I would like to work on the above issue, related to Bluetooth low Energy,a topic of my interest.
Please tell me the pre-requisites to be learnt for contributing to this task.
Where can I find relevant material to build my knowledge on these protocols.
there are multiple places. How about you start with the pages of the Bluetooth SIG ? Further the Nordic developer pages are usually having much information on BLE on them . Otherwise just start with google
as my previous speakers already mentioned there are several references to start with. Usually when I start work on a new project I begin with google, just to get an overview of the whole thing. Searching for "BLE" will give you several interesting references. One hint besides: There are also some relevant books available, e.g. "Bluetooth Low Energy: The Developer's Handbook".
Are you explicitly interested in USB HCI or do I suggest correctly that you are more interested in BLE in general? Anyway, you need to find out where you actually want spend your time and get an understanding of the respective technique.
To get familiar with RIOT in general I recommend reading through our wiki (https://github.com/RIOT-OS/RIOT/wiki) that provides some guidelines, tutorials, explanations (etc..) and execute some of our examples and tests. As Johann mentioned, we have some newcomer tasks that usually act as a training for your first contribution to RIOT.