ESMR.SMS Part Four

See also ESMR.SMS (Short Message Service): A service to send short alphanumeric
messages between devices.Spoofing: An access method that supports a very fast dial-up routine in a switched network that mimics the functionality of a packet switched data
network.Spread Spectrum: A modulation technique, also known as frequency hopping, used in wireless systems. The data is packetized and spread over a
range of bandwidth.Standby Time: The amount of time a fully charged wireless portable or
transportable phone can be on before the phone's battery will lose power. See
also Talk Time.Store-and-Forward: The ability to transmit a message to an intermediate
relay point and store it temporarily when the receiving device is unavailable.Synchronization: Also known as “replication,” it is the process of uploading and downloading information from two or more databases, so that each is
identical.2728Talk Time: The length of time one can talk on a portable or transportable
wireless phone without recharging the battery. The battery capacity of a
phone is usually expressed in terms of “minutes of talk time” or “hours of
standby time.” When one is talking, the phone draws more power from the
battery. See also Standby Time.TCP/IP (Transmission Control Protocol/Internet Protocol): The
standard set of protocols used by the Internet for transferring information
between computers, handsets, and other devices.Telemetry: A wireless or landline system for the transmission of data (either
digital or analog) for remote monitoring.TDMA (Time Division Multiple Access): A method of digital wireless
communications transmission allowing a large number of users to access (in sequence) a
single radio frequency channel without interference by allocating unique time slots to each
user within each channel. See also Digital Modulation.Telecommunications Act of 1996: Signed into law by President Clinton on February 8,
1996, it establishes a pro-competitive, deregulatory framework for telecommunications in
the United States.Third Generation:See 3G.Vocoder: A device used to convert speech into digital signals. See also Digital Modulation.Voice Mail: A computerized answering service that answers a call, plays a greeting, and records a message. Depending on the sophistication of the service, it also can notify the subscriber, via pager, that he or she has received a call. Also called voice messaging.Voice-Activated Dialing:A feature that permits one to dial a phone number by
speaking to a wireless phone instead of using a keypad. The feature contributes to
convenience as well as driving safety.WAP (Wireless Applications Protocol): A proposed protocol for wireless applications.

The protocol is designed to simplify how wireless users access electronic and voice mail,
send and receive faxes, make stock trades, conduct banking transactions, and view
miniature Web pages on a small screen.Wireless: Describing radio-based systems that allow transmission of telephone and/or data signals through the air without a physical connection, such as a metal wire or fiber optic cable.

Wireline Cellular Carrier: The Block “B” carrier. Under the FCC’s initial cellular
licensing procedures, the Block B carrier is the local telephone company’s licensee. The
FCC reserved one of the two systems in every cellular market for the local telephone
(or “wireline” company). With initial licensing complete, the distinction has slowly
disappeared. The local phone company can sell its cellular system to anyone. See also
Non-Wireline Cellular Carrier.WLL (Wireless Local Loop):A local wireless communications network that bypasses the local exchange carrier and provides high-speed, fixed data transmission.WML (Wireless Markup Language): A compact version of the Handheld Device
Markup Language. See HDML.WRC (World Radio Conference):Formerly known as WARC, or World Administrative Radio Conference, it is an international conference that sets international
frequencies.


April 2007
Wi-Fi—The Nimble Musician in Your Laptop
David G. Leeper
Intel Corp.
Fact: Jazz musician Nico Brina, born in Switzerland in 1969, is entered in Guiness World Records as the fastest piano player in the world. He has been clocked at an astounding 608 notes per minute using just one hand.

But what does this have to do with the Wi-Fi radio in your laptop?
It turns out that modern Wi-Fi radios are nimble musicians too, except that they generate radio waves rather than audio waves, and they are much, much faster than even Mr. Brina.

Figure 1. Wi-Fi analogy. The alien piano player can use multiple simultaneous notes, each with potentially different amplitudes and phases, to communicate via music.

Imagine a special piano with 52 keys on it. And, as Figure 1 shows, imagine a nimble piano player from another planet who can strike all 52 keys at once, generating a giant musical chord to communicate with a fellow alien. Further, imagine that our alien piano player has "perfect touch," in that he can strike any of the piano keys with one of 16 different precision amplitudes and one of 16 different precision time delays or phases.

Then the player can strike each individual note in the chord with one of 16 × 16 = 256 unique amplitude-phase combinations. Since 256 = 2 8, each note can therefore represent 8 bits of data. And since there are 52 notes per chord, each chord can carry 52 × 8 = 416 bits of data.
Finally, assume that our nimble piano player can strike 250,000 chords per second. This would send data at 416 × 250,000 = 104 million bits per second.

That takes care of the transmitter, but what about the receiver at the other end? Imagine that our imaginary aliens also have "perfect pitch." Not only can they hear each note separately and distinctly, they can also detect which of the 256 amplitude and delay combinations is present on each of the notes, thereby recovering the original data.

RADIOS INSTEAD OF PIANOS

If your laptop has a common Wi-Fi "g," "a," or "n" radio, it works much as our alien musicians do—except that Wi-Fi uses radio rather than acoustic waves. And instead of notes produced by piano keys, your radio uses many simultaneous sine waves or carriers that the transmitter generates. This approach, known as orthogonal frequency division multiplexing (OFDM), is now widely used for Wi-Fi, digital subscriber line, digital television, power line networking, and most recently, ultrawideband (UWB) wireless communication. The popular Wi-Fi "b" radio is not on this list because it uses a direct sequence spread spectrum modulation technique rather than OFDM—a topic for another time.

The numbers in the piano illustration are drawn from a particular specification from the Wi-Fi standards known as IEEE 802.11a. In actual practice, some of the 52 carriers are used solely to help the receiver maintain synchronization, and at least 25 percent of the bits sent over the air are used for error-correction coding. Nonetheless, in one mode of 802.11a, the user can still net as much as 54 Mbps under good conditions. And in UWB, based on a 128-carrier design, the radios deliver up to 480 Mbps over short range.

How can a real radio generate and receive so many different carriers so quickly and so accurately?

Before modern computing and integrated circuits, the task would have been nearly impossible. Building 52 oscillators with precision amplitude and phase control would have required racks of equipment consuming massive amounts of power. Instead, as Figure 2 shows, a Wi-Fi radio applies computer science to the task by mathematically computing what the waveform would look like if we had actually built all those precision oscillators. The computer technology is known as digital signal processing, and the computation algorithm is known as the fast Fourier transform.

Figure 2. Rather than building a power-hungry array of precision analog oscillators, modern computer engineering allows using digital signal processing to synthesize waveforms.
Once we have the computed stream of numbers that represent a sampled version of the desired waveform, we use a digital-to-analog converter to convert them to a true analog waveform.
Wi-Fi, UWB, and other OFDM-based systems are prime examples of how computers and radios work well together.

MULTIPATH—THE ENGINEER'S NIGHTMARE

All this is well and good except for one major problem: multipath. A Wi-Fi receiver doesn't receive just one copy of the transmitter's signal—it receives hundreds of them. Just like sound waves in a canyon or a concert hall, Wi-Fi radio waves bounce off surrounding surfaces—especially metal, but also people—and create a roaring mass of echoes at the receiver. Sometimes the echoes reinforce one another, and sometimes they tend to cancel each other out. Furthermore, the precision phases and amplitudes so carefully launched at the transmitter end up being randomly shuffled by all those echoes arriving at different times.

So, as remarkable as the transmitter is, it's even more remarkable that the receiver can deal with all that distortion and still detect the transmitted data accurately. How does it do that?
One thing works in our favor: linearity. While we might receive hundreds of copies of every individual carrier, the net result of summing all those echoes is always another carrier at the same frequency. As Figure 3 shows, adding together just two carriers of different amplitude and phase results in a carrier of the same frequency but with altered amplitude and phase.

Figure 3. Linearity guarantees that adding sine waves of the same frequency, even if they have different amplitudes and phases, produces another sine wave of the same frequency.
But if all those echoes shift the amplitude and phase of the transmitted carriers, hasn't multipath scrambled the very data we are trying to receive? The short answer is yes. And if that were all there were to it, multipath would completely destroy any chance of receiving the data correctly. Fortunately, your Wi-Fi radio plays a clever trick—it's called equalization.

At the head end of every data burst or "frame" that your radio transmits, it transmits a short fixed "training" data pattern known in advance at the receiver. The receiver compares this known pattern against the amplitudes and phases of the training-pattern carriers it actually receives, and it uses the result to build a correction vector for all the carriers that follow in that frame.
For example, your receiver might look at Carrier 37 from the training pattern and say, "Whoa! Carrier 37 should look like a sine wave with an amplitude of 0.1 volts and a phase of 90 degrees. But I actually received that carrier with an amplitude of .125 volts and a phase of 162 degrees. Therefore, for the rest of this frame, I will correct the distortion on Carrier 37 by multiplying its amplitude by 0.8 and by subtracting 72 degrees from its received phase."

Of course there's nothing magic about Carrier 37—your radio follows the same process on all 52 carriers, and it does so at blinding speeds.

This description is a simplified version of the actual process, but it captures the essence of equalization—namely, using a training pattern to create a correction vector that can be applied to all subsequent data carriers. Of course, over time, as objects in the room move about, the multipath environment changes. But the training process is repeated at the beginning of every frame, and over the duration of a frame (typically measured in milliseconds), the multipath environment changes very little.

THEN PATH LOSS, THERMAL NOISE, AND INTERFERERS

As if multipath weren't enough, your receiver has at least three other impairments to deal with. The first of these is path loss. It makes intuitive sense that the further your Wi-Fi radio is from its access point, the weaker the received signal will be. What might not be so obvious is how fast the path loss grows with distance.

The signal that your Wi-Fi radio transmits flies out from the antenna in a spherical wave front like an expanding soap bubble, and the signal energy spreads out over the surface of the bubble. The receiver's antenna captures energy from a small portion of the bubble surface. Since the area of a sphere grows as the square of its radius, the path loss will grow as the square of the distance between transmitter and receiver. Thus, every time you double that distance, you will lose at least 75 percent of your received signal strength.

When and if the received signal gets weak enough, it begins to disappear into the second impairment—thermal noise that your radio's own circuitry generates. No matter how well designed your radio is, thermal noise is always present (unless you cool the radio to zero degrees Kelvin). Finally, other radios in the vicinity on the same or nearby frequencies will add their own form of noise-like interference.

Just as you might speak more slowly or repeat yourself in a noisy environment, your Wi-Fi radio might respond to all these impairments by "down-shifting"—that is, transmitting data more slowly or by repeating it multiple times. You see the result when your radio is delivering slower-speed data transmission than you might wish it to.

With all the challenges your Wi-Fi radio faces, it might seem miraculous that it can communicate for you at all, especially at such high speeds. But thanks to the marriage of computer engineering and wireless, it really does work, giving every laptop its own "nimble musician" to send and receive data.

David G. Leeper is chief technologist for the Ultrawideband Networking Operation at Intel Corp. He received a PhD in electrical engineering from the University of Pennsylvania. Contact him at david.g.leeper@intel.com or dleeper@mail.com.

Wireless Broadband Said To Use Wrong Spectrum
By Roy Mark
April 29, 2004

WASHINGTON -- Wireless broadband is currently allocated to the wrong spectrum and the result is hampering the growth of the technology, according to former Federal Communications Commission (FCC) Chairman Reed Hundt.

Hundt, who presided over a major overhaul of U.S. telecommunications policy in 1996, said wireless broadband should be put in the same spectrum swath used by analog UHF stations, which is being vacated by broadcasters converting to digital television signals.

"Wireless broadband is being designed where the radio frequencies are very, very high and, as a result, the radio waves can not penetrate buildings," Hundt told the Senate Commerce Committee Wednesday, as lawmakers look at a possible overhaul of telecom legislation.
"Waves at lower frequencies are longer in length. Longer wave lengths hold their energy over longer distances. They can travel miles from a tower and find their way inside living rooms."
Hundt said the longer wave lengths are just as ideal for wireless broadband as they are for television broadcasting, particularly since they can also carry large amounts of information.
"Correspondingly, wireless broadband can deliver very high bit rates at lower cost and greater equality if it also uses the lower frequencies of broadcast television," he said. "It has excellent propagation characteristics that will allow the build out of an inexpensive and ubiquitous wireless broadband network."

Congress has shown an increasing interest in reforming the 1996 Telecommunications Act as the United States struggles to rollout broadband across the country. The U.S. ranks 11th worldwide in broadband deployment behind South Korea, Hong Kong, Canada, Taiwan, Denmark, Belgium, Switzerland, the Netherlands, Japan and Sweden.

Hundt told the senators, "We can lower the costs of wireless broadband in one fell swoop by 50 percent within months, if this committee will say to the whole wireless broadband industry we need to be designing new spectrum for today's analog UHF channels."

In 1997, Congress directed the FCC to allocate 24 MHz of the 700 MHz band for public safety communications and to allocate another 36 MHz of the band for commercial use to be assigned through spectrum auctions.

"In order to facilitate wireless broadband in this spectrum, Congress could amend this 1997 law to allocate 30 MHz of this commercial spectrum for unlicensed services that would not be subject to an auction," Hundt said, adding that the spectrum transformation would result in "billions of dollars of extra growth and hundreds of thousands, if not ultimately millions, of new jobs, provided it was done quickly."

Hundt described advanced wireless technology as a "chipset about as big as my thumbnail that will send out a radio signal to a box about the size of a cheeseburger and sits on a windowsill."
From there, a signal is sent to antenna located in a "breadbox" attached to lamp poles or street lights. The boxes then send signals across the air and ultimately, miles way, connect to a fiber optic Internet link.

"If you have the right radio frequencies you don't need as many boxes and you can design it better," Hundt said.

Hundt urged both Congress and the FCC to "push the recalcitrant and incentivize the willing participants" in any telecom reform.

"The current chapter in this ongoing story of facilitating the creative innovation of capitalism will be written if Congress and the FCC can find ways to let businesses use the best spectrum physics, not for UHF television, but rather for wireless broadband."

Digital Television Transition and Public Safety Act-2/17/2009
Filed in archive HDTV by itsTripple on October 28, 2007

Alert! Your analog television will no longer work after February 17, 2009. The federal government passed the Digital Television Transition and Public Safety Act law in 2005 in Oder to free up the analog air waves for emergency system broadcasts as well as other usages. The only way you will be able to use your analog TVs after this date is to purchase an HDTV converter.

Jh7

The new television broadcast standard will be high definition, better know as HDTV. To properly receive the new broadcast standard you will need two essential items. First you will need an HDTV ready television set. Preferably with a built-in HD TV tuner...

Your HDTV will need to be capable of displaying at least 720 pixels (Vertical) and 1280 pixels (horizontal). This is the standard for the basic HDTV experience. In order to receive the HDTV signal for free, you will also need a roof-top HDTV antenna (Just when you though we got rid of those darn things). The roof-top antenna is needed to receive the line-of-sight broadcast of the HDTV signal. Most cable and satellite service providers are converting customers over to cable boxes with built-in HDTV tuners but their HDTV channels are available at an additional cost.

Retailers like Best Buy are already in the process of phasing out inventory of analog televisions and HDTV manufacturers are busy developing smaller HDTV displays to fill their void.

Weak Wi-Fi?

In the beginning, you were so excited to go wireless, that you may not have paid attention to the speed. Your Internet connection works great in the computer room, but not so hot when you're in the backyard on your hammock. Maybe during your lounging, you noticed a message indicating "weak signal strength" for your wireless connection. Your DSL or cable connection is plenty fast, but it seems the further away you are from your access point, the slower your connection is. Kind of defeats the purpose of having high-speed bandwidth and a wireless router in the first place, doesn't it?

A wise old nerd once said "Your connection is only as fast as your slowest link, Grasshopper." You can have the biggest, baddest broadband connection around, but if there are inhibitors to that connection, your computer will not be able to take advantage of that speed. One inhibiting factor is distance. A standard 2.4 GHz wireless router will cover a range of about 250 feet. Check with your router's manufacturer to find out the range the router covers.

So what if you're within the recommended range distance, and are still getting a weak signal? Physical obstacles and other kinds of electronics can inhibit wireless transmission as well. You want to make sure that your router's signal isn't being blocked by cabinets, metal, glass or thick walls. Also ensure that the router is not near wireless phones, blue tooth devices, microwaves, or wireless baby monitors; these can also interfere with the router's signal. If you place your router near the center of the house, on a high shelf, that should help as well.

If your access needs exceed the recommended range, look for a higher-powered antenna, range expander or repeater that will boost the signal. The Linksys Wireless-G Range Expander is one product that I recommend. But if you want to roll your own, check out this antenna built from a Pringles can or try putting your wireless adapter in a dumpling strainer.

Change The Channel

Just like radio or television, wireless signals are transmitted via channels. By default, most routers are set to channel 6. If your neighbors are using wireless routers set to the same channel, this can degrade the strength of your signal. Use your router's administrative software to try switching the channel to 1 or 11.

Use The Latest and Greatest

Computer users often neglect keeping their devices upgraded to the latest driver releases. Make sure your router has the latest firmware; the vendor's website will usually offer the software as a free download. Additionally, make sure any devices that use your wireless network (like a laptop, for instance) has the latest drivers installed for any on-board or added wireless cards.

It's not a bad idea to do routine checkups of all computers using your wireless network for viruses and spyware (which are notorious for slowing computers down). You are running anti-virus and anti-spyware protection already, right?

Change It Up

If you have tried all the above scenarios, and are still unhappy with your wireless connection, consider an upgrade. Awhile ago Wireless-B was the standard, now the faster Wireless-G is dominant. Upgrade to a wireless-G router, but make sure that wireless cards on any computers connecting to your network are wireless-G compatible. If they are not, you will have to upgrade them as well.

A great way to test your bandwidth connection is with one of the available, free bandwidth speed tools on the internet like the Speakeasy Speed Test. You can use this to gauge the speed of all computers using your wireless router and see which ones have any deficiencies. If any of them are coming up with slower speeds, try the above tips to give your wireless connection a kick in the pants.