Uniform Encoder

Quantize and encode floating-point input into integer output

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Libraries:
DSP System Toolbox / Quantizers

Description

The Uniform Encoder block performs these two operations on each floating-point sample in the input vector or matrix:

1. Quantizes the value using the same precision

2. Encodes the quantized floating-point value to an integer value

For more information on how the block computes the output, see Algorithms.

The Uniform Encoder block operations adhere to the definition for uniform encoding specified in ITU-T Recommendation G.701.

Examples

Encode Data Using Uniform Encoder

Open the ex_uniform_encoder model.

Double-click the Uniform Encoder block and set these parameters in the block dialog box:

• Peak = 2

• Bits = 3

• Output type = Unsigned

The following figure illustrates uniform encoding.

The block quantizes the real and complex components of each input (horizontal axis) independently to one of distinct levels in the range [-2,1.5]. It then maps these components to one of integer values in the range [0,7]. The block maps:

• -2.0 to 0

• -1.5 to 1

• -1.0 to 2

• -0.5 to 3

• 0.0 to 4

• 0.5 to 5

• 1.0 to 6

• 1.5 to 7

This list shows the block output for specific inputs.

• Input = 1.6, Quantized Input = 1.5+0.0i, Output = 7+4i

• Input = -0.4, Quantized Input = -0.5+0.0i, Output = 3+4i

• Input = -3.2, Quantized Input = -2.0+0.0i, Output = 4i, Saturation (real)

• Input = 0.4-1.2i, Quantized Input = 0.0-1.5i, Output = 4+i

• Input = 0.4-6.0i, Quantized Input = 0.0-2.0i, Output = 4, Saturation (imaginary)

• Input = -4.2+3.5i, Quantized Input = -2.0+2.0i, Output = 7i, Saturation (real and imaginary)

The output data type is automatically set to uint8, the most efficient format for this input range.

Ports

Input

Input — Input signal

vector | matrix

Specify the floating-point input signal as a vector or a matrix. Inputs greater than (1−2^1−B)V or less than −V saturate at those respective values. The real and imaginary components of complex inputs saturate independently.

Data Types: single | double
Complex Number Support: Yes

Output

Output — Encoder output

vector | matrix

Encoder output, returned as a vector or a matrix. The block quantizes each sample in the floating-point input and encodes the quantized floating-point value to an integer value. For more information on how the block computes the output, see Algorithms.

Data Types: int8 | int16 | int32 | uint8 | uint16 | uint32
Complex Number Support: Yes

Parameters

Peak — Largest input amplitude to encode

1 (default) | nonnegative scalar

Specify the largest input amplitude to encode V as a nonnegative scalar. Real or imaginary input values greater than (1−2^1−B)V or less than −V saturate (independently for complex inputs) at those limits.

Bits — Number of bits

8 (default) | integer in the range [2, 32]

Specify the number of bits B that the block needs to represent the integer output. The number of bits B can be any integer value between 2 and 32, inclusive. The number of levels at which the block quantizes the floating-point input is 2^B.

Output type — Data type of block output

Unsigned integer (default) | Signed integer

Specify the data type of the block output as one of these:

• Unsigned integer –– The block maps the smallest quantized floating-point value −V to the integer 0 and the largest quantized floating-point value (1−2^1−B)V to the integer 2^B−1. It linearly (uniformly) maps the intermediate quantized floating-point values to the intermediate integers in the range [0, 2^B−1]. For efficiency, the block automatically selects an unsigned output data type (uint8, uint16, or uint32) with the minimum number of bits equal to or greater than B.

• Signed integer –– The block maps the smallest quantized floating-point value −V to the integer −2^B−1, and the largest quantized floating-point value (1−2^1−B)V to the integer 2^B−1−1. It linearly maps the intermediate quantized floating-point values to the intermediate integers in the range [−2^B−1, 2^B−1−1]. The block automatically selects a signed output data type (int8, int16, or int32) with the minimum number of bits equal to or greater than B.

This table shows the output data types that the block uses.

Bits	Unsigned Integer	Signed Integer
2 to 8	uint8	int8
9 to 16	uint16	int16
17 to 32	uint32	int32

Block Characteristics

Data Types	double | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Algorithms

The Uniform Encoder block performs these two operations on each floating-point sample in the input.

1. Quantizes the value using the same precision

2. Encodes the quantized floating-point value to an integer value

In the first step, the block quantizes an input value to one of 2^B uniformly spaced levels in the range [−V, (1−2^1−B)V], where you specify B in the Bits parameter and you specify V in the Peak parameter. The quantization process rounds both positive and negative inputs downward to the nearest quantization level, with the exception of those that fall exactly on a quantization boundary. It quantizes the real and imaginary components of complex inputs independently.

In the second step, the block uniquely maps (encodes) the quantized floating-point value to one of 2^B integer values. When you set the Output type to Unsigned integer, the blocks maps the smallest quantized floating-point value −V to the integer 0 and the largest quantized floating-point value (1−2^1−B)V to the integer 2^B−1. It linearly (uniformly) maps the intermediate quantized floating-point values to the intermediate integers in the range [0, 2^B−1]. For efficiency, the block automatically selects an unsigned output data type (uint8, uint16, or uint32) with the minimum number of bits equal to or greater than B.

When the Output type is set to Signed integer, the smallest quantized floating-point value −V is mapped to the integer −2^B−1, and the largest quantized floating-point value (1−2^1−B)V is mapped to the integer 2^B−1−1. Intermediate quantized floating-point values are linearly mapped to the intermediate integers in the range [−2^B−1, 2^B−1−1]. The block automatically selects a signed output data type (int8, int16, or int32) with the minimum number of bits equal to or greater than B.

References

[1] 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.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a