.FLYINGHEAD THE COMPUTING UNPLUGGED INTERVIEW
.TITLE A BPL manufacturer responds to all the complaints
.AUTHOR David Gewirtz
.OTHER
.SUMMARY Poor Chano Gomez! When he pitched us an interview on Broadband-over-Powerline (BPL), little did this BPL manufacturer know that he’d be touching off a firestorm of debate. Two months and more than a dozen articles later, Chano’s graciously consented to another interview, this time to answer the charges against BPL from its detractors. We have to give special "props" to Chano. Not only did he agree to step up and answer some tough questions, he also did so while on vacation in Europe. So, special thanks go out to him for taking the time to help us understand this issue more fully.
.OTHER
Poor Chano Gomez! When he pitched us an interview on Broadband-over-Powerline (BPL), little did this BPL manufacturer know that he’d be touching off a firestorm of debate. Two months and more than a dozen articles later, Chano’s graciously consented to another interview, this time to answer the charges against BPL from its detractors.
We have to give special "props" to Chano. Not only did he agree to step up and answer some tough questions, he also did so while on vacation in Europe. So, special thanks go out to him for taking the time to help us understand this issue more fully.
.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 Chano
Before answering that, let me clarify two points: the problem of making general statements about BPL technology and what the real debate is about.
Making general statements about BPL technology is like making general statements about wireless technology, including WiFi, WIMAX, 3G, etc. There are several different vendors of powerline technology, each one with unique characteristics.
Also, the BPL industry has evolved technically and at tremendous speed, with each new generation of products improving over the previous ones, both in terms of interference mitigation techniques and robustness against external interference. Most BPL vendors listen to the feedback provided by the rest of the industry (including the ARRL) and are continuously improving their products.
So, in summary, not all BPL products are the same, and BPL technology from 2001 is not the same as BPL technology from 2006.
After reading some of the comments from your readers, a person could get the false impression that the current debate regarding the BPL industry is based around the claims of two irreconcilable camps, one of them claiming that "BPL is totally safe and does not interfere with any radio service" and another claiming that "all kinds of BPL technology will interfere with existing radio services, threatening emergency service, ham operators, etc."
In practice, all industry experts (including ARRL and BPL vendors) agree on the main principles, although we disagree on specific details.
Let me give an example: we all agree that a BPL system transmitting with a power level of 1000 (arbitrary units, this is an example, after all) would have a 10% probability of interfering with ham radio users while a BPL system transmitting with power level of 1 (arbitrary units) would have a 0.001% probability of interfering. The first example would obviously be unacceptable for the ham radio community, while the second example would make the BPL industry unfeasible.
Even the ARRL would agree that setting limits that reduce the probability of interference to 0% would be unreasonable.
The key here is creating a framework that allows BPL operators to run their networks with reasonable power levels (that guarantee high performance and a very low number of interference cases), but having mechanisms to solve the small number of interference cases that may appear.
So, the question is (and here is where the different camps disagree) is whether the allowed power level should be 100 (interference in 5% of cases), 50 (1% of cases) or 10 (0.1% of cases). The position of the BPL industry is the power levels should be set in a way in which the probability of interference is reasonably low, while allowing the BPL system to operate with reasonably high performance.
We also agree that, once a system is installed and operating under FCC limits, if the BPL system causes interference to a licensed radio user, the BPL operator needs to immediately reconfigure the system to solve the interference. This is a mandate from FCC and we think that’s perfectly reasonable.
DS2 [the company Chano works for, and a key manufacturer of BPL chips] sees this situation as an opportunity to provide differentiation in our products (and here comes the marketing pitch): we think that it’s key that our chips provide the tools that allow equipment manufacturer to:
.BEGIN_LIST
.BULLET Transmit using FCC-compliant power levels.
.BULLET Adapt power levels dynamically.
.BULLET Easily notch out frequencies that cause interference to licensed users, with on-the-fly reconfigurability
.BULLET Get protection in their investment in case future FCC rulings introduce changes in power levels or prohibited frequencies.
.END_LIST
In 2003 (three years ago), DS2 introduced its second Generation powerline chipset, which was the first in the industry to provide speeds up to 200 Mbps, and 40dB programmable notches. These chips have been designed to allow BPL vendors to design equipment that meets FCC requirements, to adequately protect ham radio bands and to provide additional mitigation mechanism in case any isolated interference case is detected in a BPL network. The ARRL lab tested this technology in April this year and issued a favorable review.
.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 Chano
In this area, BPL technology has improvemented dramatically in recent years. As BPL technology providers gain more experience from real life installations, we have added better and more robust algorithms to deal with the typical noise sources found in the BPL frequency band.
If a BPL network is well designed, the probability of a service cut-off due to one of those sources is negligible.
Again, it’s important to differentiate between first generation and second generation products, as second generation products provide huge improvements in reliability.
.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 Chano
I’m not aware of any situation where real interference to those services has been reported.
In any case, in order to be on the safe side, the FCC has taken measurements to provide special protection to critical services and locations. The FCC Report & Order 04-245 on BPL includes the notion of "excluded bands" and "exclusion zones".
BPL equipment operating in overhead lines has to avoid "excluded bands" to protect aeronautical (land) stations and aircraft receivers. Also, BPL equipment operating within a certain distance from coast station facilities or Very Long Baseline Array facilities has additional prohibited frequency bands.
.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, help us understand where the ARRL’s claims may be wrong.
.A Chano
I agree with Ed in many points, but I completely disagree with him on this one. You cannot compare the trade-offs involved in designing a BPL system with the ones involved with other systems, because they are based on totally different assumptions.
When designing a new communication system, the design engineer can decide where he or she wants to put the highest cost, requirements, or complexity: either in the end-points or in the transmission media (the cables). Many communication systems put strict requirements on the cables in order to simplify their end-points. That’s probably a good idea when you don’t have restrictions. Optical communications would be a good example of this.
BPL is on the other side of the trade-off options: we do not have control over what the medium looks like (powerlines are already there, you cannot replace them), so we need to put a lot of intelligence and complexity in the end-points. Because of this, the end-points have been designed to handle the worst possible channel conditions (high attenuation, significant reflections due to impedance mismatch, time-changing characteristics, strong non-white non-Gaussian noise, etc).
To put it simply, when somebody has control over the transmission media, it makes sense to put strict requirements on the media, so that the communication equipment can be made simpler or less expensive.
Going back to Ed’s remarks:
.QUOTE I attended a presentation given by Ron Hranac, a member of the Society of Cable Communications Engineers Board of Directors. Hranac outlined the improvements that need to be made to a well-maintained cable plant to make it work reliabily for broadband use. Things like the phase characteristics and gain flatness of the system need to be closely controlled. The idea that all that really isn’t needed, and that one can just put those signals onto any old wire, is not technically supportable.
Cable-modems are designed to work with cable plants that must satisfy certain characteristics. If the cable network is not well maintained, the effects that Ed mentions can happen (phase distortion, frequency-selective channel frequency response, etc), and most cable modems are not designed to handle it (because that would add extra cost for equalizers, etc).
In the case of BPL technology, we know for sure that most cables will introduce severe phase distortion, non-flat channel frequency response, non-gaussian noise, and a lot of other interesting effects (interesting from the engineering point of view, that is) so the system is already designed to handle it. BPL systems require a lot of complex DSP (Digital Signal Processing) in order to correctly demodulate signals that have been distorted by the medium.
Improvements in DSP technology have allowed BPL technology to reach the performance and reliability that we enjoy today.
.Q David
When I spoke to you during your vacation, you told me that what the ARRL is complaining about was an older implementation of BPL. Can you elaborate on this?
.A Chano
This is related to my previous statement about first generation versus second generation BPL technology. Our second generation BPL technology, introduced in 2003, provides much better interference avoidance techniques than our first generation system. Our second generation system is capable of introducing notches in ham radio bands (and also other frequencies) with a depth of up to 40dB, which is 10 to 15dB better than BPL systems from other vendors.
You can see ARRL’s view of DS2’s second generation technology at http://www.arrl.org/news/stories/2006/03/22/1.
.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 Chano
I’m not an expert on military communication, so I cannot really give an informed opinion here. However, DS2 second generation BPL chipsets use frequencies below 34MHz, so there should be no problems there. I cannot give an opinion on other BPL systems that may use different frequencies.
In any case, as an engineer I would be surprised if a well-designed modern military communication system, that included the latest spread-spectrum anti-jamming techniques, could be interfered by a BPL service. But again, I’m not an expert on that area.
.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 Chano
As I have mentioned before, I think the problem is that many people had a bad experience with older versions of powerline technology, which were based on non-OFDM (Orthogonal Frequency-Division Multiplexing) modulation schemes.
When the first trials of BPL technology started, around seven or eight years ago, BPL systems transmitted high power levels and did not have special mechanisms to protect radio services. As the industry has learned more about the problems found with real installations, it has improved the technology, reducing power levels and providing sophisticated notching techniques to avoid interference.
State of the art BPL technology, like DS2’s 200 Mbps, provides adequate mechanism to avoid interference using programmable notches.
.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 it the aviation industry is concerned about this stuff, we should be, too?
.A Chano
As I mentioned earlier, FCC has identified which services need special protection and has included special mechanism to protect them. BPL equipment operating in overhead lines has to avoid ‘excluded bands" to protect aeronautical (land) stations and aircraft receivers.
.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. In the interests of full disclosure, can you explain how DS2 (and other industry players) stand to benefit from BPL?
.A Chano
Well, in our case, our interest is obvious. DS2 provides the chips that are the core of BPL equipment from many BPL vendors. It’s in our interest to have a reasonable and stable regulation that allows our BPL vendors and service providers to design, sell and deploy their equipment that keeps everybody happy.
.BEGIN_SIDEBAR
.H1 Product availability and resources
For more information on DS2, visit http://www.ds2.es.
For more information on ARRL’s view of DS2’s second generation technology, visit http://www.arrl.org/news/stories/2006/03/22/1.
.END_SIDEBAR
.BIO
