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Convolutional Encoder

Encode data bits using convolution coding — optimized for HDL code generation

  • Library:
  • Wireless HDL Toolbox / Error Detection and Correction

  • Convolutional Encoder block

Description

The Convolutional Encoder block encodes data bits using convolution coding. The block supports code rates from 1/2 to 1/7 and constraint lengths from 3 to 9 including both recursive and nonrecursive polynomials. The block provides an architecture suitable for HDL code generation and hardware deployment.

The block operates in three modes: continuous with an optional reset port, terminated, and truncated with optional initial state and final state ports. In Continuous mode, the block accepts data bits, along with a valid signal, and outputs encoded bits with a valid signal. In Terminated and Truncated modes, the block accepts data bits, along with a samplecontrol bus and outputs encoded bits with a samplecontrol bus.

The block supports communication standards such as Wi-Fi (802.11a/b/g/n/ac), digital satellite communications, digital video broadcast (DVB), 3GPP2, IEEE 802.16, HIPERLAN, and other technologies. You can use this block to implement other channel codes such as turbo codes, which are used in LTE standards.

This waveform shows the encoded output of the block in Terminated mode, when block parameter Constraint length is set to 7, Code generator to [133 171], and Feedback connection to 0. The input and output ctrl buses are expanded to show their control signals.

The latency of the block is three clock cycles, so the block returns the first encoded output data after three clock cycles. In the Terminated mode, after the end of the frame, the block resets the encoded states to all zeros state by appending (Constraint length – 1) bits. So, the waveform shows the frame gap of six (Constraint length – 1) clock cycles between the end of the frame (ctrlIn.endIn) and the start of the next frame ctrlln.startIn.

Ports

Input

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Input data bits, specified as Boolean or ufix1.

Data Types: Boolean | fixed point

Control signal that indicates if the input data is valid. When this value is 1 (true), the block accepts the values on the data input port. When this value is 0 (false), the block ignores the values on the data input port.

Dependencies

To enable this port, set the Operation mode parameter to Continuous.

Data Types: Boolean

Clears internal states, specified as a Boolean scalar. When this value is 1 (true), the block stops the current calculation and clears all encoder states.

Dependencies

To enable this port, set the Operation mode parameter to Continuous and select the Enable reset input port parameter.

Data Types: Boolean

Control signals accompanying the sample stream, specified as a samplecontrol bus. The bus includes the start, end, and valid control signals, which indicate the boundaries of the frame and the validity of the input samples.

  • start — Indicates start of input frame.

  • end — Indicates end of input frame.

  • valid — Indicates the data on the input data port is valid.

Dependencies

To enable this port, set the Operation mode parameter to Truncated or Terminated.

Data Types: bus

Initial state of block at every start of frame, specified as fixdt(0,constraint length -1,0). Input state is the number of binary bits in the shift register at the frame start of the block, which is read from most significant bit (MSB) to least significant bit (LSB).

double and single data types are supported for simulation, but not for HDL code generation.

Dependencies

To enable this port, set the Operation mode parameter to Truncated and select the Enable initial state input port parameter.

Data Types: single | double | fixed point

Output

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Output data, returned as 1-by-n column vector, if the code rate is 1/n. The n value ranges from 2 to 7.

Data Types: Boolean

Control signal that indicates if the data from the data output port is valid. When this value is 1 (true), the block returns valid data on the data output port. When valid is false (0), the values on data output port are not valid.

Dependencies

To enable this port, set the Operation mode parameter to Continuous.

Data Types: Boolean

Control signals accompanying the sample stream, returned as a samplecontrol bus. The bus includes the start, end, and valid control signals, which indicate the boundaries of the frame and the validity of the samples.

  • start — Indicates start of output frame.

  • end — Indicates end of output frame.

  • valid — Indicates the data on the output data port is valid.

Dependencies

To enable this port, set the Operation mode parameter to Truncated or Terminated.

Data Types: bus

Final state of frame at every frame end, returned as fixdt(0,constraint length -1,0). Final state is the number of binary bits in the shift register at the frame end of the block, which is read from most significant bit (MSB) to least significant bit (LSB).

The block returns the same as the ISt data type.

Dependencies

To enable this port, set the Operation mode parameter to Truncated and select the Enable final state output port parameter.

Data Types: single | double | fixed point

Parameters

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Main

Constraint length of the block, specified as an integer in the range [3, 9].

Code generation polynomial, specified as a 1-by-n vector of octal values, where n is the length of the polynomial ranged from 2 to 7.

Feedback polynomial, specified as a scalar octal number. If the feedback connection is 0, there is no feedback connection enabled.

To enable feedback connection, specify an octal value whose binary representation must be a K-bit number with MSB 1, where K is the Constraint length. For more information on how to construct a feedback polynomial, refer to Convolutional Codes.

Mode of operation, specified as one of these modes:

  • Continuous — In this mode, the block starts with all zeros state and retains the encoder states at the end of each input, for use with the next input.

  • Terminated — In this mode, the block considers each input frame independently. The encoder states of the block are reset to all-zeros state at the end of each frame by appending bits.

    Note

    This mode requires a minimum frame gap of Constraint length – 1 cycles between frames. If no sufficient frame gap is provided, the block stops processing the old frame and starts processing a new frame.

  • Truncated — In this mode, the block considers each input frame independently. The encoder states are reset to all-zeros state at the start of each input.

Control Ports

Select this parameter to enable the reset port. When reset is 1 (true), the block resets the encoder state in the next clock cycle.

Dependencies

To enable this parameter, set the Operation mode parameter to Continuous.

Select this parameter to enable the ISt port.

Dependencies

To enable this parameter, set the Operation mode parameter to Truncated.

Select this parameter to enable the FSt port.

Dependencies

To enable this parameter, set the Operation mode parameter to Truncated.

Algorithms

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A polynomial description of a Convolutional Encoder block describes the connections among shift registers and modulo 2 adders. This figure shows two sample encoding operations, one without feedback that has one input, two outputs, and two shift registers and the other with feedback that has one input, two outputs, and two shift registers.

b(n) represents input data bit stream and b(n-1) and b(n-2) represent the 2-bit shift register of the encoder. Out1(n) and Out2(n) represent the 2-bit output. From this figure, you can calculate the block mask parameters based on the Convolutional codes concepts. For more information about Convolution codes concepts, refer to Convolutional Codes. So, based on the connections provided in the figure, the Constraint length is 3, Code generator value is [5 7]. The Feedback connection value is 0 for the encoder without feedback connection and 6 for the encoder with feedback connection.

References

[1] Lin, Shu, and Daniel J. Costello. Error Control Coding By Shu Lin, Daniel J. Costello, Second Edition. Upper Saddle River, NJ: Prentice Hall, 2004.

Extended Capabilities

Introduced in R2019b