Introduction To The 5G Base Station Pre-Transmission Program

The 5G transport network is generally divided into fronthaul, midhaul and backhaul. Optical modules are mainly used to interconnect devices at all levels. Since 5G fronthaul belongs to the access layer, it requires the largest number of optical modules.

5G fronthaul has high requirements for both bandwidth and latency. At present, 25Gbps eCPRI interfaces are mainly used, with a latency requirement of less than 100µs.

The mainstream fronthaul solutions include fiber direct connection, passive WDM, semi-active WDM and active WDM.

1. Fiber Direct Connection Solution

Fiber direct connection uses 25G gray optical modules for direct links between AAUs and DUs, with no additional equipment required.

The block diagram is shown below:

Block diagram of fiber optic direct-drive scheme

Figure 1 Block Diagram of Fiber Direct Connection Solution

• Advantages: Simple network architecture, low technical requirements, and easy construction.

• Disadvantages: Consumes a large amount of fiber resources; cannot monitor link status in real time, making fault diagnosis and O&M difficult.

• Application: Suitable for areas with sufficient fiber resources.

2. Passive WDM Solution

The passive WDM solution connects AAUs and DUs using passive WDM multiplexers + colored optical modules. Both passive CWDM (Coarse Wavelength Division Multiplexing) and passive DWDM (Dense Wavelength Division Multiplexing) are available.

Common channel counts for passive CWDM multiplexers are 6, 8, 12 and 16; passive DWDM multiplexers typically support 6, 8, 12, 16, 32 and 40 channels.

The block diagram is shown below:

Figure 2 Block Diagram of Passive WDM Solution

• Advantages: Relatively low cost, mature technology, and fiber resource saving. Central office and remote WDM devices require no power supply.

• Disadvantages: Cannot monitor link status in real time, resulting in difficult fault diagnosis and O&M.

• Application: Currently a mainstream construction solution.

3. Semi-Active WDM Solution

The semi-active solution is upgraded from the passive WDM solution by adding active equipment at the central office for optical power monitoring and optical path protection, while passive WDM devices remain at the remote end.

In addition, two fiber routes are required: one primary and one backup. The system automatically switches to the backup fiber when the primary link fails.

The block diagram is shown below:

Figure 3 Block Diagram of Semi-Active WDM Solution

The central office can monitor the transmit and receive optical power of each service in real time, enabling accurate fault location, alarm display, statistics and handling. It also supports real-time primary/backup fiber power monitoring and automatic protection switching.

• Advantages: Greatly reduces manual O&M costs.

• Disadvantages: Requires power supply planning, and overall equipment cost is higher than the passive solution.

• Application: Suitable for areas where central office equipment rooms have convenient power supply and two sets of fibers are available. This solution is gradually becoming the mainstream for 5G base station deployment.

4. Active WDM Solution

The active WDM solution has a similar transmission principle to the semi-active solution. The key difference is that active WDM equipment is used at both the central office and remote ends.

Transmission principles are shown below:

Block diagram of the coarse active WDM solution

Figure 4 Block Diagram of CWDM Active WDM Solution

Block diagram of active dense WDM solution

Figure 5 Block Diagram of DWDM Active WDM Solution

As shown above, the WDM unit can use either CWDM or DWDM. CWDM does not support optical amplification, while DWDM supports optical amplification and is suitable for links with high fiber loss, long distances and ultra-large capacity.

Like the semi-active solution, active WDM supports link monitoring and protection, greatly reducing O&M costs. It also enables ultra-long-distance and ultra-large-capacity base station transmission.

• Disadvantages: Requires power supply planning and has high construction costs.

• Application: Suitable for areas where both central offices and remote base stations have convenient power supply, as well as densely populated regions with high Internet demand.

5. Comparison of Solutions

Table 1 Comparison of 5G Fronthaul Solutions

Fronthaul Solution	Optical Path Monitoring	Optical Path Protection	O&M Efficiency	Deployment Cost	Technical Requirements	Expected Implementation
Fiber Direict Connection	None	None	Low	Low	Low	Non-mainstream solution
Passive WDM	None	None	Low	Medium	Low	Non-mainstream solution
Semi-Active WDM	Yes	Yes	High	High	Medium	Mainstream
Active WDM	Yes	Yes	High	Ultra High	High	Non-mainstream solution

Moduletek is a major supplier of optical modules for 5G base stations, offering a full range of models at favorable prices. Welcome to purchase.

For further inquiries about the above content, please contact us at: sales@moduletek.com

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Introduction To The 5G Base Station Pre-Transmission Program