First, create a new 5G network in NetSim and design the network topology by adding gNBs, UES, Core devices and data networks required for the simulation.

Then, configure the 5G HARQ soft combining algorithm by selecting the appropriate parameters such as the (i) HARQ Process Count, (ii) CBG per TB, (iii)HARQ retry limit, (iv) modulation and coding scheme (MCS).

Then generate traffic that is transmitted over the 5G network. You can use NetSim's traffic generator to create traffic based on various traffic models.

And finally, Run the simulation and observe the results. NetSim provides various logs that can be used for in-depth analysis

5G HARQ Theory very briefly -

• Hybrid automatic repeat request (HARQ) is a combination of retransmissions and error correction. The HARQ protocol runs in the MAC and PHY layers.
• In the 5G PHY, a code block group (CBG) is transmitted over the air by the transmitter to the receiver. If the CBG is successfully received the receiver sends back an ACK, else if the CBG is received in error the receiver sends back a NACK (negative ACK).
• If the transmitter receives an ACK, it sends the next CBG. However, if the transmitter receives a NACK, it retransmits the previously transmitted CBG.
• In 5G, the incorrectly received CBG is not discarded but stored at the receiver. When the re-transmitted CBG is received, the two CBGs are combined. This is Hybrid ARQ with soft combining.

HARQ Logs

• By enabling the Code Block Log under logs in the NetSim GUI you can record low level data to analyze 5G HARQ.
• A detailed explanation of HARQ is given in section 3.9.12 of NetSim 5G Manual which can be downloaded from https://tetcos.com/downloads/v13.3/5G-NR.pdf

The best way to accurately simulate 5G HARQ soft combining operations is by using simulation software specifically designed for this purpose. There are a number of commercial and open source options available, such as OPNET Modeler, Network Simulator, and NS-3. These tools provide powerful and realistic models for simulating 5G HARQ soft combining operations. Additionally, if you have access to 5G hardware or an emulator, you can also use these to run simulations and compare the results to those generated by the software.

Thanks for the responses. I would like to know how to correct the way to set CBG errors to induce HARQ retransmissions. And how is this related to BLER?

The primary way to set CBG errors to induce HARQ retransmissions is to set the Block Error Rate (BLER) threshold target lower. Lower BLER targets will result in more retransmissions due to failing to meet the BLER threshold. The BLER is a measure of the reliability of a link, and is a ratio of the number of erroneous blocks to the total number of blocks sent over the link. A lower BLER threshold will cause the system to retransmit more frequently, hence resulting in more HARQ retransmissions.

Checkerboard error injection is used to induce HARQ retransmissions. This means injecting errors in the form of checkerboard patterns into the transmitted data, to force the HARQ receiver to request retransmissions of some of the data. This helps determine the effectiveness of the HARQ soft combining operation as well as the overall performance of the system. The BLER (Block Error Rate) is then used to measure the performance of a particular HARQ scheme, as it indicates the percentage of data blocks received where at least one bit was wrong. Thus, injecting errors in the form of checkerboard patterns can be used to modify the BLER and evaluate the performance of the system.

Waleed Algriree Is the BLER threshold computed on the init BLER or on the residual BLER?

Block Error Rate threshold in the context of Hybrid Automatic Repeat Request computed and compared to the residual BLER, not the initial BLER.

Initial BLER: This is the BLER observed after the first transmission of a data block, before any retransmissions.

Residual BLER: This is the BLER observed after one or more retransmissions of a data block. It represents the error rate after combining information from multiple transmissions,

also

the residual BLER is compared to the BLER threshold. If the residual BLER is above the threshold, the system may decide to perform another retransmission. This process can continue for a specified number of retransmissions or until the BLER falls below the threshold, indicating successful reception.

That is not correct. The outer loop link adaptation (OLLA) comparisons are based on init BLER and not on residual BLER.