Ccsds 1301 g 1 page a 1 june 2006 tm synchronization

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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 waveform. 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 process). 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 space mission. 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...
View Full Document

Ask a homework question - tutors are online