Microwave Ovens and WiFi Routers

I never cease to wonder about the electromagnetic spectrum. Much of it is invisible to our senses, and yet, we have reached a stage when it is quite impossible to survive without it.

The microwave oven in out kitchens sends out waves at around 2.45 GHz (2,450,000,000,000 vibrations/second!), heating up food at the molecular level. The ubiquitous WiFi that keeps us connected to the internet - and the rest of the world - are "harmonized" worldwide in the 2.4 and 5GHz bands. Even without getting into the world of electronic waves that send signals across great distances (radio, satellite and space probes), getting a grip on regular household devices seems complicated enough!

Both the equipment's - the microwave oven and the WFi router - produce signals in the Industrial, Scientific and Medical (ISM) bands that have been allotted by ITU for non-communication purposes. There seem to be 12 frequency ranges in the ISM band that ranges all the way from 6.78 MHz to 245 GHz. Out of this, home equipment like ovens and WiFi routers use the frequency range 2.45-2.5 GHz.

Since a licence is not required for equipment produced in this range, the part of the spectrum is also crowded with radio-communication services, including amateur satellite services. Thanks to this dual-use, the WiFi equipment you purchase from one country country is likely to interfere with the microwave oven imported from another country. So, if you are heating a mug of coffee in your microwave oven, your internet connection may get disrupted.

International standards - especially IEEE 802.11 a/b/g/n - tries to deal with this problem:

• 802.11a supports bandwidth up to 54 Mbps and signals in a regulated frequency spectrum around 5 GHz. More expensive, usually used by businesses. Higher frequency makes it difficult to penetrate walls, so its best for open areas.
• 802.11b supports bandwidth up to 11 Mbps, comparable to traditional Ethernet. Usually for home networks.
• 802.11g supports bandwidth up to 54 Mbps; uses the 2.4 GHz frequency for greater range
• 802.11n is an improvement on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one.

It is still mind boggling to think that we have actually figured out ways to precisely control devices that produce more than a trillion vibrations per second! How do we do it? And why is it that microwave ovens need chunky magnetrons to produce the same kind of signals that are produced by lightweight WiFi routers?

In an emergency, can I rig up my WiFi router to heat up a mug of coffee? :)

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LINKS

ITU - http://www.itu.int/en/Pages/default.aspx
http://www.itu.int/itu-t/recommendations/rec.aspx?

https://www.howtogeek.com/171869/why-does-running-my-microwave-kill-my-wi-fi-connectivity/

Wireless Standards - https://www.lifewire.com/wireless-standards-802-11a-802-11b-g-n-and-802-11ac-816553

WiFi and Basic Needs

This illustration says it all.

It might be stretching things a bit, but it does indicate how staying connected seems to have becomesome sort of a desperate, visceral need. We now choose hotels and eateries based on their ability to provide reliable bandwidth as much as the quality of accomodation or food. There is now a joke going around that, even at home, the best way to have a family get-together is to switch off the wireless router!

In an earlier post, I had figured that all WiFi devices talk to each other in the 2.4 GHz frequency, and that as per international protocols this band is divided into 79 channels (each 1 MHz wide) which the devices can change up to 1600 times per second, just to keep a data connection going.

I still have no idea how the scientists managed to create anything that sends out 1,000,000,000 vibrations per second, let alone how they go about slicing it like a cake and passing it around with all the icing and toppings intact.

Perhaps it is easier to understand things that are happening at an individual device level. Here are two parameters from my WiFi analyser:

The first screenshot shows that the signal strength ranges from -100 dBm (decibel milliwatts) to -40 dBm. The key unit here is that of power - Watts. It takes a thousandth (1/1000) of a Watt to send out signal equal to 0 dB.

The negative sign comes from the log scale. To quote WirelessAnnonymous:

Under a log 10 scale, a value of -2 represents 10 to the -2 power, which equals 0.01. Likewise, a negative dBm means that you're applying a negative exponent in your power calculations; 0 dBm equals 1 mW of power, so -10 dBm equates to 0.1 mW, -20 dBm equates to 0.01 mW, and so forth. It's a lot easier, and more useful in some calculations, to describe a weak signal as -100 dBm as opposed to 0.0000000001 mW.

The following shot illustrates how the signal strengh drops the further you move away from a router. The closest ones are sending out signals stronger than -50dBm while the farthest ones have the green bands diminishing into the -90 dBm range.



Then you have the next most important thing: the media access control (MAC) address.

When you have millions of data signals riding piggypack on radio waves, it is necessary to ensure that they reach the right destinations. For this, each WiFi device comes with a unique MAC address and they all use the address resolution protocol (ARP) to avoid cross-talk. If we compare the whole set up to city traffic, MAC represents the final destinations (a mall, home or fuel station). Vehicles (data packets) traveling along the roads (the internet protocol/IP) are capable of reaching anywhere but get an entry only to those places which have a matching MAC address.

This brings us to the next basic need - how do we stay safe from the carjackers, and hackers hiding in the dark streets?

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REFERENCES & LINKS

* Reading signal strength -- http://www.tomshardware.com/forum/9782-43-read-signal-strength
* How to Geek - MAC Address - http://www.howtogeek.com/169540/what-exactly-is-a-mac-address-used-for/
* Ask Leo: IP address vs. MAC address -- https://askleo.com/whats_the_difference_between_a_mac_address_and_an_ip_address/

WiFi Spectrum Anayzers

WiFi - CR Park, Delhi

These days, there are few things as indispensible as WiFi networks.

No hotel or restaurant worth its salt will scrimp on bandwidth when it comes to offering WiFi as a free service to its customers. Forget the McDonald's even most ramshackle dhaba's along the national highways are offering it as a bait for those who are hungry for data.

In this scenario, it is interesting to scan WiFi networks while you are on the move. The above screenshot was taken at CR Park market in South Delhi. Well past 8:00 PM, the analyser showed up no less than 20 separate routers in a 20 sqft area.

It is one thing to see the colorful parabola's bobbing up and down the graph and another to actually understand what they actually mean.

Why, for instance, is the signal strength in dBm (decibels milliwatts)  going upwards from negative hundred (-100 dBm) towards zero?

How does the address system in WiFi devices various devices link up to the the IP addresses? Why are these in six sets of alphanumeric characters separated by a colon, as opposed to numeric IP addresses that come in sets of four numbers each?

Why is the bandwidth restricted to 11 to 14 channels?

How do the WiFi transmitting devices manage to keep their frequencies in such a sharp range? Rather mindboggling when you learn that these signals are being sent out in Giga Hertz -- 1000,000,000 vibrations per second!

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LINKS

* dBm in Wiki -- https://en.wikipedia.org/wiki/DBm

* how to fix your wifi network - http://www.pcworld.com/article/260524/how_to_fix_your_wi_fi_network_7_tips.html

WiFi Internet Connectivity

We just graduated from a dongle to a wifi router.

I must thank BSNL, MTS, Reliance and Tata Docomo for forcing us to take this quantum leap. All four of them have been providing such pathetic internet connectivity in Noida that we never really experienced a broadband internet connection at home, until today.

BSNL had everything going for it. It was the first one to lay down optic cables and hubs in the neighborhood and it was offering the most competitive rates too. Unfortunately they also had a bunch of linemen moulded in the licence-permit Raj. Since they just could not kick the habit of demanding  "baksheesh"from customers, they always ensured that the last-mile connectivity was primed to fail, as frequently as possible.

The telecom corporates fared no better. The slick ad campaigns from Reliance, MTS and Tata Docomo offered high-speed internet of "up to 21 Mbps". In reality this meant that the speeds could be anywhere between 0 Kbps and 450 Kbps, well within their promised range!

Our new service provider, a franchisee for Triple Play, simply promises a download speed and then delivers it. We now have a plan for 4Mbps speed till 25GB for Rs. 800/month. Speedtest has consistently confirmed that - at least so far - they have exceeded promises.

Unlike last time with BSNL, we have picked a wireless router on our own from the online market. A Netgear N150 (JNR1010v2) marked with an MRP of Rs. 1600 was available in Atta Market for Rs. 1200. The same thing is on Snapdeal for Rs. 784!

How on earth do they figure a pricing strategy in a market like this?


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An attempt to make sense of the technical hocus-pocus:

Q. What is the radio frequency used by wifi routers?
A. Usually 2.4 GHz. for a maximum link speed of 150 Mbps. It is interesting to note that 'larger channel widths do not result in higher range, just faster speeds at close range'. So it is just as well that I did not buy a dual antenna N300 model for double the price!
Netgear's classification - details here.

Q. What is an "External 5dBi antenna"?
A. dBi stands for 'decibels relative to isotropic'. It represents  the direction and efficiency (Antenna Gain) with which a transmitter sends signals across distances. More here.

Q. The router conforms to four sets of international standards: Safety, EMC, Radio Spectrum and RoHS. What are these?
A. EMC = Electromagnetic Compatibility (European Standard - EN and International Electrotechnical Commission or IEC);
RoHS = Restriction of Hazardous Substances Directive  - also known as the "lead-free directive" it restricts the use of six substances in manufacturing.

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REFERENCES & LINKS

* http://www.explainthatstuff.com/wirelessinternet.html

Indian Science & Tech: The Price of Red Tape

India-born scientist, Prof. AJ Paulraj has won this years' prestigious Marconi Award. Multiple-Input and Multiple Output (MIMO) wireless technology pioneered by Paulraj now enables us to use high-speed internet connections through WiFi and 4G.

While going through the award citation and the press coverage that followed, what struck me was that unlike most NRI's scientists, Prof. Paul was originally with the Indian Navy. Its the navy that sent him for higher studies to IIT-Delhi, and then on to a PhD at Stanford.

Again, unlike most NRI's, he returned to India to found three major labs -- CAIR (Center for Artificial Intelligence and Robotics), CDAC (Center for Development of Advanced Computing) and CRL (Central Research Labs of Bharat Electronics).

And then something happened that drove Prof. Paul out of India. According to a Times of India article:

"...by 1991, according to the now familiar narrative, bureaucratic battles began to take their toll, and with the consent of the Indian Navy, he returned to the US and Stanford University. ''His departure for Stanford University was a major loss for our country and the circumstances that led to his move may explain why we have so few Nobel Laureates from India,'' Admiral Tahiliani said."

What happened?? What is the "familiar narrative"? Where were the bureaucratic battles waged?

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LINKS & REFERENCES

* Marconi Society - announcement - http://www.marconisociety.org/press/2014paulrajannouncement.html

* Chidanand Rajghatta (ToI, 23Jan14): NRI Scientist AJ Paulraj wins Tech 'Nobel' - http://articles.timesofindia.indiatimes.com/2014-01-23/us-canada-news/46513090_1_indian-navy-mimo-iit-delhi

* Introduction to MIMO technology - http://www.ieee.li/pdf/viewgraphs/wireless_mimo.pdf

* Thomas Kailath - https://en.wikipedia.org/wiki/Thomas_Kailath