Intro

Wireless communication uses electromagnetic (EM) waves to transfer information between two or more nodes without a conducting path

The complete range of frequencies of EM radiation

EM waves are carried by photons which oscillate with a specific frequency 𝑓 (in [Hz]), independent of the medium

For the purpose of information transfer, the region below the visible light spectrum is preferred

Transceivers can be much more easily constructed than for Terahertz radiation

The penetrative properties of RF allow communication through obstacles and much higher range than with infrared

Infrared (𝑓 [𝑇𝐻𝑧], 𝜆 ~ 700𝑛𝑚 … 1𝜇𝑚)

Terahertz radiation(𝑓 [𝑇𝐻𝑧 … 𝐺𝐻𝑧], 𝜆 ~ 30𝜇𝑚 … 1𝑚𝑚)

Radio Frequency (𝑓 [𝐺𝐻𝑧 … 𝐻𝑧], 𝜆 > 1𝑚𝑚

The microwave range, which contains the shortest wavelengths/ highest frequency (𝑓 ~ 300𝑀𝐻𝑧 … 300𝐺𝐻𝑧, 𝜆 ~ 1𝑚𝑚 … 1𝑚) and is used for most wireless communication technologies

The Very High Frequency (VHF) range, which is (was) used for radio and television broadcasting

The High Frequency (HF) and Medium Frequency (MF) ranges which are used for wide-range and intercontinental communication

defined by the ITU in Radio Regulations articles and (mostly) internationally agreed on

no licence costs are necessary for their usage

most common used 2.4 – 2.5GHz

structure that converts between a guided plane wave on a line and a spherical free-space wave

converts currents on a wire into RF photons, and vice versa

matched to a certain wavelength

• Dipole

• Meander

• Yagi-Uda

• Dish

• Cantenna

downsized versions of the classical BNC-type connectors for coaxial cables, called Subminiature Version A (SMA)

Typically, male connectors are used on antennas, female connectors are used on boards/dongles

Male: Inner-threaded barrel and inner pin

Female: Outer-threaded barrel and inner receptable

Male: Inner-threaded barrel and inner receptable (!)

Female: Outer-threaded barrel and inner pin (!)

RF signal sent out by an antenna gradually loses energy, with the loss proportional to the square of the distance

The weakening of a RF signal due to distance alone is termed the Free-Space Path Loss (FSPL)

assuming direct line-of-sight transmission in vacuum and that sender and receiver use ideal omnidirectional antennas

Additional losses from other factors (e. g. absorption, interference) must be considered

Superposition by other, stronger RF signals

can be mitigated by sophisticated transmission schemes

By matter in the propagation path

(e. g. water molecules in air, walls, conducting structures

Reflection in multiple directions due to small (e. g. Rayleigh scattering: d > 𝜆) or uneven objects

(e. g. dust, snow storm)

Bending of the signal path on sharp edges of objects

(e. g. buildings)

Splitting up into multiple path components due to reflections (e. g. on walls) with possible destructive interference by the delayed path components at receiver

Can be exploited for higher data rates!

Undefined range: in principle unlimited range

Shared medium: Wireless devices communicate over the same medium, wireless transmission is half-duplex only

Variable link quality: Overall quality can change rapidly in short time

Mobility of devices

All this makes the need for different routing protocols

Fokus auf Wlan, Bluetooth, Zigbee und NFC