.FLYINGHEAD THE COMPUTING UNPLUGGED INTERVIEW
.TITLE An expert’s analysis of BPL
.AUTHOR David Gewirtz
.FEATURE
.SUMMARY If you’ve been following our Broadband-over-Powerline (BPL) coverage these past weeks, you can see we’ve come up with more questions than answers. As part of our attempt to expose all sides of this issue, we’ve been looking for true experts who can help us understand the issue. As part of that research, we turned up Glenn Elmore. We’re very grateful for Glenn in helping us understand this issue in far more depth than we’ve been able to thusfar. As a radio amateur and a BPL researcher, Glenn’s getting us answers as close to the core of the problem as we think we’re going to be able to find.
.OTHER
If you’ve been following our Broadband-over-Powerline (BPL) coverage these past weeks, you can see we’ve come up with more questions than answers. As part of our attempt to expose all sides of this issue, we’ve been looking for true experts who can help us understand the issue.
As part of that research, we turned up Glenn Elmore. He had written a number of extremely lucid open letters to the FCC and he appeared to have a very good handle on the issues. Upon tracking him down, we learned that Glenn’s in a unique position.
He’s both an industry person, as founder and Chief Technical Officer of Corridor Systems and a radio amateur — call N6GN and licensed for 45 years. Furthermore, Corridor’s technology, although providing very high rate information transfer over powerlines is by no means conventional "access BPL" as described by the FCC. Access BPL rulemaking was limited by the FCC to apply only below 80 MHz, at Corridor’s request.
We’re very grateful for Glenn in helping us understand this issue in far more depth than we’ve been able to thusfar. As a radio amateur and a BPL researcher, Glenn’s getting us answers as close to the core of the problem as we think we’re going to be able to find.
I recommend reading through to the very last question. Glenn discusses some limits of EV-DO, the new wireless technology in the new Palm Treos and Windows smartphones. It’s a discussion we’ve never seen before and it showcases some important limitations of that technology.
.TEASER Tap here to read the full interview.
.Q David
Let’s start with some details about you. I know you’re in a unique position as an industry expert and an amateur radio operator. Can you expand on your background and your work with BPL?
.A Glenn
Certainly. The bulk of my career was spent with Hewlett-Packard where I worked for 27+ years in the R&D lab developing and designing various types of RF through 50 GHz test and measurement equipment, including signal generators, network analyzers and spectrum analyzers. In 2000, I left HP/Agilent and started Corridor Systems.
My interest in amateur radio started well before my professional career and was no doubt responsible for encouraging it. I was first licensed in 1961 and have remained licensed ever since. I’ve had an amateur extra class license since 1972 and my call sign is N6GN.
My radio interests have included bouncing radio signals off of meteor trails, off of the moon, very long distance communications in the VHF-microwave bands and wireless networks. In the late 1980’s, I designed and built 2 Mbps, 10 GHz and 500 kbps, 900 MHz digital ham radios which were used to create a wide area amateur radio TCP/IP network in Northern California.
I should probably add that for most of my amateur radio career, until about 10 years ago, I was a member of the ARRL but that presently I am not. While a member, I had several technical articles published in ARRL magazines, compendiums and The Radio Handbook, which is also published by them.
Like many of Computing Unplugged’s readers, I’m something of a gadget geek and have collected my share of cameras, telescopes, GPS receivers and the like. I got a Palm VII PDA when they first came out and have recently acquired another Palm OS device, the Treo 700p.
.Q David
You wrote some open letters on BPL and some of the issues involved. Can you summarize those letters for our readers?
.A Glenn
The letters were written to describe the characteristics and differences of Corridor’s technology, which was in danger of being lumped together with conventional BPL technology operating in the 4-80 MHz region.
One letter detailed the complete absence of any interference between Corridor’s 216 Mbps demonstration system and the amateur radio service. Another letter was sent to the FCC to request that BPL rules and regulations, which were intended to apply to HF-BPL technology, were not inadvertently applied to Corridor’s BPL technology as well.
The FCC, who originally coined the Broadband-over-Powerline (BPL) acronym, concurred that Corridor’s technology was completely different and should not be included in the rule making and limited the new rules to systems operating below 80 MHz.
.Q David
At Corridor, you work with Microwave BPL. What’s the difference between that and the Access BPL that we’ve been discussing?
.A Glenn
The main difference between Corridor’s technology, E-Line, and conventional BPL is information capacity. While both approaches use the existing power line as a pipe, E-Line uses only one conductor of the line in a newly invented way that allows energy transport of an extremely broad frequency range while losing relatively little along the way.
Conventional BPL is limited to a narrow frequency range, HF, because the physics of two-wire transmission lines prevents propagation once the frequency of transport gets too high compared to the spacing of the wires. When this occurs, the wires behave more as antennas than as transmission lines.
As you can see in my sidebar article "Understanding the information rate of BPL and other last-mile pipes" (elsewhere in this issue, at http://www.computingunplugged.com/issues/issue200608/00001828001.html), even common telephone lines used for DSL can have more capacity because they are quite close together. Because E-Line operates on a new and completely different principle, it does not suffer from this limitation. The sidebar article shows a comparison when up to 7 GHz of bandwidth is allowed. As you can see, The information capacity of E-Line is second only to optical fiber and can be more than 1000 times that of HF-BPL.
.Q David
Let’s start by being quite general. From your perspective, do the claims of the ARRL have any merit at all? If so, what? If not, why not?
.A Glenn
Yes, I think they do. I think that there is no question that HF-BPL systems, which are forced to share spectrum and unintentionally radiate due to the physics of the transport they use, can and will interact with licensed users of the HF spectrum. From what I can tell, the ARRL has made some of the more thorough and careful investigations of the nature and degree of this interaction, both as to system egress — interference due to BPL radiation, and ingress — the BPL system’s sensitivity to licensed radio users in the same frequency ranges.
.Q David
Detractors claim that the radio frequency band used by BPL is quite subject to interference by simple consumer devices like baby monitors. I would think that a broadband service that can be easily cut off is a bad thing. So, is the claim true from your perspective? How reliable is BPL service and what is the risk of the service stopping?
.A Glenn
My opinion is that simple consumer devices and unintentional radiators will have very little impact on HF-BPL systems, particularly as compared to the effect of much higher power licensed radio transmitters in the HF spectrum.
A computer or other information device connection to the Internet, a very complex worldwide system, is subject to many types of failure, from a crash of the local device’s operating system to a failure anywhere along the way.
However, beyond the user level, there is generally a significant amount of redundancy and provision for failures. From what I’ve seen of HF-BPL systems, I’d not expect failures due to the portion of the system they would have to dominate. There are almost always problems as new technologies are brought to market, but I see no reason to believe that BPL should be significantly better or worse than other elements of the system.
.Q David
Detractors also claim that BPL interrupts regular radio transmissions. In the FCC Report and Order, the International Municipal Signal Association claims that BPL interferes with emergency call boxes and the National Antenna Consortium claims that BPL within 20 miles of airports and antennas for ground-to-air communications and military bases, and within two miles of hospitals, police stations, and fire stations could cause interference. Can you please comment on this?
.A Glenn
It appears to me that the biggest risk of interference occurs fairly close to the power lines to users who are trying to receive a weak signal on a (un-notched) frequency that a HF-BPL system is using. This generally includes only frequencies in the 4-48 MHz range.
Even those systems reported to interfere the most appear to drop off as one gets a mile or more away. While there may be some situations where one of the licensed users you mention experience interference at greater distances, I wouldn’t expect that to be common. I should also point out that it is still too early to tell what will happen if and when a very large number of BPL systems are deployed and can collectively contribute to interference at large distances. It’s a very difficult problem to analyze and I don’t think the results on that one are in yet.
.Q David
The ARRL’s Ed Hare states "The idea that…one can just put those signals onto any old wire, is not technically supportable." Assuming BPL is technically feasible, please explain, technically, why it’s feasible and further, if not, help us understand where the ARRL’s claims may be wrong.
.A Glenn
As I said earlier, I think that the ARRL has done a good job in providing credible and objective reporting on the HF-BPL systems it has investigated.
I believe that Ed’s comment is very much in line with the description I previously gave of the differences between E-Line and HF-BPL technology. Once the dimensions of a balanced or wire-against-ground transmission line get large compared to a wavelength of the frequency being applied, it stops operating as a transmission lines and starts to operate as an antenna.
HF-BPL is definitely trying to function in a transition region for this type of transmission line and this is what limits the higher frequency operation. Although the FCC has considered the frequency range up to 80 MHz to be BPL, I don’t know of any company that is trying to use the lines above 48 MHz. Basic physics prevents them from being used effectively in this way at much higher frequencies.
.Q David
One of our readers, a very credible Lieutenant Colonel and a veteran of 24 years service with the US Army Signal Corps and two wars, tells us that "BPL will adversely affect military tactical communications since the standard FM radios (35mhz to 75 MHz) used by the Army and Marines are well within the BPL spectrum." This seems pretty worrisome. Can you comment on his concerns?
.A Glenn
Here again, I think it remains to be seen. If HF-BPL deployments continue in the same manner as the trials, I wouldn’t expect the region above about 48 MHz to be affected. If the frequency range your reader quotes is accurate, I would only expect even the potential for interference to occur between 35-48 MHz.
Whether interference is actually experienced would likely depend upon how marginal the communications was to begin with, that is, how weak the signal to be received was, and how close to the BPL lines the military radio was positioned.
.Q David
We are hearing from some extremely credible experts who are going "full goose bozo" against BPL. Usually when there’s such a fuss about something, especially when credible experts are strongly opposed, there’s some foundation in fact. If these experts are wrong, why? What are they missing? And could they possibly be right?
.A Glenn
Well, you’re probably correct that when sincere people are holding extreme and opposite views that the actuality is somewhere in between. But while some may have labeled the ARRL as being in the extremist camp, I personally think that they have come to adopt quite a reasonable position.
For one thing, they have indicated repeatedly that they are not against BPL but rather, against interference caused by BPL. Also, they have offered to cooperate with all BPL vendors in resolving the interference issues and seem to have done so, with good result, in some cases.
Their previous work with the development of the HomePlug standard achieved what seems to have been a very workable solution for all involved.
.Q David
We recently covered the Memorandum Opinion and Order adopted by the FCC on August 3rd to reject the requests by interest groups to limit the service. Now, in that coverage, we noted that it’s not just the amateur radio community, but the aviation industry and broadcasters who were also petitioning the FCC for controls. Shouldn’t we worry that if the aviation industry is concerned about this stuff, we should be, too?
.A Glenn
Yes, I think that widespread interference in the 4-80 MHz spectrum could impact people who don’t normally even know that they care. Not only do many of us use or have connections to those who regularly use the HF spectrum for short wave broadcast listening, public safety and military communications and aviation, but there are less obvious impacts if severe interference were to prevail.
The HF spectrum has some unique characteristics which can’t be replaced. The ability to communicate long distances with simple equipment is one of them. Incidentally, it was amateur radio operators who first recognized the value of this spectrum — at a time when industry and military was occupying lower frequencies because they thought HF was useless.
I’m not certain whether emergency communications from, say, a sailboat in the south seas would necessarily be affected, but it might. Having personally gained so much from having amateur radio as a playground in which to develop my own interest in electronics and engineering, I’d hate to see that eliminated for others.
.Q David
In an earlier article, I posed the question "Where’s the money?" Obviously, DS2 has a financial interest in the success of BPL, as does Corridor. Can you explain where the financial interest in BPL is for industry players? Since you’re also a radio amateur, and I raised the question about where the ARRL’s financial interests lie, perhaps you could also shed some perspective on whether you think the ARRL is approaching this strictly from a technical perspective, or whether there’s a financial or political interest here as well?
.A Glenn
Well, now you’re asking a business rather than a technical question and I may be out of my element. However, to the degree that BPL or any other technology truly addresses and significantly solves the last-mile problem, I think there should be a great deal of industry interest. We are in the Information Age and the delivered bit is the coin-of-the-realm for a great many aspects of modern life. It has a profound effect on our work and on our entertainment. It affects almost all of us socially as well as individually.
As new applications continue to cause data rates rise, such that the minimum acceptable rate delivered to the user increases to first several Mbps and then 100 Mbps and beyond, it will be very interesting to see what kind of techniques are used to support them. One very important application for BPL that seems to be driving a lot of the present interest and investment is for improving the operation of the electrical utility companies and the power grid.
As we, as a nation, consume more power and, in particular, as our peak power requirements soar, the expense of increasing the capacity of the entire grid is pretty staggering. A much preferred alternative is to shift usage patterns so that the peak/average ratio drops.
If energy use can be managed and billed on a real-time basis at the individual level, there is a huge potential for savings. For a variety of reasons, HF-BPL may make a lot of sense for this one application alone. Of course, as one interested in building out a much better alternative to HF-BPL, I would like to see a better technology which has no interference problems and is also capable of handling future individual information needs be adopted.
My opinion is that the ARRL is pretty much WSYIWYG, that there isn’t a major hidden agenda. They seek to represent a large and very diverse membership in the matter of a hobby which is primarily fueled by discretionary interest and resources by the members. It must be a bit like herding cats.
In any group that large, there will be mis-statements and actions which don’t always reflect positively on the organization but, by and large, I think that the ARRL sincerely tries to be what it purports to be: an organization that responsibly represents, supports and promotes amateur radio.
I guess I don’t see any smoking guns.
My initial open letter regarding Corridor’s technology was worded somewhat strongly because at the time, it seemed the ARRL was painting all broadband-over-powerline technology with the same brush, even after I had privately given one of the staff there the heads-up before Corridor’s first technology demonstration and prior to some of the ARRL’s early statements.
Evidently internal communications took a while to percolate, but once they understood the difference they were quite decent about taking E-Line on it’s own merits and offered to be involved in helping assess it’s relationship to amateur radio.
Corridor hasn’t taken them up on the offer yet, perhaps it will before too long. The delay is only because we’ve examined it for ourselves and know there’s no interference there at all, as I reported in the open letter.
I think that, at first, the ARRL may have gone a bit outside the technology issues in their original position but that was probably more of an errant emotional response than a political one. Since then I think they’ve communicated and acted very appropriately.
.Q David
From your description of the capabilities of your own E-Line technology, it looks like it provides good capacity without any interference problems. Can you share with us any more detail on where it’s going and when we might see it available ?
.A Glenn
Well, as I said, getting high speed information to and from the mobile information user is the toughest part of the last-mile problem. But if you can solve that one, you’ve pretty much solved it for the fixed user as well. From the information capacity plot you can see that to get truly high speed data to an end user in a typical suburban environment, it is absolutely essential that the length of the radio path be quite short.
Currently, the most popular model for designing wireless systems is to flood a large area from a central site. This is what the bulk of mobile telephone systems do. But as higher data rates are demanded, this model ceases to remain economical. It takes too much infrastructure and spectrum to provide a multitude of users quality communications in the downstream direction. And, in the upstream direction, user to base, with user transmitter power and antenna size limited to that of portable devices it ceases to even be possible.
An example of this trend can be seen in 3G smart phones. For example, the 3G standard used on my new Treo 700P is called EV-DO. However, in order to achieve a 3G downstream data rate to a user located anywhere within an existing voice coverage footprint, EV-DO requires that the entire output of the cell sector’s transmitter be used.
So, rather than allowing up to ~60 voice users to simultaneously share (and pay for) the hardware, as for a voice call, for high speed downstream data, it has to commit all the transmitter resources to a single user. This means that as additional EV-DO users come into that coverage area, the average data rate is divided down by the number of users who are sharing it.
This over-subscription rapidly makes the 3G services, like rapid Web surfing, streaming audio or video that the user was expecting to experience, impossible. Adding more transmitter carriers can help to a degree, but spectrum is scarce and hardware is not free so this flood-from-a-central-site eventually hits a dead end.
The same general problem shows up with any and every higher speed standard and technique, whether it’s mobile phone, WiFi, WiMax or another standard not yet invented. Longer radio paths in typical environments simply have too much waste to provide economic high speed data.
The only possible solution requires shortening the length of the wireless path. This achieves coverage of a smaller area, thus limiting the data-rate dilution produced by sharing and over-subscription and it reduces the waste and allows a much greater amount of energy to be transferred across the wireless link. Both of these improvements have the result of enabling much greater information rates as well as requiring lower transmitter power, smaller antennas and having longer battery life.
I believe that Corridor’s technology provides a compelling solution to the last mile problem. It can provide very high capacity transport between a fiber termination and a multitude of "emitters" located quite near the end users. These emitters can be located at every power pole if desired, thereby allowing the final radio hop to a portable information device to be both very short and very high capacity.
The characteristics of the suburban radio path shown in the sidebar article assume antennas 20 meters from the ground on one end and 2 meters at the other, which is representative of typical cell bases and users. The attenuation associated with wireless propagation is a very strong function of antenna heights. This is because the heights strongly influence how much foliage and and how many obstacles lie in the path.
By using power poles as the local antenna sites, not only are the radio paths greatly shortened but a ~15 meter high tower is available from which to transmit to the user. Also, because the electronics that attaches to the line near the pole can be so small, there is virtually no visual impact and the zoning issues which in many areas have limited network expansion can be avoided.
E-Line can be very rapidly deployed on existing power lines by crews with a minimum of training at a small fraction of the cost of an aerial fiber installation.
Although there certainly are many applications for Corridor’s technology, solving the last-mile problem for mobile users seems to be one of the best and it’s where Corridor is currently focused. I hope that you and you’re readers will be able to see and experience it first hand very soon.
.BEGIN_SIDEBAR
.H1 Product availability and resources
For more information on Corridor Systems, visit http://www.corridor.biz.
To read Glenn’s sidebar article, visit http://www.computingunplugged.com/issues/issue200608/00001828001.html.
.END_SIDEBAR
.BIO
