What factors contribute to the randomness in Channels generated by Ray Tracing?

I'm reading example CDL Channel Model Customization with Ray Tracing and have some questions.

When I changed the random stream to

channel.RandomStream = 'Global stream';

(instead of 'mt19937ar with seed' as Default), I got the different channel after each run.

My question is: What factors can contribute to this randomness?

As I know, the locations of the BS and UE are the kept the same, the rays are the same, AoAs, AoDs,... so this makes me wondering. (And when I check the code, pathFilters are the same, but pathGains is different in each run)

Thank you ^^

Answer 1

[Divyanshu]

Hello @Thien Hieu,

When the 'RandomStream' property of channel is set to 'Global stream' it uses current global random number stream for random number generation.

I think your query is what is triggering the randomness for this property. The answer is that this randomness is not sourced or impacted from any other properties of the channel, instead this randomStream is used to initialize the ray phases and coupling by choosing random number from uniformly distributed numbers.

You can refer RandomStream for more details and RayCoupling for understanding the impact of RandomStream.

Hope it helps!

[Thien Hieu]

Hi Divyanshu,

Thank you, that helps me a lot.

So I can go to nrCDLChannel and check what properties are Random (by Default) (like RayCoupling you mentioned, InitialPhases), then they are the factors that contribute to the randomness? and the others are deterministic? This can also be applied when I read other codes (not just nrCDLChannel) right?

Thank you so much for your answer.

[Divyanshu]

Yes that is the correct understanding and for other codes as well if you will refer the corresponding official documentation it would clearly specify what are default choices for each argument.

[Thien Hieu]

Thank you so much ^^ wish you all the bests