# Phorgy Phynance

## 60 GHz Wireless – A Reality Check

The wireless revolution has been fascinating to watch. Radio (and micro) waves are transforming the way we live our lives. However, I’m increasingly seeing indications the hype may be getting ahead of itself and we’re beginning to have inflated expectations (c/o the hype cycle) about wireless broadband. In this post, I’d like to revisit some of my prior posts on the subject in light of something that has recently come to my attention: 60 GHz wireless.

### Wavelength Matters

As I outlined in Physics of Wireless Broadband, the most important property that determines the propagation characteristics of radio (and micro) waves is its wavelength. Technical news and marketing materials about wireless broadband refer to frequency, but there is a simple translation to wavelength (in cm) given by:

\begin{aligned} \lambda(cm) = \frac{30}{f(GHz)}. \end{aligned}

Ages ago when I generated those SAR images, cell phones operated at 900 MHz (0.9 GHz) corresponding to a wavelength of about 33 cm. More recent 3G and 4G wireless devices operate at higher carrier frequencies up to 2.5 GHz corresponding to a shorter wavelength of 12 cm. Earlier this month, the FCC announced plans to release bandwidth at 5 GHz (6 cm).

This frequency creep is partially due to the issues related to the ultimate wireless bandwidth speed limit I outlined, but is also driven by a slight misconception that can be found on Wikipedia:

A key characteristic of bandwidth is that a band of a given width can carry the same amount of information, regardless of where that band is located in the frequency spectrum.

Although this is true from a pure information theoretic perspective, when it comes to wireless broadband, the transmission of information is not determined by Shannon alone. One must also consider Maxwell and there are far fewer people in the world that understand the latter than the former.

The propagation characteristics of 2G radio waves at 900 MHz (33 cm) are already quite different than 3G/4G microwaves at 2.5 GHz (12 cm) not to mention the newly announced 5 GHz (6 cm). That is why I was more than a little surprised to learn that organizations are seriously promoting 60 GHz WiFi. Plugging 60 GHz into our formula gives a wavelength of just 5 mm. This is important for three reasons: 1) Directionality and 2) Penetration, and 3) Diffraction.

### Directionality

As I mentioned in Physics of Wireless Broadband, in order for an antenna to broadcast fairly uniformly in all directions, the antenna length should not be much more than half the carrier wavelength. At 60 GHz, this means the antenna should not be much larger than 2.5 mm. This is not feasible due to the small amount of energy transmitted/received by such a tiny antenna.

Consequently, the antenna would end up being very directional, i.e. it will have preferred directions for transmission/reception, and you’ll need to aim your wireless device toward the router. With the possible exception of being in an empty anechoic chamber, the idea that you’ll be able to carry around a wireless device operating at 60 GHz and maintain a good connection is wishful thinking to say the least.

### Penetration

If directionality weren’t an issue, the transmission characteristics of 60 GHz microwaves alone should dampen any hopes for gigabit wireless at this frequency. Although the physics of transmission is complicated, as a general rule of thumb, the depth at which electromagnetic waves penetrate material is related to wavelength. Early 2G (33 cm) and more recent 3G/4G (12 cm) do a decent job of penetrating walls and doors, etc.

At 60 GHz (5 mm), the signal would be severely challenged to penetrate a paperback novel much less chairs, tables, or cubical walls. As a result, to receive full signal strength, 60 GHz wireless requires direct unobstructed line of sight between the device and router.

### Photon Torpedoes vs. Molasses

The more interesting aspects of wireless signal propagation are diffraction and reflection, both of which can be understood via Huygen’s beautiful principle and both of which depend on wavelength. Wireless signals do a reasonably good job of oozing around obstacles if the wavelength is long compared to the size of the obstacle, i.e. at low frequencies. Wireless signal propagation is much better at lower frequencies because the signal can penetrate walls and doors and for those obstacles that cannot be penetrated, you still might receive a signal because the signal can ooze around corners.

As the frequency of the signal increases, the wave stops behaving like molasses oozing around and through obstacles, and begins acting more like photon torpedoes bouncing around the room like particles and shadowing begins to occur. At 60 GHz, shadowing would be severe and communication would depend on direct line of sight or indirect line of sight via reflections. However, it is important to keep in mind that each time the signal bounces off an obstacle, the strength is significantly weakened.

### What Does it all Mean?

The idea that we can increase wireless broadband speeds simply by increasing the available bandwidth indefinitely is flawed because you must also consider the propagation characteristics of the carrier frequency. There is only a finite amount of spectrum available that has reasonable directionality, penetration, and diffraction characteristics. This unavoidable inherent physical limitation will lead us eventually to the ultimate wireless broadband speed limit. There is no amount of engineering that can defeat Heisenberg.

There are ways to obtain high bandwidth wireless signals, but you must sacrifice directionality. The extreme would be direct line of sight laser beam communications. Two routers can certainly communicate at gigabit speeds and beyond if they are connected by laser beams. Of course, there can be no obstacles between the routers or the signal will be lost. I can almost imagine a future-esque Star Wars-like communication system where individual mobile devices are, in fact, tracked with laser beams, but I don’t see that ever becoming a practical reality.

We still have some time before we reach this ultimate wireless broadband limit, but to not begin preparing for it now is irresponsible. The only future-proof technology is fiber optics. Communities should avoid the temptation to fore go fiber plans in favor of wireless because those who do so will soon bump into this wireless broadband limit and need to roll out fiber anyway.

Written by Eric

January 21, 2013 at 9:15 am

## The new corporate trend: “onshoring”

Ha! What did I tell you? It is wayyy past my bedtime and I should be sleeping (especially since I’m sick and feel like I’ve been run over by a truck), but just stumbled on an interesting article from one of my favorite economic development blogs: Design Nine. He points to an article in the journalgazette.net.

Recall that in the midst of all the market doom and gloom, I recently said:

I’m actually ironically optimistic about the outlook for suburban and rural economic development. A weaker dollar will make outsourcing less attractive. That will bring manufacturing jobs back home. I can imagine a boon in suburban and rural development. Just imagine if communities developed decent broadband via fiber-to-the-home/business. Suddenly, there will be attractive jobs and living standards in affordable places.

I admit that the quote is a bit misleading because Andrew Cohill has influenced the way I think about things, but still timely I think. Here is an excerpt from the article:

#### Small-town America: The new Bangalore?

[snip]

Onshoring, in fact, is becoming trendy.

Some U.S. companies recently have pulled back from India to set up shop in rural areas where access to high-speed broadband connections isn’t the problem it was just a few years ago and where lower real-estate prices and wages are attractive.

Note that the key to onshoring is an investment in telecommunications infrastructure. In particular, fiber-to-the-home. It is quite sad to see so many municipalities rest their hopes on wireless broadband. That will only end in tears as the reality of wireless broadband becomes apparent. Any community that is not investing now in fiber will lose out on an important opportunity that is now beginning to present itself: onshoring. As Andrew will tell you more eloquently than I could, an intelligent investment in a communities future MUST involve a combination of both fiber and wireless and I would put wireless as a distant second. I can explain in gory detail why wireless will fail if you like (I did my PhD in the subject), but for now need to hit the sack.

Go onshoring! Go USA!

Written by Eric

December 4, 2007 at 12:50 am

## The beginning of the end for Wi-Fi

For a couple years now (are you getting sick of me saying that yet?), again I would blabber to anyone who would listen about my thoughts on the future of wireless broadband. Wireless broadband equipment manufacturers are laughing to the bank and will continue for the near term. However, the dream that people will be walking around with their broadband wireless devices is a fantasy whose reality is about to be revealed.

The good thing about wireless broadband for manufacturers is that it it is very easy to set up very impressive demos, but the impressiveness will not scale. I’ll blabber more about this later, but for now I will leave you with this link:

IPhones flooding wireless LAN at Duke University

You will only see more stories like this in the coming months and years until people realize that ubiquitous wireless broadband is a myth.

Written by Eric

July 16, 2007 at 8:28 pm