Hi:

My experience:  The BA first creates, in an Agile fashion, the up front big picture.  This "analysis in the large" effort is used to scope out the project and to plan/prioitize the various iterations. 

Then, during the course of each iteration, the BA performs "analysis in the small" , firming up the requirements of each iteration.  If the bigger picture is quality (remember, Agile, while being about minimal documentation, is also about quality documentation), "analysis in the small", coding, and QA may be able to proceed together.

Tony