Orthogonal Frequency Division Multiplexing Quiz

Orthogonal Frequency-Division Multiplexing; a method of transmitting data by dividing a high-rate signal into multiple lower-rate subchannels, significantly reducing the disruptive effects of multipath interference.

The time duration for one symbol in a data transmission system.

Distortion of a signal caused by multiple copies of the signal arriving at the receiver from different paths, resulting in a smeared signal.

A portion of a data symbol added to the beginning of the symbol, used to maintain orthogonality of the received signals even with severe multipath conditions.

The inverse Discrete Fourier Transform algorithm used to transform a high-data-rate, short-symbol input into a lower-data-rate, lengthened-symbol output in OFDM systems.

The root-mean-square delay spread in a signal resulting from multipath propagation.

A representation of how a communication channel affects a signal in the time domain.

A type of fading where the signal strength varies significantly across different frequency components.

A type of fading where the signal strength varies roughly the same across all frequency components.

Rapid changes in signal strength due to the relative movement between transmitter and receiver.

Slower variations in signal strength than fast fading.

The range of frequencies over which the channel characteristics remain relatively constant.

The rate at which symbols are transmitted in a communication system.

The duration over which the channel characteristics remain relatively constant.

The duration of a single symbol in a communication system.

A communication technique that transmits data on multiple orthogonal subcarriers.

The number of individual carriers used in an OFDM system.

Desired characteristics of the communication channel for optimal OFDM performance.

Coherence bandwidth > symbol rate > fading rate

The bandwidth over which the channel characteristics remain relatively constant. A measure of how stable the signal is in the channel.

The smallest number of subcarriers needed for a given system to avoid significant inter-symbol interference.

The largest number of subcarriers allowed by the channel coherence time.

The duration over which the channel properties remain relatively constant.

The speed of the mobile or moving device experiencing the channel.

A modulation technique that transmits data over multiple frequencies (subcarriers) simultaneously to reduce interference.

A distortion effect in digital communication where a signal from one symbol interferes with subsequent symbols.

The statistical measure of the time difference between the strongest and all other signals.

The rate at which symbols are transmitted.

The largest amount of time a signal from one path takes to travel through the channel.

A process in OFDM where successive bits are mapped to phasors in a constellation diagram.

Binary Phase Shift Keying; uses 1 and -1 phasors to represent 1 and 0 bits.

Quadrature Phase Shift Keying; uses four phasors to represent pairs (dibits) of bits.

A complex number representing magnitude and phase in the frequency domain.

A distinct frequency component in OFDM.

Inverse Discrete Fourier Transform; converts from frequency to time domain.

Composite signal containing multiple subcarriers in time domain after Inverse Transform.

Added to the OFDM symbol to prevent inter-symbol interference.

Subcarriers that do not overlap in frequency.

Quadrature Amplitude Modulation scheme that uses 6 bits for mapping to a phasor.

A type of convolution operation performed on discrete-time signals that treats the signals as periodic. This is important in OFDM because it simplifies equalization.

A special sequence added to the beginning of each OFDM symbol, used to maintain orthogonality and turn linear convolution into circular convolution.

The property that ensures the different subcarriers in OFDM don't interfere with each other during transmission and reception.

Multiplying the spectra (frequency domain representations) of two signals in the frequency domain is equivalent to performing circular convolution on the corresponding time domain signals.

The standard convolution between two continuous-time or discrete-time signals.

The process of recovering the individual subcarrier signals at a receiver, which is important to accurately recover the transmitted data.

A mathematical tool that transforms a discrete sequence of values from the time domain to the frequency domain.

The process of adjusting signals to compensate for distortion introduced by a channel during transmission. In OFDM, a spectral scaling adjustment is often used, made easier by using Circular Convolution.

Number of independent frequency channels used in Orthogonal Frequency-Division Multiplexing (OFDM).

Number of samples used in the Inverse Discrete Fourier Transform (IDFT).

Number of samples added to the beginning of each OFDM symbol to mitigate intersymbol interference (ISI).

Total number of samples in one OFDM symbol; sum of transform size and cyclic prefix samples.

Rate at which samples are taken from the analog signal to be converted into the digital domain. Often expressed in MHz.

Duration of the actual data portion in an OFDM symbol.

Duration of the cyclic prefix in an OFDM symbol.

Total duration of an OFDM symbol, sum of data and cyclic prefix time.

Frequency with which OFDM symbols are transmitted.

Frequency difference between adjacent OFDM subcarriers.

Total spread of frequencies occupied by the modulated signal.

Long-Term Evolution standard, for 4G radio communication.

Distortion of a signal caused by the overlap of neighboring symbols.