Page 92 - Electrical Engineering Dictionary

1 values, it conveys exactly 1.0 bit (binary bit parallel a method to transmit or pro-
unit) of information; the average information cess information in which several bits are
is usually less than this. transmitted in parallel. Examples: a bit par-
allel adder with 4-bit data has 8 input ports for
bitallocation theallocationofbitstosym- them (plus an initial carry bit); an 8-bit paral-
bolswiththeaimofachievingsomecompres- lel port includes true 8-bit bi-directional data
sion of the data. Not all symbols occur with lines.
the same frequency. Bit allocation attempts
to represent frequently occurring symbols bit per second (bps) measure of trans-
fer rate of a modem or a bus or any digital
with fewer bits and assign more bits to sym-
communication support. ( See also baud and
bols that rarely appear, subject to a constraint
baud rate. bps and baud are not equivalent
on the total number of bits available. In
this way, the average string requires fewer since bps is a low-level measure and media;
bits. The chosen assignment of bits is usu- thus, itincludesthenumberofbitssentforthe
ally the one that minimizes the correspond- low-level protocol, while baud is typically re-
ing average coding distortion of the source ferred to a higher level of transmission).
over all possible bit assignments that satisfy
the given constraint. Typically sub-sources bit period the time between successive
with larger variances or energy are allocated bits in data transmission or data recording.
more bits, corresponding to their greater im- At the transmitter (or recorder) the timing is
portance. See also transform coding. established by a clock. At the receiver (or
reader)anequivalentclockmustberecovered
from the bit stream.
bit energy the energy contained in
an information-bearing signal received at a
bit plane the binary N ×N image formed
communications receiver per information bit.
by selecting the same bit position of the pix-
The power of an information bearing signal
els when the pixels of an N × N image are
at a communications receiver divided by the
represented using k bits.
information bit rate of the signal. Usually
denoted by E b as in the signal to noise ratio
bit plane encoding lossless binary en-
E b /N 0 .
coding of the bit planes is termed bit plane
encoding. The image is decomposed into a
bit error rate (BER) the probability of set of k, N × N bit planes from the least sig-
a single transmitted bit being incorrectly de- nificant bit to k − 1 most significant bits and
termined upon reception. then encoded for image compression.

bit line used in, for example, RAM mem- bit rate (1) a measure of signaling speed;
ory devices (dynamic and static) to connect the number of bits transmitted per second.
all memory cell outputs of one column to- Bit rate and baud are related but not identi-
gether using a shared signal line. In static cal. Bit rate is equal to baud times the number
RAM, the “bit” line together with its com- of bits used to represent a line state. For ex-
plemented signal “-bit” feeds a “sense ampli- ample, if there are sixteen line states, each
fier” (differential in this case) at the bottom line state encodes four bits, and the bit rate is
of the column serving as a driver to the output thus four times the baud. See also baud.
stage. The actual cell driving the bit line (and (2) the number of bits that can be trans-
-bit) is controlled via an access transistor in mitted per unit time.
each cell. This transistor is turned on/off by
a “word” line, a signal run across the cells in bit serial processing of one bit per clock
each row. cycle. If word length is W, then one sample

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