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Survey view from Belize toward Honduras, at 1000 m AMSL
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:
The effect of antenna diameter on highly refractive paths
Precise alignment of the antennas to mitigate the effect of refractivity
Optimum RF and space diversity spacing to counter elevated divergent dielectric layers
Deterministic prediction of the variations of atmospheric conditions
You may not think that 78 rpm records and microwave communications could have anything in common. But our Dick Laine finds the devil in the details between the two in Radio Heads video No. 3. (Picture: label for 1940s brand of jukebox needles for playing 78 rpm records; photo credit, Infrogmation via Wikipedia)
As he relates, even with scratches and pops, a 78-rpm record still is able to transfer aural information so that you can hear it, i.e., its availability is intact, as it does not drop performance. Scratches and pops only represent degradation in the quality of communication. But when the record is broken, an outage occurs—no record, no communication.
The same goes for wireless communication systems. If a microwave link drops 315 or fewer seconds of microwave communications per year (in increments of up to 10 seconds at a time), it is maintaining five-nines availability. The microwave link is offering 99.999 percent availability for wireless backhaul. Only if the microwave link is unavailable for more than 10 seconds has an outage occurred, for the purposes of determining if microwave communications traffic has been dropped.
Dick goes on to explain about what happened in 1949 when 78-rpm records were superseded by 45-rpm records. Dick got a sneak peek at the top-secret 45-rpm record project when he visited the legendary RCA facility in Camden, New Jersey, which played a crucial role in the development of the modern music, radio and television businesses. Unfortunately, unlike a five-nines microwave link, 78-rpm and 45-rpm records are mostly unavailable nowadays.
Because of all these models, he likes to use Vigants calculations as a “sanity check” to see that he is close to the correct result for his path engineering plans. The free Aviat Networks’ Starlink wireless path engineering tool can be used to handle Vigants calculations for Aviat Networks’ and other vendors’ equipment.
Can’t wait to hear more of Dick’s experienced views on microwave radio transmission engineering? You can get ahead of the learning curve by registering for the series and get these videos sent to your inbox as soon as they are released.
NAB 2012 was extremely well attended by both vendors (all three exhibition halls were fully occupied) and participants. Thanks to the continuing conversion from analog to digital broadcasting, TV companies are investing heavily in equipment and software solutions. Every company was presenting digital solutions from cameras to studio equipment to TV transmitters to Microwave Radio transport.
Every facet of the solution set must be upgraded to accommodate the intricacies of digital networks. In the case of the Microwave Radio, they are moving to bi-directional radios that can not only carry the studio content up to the transmitter site, but also can carry collected content from various mobile generating platforms (trucks, helicopters, etc) back to the studio for editing.
It was interesting to see Cisco, HP and other networking companies exhibiting. The integration of Internet Protocol (IP) into the broadcasting community has created a real demand for networking appliances like routers and switches. Other devices like Microwave Radio must also be able to accommodate IP protocols for efficiently carrying the video content to the various transmitters in the network.
I was amazed at the range of nationalities represented. Clearly this show offers value to broadcaster across the globe. I heard a figure of over 400 people from Brazil attended the show. I think I heard people complain about their tired feet in 25-30 different languages! The combined attraction of NAB and Las Vegas is very difficult to pass up.
See you at NAB 2013.
Randy Jenkins Director Business Development
Transmission engineering of a microwave link requires creativity and skill. So if you are looking for inspiration as well as high-quality wireless engineering instruction look no further than the “Radio Head Technology Series.” Radio Heads is a collection of videos and podcasts featuring our very own Dick Laine. Dick is arguably the most experienced microwave engineer in the wireless communication business, having spent more than 50 years working with microwave radio from its inception—here at Aviat Networks and our predecessor companies (e.g., Farinon, Harris MCD).
Dick has been involved with nearly every aspect of RF transmission, microwave link and network transmission design, and the effects of geoclimatic conditions on transmission of voice and now IP radio data packets.
In his own unique style, Dick has been teaching basic and advanced concepts for digital microwave transmission in seminars and training classes worldwide. Students who have taken his classes return years later eager to get a refresher from Dick and to hear about some of his great adventures in Asia, the Middle East, Africa and in the Americas.
In the first Radio Heads video titled “Check List for a Successful Microwave Link,” Dick explains the four key objectives or requirements for a well-done microwave link design along with “check list” items that the project manager or transmission engineer evaluates for proper design and deployment of a digital microwave link. If you have not already signed up for this video series, register to view the content.
United States radio spectrum frequency allocations chart. The FCC has freed 650 MHz of spectrum to increase sharing possibilities for 7GHz and 13GHz bands. (Photo credit: United States Department of Commerce employee via Wikipedia)
These maps are excellent at conveying the limitations of the newly released spectrum for microwave link applications in the 7 GHz (6.875–7.125) and 13 GHz (12.7–13.1) bands. After taking into account the zones that are reserved for existing Fixed and Mobile Broadcast Auxiliary Service (BAS) and the Cable TV Relay Service (CARS) users, these new bands are only available in about 50 percent of the US land mass covering only 10 percent of the population.
What do you think? Should the FCC loosen the spectrum sharing rules even more for 7GHz and 13GHz bands? Take our poll and tell us:
The ECC held a meeting in March to further consider updating regulations to allow the use of asymmetrical links in microwave backhaul (Photo credit: blese via flickr)
Last autumn we wrote about potential plans from a microwave competitor regarding using asymmetric band plans for point to point microwave communication links. To update this topic, we have put 10 things in parentheses that you should know about the current status of asymmetrical links in wireless backhaul. Last month at an Electronic Communications Committee SE19 (Spectrum Engineering) meeting this microwave technology subject was discussed again. (1) The proposal under consideration has been reduced in scope and (2) the regulators present still wish to see more evidence regarding the need for change before agreeing to such significant amendments.
Asymmetric Band Plan Altered A quick reminder of what was originally requested back in the autumn of 2011; a move from channel sizes of 7, 14, 28 and 56MHz to channel sizes of 7, 14, 21, 28, 35, 42, 49 and 56MHz in order to support different granularities of channel widths in all bands from L6GHz to 42GHz. However in March these proposals were altered to reflect channel sizes of 7, 14, 28 and 56MHz (i.e., no change to existing channel sizes) and asymmetric only in the 18GHz band and above.
The national regulatory authorities stated that even the (3) revised proposal cannot be accommodated with existing planning tools so they cannot imagine asymmetric links being deployed alongside existing links in their countries. A few stated that in block allocated spectrum the owner of the spectrum may be able to implement this channelization, but Aviat Networks believes that (4) the complexity of coordinating links even in block allocated spectrum should not be underestimated.
Traditionally, links are planned on an equal bandwidth basis, e.g., 28MHz + 28MHz, with a constant T/R spacing throughout the band in question. This new proposal would see links of 28MHz + 7MHz and furthermore makes the claim that spectrum would be saved. Numerically speaking this arrangement would save 21MHz for each pair, but (5) saved spectrum is only of value if it is reused. In many cases the “saved” spectrum would be orphaned due to difficulties coordinating it into usable pairs.
Asymmetric Channel Plan Limits Future
In our last blog on this topic we reflected on the fact that while there is some level of asymmetry today, (6) this trend may well be balanced in the near future by cloud services and other services that involve the user uploading content. We believe that (7) committing to an asymmetric channel plan now limits the future. (8) Symmetric channel planning allows networks to dynamically adjust to changing demands. A related concern is the fact that (9) spectrum once reallocated may not be easily clawed back to create symmetric pairs in the future. While some applications are experiencing asymmetry in traffic presently, we should not forget that some traffic patterns are still symmetric and where asymmetry is a feature, (10) the scale of this phenomenon may be overstated. Indeed, a major European operator present at the SE19 meeting voiced skepticism about the need for asymmetric support.
What do you think? Will mobile traffic remain or increasingly become asymmetric? Are asymmetric microwave links needed or can they be practically deployed in existing bands? Answer our poll below and tell us. Select all answers that apply.
Recently we learned that Nokia Siemens Networks (NSN) will sell its microwave business to DragonWave. This is notable in that NSN is the first of the big 5 “Telecommunications Generalists” (the others being Ericsson, NEC, Huawei and Alcatel Lucent) to depart the microwave backhaul segment.
As stated by Rajeev Suri, NSN CEO, “Our customers….do not believe a be-everything-to-everybody strategy works anymore in this sector.” In a market where the generalists promote their ‘end-to-end’ network capability as an advantage, Suri went on to suggest that, while NSN is the first to make this move, they may not be the last – “They (NSN customers) believe that we are the first company to start making these difficult choices. I think they’re looking to some of the other suppliers to make up their mind as well. So they like it. They support it.”
This move (dare we call it a “trend?”) demonstrates what we at Aviat Networks have known for a long time—that our customers benefit from having a specialist that can bring exceptional expertise and focus to their backhaul network, since as a key part of the network and a significant OPEX driver, you need to get it right.
Specialist providers like Aviat Networks are 100 percent focused on wireless backhaul—it’s all that we do. We are committed to bridging the gap between adjacent technologies to ensure seamless inter-working. As the wireless experts, we are able to bring best in class solutions that leverage the very latest in technology innovations to solve the critical challenges of operators around the world—delivering more backhaul capacity at a lower overall total cost.
Stuart Little Director of Marketing Aviat Networks
MIMP won the award with a unique comms solution that links the Adelaide Zoo with the Warrawong Wildlife Sanctuary. The sanctuary is home to 100 species of birds and native mammals, most of which are nocturnal and endangered.
The Zoo’s old system ran at 256 kilobit-per-second at a very high cost until MIMP installed four environmentally friendly microwave radios. They now have a 32 Mb/s full-duplex connection between the sites with minimal ongoing costs. Now, the radios use less power than a light bulb.
Rain fading (also referred to as rain attenuation) at the higher microwave frequencies (“millimeter wave” bands) has been under study for more than 60 years. Much is known about the qualitative aspects, but the problems faced by microwave transmission engineers—who must make quantitative estimates of the probability distribution of the rainfall attenuation for a given frequency band as a function of path length and geographic area—remains a most interesting challenge, albeit now greatly assisted by computer rain models.
A surprising piece of the puzzle is that the total annual rainfall in an area has almost no correlation to the rain attenuation for that area. A day with one inch of rainfall may have a path outage due to a short period of extremely high localized rain cell intensity, while another day of rain may experience little or no path attenuation because rain is spread over a long period of time, or the high intensity rain cell could miss the microwave hop completely.
Over the years, we have learned a lot about deploying millimeter wave microwave hops for our customers:
Rain outage approximately doubles in each higher millimeter wave band, e.g. 18 to 23 GHz
Rain outage is directly proportional to path length—assuming a constant fade margin for each hop
Rain outage in tandem-connected short hops is the same as for a single long hop—if they have the same fade margin
Multipath fading in optimally aligned millimeter wave hops does not occur during periods of heavy rainfall, so the entire path fade margin is available to combat rain attenuation fades
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