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.
A quick Google-glance around the Internet will reveal a panoply of all-outdoor radios (ODRs) in both microwave and millimeter-wave bands. ODRs do not conform to a universal norm in terms of networking features, power consumption, bandwidth scalability (i.e., capacity) or outright radio horsepower (i.e., system gain).
So if you find yourself asking the questions, “Which ODR is the best fit for my network?” or “How do I narrow the ODR field?” it is good to start with the basics.
The right product choice can be quickly resolved—or at least the candidates can be short-listed—by focusing on three ODR product attributes that most heavily influence the value-for-the-money (i.e., total cost of ownership or TCO) equation:
For many microwave backhaul networks, the growth in underlying traffic is such that products which cannot scale to 500 Mbps/1 Gbps per channel will run out of momentum too early and precipitate the dreaded “forklift upgrade” (also known as the “CFO’s nightmare”).
These same CFOs are also suffering sleepless nights due to rising energy costs—which in some countries can double year-over-year. Therefore, it behooves the operator to seek and prioritize the use of über energy-efficient products, such as the Aviat WTM 3200, which—and this is important—do not compromise on RF performance.
That brings me to my last point: System gain (RF performance) remains a core TCO factor insofar as it can drive smaller antenna usage with the concomitant capex savings. Still, there might be little to differentiate ODRs in terms of RF performance—in which case the spotlight will fall on these other attributes to sway the decision.
Having worked on the operator side and wrestled with TCO analysis on many occasions, my experience tells me that you can narrow your ODR choice quickly by reflecting on these three attributes and the TCO gains they can deliver.
Product Marketing Manager
Because of need for higher capacities, the trend toward shorter link distances for mobile backhaul and declining product costs, 70/80GHz (i.e., E-band) solutions are gathering significant interest for mobile backhaul and enterprise access applications. However, because these frequencies are new to most people, there is little understanding of costs and other issues related to licensing the 70-80GHz spectrum.
There is real concern from operators that utility, streetlight and traffic poles are not designed to meet the minimum twist and sway standards for deploying microwave solutions for small cell backhaul. Our research suggests that not all poles are created equal, however. Under certain circumstances these structures can be an option for deploying microwave backhaul for small cells.
Twist and sway requirements for towers and poles that support microwave backhaul hops are more stringent than for other RF equipment. This is especially true for deployments in frequency bands above 18 GHz where the antenna beamwidth is narrower than below 18 GHz. Standards such as the TIA-222-G set a minimum twist and sway that a structure should be able to endure for hosting a microwave installation. This creates concerns for operators interested in deploying microwave for small cell backhaul on structures including utility, streetlight and traffic poles that are not designed to meet this standard. Although the use of a sturdy structure is always recommended a close look at utility, streetlight and traffic poles suggests that under certain circumstances these structures can be an option for deploying microwave backhaul for small cell.
The installation of any equipment on existing poles—including small cell and backhaul radios and antennas—will necessarily change the weight and wind loading characteristics of the deployment pole. This will require a structural analysis to verify if the existing pole still meets the standards or the commercial criteria set by the pole manufacturer. For more information on Aviat’s analysis of pole sway for small cell backhaul see our PDF.
Marketing Engineering Specialist
There’s a lot of buzz in the microwave industry about the trend toward all-outdoor radios, but those who haven’t been through LTE deployments may be surprised to learn that based on our experience deploying LTE backhaul for some of the world’s largest LTE networks, all-indoor is actually the best radio architecture for LTE backhaul.
We can debate today’s LTE backhaul capacity requirements, but one thing we do know is that with new advances in LTE technology, the capacity needed is going to grow. This means that microwave radios installed for backhaul will likely have to be upgraded with more capacity over time. Although people are experimenting with compression techniques and very high QAM modulations and other capacity extension solutions, the most proven way to expand capacity is to add radio channels because it represents real usable bandwidth independent of packet sizes, traffic mix and the RF propagation environment.
All-indoor radios are more expensive initially in terms of capital expenditures, but they’re cheaper to expand and (as electronics are accessible without tower climb) are more easily serviced. While an outdoor radio connects to the antenna with Ethernet or coax cable, indoor radios usually need a more expensive waveguide to carry the RF signal from the radio to the antenna. So you pay more up front with an all-indoor radio but as the radio’s capacity grows you save money. There are several reasons.
When everything related to the radio is indoors, you just have a waveguide and an antenna up on the tower. To add radio channels with an all-indoor radio you go into the cabinet and add an RF unit. With an outdoor radio, you have to climb the tower, which can cost as much as $10,000. Also, when you add a new outdoor RF unit you may have to swap out the antenna for a larger one due to extra losses incurred by having to combine radio channels on tower….(read the full story at RCR Wireless).
Senior Product Marketing Manager
Historically, in many countries the 26GHz and 28GHz wireless frequency bands have been allocated to point-to-multi-point systems, such as LMDS in the United States and LMCS in Canada. However, most of these systems have failed to reach their expected potential in terms of revenue generated and, as such, much of the allocated spectrum is now unused. This, along with the growth in demand for point-to-point microwave spectrum, has meant a number of national regulators have started to consider reallocation of this spectrum.
In Canada, the spectrum allocations for both the 26GHz and 28GHz bands have been revisited, owing to their underutilization by LMCS operators, with a new band plan having been developed during the drafting of SRSP 325.25. The diagrams below show the new allocations that accommodate more FDD spectrum suitable for microwave in point-to-point usage.
While the technical details of this draft SRSP have been finalized, consideration of licensing options by Industry Canada has so far delayed the formal publication of this SRSP. Note that the remaining point-to-multipoint operators are catered to in the TDD section in the middle of the 26GHz plan.
In the Republic of Ireland, ComReg (the Irish national telecommunications regulator) recently issued a consultation resulting from an operator request to change the use of its allocated spectrum from point-to-multipoint to point-to-point. Figure 3 shows the current situation in Ireland and Figure 4 shows the same band after the proposed change of use.
In the United States, the LMDS service occupies the following spectrum blocks:
Thus, that would make a total of 1300MHz of spectrum—more than double the recent allocation at 7 and 13GHz—potentially available across the entire country. LMDS take up has been very low, and, as previously mentioned, much of this spectrum is now unused. This begs the question: Would spectrum reallocation in the U.S., as is happening in Canada and Ireland, promote its more active usage?
It is worth noting that existing users are protected in both the examples given above, but unused spectrum is now available to point-to-point operators. Therefore, it is now time to approach the FCC and request a similar exercise to be carried out for the United States. Aviat Networks intends to be one of the driving forces in requesting this reallocation of spectrum.
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!
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.