Dale’s Web Log

This is the first in a multi-part series of posts I am working on. I am attempting to familiarize myself with the 802.16 protocol standards and the WiMAX forum efforts. I find that the best way to learn stuff is to write it down. I hope this helps others out there, and by all means, if you see and error, please comment and I will correct it.

Introduction

The IEEE 802.16 working group is the standards body developing the specifications for the next generation of broadband wireless networks – both fixed and mobile. The WiMAX (Worldwide Interoperability for Microwave Access) forum is an interoperability initiative that will certify that broadband wireless radios manufactured by various vendors comply with the IEEE 802.16 specification and – more importantly – are interoperable from vendor to vendor through testing.

WiMAX Range and Throughput

The throughput and range of a WiMAX link is very dependent upon a number of factors including; transmit power, antenna gain, directionality, modulation scheme, forward error correction codes, the terrain, density, height of tree cover, presence of hills and valleys, bodies of water, etc. (nothing new here, these are all the typical issues that need to be dealt with in wireless communications). Despite this, it is not uncommon to see statements in the media describing WiMAX multipoint coverage as being capable of extending coverage up to 30 miles from a base station or tower location. In certain (very specific) cases this is true. However, typical operating ranges fall into the 8-10 mile range for line of site (LOS) installations and 4 – 5 miles for non or near-line of sight (NLOS) installations.

Realized throughput is dependent upon many of the same factors that address the achievable link distance. WiMAX supports a number of different modulation schemes and coding rates. Also, it is important to remember though that WiMAX is a shared network service, meaning that this bandwidth will be shared amongst all of the users within a given WiMAX cell – much like cable modem users share their Internet bandwidth with other subscribers in the neighborhood.

802.16 Reference Model

802.16 is essentially a wireless implementation of Layers 1 and 2 of the OSI model (Physical Layer and Link Layer). The Physical layer is referred to as the PHY. The link Layer is referred to as the MAC (Media Access Control) layer. The MAC is comprised of 3 sub-layers; the Service Specific Convergence Sub-layer (CS), the Common Part Sub-layer (CPS), and the Security Sub-layer (SS).

The Service Specific Convergence Sub-layer provides the interface between the WiMAX network and the higher level protocols. Data received from the higher layer protocols is mapped into the appropriate WiMAX identifiers for transmission over the network (for example, Ethernet Addresses are converted to WiMAX station identifiers). Currently there are only two CS interfaces defined; one for ATM traffic, and one for packet (IP) traffic.

The MAC CPS performs the bulk of the MAC layer processing. It is responsible for managing system access, bandwidth allocation, and connection management.

The MAC Security Sub-layer provides authentication, secure key exchange, and payload encryption.

The WiMAX Physical Layer (PHY) actually consists of multiple sub-specifications, each one dependent upon the application and frequency spectrum to be utilized. There are three basic frequency bands to be concerned with:

• 10 GHz to 66 GHz Licensed Frequencies
• Licensed Frequencies below 11 GHz
• Unlicensed frequencies below 11 GHz (primarily 5 to 6 GHz)

Coming next….a look at the Convergence Sublayer of the MAC.

Not that it’s a huge surprise to anyone, but the next standard speed for Ethernet will be 100Gbps.

That’s the vote from the Institute of Electrical and Electronics Engineers Inc. (IEEE) 802.3 Higher Speed Study Group (HSSG), taken during last week’s meetings in Dallas.

It’s a formality, but a necessary one, as a few other options had been mentioned since the HSSG started. (See 100-Gig Ethernet Takes First Step.) “Now we can move foward” with the work of trying to build a standard, says John D’Ambrosia, the Force10 Networks Inc. representative who’s chairing the HSSG effort.

Many discussions pitted the 100Gbps option against the possibility of 40Gbps Ethernet, a speed in step with the OC768 of Sonet/SDH. But that fight didn’t turn out to be serious; rather, a suggestion of 120Gbps was the only realistic competitor, according to D’Ambrosia.

“There was a lot of consensus around the fact that 40 Gbit/s wasn’t the speed to choose, and there was the same amount of consensus around 80Gbps,” he says.

Quite a bit of support has been behind the idea of 100Gbps Ethernet, as shown at a recent Optoelectronics Industry Development Association (OIDA) seminar on the topic. (See 100-GigE Takes Shape.) Moreover, data centers already appear likely to adopt 100Gbps Ethernet as a means of connecting machines in high-density environments.

“It’s unlikely in the longer term that telecom networks wouldn’t gravitate to what’s being used in the data networks,” says Tom Mock, senior vice president of strategic planning for Ciena Corp. (Nasdaq: CIEN - message board).

Of course, 100Gbps got all the good publicity along the way. It’s a nice round number, and companies like Lucent Technologies Inc. (NYSE: LU - message board) have been seeding the news wires with tales of 100Gbps research. (See Lucent Stretches 100-GigE.) Representatives of the numbers 40Gbps, 80Gbps, 120Gbps, and 160Gbps are expected to demand a recount.

— Craig Matsumoto, Senior Editor, Light Reading

I found a more detailed article at the IEEE Spectrum web site. It discusses power efficiencies and magnet field strengths and provides some encouraging numbers. Seems as if pacemaker wearers will even be able to be in the same room and the power radiator. An excerpt is below. You can view the full article here:
http://spectrum.ieee.org/nov06/4735

To understand how the MIT idea works, we first have to look at how a regular omnidirectional radio transmitter works. Electrical energy is pumped into such a transmitter, and the energy is then carried away by radio waves that radiate in every direction. So the amount of energy that can be picked up by a receiver located at any given point away from the transmitter’s antenna is only a fraction of the total amount of energy being put into the transmitter.

Now, in the MIT scheme, instead of familiar radio waves, energy is carried by “evanescent waves,” which owe their existence to a wrinkle in the laws that govern electromagnetism. The most important feature of evanescent waves is that although they carry energy, they don’t radiate it away. Rather, they borrow energy from the transmitter and then promptly return it. The reason evanescent waves are unfamiliar to most people—though they do have applications in the fiber-optic cables that carry most data today—is because the laws of physics dictate that they must typically have short ranges; their intensity decays exponentially with distance. That makes them unsuitable for many uses, such as carrying data signals over long distances through the air.

However, the MIT team claims that it’s possible to build a transmitter capable of setting up a field of evanescent waves with an effective range of several meters. The evanescent field doesn’t get absorbed by nearby objects, because only objects that are precisely tuned to resonate with the emitted field can absorb energy from it. An analogy is to “imagine a hundred glasses filled with different levels of water,” Karalis says, and then turn on a speaker set to “generate sound at a particular frequency. Most of the glasses won’t feel anything—but one [if it happens to be at the resonance frequency] might even break.”

A suitably resonant receiver “senses the field and literally sucks it, drains it out,” says Karalis, who estimates that over a distance of a couple of meters, the scheme could approach a power transmission efficiency of 50 percent. “So if I want to feed something with 10 watts, I just supply 20 watts from my source,” he says.

“Even if that’s too optimistic, and the efficiency is as low as 10 percent,” he adds, “for any practical purpose, that’s very good—but we expect much more than that.”

Despite the potential for high efficiencies, the strength of the magnetic fields involved is very low. Initially, the MIT team believed that the magnetic fields required would be similar to those used in MRI medical imaging machines, with field strengths of about 1 tesla. But when they finished their calculations, they were pleasantly surprised to find that to transmit a few watts over a few meters (enough to power a cellphone or to recharge a laptop), the required magnetic field should be about 10 000 times less, around the same strength as the earth’s magnetic field.

The exact design and size of the transmitter has yet to be worked out, but for home applications, a room could be energized with a loop antenna, about a meter across, mounted on the ceiling.

No really, This is great! I’ve been saying someone needed to develop a wireless power solution for years - every time I try to set up a new development lab and I need to re-wire it for more amperage and then buy over 100 power strips for all the computers, routers, and other hardware I need. A total nightmare.

The concept is based on resonance.

“When you have two resonant objects of the same frequency they tend to couple very strongly,” Professor Soljacic told the BBC News website. Typically, systems that use electromagnetic radiation, such as radio antennas, are not suitable for the efficient transfer of energy because they scatter energy in all directions, wasting large amounts of it into free space.

To overcome this problem, the team investigated a special class of “non-radiative” objects with so-called “long-lived resonances”.

When energy is applied to these objects it remains bound to them, rather than escaping to space. “Tails” of energy, which can be many metres long, flicker over the surface.

“If you bring another resonant object with the same frequency close enough to these tails then it turns out that the energy can tunnel from one object to another,” said Professor Soljacic.

Hence, a simple copper antenna designed to have long-lived resonance could transfer energy to a laptop with its own antenna resonating at the same frequency. The computer would be truly wireless.

How it works:

1) Power from mains to antenna, which is made of copper
2) Antenna resonates at a frequency of 6.4MHz, emitting electromagnetic waves
3) ‘Tails’ of energy from antenna ‘tunnel’ up to 5m (16.4ft)
4) Electricity picked up by laptop’s antenna, which must also be resonating at 6.4MHz. Energy used to re-charge device
5) Energy not transferred to laptop re-absorbed by source antenna. People/other objects not affected as (they are) not resonating at 6.4MHz

Can’t wait.

A couple of researchers have devised a way to extend the reach of free space optical (FSO) systems through clouds and fog. The minimal details provided hint to a MIMO like approach to the issue. It’s interesting that a lot of traditional RF type of technologies are now being applied in the optical world - i.e. modulation techniques, etc.

Read the article here.

http://www.photonicsonline.com/content/news/article.asp?docid=fed9dfaf-d716-4370-ab4e-9b119693da36

The system successfully transmitted a 100-GbE signal from Tampa, FL, to Houston, TX, and back again, over ten 10Gbps channels through the Level 3 network. This is the first time a 100-GbE signal has been transmitted successfully through a live production network, claim the companies.

I say….so what!! There are no great technological breakthroughs here. This is nothing more than a demonstration of a ten lambda WDM link - each wavelength rinning at 10 Gbps. Those have been operational for years in the SONET/SDH world. With link aggregation - a technology that has existed for at least a decade, they claim 100 GbE link speeds.

Tell You What, lets try to get GM to have ten cars to go down the highway at 50 mph each. Then they can issue a press release claiming the “First ever demonstration of automobile travel at 500 mph!!!” Will you write about that?