LTE Symbol Demodulator

Demodulate complex LTE data symbols to data bits or LLR values

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Libraries:
Wireless HDL Toolbox / Modulation

Description

The LTE Symbol Demodulator block demodulates complex data symbols to data bits or log likelihood ratios (LLR) values based on the modulation types supported by LTE standard TS 36.211 [1]. The block provides an architecture suitable for HDL code generation and hardware deployment. You can use this block in the development of an LTE receiver.

The block accepts data symbols, along with a valid signal, and outputs demodulated bits or LLR values with valid and ready signals. The number of demodulated bits or LLR values for a given symbol depends on the modulation type, as shown in this table.

Modulation Type	Number of Bits per Symbol (NBPS)
BPSK	1
QPSK	2
16-QAM	4
64-QAM	6
256-QAM	8

The ready output port indicates when the block can accept an input data sample. You can use ready output port to control the upstream data coming to the block.

Examples

LTE Symbol Demodulation of Complex Data Symbols

Use LTE Symbol Demodulator block to demodulate complex LTE data symbols to data bits or LLR values.

• Open Script

Ports

Input

data — Input data symbols

complex scalar

Input data symbols, specified as a complex scalar. The block performs demodulation assuming the input constellation power normalization is in accordance with LTE standard TS 36.211, Section 7.1 [1]. The normalization values are based on the modulation type.

• 1/√2 for BPSK and QPSK

• 1/√10 for 16-QAM

• 1/√42 for 64-QAM

• 1/√170 for 256-QAM

Example: For BPSK modulation, the input values can be [0.707 +0.707i; -0.707 -0.707i]

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 | signed fixed point
Complex Number Support: Yes

valid — Valid input data indication

scalar

Control signal that indicates if the input data is valid. When this value is 1 (true), the block accepts the values on the data input port. When this value is 0 (false), the block ignores the values on the data input port.

Data Types: Boolean

modSel — Modulation selection

integer from 0 to 4

Select the modulation type by specifying its corresponding value shown in this table. Valid modSel values are from 0 to 4. Each value represents a specific modulation type, as shown in this table.

Value	Modulation Type
0	BPSK
1	QPSK
2	16-QAM
3	64-QAM
4	256-QAM

If you specify a value other than one 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. double and single data types are supported for simulation but not for HDL code generation.

Dependencies

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

Data Types: single | double | signed fixed point

Output

data — Output demodulated data bits or LLR values

scalar

Output demodulated data bits or LLR values, returned as a scalar.

• When you set the Decision type parameter to Soft, the block outputs demodulated LLR values. A positive LLR output value is considered as 1 and a negative LLR output value is considered as 0. The magnitude of the output gives a piecewise linear approximation to the LLR of the demodulated bits. The algorithm used for the LLR approximation is described in [1]. The returned LLR values for the input signal located on these constellation points lie within these magnitudes.

  • 1 for BPSK

  • 1/√2 for QPSK

  • [1 3]/√10 for 16-QAM

  • [1 3 5 7]/√42 for 64-QAM

  • [1 3 5 7 9 11 13 15]/√170 for 256-QAM

  The output word length increases by 2 bits for inputs with data type signed fixed point. For input with data types double or single, the output data type is the same as the input data type.

• When you set the Decision type parameter to Hard, the block results in the output containing the bit sequences corresponding to the closest constellation points to the input. The data type of this output is Boolean.

Data Types: single | double | signed fixed point | Boolean

valid — Valid output data indication

scalar

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

Data Types: Boolean

ready — Block ready indicator

scalar

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

The ready signal remains 0 (false) until the block outputs data of the corresponding input data symbol. The number of clock cycles the ready signal remains 0 (false) depends on the selected modulation type. If the selected modulation type is 16-QAM, the ready signal remains 0 (false) for 3 clock cycles, calculated as NBPS – 1 and then it changes to 1 (true) indicating that the block is ready to accept data in the next time step.

Data Types: Boolean

Parameters

Modulation source — Source for modulation type

Property (default) | Input port

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

Modulation — Modulation type

BPSK (default) | QPSK | 16-QAM | 64-QAM | 256-QAM

Select the modulation type.

Dependencies

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

Decision type — Type of demapping

Soft (default) | Hard

Select the demapping type.

• Soft — 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.

Rounding Method — Rounding mode for internal fixed-point calculations

Floor (default) | Ceiling | Convergent | Nearest | Round | Zero

This parameter specifies the type of rounding mode for internal fixed-point calculations. For more information about rounding modes, see Rounding Modes. This parameter does not apply when the input is of data type double or single.

Algorithms

The block outputs data in the form of bits or LLR values based on the demapping type you specify for the Decision type parameter: Hard or Soft respectively. For this demapping, the block implements simplified approximate LLR algorithm [2].

Latency

The block captures output bits at valid cycles. The latency of the block is seven clock cycles.

This figure shows a Logic Analyzer waveform of the sample output and latency of the block when you set the Modulation parameter to BPSK and the Decision type parameter to Soft.

This figure shows a Logic Analyzer waveform of the sample output and latency of the block when you specify the modSel values as 0 (BPSK), 1 (QPSK), 2 (16-QAM), 3 (64-QAM), and 4 (256-QAM) and set the Decision type parameter to Hard.

Performance

This table shows the resource and performance data synthesis results of the block for soft-decision and hard-decision demapping types when you provide an input data type of fixdt(1,16,14). The modulation type is applied using the modSel input port. The generated HDL is targeted to an AMD^® Zynq^®- 7000 ZC706 evaluation board.

The design achieves a clock frequency of 475.9 MHz for soft-decision and 454.7 MHz for hard-decision.

Resource Utilization	Soft Decision	Hard Decision
Slice LUTs	234	188
Slice Registers	276	225
DSP	1	0

References

[1] 3GPP TS 36.211. "Physical channels and modulation." 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA). URL: https://www.3gpp.org.

[2] F. Tosato and P. Bisaglia. "Simplified soft-output de-mapper for binary interleaved coded OFDM with application to HIPERLAN/2." ICC 2002, Vol. 2, pp. 664–668.

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.

This block does not have any HDL Block Properties.

Version History

Introduced in R2019b