D

DAR - Digital Audio Radio.

DAS Tape - The magnetic tape that is used at the MTSO to record traffic statistics and call billing information. This tape is sent to a third-party 'billing-house' where the actual billing of the subscribers is done.

dB (decibel) - A unit stating the logarithmic ratio between two amounts of power. Typically used in receiver and transmitter measurements.

dBi - Decibel, Isotropic; decibel referenced to the gain of a theoretical isotropic radiator.

dBm - Decibel, Milliwatt; decibel referenced to one milliwatt into 50 ohms.

DBS - Direct Broadcast Satellite.

DCS - Digital Cellular System

DCS-1800 - Low power variant of GSM, with 1.8 GHz carrier, used in Europe (e.g., Mercury One-2-One)

DCS-1900 - Proposed use of GSM with 1.9 GHz carrier for PCS applications.

DCTU - Digital Cordless Telephone U.S. - a version of DECT proposed for the U.S. PCS market

DDS - Direct Digital Synthesis.

DECT - Digital European Cordless Telephone. A digital cordless telephone standard that incorporates some of the features of the cellular telephone systems. DECT telephones use picocells, and calls can be handed off from one cell to the next.

Detector (Demodulator) - The circuit in a receiver which is used to recover the intelligence (audio) from a signal.

De-Spreading - The process used by a correlator to recover narrowband information from a spread spectrum signal.

Destructive interference - Interference that occurs when waves occupying the same space combine to form a single weaker wave. This type of interference occurs when waves out of phase combine to form a composite wave which is weaker than any of it's component waves. For example if you transmitted two waves that were exactly 180 degrees out of phase, each with an amplitude of 10, they would completely cancel each other out.

DGPS - Differential GPS.

Digital modulation - A method of encoding information for transmission that will eventually replace analog transmission. Digital modulation reduces voice to binary code -- the zeros and ones of computer language. At the receiving end, the information is reconverted. Digital transmission offers stronger reception, less static, greater call handling capacity, fewer dropped calls, improved call privacy, and the potential for additional voice and data service such as fax and computer data transmission.

Direct Sequence - A pseudorandom (PN) code is added to the data signal which increases the modulation rate and signal bandwidth. This spreading of the energy over a wide bandwidth looks like a low level signal to other users in the band. The receiver must know the PN code transmitted and be synchronized to the code to assemble each data bit.

Diversity - Sharing a signal characteristic to allow more users in the same frequency band.

Diversity Receive - A method commonly employed by cellular manufactures to improve the signal strength of received signals. Uses two independent antennas that receive signals which differ in phase and amplitude resulting from the slight difference in antennas position. These two signals are either summed or the strongest is accepted by voting. The most popular methods include dual-antenna phase switching, dual-receiver audio switching and "ratio diversity" audio combining. The most effective method is ratio diversity combining.

Discontinuous Transmission (DTX) - A subscriber unit feature that allows the mobile to disable it's RF PA during conversation when the subscriber is not talking. Save on battery life to increase talk time. The cellular system must support this feature if the subscriber wants to use DTX.

DMR - Digital Mobile Radio.

DPSK - Differential Phase Shift Keying -- a simplified BPSK where only data transitions are transmitted.

Drop Out - A momentary loss of the carrier and sound, or a buildup of background noise when the transmitter is in a certain location in the room. Moving the transmitter (even a few inches) usually restores the sound to normal.

DSP - Digital Signal Processing.

DSRR - Digital Short Range Radio. The Commission of the European Community has designated 880 to 890 MHz and 933 to 935 MHz for unlicensed, business citizens band radio in Europe. For point-to-point communications over distances up to 6 km maximum, depending on antenna height.

DTMF - Dual Tone Multi Frequency. Commonly known as 'touch-tones', this in-band signaling is made up of two tones (out of a group of 8) and is used to translate dialed digits.

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