| DAC |
Digital to Analog Converter |
A device that takes a digital representation of a signal and transforms it into a facsimile of its original form. |
| D-AMPS |
Digital-Advanced Mobile Phone System |
Earlier designation of American standard for digital mobile telephony used primarily in North America, Latin America, Australia and parts of Russia and Asia. Also known as (North American) TDMA. See also TDMA and IS-136. |
| datagram |
|
In connectionless services, a discrete unit of data that can be transmitted
independent of other data units. Synonymous with "packet," the
more common term. |
| dB |
deciBel |
A technique for expressing voltage, power, gain, loss or frequency in logarithmic form against a reference. Typical references include volts, watts or Hz. DeciBels are calculated using the expression: dB = 10*log(x/y). |
| dBc |
deciBels referenced to the carrier |
A technique for expressing a power measurement in logarithmic form using the carrier power as a reference. |
| dBd |
deciBels referenced to a dipole antenna |
A technique for expressing a power gain measurement in logarithmic form using a standard dipole antenna as a reference. |
| dBi |
deciBels referenced to an isotropic antenna |
A technique for expressing a power gain measurement in logarithmic form using a theoretical isotropic antenna as a reference. |
| dBm |
deciBels referenced to a milliWatt |
A technique for expressing a power measurement in logarithmic form using 1 mW as a reference. |
| DCA |
Dynamic Channel Allocation |
An automatic process for assigning traffic channels in a frequency reuse wireless system. The base station continuously monitors the interference in all idle channels and makes an assignment using an algorithm that determines the channel that will produce the least amount of additional interference. |
| DCCH |
Dedicated Control Channel |
A dedicated channel used to carry signalling information in active GSM and cdma2000 traffic channels. |
| DCS-1800 |
Digital Communications System - 1800 |
|
| dead spot |
|
An area within the coverage area of a wireless network in which there is no coverage or transmission falls off. Dead spots are often caused by electronic interference or physical barriers such as hills, tunnels and indoor parking garages. See also coverage area. |
| DECT |
Digital European Cordless Telecommunications |
|
| demodulation |
|
Process of recovering the original modulating signal from a modulated carrier. The original modulating signal is usually the information being transmitted, typically voice or data. |
| digital |
|
Describes when information - speech, for example - is encoded before transmission using a binary code — discrete, non-continuous values. Digital networks are rapidly replacing analog ones as they offer improved sound quality, secure transmission and can handle data as well as voice. Digital networks include mobile systems GSM 900, GSM 1800, GSM 1900, D-AMPS and the cordless DECT system. |
| dispersive channel |
|
A radio channel that not only introduces AWGN, but also the effects of multipath and frequency selective fading. |
| DL |
Downlink |
|
| Doppler Shift |
|
The magnitude of the change in the observed frequency of a wave due to the relative velocity of a transmitter with respect to a receiver. |
| DPM |
Digital Phase Modulation |
A form of CPM in which the shaped symbol pulses are directly applied to the phase modulator. This technique provides the advantages of CPM techniques and is easily implemented in VLSI. It is also easier to demodulate than other types of CPM. |
| DQPSK |
Differential Quadrature Phase Shift Keying |
QPSK modulation using differential encoding of the digital information stream. |
| DS |
Direct Sequence |
A process of spectrum spreading where the digital information stream is multiplied, using an exclusive OR technique, by a high speed pseudorandom code (spreading sequence) to generate a spread spectrum signal. |
| DSSS |
Direct Sequence Spread Spectrum |
A type of spread spectrum modulation using a direct sequence technique to achieve spreading. |
| DTX |
Discontinuous Transmission |
A feature in mobile systems where transmitters mute when there is no information to send, such as during periods of silence. This feature prolongs battery life in portable phones and reduces interference in wireless systems. |
| dual band |
|
A term describing mobile phones that work on networks operating on different frequency bands. This is useful for mobile phone users who move between areas covered by different networks. For example GSM 900, GSM 1800. such as the 800 MHz digital band and the 1900 MHz digital PCS band. |
| dual mode |
|
An industry term referring to a wireless device that can operate on either an analog or digital transmission network. However, multiple digital transmission systems exist, so dual-mode phone users must ensure that their dual-mode phone will operate on the digital transmission system used by their selected service provider. |
| duplex/full duplex |
|
Simultaneous two-way transmission, such as experienced in a phone conversation. In contrast, many speakerphones are half-duplex and will transmit in only one direction phone conversation. In contrast, many speakerphones are half-duplex and will transmit in only one direction — from the loudest noise — at a time. |
| DUT |
Device Under Test |
An acronym used to describe some type of electrical apparatus connected to test instrumentation. The apparatus can range from a single component to a complex subsystem such as a mobile phone, base station or MSC. |
