What are the factors influencing Error Vector Magnitude (EVM)?

[Gsudha]

TL;DR Summary

I am studying the influence of different user position in the multi-user communication system. In some cases, when inter-user interference is lower, still I see higher EVM. How to understand the factors that could contribute to the EVM?

Error Vector Magnitude is widely used in the telecommunication industry to assess the performance of the users. In the given formula, S_r(n) is the received symbol and S_t(n) is the ideal symbol. N is the total number of symbols received. I have a Multi-User MIMO system simulation where there are 2 users served by a base station. The base station consists of 64 transmit elements and the users are equipped with linear antenna array consisting of 3 elements. The channel that I use is One-Ring channel model which is NLOS model rich in multipath with scatterers. At the receiver, thermal noise is added. I am evaluating the performance of users with EVM metric when users are at different positions. In some cases, I find that even if the interference between the users are less, EVM would be more. In such cases, what could be the other factors that could contribute to higher EVM? Is it correct to relate the inter-user interference alone to the EVM?

 

[marcusl]

Degradation in EVM can be caused by nonlinearities in your transmitter (driving the power amplifier into saturation, e.g.) or receiver (overdriving), but I'm guessing these are not a problem in your simulation. Multipath will cause an increase in EVM if the path delays are comparable to or longer than a symbol. In the latter case, the received symbol is contaminated by the presence of a previous symbol that is arriving at the same time.