DSP Blockset

Uniform Decoder

Decode an integer input to a floating-point output.

Library

Quantizers

Description

The Uniform Decoder block performs the inverse operation of the Uniform Encoder block, and reconstructs quantized floating-point values from encoded integer input. The block adheres to the definition for uniform decoding specified in ITU-T Recommendation G.701.

Inputs can be real or complex values of the following six integer data types: uint8, uint16, uint32, int8, int16, or int32.

The block first casts the integer input values to floating-point values, and then uniquely maps (decodes) them to one of 2^B uniformly spaced floating point values in the range [-V, (1-2^1-B)V], where B is specified by the Bits parameter (as an integer between 2 and 32) and V is a floating-point value specified by the Peak parameter. The smallest input value representable by B bits (0 for an unsigned input data type; -2^B-1 for a signed input data type) is mapped to the value -V. The largest input value representable by B bits (2^B-1 for an unsigned input data type; 2^B-1-1 for a signed input data type) is mapped to the value (1-2^1-B)V. Intermediate input values are linearly mapped to the intermediate values in the range [-V, (1-2^1-B)V].

To correctly decode values encoded by the Uniform Encoder block, the Bits and Peak parameters of the Uniform Decoder block should be set to the same values as the Bits and Peak parameters of the Uniform Encoder block. The Overflow mode parameter specifies the Uniform Decoder block's behavior when the integer input is outside the range representable by B bits. If Saturate is selected, unsigned input values greater than 2^B-1 saturate at 2^B-1; signed input values greater than 2^B-1-1 or less than -2^B-1 saturate at those limits. The real and imaginary components of complex inputs saturate independently.

If Wrap is selected, unsigned input values, u, greater than 2^B-1 are wrapped back into the range [0, 2^B-1] using mod-2^B arithmetic.

• u = mod(u,2^B)                    % Equivalent MATLAB code
  

Signed input values, u, greater than 2^B-1-1 or less than -2^B-1 are wrapped back into that range using mod-2^B arithmetic.

• u = (mod(u+2^B/2,2^B)-(2^B/2))    % Equivalent MATLAB code
  

The real and imaginary components of complex inputs wrap independently.

The Output type parameter specifies whether the decoded floating-point output is single or double precision. Either level of output precision can be used with any of the six integer input data types.

Example

Consider a Uniform Decoder block with the following parameter settings:

• Peak = 2
• Bits = 3

The input to the block is the uint8 output of a Uniform Encoder block with comparable settings: Peak = 2, Bits = 3, and Output type = Unsigned. (Comparable settings ensure that inputs to the Uniform Decoder block do not saturate or wrap. See the example on the Uniform Encoder reference page for more about these settings.)

The real and complex components of each input are independently mapped to one of 2³ distinct levels in the range [-2.0,1.5].

• 0  is mapped to  -2.0
  1  is mapped to  -1.5
  2  is mapped to  -1.0
  3  is mapped to  -0.5
  4  is mapped to   0.0
  5  is mapped to   0.5
  6  is mapped to   1.0
  7  is mapped to   1.5
  

Dialog Box

Peak

The largest amplitude represented in the encoded input. To correctly decode values encoded with the Uniform Encoder block, set the Peak parameters in both blocks to the same value.

Bits

The number of input bits, B, used to encode the data. (This can be less than the total number of bits supplied by the input data type.) To correctly decode values encoded with the Uniform Encoder block, set the Bits parameters in both blocks to the same value.

Overflow mode

The block's behavior when the integer input is outside the range representable by B bits. Out-of-range inputs can either saturate at the extreme value, or wrap back into range.

Output type

The precision of the floating-point output, single or double.

References

General Aspects of Digital Transmission Systems: Vocabulary of Digital Transmission and Multiplexing, and Pulse Code Modulation (PCM) Terms, International Telecommunication Union, ITU-T Recommendation G.701, March, 1993

Supported Data Types

• Double-precision floating point
• Single-precision floating point

To learn how to convert to the above data types in MATLAB and Simulink, see Supported Data Types and How to Convert to Them.

See Also

Data Type Conversion	Simulink
Quantizer	Simulink
Uniform Encoder	DSP Blockset
udecode	Signal Processing Toolbox
uencode	Signal Processing Toolbox

Also see Quantizers for a list of all the blocks in the Quantizers library.

Unbuffer

Uniform Encoder