Well...Now that I think I have a bit of understanding, I am better able to answer my own question. SINR or SNR Must be >1 (or >0 in case of dB scale). BTW on log scale, SNR is only in dB. Since it is the ratio of two similar quantities and it does not have any unit. (dBW and dBm is not same as dB).
SNR > 0 dB means that Received power - Noise > 0 and Hence Received power is more than the total Noise. Of course the more the value of SNR, the more it is better. Meaning, the more the SNR, the more Desired Signal Power component exist in the total signal. Ideally SNR can be equal to Received power when NOISE effect is ZERO. This is the max. instantaneous SNR
During the device discovery process. Any D2D device transmits a beacon with a given power. The neighbors receive the signal with channel losses. Hence based on the received power, the receiving devices will ACK to. However, to what minimum level can this signal be properly decoded by the receiver is the point of my concern.
In practice, it depends in a plethora of parameters. for example, processing power of receivers (upgraded based on the market technology) is an important factor. Theoretically, however, for a SISO channel, the Shannon formula can be used which goes C=Blog2(1+SNR). in this formula, any SNR greater than zeros will be of some use. Depending on the type of the Traffic and QoS associated parameters, however, the minimum acceptable SNR is prone to changes. More importantly, in nowadays Network, congestion will be a more important factor than SNR (or SINR). In this respect, you may follow the paper " Old Myths and Open Problems " written by Jeffrey Andrews.