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5G Mobile Optical Transmission Network Solutions

5G Mobile Optical Transmission Network Solutions


The 5G network includes large bandwidth (up to 1Gb/s), low latency (1ns) and massive connections (connection density 106/km2), which puts forward higher requirements on the bandwidth, capacity, delay and networking flexibility of the bearer network . The baseband signal of the 5G base station adopts digital transmission, adopts the eCPRI protocol interface (typical rate 25.16Gb/s), and is compatible with the CPRI protocol interface (24.33Gb/s) of the 4G site.

Optical communication equipment is the core component of the optical transmission network, which is responsible for the functions of the key network physical layer, such as photoelectric conversion, wavelength multiplexing and multiplexing, and optical power distribution. Compared with the current 3G/4G network, the biggest change in the 5G wireless bearer network is the fronthaul and midhaul. The 5G fronthaul refers to the connection between the base station AAU and the DU, while the 5G midhaul refers to the connection between the DU and the CU, that is, the time protocol and service.

Wireless base stations are usually installed on the roof of communication towers or buildings, and the optical equipment used in the fronthaul and midhaul needs to meet the use of outdoor scenes. The most important thing is that the operating temperature range of the device needs to meet the industrial-grade requirements, that is, from -40°C to 80°C; the other is the commercial-grade temperature requirements for indoor scenes, that is, from 0°C to 75°C.

In the fronthaul scenario, most transmission distances are below 10km, of which about 80% are below 5km, and about 20% are between 5km and 10km. In fact, there will be a certain gap between the theoretical value and the actual application, and there will be a problem that the link attenuation will increase with the aging of the fiber. The distance of the coverage area may reach a critical value, so the transmission distance of more than 10km, like 20km , 40km, etc. are also needed.
In the mid-transmission scenario, the transmission distance is between 10-40km, and there are also two industrial and commercial operating temperature requirements.

For 5G fronthaul and midhaul applications, Xuchuan Telecom has launched a series of industrial-grade optical modules, including 25G BiDi/CWDM/DWDM/Tunable SFP28 modules, 10km/20km for 5G fronthaul networks and 100GBASE-LR4/4WDM-40 QSFP28 modules And 400G QSFP56 high-speed modules for 10km/20km/ 40km applications in 5G medium-range (and backhaul) networks. In addition, we also provide industrial-grade passive optical components, such as 5G OMUX, CCWDM, etc.

Figure 1. The data rates and distances of 5G fronthaul and middlehaul
 

Optical transceiver is photoelectric conversion, using optical fiber as the transmission medium. This means that the biggest investment in optical networks is always fiber resources, so the first thing to consider when choosing equipment and devices is how to save fiber.

For different scenarios of 5G fronthaul, three solutions (25G SFP28 transceiver) are now available to choose from.

Option 1:
The fiber direct connection solution (ie, One Fiber One Cell) deploys 25G BiDi SFP28 optical modules for 10km/20km transmission. Generally speaking, a base station has three cells, and the BiDi solution only needs 3 fibers to meet the fronthaul traffic of a base station, which is conducive to high-precision clock synchronization.

Figure 2. The scheme of optical fiber direct connection for 5G fronthaul
 

Option II
In a scenario where fiber resources are scarce, a WDM solution that multiplexes all service wavelengths of a base station onto a single fiber or a pair of fibers to save fiber resources. Although a large number of colored optical modules are required in the WDM solution, which will cause inconvenience in installation, spare parts and maintenance, tunable transceivers can be used to solve this problem.
Therefore, this scenario mainly uses 25G CWDM/DWDM/tunable SFP28 optical modules (O-band or C-band) and industrial-grade passive optical components such as 5G OMUX and CCWDM modules.

Figure 3. Passive WDM scheme for 5G fronthaul
 

Option III
In scenarios where backbone fiber resources are scarce, the P2MP (P2MP) passive wavelength division scheme can be deployed to converge the traffic of multiple base stations into one DU.
For example, the commonly used 40-channel AAWG DWDM Mux/Demux can cover 6 base stations, that is, each base station has 3 sectors, a total of 18 AAUs, 20 uplink channels, and 20 downlink channels. This structure is an optical passive network based on PON, making the most of the existing ODN network.

At present, commercial-grade AWGs are relatively mature, with operating temperatures ranging from 0°C to 75°C. In future WDM-PON and 5G fronthaul solutions, the operating temperature range of AWG needs to be upgraded to industrial grade -40°C to 80°C, resulting in higher requirements for heat dissipation and athermal packaging, and chip-level requirements for athermal AWG Will be higher.
The industrial-grade AWG is immature, and the installation environment does not meet the commercial-grade temperature but can meet the link optical power budget. You can consider using a PLC splitter.

P2MP scenarios mainly use 25G CWDM/DWDM/adjustable SFP28 optical modules (O-band or C-band) and industrial-grade passive optical components such as 5G OMUX, CCWDM, AWG or PLC splitters.

Figure 4. The P2PM Passive WDM scheme for 5G fronthaul