Encode binary data using parallel concatenated encoding scheme
Convolutional sublibrary of Error Detection and Correction
The Turbo Encoder block encodes a binary input signal using a parallel concatenated coding scheme. This coding scheme employs two identical convolutional encoders and one internal interleaver. Each constituent encoder is independently terminated by tail bits.
The previous block diagram illustrates that the output of the Turbo Encoder block consists of the systematic and parity bits streams of the first encoder, and only the parity bit streams of the second encoder.
For a rate onehalf constituent encoder, the block interlaces the three streams and multiplexes the tail bits to the end of the encoded data streams.
For more information about tail bits, see the terminate Operation mode on the Convolutional Encoder block reference page.
This block accepts an Lby1 column vector input signal and outputs an Mby1 column vector signal. For a given trellis, M and L are related by:
$$M=\text{\hspace{0.17em}}L\cdot (2\cdot n1)+\text{\hspace{0.17em}}\text{}2\cdot numTails$$
and
$$L=\text{\hspace{0.17em}}\frac{(M2\cdot numTails)}{(2\cdot n1)}$$
where
L = encoder input length
M = encoder output length
n = log2(trellis.NumOutputSymbols), for a rate 1/2 trellis, n = 2
numTails = log2(trellis.numStates) * n
The previous schematic shows the encoder configuration for a trellis specified by
the default value of the Trellis structure parameter,
poly2trellis(4, [13 15], 13)
. For an input vector length of
64 bits, the output of the encoder block is 204 bits. The first 192 bits correspond
to the three 64 bit streams (systematic (X_{k}) and parity
(Z_{k}) bit streams from the first encoder and the parity
(Z^{’}_{k}) bit stream of the second
encoder), interlaced as per X_{k}, Z_{k},
Z^{’}_{k}. The last 12 bits
correspond to the tail bits from the two encoders, when the switches are in the
lower position corresponding to the dashed lines. The first group of six bits (three
systematic bits and three parity bits) are the output tail bits from the first
constituent encoder. The second group of six bits (three systematic bits and three
parity bits) are the output tail bits from the second constituent encoder.
Due to the tail bits, the encoder output code rate is slightly less than 1/3.
Trellis structure of constituent convolutional code.
Specify the trellis as a MATLAB^{®} structure that contains the trellis description of the
constituent convolutional code. Alternatively, use the
poly2trellis
function to create a custom trellis
using the constraint length, code generator (octal), and feedback
connections (octal).
This block supports only rate 1byN trellises where N is an integer.
The default structure is the result of poly2trellis(4, [13 15], 13).
Specify the source of the interleaver indices as
Property
or Input
port
.
When you set this parameter to Property
, the
block uses the Interleaver indices parameter to specify
the interleaver indices.
When you set this parameter to Input port
, the
block uses the secondary input port, IntrInd, to specify the interleaver
indices.
Specify the mapping that the block uses to permute the input bits as a
column vector of integers. The default is (64:1:1).'
.
This mapping is a vector with the number of elements equal to the length,
L, of the input signal. Each element must be an
integer between 1 and L, with no repeated values.
Specify if the block simulates using Code
generation
or Interpreted
execution
. The default is Interpreted
execution
.
Port  Supported Data Types 

In 

Out 

For an example that uses the Turbo Encoder and Turbo Decoder blocks, see the Parallel Concatenated Convolutional Coding: Turbo Codes example.
[1] Berrou, C., A. Glavieux, and P. Thitimajshima. "Near Shannon limit error correcting coding and decoding: turbo codes,” Proceedings of the IEEE International Conference on Communications, Geneva, Switzerland, May 1993, pp. 1064–1070.
[2] Benedetto, S., G. Montorsi, D. Divsalar, and F. Pollara. “ SoftInput SoftOutput Maximum A Posterior (MAP) Module to Decode Parallel and Serial Concatenated Codes,”Jet Propulsion Lab TDA Progress Report, Vol. 42–27, Nov. 1996.
[3] Schlegel, Christian B. and Lance C. Perez. Trellis and Turbo Coding, IEEE Press, 2004.
[4] 3GPP TS 36.212 v9.0.0, 3rd Generation partnership project; Technical specification group radio access network; Evolved Universal Terrestrial Radio Access (EUTRA); Multiplexing and channel coding (release 9), 200912.