LTE CRC Decoder

Detect errors in input samples using checksum

Libraries:
Wireless HDL Toolbox / Error Detection and Correction

Description

The LTE CRC Decoder block calculates a cyclic redundancy check (CRC) and compares it with the appended checksum, for each frame of streaming data samples. You can select from the polynomials specified by LTE standard TS 36.212 [1]. The block provides a hardware-optimized architecture and interface.

This block uses a streaming sample interface with a bus for related control signals. This interface enables the block to operate independently of frame size, and to connect easily with other Wireless HDL Toolbox™ blocks. The block accepts and returns a value representing a single sample, and a bus containing three control signals. These signals indicate the validity of each sample and the boundaries of the frame. To convert a matrix into a sample stream and these control signals, use the Frame To Samples block or the whdlFramesToSamples function. For a full description of the interface, see Streaming Sample Interface.

Examples

Check for CRC Errors in Streaming Samples

Use LTE CRC Decoder block to check encoded data, and how to compare hardware-friendly design with results from LTE Toolbox™.

Open Script

Ports

Input

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data — Input sample
binary scalar | unsigned integer scalar | binary vector

Input sample, specified as a binary scalar, unsigned integer scalar, or binary vector. The vector size must be less than or equal to the length of the polynomial. The CRC length also must be divisible by the vector size. For example, for polynomial type CRC24A, the valid vector sizes are 24, 12, 8, 6, 4, 3, 2, and 1. An integer input is interpreted as a binary word. For example, vector input [0 0 0 1 0 0 1 1] is equivalent to uint8 input 19.

double and single are supported for simulation but not for HDL code generation.

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

Output

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data — Output sample
binary scalar | integer scalar | binary vector

Output sample, returned a binary scalar, unsigned integer scalar, or binary vector of the same data type and size as the input samples. The checksum is removed from the end of the frame.

double and single binary values are supported for simulation but not for HDL code generation.

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

err — Indicator of checksum mismatch
binary scalar | integer scalar

Indicator of checksum mismatch, returned as a binary scalar or an integer scalar. If you select Full checksum mismatch, this port returns the integer XOR result of the calculated checksum against the appended checksum. The err value is valid when ctrl.end is 1 (true). The data type of this port matches the data type of the input samples.

Parameters

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CRC Type — Encode polynomial
`CRC16` (default) | `CRC8` | `CRC24A` | `CRC24B`

The encode polynomial options are the four CRC types described in the LTE standard TS 36.212 [1], Section 5.1.1.

Full checksum mismatch — Return bit-by-bit mismatch information
off (default) | on

When this parameter is not selected, the err port returns a Boolean value indicating whether any checksum bits are mismatched, after applying CRC Mask. When this parameter is selected, the err port returns an integer that represents the locations of bit mismatches in the checksum.

CRC Mask — Mask applied to checksum
0 (default) | integer from 0 to 2^CRCLength – 1

Mask applied to checksum, specified as an integer representing a binary word from 0 to 2^CRCLength – 1. This mask is typically a Radio Network Temporary Identifier (RNTI).

Dependencies

This parameter appears when Full checksum mismatch is cleared.

Algorithms

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When you use vector or integer input, the block implements a parallel CRC algorithm [2]. The implementation is the same as the algorithm used by the Communications Toolbox™ blocks General CRC Generator HDL Optimized and General CRC Syndrome Detector HDL Optimized.

To provide high throughput for modern communications systems, the block implements the CRC algorithm with a parallel architecture. This architecture recursively calculates M bits of a CRC checksum for each W input bits. At the end of the frame, the final checksum result is appended to the message. For a polynomial length of M, the recursive checksum calculation for W bits in parallel is

$X^{'} = F_{W} (\times) X (+) D .$

F_W is an M-by-M matrix that selects elements of the current state for the polynomial calculation with the new input bits. D is an M-element vector that provides the new input bits, ordered in relation to the generator polynomial and padded with zeros. The block implements the (×) with logical AND and (+) with logical XOR.

Architecture diagram of the CRC algorithm.

Latency

This waveform shows a 40-sample frame, input two samples at a time, encoded with a CRC16 polynomial. There is no gap between input frames. The output stream has removed the checksum, so there are eight cycles between output frames. The latency of the decoder is 3*CRCLength/InputSize + 5, assuming contiguous valid input samples.

Performance

These resource and performance data are the synthesis results from the generated HDL targeted to an AMD^® Zynq^®-7000 ZC706 board. The implementation is for a CRC24 polynomial, with no CRC Mask or output checksum mismatch, and scalar input. The design achieves 526.31 MHz clock frequency.

Resource	Uses
LUT	210
LUTRAM	8
FFS	305
Block RAM (16K)	0

A larger input vector size increases throughput and increases resource use.

References

[1] 3GPP TS 36.212. "Multiplexing and channel coding." 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA). URL: https://www.3gpp.org.

[2] Campobello, Giuseppe, Giuseppe Patane, and Marco Russo. "Parallel CRC Realization." IEEE Transactions on Computers. Vol. 52, No. 10, October 2003, pp. 1312–1319.

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).

Version History

Introduced in R2017b

LTE CRC Decoder

Description

Examples

Check for CRC Errors in Streaming Samples