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Technical keys to successful network modernization: weight and wind load
Ensure you achieve your modernization goals by focusing on key areas
Philip Sorrells, Dale Heath, Chris Stockman, Lou Meyer
White paper
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ContentsIntroduction 3
Fourtechnicalkeys 3
Weightandwindload 3
Antennasconsideration 4
Fiberconnectivity 4
Structuralsupport 5
Aquickhistorylesson 5
Whystructuralsupportissoimportant 5
Topstructuralsupportconsiderations 5
Theevolutionofthestructuralmount 6
Conclusion 6
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Wireless tower structure, architecture and equipment configuration have gone through an evolution in recent decades. Throughout this evolution, a major concern has been weight and wind load. It’s a particularly urgent concern today for several reasons.
As wireless services continue to soar, providers are deploying more and more base station antennas, fiber connections and other equipment in order to meet the growing demand. The result is towers, support structures and mounts being pushed to the limits of their load capacity. That makes it especially important for wireless service providers and tower owners to understand the impact each antenna, connection, mount and piece of equipment has on the overall tower weight.
In addition, antennas, connections, mounts and equipment add load to the towers not only due to their mass, but also in the form of additional dynamic loading caused by the wind. Depending on the aerodynamic efficiency of the overall tower, the increased wind load can be significant.
So how do weight and wind load factors impact the modernization of your network? What is the connection to performance, safety and other factors? Most importantly, will your antenna, connections, structural support and tower design choices impact your bottom line?
Four technical keys
It’s a lot to think about. But one practical way to approach network modernization is to take a holistic approach and try and look at the “big picture.” Look at upgrading your network from the point of view of a puzzle with several key pieces. These are rather large pieces of the puzzle that are technical in nature, yet crucial to the overall success of the effort. These mission-critical technical keys include:
• Fiber technology in FTTA solutions
• Ultra-wideband antennas
• Weight and wind load
• Passive intermodulation (PIM)
Each of these topics is a complex discussion that warrants its own white paper. Therefore, CommScope has created a Technical keys to successful modernization series of white papers that explore each area. This document, where we’ll explore weight and wind load in greater detail, is the third in the series.
Weight and wind load
Why is it important to focus on weight and wind load for a wireless tower? There are many major areas where weight and wind play a key role. These include:
• Performance
• Revenue
• Expenses (more weight and space on the tower increases leasing costs)
• Safety
When you think about it, it’s easy to see how weight and wind can impact the performance of a wireless system on a tower. Improperly designed, configured or installed equipment on a tower—or even choosing the wrong mount—can cause misalignments and even total failure. Drawing a direct line from those kinds of impacts to revenue is easy.
In terms of expenses, in many cases, the cost of leasing tower space is based largely on how much loading a base station antenna adds to the tower structure. That’s why wireless operators often use wind load data presented by base station antenna manufacturers when deciding on which antennas to deploy. Therefore, it is important for operators and tower owners to fully understand how wind load data is calculated so fair comparisons can be made between various antennas.
Safety must always be paramount to operators as well. As networks become larger and more complex, overweighted towers or configurations that present wind resistance can cause equipment to loosen or mounts to fail, which can represent a danger to residents nearby. The safety of maintenance crews must always be taken into consideration, since overloaded towers or those with little concern for weight and wind load can present a danger to even veteran crew climbers.
kg
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Now that we know why, in general, it’s important to consider weight and wind load, let’s look at four factors that touch upon nearly all these areas:
Antennas considerationDeploying more and more antennas in order to meet growing demand only results in antenna towers and support structures being pushed to the limits of their load capacity. As you look at modernizing your network, it is important to understand the impact your antenna choice has on the overall tower load.
Frontal wind loading and overall weight are important factors. Performance factors aside, antennas with better frontal loading design and lesser weight will decrease overall tower weight and wind load issues.
Base station antennas add load to the towers not only due to their mass, but also in the form of additional dynamic loading caused by the wind. Depending on the aerodynamic efficiency of the antenna, the increased wind load can be significant. Additionally, there are other location-specific factors to consider when calculating antenna wind load. These include geographic location, tower height, tower or building structure, surrounding terrain, and shielding effects from other mounted antennas.
This is one of the major advantages of ultra-wideband antenna technology. This more versatile technology enables wireless operators to install one antenna where multiples were previously needed. For example, CommScope’s ultra-wideband antenna system is capable of supporting the four major air-interface standards in almost any wireless frequency range. Operators can reduce the number of antennas in their networks, which not only lowers tower weight and wind load risks, but may decrease leasing costs while increasing speed to market capability.
Antennas are continuing to evolve to offer as many as eight connectors in the same space and weight. Engineers have figured out how to fit the same RF performance into the same size package and form factor. This is a huge benefit to tower operators, and can also reduce the possibility of having to deal with rezoning issues and the time and money caused by having to issue new zoning permits.
Ultimately, the challenge of weight and wind load must be addressed by assessing site towers from a total system standpoint, in contrast to a narrower component perspective. When assessed in this more holistic way, adding more antennas is the least advantageous approach.
From a technical perspective, the impact of adding individual technologies to the tower with a separate antenna for each technology creates a multiplier effect on weight and wind load, as represented in the figure 1 below. This is in comparison to figure 2, a single ultra-wideband antenna that’s designed for multiple technologies.
Figure1:Addingmoreantennastosupportmultipletechnologiescreatesamultipliereffectonweightandwindload
Figure2:Asingleultra-widebandantennaisdesignedformultipletechnologieswhichreducesweightandwindload
Fiber connectivityThe trend toward advanced optical fiber and hybrid cables supplanting coaxial cable in support of the latest antenna applications also has a significant impact on tower weight and wind load. A single hybrid cable can do the work of eight or more power and fiber cables, supporting multiple remote radio units (RRUs).
For example, HELIAX® FiberFeed® (HFF) hybrid cabling can help reduce tower loading, which can also result in potential cost savings. This solution can help reduce tower loading and tower lease-hold costs by eliminating conduit and extra cable runs.
Since a hybrid cable requires a smaller surface area—compared to a group of cables or larger conduit—it lessens the load on the tower, freeing capacity needed by the RRUs. The total load of RRUs plus the hybrid cable will be less than the total load of RRUs plus separate power and fiber cables. This extra margin may mean the site can be installed as planned without the need for tower reinforcement or the forced locating of RRUs at the base.
In terms of weight alone, hybrid cables will, individually, weigh more than traditional coaxial cable. They may, in fact, be close to double the weight. However, by virtue of the fact that you may be installing only one line instead of multiple lines, your total weight savings can be significant.
Another major advantage is being able to connect directly to the RRU, which eliminates the use of a heavy junction box. Our research shows that eliminating a junction box in a typical installation—combined with the CommScope HFF direct compact design—can result in a wind load reduction of up to 33 percent, as compared to other cell tower configurations.
Antennas Fiber connectivityStructural supports
kg
800/900MHz1800/1900MHz
2.1GHz600MHz700MHz1400MHz2.6GHz
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HELIAXFiberFeeddirectreduceswindloadupto33%
Structural support LTE installations involve dozens of components, including antennas, RRUs, trunk and sector fiber, matching connectors, and jumper cables. Plus, there’s a long list of support components—such as hangers, hoists and junction boxes—all mounted on a structural support. With this amount of gear, it can be very problematic to manage all this on existing TDMA/GSM sector frames designed for smaller and lighter antennas and less equipment. You also have to consider the tower structure itself may be designed to hold much less equipment.
A quick history lesson
When we consider weight and wind load as they relate to the structural support variables of a tower, it’s important to start with a bit of a history lesson. Overall, as the technology has grown, evolved and changed, so have structural supports and mounts.
First, we had robust structures with heavy-duty mounts. As antennas decreased in weight and size, so did the structures and mounts. As a result, less loading needs led to less robust structures. But, as heavier 3G antennas and equipment rolled onto the market, loading was impacted, deflection increased, and issues with twist and sway became more and more prevalent.
Now, with LTE technology, there are even heavier antenna piping and antennas, as well as RRUs, fiber boxes and other necessary equipment. Failures to address the appropriate mounts and structures have started to become more evident as towers have fallen or been damaged due to vibration and torsion.
Bottom line, years ago tower mounts were designed to meet lower criteria. For example, under the old critera, a t-frame mount from just ten years ago was designed to meet 150 mph loading, which was considered a strong design at the time. Now, that same frame does not meet LTE criteria. By contrast, today’s CommScope v-frames are designed to meet LTE criteria, and are four times stronger than its predecessor.
Why structural support is so important
As we’ve discussed, when there is a need to increase capacity, modernizing a network by adding new LTE equipment to existing networks is a good option. However, a migration from older technology to LTE can add an average of 750 lbs of equipment and an additional 50 square feet per sector of effective projected area (EPA) to the top of the tower, which can have a tremendous impact on performance.
Although well-made mounts can help antennas maintain optimum performance, too little attention is paid to the impact of mounts, such as their physical properties and their ability to support LTE components for the long term. Less expensive, low-grade structural components such as mounts, brackets, and fasteners may have difficulty preventing antenna tilt, twist, sway and vibration. Over time, these issues can cause antennas and entire networks to underperform.
When low-quality mounts fail, sites can—and do—go down. Operators must pull personnel and equipment from other sites to restore connectivity, negatively affecting productivity. And, of course, there’s the potential to destroy personal property or cause serious injury or death.
Other possible ramifications of a structural failure due to weight and wind load issues include:
• Expenses are impacted by the deployment of emergency mobilization crews, expedited equipment shipping costs, labor overtime and temporary cells on wheels (CoWs).
• Customers may switch carriers if they consistently experience dropped calls and slow data rates, negatively impacting operator image and revenue.
• Urban cell site downtime can result in a significant loss of roaming charge revenues, as well as negatively impact the company’s image.
• Customers or public safety officials may have difficulty communicating during emergencies, affecting safety and security, which could also lead to litigation.
Top structural support considerations
When engineers design towers today, or look at the prospect of adding equipment, such as an antenna, there are several critical factors they should look at closely to ensure future tower stability and network performance. Among these critical factors are mounts.
Tower mounts should be chosen carefully based on the projected weight of the antennas. Any overloading can create movement that can have a negative impact on safety and performance. In fact, failure to choose the right mount can result in damage or destruction of structure legs, with the possibility of the tower falling. Overloaded mounts can also result in twisting and instability from the tensional forces, which can lead to network failures.
In simple terms, overloading of an existing infrastructure occurs when the tower and mounts are saddled with an amount of equipment the structure was not designed to handle. Engineers and operators who take a piecemeal approach to tower construction or network modernization risk putting their entire system at risk. In addition to the obvious safety issues, performance can be degraded, which can ultimately lead to loss of revenues.
1G – PCSDesigned to withstand
multiple pieces, heavy and cumbersome antennas
2G – TDMA/CDMAEquipment becomes lighter and
structures adapt for these changes
3G GSM/WYMAX/EVDOStructures hold multiple
antennas; greater need for microwave antennas for backhaul
4G/LTEHeavier 4G antennas and equipment add
significant weight and EPA
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With the many pieces that constitute a wireless tower, this lends credibility to approaching the structure as a complete solution and system. When performance and reliability are the goals in any system, it’s important to take this holistic approach. It’s also vital to partner with a proven supplier that understands every aspect of cell tower construction or upgrades, and how any changes will impact structural stability.
A piecemeal approach using multiple suppliers can also create problems. While reducing cost is always a top priority, operators that price shop for the best bargains risk piecing together a structure comprised of multiple low-quality components that ultimately cannot safely withstand the elements or ensure network dependability. When you consider the significant expenditures involved in creating a wireless network path, installing poor-quality mounts is akin to mounting the cheapest tires on a high-performance race car.
The evolution of the structural mount
Thedesignpersectorcriteriaforeffectiveprojectedsurfacedarea(EPA)andweightlimitshavechangeddramaticallyfromearliertechnologiesthroughthe
evolutiontoLTE.
With the majority of towers in the U.S. being manufactured for multiple carriers, it should also be noted that failure to take into account critical structural support variables can have a multiplying impact on revenue losses. For example, a typical 300-foot tower might facilitate four carriers with four antenna mounts and a total of 12 antennas, as well as all the required equipment.
In the past, 250 pounds per sector was the standard, with a recommended EPA of 16. Towers were designed for those criteria. Nowadays, however, many mounts on multi-operator towers in the U.S. exceed those limits substantially. So, should one mount fail in one carrier sector, the resulting tower tension, vibration and instability may multiply the impact on the other three sectors. This can cause an entire structure to fail or, at the very least, cause the system to perform poorly for some or all of the other carriers. The resulting loss of revenues can be devastating.
So, when it comes to structural support, the key takeaways are to approach network modernization for towers holistically and as a complete system. And make sure you choose a single supplier with the expertise to deliver LTE antenna mounting solutions that enhance structural integrity and properly support the weight and wind load criteria for today’s 4G equipment.
CommScope white paper series: Technical keys to successful modernization
In order to meet these challenging needs, each of the four technical areas identified in the introduction of this white paper must be addressed when updating your network. They are, in fact, the four pillars of successful network modernization. That’s why CommScope has created a series of four white papers that address each of these keys individually. By addressing these technical areas, you’ll not only create a strong foundation for today, but ensure your network is ready to deploy future technologies to meet tomorrow’s demands.
We encourage you to read the other white papers in our series to get a complete view of the four network modernization keys.
• Cost-effective modernization
• Fiber technology in FTTA solutions
• Ultra-wideband antennas
Conclusion The evolution of the cell tower structure has made weight and wind load an industry-wide issue that must be addressed. And that’s not just for safety concerns. Structures that fail to take into account weight and wind load when implementing upgrades or modifications risk bringing their network down—or, at the very least, degrading performance. In today’s competitive market with discerning consumers who demand reliable services, you don’t want to risk losing customers.
The good news is that there are many very good solutions for upgrades that allow for adding antennas, connections, mounts and equipment that can help your structures remain stable for continued performance.
Finally, when taking a good hard look at these issues, it’s important for operators to avoid a disparate approach to network modernization or new tower construction that involves multiple vendors and suppliers. Doing so increases the risk of mixing together incompatible equipment and support structures that will load your tower with too much weight or surface area. A trusted single-source partner ensures that your structure meets or exceeds requirements for safety and performance
4G / LTE mount design per sector:
64 sq Ft (6 sq m) EPA 750 lbs 350(kg)
4G / LTE
Standard GSM mount design per sector:
16 sq Ft (2 sq m) EPA 250 lbs 113(kg)
1G to 2G
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