The right approaches to site selection and acquisition, backhaul, power, provisioning, installation, commissioning and approvals are key to successful metro cells deployments.
Metro cells bring new challenges
Metro cells are cost effective and can be quickly placed just about anywhere coverage and capacity are needed. A well-designed metro cell is also energy efficient and can add massive capacity without cluttering the skyline. However, along with their many benefits, the mass adoption of metro cells also brings mobile network operators (MNOs) new deployment challenges:
- Selecting and acquiring sites: Finding enough available and appropriate sites
- Providing backhaul: Accessing existing or building new backhaul networks
- Ensuring power: Providing power and cost-effective battery backup where necessary
- Provisioning, configuring and optimizing networks: Creating self-organizing networks (SONs)
- Accelerating installation: Simplifying processes to reduce costs
- Commissioning and integrating sites: Designing a high level of process automation
- Getting regulatory, municipal and community approvals: Managing potentially lengthy bureaucratic processes
Selecting sites for metro cells requires new models, tools and methodologies.
Metro cells provide coverage and capacity to small areas or hotspots within the larger macro network. A hotspot usually ranges from 70 m to 100 m in diameter and occupies only about 8 percent of a typical macro cell coverage area. As a result, the planning and design tools used for macro networks are inaccurate and ineffective for metro cells.
A heat map helps MNOs pinpoint traffic hotspots to determine cell placement (Figure 1). Creating a heat map involves:
- Collecting subscriber call records over a period of time
- Geo-locating the calls on a map
- Extracting the packet data volumes to determine the amount of data being used by location
The heat map helps MNOs to identify which macro cells are the best candidates for offload, and then for each candidate identified to determine the number and precise placement of metro cells needed to maximize offload.
However, offload potential is not the only factor that is important when selecting metro cell sites. To ensure easy deployments and low site rental costs, MNOs must also:
- Avoid shared-carrier exclusion zones and interference with adjacent metro cell sites
- Identify sites with friendly landlords and easy access to power and backhaul
Metro cells are deployed in mass numbers on lampposts, utility poles and building walls rather than towers and rooftops. That means negotiating site rental leases is a very different process than it is for macro cells.
MNOs need to find many suitable sites with low rental fees, readily available power and access to backhaul. By forming strategic relationships and partnerships, MNOs can negotiate right-to-use agreements with the municipalities and companies that own or have access to the infrastructure (Figure 2):
- Municipalities and transport authorities own lampposts, traffic lights and other structures.
- Utilities have thousands of power poles.
- Wireline service providers have telephone poles and other infrastruc¬ture. For example, Digital Subscriber Lines (DSLs) and Gigabit Passive Optical Networks (GPONs) sites provide a place to mount metro cells and easy access to backhaul.
- Cable providers often have extensive above-ground cable strands that can provide metro cell mounting sites, and also power and backhaul.
- Wi-Fi® providers have thousands of locations that can provide mounting beachheads for metro cells along with the necessary power and backhaul.
In addition, by negotiating right-to-use agreements for many sites at once, MNOs can keep rental fees for individual sites low.
Because metro cells will substantially increase the number of sites, backhaul costs can make or break the business case. Backhaul performance, availability, maintainability and scalability all affect total cost of ownership (TCO). Important planning questions must be answered:
- What availability, throughput and latency should the backhaul support?
- Does the site need to feed other locations in a ring, tree or daisy chain, or is it the end of the line?
- Can the backhaul for a set of physically close metro cells be shared to lower costs?
- Is there a clean line of sight from a potential site to an aggregation node? If so, how far away is it?
- Can existing fiber, conduits or other wireline assets be used?
An MNO’s reasons for deploying metro cells will also impact backhaul performance requirements. For example, 3G metro cells deployed in dense urban areas only for data offload may require less stringent backhaul (since they will not carry high-latency sensitive voice) than Long Term Evolution (LTE) metro cells deployed for coverage indoors and at the macro cell edge in high spectral bands.
The backhaul network must also:
- Enable fast, efficient installation and turn up of metro cells
- Scale quickly and cost effectively to keep pace with metro cells deployments
- Require minimal maintenance to keep site visits and costs down and to accelerate time-to-market
- Support a wide diversity of cost and performance points ranging from low (e.g. Wi-Fi) to high (e.g. GPON)
The preferred location of the metro cell from an RF perspective may not coincide with the best location from a power availability perspective. Power may not be available at all, or it may be difficult or costly to access. These challenges can create a serious dilemma for MNOs:
- Should metro cells be deployed in locations where power is readily available, even if it means deploying more metro cells to meet capacity and coverage requirements?
- Should metro cells be deployed in the optimal location from an RF perspective, but at the expense of longer cabling, and possibly extended civil works to bring power to the metro cell? Or is it possible to use alternative power sources, such as solar panels or fuel cells, to power metro cells?
In answering these questions, MNOs must consider how these challenges can be addressed in a low-cost and effective way.
When planning power for metro cells, MNOs must also consider:
- Operational requirements, such as the need for battery backup, and how the battery backup system aesthetically fits in with the metro cell deployment environment
- Regulatory requirements that specify how metro cells can be powered, where and how metro cells can be connected to a power source and who is allowed to install such a power connection
- Strategies to reduce power costs, such as identifying suitable sites with existing power
SON for provisioning, configuring and optimizing networks
Metro cells are expected to be deployed much more densely than macro cells. The resulting increase in the number of access points means conventional manual provisioning, configuration, and network optimization approaches are not practical for metro cells.
Therefore, it is vitally important that metro cells support self-organizing and self-optimizing network (SON) capabilities to free operators from many of these manual processes and decrease operational costs.
For LTE networks, SON will also increase spectral efficiency and optimize the performance of the heterogeneous network (HetNet) by enabling LTE- Advanced features such as Coordinated Multi-Point (CoMP) and Enhanced Inter-Cell Interference Coordination (eICIC). However, SON must not be used as a justification for the implementation of proprietary interfaces. To guarantee that a diverse ecosystem exists for HetNets, it is important that operators ensure the effectiveness of 3GPP open interfaces, such as X2 and S1, by including multi-vendor interoperability testing (IOT) in their requirements.
While macro cells typically take 2 persons up to 2 days to install, metro cells can be installed by a single person in much less time. The challenge comes when a large number of metro cells must be deployed.
To keep costs low, MNOs must optimize the installation team’s productivity. Each installer must be able to install multiple metro cells per day, by quickly moving in and out of urban sites with heavy traffic. That means special equipment, such as bucket trucks, should be avoided. Even using a ladder, which always needs to be sup¬ported by a second person, effectively doubles the size of the field force.
To optimize installation, MNOs need a metro cell that is simple to install, yet secure enough to avoid tampering.
Commissioning and integrating sites
Once a metro cell is installed, it needs to be turned on and connected to the network. In macro networks, commissioning and integration requires the use of specialists, which tends to be expensive. To keep metro cell deployment costs low, MNOs must minimize or eliminate the use of specialized labor.
Ideally, most commissioning and integration tasks for metro cells should be carried out remotely. Only low-tech operations, simple enough to be performed by the less-skilled installers, should be done on-site. Furthermore, on-site tasks must not require the use of a laptop or complex test equipment and must be executable from the ground rather than up a ladder.
Getting regulatory, municipal and community approvals
To successfully deploy metro cells, MNOs need to secure the appropriate regulatory and municipal approvals and get community buy-in. Challenges from any of these groups can result in months or even years of delay and can destroy the metro cells business case.
To secure the necessary approvals, MNOs must usually:
- Provide a certificate of compliance that confirms the metro cells comply with RF exposure limits
- Complete municipal processes to obtain all necessary permits and rights-of-way, including building, installation and service operation permits and rights-of-way for installing backhaul equipment, if required
Depending on the location, MNOs may also have to comply with other regulations, such as those concerning:
- Provisioning of backup power
- The amount of time the metro cell must be powered by batteries if there is a power outage
- Land use
- Building codes
- Historic preservation rules
- Environmental regulations
Metro cells will be deployed in large numbers and located close to people. As a result, they are likely to raise health and safety questions relating to electromagnetic field (EMF) radiation. To quickly secure local approvals for deployment, MNOs and authorities will have to alleviate radiation exposure concerns from the community.
Finding a solution that addresses challenges
To help MNOs address the deployment challenges described above, metro cells solutions should support:
- A hotspot geo-location service to accurately pinpoint hotspots, customer-friendly sites and sites with power and backhaul
- Site selection consulting service to help the MNO quickly locate many suitable sites for the deployment of metro cells
- A number of backhaul technologies to meet diverse site requirements and topologies to deliver the required availability with the lowest cost possible
- Multiple power sources, including alternative power solutions
- SON technology to reduce network planning, deployment and optimization costs.
- Easy installation to eliminate the need for bucket trucks and experts
- Simplified commissioning and integration to minimize or eliminate the use of specialized labor
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