Course

Wireless and Mobile Networks: why the signal stops where it does

Name: Wireless and Mobile Networks: why the signal stops where it does
Price: 1799 BDT

Radio, Wi-Fi, mobile and satellite are one phenomenon at different frequencies, and the frequency decides almost everything. Work out why a remote must be pointed and Wi-Fi need not be, then stand a router in a real flat and find the rooms it cannot reach.

38 lessons3h 25mEnglish

What you'll learn

Explain why coverage is drawn as hexagons and size a cell from a propagation model
Predict what a move to a higher band does to the number of masts a city needs
Name a task a generation cannot serve and say which of its two requirements blocks it
Explain why a handover rule needs hysteresis, and what is lost at each end of that dial
Derive a satellite round trip from its altitude, and say which tasks that rules out at any bandwidth
Explain why one weak device slows a whole Wi-Fi cell, and choose the repair that actually helps
Explain why Wi-Fi uses random backoff and why carrier sensing cannot prevent hidden-station collisions
Say what a shared network password does and does not protect you from, and what HTTPS adds
Decide what to do on a public network, and defend the choice against what is actually exposed
Place radio, microwave, infrared and visible light on one axis and read the gaps between them
Calculate a wavelength from a frequency and say it in units a person would use
Explain why a phone has no visible aerial and a car radio did
Predict which bands need a clear line of sight, before checking
Explain why an infrared remote must be aimed and a Wi-Fi router need not be
Read a signal level in dBm and say what a person could do standing there
Separate a room that is weak because it is far from a room that is weak because of what is in the way
Choose where one access point should stand in a real floor plan, and defend the choice
Explain how voice or video becomes packets, crosses a radio access network and is reconstructed at the receiver
Compare amplitude and phase modulation and show how noise can change the recovered bits
Explain why adding receivers does not add terrestrial broadcast streams, while unicast load grows with viewers
Tune a live-stream buffer and explain why avoiding stalls places playback farther behind the event

Requirements

Comfort with powers of ten. The spectrum axis multiplies at every step and the arithmetic is not explained again
No prior networking knowledge. The course starts in the air, not at a cable

Course content

38 lessons · 3h 25m

The invisible spectrum

Radio, microwaves, infrared and light are one thing at different rates, and the rate fixes the wavelength. Three short lessons build that one idea, and the fourth spends it on a real flat with a real router in it.

0/5

One phenomenon, many names

Radio, microwave, infrared and light on one axis, where each labelled step multiplies by ten.

Preview6m 2.

How long is one wave?

One wavelength beside something you could hold, and the antenna length that follows from it.

Preview6m

What stops a signal

The same wall, every band. A remote is stopped by paper and Wi-Fi crosses brick, for one reason.

Where the router should stand

Three lessons of physics applied to one flat, where two rooms fail for opposite reasons.

Chapter check: the invisible spectrum

Four questions on the axis, on wavelength, on what stops a signal, and on placement.

Towers and generations

A generation is a position on a trade, not a place in a queue. A higher band carries more and reaches less, and because a cell is an area that small loss of reach becomes a large bill. Then the second half, which the advertising never mentions: what changed most recently was the round trip.

0/5

One tower, one hexagon

Why coverage is drawn as hexagons, and how far one mast on an old band actually reaches.

Preview6m 2.

The square that decides the cost

Halving the reach quadruples the towers, which is most of the economics of every rollout.

Preview7m

Two numbers, not one

Every task needs a data rate and a round trip, and generations are compared on only one of them.

What 5G actually changed

The reachable region stops growing sideways and jumps upward. That jump is the round trip.

Chapter check: towers and generations

Four questions on cell size, on the square law, on latency, and on what a generation is.

A phone that moves

Everything so far assumed the phone stands still, which is the assumption that makes cellular look simple. A call is held by one mast at a time, so a moving phone has to be passed to the next one. The rule that decides when looks obvious, fails badly, and the fix costs something at the other end.

0/3

The obvious rule fails

Always using the strongest mast hands one call over eleven times to cross a single boundary.

Preview8m 2.

A margin, and its price

Hysteresis stops the ping-pong. Too much of it and the phone clings to a mast until the call dies.

Preview8m

Chapter check: a phone that moves

Three questions on ping-pong, on hysteresis, and on what is being traded.

The longest wire

Every limit so far gives way to money. A weak room gets a second access point, a city gets more masts, a slow band gets refarmed. Distance gives way to nothing, because the signal travels at the speed of light, and a satellite is very far away.

0/3

Half a second of nothing

Why satellite television is excellent and a call over the same satellite has never been usable.

Preview7m 2.

Flying lower, and what it costs

Low orbit cuts the delay sixty times, and pays for it with the last two chapters over again.

Preview8m

Chapter check: the longest wire

Three questions on the round trip, on what it rules out, and on what low orbit costs.

The air is shared

Chapter 1 judged each room on its own signal, and that is not the whole account. A switch gives every device its own wire; Wi-Fi gives them all the same air, so they take turns, and what they take turns at is time. A room that is merely usable therefore slows down every other room in the house.

0/4

Taking turns

One device in the far bedroom holds nearly nine tenths of the channel, and everybody waits.

Preview8m 2.

Fix the worst room

Moving one tablet takes the house from 21 Mbps to 132. A faster router would have done nothing.

Preview8m

Listen, wait, collide

Carrier sensing and random backoff reduce collisions, until two hidden senders both hear silence.

Chapter check: the air is shared

Three questions on what is shared, on who holds the channel, and on what to buy.

Who can read it

Chapter 1 ended on a fact and left it hanging: radio reaches everyone in range, so nothing decides who receives your signal. What is left to decide is who can make sense of it, and that happens in two separate places protecting two different things. Both have a hole that almost nobody knows about.

0/3

The password on the wall

A shared password is a shared key, so on WPA2 the next table can read what you typed.

Preview8m 2.

What the padlock does not cover

HTTPS hides what you sent and not where you sent it, and two rows never go dark at all.

Preview8m

Chapter check: who can read it

Three questions on shared keys, on what HTTPS covers, and on what radio always reveals.

One live call

Bring the course together by following one instant of speech from air pressure to encoded packets, from digital decisions to a radio wave, and through a moving mobile network to another person.

0/4

Sound becomes data

Capture, encoding and packetisation turn continuous media into data a network can carry.

Preview8m 2.

Bits become a wave

A modem maps discrete bits onto changes in a continuous carrier and recovers decisions through noise.

Preview8m

The whole call

A voice or video call crosses encoding, security, radio access, network transport and reconstruction.

Chapter check: one live call

Four questions on encoding, modulation, loss and the end-to-end call path.

One programme, many receivers

Compare how one programme reaches an audience, then follow an internet livestream from camera to viewer and tune the delay that keeps playback resilient.

0/3

Three ways to reach an audience

Audience growth costs terrestrial broadcast, multicast and unicast networks differently.

Preview8m 2.

How live is live?

Segments, CDN delivery and viewer buffering trade immediacy for uninterrupted playback.

Preview8m

Chapter check: one programme, many receivers

Four questions on capacity, return paths, multicast scope and personalization.

About the creator

Classytic