Turbo codes

Turbo codes are a type of error-correcting code that are designed to provide very high levels of error correction while still maintaining a reasonable data rate. They were developed in the 1990s and have since become widely used in a variety of applications, including satellite communication, wireless communication, and data storage.

Turbo codes work by encoding the data to be transmitted using two or more simple error-correcting codes, known as constituent codes. The encoded data is then transmitted over the communication channel, and any errors that occur during transmission are detected and corrected using an iterative decoding process known as "turbo decoding." This process involves passing the received data through a series of decoders and then using the output of these decoders to improve the accuracy of the final decoding.

Turbo codes are able to provide very high levels of error correction because they use multiple constituent codes and the iterative decoding process. They are also relatively easy to implement and can be used with a variety of different modulation schemes. However, they do require more processing power and complexity than some other error-correcting codes, which can make them less practical in some applications.

 

Here is an example of how a turbo code might be used to encode and transmit data over a communication channel:

1. The data to be transmitted is first divided into blocks of a fixed size, such as 256 bits.
2. Each block of data is then encoded using two simple error-correcting codes, known as constituent codes. These codes add extra parity symbols to the data, which can be used to detect and correct errors that may occur during transmission.
3. The encoded data is then transmitted over the communication channel, which may introduce errors in the data due to noise or interference.
4. The received data is then passed through a series of decoders, which use the parity symbols added by the constituent codes to detect and correct any errors that occurred during transmission.
5. The output of the decoders is then fed back into the decoding process to improve the accuracy of the final decoding. This process is known as "turbo decoding."
6. The final decoded data is then checked for errors, and if any are detected, the process is repeated until the data is successfully decoded.

 

 

Here is a sample VHDL code for a Turbo Encoder:

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;

entity TurboEncoder is
  Port ( clk : in std_logic;
         reset : in std_logic;
         data_in : in std_logic_vector (k-1 downto 0);
         enc_out1 : out std_logic_vector (n-1 downto 0);
         enc_out2 : out std_logic_vector (n-1 downto 0));
end TurboEncoder;

architecture Behavioral of TurboEncoder is
  signal int_state1, int_state2 : std_logic_vector (k-1 downto 0);
  signal int_output1, int_output2 : std_logic_vector (n-1 downto 0);
begin
  -- encoder 1
  process(clk, reset)
  begin
    if reset = '1' then
      int_state1 <= (others => '0');
    elsif rising_edge(clk) then
      int_state1 <= data_in;
      int_output1 <= encode(int_state1);
    end if;
  end process;
  
  -- encoder 2
  process(clk, reset)
  begin
    if reset = '1' then
      int_state2 <= (others => '0');
    elsif rising_edge(clk) then
      int_state2 <= data_in;
      int_output2 <= encode(int_state2);
    end if;
  end process;
  
  enc_out1 <= int_output1;
  enc_out2 <= int_output2;
end Behavioral;

-- function to implement the encoding algorithm
function encode(data : std_logic_vector(k-1 downto 0)) return std_logic_vector is
  -- implementation of the encoding algorithm
begin
  -- add your code here
end function;

Here is a sample VHDL code for a Turbo Decoder:

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.numeric_std.all;

entity TurboDecoder is
  Port ( clk : in std_logic;
         reset : in std_logic;
         dec_in1 : in std_logic_vector (n-1 downto 0);
         dec_in2 : in std_logic_vector (n-1 downto 0);
         data_out : out std_logic_vector (k-1 downto 0));
end TurboDecoder;

architecture Behavioral of TurboDecoder is
  signal int_input1, int_input2 : std_logic_vector (n-1 downto 0);
  signal int_state : std_logic_vector (k-1 downto 0);
begin
  -- decode data from both inputs
  process(clk, reset)
  begin
    if reset = '1' then
      int_input1 <= (others => '0');
      int_input2 <= (others => '0');
    elsif rising_edge(clk) then
      int_input1 <= dec_in1;
      int_input2 <= dec_in2;
      int_state <= decode(int_input1, int_input2);
    end if;
  end process;
  
  data_out <= int_state;
end Behavioral;

-- function to implement the decoding algorithm
function decode(dec_in1, dec_in2 : std_logic_vector(n-1 downto 0)) return std_logic_vector is
  -- implementation of the decoding algorithm
begin
  -- add your code here
end function;

This is just a sample code to give you an idea of how a Turbo Decoder can be implemented in VHDL. The actual implementation of the decoding algorithm will depend on the specific coding scheme being used for the Turbo Code. You may need to modify the code based on your specific requirements.