Industries > IP STL : A Broadcaster’s Guide
Television and radio Broadcasters are relied upon, now more than ever, for a constant flow of information and entertainment. Studio-to-Transmitter Links (STLs) are critical for Broadcaster's deliver of media. The process of delivering audio and/or video data from the station to the transmit tower has traditionally been accomplished using uni-directional microwave. However, over the last 10 years, this legacy form of STL has been increasingly replaced by wireless links utilizing Internet Protocol (IP). These IP STLs represent an exciting alternative for savvy broadcasters to exploit.
As an established wireless expert, DoubleRadius, Inc. has been designing wireless networks since 2001 and engineering IP STLs since 2007. Over the years, we’ve gained invaluable experience working with a host of broadcasters around the country. These critical insights have now been gathered here for you in our free IP STL : A Broadcaster’s Guide, which outlines ways to effectively set up and operate an IP STL. This guide is designed primarily for Broadcast Station Engineers and IT Directors in charge of STLs. We believe this will be an invaluable resource when designing your IP STL.
BROADCAST TEAM MEMBERS - BE SURE TO SHARE THIS WITH YOUR STATION MANAGERS, ENGINEERING PARTNERS, AND OTHER STAFF SEEKING TO UNDERSTAND IP STL TECHNOLOGY!!
Chapter 1 - Understand FCC Part 101
FCC Part 101 Defines the Rules
The Federal Communications Commission (FCC) governs all wireless communications, including IP STLs, which are considered fixed microwave. These systems exchange information and data between two points, or multiple points. FCC Part 101 rules pertain to the operation of fixed microwave services, which have been utilized by thousands of private enterprises, across a broad spectrum of industries, for many years.
Changes to FCC Part 101
Key changes to FCC Part 101 rules in 2011 opened up the technological and financial benefits of fixed microwave to broadcasters that many other markets previously enjoyed. Specifically, the “last link” rule was vacated. The dissolve of this rule allowed broadcasters to utilize licensed microwave for station-to-transmit locations.
Taking Advantage of Change
As a result of the dissolve of the rule, broadcasters have increasingly migrated with confidence from traditional non-IP microwave and expensive leased lines with recurring costs, to fixed microwave IP STL solutions. In addition to significant savings over leased lines, broadcasters are benefiting from IP STL advantages such as:
- Uncompromised reliability (guaranteed in licensed bands)
- Bi-directional communications
- High throughput / capacity
- Flexibility from significant bandwidth availability
- Rapid deployment
- Integration of transmitter within the LAN
- Ability to add Voice over IP (VoIP) telephony and video surveillance /
- Remote control
Adding It Up
Broadcasters have more incentive than ever to utilize IP STL. Thanks to changes in FCC Part 101, they are no longer limited to inadequate non-IP microwave functionality, or the time and cost restrictions of trenching. Those who embrace the future of broadcast will reap the benefits, while those who don’t, will miss the opportunity for progress. One benefit of the future of broadcast is operating in a licensed frequency, which is covered in the next chapter.
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Check out this blog page on Broadcast: Getting Content to and from the Transmitter Webinar. The webinar recording featured in this post is worth watching in its entirety. However, take a few minutes right now to review the segment between 21:45 - 24:15, which covers the advantages of IP STL and provides a comparison of unlicensed vs licensed (Part 101) IP STLs.
Chapter 2 - License Away Interference
Protecting Your Link
Operating in a license-free band such as 5.8 GHz has the appeal of free and instant gratification. There is no initial cost or red tape beyond engineering your link and purchasing the equipment. However, the door is left open for neighbors to transmit on the same frequency and channel in your path area, causing interference for your signal. Poor link performance and the additional expenses required to overcome it, may prove cumbersome in the long run. For a comparison of unlicensed vs licensed IP STL performance, read Wheatstone’s post Life on the Edge: STL via IP Microwave.
Thanks to the FCC Part 101 change covered in the last chapter, the alternative is to invest resources into acquiring an FCC license for operation in licensed bands. Some broadcasters may already be familiar with the process of licensing non-IP STLs in bands such as 950 MHz, 7 GHz, and 13 GHz. Having a licensed link guarantees that your link will be the only legal transmission on your specific frequency and channel within your path area. The result will be excellent link performance—free of interference. Operators needing a link with high performance and reliability will find a license to be well worth it.
Steps to Acquire a Licence
So what should you expect from the FCC licensing process? The major steps are outlined
- 601 Documents
Form FCC 601 is required when applying for radio service authorization. More specifically, it is, “a multi-purpose form used to apply for an authorization to operate radio stations, amend pending applications, modify existing licenses, and perform a variety of other miscellaneous transactions in the Wireless Telecommunications Bureau (WTB) and/or the Public Safety and Homeland Security Bureau (PSHSB) radio services.” You’ll need to provide completed 601 paperwork for the link, and then again for each site of the link to Comsearch, Micronet, or any engineering firm of choice. It’s smart to double-check your data for accuracy, because this is the information that will be filed with the FCC for your link. You don’t want to be incorrect or you could be interfering with another link in your area or vice versa.
- Channel Interference Study and PCN
After completing your 601 documents, you’ll then need to run a channel interference study and start the Prior Coordination Notice (PCN) process. This is where all the license holders in your IP STL area are notified that you are filing for a license. License holders have 30 days to reply with an objection.
Upon completion of your PCN, you’ll prepare and review your application before submitting to the FCC. Once submitted, it can take up to 90 days for your license to be approved, at which time you will receive a letter. Provided there were no warnings on your PCN, you are able to install your link and commence use.
Exceptions for use are within Washington, D.C., proximity of international borders, or Earth stations conducting telecommunications with a spacecraft. In those cases, verify with your engineering partner that you’re cleared for use of your new link. When you receive your license, if you have not already constructed your link, you have 18 months from the issue date to construct and utilize your fixed microwave backhaul.
Licensed frequencies offer excellent link performance that is free from interference. Another area of consideration when planning your IP STL is assessing the terrain where your link will be set up, explored in the next chapter./p>
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Chapter 3 - Know Your Terrain
Not So Fast!
Even though the advantages of IP STLs were outlined in the first chapter, there are significant challenges to effectively use this technology. Challenges include:
- Topological and meteorological impediments
- Transmission capacity limitations
- Distance limitations
Know What You’re Up Agains
The good news is that these potential issues can be mitigated or reduced by good engineering.
The major factors to consider are listed below.
Map Review - Determines factors like:
- Location coordinates
- Mounting heights
- Azimuth - the horizontal angle or direction of a compass bearing
- Antenna types
- Transmission quality calculations
- Provisional path profile
- Site Survey - Identifies all locations-based information relevant to the installation
of equipment such as:
- Rack space
- Power supply
- Cable ducts
- Retail tower space
- Type of tower / wind load capacity
- Future plans of neighbors - visit your county planner’s office to gather
intel on any plans for new construction
Also assessing the need for any civil work required (poles, roads, fencing, cable trays, etc.) and checking for near field line-of-sight (LOS) obstructions.
- Path Study - Analyzes the more technical aspects including:
- Fresnel zone obstructions
- Secondary reflections
- Interference analysis
- Frequency planning
- Capacity planning (what your facility needs)
- Final calculations of transmission performance
Additionally, it’s important to consider if you will use an all indoor, all outdoor, or split mount system, since your configuration affects the capacity and application. Read about configuration in Chapter 5
The Leg Work Will Pay Off
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Doing your due diligence will pay dividends in the long run. Don’t cut corners when it comes to knowing your terrain. The next chapter reviews one of the most critical areas touched on above—the path study.
Chapter 4 - Study Your Path
The Attention It Deserves
A path study is a critical part of planning your IP STL. In fact, a path study is so critical to the success of the link that we are devoting this entire chapter to explaining it in greater detail.
Crunch the Data
To review, a path study involves:
- Fresnel zone obstructions
- Secondary reflections
- Interference analysis
- Frequency planning
- Capacity planning
- Final calculations of transmission performance
The path study will dictate the frequency range and antenna size used. Also, it will take into account factors such as distance, rain fade, trees / foliage, and height.
Path studies usually are calculated on the The International Telecommunication Union (ITU) method or Vigants-Barnett method. These are the two most commonly used prediction models for microwave links. The Vigants-Barnett method is considered more conservative since it uses harsher parameters. For more information on these methods, see Comparison of Microwave Links Prediction Methods: Barnett-Vigants vs. ITU Models.
Once the data is collected, a path calculation tool is employed to assess path integrity, performance, and reliability. There are numerous path study tools and programs available on the market, however, Pathloss may be the most commonly used and accepted path calculator. You can find a number of free link calculators available from various manufacturers.
Getting Down to the Details
All path analysis tools enable the user to adjust and modify countless system parameters to arrive at the optimum microwave link design based on topological, weather, or physical site factors. It is wise to verify your data several times so that costly errors are not made. An example would be selecting a parabolic dish size that the existing tower structure is unable to support based on wind load, twists, or sway.
Selection of channel size is another important factor that affects throughput and reliability. This decision may be influenced by interference and high RF noise floors. The FCC allows channel sizes up to 80 MHz, depending on the frequency band. Another example of FCC rules that may alter system design, is the permission of parabolic dish sizes less than 6’ in the 7 GHz band.
Choosing Your Antenna Category
Utilization of Category A, high performance antennas, over Category B products will minimize side lobe propagation, reduce interference, and enhance system performance. As a general rule, the selection of slightly higher priced, Category A, antennas for licensed microwave solutions is a better long term system investment.
Adaptive modulation is a feature that allows your microwave the ability to slow down the speed of the transmission. This increases reliability based on intermittent conditions of interference or adverse weather. Slowing down the speed increases the receive sensitivity, thus increasing the reliability of the link. When gathering the information from your path study, make sure your fade margin is acceptable at each of the modulation schemes. This will increase reliability when inclement weather surfaces in your area.
Five 9’s Reliability
Reliability is the most important measure of success for your path. Reliability is measured by downtime, and what’s acceptable varies by industry. Public safety, emergency services, and broadcast customers generally require four to five “9’s” reliability to be considered mission essential or mission critical. Achieving the “five 9’s” standard means that your link is up 99.999% of the time. Over the course of a year, that calculates to a link being down for a little more than 5 minutes.
Upon completion of the path study, you will need to decide what configuration you’d like for your microwave solution. The three different types are outlined in the following chapter.
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Key #5 - Configure Your Solution
Consider Your Options
There are three types of deployment configurations to consider for a microwave solution: all indoor, all outdoor, and split system.
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In an all indoor solution, the electronics are located at the base of the tower in a weatherproof enclosure, building, or in a secure rooftop location, depending on the site. The electronics bank is normally rack-mounted, connecting to the antenna system via elliptical waveguide.
This configuration provides the best weather protection for the equipment and is the least susceptible to lightning surges. All indoor systems routinely offer various connectivity options such as ASI, Ethernet, T-1, fiber, and DS3. Output power on the indoor chassis is normally greater to accommodate signal loss across long cable runs. Whereas, all outdoor solutions are coupled directly to the antenna, eliminating long cable runs and accompanying signal loss. Another convenience of an all indoor solution is that troubleshooting or installing electronics doesn’t require a tower climb.
Transmitters and antennas (parabolic dishes) are coupled together on the tower or building in an all outdoor solution. Power over Ethernet (PoE) is usually the power source, although some manufacturers offer DC power choices. Connectivity options for the all outdoor solution include Ethernet, T-1, and fiber. This system is more susceptible to lightning surge and damage than an all indoor configuration. Another potential disadvantage is susceptibility to interference from your own high power FM transmitters.
Split System (Hybrid)
A split system, or hybrid, configuration utilizes an indoor power supply and connectivity options along with an outdoor transmitter and antenna mounted to a tower. The system uses an Intermediate Frequency (IF) cable, usually half inch heliax or coax, depending upon the length of the cable run. Connectivity options are similar to the other solutions, and your current equipment will help drive your connectivity options. For example, you are using T-1 or ASI, you can connect into the available T-1 or ASI ports while concurrently using excess bandwidth for IP traffic. Deploying audio or video codecs is as simple as plugging into an available IP port on the chassis.
Tie It All Together
Your budget and performance requirements, together with all of your findings about your terrain and path, will inform your decision of the configuration that works best for you. Calculating your bandwidth requirements, covered in the next chapter, is the next step in setting up your IP STL.
Key #6 - Calculate Bandwidth Requirements
Add It Up
Knowing exactly what you’ll need for your bandwidth can be a challenge. You should ask yourself these questions to assist you in calculating your bandwidth requirements.
What throughput does your specific codec manufacturer require?
How many channels are being shot to the transmission site?
Do you require remote monitoring, VoIP, or video security?
How will your link requirements change over the next five to 10 years?
Plan for Today and Tomorrow
When designing your system, you should plan for growth and calculate future bandwidth
projections. Throughputs of 200 Mbps to multiple gigabits are now possible for
an IP STL, depending on manufacturer, model, and channel size. Be sure to think not
only of your current link requirements, but the possible requirements in the next five to
Account for All Application
You’ll soon realize that having your transmitter site on the local network will be handy for applications such as:
- Offsite data backups
- Alarm status
- Security cameras
- Network-aware HVAC controls
These applications are beneficial, but they consume significant bandwidth. Even if you don’t plan to add them this season, you may wind up adding them in the future. It’s important to factor all of the possible usage into the equation from the beginning, to ensure that you have enough bandwidth to support everything you might want to do. In consideration of this, some additional questions to ask yourself are:
Can my network support this additional traffic?
Is there a VLAN requirement involved?
What about Audio over IP (AoIP)?
Factor in Your License
Thinking ahead is especially important when planning a link on a frequency requiring a license from the FCC. Fixed microwave licenses are for a 10 year duration, so it’s good to plan for projected growth in bandwidth consumption now rather than later. Otherwise, you may need to file and pay for a license revision if you change the specs of your link.
An FCC license indirectly impacts your bandwidth. For example, when applying for a link license, the licensee must declare factors such as the transmitter manufacturer, frequency, antenna size, and height. These factors all come with inherent bandwidth limitations.
Example of License Revision
Take the example of a 30 MHz channel that gives you 200 Mbps. If your requirements change to 400 Mbps, you would need to file a major modification and a Prior Coordination Notice (PCN), as you would need an additional 30 MHz of spectrum, or a total of 60 MHz.
Having reviewed bandwidth requirements and factors, the next key focuses on preparing for the impact of the repack of TV broadcasting.
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Chapter 7 - Prepare for TV Repack
Broadcasters Tune In!
In November 2015 the FCC began rolling out plans for the Broadcast Incentive Auction initiative. Under this plan, two auctions took place between March 2016 and March 2017. The Reverse Auction (Auction 1001) allowed stations to sell off broadcast spectrum
rights, while the Forward Auction (Auction 1002) allowed stations to purchase new 600 MHz band flexible-use licenses. “The auction used market forces to align the use of broadcast airwaves with 21st century consumer demands for video and broadband services,” according to the FCC’s Broadcast Incentive Auction and Post-Auction Transition.
Upgrade to ATSC 3.0 During Repack
The transition, or repacking, of TV stations to their new channel assignments starts in November 2018. If your TV station is directly involved in the repack, you may already be preparing for necessary infrastructure or technology changes. With the TV broadcast world racing toward the new Advanced Television Systems Committee (ATSC) 3.0 standard, this may be the right time to transition your equipment to ATSC 3.0. Watch the ATSC 3.0 Next Generation Broadcasting video and dig into more information on the ATSC website.
Watch Out for the Ripple Effect
The National Association of Broadcasters (NAB) comments on spectrum repacking saying that, “radio stations and non-repacked television stations may also be affected [by the repack] if they are located on or near a tower with a repacked television station.” You need to be mindful of upcoming changes in your RF environment, even if your station is not directly involved in the repack. To learn which stations are directly involved in the repack, view the FCC Public Reporting System.
Be Prepared Beyond the Repack
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Now that you’ve got the scoop on the repack and ATSC 3.0, it’s time to address the issue of redundancy. Being vigilant is not only important for avoiding trouble during the repack, but for protecting the reliability of your network from any and all potential issues.
Chapter 8 - Rely on Redundancy
Have a Contingency Plan
Having a backup path in case of an unexpected issue provides peace of mind. The current solutions available in FCC Part 101 provide many backup options. The most common methods to improve reliability or add redundancy are highlighted below:
1+1 Hot Standby
When designing a 1+1 link you have two options. The first option is to use a single antenna with a coupler. The coupler actually marries two separate transmitters to the same antenna. This gives you the ability to run redundancy without adding antenna load to your tower. You will need to run separate transmission lines but not separate antennas.
The second option for 1+1 is to use two different antennas, making this a true 1+1 redundant link. When running a 1+1 you must configure your network switch to handle the swap-over, unless you are running a codex, which does this automatically.
Spatial diversity is actually another version of a 1+1 scenario but has a key performance booster; spatial diversity is used for longer links to increase reliability. Two separate antennas on the same frequency are spaced the right distance apart, and will pick up the multipath created by the distance. You can take those signals and build the data back in the switch, ensuring that all data is getting across. The best feature of spatial diversity is that if one transmitter fails, the other link will act as a single link and continue running.
The 2+0 method involves licensing two separate channels and running them at the same time. Like a 1+1 design, you can couple these to the same dish or run separate dishes. The difference is there is no failover because they are both running 100% of the time. If one of your paths has a mechanical or line failure, the other is still running full speed.
When multiple sites are spread throughout your area, a ring architecture design might be the most cost-effective way for redundancy. This ring is exactly what it sounds like - a circle with no beginning or end. Because all the points are tied together, and the links carry the same amount of throughput in both directions, you have fail over at all points.
For example, consider a system set up with 4 locations: A, B, C, and D
- Site A connects to Site B
- Site B connects to Site C
- Site C connects to Site D
- Site D connects to Site A – closing the ring
If the link running from Site B to Site C fails, traffic from Site B will route back through Site A and Site D to get back to Site C. There is a level of routing knowledge needed to set this up but it is commonly used.
Have Spares on Hand
Having a contingency plan as outlined above will keep station operations running smoothly when issues arrive. However, repairs and replacements will be required to protect against the next potential issue. One way to bounce back after a problem is to have a spare transmitter or two on-hand. In the event of an outage or failure, you can be prepared to meet your tower crew with pre-configured equipment. Having the cold standby can save you after a lightning strike.
Broadcast with Confidence
Whichever redundancy method you choose, your IP STL will have a contingency plan on autopilot to keep your broadcast live. Potential everyday problems and issues related to the repack will be prevented through solid redundancy engineering (and those spares). You’ll be able to focus on programming content instead of technical broadcasting problems.
Get Help if You Need
It Almost done! The first eight chapters have covered many aspects of successfully implementing and operating an IP STL. In the case that you find yourself needing help with tackling all of these areas, our last chapter is devoted to the benefits of working with an engineer.
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Chapter 9 - Engineer Success
Utilize an Engineer
Although the benefits of IP STLs are many, you may feel that dealing with all of this on your own is a bit over your head. There are many technical aspects of designing an IP STL, and there’s a lot to consider. It can be a daunting project to take on without the proper knowledge, experience, and expertise. Potential issues can be mitigated or reduced by proper link engineering. If you are not prepared to take on the engineering and design of your link by yourself or with your internal team, selecting a qualified engineering partner to design your link can make all the difference in the world - especially when licensing is involved.
Engineered well, your IP STL will perform optimally; you will benefit without dealing with the potential headaches. A seasoned Microwave Solutions Engineer can guide you through the proper steps of deploying a successful IP STL.
Get the Most Out of Your IP STL
There are a wide variety of unlicensed and licensed IP STL solutions available to the broadcast industry. Variations in solutions include manufacturer, protocol, bandwidth, technology types, and installation parameters. Despite their variations, they all possess the business driving advantages of deploying an IP STL.
Utilizing an engineering partner will enable you to get the most out of whichever solution you choose. You can have the best equipment on the market, but if your IP STL is not designed and installed properly it will not perform up to its potential. Taking the extra step and leaning on an engineering partner will save you a world of time troubleshooting in the future. Each of the IP STLs mentioned in Wheatstone’s Life on the Edge: STL via IP Microwave is an example of a station relying on a engineer to get it right.
When the time comes to tell your story, make sure that
it’s a story of success, by enlisting the help of an engineer.
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Chapter 10 - Review Your Resources
We hope that all you’ve learned throughout this guide will lead you down the path of
successful broadcasting for years to come. To make it easier for you to review the the helpful resources referenced in the chapters, we have listed them here below:
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