openairinterface5g/openair1/PHY/CODING/DOC/LDPCImplementation.md

LDPC coding implementation

The LDPC encoder and decoder are implemented in a shared library, dynamically loaded at run-time using the oai shared library loader. Two types of library are available with two different interfaces. There are libraries implementing the encoder and decoder of slots and libraries implementing the encoder and decoder of code segments.

LDPC slot coding

The interface of the library is defined in nrLDPC_coding_interface.h. The code loading the LDPC library is in nrLDPC_coding_interface_load.c, in function load_nrLDPC_coding_interface, which must be called at init time.

Selecting the LDPC library at run time

By default the function int load_nrLDPC_coding_interface(void) looks for libldpc.so.
This default behavior can be changed using the oai loader configuration options in the configuration file or from the command line as shown below:

Examples of ldpc shared lib selection when running nr softmodem's:

loading default libldpc.so:

./nr-softmodem -O libconfig:gnb.band78.tm1.106PRB.usrpx300.conf:dbgl5
.......................
[CONFIG] loader.ldpc.shlibversion set to default value ""
[LIBCONFIG] loader.ldpc: 2/2 parameters successfully set, (2 to default value)
shlib_path libldpc.so
[LOADER] library libldpc.so successfully loaded
........................

libldpc.so has its decoder implemented in nrLDPC_coding_segment_decoder.c.
Its encoder is implemented in nrLDPC_coding_segment_encoder.c.

loading libldpc_t2.so instead of libldpc.so:

make ldpc_t2

This command creates the libldpc_t2.so shared library.

Building C object CMakeFiles/ldpc_t2.dir/openair1/PHY/CODING/nrLDPC_coding/nrLDPC_coding_t2/nrLDPC_coding_t2.c.o
Linking C shared module libldpc_t2.so

At runtime, to successfully use LDPC accelerators (e.g., Xilinx T2/Intel ACCs), you will need to install the corresponding drivers and tools. Please refer to the dedicated documentation at LDPC_T2_OFFLOAD_SETUP.md.

./nr-softmodem -O libconfig:gnb.band78.sa.fr1.106PRB.usrpb210.conf:dbgl5 --rfsim --rfsimulator.serveraddr server --log_config.gtpu_log_level info --loader.ldpc.shlibversion _t2 --nrLDPC_coding_t2.dpdk_dev 01:00.0 --nrLDPC_coding_t2.dpdk_core_list 0-1

.......................
[CONFIG] loader.ldpc.shlibversion set to default value ""
[LIBCONFIG] loader.ldpc: 2/2 parameters successfully set, (1 to default value)
[CONFIG] shlibversion set to  _t2 from command line
[CONFIG] loader.ldpc 1 options set from command line
shlib_path libldpc_t2.so
[LOADER] library libldpc_t2.so successfully loaded
........................

libldpc_t2.so has its decoder and its encoder implemented in nrLDPC_coding_t2.c.

loading libldpc_xdma.so instead of libldpc.so:

make ldpc_xdma or ninja ldpc_xdma

This command creates the libldpc_xdma.so shared library.

ninja ldpc_xdma
[2/2] Linking C shared module libldpc_xdma.so

At runtime, to successfully use the xdma, you need to install vendor specific drivers and tools.
Please refer to the dedicated documentation at LDPC_XDMA_OFFLOAD_SETUP.md.

./nr-softmodem -O libconfig:gnb.band78.sa.fr1.106PRB.usrpb210.conf:dbgl5 --rfsim --rfsimulator.serveraddr server --log_config.gtpu_log_level info --loader.ldpc.shlibversion _xdma --nrLDPC_coding_xdma.num_threads_prepare 2

.......................
[CONFIG] loader.ldpc.shlibversion set to default value ""
[LIBCONFIG] loader.ldpc: 2/2 parameters successfully set, (1 to default value)
[CONFIG] shlibversion set to  _xdma from command line
[CONFIG] loader.ldpc 1 options set from command line
shlib_path libldpc_xdma.so
[LOADER] library libldpc_xdma.so successfully loaded
........................

libldpc_xdma.so has its decoder implemented in nrLDPC_coding_xdma.c.
Its encoder is implemented in nrLDPC_coding_segment_encoder.c.

Note: libldpc_xdma.so relies on a segment coding library for encoding. The segment coding library is libldpc.so by default but it can be chosen with option --nrLDPC_coding_xdma.encoder_shlibversion followed by the library version - like with --loder.ldpc.shlibversion in the segment coding case above -

Examples of ldpc shared lib selection when running ldpctest:

Slot coding libraries cannot be used yet within ldpctest.

But they can be used within nr_ulsim, nr_dlsim, nr_ulschsim and nr_dlschsim.
In these PHY simulators, using the slot coding libraries is enabled in the exact same way as in nr-softmodem.

LDPC libraries

Libraries implementing the slotwise LDPC coding must be named libldpc<_version>.so. They must implement four functions: nrLDPC_coding_init, nrLDPC_coding_shutdown, nrLDPC_coding_decoder and nrLDPC_coding_encoder. The prototypes for these functions is defined in nrLDPC_coding_interface.h.

libldpc.so is completed.

libldpc_t2.so is completed.

libldpc_xdma.so is completed.

LDPC segment coding

The interface of the library is defined in nrLDPC_defs.h as typedefs of the functions of the interface. The name of the functions implementing these typedefs can be found in nrLDPC_extern.h.

LDPC segment coding libraries are not loaded directly by OAI but are statically linked in libraries implementing the LDPC slot coding interface using an adaptation layer between the slot coding interface and the segment coding interface.
This way, these libraries can be loaded to implement the slot coding interface as well as the segment coding interface in ldpctest.
ldpctest therefore loads directly the segment coding interface with the loader implemented in nrLDPC_load.c as function load_nrLDPClib.

Selecting the LDPC library at run time

By default the function int load_nrLDPClib(void) looks for libldpc.so, this default behavior can be changed using the oai loader configuration options in the configuration file or from the command line as shown below:

Examples of ldpc shared lib selection when running nr softmodem's:

loading libldpc_orig.so instead of libldpc.so:

./nr-softmodem -O libconfig:gnb.band78.tm1.106PRB.usrpx300.conf:dbgl5  --loader.ldpc.shlibversion _orig
.......................
[CONFIG] loader.ldpc.shlibversion set to default value ""
[LIBCONFIG] loader.ldpc: 2/2 parameters successfully set, (1 to default value)
[CONFIG] shlibversion set to  _orig from command line
[CONFIG] loader.ldpc 1 options set from command line
[LOADER] library libldpc_orig.so successfully loaded
........................

loading libldpc_cl.so instead of libldpc.so:

make ldpc_cl

This command creates the libldpc_cl.so shared library. To perform this build successfully, only the OpenCL header /usr/include/CL/opencl.h and library /usr/lib/x86_64-linux-gnu/libOpenCL.so are required, they implement OpenCL API support which is not hardware dependent.

Scanning dependencies of target nrLDPC_decoder_kernels_CL
Built target nrLDPC_decoder_kernels_CL
Scanning dependencies of target ldpc_cl
Building C object CMakeFiles/ldpc_cl.dir/usr/local/oai/oai-develop/openairinterface5g/openair1/PHY/CODING/nrLDPC_decoder/nrLDPC_decoder_CL.c.o
In file included from /usr/include/CL/cl.h:32,
                 from /usr/include/CL/opencl.h:38,
                 from /usr/local/oai/oai-develop/openairinterface5g/openair1/PHY/CODING/nrLDPC_decoder/nrLDPC_decoder_CL.c:49:
/usr/include/CL/cl_version.h:34:9: note: #pragma message: cl_version.h: CL_TARGET_OPENCL_VERSION is not defined. Defaulting to 220 (OpenCL 2.2)
 #pragma message("cl_version.h: CL_TARGET_OPENCL_VERSION is not defined. Defaulting to 220 (OpenCL 2.2)")
         ^~~~~~~

Building C object CMakeFiles/ldpc_cl.dir/usr/local/oai/oai-develop/openairinterface5g/openair1/PHY/CODING/nrLDPC_encoder/ldpc_encoder_optim8segmulti.c.o
Linking C shared module libldpc_cl.so
Built target ldpc_cl

At runtime, to successfully use hardware acceleration via OpenCL, you need to install vendor specific packages which deliver the required drivers and tools to make use of their GPU (Nvidia, Intel...) , fpga (Xilinx, Intel) or CPU (Intel, AMD, ARM...) through OpenCL.

./nr-softmodem -O libconfig:gnb.band78.sa.fr1.106PRB.usrpb210.conf:dbgl5 --rfsim --rfsimulator.serveraddr server --log_config.gtpu_log_level info --loader.ldpc.shlibversion _cl

------------------------------------------------
[LOADER] library libldpc_cl.so successfully loaded
[HW]   Platform 0, OpenCL profile FULL_PROFILE
[HW]   Platform 0, OpenCL version OpenCL 2.1 LINUX
[HW]   Device 0 is  available
[HW]   Device 0, type 2 = 0x00000002: cpu 
[HW]   Device 0, number of Compute Units: 8
[HW]   Device 0, max Work Items dimension: 3
[HW]   Device 0, max Work Items size for dimension: 0 8192
[HW]   Device 0, max Work Items size for dimension: 1 8192
[HW]   Device 0, max Work Items size for dimension: 2 8192
[New Thread 0x7fffcc258700 (LWP 3945123)]
[New Thread 0x7fffc3e57700 (LWP 3945124)]
[New Thread 0x7fffcbe57700 (LWP 3945125)]
[New Thread 0x7fffcba56700 (LWP 3945126)]
[New Thread 0x7fffcb254700 (LWP 3945128)]
[New Thread 0x7fffcb655700 (LWP 3945127)]
[New Thread 0x7fffcae53700 (LWP 3945129)]
[HW]   Platform 1, OpenCL profile FULL_PROFILE
[HW]   Platform 1, OpenCL version OpenCL 2.0 beignet 1.3
[New Thread 0x7fffc965a700 (LWP 3945130)]
[Thread 0x7fffc965a700 (LWP 3945130) exited]
[HW]   Device 0 is  available
[HW]   Device 0, type 4 = 0x00000004: gpu 
[HW]   Device 0, number of Compute Units: 20
[HW]   Device 0, max Work Items dimension: 3
[HW]   Device 0, max Work Items size for dimension: 0 512
[HW]   Device 0, max Work Items size for dimension: 1 512
[HW]   Device 0, max Work Items size for dimension: 2 512
-----------------------------------------------------------------

./nr-uesoftmodem -r 106 --numerology 1 --band 78 -C 3619200000 --rfsim -O libconfig:/usr/local/oai/conf/nrue_sim.conf:dbgl5 --loader.ldpc.shlibversion _cl --log_config.hw_log_level info

............................................................
[CONFIG] segment_shlibversion set to  _cl from command line
[CONFIG] loader.ldpc 1 options set from command line
[LOADER] library libldpc_cl.so successfully loaded
[HW]   Platform 0, OpenCL profile FULL_PROFILE
[HW]   Platform 0, OpenCL version OpenCL 2.1 LINUX
[HW]   Device 0 is  available
[HW]   Device 0, type 2 = 0x00000002: cpu 
[HW]   Device 0, number of Compute Units: 8
[HW]   Device 0, max Work Items dimension: 3
[HW]   Device 0, max Work Items size for dimension: 0 8192
[HW]   Device 0, max Work Items size for dimension: 1 8192
[HW]   Device 0, max Work Items size for dimension: 2 8192
[New Thread 0x7fffecccc700 (LWP 3945413)]
[New Thread 0x7fffec8cb700 (LWP 3945415)]
[New Thread 0x7fffec4ca700 (LWP 3945414)]
[New Thread 0x7fffdf7fd700 (LWP 3945417)]
[New Thread 0x7fffdfbfe700 (LWP 3945418)]
[New Thread 0x7fffdffff700 (LWP 3945416)]
[New Thread 0x7fffd73fc700 (LWP 3945419)]
[HW]   Platform 1, OpenCL profile FULL_PROFILE
[HW]   Platform 1, OpenCL version OpenCL 2.0 beignet 1.3
[New Thread 0x7fffde105700 (LWP 3945420)]
[Thread 0x7fffde105700 (LWP 3945420) exited]
[HW]   Device 0 is  available
[HW]   Device 0, type 4 = 0x00000004: gpu 
[HW]   Device 0, number of Compute Units: 20
[HW]   Device 0, max Work Items dimension: 3
[HW]   Device 0, max Work Items size for dimension: 0 512
[HW]   Device 0, max Work Items size for dimension: 1 512
[HW]   Device 0, max Work Items size for dimension: 2 512 
------------------------------------------------------------

A mechanism to select ldpc implementation is also available in the ldpctest phy simulator via the -v option, which can be used to specify the version of the ldpc shared library to be used.

Examples of ldpc shared lib selection when running ldpctest:

Loading libldpc_cuda.so, the cuda implementation of the ldpc decoder:

$ ./ldpctest -v _cuda
ldpctest -v _cuda
Initializing random number generator, seed 0
block length 8448: 
n_trials 1: 
SNR0 -2.000000: 
[CONFIG] get parameters from cmdline , debug flags: 0x00400000
[CONFIG] log_config: 2/3 parameters successfully set 
[CONFIG] log_config: 53/53 parameters successfully set 
[CONFIG] log_config: 53/53 parameters successfully set 
[CONFIG] log_config: 16/16 parameters successfully set 
[CONFIG] log_config: 16/16 parameters successfully set 
log init done
[CONFIG] loader: 2/2 parameters successfully set 
[CONFIG] loader.ldpc: 2/2 parameters successfully set 
[LOADER] library libldpc_cuda.so successfully loaded
...................................

Loading libldpc_cl.so, the opencl implementation of the ldpc decoder:

make ldpc_cl

$ ./ldpctest -v _cl
Initializing random number generator, seed 0
block length 8448: 
n_trials 1: 
SNR0 -2.000000: 
[CONFIG] get parameters from cmdline , debug flags: 0x00400000
[CONFIG] log_config: 2/3 parameters successfully set 
[CONFIG] log_config: 53/53 parameters successfully set 
[CONFIG] log_config: 53/53 parameters successfully set 
[CONFIG] log_config: 16/16 parameters successfully set 
[CONFIG] log_config: 16/16 parameters successfully set 
log init done
[CONFIG] loader: 2/2 parameters successfully set 
[CONFIG] loader.ldpc: 1/2 parameters successfully set 
[LOADER] library libldpc_cl.so successfully loaded
[HW]   Platform 0, OpenCL profile FULL_PROFILE
[HW]   Platform 0, OpenCL version OpenCL 2.1 LINUX
[HW]   Device 0 is  available
[HW]   Device 0, type 2 = 0x00000002: cpu 
[HW]   Device 0, number of Compute Units: 8
[HW]   Device 0, max Work Items dimension: 3
[HW]   Device 0, max Work Items size for dimension: 0 8192
[HW]   Device 0, max Work Items size for dimension: 1 8192
[HW]   Device 0, max Work Items size for dimension: 2 8192
[HW]   Platform 1, OpenCL profile FULL_PROFILE
[HW]   Platform 1, OpenCL version OpenCL 2.0 beignet 1.3
[HW]   Device 0 is  available
[HW]   Device 0, type 4 = 0x00000004: gpu 
[HW]   Device 0, number of Compute Units: 20
[HW]   Device 0, max Work Items dimension: 3
[HW]   Device 0, max Work Items size for dimension: 0 512
[HW]   Device 0, max Work Items size for dimension: 1 512
[HW]   Device 0, max Work Items size for dimension: 2 512
................................

LDPC libraries

The prototypes for the functions of the interface are defined in nrLDPC_defs.h as typedefs. Libraries implementing the LDPC algorithms must be named libldpc<_version>.so, they must implement four functions with the names and types:

• LDPCinit implementing type LDPC_initfunc_t *
• LDPCshutdown implementing type LDPC_shutdownfunc_t *
• LDPCdecoder implementing type LDPC_decoderfunc_t *
• LDPCencoder implementing type LDPC_encoderfunc_t *

libldpc_cuda.so has been tested with the ldpctest executable, usage from the softmodem's has to be tested.

libldpc_cl.so is under development.

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