Page 173 - Electrical Engineering Dictionary

The convolution of two discrete time sig- constraint length, the higher the code protec-
nals f 1 [k] and f 2 [k] is defined by tion for a given code rate. See also block
coding, error control coding.
∞
X
f 1 [k]∗ f 2 [k]= f 1 [i]f 2 [k − i]
cooling tower a reinforced-concrete,
i=−∞
k spool-shaped structure in a thermal power
X
= f 1 [i]f 2 [k − i] if f 1 [k],f 2 [k]= 0,k < 0 plant in which condenser cooling water
i=0 is itself cooled by convectively-driven air
streams.
The summation on the right-hand side of the
above equation is called the convolution sum.
Cooper, Leon Niels (1930– ) Born: New
Convolution is useful in computing the sys-
York, New York, U.S.A.
tem output of LTIL systems.
Cooper is best known for his work on su-
convolution integral See convolution, perconductivity, resulting in a Nobel Prize
superposition integral. he shared with John Bardeen and J. Robert
Schrieffer. He postulated the idea that is now
convolutional code (1) a code generated known as Cooper pairs, as part of the expla-
by passing the information sequence to be nation of why some metals loose their con-
transmitted through a linear finite-state shift ductivity at very low temperatures.
register and the coder memory couples the
currently processed data with a few earlier coordinate system a system for defining
data blocks. Thus the coder output depends the location of a point in space relative to
on the earlier data blocks that have been pro- some reference point and for defining a set of
cessed by the coder. reference directions at each and every point
(2) a channel code based on the trellis cod- in space.
ing principle but with the encoder function
(mapping) determined by a linear function coordinated rotation digital computer
(over a finite alphabet). The name “convo- (CORDIC) algorithm for calculating
lutional code” comes from the fact that the trigonometric functions using only additions
output sequence is a (finite alphabet) convo- and shift operations.
lution between the input sequence and the
impulse response of the encoder.
coordinating unit See coordinator unit.
convolutional coding a continuous er-
ror control coding technique in which con- coordination process of influencing —
secutive information bits are combined al- by the coordinator — the local units in such
gebraically to form new bit sequences to be a way as to make their behavior or deci-
transmitted. The coder is typically imple- sions consistent with the objectives of the
mented with shift register elements. With coordinator unit; coordination can be either
each successive group of bits entering the iterative or periodic; iterative coordination
shift register a new, larger set of bits are cal- plays an essential role in multilevel optimiza-
culated for transmission based on current and tion. See also direct method, mixed method
previous bits. If for every k information bits coordination, price method coordination.
shifted into the shift register, a sequence of n
bits are calculated, the code rate is k/n. The coordination by exception coordination
length of the shift register used for storing performed only in unusual (emergency) situ-
information bits is known as the constraint ations, otherwisethecontrolordecisionmak-
length of the code. Typically, the longer the ing is designed to be fully decentralized.

c
2000 by CRC Press LLC