White Noise Level in OFDM & SNR Definition

Hi All,

I have this problem on the level of white noise to be added into an OFDM
system.  Firstly, I have series of symbols mapped to a series of
subcarriers and then go through an IFFT (size 2048).  For simplicity, I
assumed that it goes through a 1 path channel (i.e. no change to the OFDM
signal).  I then added some white guassian noise.  Now here is the problem,
if say I want a SNR of 10 dB, do I add:

1) sqrt(2048) x 1/(sqrt(2 x 10^(SNR/10))) so that EACH SUBCARRIER gets hit
with -10 dB of noise relative to its each subcarrier signal OR
2) 1/(sqrt(2 x 10^(SNR/10))) so that the OFDM SIGNAL gets hit with -10 dB
of noise relative ot the OFDM signal

I used option 1) above and the constellation of the received signal is all
over the place.  I recalculate each of the noise per subcarrier and it is
about -10 dB as expected.  I have to increase the SNR to 50 dB before the
constellation of the receive signal look clean.  For 10 dB per subcarrier,
it is about 23 dB of noise relative to the OFDM signal which is pretty
high. 

My question is how would one define SNR when evaluating the performance. 
Is it SNR per subcarrier or SNR of the OFDM Signal?  Would one expect a
very poor performance with a seemingly high SNR of 10 dB per subcarrier (ie
using option 1 above).

Thanks.