Quadriga is an open-source channel simulator that is highly inspired by the 3GPP specifications: https://quadriga-channel-model.de

Agree with Emil , for reference you can also see the " signals and systems using MATLAB".you can get some idea.

1) 3GPP Channel Models:

MATLAB code (free license for academic use): https://www.nt.tuwien.ac.at/research/mobile-communications/vccs/vienna-5g-simulators/ (based on implementation in 5G Vienna Simulators)

References:

(a) 3GPP TR 36.873 - https://www.3gpp.org/ftp/Specs/archive/36_series/36.873

(b) 3GPP TR 38.900 - https://www.3gpp.org/ftp/Specs/archive/38_series/38.900

(c) 3GPP TR 38.901 - https://www.3gpp.org/ftp/Specs/archive/38_series/38.901

(2) NYUSIM

MATLAB code (open source): https://wireless.engineering.nyu.edu/nyusim-5g-and-6g/

References:

(a) M. K. Samimi and T. S. Rappaport, “3-D Millimeter-Wave Statistical Channel Model for 5G Wireless System Design", IEEE Transactions on Microwave Theory and Techniques, vol. 64, no. 7, pp. 2207-2225, July 2016.

(b) S. Sun, G. R. MacCartney, and T. S. Rappaport “A novel millimeter-wave channel simulator and applications for 5G wireless communications", 2017 IEEE International Conference on Communications (ICC), May 2017, pp. 1-7.

(3) QuaDRiGa

MATLAB code (open source): https://quadriga-channel-model.de/

QuaDRiGa MATLAB code is also integrated in the Vienna 5G System Level Simulator (https://www.nt.tuwien.ac.at/research/mobile-communications/vccs/vienna-5g-simulators/)

References:

(a) S. Jaeckel, L. Raschkowski, K. Brner, and L. Thiele, “QuaDRiGa: A 3-D Multi-Cell Channel Model With Time Evolution for Enabling Virtual Field Trials," IEEE Transactions on Antennas and Propagation, vol. 62, no. 6, pp. 3242-3256, 2014.

(b) S. Jaeckel, M. Peter, K. Sakaguchi, W. Keusgen, and J. Medbo, “5G Channel Models in mm-Wave Frequency Bands," in European Wireless 2016; 22nd European Wireless Conference, 2016, pp. 1-6.

(4) Other 5G channel model implementations:

(i) mmMAGIC, (ii) 5GCMSIG, (iii) METIS (iv) COST 2100, (v) MiWEBA, (vi) IMT-2020, etc.

Reference:

(a) C. Wang, J. Bian, J. Sun, W. Zhang, and M. Zhang, “A Survey of 5G Channel Measurements and Models," IEEE Communications Surveys Tutorials, vol. 20, no. 4, pp. 3142-3168, Fourthquarter 2018.

NetSim has some options as shown in https://tetcos.com/5g.html

You can look for the simulation codes at https://researcherstore.com/product-category/simulation-codes/ . Some interesting work has been shared in the similar domain.

NYUSIM: The open source 5G and 6G channel model simulator software

QuaDRiGa: The next generation radio channel model

Conventional channel models are still used such as Rice, Rayleigh, nakagami

Conventional channel models are still used such as Rice, Rayleigh, nakagami

There is a Git with Function coded from scratch, easy to understand

https://gitlab.com/daniel.riviello/3gpp-channel-model-tr-38901/-/blob/main/README.md