DVB-S2 Symbol Demodulator

Demodulate complex constellation symbol to set of LLR values or data bits according to DVB-S2 standard

Since R2021b

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Libraries:
Wireless HDL Toolbox / Modulation

Description

The DVB-S2 Symbol Demodulator block demodulates complex data symbol to log-likelihood ratio (LLR) values or data bits based on the modulation types supported by the Digital Video Broadcast Satellite Second Generation (DVB-S2) standard [1]. The block accepts equalized complex data symbols and a samplecontrol bus or a valid signal. It outputs demodulated LLR values or data bits and a samplecontrol bus or a valid signal based on the selected output type. The block provides an option to select the output type as vector or scalar. The number of demodulated LLR values or data bits for a given symbol depends on the modulation type, as this table shows.

Modulation Type	Number of LLR Values or Data Bits Per Symbol
π/2-BPSK	1
QPSK	2
8-PSK	3
16-APSK	4
32-APSK	5

The block provides an architecture suitable for HDL code generation and hardware deployment. You can use this block in the development of a DVB-S2 receiver.

Examples

DVB-S2 Symbol Demodulation of Complex Data Symbols

Demodulate complex data symbols to LLRs or data bits.

Open Script

Ports

Input

data — Data symbols

real-valued scalar | complex-valued scalar

Data symbols, specified as a real- or complex-valued scalar.

The software supports double and single data types for simulation, but not for HDL code generation.

For HDL code generation, the input data type must be signed fixed point and the maximum input word length the block supports is 32 bits.

Data Types: single | double | int8 | int16 | int32 | signed fixed point
Complex Number Support: Yes

ctrl — Control signals accompanying sample stream

samplecontrol bus

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 samples.

• start — Indicates the start of the input frame

• end — Indicates the end of the input frame

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

For more details, see Sample Control Bus.

Data Types: bus

valid — Indication of whether input data is valid

scalar

Control signal that indicates whether the input data is valid. When this value is 1, the block accepts the values on the data input port. When this value is 0, the block ignores the values on the data input port.

Dependencies

To enable this port, set the Output type parameter to Scalar.

Data Types: Boolean

modIdx — Modulation index

0 | 1 | 2 | 3 | 4

Modulation index, specified as 0, 1, 2, 3, or 4. Each value represents a specific modulation type, as the table shows.

Modulation Index	Modulation Type
0	QPSK
1	8-PSK
2	16-APSK
3	32-APSK
4	π/2-BPSK

If you specify a value other than ones listed in this table, the block displays a warning message and applies QPSK modulation. For HDL code generation, specify this value in fixdt(0,3,0) format.

Dependencies

To enable this port, set the Modulation source parameter to Input port.

Data Types: single | double | fixdt(0,3,0)

codeRateIdx — Code rate index

5 | 6 | 7 | 8 | 9 | 10

Code rate index, specified as 5, 6, 7, 8, 9, or 10. Each value represents a specific code rate, as this table shows.

Code Rate Index	Code Rate
5	2/3
6	3/4
7	4/5
8	5/6
9	8/9
10	9/10

The code rates in this table apply to the modIdx input port values 2 and 3, which indicate 16-APSK and 32-APSK modulation, respectively. When you set the modIdx port value to 0, 1, or 4, the block ignores the codeRateIdx input port values.

Specify this value in fixdt(0,4,0) format.

Dependencies

To enable this port, set the Modulation source parameter to Input port.

Data Types: single | double | fixdt(0,4,0)

nVar — Noise variance

real-valued positive scalar

Noise variance, specified as a real-valued positive scalar.

This value must be of data type fixdt(0,k,m), where k is less than or equal to 16 and m is less than or equal to k.

When the Output type parameter is set to Scalar, the block samples the nVar port when the input valid is 1.

When the Output type parameter is set to Vector, the block samples the nVar port based on the samplecontrol bus.

The software supports double and single data types for simulation, but not for HDL code generation.

Dependencies

To enable this port, select the Enable noise variance input port parameter.

Data Types: single | double | uint8 | uint16 | unsigned fixed point

Output

data — Demodulated LLR values or data bits

scalar | eight-element real-valued column vector

Demodulated LLR values or data bits, returned as a scalar when the Output type parameter is set to Scalar and as an eight-element real-valued column vector when the Output type parameter is set to Vector.

• When the Decision type parameter is set to Approximate log-likelihood ratio:

  • For double and single inputs, the output data type is the same as the input data type.

  • For fixed point inputs, the block provides the output with an integer bit growth of 14 bits when you select the Enable noise variance input port parameter and with an integer bit growth of 3 bits when you clear the parameter.

• When the Decision type parameter is set to Hard, the output data type is Boolean for any supported input data type.

Data Types: single | double | int8 | int16 | int32 | Boolean | fixed point

ctrl — Control signals accompanying sample stream

samplecontrol bus

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 the start of the output frame

• end — Indicates the end of the output frame

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

For more details, see Sample Control Bus.

Data Types: bus

valid — Valid output data indication

0 | 1

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

Dependencies

To enable this port, set the Output type parameter to Scalar.

Data Types: Boolean

ready — Indicates block is ready

0 | 1

Control signal that indicates when the block is ready to accept new input data. When this value is 1, the block accepts input data in the next time step. When this value is 0, the block ignores the input data in the next time step.

The ready signal remains 0 until the block outputs data of the corresponding input data symbol. The number of clock cycles the ready signal remains 0 depends on the selected modulation type.

Dependencies

To enable this port, set the Output type parameter to Scalar.

Data Types: Boolean

Parameters

Modulation source — Source for modulation type

Input port (default) | Property

To specify the modulation type using the Modulation parameter, select Property. To specify the modulation type using the modIdx port during run time, select Input port.

Modulation — Modulation type

QPSK (default) | 8-PSK | 16-APSK | 32-APSK | pi/2-BPSK

Select the modulation type.

Dependencies

To enable this parameter, set the Modulation source parameter to Property.

Code rate — Code rate

3/4 (default) | 2/3 | 4/5 | 5/6 | 8/9 | 9/10

Select the code rate.

Dependencies

To enable this parameter set the Modulation source parameter to Property and the Modulation parameter to 16-APSK or 32-APSK.

Decision type — Type of demapping

Approximate log-likelihood ratio (default) | Hard

Select the demapping type.

• Approximate log-likelihood ratio — Demap data symbols to LLR values. This LLR value for each bit indicates how likely the bit is 1 or 0.

• Hard — Demap data symbols to bits 1 or 0.

Output type — Type of output

Vector (default) | Scalar

Select the type of output as Vector or Scalar.

• Vector — Use this option to receive data in 8-element column vector format from the output data port.

• Scalar — Use this option to receive data in scalar format from the output data port.

Unit average power — Unit average power

off (default) | on

Select this parameter to perform symbol demodulation with a normalized constellation. Clear this parameter to perform symbol demodulation using the constellation defined in the standard [1].

When you specify 0, 1, or 4 in the modIdx input port or set the Modulation parameter to QPSK, 8-PSK, or pi/2-BPSK, the block ignores this parameter during its operation.

Dependencies

To enable this parameter, set the Modulation source parameter to Input port or set the Modulation source to Property and the Modulation parameter to 16-APSK or 32-APSK.

Enable noise variance input port — Enable noise variance port

off (default) | on

Select this parameter to enable the noise variance input port.

Dependencies

To enable this parameter, set the Decision type parameter to Approximate log-likelihood ratio.

Algorithms

The block uses the soft-decision approximate LLR or hard-decision algorithms to demodulate complex data symbols according to the DVB-S2 standard.

In soft-decision approximate LLR, the block computes the approximate LLR by using the nearest constellation point to the received signal with a 0 (or 1) at that bit position. The LLR for a bit b can be defined as:

$$LLR(b)=\frac{1}{{\sigma }^2}\left(\underset{s\in S_1}{\min }|z-s{|}^2-\text{}\text{}\underset{s\in S_0}{\min }|z-s{|}^2\right)$$

where σ² is the noise variance, z is the received sequence, s is a symbol from the constellation, and S₀, S₁ is the set of symbols that corresponds to bits being 0 and 1 respectively. For more information, see [2].

In hard-decision algorithm, the block computes the magnitude and phase angle of the input data and outputs the data bits based on the decision boundaries. For more information, see [3].

Latency

The latency of the block varies based on the input data type, modulation type, decision type, and output type.

This figure shows a sample output and latency of the block for input data of type fixdt(1,16,14) when you set the Modulation source parameter to Property, the Modulation parameter to QPSK, the Decision type parameter to Approximate log-likelihood ratio, and the Output type parameter to Scalar, and select the Enable noise variance input port parameter. The latency of the block is 41 clock cycles.

This figure shows a sample output and latency of the block for input data of type fixdt(1,16,14) when you set the Modulation source parameter to Input port, the Decision type parameter to Hard, and the Output type parameter to Vector, and specify the modIdx input port value as 3 (32-APSK). The latency of the block is 59 clock cycles.

Performance

The performance of the synthesized HDL code varies with the target and synthesis options. The performance also varies based on the input data type and the selected modulation type, decision type, output type, and noise variance data type.

This table shows the resource and performance data synthesis results of the block for an input data of type fixdt(1,16,14) when you set the Modulation type parameter to Input port, the Decision type parameter to Approximate log-likelihood ratio, and the Output type parameter to Scalar, as well as select the Enable noise variance input port parameter and specify the nVar data type as fixdt(0,10,8). The generated HDL code is targeted to a Xilinx^® Zynq^®- 7000 ZC706 evaluation board. The design achieves a clock frequency of 253.49 MHz.

Slice LUTs	Slice Registers	DSPs	Block RAM
12214	12956	83	0

References

[1] ETSI Standard EN 302 307 V1.4.1: Digital Video Broadcasting (DVB); Second generation framing structure, channel coding and modulation systems for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications (DVB-S2), European Telecommunications Standards Institute, Valbonne, France, 2005-03.

[2] Viterbi, A.J. “An Intuitive Justification and a Simplified Implementation of the MAP Decoder for Convolutional Codes.” IEEE Journal on Selected Areas in Communications 16, no. 2 (February 1998): 260–64. https://doi.org/10.1109/49.661114.

[3] Sebesta, J. “Efficient Method for APSK Demodulation.” Selected Topics on Applied Mathematics, Circuits, Systems, and Signals (P. Pardalos, N. Mastorakis, V. Mladenov, and Z. Bojkovic, eds.). Vouliagmeni, Athens, Greece: WSEAS Press, 2009.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

This block supports C/C++ code generation for Simulink^® accelerator and rapid accelerator modes and for DPI component generation.

HDL Code Generation

Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

HDL Architecture

This block has one default HDL architecture.

HDL Block Properties

ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays within your design. Distributed pipelining does not redistribute these registers. The default is 0. For more details, see ConstrainedOutputPipeline (HDL Coder).
InputPipeline	Number of input pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is 0. For more details, see InputPipeline (HDL Coder).
OutputPipeline	Number of output pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is 0. For more details, see OutputPipeline (HDL Coder).

Restrictions

You cannot generate HDL for this block inside a Resettable Synchronous Subsystem (HDL Coder).

Version History

Introduced in R2021b

R2022a: Block enhancements

In 2021b, the block was named DVBS2 Symbol Demodulator, and now in R2022a it is renamed to DVB-S2 Symbol Demodulator.

In 2022a, the block supports demodulation of a complex constellation symbol to a set of data bits. Also, the block provides parameter options to select:

• Output type — Scalar or Vector

• Decision type — Hard or Approximate log-likelihood ratio

• Noise variance input port