Page 127 - Electrical Engineering Dictionary

arithmetic pipeline; used in vector computers quencies from 50 Hz to 15 KHz (Channel A)
to improve their performance. and 15 KHz to 75 KHz (Channel B) which
frequency modulate the main carrier of an
chaining of fuzzy rules a reasoning strat- FM stereo transmitter. Example 2: A portion
egy which searches the knowledge base and of the electromagnetic spectrum assigned for
chain from rule to rule to form inferences and operation of a specific carrier from the FM
draw conclusions. In forward chaining, a broadcast band (88 to 108 MHz) of frequen-
chain of data-driven rules are evaluated for cies 200 KHz wide designated by the center
which the conditional parts are satisfied to frequency beginning at 88.1 MHz and con-
arrive at the conclusion. Backward chain- tinuing in successive steps to 107.9 MHz.
ing is goal-driven in which subgoals are es-
tablished, where necessary, through which a channel allocation the act of allocating
chain of rules are selected, eventually satis- radio channels to cells, base stations, or cell
fying the goal. sectors, in a radio network, also referred to
as frequency allocation, or frequency plan-
chamfer distance a digital distance based ning. The allocation typically follows an al-
on a chamfer mask, which gives the distance gorithm that attempts to maximize the num-
between a pixel and those in its neighbor- ber of channels used per cell and minimize
hood; then the chamfer distance between two the interference in the network.
non-neighboring pixels (resp., voxels) is the
smallest weighted length of a digital path channel architecture a computer sys-
joining them. The word “chamfer” comes tem architecture in which I/O operations are
from the fact that with such a distance a circle handled by one or more separate processors
is in fact a polygon. The n-dimensional Man- known as channel subsystems. Each chan-
hattan and chessboard distances are chamfer nel subsystem is itself made up of subchan-
distances; the Euclidean distance is not. In nels, in which control unit modules control
the 2-D plane, the best chamfer distances are individual I/O devices. Developed by IBM,
given by the (3, 4) and (5, 7, 11) Chamfer and used primarily in mainframe systems, the
masks: in the (3, 4) mask, a pixel is at dis- channel architecture is capable of a very high
tance 3 from its horizontal/vertical neighbors volume of I/O operations.
and at distance 4 from its diagonal neigh-
bors, while in the (5, 7, 11) mask, it is at channel capacity a fundamental limit on
distance 5 from its horizontal/vertical neigh- the rate at which information can be reliably
bors, at distance 7 from its diagonal neigh- communicated through the channel. Also re-
bors, and at distance 11 from its neighbors ferred to as “Shannon capacity,” after Claude
distant by 1 and 2 respectively along the two Shannon, who first formulated the concept of
axes. See chessboard distance, Euclidean channel capacity as part of the noisy channel
distance, Manhattan distance. coding theorem.
For an ideal bandlimited channel with ad-
channel (1) the medium along which data ditive white Gaussian noise, and an input av-
travel between the transmitter and receiver in erage power constraint, the channel capacity
a communication system. This could be a is C = 0.5 log(1 + S/N) bit/Hz, where S/N
wire, coaxial cable, free space, etc. See also is the received signal-to-noise ratio.
I/O channel.
(2) the conductivity path between the channel code a set of codewords used to
source and the drain of a field effect tran- represent messages, introducing redundancy
sistor. in order to provide protection against errors
(3) a single path for transmitting electri- introduced by transmission over a channel.
cal signals. Example 1: The band of fre- See also source code.

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2000 by CRC Press LLC