5G Bearer Network

According to 3GPP planning, 5G standards are divided into NSA and SA(Standalone, independent networking). Among them, 5G NSA networking mode needs to use 4G base station and 4G core network, with 4G as the anchor point of the control surface, to meet the needs of radical operators to use existing LTE network resources to realize rapid deployment of 5G NR(New Ratio).

On June 14, 2018, 3GPP held a plenary meeting in the United States to formally approve the freezing of the fifth generation mobile communication technology standard (5G NR) independent networking (SA) function. The 5G NR Non-Independent Networking (NSA) standard was frozen in December last year, so that the first phase of the full-featured full version of the 5G standard was officially released, 5G commercial into the full sprint stage.

5G network to provide services include large bandwidth (user experience rate up to 1Gbps), low latency (1ns) and massive connectivity (connection density 106/km2), thus putting forward new requirements for the bearer network in terms of bandwidth, capacity, delay and networking flexibility. The baseband signal of 5G base station AAU is transmitted in digital mode. The air interface adopts eCPRI protocol interface with a typical rate of 25.165824Gbps. Considering the common station scenario with 4G, it is necessary to be compatible with CPRI option10 rate of 24.33024Gbps.

5G has come. As a member of the optical communication device industry, let's talk about the optical devices that will be used in 5G networks. They are all massive demands of tens of millions of levels.

optical communication devices are the core components of optical transmission networks, carrying key network physical layer functions such as photoelectric conversion, multiplexing and demultiplexing of optical wavelengths, and distribution of optical power. Compared with the current 3G 4G network, 5G has changed the most in the wireless bearer network in the field of forward transmission and medium transmission. The forward transmission is to connect the base station to DU(Distribute Unit, distribution unit, responsible for processing physical layer protocols and real-time services), while the medium transmission is to connect DU to CU (Centralized Unit, centralized unit, responsible for processing non-real-time protocols and services).

wireless base stations are usually installed on the top of communication towers or buildings and are exposed to the sun and wind. Therefore, the optical devices used in the forward transmission need to meet the use of outdoor scenes. The most important thing is that the working temperature of the devices should meet the industrial requirements, ranging from -40 ℃ to 85 ℃. By the way, another indoor scene is generally the requirement of commercial temperature, 0~70 ℃.

In the prequel scene, most of the transmission distances are required to be below 10km LR, of which less than 5km accounts for about 80% and 5~10km accounts for 20%. Of course, there will be a gap between the theoretical value and the actual application of the current network, and there will definitely be problems such as increased attenuation of the fiber aging link and critical distance of the coverage area. Therefore, transmission distance specifications above 10km, such as 20km ER, are still required. In the mid-pass scene, the transmission distance is required to be between 10 ~ 40km, and there are two operating temperature requirements for industrial and commercial grades. Yi Feiyang Company has introduced or is currently introducing a series of optical module solutions for forward transmission and medium transmission applications, including 25G LR/ER,25G LR/ER BIDI,25G CWDM/DWDM ER,25G SFP28 TUNABLE, 100G QSFP28 LR4/4WDM 40,200G QSFP56 LR4 and other industrial-grade optical module products returned by medium transmission. At the same time, it also provides industrial-grade passive products 5G OMUX, CCWDM, AAWG, of which AAWG products to be launched after the maturity of industrial-grade chips.

the optical module is photoelectric conversion, the transmission medium in the middle is optical fiber, and the largest investment in the optical network is always optical fiber resources, so the first consideration in the selection of equipment and devices is optical fiber. Due to policy and population factors, optical fiber resources in Chinese cities and most regions are relatively rich, but optical fiber resources in Chinese villages and most regions abroad are very scarce. Optical fiber resources are precious, so there are three schemes for 5G prequel.

1. scenes with rich optical fiber resources, using optical fiber direct connection, one sector one optical fiber (One Fiber One Cell), and 25G LR/ER BIDI for optical modules. Generally, a base station has 3 sectors. BIDI scheme only needs three optical fibers to meet the traffic forward transmission of a base station, which is conducive to high-precision clock synchronization. It is not clear whether the downstream wavelength standard is 1310nm or 1330nm.

Of course, the more efficient way to return the network is that the wavelength division equipment directly sinks to the base station and DU, that is, the active WDM scheme, which can be compatible with 2G/3G/4G services in the current network, and can realize more L3 layer service management and optimization functions. Of course, this will increase CAPEX.

3. backhaul backbone fiber resources are extremely scarce, the traffic of multiple base stations needs to be collected to a DU for backhaul, which is called One Fiber N Sites (Base-station)(N base stations and a backbone fiber). This is a point-to-multipoint WDM passive scheme. For example, the commonly used AAWG 40 wavelength can cover 6 base stations (each base station has 3 sectors, a total of 18 AAU,20 wave uplink/20 wave downlink). This topological structure conforms to the PON-based optical passive network, making maximum use of the old ODN network.

industry, with the operating temperature range of 0 ℃ ~ 75 ℃. In the future WDM-PON network and even 5G forward transmission solutions, the demand for AWG operating temperature range will be further increased to -40 ℃ ~ 85 ℃ of industrial grade, putting forward more stringent requirements for thermal and non-thermal packages, and further improving the requirements for chip-level non-thermal AWG, which still requires colleagues in the industry to make efforts to break through. If the industrial AWG is still immature and the installation environment is inconvenient to meet the commercial working temperature, when the link optical power budget can be met, the splitter PLC splitter can be considered. Splitter products can fully meet the requirements of the industrial working temperature at present.

P2MP scene mainly uses optical modules 25G CWDM/DWDM LR/ER,25G SFP28 TUNABLE LR/ER, wavelengths can be O-band and C- band, and industrial passive WDM products 5G OMUX,CCWDM,AWG or PLC Splitter.