Today, there are more than 200 commercial 5G networks worldwide, and the pace of adoption is only moving faster. Yet even as 5G networks and devices become mainstream, the technology continues to evolve. A range of new 5G initiatives are being deployed to achieve greater performance, efficiency and scalability, with centralized RAN (C-RAN) architecture being implemented by an increasing number of communications service providers (CSPs). In fact, according to research by analyst firm Heavy Reading, 71 percent of North American CSPs are expected to roll out C-RAN by 2025.
C-RAN technology enables Layer 2 processing and higher baseband functionalities to be migrated out of the cell site and centralized in order to pool resources. This centralization allows cell site deployment to be simplified, reducing operational costs and total cost of ownership (TCO). Moreover, the transition to a C-RAN architecture enables improved RAN performance and increased network resiliency by centralizing baseband elements as well as the timing source. The ability to increase resiliency is critical to differentiating new 5G networks and services, since discrepancies in timing and synchronization can quickly lead to increased interference, dropped calls and poor overall quality of experience (QoE).
Tailored Transport
However, as CSPs transform their 5G networks to adopt centralized RAN, the complexities of this architecture can greatly complicate planning and deployment. One particularly important planning consideration is how to manage the interdependencies between the RAN and transport network. To ensure the transport network will provide sufficient capacity and performance as their 5G network grows, CSPs need to consider the radio spectrum capacity, coverage and latency requirements for each new service type to be deployed.
Building out new fiber can be prohibitive due to the time and cost, so the fastest option is to use existing dark fiber when available. However, the availability of dark fiber that meets specific latency and capacity requirements, including the needs of urban deployment sites, will vary from region to region.
Transport planning is further complicated by the deployment of small cells and picocells to complement coverage reach and capacity of the macro cell sites, as well as network slicing to accommodate different service offerings. And finally, let’s not forget the need to handle legacy 4G traffic over the same transport network.
As a result, the typical CSP will need a range of 5G transport solutions to accommodate and enhance existing fiber resources, addressing the many new applications and opportunities 5G technology offers.
C-Band Capacity Boost
Escalating demands for data over 5G continue to push capacity requirements to the limits. For example, when planning 5G capacity using C-Band radio spectrum in combination with legacy 4G traffic, the average network may require up to 400 Gbps of capacity per macro cell site in a centralized RAN topology. The capacity needs of this application can be efficiently addressed with a fiber relief method that uses a transponder-based wavelength-division multiplexer (WDM) technology or a combination of IEEE 802.1CM-based time-sensitive networking (TSN) platform and O-Band optics. Both technologies aggregate payloads over the xHaul using a single fiber.
The space-saving IEEE 802.1CM TSN platform makes use of packet technology to aggregate 5G eCPRI, 4G CPRI and Ethernet channels over high-speed 100G links for fiber relief in the fronthaul. Using IEEE 1588v2 for precision time protocol (PTP), the TSN platform provides economical distribution of timing and synchronization to minimize dependency of GPS and atomic clock sources, improve resiliency and offer greater service availability without the need for GPS receivers at the cell sites.
In this fiber relief method, O-Band 100G pluggable optics are used in place of broadband optics on the TSN platform’s high-speed links, using the O-Band optical spectrum to offer better dispersion characteristics and lower cost than traditional C-Band optics used in Dense wavelength-division multiplexing (DWDM) and coherent optical technology, respectively. As 5G eCPRI, 4G CPRI and Ethernet channels are added to the TSN platform, the 100G O-Band high-speed links provide pay-as-you-grow scalability.
This transport method allows the 100G O-Band links to be aggregated onto a passive, bidirectional WDM for a fiber relief solution at 400G capacity over a single fiber. The second fiber in the pair can be used for maintenance and future scaling. At full capacity, this approach results in a fiber savings of 8 to 1, while enabling rapid service turn-up and centrally SDN-managed remote operations, administration and management (OA&M) service visibility.
Large Capacity Transport for Small Cells
As CSPs strive to build out ubiquitous 5G coverage and capacity, increasing cell densification is necessary, particularly when using higher frequency bands such as the millimeter wave (mmWave) spectrum. This means a growing number of small cells with radios deployed on streetlights, utility poles, rooftops and on the sides of buildings. Each of these sites require fiber facilities for each radio channel; however, they have very limited access to electrical power and footprint.
Fortunately, this challenge can be addressed with innovative optics at the 10G and 25G rates replacing the optics in the mmWave radios. At these lower rates, C-Band optical spectrum in a smart, self-tuning pluggable is connected to a passive bidirectional WDM, offering transport to each cell site with a single fiber. Plus, because the WDM is passive and has its own small outside plant enclosure about the size of a shoebox, no additional power or substantial space is needed for this transport solution.
The smart self-tuning DWDM optics and passive multiplexer can be used as a standalone, passive transport solution at the hub location for connection to distributed units (DUs), baseband units (BBUs) and routers. If remote OA&M visibility is needed, an active transponder-based or TSN aggregation platform is added at the hub location, enabling service channel access in the smart optics out to the cell site and integration into the software-defined networking (SDN) management system. With smart optics disaggregated from the transport system and plugged directly into radios at the small cell sites, power and space challenges can be resolved.
Moreover, as a passive transport solution, these 10G and 25G self-tuning optics offer fast, automated service turn-up to reduce provisioning time by 98 percent – from hours to minutes — as compared to a transponder-based optical transport system. And two of these smart self-tuning optics replace 40 fixed, DWDM optics, resulting in spares inventory savings of 95 percent.
Fiber Relief Ecosystem
The ability to bring faster, higher capacity 5G connectivity closer to subscribers allows CSPs to improve reliability, QoE, and ultimately, revenue. Yet achieving this goal while also evolving the network to keep pace with new 5G innovations using centralized RAN presents a substantial challenge. By taking advantage of an available transport ecosystem designed to provide fiber relief, CSPs can simplify the complexities of next-generation architecture to achieve optimum performance and capacity while minimizing the time and cost of building out reliable 5G transport.
