- Rajeev Suri, CEO of Nokia Siemens Networks
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.
Director of Marketing
- August 11, 2011
- antenna, antenna decoupling, Aviat Networks, backhaul, beamwideth, bigger isn't better, Construction Installation and Maintenance, dB, decibels, digital microwave, Director of Corporate Marketing, Equipment, frequency diversity, k-factor, microwave communication, Microwave transmission, Radio, receive signal level, RSL, Stuart Little, Telecommunication, wind load, wireless, Wireless network, wireless transmission engineers
Terrestrial microwave radio system with two antennas employing space diversity. (Image via Wikipedia: Photo credit David Jordan)
Antenna gain is directly related to the size (diameter) of the antenna, and wireless transmission engineers looking for more system gain to improve link performance on long or tough paths in frequency bands below 10 GHz may resort to using very large antennas with diameters of 12 feet (3.7 m) or more. However, bigger is not always better. In fact, large antennas should only be used under the most unusual of circumstances.
Use of large, oversized antennas was commonplace during the 1960s and 1970s, for analog FM-FDM heterodyne microwave communication high-capacity links operating in the L6 GHz band. This was for good reason. Communications paths consisting of multiple radio links required very high receive signal levels, and fade margins of up to 50 dB, on each link to meet end-to-end noise objectives. The large antennas helped cut baseband thermal noise by more than 3 dB, which is half that of smaller antennas. Many of these paths were relatively short and many of these analog wireless links employed frequency diversity, so higher fade margins were needed to reduce outage—especially in N+1 hops. This reliance on large antennas is often still prevalent in the minds of many wireless transmission engineers.
Today’s Digital Microwave Systems
In contrast to old analog systems, digital microwave operates essentially error-free (i.e., with a bit error rate of 1 in 1,013 transmitted bits), even with much smaller fade margins. Adequate path clearance, optimal selection of diversity arrangements using smaller antennas and the precise alignment of antennas are far more effective to ensure that error performance objectives for microwave communications are met.
Big Antennas = High TCO
So because big antennas are not really needed to ensure high path availability, they do directly impact the total cost of deploying and operating a microwave link, namely:
- Wind Loading—There is more wind loading because of the larger surface area. A 12-ft antenna has 45 percent more loading (e.g., 1,400 lbs wind load in a 70mph wind) compared to a 10-ft antenna (e.g., 980 lbs wind load). This means the microwave tower needs to be stronger to be less susceptible to the sway that results in antenna misalignment. Stronger towers mean more costly new towers, or expensive upgrades to existing towers
- Beamwidth—Beamwidth of a 12-ft dish is 25 percent narrower compared to a 10-ft antenna, which further increases the tower’s rigidity requirements and thus cost
- Non-Diversity vs. Diversity—Large 12-ft antennas are sometimes justified by assuming that the single large dish is more cost-effective and/or has performance characteristics as good as two smaller diversity dishes. A single 12-ft dish with its 1,400-lb single-point wind load—and narrower beamwidth—puts far more stress on a structure than dual 8-ft diversity dishes with a distributed wind load of 1,260 lbs (2x630lbs) and much wider beamwidths. Smaller diversity dish arrangements also increase the wireless link’s performance by reducing multipath outage by more than 80 percent compared to a single 12-ft dish deployed in a non-diversity hop
- Antenna Decoupling and Alignment—The smaller beamwidth of larger antennas also increases the difficultly to align accurately, and the risk of antenna decoupling due to angle-of-arrival variations during nocturnal atmospheric (k-factor) changes. Antenna decoupling, directly proportional to path length, is increased on those longer paths in difficult geoclimatic areas that attract the use of 12-ft dishes. It can be a death spiral—the longer, more difficult paths that attract the use of larger, narrower beamwidth antennas are those that are even more sensitive to the resulting geoclimatic conditions!
- Aesthetics—Bigger isn’t better when deploying dishes on towers, buildings and—especially—mountaintop sites, due to aesthetic concerns, building/tower owners’ concerns and local planning limitations. These can often be mitigated by using smaller antennas
- Deployment Costs—The overall deployment cost differential between a single 10-ft and 12-ft antenna can exceed $10,000 when transport, installation and ancillary hardware are taken into consideration, and this does not include the potential cost of added tower strengthening and increased monthly tower lease charges
So before you consider using large 12-ft+ antennas, think again and consider the bigger picture. You may well end up spending a lot more money for a path that may perform more poorly than it would have if smaller antennas had been used.
For more tips, we’ve also included some wireless transmission engineering guidelines for antennas and other wireless equipment.
Director of Corporate Marketing, Aviat Networks