ccsdsSCPPMDecode

Decode CCSDS-compliant SCPPM codes

Since R2022b

Syntax

[decoded,crcErr] = ccsdsSCPPMDecode(code,r,m)

[decoded,crcErr] = ccsdsSCPPMDecode(code,r,m,maxIter)

Description

[decoded,crcErr] = ccsdsSCPPMDecode(code,r,m) decodes the soft bits in code using a Consultative Committee for Space Data Systems (CCSDS)-compliant serially concatenated pulse position modulation (SCPPM) decoder, as defined in the Coded Modulation for the Deep-Space Optical Channel, volume 42-161 section III.A [1]. r is the outer convolutional encoder code rate and m is the modulation order. The function returns the decoded data decoded which includes the cyclic redundancy check (CRC) and termination bits. The function also returns the CRC error status crcErr.

[decoded,crcErr] = ccsdsSCPPMDecode(code,r,m,maxIter) also specifies the maximum number of decoding iterations.

Examples

Transmit and Decode CCSDS SCPPM Encoded Data

Transmit CCSDS SCPPM encoded data over a noiseless channel, and then decode this data using a CCSDS SCPPM decoder with a maximum of eight decoding iterations.

Encode a message using a CCSDS SCPPM encoder for a single frame. Use the crcGenerate function to generate CRC code bits and append these bits to the input data.

Note: As specified in CCSDS 142.0-B-1 section 3.6:

• Fix the generator polynomial for the CRC algorithm to "x^32+x^29+x^18+x^14+x^3+1".

• Set the initial states of the internal shift register to 1.

infoSize = 7526;                       % Information block size without CRC
crcCfg = crcConfig(...
   Polynomial = "x^32+x^29+x^18+x^14+x^3+1", ...
   InitialConditions = 1, ...
   DirectMethod = true);
crcIn = randi([0 1],infoSize,1);
crcOut = crcGenerate(crcIn,crcCfg);        % Codeword frame with CRC bits appended

Add termination bits to terminate the outer convolutional encoder.

msg = [crcOut; 0; 0];

Specify the modulation order, and then encode the message using the CCSDS SCPPM encoder.

mod = 6;
[sym,info] = ccsdsSCPPMEncode(msg,mod);

Display the outer convolutional encoder information info.

info

info = struct with fields:
           OuterEncoderCodeRate: "1/2"
    OuterEncoderPuncturePattern: [1 1 0 1 1 0]

Modulate the data using the M-ary pulse position modulation (PPM) technique, and pass the modulated data through a noiseless channel.

M = 2^mod;                               % M-ary PPM
modData = zeros(length(sym)*M,1);
mapIdx = (0:length(sym)-1)'*M + sym + 1; % Modulate data
modData(mapIdx) = 1;
code = 2*modData - 1;                    % Pass through noiseless channel

Set the maximum number of decoding iterations to eight. Decode the encoded SCPPM data.

maxIter = 8;
r = info.OuterEncoderCodeRate;
decoded = ccsdsSCPPMDecode(code,r,mod,maxIter);

Display the total number of bit errors in the decoded data.

fprintf("Number of bit errors = %f\n",sum(msg~=decoded));

Number of bit errors = 0.000000

Input Arguments

code — Encoded soft bits

column vector

Encoded soft bits, specified as a column vector.

The function considers negative soft input bits to be 0s and positive soft input bits to be 1s.

Data Types: double

r — Outer convolutional encoder code rate

"1/3" | "1/2" | "2/3"

Outer convolutional encoder code rate, specified as "1/3", "1/2", or "2/3".

Data Types: char | string

m — Modulation order

integer in the range [2, 8]

Modulation order, specified as an integer in the range [2, 8]. This value specifies the number of bits mapped to one constellation symbol.

Data Types: double | uint8

maxIter — Maximum number of decoding iterations

10 (default) | positive integer

Maximum number of decoding iterations, specified as a positive integer.

Data Types: double | uint8

Output Arguments

decoded — Decoded information bits

binary column vector

Decoded information bits, returned as a binary column vector. This data includes CRC and termination bits.

Data Types: int8

crcErr — CRC error status

false or 0 | true or 1

CRC error status, returned as one of these numeric or logical values.

• 0 (false) — Returned when early termination using CRC passes.

• 1 (true) — Returned when CRC fails after completing the maximum number of decoding iterations.

Data Types: logical

References

[1] Moision, B., and J. Hamkins. "Coded Modulation for the Deep-Space Optical Channel: Serially Concatenated Pulse-Position Modulation." The Interplanetary Network Progress Report, vol. 42-161 (May 15, 2005): 1–25.

[2] The Consultative Committee for Space Data Systems. Optical Communications Coding and Synchronization, Recommended Standard, Issue 1. CCSDS 142.0-B-1. Washington, D.C.: CCSDS, August 2019.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2022b