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Wireless Pi

Discover the Joy of Signals, DSP and Wireless Communications


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HOME

Wireless Communications from the Ground Up – An SDR Perspective
Software Defined Radio – From 0 to 1
5G Physical Layer – An Easy Guide to Key Technologies

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One of the most memorable phrases in television history is the command from
Captain Kirk to his chief engineer Scotty in the science fiction series Star
Trek:

“Beam me up, Scotty!”

It refers to the futuristic teleportation machine, known as a Transporter, which
disassembles a person or object into an energy pattern, then beam it to a target
site where it is reassembled into the original matter.




FROM MECHANICS TO ENERGY BEAMS

--------------------------------------------------------------------------------

Imagine that such a device is invented at a point in the future. Until then, the
knowledge of a person relating to transportation through automobiles is based on
an internal combustion engine, pistons, crankshaft and so on. Suddenly we find
ourselves in a completely different territory because designing and building the
technology for transporting a person from location A to location B is now based
around mass-energy equivalence in physics, according to which mass and energy
are the same physical entity and can be converted into each other. Not only do
we need to understand
E=mc2E=mc2
from Albert Einstein’s theory of special relativity but also come up with
optimal strategies to reproduce as closely as possible the said person or object
from the incoming beam. This is a process that requires excellent mental models
of the underlying mass ↔↔ energy conversion phenomena, not the mechanics of the
engine.




FROM ELECTRONICS TO DSP

--------------------------------------------------------------------------------

In not as dramatic but still a similar manner, wireless communications has
profoundly transformed as a science in the previous years due to the digital
revolution.

 * On the transmitter side, we have become able to send into air a sequence of
   numbers stored in a processor memory.
 * On the receiver side, we have become able to acquire the momentary value of
   the incoming analog signal and convert it into its digital representation
   which is nothing but a sequence of numbers, known as a discrete-time
   sequence.

After the great advancement in computational power, most of the radio circuits
capable of performing analog signal processing (e.g., by using resistors,
capacitors, inductors, op amps — basically physics and devices) have been
replaced by powerful digital processors that can perform the necessary number
crunching (basically algorithms run by computer programs) to unravel the
original digital information. In a true software radio, this is a process that
requires excellent mental models of the underlying discrete-time sequences, not
the electronics of the circuits.



Shown on the right side above is a discrete-time sequence that consists of a few
random bits 0s and 1s mapped to signal levels -1s and +1s, respectively. Why
does it look more complicated than a stream of -1s and +1s? Because in the real
world, this signal has been distorted by the following impairments before
presenting itself to the Rx processing machine.

 * Carrier phase offset: 17˚
 * Timing phase offset: 31% of a bit time
 * Carrier frequency offset: 11% of the bit rate
 * Multipath channel: A direct path and two reflected paths with relative
   amplitudes of 0.6 and 0.2 arriving after relative delays of 0.76 and 1.03,
   respectively

(If you are unfamiliar with the above terms, there is no need to worry. This
website has plenty of explanations on these topics.) The I and Q parts shown in
the above figure are the two components of a complex signal. I cover complex
numbers as a starting point to build our Digital Signal Processing (DSP)
toolkit. Also, I like to view the same IQ signal in a 3D figure as shown below
which offers several advantages over the separate two 2D figures.



By just looking at the above figure, it is hard to believe that extracting the
original stream of bits 0s and 1s from this complex sequence is even possible
after so much distortion. Nevertheless, this amazing (ad)venture can be
accomplished through implementation of DSP algorithms in a programming language
such as Python or Matlab. This is all a Software Defined Radio (SDR) is about,
see the figure below.



To find out how this is done, you can see my book for background theory and the
SDR course for implementing an actual wireless communication system.




WHY WIRELESS PI?

--------------------------------------------------------------------------------

My name is Qasim Chaudhari and I write about software defined radio and wireless
communications in a different style as compared to several other wonderful
resources available on these topics.

 * As you will find in the introduction of my book, any language, including that
   of mathematics, is an unnatural mode of communication. On the other hand,
   showing an image makes almost every single person on the planet immediately
   get the concept. A figure imprints a massive amount of parallel information
   in our brains that is much easier to process and recall later. Since a human
   mind handles images very well, I make the reader visualize the equations
   through beautiful figures.
 * I only rely on school level mathematics to explain all the concepts. The only
   things to know are a sine, cosine and a summation as well as (occasionally) a
   derivative.
 * Almost everything I have written has been built from the ground up and
   intuitive explanations are presented behind the ideas.

In the past when only humans could read, we wrote scientific material in a
machine-like manner. Now when the machines are learning to read, why not turn
towards a more human-like style. In my opinion, there is no harm in writing
technical stuff with a human touch, see some examples below.


POPULAR ARTICLES

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I/Q Signals 101 – Neither Complex nor Complicated
A Beginner’s Guide to OFDM
A Real-Imaginative Guide to Complex Numbers

--------------------------------------------------------------------------------

A Tutorial on Intelligent Reflecting Surfaces (IRS)
Beamforming in 5G Systems
Phase Locked Loop (PLL) in a Software Defined Radio (SDR)


JOIN ME

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