Page 128 - Electrical Engineering Dictionary

channel coding the process of intro- channel I/O an approach to I/O process-
ducing controlled redundancy into an infor- ing in which I/O operations are processed in-
mation sequence mainly to achieve reliable dependent from the CPU by a channel sys-
transmission over a noisy channel. Channel tem. See also channel architecture.
coding can be divided into the areas of block
coding and trellis coding. Also called error channel matched VQ See channel
control coding. See also block coding, trellis optimized vector quantization.
coding and convolutional coding.
channel measurement See channel
sounding.
channel command word an “instruc-
tion” to an I/O channel. The commands con-
channel modeling the act of describing
sists of parameters (e.g., “operation,” “data
the effect of the (radio) channel on the trans-
address,” “count”) giving the channel pro-
mittedsignalinaformsuitableformathemat-
cessor information on type of I/O operation
ical analysis, computer simulation or hard-
requested (e.g., “read” or “write”), where the
ware simulation. A channel model is a col-
data is to be read or written, and the number
lection of channel characteristics essential to
of bytes involved in the data transfer.
the performance of the communication sys-
In the IBM mainframe architecture there tem under study, organized in such a way that
are six different types of channel con- the basic performance trade-offs of the sys-
trol words: READ, READ BACKWARD, tem can be analyzed or simulated without
WRITE, CONTROL, SENSE, and JUMP. having to construct prototypes or carry out
field tests.
channel control word See channel
channel optimized vector quantization
command word.
(COVQ) a combined source-channel
code for block-based source coding (vector
channel encoder a device that converts
quantization) and block channel coding. A
source-encoded digital information into an
channel optimized vector quantizer can be
analog RF signal for transmission. The type
designed using a modified version (taking
of modulation used depends on the particu-
channel induced distortion into account) of
lar digital audio broadcasting (DAB) system,
the generalized Lloyd algorithm). Also re-
although most modulation techniques em-
ferred to as channel matched VQ. See also
ploy methods by which the transmitted sig-
noisy channel vector quantization.
nal can be made more resistant to frequency-
selective signal fading and multipath distor-
channel program the set of channel con-
tion effects.
trol words that make up the instruction se-
quence that controls an I/O channel. See also
channel estimation estimation of the ra- channel control word.
dio channel parameters in the receiver. Typi-
cally delays, amplitudes, carrier phases, and channel reliability function the rate
direction-of-arrivals need to be estimated de- function with infinitesimal error probability
pending on the receiver configuration. Chan- expressed by
nel estimation is a modern way to look at re-
( 1 1
ceiver synchronization based mainly on feed- 2 C ∞ 0 ≤ R ≤ C ∞
4
back control loops, since in principle any E(R) = √ √ 2 1
C ∞ − R C ∞ ≤ R ≤ C ∞
method known to estimation theory can be 4
applied to achieve synchronization of the re- for transmission of orthogonal or simplex
ceiver over an unknown radio channel. signal over infinite bandwidth AWGN chan-

c
2000 by CRC Press LLC