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5G bearer optical module

The fifth generation mobile communication (5G) technology is about to enter the commercialization process, and its new service characteristics and higher index requirements pose new challenges to the bearer network architecture and technical solutions of each layer.

For 5G bearers, 25/50/100Gb/s new high-speed optical modules will be gradually introduced at the fronthaul, midstream and backhaul access layers, and N×100/200/400Gb/s high-speed optical modules will be introduced at the backhaul aggregation and core layers. 5G optical modules have different schemes in terms of transmission distance, modulation mode, operating temperature and packaging, which need to be selected according to application scenarios, cost and other factors. The following mode communication introduces you to optical modules and 5G bearer networks.

optical module

Optical module is an optical device that realizes high-speed conversion between optical signal and electrical signal in optical communication system. It is the basic component unit of 5G network physical layer and is widely used in wireless and transmission equipment.

The basic structure of optical module includes laser (TOSA) and driving circuit, detector (ROSA) and receiving circuit, multiplexer (MUX), demultiplexer (DEMUX), interface, auxiliary circuit, shell and so on.

Optical module classification

5G network architecture

5G RAN Access Network Architecture:

In 5G, RAN access network changes from original BU and RRU two-level structure to three-level structure, EPC is divided into New Core and MEC two parts, and sank.

CU (Centralized Unit): Non-real-time processing, centralized deployment, general purpose hardware.

DU (Distribution Unit): HARQ flow, high real-time digital signal processing, air-interface oriented, ensuring spectral efficiency.

AAU (Active Antenna Unit): eCPRI package, bandwidth convergence, independent of the number of antennas, load dependent.

CU/DU determined in standardization are logical network elements. In practice, the two can be separated or deployed as a whole, which can be divided into D-RAN (Distributed RAN) and C-RAN (Centralized RAN).

5 g bearer network

Due to RAN separation, the bearer network is divided into three parts

Fronthaul: Between AAU and DU

Midhaul: between DU and CU

Backhaul: Above CU

prequel

The prequel is the bearer of this part between AAU and DU. The distance is within 1~2km, and the delay requirement is high. It includes the following connection methods:

l Fiber optic direct connection

Each AAU and DU are all connected by optical fiber point-to-point networking, which takes up a lot of optical fiber resources and is more suitable for areas with rich optical fiber resources.

Generally, 25Gb/s gray optical module is adopted, which supports two types of bidirectional and single-fiber bidirectional, mainly including two transmission distances of 300m and 10km.

Passive WDM

Passive WDM includes point-to-point passive WDM and WDM-PON.

The optical module is installed on the AAU and DU, and the WDM function is completed through passive equipment. A pair or one fiber is used to realize the connection between multiple AAUs and DUs. Generally, 10Gb/s or 25Gb/s color optical module is required.

Although passive WDM saves fiber resources, it also has some problems such as difficult operation and maintenance, difficult management and difficult fault location.

l Active WDM/OTN Active WDM/OTN

Corresponding WDM/OTN equipment is configured in the AAU site and DU room, and multiple pre-transmission signals share optical fiber resources through WDM technology.

10Gb/s or 25Gb/s short-range gray optical module is generally required between AAU/DU and WDM/OTN/SPN equipment, and N×10/25/50/100Gb/s dual-fiber bidirectional or single-fiber bidirectional color optical module is required between WDM/OTN/SPN equipment.

Compared with passive WDM scheme, this scheme is more flexible in networking (supporting point-to-point and group ring networks), while the consumption of optical fiber resources does not increase.

Forward optical module

Medium/Return

The backhaul in 5G covers metro access layer, aggregation layer and core layer. The required optical module technology is not much different from that used in existing transmission network and data center. Gray light or color light modules with 25Gb/s, 50Gb/s and 100Gb/s will be mainly adopted in access layer, and DWDM color light modules with 100Gb/s, 200Gb/s and 400Gb/s will be adopted in aggregation layer and above.

Packet Enhanced OTN+IPRAN

The packet enhanced OTN equipment with routing and forwarding function is used to form the middle transmission network, the backhaul part continues to use the existing IPRAN (IF Radio Access Network) architecture, and the BGP protocol is used for routing and forwarding between OTN and IPRAN.

In order to meet the bearer requirements of 5G bearers for large capacity and network slices, IPRAN needs to introduce high-speed interface technologies such as 25GE, 50GE and 100GE, and consider adopting new interface technologies such as Flexible Ethernet (Flexible Ethernet) to achieve physical isolation and provide better bearer quality assurance.

End-to-end packet enhanced OTN

The medium transmission and backhaul networks are all networked using packet enhanced OTN equipment.

Compared with the packet enhanced OTN+IPRAN scheme, the scheme can avoid the problems of interconnection and interworking between packet enhanced OTN and IPRAN and cross-discipline coordination, so as to better exert the powerful networking capability and end-to-end maintenance and management capability of packet enhanced OTN.

5G medium return optical module

Current development level of 5G bearer optical module industry

Domestic and foreign optical module manufacturers actively carry out R & D of 5G bearer optical modules around 5G applications. The current productization capabilities are shown in the table below.

In terms of 5G forward transmission 25Gb/s optical module, wavelength tunable optical module is in the research stage, BiDi optical module is in the sample stage, and other types of optical modules are mature. The application scale of 100Gb/s BiDi optical module is relatively small, and 200Gb/s BiDi optical module and 100Gb/s 4WDM optical module are mature.

5G backhaul 50Gb/s PAM4 BiDi 40km optical module, 400Gb/s direct modulation and coherent optical module are in the research stage, other types of optical modules have been basically mature.

Low cost is the main demand point of the industrial chain for 5G optical module. Specification classification, industrial chain sharing, technological innovation and localization substitution are several main means to realize low cost.

"5G commercial, bearer first." With the acceleration of 5G network scale pilot and pre-commercial process, 5G bearer technology solutions will continue to strengthen convergence innovation.

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