Tag Archives: Wi-Fi

Real-world wired vs wireless speeds

My mantra is, “Wireless should be your last choice, not your first choice.”

While at a client’s site last week, I needed to copy about 65 gigabytes of data from one networked PC to another. The source PC was running Windows XP and was connected to the lightly-loaded switched local area network (LAN) via 1 gigabit per second Ethernet. The destination PC was running Windows 7 and was connected to the same LAN via IEEE 802.11g Wi-Fi. I began the copy operation. Windows reported that the transfer speed was about 1.5 megabytes per second. It claimed that the entire copy operation would require about 17 hours.

I reconfigured the destination PC to use its 100 megabits per second Ethernet port instead of its wireless adapter and plugged in the network cable. The entire copy operation was completed within an hour, not 17 hours.

This is about average. I normally see at least a ten-to-one throughput advantage when comparing the real-world speed of a wired- versus a wireless- network connection.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

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FCC Chairman Genachowski steps down

FCC Chairman Julius Genachowski announced on Friday that he will leave his office “in the near future” and President Obama thanked him for his service.

Julius Genachowski
Julius Genachowski

For consumers, Mr. Genachowski’s 4-year reign has been both good (opposed AT&T / T-Mobile “merger”) and bad (continued growth of de facto broadband shared monopoly). The FCC has been a political playground for decades: Genachowski was a Harvard Law buddy of Mr. Obama.

Like most federal agencies, the FCC provides a cushy resting-place for ambitious lawyers who change chairs every time the music stops. Inevitably, at least one of those chairs resides within an enterprise that the agency regulates.

Lawyers have run the show at the FCC for too long.

I’d like to see an engineer appointed FCC Chairman. Absent that pipe-dream, I’d like to see Susan Crawford appointed Chairwoman. I like her motives, but I fear that, like most lawyers, she thinks that every problem can be fixed with a new law.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Super Wi-Fi Bowl

Yesterday’s Superbowl attendees could reportedly access free Wi-Fi while in the stadium. This Fiercebroadbandwireless article discusses security measures at the stadium to protect the 802.11n frequencies from interference during the game. Apparently at least 700 wireless access points were deployed within the stadium, theoretically providing enough aggregate bandwidth for 30,000 users. Total attendance was about 71,000. Verizon Wireless paid for the installation.

IEEE (finally) ratifies 802.11N WiFiI’d guess that the way to ensure that this works with minimal “intra-cell” interference would be to deploy many hundreds of wireless access points (APs), reduce each AP’s transmit power to a low value (thus creating “micro-cells”), and coordinate AP frequencies so that adjacent “cells” don’t share common frequencies.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

T-Mobile’s VoIP 9-1-1 Strategy

Yesterday, my T-Mobile home page included a link to their page titled Wi-Fi Calling and 9-1-1 Address. This describes their method of providing 911 caller geo-location information when using a T-Mobile phone that’s connected via a Wi-Fi access point. [“Wi-Fi Calling” is their tradename for VoIP (Voice over Internet Protocol).]

Like their cellular phone 9-1-1 location strategy, it doesn’t rely on the caller phone’s GPS receiver. Also like their cellular geo-location strategy, it tries the most precise method first, and falls back to progressively less precise methods. I guess that the other U.S. cellular companies employ a similar VoIP 9-1-1 strategy.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Hollywood Florida’s Municipal Wi-Fi Failure

About ten miles south of me, the city of Hollywood (pop. 142,000; 27 square miles; 70 square km) has apparently abandoned hopes of providing free municipal Wi-Fi to its residents. It is attempting to recover up to $3.8 million from the chief contractor, Johnson Controls. Hollywood had been named a top 10 digital city multiple times by the Center for Digital Government.

http://www.hollywoodgazette.com/2009/latest/849-city-wide-wi-fi-doesnt-happen-for-hollywood

From http://articles.sun-sentinel.com/2012-07-02/news/fl-hollywood-failed-wi-fi-20120630_1_wi-fi-wireless-hollywood-transmitters-without-signal-interference

In 2008, the city signed a contract with Johnson Controls to install Wi-Fi for $3.8 million, an automated water-meter reading system for $9.2 million, and solar-powered parking meters for $3.1 million.

http://city-countyobserver.com/2012/06/09/johnson-controls-municipal-wifi-project-in-hollywood-fl-called-a-flop/

http://www.dslreports.com/shownews/Hollywoods-WiFi-Effort-Collapses-in-a-Heap-120580

It sounds like this project failed because:

  • The city’s wireless access points (APs) share the same channels with residents’ privately owned APs in their homes — a recipe for interference problems.
  • Large buildings interrupt Wi-Fi signal.
  • Providing adequate backhaul bandwidth from the APs to the city’s network backbone requires either dedicated fiber to each AP or a dense switched mesh network; neither option is cheap.
  • The Wi-Fi spec doesn’t accommodate seamless handover.

I hope that the parking meter and water meter data aren’t being transported on Wi-Fi channels; the unlicensed 902 to 928 MHz ISM (industrial, scientific, and medical) band or a licensed frequency would make sense for those applications.

Apparently part of the contract includes deployment of a licensed 4.9 GHz radio system for its police department.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Comcast opens its NJ Wi-Fi hotspots for Hurricane Sandy recovery.

Here’s Hurricane Sandy news from my sister:

To help residents and emergency personnel cope with the aftermath of the storm, Comcast is opening up its Xfinity WiFi hotspots to anyone who needs them – including non-Comcast users. As you may be aware, Comcast owns and operates thousands of WiFi hotspots throughout its New Jersey service area.

Non-Xfinity Internet users should search for the “xfinitywifi” network name and click on the “Not a Comcast subscriber?” link at the bottom of the Sign-In page. Then, select the “Complimentary Trial Session” option from the drop down list. Users will be able to renew their complimentary sessions every two hours through Wednesday, November 7. For a map of XFINITY WiFi hotspots, which are located both indoors and outdoors in malls, shopping districts, parks, train platforms and other areas, visit www.xfinity.com/wifi .

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Wireless hype existed a hundred years ago, also.

I came upon this hundred-year old magazine article in which Guglielmo Marconi predicts that wireless will bring wonderful things, including wireless lighting, heating and transmission of motor power. He echos Tesla’s prediction of wireless power transmission a decade earlier.

Today we read more subdued yet equally naieve predictions about wireless. The authors forget the laws of physics, that RF spectrum is a limited resource, and that since 1948 Claude Shannon’s information theory defines exactly how much information we can squeeze into one radio signal. Many of the recent utopian predictions for wireless have failed to come true, for both technical and political reasons. Many municipal Wi-Fi systems have failed because it’s impossible to squeeze a gallon of information into a pint-size jar.

I wonder how much of the 2009 Broadband Initiative money was spent on failed “shovel ready” municipal Wi-Fi systems?

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Android-based WiFi spectrum analyzer in my pocket

Display nearby WiFi access points in the palm of your hand.

Meraki website
screenshot: PC Magazine

When I arrive at the site of a client who needs WiFi help, my first step is to survey the site for existing WiFi RF signals. I usually use NetStumbler on a netbook. Now I can perform a similar survey on my Android phone, which I carry in my pocket.

I’ve tried Meraki WiFi Stumbler and Wigle WiFi Wardriver. For this survey application, I prefer Meraki WiFi Stumbler. It provides a bar chart with WiFi channel numbers on the x-axis and wireless access points’ (identified by their SSIDs) signal strengths in dB on the y-axis. It seems to be less sensitive and scan slower than Wigle, but its display is ideal for a quick WiFi site survey. Wigle is more comprehensive and an impressive piece of work, but its added features aren’t needed for ad-hoc WiFi site surveys.

My headline calls this hardware/software system a “spectrum analyzer”. That’s not strictly true. A full-blown spectrum analyzer displays all of a signal’s blemishes: distortion products, noise sidebands, harmonics, etc. The graph displayed by Meraki is merely a symbolic representation of nearby WiFi signals, after filtering out their blemishes. In most cases, it’s all the information that I need.


Oct 22: I’ve begun to use WiEye. I like it. Its display is simple, provides excellent resolution, and quick response. I found it in the Google Play Store.

spectrum analyzer photo: Vonvon

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Steerable antennas

Steerable directional antennas offer advantages that justify their difficult fabrication.

My old 75-meter parasitic array

When designers need to improve the performance of any radio system, they turn their attention to improving the antennas, which improves system transmit AND receive performance. When I was a teenager, I was a ham radio nut. Most of my radio adventures took place in the HF (high frequency) amateur radio bands between 2 and 30 MHz — a fraction of the 2.4 and 5 GHz (GigaHertz) frequencies where today’s WiFi action is. A wavelength at 4 MHz (MegaHertz) is about 75 meters — antennas in this range are large. I strung a simple 75 meter band half-wave horizontal dipole antenna atop my parent’s house; it radiated in the east-west directions, was about 120 feet long, and worked fine. I had no money to invest, but wanted better antenna performance. I settled on constructing a 2-element parasitic array, which I did by adding a second horizontal dipole more or less in parallel, spaced about 1/8 wavelength apart from the first dipole. I ran a half-wavelength open-wire transmission line from my station in the basement to the center of the second dipole. I was able to electrically shorten and lengthen the second dipole by placing a variable capacitor across the end of the transmission line. The second (“parasitic”) antenna element’s radiation would either reinforce or subtract from the driven element’s signal, depending upon what reactance I added at the far end of that 1/2 wavelength transmission line.

How well did it work?

Because of physical constraints, none of this array’s dimensions was ideal, but it did yield about a 2 to 3 dB (decibel) front-to-back ratio, in either the East or West direction as I chose. Not great numbers, but I knew nobody else who could “steer” his antenna at such a long wavelength. I noticed the improvement when receiving: the signal to noise ratio (SNR) would improve slightly when I steered the antenna in the direction of the transmitting station, which was usually hundreds of miles away.

In theory, the array’s vertical angle of radiation was lower than that from a single dipole. I never measured this, but the array did seem to work better on long skip propagation than did the dipole.

Steerable Parasitic Antenna Array, 5 GHz
Illustration: L. Petit, L. Dusopt and J. Leheurte, “MEMS-Switched Parasitic-Antenna Array for Radiation Pattern Diversity” IEEE Transactions on Antennas and Propagation, vol, 54, M. 9, Sep 2006.

Steerable WiFi Antenna Arrays

Today the same principle is being applied to electronically steerable parasitic element antennas in the GHz (GigaHertz) range. At 2.5 GHz, a wavelength is only about 5 inches, so construction is relatively easy. They’re often constructed as illustrated: etched from a copper laminate on a non-conductive substrate, so dimensions are tightly controlled. They’re steered under program control, not by a kid sitting in the basement. I’ve not tested their performance, but I’ll bet that they beat my old 75-meter band parasitic array by a wide margin.

Electronically steerable antenna arrays are now used in some new MIMO (multiple-input and multiple-output) wireless WiFi access points. The relatively new WiFi standard known as IEEE 802.11n specifies MIMO, which allows greater throughput with less signal fade. Each antenna is dynamically steered as required by each frame: at 2.5 GHz, that’s just a hundredth of a microsecond or so. The exact steering of the antenna may be varied from frame to frame. IEEE 802.11n provides for four steerable antennas per transceiver. That requires a ton of high-speed computing power just to steer the antennas!

AWACS antenna photo by Daderot
Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Facebook quickly withdraws its stalker’s app

Facebook Friendshake screen
screenshot: facebook
Another reason why I’m glad I don’t have a Facebook account.

 

Months ago, Facebook acquired Glancee, a small company that had developed a smartphone app that used smartphones’ GPS information to locate people. Facebook renamed it Friendshake, while they tested it within their Facebook mobile apps. In June they renamed it “Find Friends Nearby” (FFN) and quietly rolled it out.

The FFN app was quickly dubbed “the stalker’s app” and within 10 days of release, Facebook withdrew it. You can see if it works or not by going to www.fb.com/ffn.

I’m surprised that Facebook and other social networks can change their games’ rules, as the games are being played. What sort of Terms Of Service (TOS) have Facebook users signed? Apparently it’s a carte blanche.

If you provide an online service, try to change your privacy policy. Most jurisdictions will require that all existing users first agree to the change. The U.S. is lax in its privacy protection, but the EU is strict. I won’t be surprised if they bring suit against Facebook over “Find Friends Nearby”.

What will DOJ and EU do about Google’s wardriving?


Google Streetview cars
parked in front of Gate-One hotel in Bratislava, Slovakia
photo: Loskutak
Google’s “rogue engineer” is the author of NetStumbler.

What’s NetStumbler? It’s a program that’s been used since the early 2000’s by wardrivers — people who drive around with laptop PCs, a WiFi interface adapter, a GPS receiver, and software to look for wireless access points. (“What is Wardriving and What Can I Do to Prevent It?”) Their software of choice: NetStumbler.

I’ve used NetStumbler many times to survey clients’ sites. It turns your laptop into a simplified spectrum analyzer, dedicated just to WiFi channels. It allows me to place a client’s new wireless access point (WAP) on the least occupied channel.

Although I’ve never used its geo-tracking ability, NetStumbler will also record, using input from a GPS receiver, the geographic coordinates of each wireless access point. Apparently Google claims that its managers weren’t aware that its Streetview cars were recording wireless access point data and their coordinates. Google blamed it on a “rogue engineer”.

It turns out that Marius Milner, the author of NetStumbler, is/was a Google employee who developed software for the Streetview project. I’m not sure whose jurisdiction in the US this falls under. In general the FCC (Federal Communications Commission) cares only about radio frequency signals that are transmitted, not who’s receiving them. European authorities are stricter about the reception of radio signals.

I suspect that this issue has a long way to go through investigation before any law enforcement action is taken by any government agency.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Dramatically improve WiFi signal for almost no money

Their form may not be lovely, but they function beautifully.

Linksys WRT54GS with reflectors

Last August I wrote about connecting the LANs (Local Area Networks) in two separate buildings with WiFi (Connect buildings with a wireless bridge). Occasional streaming video dropouts across the WiFi link prompted me to improve the WiFi link’s fade margin by increasing the antennas’ forward gains at both ends of this client’s WiFi link.

I followed the Ez-12 Parabolic Reflector plans and fabricated two 6-inch wide parabolic reflectors for use on the twin-antenna Linksys WRT54GS inside the remote building. The SNR (Signal to Noise Ratio) of the WiFi link improved by 5 to 10 dB (decibels). Then I added a 7-inch parabolic reflector to the single antenna on the Netopia router inside the main building. The WiFi link’s SNR increased by another 3 to 6 dB.

The reflectors are flimsy (they’re just made of stiff file folders and aluminum foil) and look slightly comical, but they do work!

So, for maybe 50 cents worth of material, the link’s fade margin improved by 8 to 16 dB. (The decibel scale is logarithmic: a 10 dB improvement is equivalent to multiplying the power by a factor of 10.) How could you ask for anything more?

Assembly note: I made the tabs on the support longer than the template indicates, which allowed me to fold them over against the backside of the reflector. Then I used inch-long paper tape strips to stick each folded tab to the reflector’s backside. Otherwise, my reflectors kept falling apart.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

How not to install Internet service.

I knew that Comcast was not a business-grade ISP (despite their ads), but this low-rent installation surprised even me.

illustration by Russ Bellew

A friend recently (against my recommendation) switched his business’ Internet Service Provider (ISP) from AT&T DSL to Comcast cable. I visited his small business to see the new installation.

Roughly 75 feet separates the outside walls of his adjoining shop and office. They share a common supporting wall. The existing AT&T phone and DSL service entrance point is in his office. For some reason, the new Comcast cable service entrance point is in his shop. Rather than run a cable from the Comcast service entrance point to his existing router in the office, the installer chose to terminate at the new Comcast entrance point, install a second Comcast router in the office, and link them wirelessly. I’d estimate that he saved about 1 hour of labor.

This should have failed a quality control inspection.

If I had been on site, I wouldn’t have accepted this installation. Why? Because this installation violates Russ Bellew’s First Law Of WiFi: Wireless should be your last choice, not your first choice. It also violates my Second Law Of WiFi, which is If both points are fixed (not mobile), connect them with cable, not wireless. Worse, by needlessly occupying a WiFi channel, he’s crowded limited WiFi spectrum and restricted the business owner’s future WiFi expansion possibilities (and maybe those of his neighbors).

Q: Does WiFi ever make sense between fixed points?

A: Yes. Here’s one case:
Connect buildings with WiFi

Although the bandwidth of 802.11g is published as 54 Mbps, its real data throughput is about half of that, due to 802.11’s high protocol overhead. Also, 802.11g is half-duplex, as opposed to 100baseT’s full duplex communication. In short, wireless should have been the installer’s last choice.

I’d guess that to run a cable from the outside wall of the shop to the outside wall of the office would require about 1 hour of labor. The cable could be run either within the building or along its outside wall. This must have looked like hard work to the installer.

 

The old Bell System published and adhered to its standards and practices, which specified the right way to do everything. Customer premise wiring, when done by a Bell System installer, was done properly.

Does Comcast have any quality control?

This installation was probably done by a Comcast contractor, who’s paid per installation. He wants to complete each job as quickly as possible, even if that means taking shortcuts. What standards must Comcast contractors follow? Who oversees quality control of business premise installations?

I see dumb WiFi setups every week, but they’re always cobbled together by naïve end-users. This is the first time that I’ve seen a dumb WiFi lash-up by an ISP. This is one more piece of evidence that Comcast is not REALLY ready for business class service (despite their advertisements).

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

LightSquared’s problems highlight RF spectrum limits.

Navstar 2F GPS satellite
Navstar-2F satellite of the Global Positioning System (GPS)
photo: USAF
Big money wants to deliver wireless broadband everywhere. Doing so may deliver big problems everywhere.

About a year ago, a combined satellite and terrestrial cell-tower broadband network named LightSquared announced its intentions. It looked like LightSquared had its FCC (Federal Communications Commission) ducks in a row so that it could begin building immediately.

Now, US armed forces, who created, maintain, and depend upon the Global Positioning System (GPS) think that LightSquared’s plans may interfere with GPS signals. In June, a report demonstrated that GPS signals will indeed be interfered with everywhere by LightSquared’s cell towers (which could number 40,000).

photo: Darrenm540

The frequencies in question are in the L-band (1 to 2 GHz). I remember when this band was almost empty. Now it’s a crowded superhighway for many satellite signals, GSM cellphones, GPS signals, radar signals, etc. (Link to graphic image of America’s ridiculously crowded radio frequency resource.)

GPS signals are vulnerable
According to L-band authority Richard Abrahams, “GPS signals are generally very weak and need to be well-protected.”

So far, it looks like the Pentagon will oppose LightSquared’s ambitious plans, as will most players in the GPS equipment marketplace. But the battle is heating up and who will win is unclear. Big dollars are at stake, and that will draw politicians.

I’d like to see LightSquared’s plans defeated. Allow Verizon, Sprint, et al to roll out their 4G wireless networks as they’re doing and don’t jeopardize the GPS system.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Connect buildings with a wireless bridge.

Here’s a low-cost way to expand your network into nearby buildings, even if they’re separated by public streets.

illustration by Russ Bellew
Two nearby buildings share network resources via a wireless bridge

A growing business needs floor space to expand. Frequently, this means leasing space in detached buildings. How can we tie everyone together, so they can work on the same databases, share the same printers and Internet firewall, etc? At one time this would mean running fiberoptic cable or establishing a microwave link between the two buildings. Today, we can often use low-cost consumer-grade WiFi components to do the job.

WRT54G router
Linksys WRT54GS

I helped a client, Autobahn Performance Inc., expand their growing network into a leased building across the street from their main building — a distance of about 180 feet. We did it by using a low-cost off the shelf router/wireless access point (“AP”), replacing its firmware, and configuring it so that it, together with the existing AP in the main building, forms a wireless bridge into the new leased building.

We chose the Linksys WRT54GS because it’s very popular and third-party open-source firmware is readily available at little or no cost. We replaced the Linksys firmware with the popular DD-WRT firmware, specifically, DD-WRT v24-sp2 (12/18/09) mini. The DD-WRT firmware includes options to configure the wireless router as the client side of a wireless bridge and as a wireless repeater. I chose the “mini” version of DD-WRT because it fits within the 3 Megabytes of memory that’s occupied by Linksys’ firmware. The hardest part of getting started was finding an image file (with a .bin extension) of Linksys’ latest firmware. They removed it from the download section of their website at the end of July. I eventually found a copy on a UK-based site, and updated our WRT54GS with it, before replacing it with DD-WRT v24-sp2 (12/18/09) mini. We configured it so that it’s a client of the existing WiFi (IEEE 802.11b/g) network.

DD-WRT wireless screen.
Click to enlarge.

How well does the new wireless bridge work?

The results, with very little effort, exceeded my expectations. The wireless link has been rock-solid, with a 25 to 35 dB (deciBel) signal-to-noise ratio (SNR). (20 dB is considered to be a good minimum.) We briefly experimented with adding reflectors behind the two antennas of the WRT54GS, and saw the SNR increase by 3, 6, maybe even 10 dB with no effort. We’ll probably add a permanent reflector later.

In the meantime, this low-cost wireless bridge not only is used during the day by Autobahn’s employees in the remote building to access company data, but allows the business owner to add a second DVR (digital video recorder) and surveillance cameras to his newly leased building, and monitor them remotely from his smartphone, just as he now monitors his main building’s cameras.

photo: Cisco

Update October 23, 2011: Last week, this bridge stopped working. (Routers and bridges will periodically halt without warning. They are, after all, merely special-purpose computers.) Maybe the DD-WRT firmware isn’t well-behaved. To repair the problem, a user in the remote building pressed the WRT54G’s reset button with no improvement. If your wireless bridge stops working, don’t press its reset button! Instead, remove its power for 30 seconds, and then restore its power. Pressing the reset button removes the configuration and restores it to DD-WRT’s default settings. (This is not what you want.) Just removing its power and then restoring power resets the CPU, while retaining the configuration. After restoring the configuration, the bridge resumed working. All’s well that ends well.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695