Fundamentals of Wireless Communications Lecture Notes

This set of vocabulary flashcards covers concepts from the Fundamentals of Wireless Communications lecture, including radio propagation modes, atmospheric layers, frequency bands, transmission impairments, antenna types, signal fading models, and error compensation mechanisms.

Ground wave propagation

A form of radio wave propagation that follows the contour of the earth and can propagate considerable distances well over the visual horizon, typically found in frequencies up to about $2\,MHz$.

Sky wave propagation

A signal from an earth-based antenna reflected from the ionized layer of the upper atmosphere (ionosphere) back to earth, capable of traveling thousands of kilometers through multiple hops.

Line-of-Sight (Space-wave) propagation

Propagation required for frequencies above $30\,MHz$ where transmitting and receiving antennas must be within an effective line of sight of each other.

Ionosphere

The ionized layer of the atmosphere located between $80\,km$ and $720\,km$ that reflects sky wave signals.

ELF (Extremely Low Frequency)

A radio frequency band ranging from $30\,Hz$ to $300\,Hz$ typically used for power line frequencies and some home control systems.

SHF (Super High Frequency)

A frequency band from $3\,GHz$ to $30\,GHz$ used for satellite communication, radar, and terrestrial microwave links.

Free space loss

The attenuation of a transmitted signal over distance due to the dispersion or spreading of the signal over a larger area.

Atmospheric Absorption (Water Vapour)

A signal impairment where peak attenuation occurs in the vicinity of $22\,GHz$ due to moisture in the air.

Atmospheric Absorption (Oxygen)

A signal impairment that results in an absorption peak in the vicinity of $60\,GHz$.

Multipath

An impairment where a transmitted signal is reflected by obstacles, causing the receiver to capture multiple copies of the signal with varying delays.

Refraction

The bending of radio waves as they propagate through the atmosphere due to changes in signal speed with altitude.

Omni-directional antenna

An antenna that radiates radio wave power uniformly in all directions in one plane.

Directional (Beam) antenna

An antenna that radiates greater power in one or more directions for increased performance and reduced interference.

Isotropic antenna

An ideal antenna that radiates the same intensity of radiation in all directions with no preferred direction.

Dipole antenna

The simplest class of antenna consisting of two identical, bilaterally symmetrical conductive elements like metal rods.

dBm

A unit of power level in decibels relative to one milliwatt ($1\,mW$), calculated as P(dBm) = 10\text{log}_{10}[P(mW)/(1\,mW)].

Antenna Gain (dBi)

The gain of an antenna expressed in decibels relative to an isotropic radiator.

Free Space Path Loss (FSPL)

A measure of signal attenuation representing the difference between effective transmitted power and received power in a perfect environment.

Reflection

Propagation behavior occurring when a wave impinges on an object that is large compared to its wavelength, such as the surface of the Earth or buildings.

Diffraction

A propagation behavior where waves bend around obstacles with sharp irregular edges, allowing signals to be received even when a line-of-sight path is obstructed.

Scattering

Occurs when an incoming signal hits an object whose size is in the order of the signal wavelength or less, such as foliage or lamp posts.

Fast Fading

Also called small-scale fading, it refers to rapid variations in signal strength occurring over short distances of about one-half of a wavelength.

Slow Fading

Also called large-scale fading or path loss, it refers to long-term variation in mean received power level due to transmitter-receiver separation distance.

Shadowing

A fading effect caused by large objects like buildings or hills that block the transmitted signal, typically described by a lognormal distribution.

Flat Fading

A type of fading where all frequency components of the received signal fluctuate in the same proportions simultaneously; occurs when B_s \text{<

Frequency-Selective Fading

Fading that affects different spectral components of a radio signal unequally; occurs when $B_s > B_c$.

Rayleigh Fading Channel

A fading model used when there are multiple indirect paths between transmitter and receiver but no distinct dominant line-of-sight path.

Rician Fading Channel

A fading model used to characterize situations where there is a direct line-of-sight path in addition to multiple indirect multipath signals.

Delay Spread

The effect where multiple signal paths with different lengths cause versions of the signal to arrive at different times, potentially causing intersymbol interference (ISI).

Intersymbol Interference (ISI)

A distortion in digital communications caused by delay spread where energy from one symbol spills into the next symbol's time interval.

Coherence Bandwidth ($B_c$)

A statistical measure of the range of frequencies over which the channel can be considered "flat," approximately related to delay spread ($t_d$) by B_c \text{≈} \frac{1}{2\text{π} t_d}.

Doppler Effect

The change in frequency of a received signal caused by the relative motion between a wave source and a receiver.

Doppler Shift ($f_D$)

The magnitude of the frequency change due to motion, calculated as f_D = \frac{v}{\text{λ}}\text{cos}(\text{θ}).

Forward Error Correction (FEC)

A digital error compensation mechanism where the transmitter adds redundant bits so the receiver can detect and correct bit errors without retransmission.

Adaptive Equalization

A compensation mechanism used to combat ISI by gathering dispersed symbol energy back into its original time interval.

Diversity Techniques

A method for improving reception by processing multiple versions of the same signal received through different paths, times, frequencies, or polarisations.