Page 119 - Electrical Engineering Dictionary

is the frequency of the triangle waveform that ing what is termed a “pilot tone” at the carrier
the control or modulating signal is compared frequency.
to.
carrier synchronization a synchroniza-
carrier lifetime the average duration an tion technique used in radio receivers. In all
electron or a hole stays in a certain state. radio receivers some sort of carrier frequency
synchronization is required; the phase syn-
carrier phase the phase of a sinusoidal chronization is needed only if phase coherent
signal that is the carrier in a modulation demodulation is desired. Can be categorized
scheme such as AM, FM, SSB, etc. The car- as open and closed loop carrier synchroniza-
rier may be defined in the form A cos(ω c t + tion.
φ). The carrier is specified by the parameters
A (amplitude), ω c (carrier frequency), and φ carrier-sense multiple access (CSMA) a
(carrier phase). random-access method of sharing a bus-type
communications medium in which a poten-
carrier shift the difference in frequency tial user of the medium listens before begin-
between the steady state, mark, and space in ning to transmit. The channel sensing signif-
frequency shift keying (FSK) systems. icantly reduces the probability of collisions.
Compare with ALOHA.
carrier signal the RF signal in a com-
munications system that has the modulating carrier-to-interference ratio (CIR) sim-
signal superimposed on it. This signal may ilar to signal-to-interference ratio but usu-
haveitsfrequency, amplitude, orphasevaried ally used in cellular communication systems
to form a modulated signal. Without modu- where the carrier refers to the signal of inter-
lation it is a simple RF signal. est and the interference refers to interference
Many communication systems rely on the from other transmitters in the system. See
concept of sinusoidal amplitude modulation, also signal-to-interference ratio.
in which a complex exponential signal c(t)
has its amplitude multiplied (modulated) by carrier-to-noise ratio the ratio of the am-
the information-bearing signal x(t). This plitude of the carrier signal to that of the noise
signal x(t) is typically referred to as the mod- in the IF bandwidth measured at any point
ulating signal and the signal c(t) as the carrier in the receiver before any nonlinear process
signal. The modulated signal y(t) is then the such as amplitude limiting or detection. The
product of these two signals. carrier to noise ratio is typically expressed in
decibels.
y(t) = x(t)c(t)
carrierless amplitude/phase modulation
(CAP) an implementation of a quadrature
carrier suppression in SSB communi- amplitude modulation transmitter in which
cations, the degree to which the carrier am- the passband in-phase and quadrature signals
plitude is reduced from its original value are generated directly via quadrature digi-
out of the modulator. ( See also balanced tal filters. A recent application for CAP is
modulator. ) Carrier suppression is gen- high-speed digital subscriber lines. See also
erally used as a method to significantly re- quadrature amplitude modulation.
duce the amount of unnecessary transmitted
power, based upon the fact that no informa- carry overflow signal that occurs when
tion is contained within the carrier amplitude the sum of the operands at the inputs of the
in an AM waveform. It is sometimes desir- adder equalsthebase. A binaryadder, adding
able to only partly suppress the carrier, leav- 1 + 1 will produce a sum of 0 and carry of 1.

c
2000 by CRC Press LLC