By Stuart Little, Director of International Product Line Marketing, US
Space diversity has been an important feature in long haul microwave systems for many years to counteract the effects of multi-path fading. Space diversity enables very long links over highly reflective surfaces such as bodies of water for example, where a non-diversity link would not deliver the high availability required.
When designing microwave networks, backhaul engineers have a wide variety of techniques at their disposal. One method that remains highly effective is Space Diversity (SD). With SD, two antennas separated by some distance can increase the availability of a link from something less than 99.999 percent to in excess of five-nines uptime. However, the introduction of a second parabolic antenna on a microwave path poses a substantial increase in the capital expenditure (capex) budget.
- September 18, 2012
- Antenna diversity, Antennas, China Basin, Dick Laine, horn antenna, microwave, microwave propagation, Principal Engineer, Radio Head Technology Series, Radio Heads, Radiohead, San Francisco, Space Diversity
Horn antennas on the roof of a microwave relay station near Madison St. and 17th Ave, Capitol Hill, Seattle, Washington state, USA. (Photo credit: Vladimir Menkov via Wikipedia)
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!
- July 4, 2012
- Antenna diversity, Dick Laine, diversity arrangements, frequency diversity, Microwave transmission, protection schemes, Radio frequency, Radio Head, Radio Head Technology Series, Space Diversity, wireless
The BT Thornhill microwave radio tower above demonstrates a Space Diversity protection scheme with its parabolic antennas placed apart from one another (Photo credit: Peter Facey via Wikipedia)
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.
- June 12, 2012
- Atlantic Ocean, Aviat Networks, Belize, frequency diversity, Honduras, hybrid diversity, Internet Protocol, microwave, Microwave transmission, Space Diversity
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
- Multi-path propagation delay
To read more about this world-record Hybrid Diversity IP microwave link, download the full article.
Senior Network Engineer
Successfully Implementing a 193-km Microwave Link over Water to Deliver 99.9995 Percent Availability
For most designers of microwave transmission paths, engineering a reliable link over water can be a daunting task. Reflections off the water surface can play havoc with the received signal, leading to high levels of interference resulting in fading and ultimately a high level of errors and signal interruptions. For these types of paths, performance calculations using commercially available software planning tools will be insufficient to ensure superior path performance. In these cases, experience and understanding of the key parameters that influence microwave performance are critical.
Recently, Aviat Networks and our agent, Telecomunicaciones y Sistemas S.A. (TELSSA), deployed an Eclipse microwave link for Central American Corporation for Air Navigation Services (COCESNA) in Honduras that crosses over 193 km, most of which is over water. With careful design and installation, this link is now operating successfully.
COCESNA is responsible for the air traffic control over Central America territory and oceanic areas, therefore, availability of service is a critical issue.