This is the way how to make IPC through public render parameter in Liferay DXP(Lfieray 7).

Key point:

     You need to add a supported render parameter in all portlet's Component Annotation.

     "javax.portlet.supported-public-render-parameter=message"

     The "message" is the public render parameter name.

    After you have done this you can use this parameter as a regular render parameter in the portlet. 

    In your link you can add the parameter like this:

    <portlet:renderURL var="senderURL">