Advanced technology plays a crucial role in shaping the future of communication systems, especially with the emergence of 5G. One of the key technologies enabling this transformation is WDM-PON (Wavelength Division Multiplexing Passive Optical Network), which supports various 5G application scenarios.
1. WDM-PON and 5G Application Scenarios
1.1 Defining the 5G Pre-Transmission Network Architecture
As mobile internet continues to evolve and new applications like IoT emerge, the demand for handling massive data traffic and connecting countless devices has led to the development of 5G technology. In 2015, ITU-R defined three main 5G use cases: eMBB (enhanced Mobile Broadband), mMTC (massive Machine Type Communication), and URLLC (Ultra-Reliable Low Latency Communication). These scenarios cover high-speed video streaming, large-scale IoT services, and critical applications such as autonomous driving and industrial automation, all requiring low latency and high reliability.
In 2016, China Mobile released a white paper on 5G C-RAN requirements, architecture, and challenges. The BBU (Baseband Unit) function was restructured into two entities: CU (Centralized Unit) and DU (Distributed Unit). The CU handles non-real-time wireless protocol stack functions and supports some core network functions, while the DU manages real-time physical layer tasks. This two-tier architecture allows for more flexible deployment options and improved network efficiency.
The introduction of the CU enables centralized processing, while the DU can be deployed in a distributed manner. This setup supports both DU pooling and CU pooling, enhancing network scalability. The pre-transmission part of the network, known as Fronthaul, supports protocols like eCPRI, while Midhaul connects the DU and CU. Both segments have different latency and bandwidth requirements based on the 5G service type.
1.2 WDM-PON Supporting 5G Applications
WDM-PON is particularly well-suited for 5G due to its ability to handle high bandwidth and low latency. It is ideal for scenarios where operators need to centralize DU or BBU functions, especially in dense urban areas or new service environments that combine wired and wireless access. By leveraging existing fiber infrastructure, WDM-PON helps reduce costs and improve coverage.
For URLLC services, it’s recommended that the CU shares the same site as the OLT and DU. This co-location minimizes transmission delays and improves coordination between DUs. WDM-PON also supports efficient resource sharing, making it a strong candidate for future fixed-mobile convergence networks.
2. Implementation of WDM-PON and Its Significance for 5G
Key technologies in WDM-PON include colorless ONU technology and auxiliary management channel (AMCC) technology. Colorless ONUs allow for flexible wavelength allocation, while AMCC enables efficient management through techniques like RF Pilot-tone and Baseband Overmodulation.
WDM-PON offers several advantages for 5G pre-transmission, including low latency, high bandwidth, and efficient transmission. It supports 10G and 25G per channel, meeting the demands of eCPRI signals. Additionally, it reduces fiber usage and improves network efficiency by utilizing AWG (Arrayed Waveguide Grating) instead of traditional splitters.
WDM-PON also helps operators save on infrastructure costs by reusing existing fiber networks. It enables shared access for home users, enterprises, and 5G base stations, improving equipment utilization and reducing the need for additional equipment rooms.
2.1 Pre-Transmission Solution
WDM-PON provides an efficient solution for 5G pre-transmission by connecting DU pools and RRU units through a passive optical network. This approach ensures reliable and high-performance connectivity for 5G, government, and enterprise services.
2.2 WDM-PON Standards and Operator Demands
Currently, WDM-PON standards focus on systems operating below 10G per wavelength. However, with the rise of 25G per channel systems, there is growing interest in WDM-PON for 5G pre-transmission. Operators worldwide are exploring its potential, with many testing and deploying WDM-PON solutions in their 5G networks.
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