Wireless Networking Fundamentals

Full Course: https://www.youtube.com/playlist?list=PLUoixF7agmIsn411Kop8v2x8IwngOF7OB

Wireless Transmission Methods
2.1. Microwave Line of Sight
Data transmissions in the microwave frequencies (20 – 50 Mbps)
Microwave: High frequency form of radio wave with short (1 cm to 1 m) wavelength
Requires line-of-sight
They are blocked by buildings, hills, and even the curvature of the Earth
To overcome obstacles microwave antennas are often placed on towers or hill tops
Also used in cellular phones and space communications (including satellite communications)

2.2. Transmission Through Satellites (20 – 50 Mbps)
Recently 3600+ satellites in orbit (1000+ are operational)
Geostationary Satellites:
Orbit the earth at a velocity to overcome the force of gravity
Orbital speed exactly matches the rotational speed of the Earth
35,786 km (22,280 miles) from the earth’s surface
These satellites seem to hang over a fixed spot on the Earth
A typical geostationary satellite has several dozen transponders (relay amplifiers), each with a bandwidth of tens of MHz
Frequency bands (downlink/uplink):
L (1.5/1.6 GHz)
S (1.9/2.2 GHz)
C (4/6 GHz)
Ku (11/14 GHz)
Ka (20/30 GHz)

Low earth orbit satellites (LEOS) and Middle earth orbit satellites (MEOS): Below 35,786 km
A LEOS attempt: Motorola’s Iridium for a global cell phone service (in the 1990s; failed due to high service cost compared to local terrestrial cell phone services):
Six orbits of 11 satellites each
Several satellites move across the sky over any location on earth
Support for almost a quarter of a million conversations
Calls can be relayed from satellite to satellite

Low Earth Orbit Satellites (LEOS)
Iridium-NEXT: A second-generation worldwide network of
telecommunications satellites (2016)
17.01.2017: SpaceX launches first batch of Iridium satellites
25.06.2017: SpaceX launches second batch of Iridium satellites
09.10.2017: SpaceX launches third set of Iridium satellites
24.11.2017: SpaceX launches fourth set of Iridium satellites
18.03.2018: SpaceX launches fifth set of Iridium satellites
11.01.2019: Iridium completes historic satellite launch campaign

Transmission Through Satellites: Challenges
Propagation Delay: Substantial time necessary for a satellite message to travel
This delay makes satellite transmission unsuitable for timed communications protocols (e.g., Ethernet)
Actually Starlink provides good throughput (50+ Mbps) and latency (50 ms) which is enough for even online gaming but since satellites are in motion, switch between satellites can cause momentary disruption
Security: Satellites can not be aimed
Therefore, they broadcast their messages to an entire hemisphere
Anyone with the appropriate receiver can intercept the transmission
If security is a concern some sort of encryption must be employed

2.3. Transmission Through Cellular Systems
Signals travel between a cell phone and a local base station antenna which is hard wired into the public switched telephone network
A geographic region such as a city or suburb is divided into geographic sub-regions called cells
A base station at the center of each cell
Nearby base stations are wired into a switching computer (the mobile switching center or MSC) that provides a path to the telephone network
When necessary, connectivity is changed from one base station to an adjacent one, namely handoff

2.4. Ad Hoc Networks
Dynamic, decentralized, self-configuring networks
No pre-existing infrastructure (e.g., no routers in managed wired ad hoc networks or no access points in managed wireless networks)
Each node participates in routing by forwarding data for other nodes based on the dynamics of network connectivity and the routing algorithm in use
Also known as multi-hop radio networks
Sample applications of ad hoc networks
Mobile ad hoc networks (MANETs, aka. wireless ad hoc network or ad hoc wireless network)
Vehicular ad hoc networks (VANETs): Used for instant communication between vehicles and roadside equipment (a major research topic for AI)
Smart phone ad hoc networks (SPANs): Employs smartphones to create peer-to-peer networks without relying on cellular carrier networks, wireless access points, or traditional network infrastructure (e.g., multi-peer ad hoc mesh networking capability since Apple iOS 7.0)
Army and navy tactical MANETs
Air Force unmanned aerial vehicle (UAV) Ad hoc networks
Ad hoc home smart lighting (to control lights over a smart phone or via a computer, e.g. ZigBee)
Most wireless ad hoc networks do not implement any network access control!
Vulnerable to resource consumption attacks (a malicious node injects packets into the network for depleting the resources of the nodes relaying the packets)
(Even with authentication) vulnerable to packet dropping or delaying attacks: An intermediate node drops the packet or delays it, rather than sending it to the next hop

2.5. Wireless Sensor Networks
#networksecurity #cybersecurity #wireless .