As mobile phone and other wireless networks “densify” in the parlance of the day, airwave congestion will inevitably rise causing greater interference. Generally, microwave path planners will use dish antennas that provide tighter radiation patterns with more focused main beams and smaller side lobes to overcome interference that results from congestion.
To indicate the tightness of their radiation patterns ETSI (European Telecommunications Standards Institute) classifies antennas from 1 to 4 with higher classifications having tighter radiation patterns. Until recently, to fight interference in most circumstances wireless transmission engineers would resort to Class 3 antennas for deployment scenarios where “very high interference potential” existed.
However, the situation has changed. More drastic implementation scenarios now drive path planners to invoke more dramatic solutions. That includes use of Class 4 antennas, which are for “extremely high interference potential” situations, according to ETSI. For a more detailed treatment of antenna classifications and radiation patterns, see the ETSI document “Fixed Radio Systems; Point to Point Antennas.”
It’s an urban thing
In most cases, microwave radio congestion that leads to interference problems occurs primarily in urban locations. With wireless backhaul sites in much closer proximity in urban areas than in rural or suburban locales, there it’s more likely that side lobes from microwave transmitters could become sources of secondary RF radiation, which can overlap with point-to-point links between neighboring sites.
For example, according to an Aviat Networks analysis of three wireless sites in South America that recently experienced interference issues, at one site the congestion was so intense as to make one complete channel unusable. Even if Class 3 antennas were used, the interference levels were too high to be able to reactivate the disabled microwave channel.
Wider channels, larger capacity
For situations where the operator needs to increase capacity from a wireless backhaul site, the easiest way remains widening the channel size. But at sites that experience extremely high interference, the operator may not be able to coordinate radio frequency pairs in wide channels with Class 3 antennas. However, moving up to Class 4 antennas would allow the operator to optimize the signal-to-noise ratio and let higher modulations come into play, so wide channels could be coordinated with correspondingly higher data rates.
Smaller is more
In cases of high interference, larger antennas can be used to reduce it. For a subset, smaller Class 4 antennas can be used instead of their oversize Class 3 counterparts. Thus, operators who deploy Class 4 antennas gain the added benefit of dropping down a parabolic dish antenna size as compared to a Class 3 antenna in the same application. In general, smaller dishes advantage the operator due to their lighter weight and lower opex tower charges, albeit with an initially bigger upfront capex. Because Class 4 antennas represent an elevated level of precision tooling and more detailed manufacturing versus lower class antennas, capex of these passive, higher-performance infrastructure pieces always weighs in the balance.
As we’ve seen, Class 4 microwave antennas have many general uses. They also are very good alternative solutions for specific industries. For example, utilities often find it difficult to implement Adaptive Coding and Modulation schemes in their backhauls, so Class 4 antennas can provide another way for them to achieve their connectivity and capacity goals.
Lower frequency bands (i.e., less than 11 GHz) have long had access to Class 4 antennas. More recently, antenna manufacturers such as Commscope have begun to make Class 4 antennas for higher frequency bands (e.g., 13, 15, 18, 23 GHz). And RFS has also expressed interest in supplying higher frequency class 4 antennas.
This overview has provided a broad grounding in Class 4 microwave antenna subject matter, but for more in-depth information please download the Aviat white paper “Use of Class 4 Antennas” for which no signup is necessary.Read More
Designing and engineering microwave radio networks has always been challenging and a bit of an art—especially when they are ultra-long point-to-point wireless networks. In an article published February 25, 2013, Aviat’s solutions architect Charles Dionne outlines some of the key considerations that need to be made when designing and building these ultra-long microwave backhaul links for point-to-point wireless networks.
The article on RCR Wireless provides an overview and detailed checklist of the relevant items for designing ultra-long point-to-point wireless microwave links including:
Readers will take away more than just a laundry list of potential pitfalls; they will gain an enhanced appreciation of the very specialized skills and thorough understanding of microwave technology that is necessary for successfully implementing point-to-point wireless microwave backhaul.
Between any two microwave radio antennas, there is one direct ray and multiple refractive/ reflective multi-path rays. In the eighth and last installment of our Radio Head Technology Series, Aviat Networks Principal Engineer and master storyteller, Dick Laine, relates how restrictive tower rules for San Francisco’s historic China Basin Building required fine adjustments of a horn antenna to resolve reflective rays from the surrounding bay.
As Dick tells it, to accommodate a Space Diversity arrangement, one horn antenna on the building had to be hung upside down. During the installation process, the alignment for the upside-down diversity antenna created a reflection point 3 miles out into the bay. The performance was horrible, but at the time, no one knew why. So when a little speedboat or anything larger went through the reflection point, there would be an outage as the signal was interrupted. There did not seem to be an obvious fix to the alignment issue. The horn antenna did not have a way to check the alignment on the horizontal with a bubble level.
To find out how Dick solved this antenna mystery, register for the Radio Head series (it’s free). Then to put it all in context, Dick goes over Huygens’ Principle as it applies to microwave signal diffraction. And if you ever wondered what happened to periscope antennas, Dick provides some key insight! Tune in to find out!
Microwave radios come and microwave radios go, but the sage advice of Aviat Networks Principal Engineer, Dick Laine, has no end-of-life. In our seventh installment of the very popular video blog Radio Head Technology Series Dick talks about the diversity of diversity schemes and other protection methods available to microwave networking engineers.
Using examples from the radio legacy of Aviat Networks (e.g., Constellation, MegaStar—you must remember these, it hasn’t been that long) and our current microwave networking solutions (e.g., Eclipse, TRuepoint 6500, WTM 6000) he expounds on the past, present and future of protection. From Angle Diversity (one of the earliest diversity schemes used in Line-of-Sight digital microwave) to Hybrid Diversity (HD) and Frequency Diversity (that need licensing waivers to be used in many applications) to comparisons of fiber-like protection methods, Dick covers it all. For example, did you know that a four-dish HD antenna arrangement offers little to no performance improvement over a three-dish HD configuration?
So with free registration to the video series you can have the benefit of all of Dick’s wisdom and nonpareil presentation style on Diversity. You get access to all the earlier videos, too. (Did we mention there are six previous episodes?) And the presentation slides. And the podcast. And all for FREE! Wow! If you don’t see a topic that you think needs to be covered, feel free to submit your suggestion into our inbox. Register today!
Do not be Alarmed by this latest video in the Radio Head Technology Series (complimentary registration). For the insider’s perspective on Hot Standby, we will not keep you waiting. Dick Laine, Aviat Networks’ principal engineer, has many informed views on Diversity and relates them in his familiar relaxed presentation style.
All puns aside, Dick covers the multitude of options available in Diversity Schemes (and all their acronyms!). Plus, there is a lot to know about the differences in asymmetrical splitters for digital radios and their analog predecessors. Turns out there is no point in using symmetrical splitters in digital microwave radios. Even a heavily asymmetrical split provides as much protection as a symmetrical split but it avoids 2-3 dB in fade margin losses, providing significantly more uptime.
And if there is anything you need to know about Alarms, Dick takes a fine-toothed comb to the subject and teases out the details, providing context for the strategy of how they function in keeping your wireless communication network online. Dick will also tell you how improvement in digital radios has led to large gains in recovery time when radios in a Hot Standby arrangement are switched and quadrature relock can now essentially be avoided. On errorless switching, although it has greatly benefitted microwave radio usage, Dick will tell you the importance of early warning alarms to it.
So make no mistake, Dick is your information source for all things microwave radio—wrap your head around it!
Public safety agencies will soon experience a dramatic improvement in communications capabilities enabled by advances in technology. New broadband multimedia applications will give first responders and commanders alike far better situational awareness, thereby improving both the effectiveness and safety of all personnel charged with protecting the public.
The specific technology, now mandated by the U.S. Federal Communications Commission (FCC) for all new emergency communications networks, is Long Term Evolution, or LTE—a fourth-generation (4G) broadband solution. The FCC has also allocated licensed spectrum to ensure the best possible performance in these new networks. These FCC rulings support the goal of achieving an interoperable nationwide network for public safety agencies.
The FCC chose LTE based on its proven ability to support voice, video and data communications at remarkably high data rates that were previously only possible with wired links. Although there will be some differences in a nationwide public safety network involving capacity and coexistence with Land-Mobile Radio communications, lessons learned from LTE’s deployment in large-scale commercial mobile operator networks will help ensure agencies are able to achieve the FCC’s goal cost-effectively.Read More
Traffic disconnect is unacceptable for most microwave systems, especially for homeland security and utilities. But Aviat Networks Principal Engineer Dick Laine says that it is economically unviable to have a microwave radio system that provides absolutely 100 percent uptime to accommodate every possible traffic downtime scenario. He adds that towers, waveguides and all other hardware and infrastructure would have to be completely bulletproof. This is true of every telecommunication system.
However, with protection schemes and diversity arrangements in today’s wireless communication solutions, microwave transmission can get very close to mitigating against long-term traffic outages (i.e., > 10 CSES, consecutive severely errored seconds) and short-term traffic outages (i.e., < 10 CSES).
In pursuit of the 100 percent uptime goal, Dick goes over many of the strategies available in the newest video in the Radio Head Technology Series, for which there is complimentary registration. For example, there are many approaches to protection, including Hot Standby and Space Diversity. In particular, Dick points out Frequency Diversity has advantages over many protection schemes, but few outside the federal government are able to obtain the necessary waivers in order to use it. Hybrid Diversity uses both Space Diversity and Frequency Diversity to create a very strong protection solution. A case study outlining Hybrid Diversity is available.
Other concepts Dick covers in this fifth edition of Radio Heads includes error performance objectives, bit error rate, data throughput, errorless switching, equipment degradation, antenna misalignment, self-healing ring architecture and something called the “Chicken Little” alarm.
Ever wonder which antenna polarization is more susceptible to rain outage? Vertical? Horizontal? Which should you use for very long hops?
What would you do besides add extra fade margin to mitigate rain outage? Design a shorter path or use a lower frequency band?
Aviat Networks’ microwave radio guru, Principal Engineer Dick Laine, tackles these tricky questions and others in the latest episode of our Radio Head Technology Series of videos.
Dick also talks about rain outage—as calculated by ITU using a simple scientific calculator, or computer programs (Starlink) that use the Crane model. He goes through an ITU-R availability calculation in one example, noting specifically about rain attenuation calculation above and below 30 degrees latitude. Dick then proceeds into a deep dive on calculating outage when you know the fade margin, followed by a discussion on the Crane rain attenuation model.
Aviat Networks invites our readers to register to be added to our Radio Heads distribution list to get notified of new Radio Head Technology Series releases and links to replays.
Link between Honduras and Belize Crosses Water and Land
Last year I wrote about the world’s longest all-IP microwave link, stretching 193 km over the Atlantic Ocean in Honduras. Aviat Networks and Telecomunicaciones y Sistemas S.A. (TELSSA) designed and implemented this link together. This year, Aviat Networks and TELSSA again worked together to build another link and achieve another record—an Eclipse microwave link between Honduras and Belize that crosses 75 km of the Atlantic Ocean and 105 km of rugged terrain for a total path length of 180 km. This is a new world record for a hybrid diversity microwave link!
After the success of implementing the 193km link over water, Aviat Networks and TELSSA were eager to meet the challenge to connect Honduras and the neighboring nation of Belize using a single microwave link. Aviat Networks network engineers and TELSSA engineers were able to use their extensive knowledge of local propagation conditions, thorough understanding of long path design principles and precise installation practices to successfully implement this 180km microwave link.
Long Path Design Considerations
As outlined in the article last year for the longest all-IP hop, a deep understanding of path design considerations and experience in microwave transmission path design are necessary to successfully complete a long path design. Key considerations involved:
To read more about this world-record Hybrid Diversity IP microwave link, download the full article.
Senior Network Engineer