Most of the polls and predictions give about 70% of the people against independence and Alex Salmond knows it. That's unlikely to change much for some time.
That's why Wendy Alexander, when she was still a power in Scottish politics, said "Bring it on." when asked about such a referendum, and that's why the main opposition parties were so stupid when they combined to prevent it in the last Parliament.
She knew, and they didn't, that Salmond would suffer such a humiliating defeat that he would have been finished as party leader, and the SNP would have been a spent force in Scottish politics for at least a generation.
They played right into his hands.
He has already said that the referendum will be in the second half of the parliament. I suspect it will be around the last twelve months or so, so that he will be able to fight the next election saying "We promised a referendum and we delivered it, and you'd have got it sooner if the other parties had not denied you a voice. The people of Scotland have spoken", or words to that effect, and he will appear to be Oh so reasonable.
He's a canny lad is Big 'Eck!