Android, Xamarin and app sleep?

Question

Android

Hello!
I'm writing my first android app using xamarin and I've run into a problem that's stumping me. In general terms, the problem is as follows, architecturally, the application contains a service that is designed to periodically request some information from the server. But if the application is minimized and the phone screen is turned off, requests to the server stop coming. If I turn on the screen or just put the phone on charge, sending requests resumes. I suspect that the matter is in the power consumption policy, and perhaps the problem can be solved with additional PowerManager control, or perhaps when the screen is turned off, gprs also turns off and you need to turn it on yourself, or perhaps you can get by with connecting some manifest ...
Tell me please, what could be the problem, I will be grateful for any thoughts on the topic :)
Ps Tested on android version 2.3.5 and 4.2.2.