Uniform Decoder
Decode integer input into floatingpoint output
Library
Quantizers
dspquant2
Description
The Uniform Decoder block performs the inverse operation of the Uniform Encoder block, and reconstructs quantized floatingpoint values from encoded integer input. The block adheres to the definition for uniform decoding specified in ITUT 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 floatingpoint values, and then uniquely maps (decodes) them to one of 2^{B} uniformly spaced floatingpoint values in the range [V, (12^{1B})V], where you specify B in the Bits parameter (as an integer between 2 and 32) and V is a floatingpoint value specified by the Peak parameter. The smallest input value representable by B bits (0 for an unsigned input data type; 2^{B1} 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^{B1}1 for a signed input data type) is mapped to the value (12^{1B})V. Intermediate input values are linearly mapped to the intermediate values in the range [V, (12^{1B})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. When you select Saturate, unsigned input values greater than 2^{B}1 saturate at 2^{B}1; signed input values greater than 2^{B1}1 or less than 2^{B1} saturate at those limits. The real and imaginary components of complex inputs saturate independently.
When you select Wrap, unsigned input values,
u
, greater than 2^{B}1 are wrapped back
into the range [0, 2^{B}1] using
mod2^{B} arithmetic.
u = mod(u,2^B)
Signed input values, u
, greater than
2^{B1}1 or less than 2^{B1} are
wrapped back into that range using mod2^{B} arithmetic.
u = (mod(u+2^B/2,2^B)(2^B/2))
The real and imaginary components of complex inputs wrap independently.
The Output type parameter specifies whether the decoded floatingpoint output is single or double precision. Either level of output precision can be used with any of the six integer input data types.
Examples
See example model ex_uniform_decoder.
In this example, the input to the block is the uint8
output of a
Uniform Encoder block. This block has 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 block reference page for more about these
settings.)
The real and complex components of each input are independently mapped to one of
2^{3} 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
Parameters
 Peak
Specify 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
Specify 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
Specify the block's behavior when the integer input is outside the range representable by B bits. Outofrange inputs can either saturate at the extreme value, or wrap back into range.
 Output type
Specify the precision of the floatingpoint output,
single
ordouble
.
References
General Aspects of Digital Transmission Systems: Vocabulary of Digital Transmission and Multiplexing, and Pulse Code Modulation (PCM) Terms, International Telecommunication Union, ITUT Recommendation G.701, March, 1993
Supported Data Types
Port  Supported Data Types 

Input 

Output 

See Also
Data Type Conversion (Simulink)  Simulink 
Quantizer (Simulink)  Simulink 
Scalar Quantizer Decoder  DSP System Toolbox 
Uniform Encoder  DSP System Toolbox 
udecode  Signal Processing Toolbox 
uencode  Signal Processing Toolbox 