Recently, telecom research firm Heavy Reading conducted a survey of mobile network operators (MNOs) from the around the world exclusively for Aviat Networks. The goal of the survey was simple: determine the sentiment of MNOs to provide fixed wireless services to enterprise customers.
Now that the growth rate of individual wireless subscribers has leveled off in many nations with mobile penetration rates near and even exceeding 100 percent, MNOs have begun to look very seriously at alternate sources of revenue growth. And one of those alternatives is fixed wireless enterprise services, which according to Heavy Reading, MNOs rank as a co-strategic priority along with their core subscriber business.
Enterprise services are all very well and good but how does an MNO deliver them? The answer is not as complex as you may imagine but somewhat more difficult in reality. While MNOs have robust infrastructure based on rock-solid microwave backhaul technology to the cell sites at the edges of their networks in the majority of cases, they do not have an easily deployable method of supporting fixed wireless services to enterprises. One such way would be via Layer 3. In the survey, Heavy Reading found that a supermajority, or 70 percent, of MNOs believe that Layer 3 (L3) capability from the cell site is “critical” or “very important” to enable new service delivery.
However, L3 capabilities are not the end of the story. Layer 3 services are packet-based and require IP/MPLS routing functionality in order to operate. Accordingly, the MNOs surveyed by Heavy Reading reflect this outlook by an overwhelming 75 percent stating that IP/MPLS is “critical” or “very important” for offering fixed wireless services to enterprises. In addition, 75 percent of MNOs also believe it is “critical” or “very important” that existing cell site equipment be made capable of delivering these fixed wireless enterprise services. The existing cell site equipment is quite capable of delivering Layer 2 (L2) fixed wireless services, but help is needed to go the next step up to L3.
“Whilst L2 can be used to deliver business services, our survey results suggests that most mobile operators are very interested in the additional benefits of L3 including MPLS,” says Patrick Donegan, senior analyst, Heavy Reading. “They also tend to value very highly the ability to deliver those business services from existing equipment at their cell sites.”
Donegan goes on to elaborate further in the complete survey results where he reveals more eye-opening insights. To find out these and more click here.
FirstNet is facing technological challenges as it careens toward key decisions for the Nationwide Public Safety Broadband Network. That was the key takeaway when APCO held its Public Safety Broadband Summit in Washington D.C., May 13-14. In that context, backhaul continues to be a hot topic. Typically more of an afterthought in commercial telecom systems, backhaul becomes the 900-pound gorilla in the room when defining high reliability telecom networks such as mission-critical public safety networks. This is due to the extremely high cost of fiber—CAPEX for new runs and OPEX for leasing—as well as its proven lack of survivability in worst-case scenarios.
For example, during Superstorm Sandy, 25 percent of all affected commercial mobile sites were down, and most had to be propped up by temporary microwave radio backhaul solutions due to the lengthy time needed to replace the damaged fiber. Chief Dowd of NYPD provided insight into the situation stating that the network’s reliability is defined during worst-case conditions, not during sunny days.
Aviat Networks’ APCO presentation, below, from the Broadband Summit dives deeper into these issues:
Or we can talk to you directly about your concerns for your mission-critical Public Safety network requirements.
Director, Business Development
Competitive licensing of fixed microwave backhaul bandwidth is a bad idea. And it should not go any further. The reasons why are laid bare in a new article in IEEE Spectrum by former electrical engineer and current telecom law firm partner Mitchell Lazarus. In general, he argues against federal spectrum auctions for microwave frequencies, and in particular for fixed microwave links. Undoubtedly, readers are familiar with the large cash bounties governments around the world have netted from competitive bidding on cellular bandwidth—first 3G and now 4G. An inference can be drawn from Lazarus’ article that some governments (i.e., the United States, the United Kingdom) had in mind a similar, if perhaps smaller, revenue enhancement through competitive auctions of microwave channels.
The problem lies in the fallacious thinking that operating fixed point-to-point wireless backhaul bandwidth is comparable to that of mobile spectrum. Whereas mobile spectrum license holders can expect to mostly—if not fully—use the frequencies for which they have paid top dollar, the same has not historically been true of license holders of microwave backhaul bandwidth. In most cases, mobile license holders have a virtual monopoly for their frequencies on a national, or at least regional, basis. Their base stations send and receive cellular phone signals omnidirectionally. They expect throughput from any and all places. So they have paid a premium to make sure no competitors are on their wavelengths causing interference.
On the other hand, U.S. holders of microwave backhaul licenses have specific destinations in mind for the operation of their point-to-point wireless networks. They only need to communicate between proverbial Points A and B. And, historically, they have only sought licenses to operate in their particular bandwidth on a particular route. They had no need to occupy all of their licensed frequency everywhere. That would be a waste. They just have to make sure they have a clear signal for the transmission paths they plan to use. To do that, before licensing, they would collaborate with other microwave users in the vicinity and a frequency-coordination firm to establish an interference-free path plan. Any conceivable network issues would usually be resolved at this stage prior to seeking a license from the Federal Communications Commission. Essentially, the FCC is just a glorified scorekeeper for fixed microwave services, passively maintaining its transmitter location license database.
But starting in 1998, with dollar signs in their eyes, governmental spectrum auctioneers started to sell off microwave frequencies in block licenses. The need for fixed microwave wireless services then was growing and has only grown fiercer with each additional iPhone and iPad that has been activated. However, access device throughput demand on one side of a base station does not necessarily fully translate all the way to the backhaul. Lazarus points out the example of now defunct FiberTower and its failure to make block microwave licenses work economically. After buying national block microwave backhaul licenses at 24 and 39 GHz, Lazarus notes, the firm resold the frequencies to Sprint and a county 911 emergency network operator. But those were the only customers. Lacking a robust enough utilization of its licensed backhaul frequencies, FiberTower had several hundred of its licenses revoked by the FCC and was forced into bankruptcy November 2012.
Subsequent auctions have attracted far fewer bidders and generated much less income for the Treasury Department. Much bandwidth has lain fallow as a result. And infrastructure buildout has stagnated.
Regulators should return the microwave backhaul licensing process to that of letting wireless transmission engineers cooperate informally among themselves, with the help of frequency-coordination firms, to arrive at fixed point-to-point wireless plans in the public interest. These are then submitted only for maintenance by the FCC or other regulators for traditionally nominal license fees—currently $470 per transmitter site for 10 years in the U.S., per Lazarus.
Forget the quixotic quest for chimerical hard currency. The commonweal demands it. You should demand it of the regulators—you can still give input regarding this scheme in some jurisdictions where it is under consideration. Clearly, the most efficient use of spectrum is to make it openly available to all because it means that every scrap of commercially useful spectrum is picked clean. We welcome your comments pro or con.
Germany is well-known for its autobahn highway system, where there are no official speed limits. Now there is a new high-speed network that traverses Western Europe from Frankfurt in Germany to London in the UK.
In addition, you may have read elsewhere in recent weeks about low latency microwave networks being constructed in the United States in support of the financial markets. The busiest route there is between the financial centers in Chicago and New York, where microwave can shave off 5 milliseconds off the transmission time along the 700 mile (1,000 km) route when compared to fastest fiber network (13 milliseconds). This saving directly equates to revenue for trading houses that are able to leverage this speed advantage.
In the United States, planning and deploying a point-to-point (PTP) microwave network is relatively predictable and straightforward: acquire sites and avoid interference from other network operators. Where PTP wireless networks cross state boundaries, a network operator need only deal with the national telecom regulator, the Federal Communications Commission (FCC), when obtaining required licenses to operate the microwave system.
But in Europe, this is a very different matter. While trans-European fiber networks have been a reality for many years, a microwave route like London to Frankfurt must traverse several national borders, forcing operators to deal with multiple regulators, with complex negotiations needed for microwave paths that cross national boundaries. For this reason very few—if any—microwave networks of this type have been built, up until now. However, the opportunities offered by the combination of the new low latency sector, along with the performance advantage of microwave over fiber, have now made the case for these kinds of networks compelling enough to outweigh the challenges, and costs, of planning and implementing them.
For a low-latency microwave network servicing the financial sector on the London-to-Frankfurt route, there are a number of major challenges beyond just identifying and securing suitable sites and coordinating frequencies. The difficulty of planning a long trunk route is also greatly exacerbated by going through the densely urbanized region of Western Europe. This results in a constant iteration between finding the right route, identifying accessible sites, and securing required microwave frequencies. To be successful you need all three—a site on a great route is useless if no microwave spectrum is available. All the while, there are other competing providers all trying to complete the same route in the fastest time possible—not only in latency terms, but also time to revenue.
This poses huge potential pitfalls in having to take the long way around, requiring additional sites and links, if a site is not available. The added latency caused by any such deviation could kill the entire project. This race is like no other in the microwave business—whoever is fastest wins first prize, and it is winner take all in this competition. The potential revenue for the London-to-Frankfurt low-latency path is quite staggering, even on a regular day, but on busy days when the market is volatile the potential can be much higher. Operators can plan on recouping their total investment in the microwave network in well under a year. Then once you have the most direct route, compared to your competitors, your problems may not be over, so it can come down to squeezing those extra few microseconds, or even nanoseconds, out of your equipment.
On this particular route there is also one significant natural barrier to contend with—the English Channel. There are only a few ways across that are short enough to allow a reliable microwave path, space diversity protection is a must and only a few towers are tall enough to support these distances. Even though there are no obstacles over the channel (apart from the occasional container ship), towers need to be high enough to allow the microwave signal to shoot over the bulge of the earth. Again, securing tower space at these sites is critical to success, but also obtaining the right to use one or more of a finite pool of available frequency channels, otherwise fiber may be needed across this stage, adding latency. One group even took the step of purchasing a microwave site in the Low Countries to secure it precisely for this purpose.
London to Frankfurt will only be the start for low latency microwave networks in Europe, as there is always a need and an opportunity to provide competitive transmission services to other financial centers throughout the continent. The winners will be those with the speed and agility to quickly seize these opportunities, along with working with the right microwave partner who can help them with the intensely complex business of planning and deploying these trans-national networks, and who can also supply microwave systems with ultra-low latency performance.
We will have more to say publicly on this topic in the near future. Or if you prefer not to wait that long, we would be more than happy to have a private conversation about low-latency microwave with you.
1. What is QAM?
Modulation is a data transmission technique that transmits a message signal inside another higher frequency carrier by altering the carrier to look more like the message. Quadrature Amplitude Modulation (QAM) is a form of modulation that uses two carriers—offset in phase by 90 degrees—and varying symbol rates (i.e., transmitted bits per symbol) to increase throughput. The table in this blog post (Figure 1) describes the various common modulation levels, associated bits/symbol and incremental capacity improvement above the next lower modulation step.
2. Must all operators who use microwave backhaul use higher-order QAMs?
Higher-order QAMs are not necessarily a must-have for all network operators. However, higher-order modulations do provide one method of obtaining higher data throughput and are a useful tool for meeting LTE backhaul capacity requirements.
3. What is the main advantage of using higher-order QAMs with microwave radios?
The main advantage is increased capacity, or higher throughput. However, capacity improvement diminishes with every higher modulation step (i.e., moving from 1024QAM to 2048QAM the improvement is only about 10 percent!), so the real capability of higher-order modulations alone to address the objective of increasing capacity is very limited. Other techniques will be needed.
4. What are the tradeoffs of higher-order QAMs on RF performance?
First, with each step increase in QAM the RF performance of the microwave radio is degraded as per the Carrier-to-Interference (C/I) ratio. For example, going from 1024QAM to 2048QAM will produce an increase of 5 dB in C/I (Figure 2). This results in the microwave link having much higher sensitivity to interference, making it more difficult to coordinate links and reducing link density. Along with this increase in phase noise there will be an increase in design complexity cost.
Also, by increasing from 1024QAM to 2048QAM, system gain will decrease from above 80 dB to just above 75 dB (Figure 2). With much lower system gain microwave links will have to be shorter and larger antennas will have to be employed—increasing total cost of ownership and introducing additional link design and path planning problems.
All of the above are the results of linear functions: they degrade in a one-to-one relationship with the move to higher-order QAMs. Meanwhile, the capacity increases derived from higher-order QAMs are the function of a flattening curve: Each step increase in QAM results in a reduced percentage increase in capacity compared to prior increases in QAM. The added capacity benefits are diminished when considering the added costs of higher C/I and lower system gain.
5. Do you need to use Adaptive Coding and Modulation (ACM) while using higher-order QAMs?
ACM should be implemented while employing high-order QAMs to offset lower system gain. However, while ACM does help mitigate the effects of more difficult propagation when using higher-order modulations, it cannot help offset increased C/I.
6. What gives Aviat Networks a “heads-up” here when other big name companies seem to be supporting the technology?
Aviat Networks realizes higher-order modulations are not a panacea—a cure-all. While every minor technology improvement in throughput can help, a focus on technologies that grow capacity in hundreds of percentage points vs. tens of percentage points is most critical now. Aviat believes that these hundreds-of-percentage-points-of-improvement-in-capacity solutions will be the most important moving forward. It is in these technologies that Aviat has a “heads-up.” Such techniques include deploying more spectrum—particularly in the form of multichannel RF bonding (N+0) solutions—to achieve a minimum of 200 percent capacity increase. This technique is subject to frequency availability, but with flexible N+0 implementations (such as being able to use frequency channels in different bands and different channel sizes) many congestion issues can be avoided.
Second, intelligently dimensioning the backhaul network based on proven rules, best practices and L2/L3 quality of service (QoS) capabilities is another technique to provide potentially very large gains in backhaul capacity. Higher-order modulations can be one tool to achieve required capacity increases in the backhaul network. However, their inherent drawbacks should be well understood, while the most attention should be paid to other techniques that deliver more meaningful and quantifiable benefits.
7. Will operators need to “retrofit” microwave radios to be capable of higher-order QAM operation in their existing microwave infrastructure? Or will completely new hardware be required?
This depends on the age and model of the existing radios. Older microwave systems will likely need to be “retrofitted” to support 512QAM and higher modulations. Recently installed microwave systems should be able to support these technologies without new hardware.
8. How will QAM evolve in the future? Is the introduction of higher-order QAMs an indefinite process, with no end in sight?
The introduction of higher-order QAMs is not an endless process. As per Figure 1 above in this blog post, the law of diminishing returns applies: Throughput percentage improvement declines as modulation rates increase. The cost and complexity of implementing higher-order QAMs probably is not worth the capacity increase benefits derived—not past 1024QAM, in any event.
Director, Marketing and Communications
A different solution to handle the burgeoning demand for mobile broadband capacity will be needed. More spectrum coupled with more spectral efficiency will not be sufficient. A clear solution is more sites, but deploying more macro-sites in urban and dense urban areas (where most of the traffic will be needed) will not be feasible.
Small cells promise a new “underlay” of outdoor and indoor, low power micro-cells that are deployed on public and private infrastructure within the urban clutter, are seen as seen as a likely solution. Sites being considered include:
These new sites will need to be compact, simple to install, energy efficient and incorporate an organically scalable and tightly integrated backhaul solution. As a result, there will be many more sites—some projections estimate that up to 10 small cells will be deployed for every macro-site. Small cells hold out the promise of great gains for the end users but massive challenges for the operators.
Small cell deployments so far have mainly been concentrated in Europe (3G) and the USA (LTE). 3G small cells may also be deployed in other regions as a means to avoid the difficulties in obtaining planning approval for larger macro-cell sites.
It’s Still Early
Today, as far as wireless small cell backhaul (SCBH) solutions are concerned, there is evidence of product immaturity and hyperactivity in equal measure.
There is profusion of aggressively hyped solutions, including many that are a rehashing existing/niche solutions and at the opposite extreme some very new and unproven technologies. In practice, these solutions are jockeying for position while operators grapple to understand the formidable planning and infrastructure challenges being thrown up by their small cell ambitions. It is apparent that few appear that they will fully satisfy the anticipated and emerging requirements in terms of performance (i.e., capacity, latency, availability), size/shape, ease of deployment and most importantly, total cost of ownership. For the complete article, download the PDF.
Stuart D. Little
Director, Product Marketing
If you look in the November issue of MissionCritical Communications, you will see an article by Aviat Networks director of marketing and communications, Gary Croke. In his article “Know Your Microwave Backhaul Options,” Gary covers:
You can read Gary’s article (on page-30) here—MissionCritical Communications—November 2012.
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