My Antenna is Bigger than your Antenna

Have you seen the Wireless Antenna disguised as a Fir Tree a sort of urban utility scarecrow. In today’s communication world antennas are frequently hidden or masked.

(Image links from Google)

My parents talk about the Over the Air antenna that used to dot roofs or Rabbit Ears on the TV table top. Cell phones and cordless phones had their own visible antennas as did car radios..

Antenna’s are categorized by their size, type and functional design. Passive antennas are the most basic kind and do not amplify the signal in any way they simply radiate the RF energy received from a transmitter in one direction. Active antennas are basically passive antennas with an amplifier built-in.

Size and shape of an antenna depend on the frequency on which the antenna will transmit and receive signals. The direction of the radiated electromagnetic wave and [ower with which the antenna must transmit. Antenna size is inversely proportional to the wavelength it is designed to transmit or receive. Lower frequency signals require larger antennas

There are two major kinds of antennas – directional antennas and omni-directional antennas. The latter are used to transmit and receive signals from all directions with relatively equal intensity whereas directional antennas transmit a signal in one direction only.

Distance between the transmitter and receiver generally determines the strength of the signal. Antenna performance is measure of how efficiently an antenna can radiate an RF signal that ensure maximum signal strength at the receiver.

Antennas emit signals in two dimensions horizontally and vertically. Antenna polarization is the orientation of the wave leaving the antenna. Vertical polarization

Sine waves travel up and down when leaving antenna. Horizontal polarization

Sine waves travel from side to side on a horizontal plane. Most efficient signal transmission and reception is experienced when both antennas are equally polarized

The height and location of the antenna and distance between transmitter and receiver are the critical variables in of “line of sight” versus “non-line of sight”. There are 3 RF waves types defined - Ground waves that follow the curvature of the earth. Sky waves that bounce between the ionosphere and the surface of the earth. Finally, line-of-sight used by RF waves transmitted in frequencies between 30 MHz and 300 GHz. Directional antennas are the most common and reliable method of transmitting RF waves. Antennas for mobile hand held devices have evolved since their introduction

Whips Retractables Stubbies Embedded

Reduction in size and appearance of the antenna (internal or external) has introduced more complexities. Last year, we had an Antenna-gate [ http://www.pcworld.com/article/201297/apples_iphone_4_antennagate_timeline.html ] . The suffix to this news worthy story became clear only when I finally grasped the context of President Nixon’s cover up and connected the dots. Most of the news stories that covered this issue discussed how the bars on the iPhone4 changed based on the grip. Steve Jobs even hosted a complete press conference on this issue.

http://www.anandtech.com/show/3794/the-iphone-4-review/2

The link above from the AnandTech blog discusses how attenuation gets measurably worse depending how you hold the phone. Squeezing it really tightly, you can drop as much as 24 dB. Holding it naturally, I measured an average drop of 20 dB. The article also discusses how the iOS reports the quality metric with a compressed, optimistic dynamic range. On iOS, 4 bars begins at around -99 to -101 dBm. Three bars sits around -103 dBm, 2 bars extends down to -107 dBm, and 1 bar is -113 dBm. To give you perspective, for a "3G" plant, -51 dBm is the best reported signal you can get - it's quite literally standing next to, or under a block away from a tower. At the other extreme, -113 dBm is the worst possible signal you can have before disconnecting entirely. With a few exceptions, signal power as low as -107 dBm is actually perfectly fine for calls and data, and below that is where trouble usually starts. However, the article notes just how little dynamic range iOS 4 has for reporting signal; over half of the range of possible signal levels in dBm (from -99 dBm to -51 dBm) is reported as 5 bars

The technical explanation for drop in signal written in the article notes is because humans are mostly water and material which happens to be pretty good at attenuating RF - thus increasing path loss between the handset and cellular base station. There's nothing Apple or anyone else can do to get around physics, plain and simple. It's something which demonstrably affects every phone's cellular reception.

Let's Make Some Noise

In The Bell System Technical Journal, Vol. 27, pp. 379–423, 623–656, July, October, 1948, Claude Shannon a mathematician and engineer wrote a simple and foundational paper called “A Mathematical Theory of Communication," [http://cm.belllabs.com/cm/ms/what/shannonday/shannon1948.pdf ]. The article is prefaced by Warren Weaver's introduction, ``Recent contributions to the mathematical theory of communication”. Together the contributions were called the “Shannon-Weaver model of communication”.

Claude Elwood Shannon is famous for having founded an entire new field called information theory with this one landmark paper. He also has numerous contributions to digital computer and digital circuit design, when, as a 21-year-old master's student at MIT, he wrote a thesis demonstrating that electrical application of Boolean algebra could construct and resolve any logical, numerical relationship. It has been noted in Wikipedia that this was the most important master's thesis of all time.

The Shannon-Weaver model is simply and elegantly designed to define the effective communication between a sender and receiver. Also defined are variables which affect the communication process and labeled “Noise”. The model simplifies the definition of key communication channel components like Information source, transmitter, Noise, channel, message, receiver, channel, information destination, encode and decode.

The noise classifications common to the communication channels (wired and wireless) include Thermal Noise, Intermodulation noise, Crosstalk and Impulse Noise. The definitions in the book (Fundamentals of Telecommunications, Second Edition 2005, Roger L. Freeman) describe each of these types.

Thermal Noise is a function of temperature that excites electrons and is a noise source that cannot be eliminated. The noise is quantitatively expressed as amount of thermal noise to be found in a bandwidth of 1Hz in any device or conductor is:

N0=noise power density in watts per 1 Hz of bandwidth

k=Boltzmann's constant=1.3803 x 10-23J/K

T=temperature (in Kelvin)/absolute temperature

Intermodulation noise is variant that is created when signals with different frequencies share the same medium. Interference is caused by a signal produced at a frequency that is the sum or difference of original frequencies. This is a noise type that can be estimated if the variables are known and can be removed.

Crosstalk noise is an undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or channel, to another. It is a phenomenon by which a signal transmitted on one channel creates an undesired effect in another channel. This is also a noise type that can estimated if the coupling and variables are precisely known. In real world these are typically not known. Crosstalk can be minimized and there are many optimal transmission techniques used to cancel crosstalk.

Impulse noise is an irregular, non-deterministic spike of noise pulses. These are defined as function of duration and high amplitude. They are Generally caused by external electromagnetic interference sources in the communications system such as power surges etc. They are common and if characterized accurately the impacts of impulse noise on data transmission or communication can be minimized by various forward error correction (FEC) coding techniques.

Wireless Pathways

Have you stared at the bars on your wireless phone or the strength of your Wi-Fi signal and wondered why it keeps changing and what could make your bits fly a little faster. As much as I love being un-tethered and the freedom of using my laptop or phone anywhere, I sometimes miss the predictable performance of the trusted thin blue Ethernet cable. How do the laws of physics explain the difference between the two mediums? What are the considerations to establish a reliable wireless link?

First the channel of communication over a wired connection operates in a more shielded (for interference) environment that attenuates at a slower rate. Attenuation is defined in Wikipedia as the gradual loss in intensity of any kind of flux (energy) through a medium (either cable or wireless). (The reference to flux reminded me immediately of Doc Brown’s invention of the Flux Capacitor used in the DeLorean Time Machine from the film, Back to the Future.(http://en.wikipedia.org/wiki/DeLorean_time_machine#Flux_capacitor but I digress …) Wireless channels of communication are generally in a shared environment exposed to interference and also increased “attenuation”. My respect for the blue thin cable just went up.

To understand a wireless channel, I had to first visualize the path a wireless signal takes from transmitter to receiver. There isn’t a single path dedicated to the signal but is defined in a two spatial scales of multi-path fading. The first is large scale fading of the signal based on path loss (attenuation) and shadowing. The second is small scale fading based on multi-path fading and Doppler effects.

(Source: digitalradiotech.co.uk)

Path loss in this context (or path attenuation) is defined as the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. Path loss may be due to many effects of the signal, such as free-space loss, refraction, diffraction, reflection, aperture-medium coupling loss, and absorption. As can be observed in the figure path loss is also influenced by terrain contours, environment (urban or rural, vegetation and foliage), propagation medium the distance between the transmitter and the receiver, and the height and location of antennas. Path loss can be estimated through various models – simple ones and complex ones. The base model which is also called “free space” loss model is considered too simplistic for use and the original Maxwell’s equations are too impractical for the real world conditions. The models in use are hybrids of empirical models and theoretical models with many approximations.

Wikipedia also defines deterministic methods based on the physical laws of wave propagation are also used; ray tracing is one such method. These methods are expected to produce more accurate and reliable predictions of the path loss than the empirical methods; however, they are significantly more expensive in computational effort and depend on the detailed and accurate description of all objects in the propagation space, such as buildings, roofs, windows, doors, and walls. For these reasons they are used predominantly for short propagation paths.

Professor Rajaraman’s CSG 250 course materials from Northeastern University (www.ccs.neu.edu/home/rraj/Courses/.../TransmissionFundamentals.ppt) describe the effect of multi-path fading in two ways. First, multiple copies of a signal may arrive at different phases. If phases add destructively, the signal level relative to noise declines, making detection more difficult. Second, Intersymbol interference (ISI) is caused when one or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit.

Wireless Patent Gold Rush – Back to the Future

The stock soared 7 fold supported by a patent war chest and powerful backing of the industry giants of the day. Are you thinking Apple or Google? Well, this isn’t 2011, it is 1900 and the Marconi Wireless Telegraph Company, Ltd. began thriving in the stock markets, run by a young Italian inventor backed by Edison and Andrew Carnegie. These facts are fascinating especially in the context of 2011.

As was documented in the PBS history series on inventors http://www.pbs.org/tesla/ll/ll_whoradio.html ] The roots of the invention can be traced to Tesla and his design of coils that transmitted and received radio signals when they were tuned to resonate at the same frequency. When the coil was tuned to a signal of a particular frequency it magnified the incoming electrical energy through resonant action. Tesla filed his basic radio patent applications in 1897. They were granted in 1900, giving him the earliest rights to one of the greatest inventions of the era.

Marconi's first patent application in America, filed on November 10, 1900, was turned down. Marconi's revised applications over the next three years were repeatedly rejected because of the priority of Tesla and other inventors.

The vagaries of the patent office caused an about turn in 1904 and gave Marconi a patent for the invention of radio. As the story from PBS states, the reasons for this were never fully explained, but the powerful financial backing for Marconi in the United States suggests one possible conspiracy theory. Add insult to injury, Marconi won the Nobel Prize in 1911.

Tesla turned around and decided to fight in the courts. He sued the Marconi Company for infringement in 1915, but because of poor financial conditions he was unable to fight the case adequately. Despite many setbacks he was hopeful that he would eventually prevail. It wasn't until 1943 that the U.S. Supreme Court, in the court case “Marconi Wireless Telegraph Co. of America v/s United States,” upheld Tesla's radio patent number 645,576 (1897) over Marconi’s patent number 763,772 (1904). The Court had a selfish reason for doing so: the Marconi Company was suing the United States Government for use of its patents in World War I. The Court simply avoided the action by restoring the priority of Tesla's patent over Marconi. Tesla was not around to savor the vindication- he had died a few months earlier.

Here we are in 2011, a consortium of Silicon Valley companies including Apple successfully bid for important patents from the wreckage of a bankrupt company called Nortel. The losing bid was from another company called Google. Google is fighting back by buying patents from IBM and others. Also, calling attention to the collusion by Apple and its partners Microsoft and Oracle. [ http://arstechnica.com/tech-policy/news/2011/08/google-publicly-accuses-apple-microsoft-oracle-of-patent-bullying.ars ]. Meanwhile, the Justice Department is investigating the bids to see if there are any anti-trust implications and the sale was not done to hobble competition.

The patent wars of the 21^st century may well be underway. The patents from financially bankrupt companies and inventors will be the weapons of choice. Will history repeat itself at the Supreme Court and Patent Office?

Look Mom, No Wires!

In just the last few years, I have been experiencing the joy of being un-tethered every time we change a gadget that was previously connected to cables and unshackle it. It began with the first wireless phone in our home, then all our laptops and then the gaming console to our printers and AV speakers and then our TV set top box to the tablets and smart phones… at any given time over 7 devices are all using the airwaves to do their special “thing”. What were the original inventions and discoveries that paved the way to what we take for granted today? Was there a Eureka moment and a single inventor to thank? I began a little research, double clicked my way through many links and realized it is a path that is rich in theory, helped by many different accidental discoveries and stirred by lot of contentious debates.

Wireless telegraphy was the killer app of the day during the decades from 1897 to 1920. The term originated to describe primitive electrical signaling without the electric wires to connect the end points. The intent was to distinguish it from the conventional electric telegraph signaling of the day that required wire connection between the end points. The term was initially applied to a variety of competing technologies based on the theory of information transfer with radiant waves. The communication messages encoded as symbols largely grew as Morse code transmissions with electromagnetic waves.

While it may naively appear to have been a simpler time and the golden age of inventions, it was no less contentious than today’s competitive playing field. Theories and practice were vigorously challenges and debated.

In 1878 British scientist (http://en.wikipedia.org/wiki/David_E._Hughes) David E. Hughes noticed that sparks could be heard in a telephone receiver when experimenting with his carbon microphone. He developed this carbon-based detector further and eventually could detect signals over a few hundred yards. He demonstrated his discovery to the Royal Society in 1880, but was told it was merely induction, and was forced to abandon further research.

Between 1886 and 1888, Heinrich Rudolf Hertz demonstrated the transmission and reception of the electromagnetic waves predicted by Maxwell and intentionally transmitted and received radio ( http://en.wikipedia.org/wiki/Invention_of_radio ). Hertz changed the frequency of his radiated waves by altering the inductance or capacity of his radiating conductor or antenna, and reflected and focused the electromagnetic waves, thus demonstrating the correctness of Maxwell's electromagnetic theory of light. Hertz’s setup for a source and detector of radio waves (then called Hertzian waves[33] in his honor) was the first intentional and unequivocal transmission and reception of radio waves through free space. Famously, he saw no practical use for his discovery

As the Tesla Society notes (http://www.teslasociety.com/radio.htm) early as 1892, Nikola Tesla created a basic design for radio. On November 8, 1898 he patented a radio controlled robot-boat. Tesla used this boat which was controlled by radio waves in the Electrical Exhibition in 1898, Madison Square Garden. Tesla's robot-boat was constructed with an antenna, which transmitted the radio waves coming from the command post where Tesla was standing. Those radio waves were received by a radio sensitive device called coherer, which transmitted the radio waves into mechanical movements of the propellers on the boat. Tesla changed the boat's direction, with manually operated controls on the command post. Since this was the first application of radio waves, it made front page news, in America, at that time.

Many think of Guglielmo Marconi as the father of Radio and Tesla is unknown for his work in radio. Marconi claimed all the first patents for radio, something originally developed by Tesla. Nikola Tesla tried to prove that he was the creator of radio but it wasn't until 1943, where Marconi's patents were deemed invalid; however, people still have no idea about Tesla's work with radio.

So when you hear about Tesla today and a visual of a red electric convertible roadster ( http://www.teslamotors.com/ )comes to mind also thank him for the Cell phone and Bluetooth accessories needed when you are in the car.

Yes, I Think He Did Invent the Internet

This past summer, I got to read two papers on the Internet and more quaintly they were titled “Man-Computer Symbiosis” and “The Computer as a Communication Device”. http://memex.org/licklider.pdf. The common link for the two papers was the author Dr J.C.R Licklider. http://en.wikipedia.org/wiki/J._C._R._Licklider The first paper was published in 1960 and the second in 1968.

My reaction at first when I got the two white papers was that they would put me to sleep. I was wrong. These papers were written in a simple and elegant way that endeared me to appreciate the premise of the two papers. Even more remarkable was the vision of the two papers. Beyond the technical vision of the applications was a section in the second paper that simply titled “Who can afford it”. It went on to discuss the concept of “on line” communities and said what good is it if it cannot be afforded by all. The papers did end on an optimistic tone that effectively predicted the need for a “Moore’s law” and its extension into Communication [ http://en.wikipedia.org/wiki/Moore%27s_law ] . Worth noting that Gordon Moore had not conceived of Intel yet.

Many if not all the technical visions of this paper and others projects from the early days of the Internet have been realized at least at one layer. One may even argue that the promise to make the technology within economic reach of the urban global citizen has been realized.

The fact remains that there is a vast swath of rural America and the developing world that is yet to understand and fulfill the promised “Man-Computer Symbiosis” and get to see what we know as “The Computer as a Communication Device”.

Utility for the 21st Century – Thoughts from Summer of 2010

It was the summer of the iPad and the iPhone 4 from the beach. The ability to Skype and access Netflix from every place we traveled and the use of Google maps every time we got lost. The ability to lookup or download any digital book, song or trivia that came up. I took my ability to access this Internet for granted. It is my 21st century utility.

Going back to summer of 2009 when I camped out in the Redwoods along the Northern California coast for a week or went on a 50-mile backpacking trip into the Emigrant National Forest beyond Yosemite, I felt the Internet umbilical cord being cut as we interleaved into rural America and the wilderness. The odd question that came to mind was does the population (small though in number and varying by season) in these rural parts of America have a right to this 21st Century utility.

It was not a vastly different experience during the summer of 2008 when I was traveling in one of the developing countries also referred to many times as an emerging economy. Every time we left the urban expanse information and connectivity to our vast digital world was cut off abruptly. The same question came to mind does this global population (large in number and hungry for information) have the right to demand the same 21st Century utility that the rest of us take for granted.

This blog is dedicated to the question of Internet utility for the rest of us.