Unformatted text preview: ta stream. The data stream here consists of the codewords generated by the outer
decoder. Modulating Waveform: A way of representing data bits (‘1’ and ‘0’) by a particular
NRZ-L: A modulating waveform in which a data ‘one’ is represented by one of two levels,
and a data ‘zero’ is represented by the other level. CCSDS 130.1-G-1 Page A-1 June 2006 TM SYNCHRONIZATION AND CHANNEL CODING —SUMMARY OF CONCEPT AND RATIONALE NRZ-M: A modulating waveform in which a data ‘one’ is represented by a change in level
and a data ‘zero’ is represented by no change in level.
Octet: An 8-bit word consisting of eight contiguous bits.
Outer Code: In a concatenated coding system, the first encoding algorithm that is applied to
the data stream.
Packet: An efficient application-oriented protocol data unit that facilitates the transfer of
source data to users located in space or on Earth.
Protocol: A set of procedures and their enabling format conventions that define the orderly
exchange of information between entities within a given layer of the TM System.
Reed-Solomon (‘R-S’) Symbol: A set of J bits that represents an element in the Galois field
GF(2J), the code alphabet of a J-bit Reed-Solomon code.
Reliable: Meets the quality, quantity, continuity and completeness criteria which are
specified by the TM System.
Segment: A protocol data unit which facilitates telemetry flow control through the breaking
of long source packets into communications-oriented data structures.
Systematic Code: A code in which the input information sequence appears in unaltered form
as part of the output codeword.
Telemetry System: The end-to-end system of layered data handling services which exist to
enable a spacecraft to send measurement information, in an error-controlled environment, to
receiving elements (application processes) in space or on Earth.
Transfer Frame: A communication oriented protocol data unit that facilitates the transfer of
application oriented protocol data units through the space-to-ground link.
Transparent: The invisible and seemingly direct (virtual) transfer of measurement
information from the spacecraft source application process to the user (receiving application
Transparent Code: A code that has the property that complementing the input of the encoder
or decoder results in complementing the output.
User: A human or machine-intelligent process which directs and analyzes the progress of a
Virtual Channel: A given sequence of Transfer Frames, which are assigned a common
identification code (in the Transfer Frame header), enabling all Transfer Frames who are
members of that sequence to be uniquely identified. It allows a technique for multiple source
application processes to share the finite capacity of the physical link (i.e., through
multiplexing). CCSDS 130.1-G-1 Page A-2 June 2006 TM SYNCHRONIZATION AND CHANNEL CODING —SUMMARY OF CONCEPT AND RATIONALE Virtual Fill: In a systematic block code, a codeword can be divided into an information part
and a parity (check) part. Suppose that the information part is N symbols long (symbol is
defined here to be an element of the code’s alphabet) and that the parity part is M symbols
long. A ‘shortened’ code is created by taking only S (S<N) information symbols as input,
appending a fixed string of length N-S and then encoding in the normal way. This fixed string
is called ‘fill’. Since the fill is a predetermined sequence of symbols, it need not be
transmitted over the channel. Instead, the decoder appends the same fill sequence before
decoding. In this case, the fill is called ‘Virtual Fill’.
Connection Vector (Forward): In convolutional and turbo coding, a vector used to specify
one of the parity checks to be computed by the shift register(s) in the encoder. For a shift
register with s stages, a connection vector is an s-bit binary number. A bit equal to one in
position i (counted from the left) indicates that the output of the ith stage of the shift register
is to be used in computing that parity check.
Connection Vector (Backward): In turbo coding, a vector used to specify the feedback to the
shift registers in the encoder. For a shift register with s stages, a backward connection vector
is an s-bit binary number. A bit equal to one in position i (counted from the left) indicates
that the output of the ith stage of the shift register is to be used in computing the feedback
value, except for the leftmost bit which is ignored.
Trellis Termination: The operation of filling with zeros the s stages of each shift register used
in the turbo encoder, after the end of the information block. During trellis termination the
encoders continue to output encoded symbols for s-1 additional clock cycles.
Turbo Code: As used in this document, a block code formed by combining two component
recursive convolutional codes. A turbo code takes as input a block of k information bits. The
input block is sent unchanged to the first c...
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- Spring '14
- Information Theory, ........., Error detection and correction, CCSDS