Home of RF and Wireless Vendors and Resources

One Stop For Your RF and Wireless Need

CTC(Convolutional Turbo Code) basics and specifications

This section of MATLAB source code covers CTC Encoder or Convolutional Turbo code matlab code.

The Convolutional Turbo Code Encoder or CTC Encoder is depicted in the following figure including constituent encoder. It uses double binary circular recursive systematic convolutional code.The following is the matlab code for the CTC structure defined in the figure.

CTC encoder

Refer Turbo encoder page which describes basics of CTC Encoder or Convolutional Turbo Encoder technique with rate 1 by 3 example used for forward error correction.

The difference between convolutional encoder and turbo encoder is that in convolutional encoder input bits are not preserved and are altered. While in the case of turbo coding input bits are preserved and are multiplexed with other altered bits generated through encoder and (interleaver+encoder) modules.

CTC Encoder MATLAB Code

function OutBits = CTCEncoder(InpBits, N, P)

CircularStateTable = [
0 6 4 2 7 1 3 5;
0 3 7 4 5 6 2 1;
0 5 3 6 2 7 1 4;
0 4 1 5 6 2 7 3;
0 2 5 7 1 3 4 6;
0 7 6 1 3 4 5 2];

InitState = [0 0 0];
[Junk FinalState] = CTCRSCEncoder(InpBits, N, InitState);
Ri = mod(N, 7);
Ci = FinalState(1)*4 + FinalState(2)*2 + FinalState(3);
CS = CircularStateTable(Ri, Ci+1);
InitState(1) = floor(CS/4);
CS = mod(CS,4);
InitState(2) = floor(CS/2);
CS = mod(CS,2);
InitState(3) = CS;
[p1 FS] = CTCRSCEncoder(InpBits, N, InitState);
if sum(FS == InitState) ~= 3
disp('P1 mismatch')
return
end
IB = CTCInterleaver(InpBits, N, P);
InitState = [0 0 0];
[Junk FinalState] = CTCRSCEncoder(IB, N, InitState);
Ri = mod(N, 7);
Ci = FinalState(1)*4 + FinalState(2)*2 + FinalState(3);
CS = CircularStateTable(Ri, Ci+1);
InitState(1) = floor(CS/4);
CS = mod(CS,4);
InitState(2) = floor(CS/2);
CS = mod(CS,2);
InitState(3) = CS;
[p2 FS] = CTCRSCEncoder(IB, N, InitState);
if sum(FS == InitState) ~= 3
disp('P2 mismatch')
return
end

OutBits = zeros(6*N, 1);
for k = 0:N-1
OutBits(6*k+1) = InpBits(2*k+1);
OutBits(6*k+2) = InpBits(2*k+2);
OutBits(6*k+3) = p1(2*k+1);
OutBits(6*k+4) = p2(2*k+1);
OutBits(6*k+5) = p1(2*k+2);
OutBits(6*k+6) = p2(2*k+2);
end

function [ParityBits, FinState] = CTCRSCEncoder(InpBits, N, InitState)
%[ParityBits, FinState] = CTCRSCEncoder(InpBits, N, InitState)
%InitState = initial state of encoder (0 to 7) in binary
%FinState = final state of encoder (0 to 7) in binary

load 'CTCEncTable'
TNxt = CTCEncTable(:, 6:8);
TOut = CTCEncTable(:, 9:10);
ParityBits = zeros(2*N, 1);
CS = InitState;

for k = 0:N-1
A = InpBits(2*k+1);
B = InpBits(2*k+2);
m = CS(1)*16 + CS(2)*8 + CS(3)*4 + A*2 + B;
NS = TNxt(m+1, :);
Pb = TOut(m+1, :);
ParityBits(2*k+1) = Pb(1);
ParityBits(2*k+2) = Pb(2);
CS = NS;
end
FinState = NS;

function InterleavedBits = CTCInterleaver(InpBits, N, P)
%InterleavedBits = CTCInterleaver(InpBits, N, P)
%N - Length of input bit in pairs
%P - [p0 p1 p2 p3], interleaver parameters

InterleavedBits = zeros(2*N, 1);
xI = zeros(N, 2);
for k = 0:N-1
m = CTCGetInterleavedAddress(k, N, P);
A = InpBits(2*m+1);
B = InpBits(2*m+2);
if mod(k, 2) == 1
InterleavedBits(2*k+1) = A;
InterleavedBits(2*k+2) = B;
else
InterleavedBits(2*k+1) = B;
InterleavedBits(2*k+2) = A;
end

end

Useful Links to MATLAB codes

Refer following as well as links mentioned on left side panel for useful MATLAB codes.
OFDM Preamble generation  Time off estimation corr  Freq off estimation corr  channel estimation  11a WLAN channel  PN sequence generation  OFDMA Tx Rx  AES DES  carrier aggregation  CCDF  FIR Filter  IIR Filter  Low Pass FIR  Viterbi decoder  CRC8 CRC32 

RF and Wireless tutorials

WLAN  802.11ac  802.11ad  wimax  Zigbee  z-wave  GSM  LTE  UMTS  Bluetooth  UWB  IoT  satellite  Antenna  RADAR 


Share this page

Translate this page