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Wireless Protocols

Title: Wireless Protocols

Introduction

This document is a high level view of few prevalent wireless technologies.

The aim is to create a perspective about technology that we popularly refer to as wireless – in these cases devices communicate in isolation or as part of a larger, more complex network.

The following information is provided in the comparison table below:

Comment

A small comment on the technology.

Protocols

There are a large number of protocols.  This can be very confusing to the beginner. The protocols mentioned here are popular and indicative ones for that technology – not an exhaustive list. This value is provided here only for information, just to help make the association, and as a pointer to further details to help understand what they do with respect to addressing, handshaking, data transmission, encoding; point to point or broadcast; node/ instrument profile as transmitter, receiver, repeater, master, slave, etc.

Very often the protocols that these technologies are referred to by are the low level protocols (Layers 1 & 2 as per OSI model).

For example:

  • The 802.* series.
  • Phone manufacturers that support WiFi will say that they support IEEE 802.11 a/b/g/n

Frequency

Is provided for information purposes only. The frequency range gives an idea about the transmission characteristics.

The characteristics vary widely across different spectrum bands. There is no definite trend, and each one is different.

For example, low frequencies ( long wave)may travel longer distances since they are reflected by the earth and the atmosphere.

Frequencies in the optical range have their own unique properties. Very high frequencies have good penetration, and can pass through barriers like walls, for example.

Other generalizations, not wholly accurate, are that at higher frequencies more data can be transferred, as compared to lower frequencies. Also higher frequencies consume more energy (in part due to the absorption characteristics of the media)

A popular classification is of the kind to ULF, VLF, VHF, EHF, etc.

http://en.wikipedia.org/wiki/Radio_spectrum#By_frequency

Range

In case of wireless communication, the range that can be covered depends upon the power available. Frequency bands to transmit information are an important and precious resource, and this controlled by a regulatory body.

All the technologies that we look at here operate locally (except mobile technologies) over small distances, and come under the ISM (Industrial, Scientific and Medical) band. ISM operates at 868 MHz in Europe, 915 MHz in the USA and Australia and 2.4 GHz in most jurisdictions worldwide. Data transmission rates vary from 20 kilobits/second in the 868 MHz frequency band to 250 kilobits/second in the 2.4 GHz frequency band.This band allows people/devices to communicate locally wirelessly. The regulation controls the range over which the devices can transmit.It does so by limiting/specifying the power rating.

The value here gives an idea of usual ranges in domestic applications.  Like between point to point communication. Or between a transmitter and a receiver. As opposed to between nodes in a network. Continue reading

Sight

This is rambling article about human vision.

Blind spot
It all started when we were having fun with the “blind spot”. Its been known for ever that the blind spot exists. It is now well-known that is the position in the eye which has no receptor cells from where the optic nerve leaves for the brain.

I couldnt get it to work for it – but the wikipedia page worked perfectly for me. It was awesome !!!

http://en.wikipedia.org/wiki/Blind_spot_(vision)

Colourscolours

Colours have always been fasicnating. Aesthetically, scientifically. We know that there are basic colours – red, blue and green – from which all other colours can be derived. Changing the intensities of these colours and mixing them can produce virtually every other colour. And can be very entertaining too. It doesnt have to be exactly these three colours, but can be any three colours from three appropriate group. Why 3 ? It turns out, and it seems so obvious in retrospect, that there are three kinds of cone cells in the eyes. These cone cells are responsible for colour perception and their photoreceptors are of three kinds – most sensitive to red, geen and blue !

It turns out then – that night vision – vision in dim light – which is colourless – is due to biology again. Rod cells are responsible for this vision, as opposed to cone cells. And unlike cone cells they dont have the photopigment in them.

Some notable scientific greats have been intrigued with colour and have focussed their energies there.
Schrodinger, the genius who did many things, but is mostly known as one of the founding fathers of the quantum theory, and his quantum mechanical wave equation. He published a number of papers in the field of color, color perception and colorimetry.
While on the topic, it was Schrodinger’s book “What is Life?” that led to an entire generation turning their energies to research in that line that eventually led to the discovery of genes and established the field of genetics. Continue reading

Rosetta – Philae and the Comet

Rosetta_NAVCAM_comet_67P_20140919_mosaic_625A news that caught my attention recently was about the spacecraft Rosetta, and that it had landed a module, Philae, on a comet.

I thought it was special because-
As compared to planets which seem stable and calm, a comet in my mind is a racing ball of fire.
Also a planet is this large thing, and a comet is small.

So am I implying that landing a vessel on a planet is common, but its special if on a comet ?

Of course there is no basis for my idle perceptions.
Landing sites on the Moon and Mars are pin-pointed in advance, and well achieived too. A planet is this huge hurtling, spininng massive sphere – subject to great forces, and creator of its own.
Exploratory vessels have their trajectories defined for years in advance. Satellites have their orbits planned, monitored and corrected. Its all very amazing and hi-tech.

Am I implying now that a comet landing is also no great deal ? :)

I guess I still find the idea of a comet landing very fascinating, almost unreal.
Here a some more stunning facts:

  • The Rosetta spacecraft was launched in 2004 – 10 years ago.
  • The comet, 67P/Churyumov-Gerasimenko, is a big rock, about 4 kms in it longest dimension.
  • On its way to comet 67P, Rosetta passed through the main asteroid belt, and made the first European close encounter with several of these primitive objects.
  • Rosetta was the first spacecraft to fly close to Jupiter’s orbit using solar cells as its main power source.

Continue reading

Acharya Sir Jagadish Chandra Bose

Archarya Sir Jagadish Chandra Bose is one of the leading luminaries of Indian Science.

Incidences from the life of this extrememly talented individual highlight his exemplary value J_C_Bosesystem, his humility and his grit and determination. For example, when he was faced with discrimation he declined his salary and continued to work for 3 years, his research conducted in trying circumstances with meagre resources, or his disinclination of filing patents for his inventions.

However in this small article we only aim to highlight 2 of his inspiring efforts.

 

Radio research and wireless signalling – including use of semi-conductor

Sir Bose’s research in microwave waves allowed him to generate waves in the millimetre level (about 5 mm wavelength).

The first remarkable aspect of Bose’s follow up microwave research was that he reduced the waves to the millimetre level (about 5 mm wavelength). He realised the disadvantages of long waves for studying their light-like properties.

During a demonstration at Town Hall of Kolkata in the 1890s, Bose ignited gunpowder and rang a bell at a distance using millimetre range wavelength microwaves.
He used waveguides, horn antennas, dielectric lenses, various polarisers and even semiconductors at frequencies as high as 60 GHz. Which is quite mind-boggling, given the time and circumstances.
Continue reading