I think dig's $20m referred to a proportion of a $2bn DoD budget and was at most experimental.
Your $20bn looks like it refers to the whole market.
I suppose the whole market may be three orders of magnitude larger than the DoD. But if you are both right, then that means the total market size is 1 1/2 billion units. Maybe you are including mobile phones.
As an alternative, I would suggest dig multiples his number by five and you divide the number of units by three. That would yield a potential total enterprise market of around $33bn.