xMax and the “cloak of secrecy”

Given my promise to respond to questions I feel obligated to respond to a number of recent e-mails about xMax, even though my interest in this topic is rapidly decreasing. The point these e-mail were making is that because XG Technology has been keeping the details of xMax under wraps, it is not possible for an outsider to evaluate the viability of the technology, and therefore my xMax related postings must be unfounded. This is simply not true for the following reasons.

First, it should be firmly understood that one can make statements which apply to any communication system. The performance of communication systems is limited by the presence of noise, and the availability of signal power and bandwidth. Surely it is not too difficult to understand that given a finite amount of resources (power, bandwidth) and the inevitable presence of noise, there are limits on what can be done. These limits are well established and well understood by communication engineers, and have been for many years. These limits apply to any communication system, past, present or future, and they can be stated without knowing anything about the details of any particular system. My posts on “xMax meets Shannon”, “xMax meets Shannon once again”, and “xMax and waveform communication”, attempted to discuss these limits and show that one of their consequences is the immediate refutation of the performance claims made about xMax.

Second, it should be noted that some information about xMax performance (not design details) is readily available on the web. The operating parameters of several experiments/demonstrations have been presented by XG Technology. Any competent communication engineer can analyze these data and draw the conclusion that the xMax performance claims are not supported by the published data. There is no need to know anything about how the xMax technology works in reaching these conclusions, because the point of the analysis was that conventional systems operating under the same conditions will also provide the reported performance. In other words what we need to know to reach these conclusions is the performance characteristics of conventional communication systems, not how xMax operates.

Given the available evidence it is very clear that the xMax performance claims are false. Knowledge of the details of how xMax operates can not change this fact. Such knowledge can only be useful in revealing the precise conceptual flaws which lead the xMax developers to believe that their claims are true. One can make a fairly good guess at the nature of these conceptual flaws from reading the patents and various statements by Mr. Bobier. However, no such guessing is needed to refute the published xMax performance claims. The only thing that the continued “cloak of secrecy” is accomplishing is the perpetuation of these unfortunate conceptual errors. It is too bad they are not seeking opposing views. They should be aware of the old saying:

“If anyone can show me, and prove to me, that I am wrong in thought or deed, I will gladly change. I seek the truth, which never yet hurt anybody. It is only persistence in self-delusion and ignorance which does harm.”
–Marcus Aurelius

I should once again emphasize that there is every reason to believe that the xMax technology works. My comments are only meant to explain that its performance is not and can not be better than that of conventional systems. Nor am I making any comments or predictions about the business aspects of this technology. I am only addressing purely technical issues.

xMax and the media

Media reporting of science and technology is in general notoriously poor. Media coverage of xMax is no exception. With depressing consistency these reports present the story given to them by XG Technology with no attempt whatsoever at a critical evaluation or a balanced presentation of differing points of view. At best there are some token statements about the fact that the technology is yet to be fully proven, or some other vague comments designed to give the illusion of being even handed.

It is not difficult to understand why this is so. The journalists and reporters are not, and can not be expected to be, experts on the technology which they are writing about. So they can not make any reasonable assessment of the technology of their own knowledge. They must rely on “the kindness of strangers” in order to form an opinion. To get a balanced coverage is quite difficult. You need to identify and contact a number of independent experts in the specific technology area, convince them to invest the time and effort to study the technology in question (for free!), and to present the results to you in a language comprehensible to a layman. You then need to understand and organize all that information in a way that would be understandable to the reader. This is a lot of work. On the other hand, you could just paraphrase the material handed out by the company, add a few obligatory non-specific statements on the need for caution, and be done with it in a jiffy. So guess which approach you are most likely to take?

Another important force operating here is that the media naturally wants to write about stories which are interesting. Now a story which talks with unbridled enthusiasm about an exciting revolutionary technology which is going to change life as we know it , is far more interesting that a story which discusses the technology in a calm, fair and balanced manner. Hmmm, you have to choose between the exciting and the boring – I wonder what you will do …

There are some exceptions to this rule. Consider for example a recent article by Peter Judge on the xMax technology. Some of his earlier articles were also more balanced than most. Sadly such exceptions are few and far between.

Wi-Fi Wants to Kill Your Children

On the dark side of wireless the reader is advised to browse Ben Goldacre’s wonderful BadScience discussing a recent BBC program on the dangers of WiFi . A recent Yahoo article “Wi-Fi smog threatens Britain’s school kids” is also worth reading. There is no reason to panic however. You can make your own tin-foil hat to protect you from the evil WiFi, or buy a “professional” model.

Have you been feeling dizzy lately? Getting headaches? Now you know why … (especially if you are elecrosensitive )

The ultimate in wireless access

Well, I have finally seen the ultimate solution to “wireless broadband anytime anywhere”. Brought to you by the folks at DARPA. In a current request for proposal they describe a collection of robotic wireless routers with tank treads called Landroids:

They would be dropped in urban warfare areas and would move around on their own to blanket an area with wireless coverage. These units would be disposable, meaning if one gets blown up, the others will rearrange themselves to make up for the loss of coverage.

Now the civilian use is obvious. We can each have a Landroid follow us around wherever we go, guaranteeing that we will never be out of WiFi range! This gives a completely new meaning to the concept of mobile wireless communications ….

Move over 4G, here come the Landroids.

A Technology Breakthrough (part 1)

Our company is introducing a new technology which will revolutionize the wireless industry as we know it. It is expected to replace 3G/4G at a fraction of the cost and provides 100X performance compared to existing systems. Details to be announced in an upcoming press conference.

All of the major cell phone companies have started discarding their existing phones which are now obsolete in view of our revolutionary technology.

xMax “disclaimer”

Because I seem to be writing quite a few posts about xMax, let me make the following “disclaimer”. I have no interest in or connection to XG Technology, nor do I stand to gain or lose financially from this company’s success or failure. My interest in xMax is purely technical/scientific. I have been interested in communications most of my life and know quite a bit about the topic, both theory and practice. I got interested in xMax a couple of years ago when a friend sent me a link to an article which claimed that xMax requires orders of magnitude less power than conventional techniques. I have been following the story since then because it is such a fascinating combination of truth and fiction. The truth being that this is an unconventional modulation technique which certainly should work. The fiction being the highly exaggerated performance claims which seem to be based on some fundamental lack of understanding of communication theory by some of the people involved.

Another thing that happened a couple of years ago is that I gave a number of talks on “Wireless Facts and Fiction” which addressed other (non xMax related) extraordinary claims prevalent in the wireless industry. As a result, quite a few people know me, and some of them have been sending me questions about xMax and other technologies which make “incredible claims”. Instead of answering them individually I thought it would be easier and better to do this by starting this blog. The focus of this blog is not on xMax but on “Wireless Fiction” in general. However, as long as I get questions about xMax I will try to respond. Hopefully this topic will gradually disappear once reality rears its ugly head ….

xMax performance claims can be easily tested. Why aren’t they?

In an earlier post I said

“There are, of course, standard ways to evaluate the performance of any digital communication system. The most basic one is to measure the bit-error-rate (BER) of the system for different signal to noise ratios at the receiver. The BER vs. SNR (or BER vs. Eb/N0) plots for conventional communication techniques, both measured and theoretical, appear in numerous books, papers and reports. Having an independent laboratory measure the BER vs. SNR plot for xMax would immediately establish its performance relative to existing techniques in a direct and convincing manner. This is a simple and completely routine test. It should be noted that this type of performance curve provides no information about the design or the internal workings of the communication system. Thus, concerns about revealing intellectual property related to the communication system are not a legitimate reason for avoiding publication of such results.”

I received a number of inquiries about this paragraph, so let me elaborate a bit.

Explanations of what is Eb/No can be found on Wikipedia and elsewhere on the web and of course in any standard text on digital communications. The useful aspect of Eb/N0 is that it allows a simple comparison of different modulation because it involved only the energy per bit (Eb) and the noise spectral density (N0) which is simply the noise power per Hz. In particular, Eb/N0 can be used to compare communication systems with different channel bandwidth and symbol rates.

An example of a BER vs. Eb/N0 curve is given by

The vertical axis shows the bit-error-rate and the horizontal axis the Eb/N0 (normalized SNR) values. The figure shows the BER curves for three conventional modulation techniques. This type of graph is the standard performance measure used to evaluate digital communication systems. You can find a very large number of examples of these curves for conventional communication systems. There is test equipment specifically designed to measure this curve, but it can also be measured by standard RF laboratory equipment.

The points I was trying to make related to xMax are:

(i) So far they did not publish this standard performance curve, which would establish immediately and conclusively the claimed performance advantage of xMax. If xMax has the claimed power efficiency its BER curve would be shifted significantly to the left of corresponding BER curves for conventional systems.

(ii) This type of curve reveals absolutely nothing about how the given communication system is designed. It is not possible to “reverse engineer” anything from this curve. Thus, concerns about revealing intellectual property can not be the reason for not publishing this type of curve.

Given the extraordinary nature of the xMax claims and the ease with which these claims can be verified or falsified (without revealing any technology secrets), it is puzzling, to say the least, that such a standard performance benchmark is not readily available.

Now it is possible that this information is available and I am simply unaware of it. I would appreciate if a reader aware of such information will point me to the source.

xMax and waveform communications

The XG Technology web page states that “xG Flash Signal uses breakthrough single cycle modulation to deliver longer range and lower power RF communications. Single cycle modulation is implemented when individual sinusoidal cycles of RF energy are modulated to represent one or more bits of data.” While a detailed description of the “breakthrough single cycle modulation” is not available, examination of some of the related patents by J. Bobier (such as (i) “missing cycle based carrier modulation”, Patent no. 6968014, dated 11/22/05; (ii) “suppressed cycle based carrier modulation using amplitude modulation” Patent no. 6901246, Dated 5/31/05; (iii) “tri-state integer cycle modulation”, Patent no. 7003047, dated 2/21/06) is quite revealing. To understand what is revealed we need to present a bit of communication theory, so here goes.

All digital communication systems involve waveform communication, that is to say, the information to be transmitted is encoded in a set of waveforms. Let us say that you want to transmit bits. If the bit value is `0′ you transmit one waveform, and if its value is `1′ you transmit a second waveform. Different modulation techniques use different waveforms. The two waveforms may have different shapes (e.g. orthogonal modulation, FSK), or the same shape but different amplitudes and phases (QAM, PAM, PSK). At the receiver the communication signal is passed through one or more matched filters. The function of the matched filter is to reduce the noise and to discriminate between the transmitted waveforms (if they have different shapes). It is well established that in the presence of Gaussian noise, the optimal receiver (i.e. the receiver which has the best possible performance) will use matched filters.

Now here is the interesting part for our discussion. The performance of the communication system does not depend on the actual shape of the waveforms used, only on some high level properties. Specifically, their energy (power times duration), bandwidth, and the correlation or “angle” between two waveforms. For example, if you use a given waveform (for `0′) and the negative of that waveform (for `1′) we say that there is a 180 degree “angle” between the two waveforms. If you use orthogonal waveforms (e.g. two sinusoids with appropriately chosen frequencies) we say that there is a 90 degree “angle” between the two waveforms. These three parameters: energy, bandwidth and “angle”, are all we need to know about the waveforms. If you look in standard textbooks on communications, even relatively old ones such as the book by Wozencraft and Jacobs (later of Qualcomm fame) “Principles of Communication Engineering” 1965 , you find that this observation is made early in the book and the shape of the waveforms then “disappear” from further discussion. This is important because there are an infinite number of waveforms which have the same energy, bandwidth and angle, but because they all have the same receiver structure and  performance there is no need to discuss them separately.

Conventional communication systems have chosen particular sets of waveforms which were easy and cheap to implement. For example, a BPSK system uses a part of a sinusoidal waveform whose phase is 0 or 180 degress depending on the value of the transmitted bit. However, there is nothing to prevent someone from using completely different unconventional waveforms – after all there is an infinite set to select from! Of course the performance of the system which uses the new waveform will be the same as that of systems using other waveforms with the same energy, bandwidth, and “angle”.

Bobier’s patents propose a particular class of such unconventional waveforms. The different patents present variations on the basic theme of modulating a single cycle at a time, instead of a large group of cycles. How novel are these waveforms is unclear, but that is not really important here. The statements made in these patents reveal a lack of understanding of the fundamental equivalence of communication techniques which use very different waveforms with the same energy, bandwidth and “angle”. The inventor seems completely unaware that there are an infinite number of such waveforms yielding the same performance, and that he has chosen just one of them. My conjecture is that this misunderstanding has to do with the inventor’s lack of mathematical background (however, not having met or talked with the inventor this is only a conjecture). The language of mathematics is needed to abstract the problem so that one can see and understand the essential equivalence of practical engineering implementations which look very different in their details, but are just different faces of the same coin. In my consulting activities I have seen this problem more then once where otherwise creative and highly competent engineers were unable to understand important concepts which required this level of abstraction.

So what should we conclude from this about xMax? There is no reason to doubt that is uses an “unconventional” waveform (although it seems closely related to the VMSK idea) , and that it does work. At the same time there should be no doubt that its performance can not be better than that of “conventional” well established communication techniques. The claim that a new modulation technique (i.e. a new waveform or set of waveforms) can provide large performance gains is certainly false, and shows some basic misunderstanding of well known and well established principles of communications.

xMax meets Shannon once again …

I have received several inquires related to my post “xMax meets Shannon” which indicate that I may not have been sufficiently clear in my explanation of the relevance of the Shannon theorem to the claims made about xMax. So let me try one more time, intended to be my last.

It is now almost 60 years since Shannon published “A Mathematical Theory of Communications”. He actually presented a number of important results, not just one. Here we consider what is often referred to as the Shannon-Hartley theorem which establishes the channel capacity for a finite-bandwidth channel subject to Gaussian noise. The theorem states a relationship between the maximum data rate which can be reliably transmitted, the bandwidth occupied by the communication signals, and the ratio of the received signal power to the noise power, or SNR (for signal to noise ratio). The received signal power depends on the transmitted power, the path loss (representing how much power is lost during the trip from transmitter to receiver), and the gains of the antennas used by the transmitter and receiver. The noise power referred to here is the electronic noise generated in the circuitry of the receiver. The nature of this noise is very well understood and its power can be easily calculated. It turns out that this power is proportional to the bandwidth.

Consider a scenario where we want to communicate from point A to point B using a given set of antennas. In this case the received power is some fixed fraction of the transmitted power. If we want to double the received power, we must double the transmitted power. For simplicity assume we have fixed the bandwidth (for example, we are allocated a channel with a given bandwidth by the FCC). Then the noise power is also fixed. In other words the SNR depends entirely on the transmitted power.

Going back to the Shannon theorem – its implication can now be stated as follows: the maximum data rate which can be reliably transmitted is limited by the SNR at the receiver, or equivalently by the transmit power. For a given transmit power there is a maximum data rate you can achieve and no more. Conversely, for a given desired data rate there is a minimum transmit power you need, and you can not do with less.

It should be emphasized that this constraint is an absolute mathematical fact. It does not depend on the specific design of the communication system. This notion of an absolute limit seems to be a difficult for some people to grasp (or perhaps to accept), so let me try to illustrate it by an analogy.

Let us say that we want to travel from point A to point B using some vehicle. Assume that the shortest distance (as the crow flies) between the two point is D and that the vehicle has a maximum speed of V. It follows that the travel time must be larger than D/V. This is true regardless of what route you choose or what kind of vehicle you use. In other words D/V is an absolute lower limit on the travel time. In an analogous way, the Shannon theorem provides an absolute lower limit on the amount of transmit power in the scenario discussed above. Because we all have experience with traveling from point A to point B, it is easy to accept the minimum travel time constraint. However most people have not studied communication theory nor the Shannon theorem, and they often find it difficult to accept the minimum required power constraint.

Now here is where it gets relevant to the xMax discussion. Over the years engineers have developed increasingly sophisticated high performance communication systems. Current systems are power efficient, i.e. they operate close to the power constraint discussed above. In other words, to deliver a given data rate they require a transmit power which is close to the minimum required power. This does not mean that further power reductions are impossible, only that such improvements must be small, because there is not much room left. Reducing the required power by, say, a factor of 5, may be possible, albeit very difficult.

So when one evaluates a claim such as “xMax can use 1,000 to 100,000 times less power than comparable transmission technologies”, one can say with outmost certainty that this claim is false. One does not need to know a single thing about how xMax works in order to reach that definitive conclusion. To use the earlier analogy: if someone tells you they developed a new revolutionary vehicle which has a top speed of 60 MPH and can travel from San-Francisco to Los-Angeles in 2 hours, you can dismiss their claim out of hand even if you know nothing about the design of the vehicle or the route they plan to travel.

Well, off course they could load the vehicle on a 747 at SFO and land it LAX, but that is another story :=)

Wild Wireless

When it comes to really wild wireless ideas, consider Gaiacomm International Corporation. On its welcome page we read that the company will be “Bringing the next generation of global wireless communication technology to life. Gaiacomm International Corporation is committed to developing an Earth-friendly 4G specification that will transform communication technology worldwide”. So far so good. We then learn that “Our goal is to have data rates up to 100 Tbps, tera-bits-per-sec. New design techniques, however, are needed to make this happen at our desired target of one-tenth the cost of 3G.” A Terabit, in case you don’t happen to know, is a thousand Gigabits, or a million megabits. It certainly is a lot of bits. Among the publications on their web site we find a fascinating interview with Frost & Sullivan and a document titled 4G Wireless Communication. We also note that Frost & Sullivan Honors Gaiacomm International with 2004 Wi-Max Technology Innovation of the Year Award! Continuing to read we find statements such as:

“GWC is intended to provide high speed; high capacity, low cost per bit, IP based services, fiberoptic wireless connection and a truly global wireless communications system operating in frequency ranges that surpass all other telecommunication companies on planet earth.”

“[Our technology] will allow enlightened minds to devote themselves into other areas of intellectual and technical enquiry. By encouraging a transparent exchange of information, peace and goodwill will undoubtedly be fostered.”

“Gaiacomm International Corporation has developed and refined a communications system that is virtually wireless on all fronts. By using the natural frequencies generated by the Earth and other bodies, Gaiacomm determined that it is scientifically possible globally to transmit a signal of any strength to all parts of the planet up to and including inner space and outer space. In all respects, this means that a form of sub-space communications has been discovered using the governing dynamics existing in the electromagnetic spectrum that radiates globally and interstellar in all forms, including the sought after ‘Dark Matter’ radiation.”

“Numerous business markets, both vertical and peripheral, will flourish because Gaiacomm exists. Which is to say, that because of the power that Gaiacomm’s terahertz technology will provide, and the inadequacy of 3rd Generation wireless technology to meet the needs of the marketplace, a move from 3G developments to 4G will occur rapidly once the opportunities for new applications, and new features for old applications, becomes evident. Now there has been heavy investment in 3G, and many will resist at first, but soon even the most obstinate of these businesses will come to accept that trying to build on the backbone of 3G wireless symbolizes a pointless tussle with the obsolete.”

“What is unique about Gaiacomm’s value proposition for the wireless communication sector? Our Antennae/Amplifiers cover a broadcast range of five million square surface miles, using the magnetic fields of the earth. Our name, in fact, Gaiacomm, is the combination of telescoping two words — “Gaia”, the Greek word for earth or earth-friendly, and “comm”, short for communications — to derive its message of using the natural properties of the planet to enable telecommunications. With nine of these Antenna/Amplifier towers and 27 attendant CRITERIA towers (3 per A/A tower) to handle billions of calls and data transmissions, there will not be a place on the earth, or below it, that cannot be served. And due to the strength of its near infrared spectrum wavelength, no natural impediments or physical barriers will disrupt the signal in any measurable form. Some day in the not-too-distant future, those born today will view old Verizon commercials — the ones with the catchphrase, “Can you hear me now?” — and they will ask incredulously, “What was that all about?” “

This is pretty powerful stuff – no false modesty here!  Now GWC is not claiming that it has this technology available (or does it?). It apparently was seeking funding to develop the technology. One wonders what happened to this revolutionary technology since 2004.