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OQPSK Demodulator Baseband - Demodulate OQPSK-modulated data

Library

PM, in Digital Baseband sublibrary of Modulation

Description

The OQPSK Demodulator Baseband block demodulates a signal that was modulated using the offset quadrature phase shift keying method. The input is a baseband representation of the modulated signal.

The input must be a discrete-time complex signal. The input can be either a scalar or a frame-based column vector. The block accepts the data types double, single, and signed fixed-point.

If the Output type parameter is set to Integer, then the block outputs integer symbol values between 0 and 3. If the Output type parameter is set to Bit, then the block outputs 2–bit binary representations of such integers, in a binary-valued vector whose length is an even number.

The block produces one output symbol for each pair of input symbols. The input symbol period is half the period of each output integer or bit pair. The constellation used to map bit pairs to symbols is on the reference page for the OQPSK Modulator Baseband block.

Sample-Based Inputs

If the input is a sample-based scalar, then the block outputs a single integer symbol (or one pair of bits) for each output time step. The input sample period is half the output symbol period, in this case.

To open the completed model, click here in the MATLAB Help browser

Frame-Based Inputs

If the input is a frame-based column vector, then the block processes several integer symbols (or several pairs of bits) for each time step. In this case, the frame-based output port frame time equals that of the input.

The output frame length is adjusted based on the input frame length and the setting for the Output type parameter. When you set the Output type parameter to Integer, the output frame length is half that of the input frame length. When you set the Output type parameter to Bit, the output frame length equals the input frame length (because each symbol is two bits).

Note The input frame length must be even or else the block will error out.

To open the completed model, click here in the MATLAB Help browser

Delays

The modulator-demodulator pair incurs a delay, as described in Delays in Digital Modulation.

Signal Flow Diagram

OQPSK Fixed-Point Signal Flow Diagram

Note Every two input samples produce one output symbol. In the preceding figure, the dotted line represents the region comprised of input sample processing.

OQPSK Floating Point Signal Flow Diagram

Note Every two input samples produce one output symbol. In the preceding figure, the dotted line represents the region comprised of input sample processing.

Dialog Box

Phase offset (rad): The amount by which the phase of the zeroth point of the signal constellation is shifted from π/4.
Output type: Determines whether the output consists of integers or pairs of bits.

Data Type Pane

Output

For bit outputs, the output data type can be set to 'Inherit via internal rule', 'Smallest unsigned integer', double, single, int8, uint8, int16, uint16, int32, uint32, or boolean.

For integer outputs, the output data type can be set to 'Inherit via internal rule', 'Smallest unsigned integer', double, single, int8, uint8, int16, uint16, int32, or uint32.

When this parameter is set to 'Inherit via internal rule' (default setting), the block will inherit the output data type from the input port. The output data type will be the same as the input data type if the input is a floating-point type (single or double). If the input data type is fixed-point, the output data type will work as if this parameter is set to 'Smallest unsigned integer'.

When this parameter is set to 'Smallest unsigned integer', the output data type is selected based on the settings used in the Hardware Implementation pane of the Configuration Parameters dialog box of the model.

If ASIC/FPGA is selected in the Hardware Implementation pane, and Output type is Bit, the output data type is the ideal minimum one-bit size, i.e., ufix1. For all other selections, it is an unsigned integer with the smallest available word length large enough to fit one bit, usually corresponding to the size of a char (e.g., uint8).

If ASIC/FPGA is selected in the Hardware Implementation pane, and Output type is Integer, the output data type is the ideal minimum two-bit size, i.e., ufix2. For all other selections, it is an unsigned integer with the smallest available word length large enough to fit two bits, usually corresponding to the size of a char (e.g., uint8).

Derotate factor

This parameter only applies when the input is fixed-point and Phase offset is not a multiple of .

This can be set to Same word length as input or Specify word length, in which case a field is enabled for user input.

Accumulator

Specify the data type for the Accumulator. You can set this parameter to Inherit via internal rule, Same as input or Binary point scaling.

The Accumulator parameter only applies for fixed-point inputs. The selections you make for the Rounding and Overflow parameters affect the Accumulator.

Fixed-point Communications Blockset blocks that must hold summation results for further calculation usually allow you to specify the data type and scaling of the accumulator. Most such blocks cast to the accumulator data type prior to summation:

See the reference page of a specific block in the Block Reference for details on the accumulator data type of a specific block.

Use the Accumulator—Mode parameter to specify how you would like to designate the accumulator word and fraction lengths:

When you select Inherit via internal rule, the accumulator output word and fraction lengths are automatically calculated for you. Refer to Inherit via Internal Rule for more information.
When you select Same as product output, these characteristics match those of the product output.
When you select Same as input, these characteristics match those of the first input to the block.
When you select Binary point scaling, you are able to enter the word length and the fraction length of the accumulator, in bits.
When you select Slope and bias scaling, you are able to enter the word length, in bits, and the slope of the accumulator. The bias of all signals in Signal Processing Blockset software is zero.

Rounding

The block uses the Rounding method when the result of a fixed-point calculation does not map exactly to a number representable by the data type and scaling storing the result. For more information, see Rounding Modes in the Signal Processing Blockset User's Guide or Rounding Mode: Simplest in the Simulink Fixed Point documentation.

Overflow

Specify the method of storing the result when the magnitude of a fixed-point calculation result that does not does not fit within the range of the data type selected. You can select either Wrap or Saturate for this parameter.

For more information refer to Overflow in the Precision and Range subsection of the Signal Processing Blockset Getting Started Guide.

Mapping input