed indoors or outdoors at a remote site. The remote node comprises a filter for coarse WDM (CWDM) and a filter for dense WDM (DWDM) and supports an optical ring topology between the first stage nodes - called the main radio node - as well as multi-stage node configurations such as a main and sub radio nodes (see the diagram below).
Different 5G-PON configurations. SK Telecom favours a single-fibre ring arrangement. Source: SK Telecom
The central office terminal has knowledge of the order and location of the remote site nodes. This ensures a seamless service by performing delay equalisation due to optical path differences while executing ring protection switching within 50ms when a fibre is cut.
Meanwhile, the tunable SFP is installed at the cellular remote radio head (RRH). The tunable SFP is a low-cost design; it does not use a wavelength locker such that the SFP’s tunable laser is not dependent on a specific wavelength grid. The SFP is operated at the remote radio head using a software wavelength locking function that tracks the centre of the WDM filter using received optical power information from the central office terminal sent via an auxiliary management and control channel.
5G-PON has halved the cost of installation while operations and maintenance costs have been reduced 70 percent
CWDM architecture
5G-PON’s WDM-PON architecture uses CWDM with sub-channels.
The architecture can use existing installed fibre and filters while expanding capacity to a total of 256 wavelengths (16 sub-channels in each of 16 CWDM 20nm-wide bands), such that it can work alongside existing CWDM, DWDM and time-division multiplexing PON (TDM-PON) deployments.
“To expand network capacity in an area, operators can easily deploy a basestation using their existing fibre infrastructure, saving a great amount of installation cost,” says Hong. “5G-PON also allows operators to cover new areas with the least amount of cost.”
Hong says deploying 5G-PON has halved the cost of installation while operations and maintenance costs have been reduced 70 percent due to the intelligent operation and management of the passive nodes and the use of tunable SFPs at the remote sites.
SK Telecom has worked with local vendors including Solid, HFR, SunwaveTec and Coweaver to develop the 5G-PON architecture.
Status
The 5G-PON deployed for SK Telecom’s LTE front-haul network uses single-fibre bidirectional 3-gigabit and 6-gigabit 20km tunable SFPs that support 96 optical links on CPRI/ OBSAI interface channel cards.
Hong says that in 2018, SK Telecom will have bidirectional 10-gigabit tunable SFPs and will start developing of 25-gigabit bidirectional tunable SFPs and eCPRI interface channel cards for its 5G radio access network.
SK Telecom’s own preference is to use 5G-PON in a ring architecture to ensure service continuity in the event of a fibre cut. But depending on the operator, various topologies can be supported.
The operator plans to roll out 5G-PON in 85 areas nationwide, with further deployments expected thereafter.
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Melding networks to boost mobile broadband
In a Q&A, Bryan Kim, manager at SK Telecom's Core Network Lab, discusses the mobile operator's heterogeneous network implementation and the service benefits.
SK Telecom has developed an enhanced mobile broadband service that combines two networks: 3G and Wi-Fi or Long Term Evolution (LTE) and Wi-Fi. The mobile operator will launch the 3G/ Wi-Fi heterogeneous network service in the second quarter of 2012 to achieve a maximum data rate of 60 Megabits-per-second (Mbps), while the LTE and Wi-Fi integrated service will be offered in 2013, enabling up to a 100Mbps wireless Internet service.
Q. What exactly has SK Telecom developed?
A. SK Telecom has developed a technology that provides subscribers with a faster data service by using two different wireless networks simultaneously. For instance, customers can enjoy a much faster video streaming service supported by either 3G and Wi-Fi, or LTE and Wi-Fi networks.
To benefit, a handset must use two radio frequencies at the same time. We have also built a system that is installed in the core network for simultaneous transmission.
"If it takes 10s to download a 10MB file using a 3G network and 5s to download the same file using the heterogeneous solution, the impact on the battery life is the same."
Bryan Kim, SK Telecom
Q. LTE-Advanced is standardising heterogeneous networking. This suggests that what SK Telecom has done is pre-standard and proprietary. What have you done that is different to the emerging standard?
A. SK Telecom is not talking about LTE-Advanced technology. This is a technology that enables simultaneous use of heterogeneous wireless networks we’ve deployed.
Q. What are the technical challenges involved in implementing a heterogeneous network?
A. It is technically difficult to realise the technology as it involves using networks with different characteristics in terms of speed and latency. At the same time, the technology is designed to minimise the changes required to the existing networks.
There has not really been challenges when linking the two separate networks but it is always a challenge to analyse the real-time network status to provide fast data services.
Q. What impact will simultaneous heterogeneous network operation have on a smartphone's battery life?
A. Using the heterogeneous network integration solution does increase the battery consumption: the device is using two radio frequencies. However, from a customer's perspective, if it takes 10s to download a 10MB file using a 3G network and 5s to download the same file using the heterogeneous solution, the impact on the battery life is the same.
SK Telecom also plans to apply a scanning algorithm for selecting qualified Wi-Fi networks.
Q. What services can SK Telecom see benefiting from having a 3G/ LTE network combined with a Wi-Fi network?
A. Customers will experience greater convenience when using multimedia services and network games, for example, with increased available bandwidth.
Source: SK Telecom
Heavy users tend to consume a lot of video services through mobile broadband. With this solution, SK Telecom will be providing faster data services to customers compared to when using only one network. This will enhance data service markets. The company has no plans for now to provide services directly.
Q. What mobile services come close to using 60Mbps or 100Mbps?
A. The 60Mbps and 100Mbps are theoretical maximum speeds. People who sign up for a 100Mbps fixed-line network service rarely experience the 100Mbps speed. With this technology, SK Telecom aims to increase the amount of wireless network resources for subscribers by using two different types of networks in a simultaneous manner, which in turn will boost the services that require wider bandwidth including video streaming service and network games.
Q. With a combination of Wi-Fi and cellular, most operators want to get traffic off the cellular network onto the ‘hot spot’. Does SK Telecom really want to fill their cellular network by providing higher speeds?
A. From the customer’s perspective, a Wi-Fi network offers narrow coverage and small capacity and since it is not a managed network, wireless data access is made upon request from customers. Thus, data offloading often does not work as intended by the mobile carriers.
In contrast, cellular networks provide national coverage so if there is an available Wi-Fi network to add to the cellular network, we can simultaneously use the cellular and Wi-Fi networks to offer a data service. By doing so customers will enjoy greater speed data services and mobile operators will be able to naturally offload data.