Looking through the proposal I mostly see your translation of the idea from the GSoC ideas list to a proposal format. All of that is fine, but we've already decided this is a reasonable idea and the proposal should convince us that you're the right person to work on it.
I'll point out *some* specifics but please don't just list responses to these things in the proposal. Rather reshape it to giving us an idea of what you want to do (which you have) and why you're the right person. The list I'm providing is not meant to be exhaustive, and I'm not suggesting that you're not the right person to do this, just that you haven't addressed that (or your eligibility for GSoC in your proposal. It's also possible I am being dense and missed some of this information.
From the page I linked you're missing:
* Proof of your coding capabilities (this is the big one)
* University and student status (more of a formality)
* why do you want to do *this* project? (this is not critical, but if you've done any classes or work in areas related to your proposal idea than that looks very good)
Ideally this is all more than a single sentence that says "I did a matlab simulation once in a class and it was cool", but much less than a college admissions essay on why DSP will save the world.
Looking forward to the next draft (and hopefully faster turnaround),
-Nathan
PS - most of this email can be copy and pasted as feedback for several other proposals I've read so far.