Glossary

802.11

The family of standards developed by an IEEE working group for wireless local area networks. There are currently several specifications for WLAN technology, such as 802.11, 802.11a, 802.11b, 802.11e, 802.11g, and 802.11n. The 802.11 and 802.11b specifications operate at frequencies in the 2.4 GHz region of the radio spectrum and offer data rates of 1 Mbps or 2 Mbps for 802.11, and 5.5 Mbps or 11 Mbps for 802.11b. The 802.11a specification operates at a 5 GHz frequency and provides a data rate up to 54 Mbps. The 802.11g operates at 2.4 GHz but offers data rates as high as 802.11a (54 Mbps). The 802.11e specification includes encryption algorithms for added security to WLANs.

802.15

The family of standards developed by an IEEE working group for wireless personal area networks. The specification includes 802.15.1, which defines Bluetooth with 1Mbps; 802.15.3, which defines the high-data-rate WPAN for multimedia and digital imaging applications; and 802.15.4, which is the specification for low-data-rate WPANs such as interactive toys and sensor and automation applications.

additive white Gaussian noise (AWGN)

Also known as thermal noise. AWGN is created by dissipative devices in transmitters and receivers. AWGN has flat power spectral density (that is, equal power per all frequencies) and is uncorrelated at various segments of time.

analog-to-digital converter (ADC)

Converts analog signals to digital signals using sampling and quantization techniques.

binary phase shift keying (BPSK)

Also known as bi-phase shift keying. A digital modulation technique in which the data is modulated based on two possible values for its RF carrier phase, by 0 degrees or 180 degrees in accordance with the transmitted bit stream.

bit error rate (BER)

In digital communication systems, the percentage of bits that have errors relative to the total number of bits received in a transmission. For example, BER = 10⁶ indicates that only one erroneous bit was received out of 1,000,000 bits transmitted.

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

A network control protocol in which each device sends a request signal for its intent to transmit before the actual transmission. This prevents collisions that can result from the transmissions of two or more devices.

classical matched filter (CMF)

A simple and optimal method for detecting a signal in random noise based on the correlation process.

Code Division Multiple Access (CDMA)

A spread spectrum technique for digital transmission of radio signals in multiuser applications such as mobile station and base station scenarios. In this technique each user is identified by a unique code that allows users to overlap in both the time and the frequency domains. This technique was originally developed for military use in the 1940s.

complementary metal-oxide semiconductor (CMOS)

A semiconductor technology used in many integrated circuits. CMOS technology has insignificant static power dissipation and is considered the best choice for low-power designs.

decibel (dB)

A logarithmic measurement unit named after Alexander Graham Bell that describes the power ratio of two signals. In system use, decibel is a measure of the voltage ratio of two signals when they are measured across a particular impedance.

decibel in milliwatts (dBm)

A logarithmic measure of power in communications. It expresses an electrical power level, referenced to 1 milliwatt (that is, 0 dBm = 1 mW).

delay-hopped transmitted reference (DH-TR)

A modulation technique used in ultra-wideband multiple-access systems in which each user is distinguished by a unique delay code.

digital visual interface (DVI)

A standard that defines the digital interface between digital devices. Using this interface, standard digital-to-digital connections can be made between devices, eliminating the need for conversion to analog. The result: flawless images in HDTVs or set-top boxes.

direct sequence spread spectrum (DSSS)

A type of spread-spectrum radio transmission that spreads its signal continuously over a wide frequency band. The data in DSSS is modulated by a specific code pattern that adds redundancy to each transmitted bit. This redundancy offers more security and a higher percentage for data recovery. CDMA is a DSSS technique.

direct sequence ultra-wideband (DS-UWB)

A technique being considered for UWB standardization in which data is modulated by a unique code for UWB pulses; similar to CDMA.

drift step recovery diode (DSRD)

Fast semiconductor switches that can generate short-duration electromagnetic pulses.

equivalent isotropic radiated power (EIRP)

Expressed in dBm, EIRP is a measurement of the strength of the signal leaving an antenna in a given direction relative to the performance of a theoretical (isotropic) antenna.

European Telecommunications Standards Institute (ETSI)

An international standards body that recommends standards for wireless technology in Europe.

Fast Fourier Transform (FFT)

An algorithm for computing the frequency characteristics of a set of discrete data values. Using FFT and inverse FFT, both the frequency and the time components of a signal can be detected.

Federal Communications Commission (FCC)

The U.S. government agency, located in Washington, D.C., that is responsible for regulating telecommunications in the United States.

finite difference time domain (FDTD)

A well-known electromagnetic modeling technique that enables precise characterization of complex structures for which analytical methods are not suitable.

Frequency Division Multiple Access (FDMA)

A multiuser detection technique that allows multiple users to transmit and receive data in different frequency slots while sharing the same transmission time.

frequency-hopping spread spectrum (FHSS)

A modulation technique in which data is transmitted according to code that defines various frequency channels. The data hopping between frequency channels occurs very quickly, so the transmission is highly secure for military applications. The FHSS technique was co-invented by actress Hedy Lamarr in 1942 under Patent No. 2,292,387, titled "Secret Communication System."

Global Positioning System (GPS)

A space-based radio positioning system used to compute positions on the Earth. GPS consists of 24 satellites orbiting above the Earth and a set of receivers that detect signals from the satellites and translate them into accurate position, velocity, and timing information. GPS accuracy is around 30 to 90 feet.

Global System for Mobile Communications (GSM)

An international standard for digital cellular systems that allows each user to have one phone number worldwide. GSM is based on time-division multiplexing (TDM) and is currently used in 900 MHz and 1800 MHz bands.

ground-penetrating radar (GPR)

A detection technique in which RF pulses are transmitted into the ground and are reflected by materials with differing electrical properties, thereby providing depth sections that look like seismic sections. This technique is widely used in geophysics applications as well as in some types of rescue and recovery attempts.

Interim Standard 95 (IS-95)

Pioneered by Qualcomm under the brand name cdmaOne, IS-95 is the first CDMA-based digital cellular standard, operating at 800 MHz.

intermediate frequency (IF)

In heterodyne transmitter/receiver pairs, the desired RF signals are first translated to an intermediate frequency stage for ease of filtering before being converted to the intended frequency band.

ISM band

Short for industrial, scientific, and medical band, the ISM band covers the frequencies reserved for radiation by various equipments without license. Equipments in the ISM band should be able to tolerate interference from other devices sharing the same frequency band.

light-activated silicon switching (LASS)

Technique in which a laser light is employed to activate semiconductor switches for generating short-duration pulses.

liquid crystal display (LCD)

A display composed of two polarizing panels with liquid crystal solution between them. An electric current can cause the crystals to align and block certain areas to prevent light from passing through. LCDs are used in digital watches and many portable electronic devices.

medium access control (MAC)

The lower of two sublayers in the 802.X standard specification that make up the OSI data link layer. The MAC manages access to the physical network and handles error control.

on-off keying (OOK)

A type of modulation that represents digital data as the presence or absence of a carrier wave or a pulse in UWB communications. In its simplest form, the presence of a carrier/pulse represents a binary one, while its absence represents a binary zero.

orthogonal frequency-division multiplexing (OFDM)

A spread-spectrum technique that transmits data across several carrier frequencies to achieve high data rates with low symbol rates.

power spectral density (PSD)

A signal's power in the frequency domain.

processing gain (PG)

In telecommunications, processing gain is defined as the signal-to-noise ratio of the processed signal divided by the SNR ratio of the unprocessed signal.

pulse-amplitude modulation (PAM)

A technique in which digital information is encoded and decoded based on the amplitude of pulses or waveforms carrying the data.

pulse-position modulation (PPM)

A form of signal modulation in which the digital information is encoded based on the exact position between pulses in a sequence of signal pulses.

pulse-position modulation with time hopping (TH-PPM)

A UWB modulation technique in which each user's information is encoded based on the PPM technique. In addition, users are separated in time to avoid catastrophic collisions in multiple-access channels.

radar

Originally an acronym for radio detection and ranging, radar is a radio device or system for locating a target by transmitting high-frequency radio signals to the target and using the reflected signals to detect the target's distance.

radio frequency (RF)

Refers to any frequency within the electromagnetic spectrum associated with radio wave propagation.

step recovery diode (SRD)

Electronic component used to generate short-duration electromagnetic pulses using a PN junction in which a forward bias is rapidly changed to a reverse bias.

Time Division Multiple Access (TDMA)

A digital wireless telephony transmission technique used for multiuser systems. In this technique, each user has a different time slot on a given frequency. Using this method a single frequency can support multiple simultaneous data channels.

transmitted reference (TR)

A popular UWB modulation technique in which data is represented by two pulses separated by a specific delay. This method has been used widely for synchronization of spread-spectrum systems prior to its use in UWB technology.

tunnel diode (TD)

Electronic component used to generate short pulses with very fast switching speeds, caused by quantum mechanical effects.

ultra-high frequency (UHF)

A range of radio frequencies that extends from 300 MHz to 3 GHz.

ultra-wideband (UWB)

A wireless technology that uses short-duration pulses to transfer digital information over a very wide frequency spectrum.

ultra-wideband multiple access (UWB-MA)

A method in which multiple UWB devices transmit to a single or multiple receivers simultaneously.

wireless local area network (WLAN)

A recently standardized technology for high-speed wireless data communication in local network environments.

wireless local loop (WLL)

A radio access technology that links subscribers into a fixed public switched telephone network (PSTN) using radio signals. This includes cordless access systems, proprietary fixed radio access, and fixed cellular systems.

wireless personal area network (WPAN)

A wireless network that serves only an individual wireless user. This type of wireless network usually relates to Bluetooth technology for personal networking.

ZigBee

A class of WPANs operating in the 2.4 GHz radio band that defines low-power, low-data-rate communications.