Channel values can be sent directly in Mobile SDK call without setting up a Processing Rule.
It can be added in the java code of App.
Steps are as follows:
1. Create a context data variable
2. Set the channel variable as "&&channel" within the context data variable
3. Pass the context data variable in trackState or trackAction call of Analytics.
Sample code snippet:
HashMap<String,Object> cdata=new HashMap<String,Object>();