Service providers all over the world are striving to build and commercialize 5G networks, of which densification is a key aspect. Providers can provide gigabit wireless transmission speeds by adding street-level sites operating in the high-band (millimeter wave-millimeter wave) or mid-band spectrum, or by using massively multiple-input multiple-output (M-MIMO) radios . These sites, whether they are low-power distributed radios, high-power urban macros, or points in between, are a growing segment. Crown Castle CEO Jay Brown stated on an investor conference call that they expect to deploy approximately 10,000 small cell nodes in 2020 (RCR Wireless March 2, 2020). All people face key challenges in connectivity, power, and space.

Customer solutions, transportation product solutions

Customer solutions, transportation product solutions

Customer solutions, transportation product solutions

Densely populated urban areas with tall buildings require two layers of radio coverage, one on the street level and one on the roof level. Street sites can be placed 15 to 30 feet above the ground, usually short distances (a few hundred feet), especially those with millimeter wave 5G radios. These sites can be placed on lamp posts, telephone poles or even the sides of buildings. For these deployments, the space, power, and connectivity requirements are the same as those for macro cells, but the number is significantly larger, the deployment location is more challenging, and the market segmentation and licensing requirements vary. This blog will focus on the available connection options.

Traditional optical fiber connection of CPRI or Ethernet...

Due to space constraints, many street-level sites will use Common Public Radio Interface (CPRI) to remotely connect to the baseband in a centralized RAN (C-RAN) configuration. In C-RAN, the distance between the long-range radio and the baseband will be limited by the one-way CPRI fronthaul delay constraint of 75µs. The optical fiber delay is 5µs/km, and the distance from the radio to the baseband hub is limited to 15km (15km x 5µs/km = 75µs). Therefore, these deployments need to consider the 15-kilometer distance (delay) limit when planning connections.

For street stations that include both radio and baseband, backhaul connections must be provided. Compared with the fronthaul of C-RAN, the delay requirements of this connection are not so strict, but the capacity requirements may be large, because each radio + baseband requires up to 10GB of backhaul.

Assuming there are enough fiber bundles at the desired location, the provider only needs to connect each radio to the dark fiber for the fronthaul or backhaul. The number of dark fibers depends on the type of radio, the number of sectors, and the frequency band deployed. Take a three-sector deployment with a single-band radio (non-MIMO or millimeter wave) as an example. Each radio has an optical transceiver and requires two fiber bundles—one for transmission (TX) and one for reception (Rx)—a total of 6 fiber bundles for three-sector deployment. Before the provider decides to superimpose NR with existing LTE or use millimeter wave (mmW) or multi-user multiple input multiple output (M-MIMO) radio, the number of fiber bundles at each location may be controllable. Some millimeter wave and M-MIMO radios require two to four optical transceivers per radio-yes, each radio! Calculate, the worst-case fiber requirement for a three-sector deployment is 24 fibers-3 radios x 4 transceivers/radio x 2 fibers/transceivers. Suddenly, the provider needs 24 fibers to connect to the side of a street pole or building, or more fibers may be needed if it overlaps with existing low-band radios. Does this amount of fiber resources exist in every location, or can they continue to exist in every market that needs densification?

A simple button for 50% fiber reduction...

Enter deployment options-gray bidirectional transceiver (aka BiDi SFP). These transceivers place two separate wavelengths on a single fiber. One wavelength is transmission (Tx) and the second wavelength is reception (Rx). A typical BiDi SFP uses 1270nm and 1330nm as Tx and Rx wavelengths. The transceivers are a matched pair-meaning that site A has Rx @ 1270nm and Tx @ 1330nm, while site B has Rx @ 1330nm and Tx @ 1270nm. These same BiDi SFPs can be used for fronthaul or backhaul. Since most connections will be based on fronthaul CPRI, the maximum fiber distance of 15 kilometers should still be taken into consideration. By using BiDi SFP, the provider will reduce fiber consumption by 50% based on two wavelengths sharing a single fiber. For suppliers, this is a very feasible and economical solution.

However, this may be a short-term solution based on the provider's mmW or M-MIMO radio expansion plan. Taking the millimeter wave radio example above as an example, each radio has 4 optical transceivers and three sectors on a single pole, and the supplier still needs 12 strands of fiber-3 radios x 4 transceivers/radio x 1 fiber /transceiver. Although a 50% reduction in fiber sounds high, it may not be enough to reduce the number of fiber bundles required for a specific location (telephone pole, side of a building, etc.) to support high-band mmW and M-MIMO radio extensions.

A 50% reduction is not enough...what's the next step?

Providers may have fiber optic connectivity options available for street-level deployments, but usually do not have new high-capacity radios or the number of fiber bundles needed to support multi-band coverage. Taking the above-mentioned three-sector deployment example of millimeter wave radio as an example, each deployment requires four optical transceivers, each transceiver requires two optical fiber bundles, and this single location requires twenty-four (24) optical fiber bundles. Using Dense Wavelength Division Multiplexing (DWDM) technology, combining dense wave with Coarse Wavelength Division Multiplexing (DWDM+CWDM) solutions, the number of fibers can be reduced by 24:1, up to 28:1. These xWDM solutions should be optimized to support the 75µs delay limit of fronthaul CPRI transmissions while addressing the number of service connections required by the radio. The xWDM solution also supports backhaul transmission of radio + baseband sites. Note: WDM technology requires the placement of DWDM transceivers (aka DWDM SFP) and optical filters at each end of the fiber connection (remote and hub) in the radio and baseband equipment to combine or separate multiple wavelengths or "color" single fiber bundles . Please refer to the figure below, which includes CPRI and DWDM-based Ethernet transmission.

Although WDM technology solves the optical fiber limitation, it brings new challenges in placing optical filters in remote radio and baseband hub locations. The hub location may be a central office environment or a shelter with a telecommunications rack. The placement of filters in this space must be optimized to save space and support the typical 19 inches. Rack mount option.

It is often more challenging to place filters in remote locations to support the radio. Most deployments will take place outdoors and are subject to municipal zoning and permit requirements. The consistent "look and feel" of radios and filter housings is the key to timely municipal approvals and permits. Ideally, the construction practices used for the filter housing should be consistent with the radio solution. This method optimizes the operational impact by using the same installation training, the same installation procedure method (MOP), materials (brackets, nuts, bolts), tools, spare parts, etc., while minimizing the total installation time. In addition, various filter housing options to meet different installation locations and environmental requirements can help suppliers meet their aggressive deployment plans.  

Examples of filter housing options include radio "backpack" housings-housings that match the radio unit to be placed on a pole or in a shield, and IP-68 compliant housings that can be placed in a pole or below grade in a fiber optic handle . Therefore, service providers have a deployment toolbox for optical filters and filter housings to support various transmission needs and deployment environments, while meeting different market segments and licensing requirements.

Learn about Ericsson's light prequel

Although fiber optics is the choice of most mobile providers, it is not always available at the required price point or the required time frame. If there is no fiber, what are our connection options? Welcome back to our often overlooked transmission toolbox for connecting friends with microwave radio technology. Microwave is widely used in all regions of the world to meet the needs of fronthaul and backhaul connections. In North America where optical fiber is more readily available, it is not widely used, but as a viable and capable technology to increase optical fiber, because they can increase the density of the network, it becomes more and more attractive to suppliers. .

The fronthaul microwave solution can use E-band radio (70/80GHz) to support CPRI 3-7 transmission, with a radio link speed of up to 10GB. The radio link can be 2-3 kilometers per hop, with a delay of less than 20 microseconds. Depending on the radio type, the CPRI interface can also be cascaded to other sector radios. Therefore, the microwave fronthaul option provides suppliers with a flexible, fast-to-market alternative to build more fibers or extend them to the desired site.

For the backhaul, a variety of microwave technologies can be used. Options include V band (60GHz unlicensed) or E band (70/80GHz lightly licensed). The choice of which technology to use depends on the capacity, size, and hop length. 60GHz unlicensed radio can provide 1GB capacity for 1-2km, while 70/80GHz E-band can provide 10-20GB capacity for 2-3km. Microwave radios have the option of integrating Ethernet switch ports to support multi-site and multi-band aggregation. By utilizing the integrated Ethernet switch port, daisy chaining of multiple sites can be supported. These connectivity options provide flexibility for service providers to deploy networks in all-outdoor, zero-footprint nodes, helping them meet time-to-market (TTM) requirements. For more information on microwave transmission technology and connection options, please download the Ericsson Microwave Outlook report.

Finally, another wireless backhaul option introduced in 3GPP Release 16 is Integrated Access and Backhaul (IAB). For IAB, mobile spectrum is also used for backhaul, which is especially important for high frequency bands with bandwidths of hundreds of megahertz. Backhaul and access can be on the same or different frequency bands, called in-band and out-of-band. In-band IAB is more concerned because it can provide backhaul without any additional equipment. However, it is also more challenging, requiring close intercommunication between access and backhaul to avoid interference within radio nodes and between the entire radio network. As IAB enters the market, careful planning is required to meet the target user experience during peak hours. Topologies with a limited number of aggregated relay nodes and few hops are expected to be the most common.

A transportation tool designed by Radio for Radio. The transmission product is part of the Ericsson radio system, and all versions are consistent. Transport products use the same form factor to facilitate licensing and network deployment. They have the same management system and support the same operation, management, and management (OA&M) functions, such as automatic integration. This brings lower integration costs and faster time to market for our customers.

Ericsson is committed to helping operators make full use of 5G through the transmission network product portfolio developed together with our radio product portfolio to support all 5G deployment scenarios. Ericsson's strength lies in the construction and support of comprehensive solutions, whether it is transmission mode, optical fiber or microwave. Ericsson becomes a partner in the field of 5G RAN and transmission. You can establish a technological leadership in new markets, attract early adopters, and provide enhanced mobile broadband, fixed wireless access and private network solutions that utilize the new 5G spectrum.

To learn more about this topic and options for minimizing TCO, see the Ericsson Technical Review article.

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