On the capacity of strong asynchronous multiple access channels with a large number of users
Sara Shahi, Daniela Tuninetti, Natasha Devroye · 2016
This paper studies the impact of block asynchronism on the capacity of a slotted Multiple Access Channel (MAC) whose number of users Knincreases with the blocklength n. In a slotted strong-asynchronous MAC, the Knusers have independent transmission start times that are integer multiples of n (slotted) which are uniformly distributed on a window of length An= enα(strong-asynchronism). All users' messages as well as transmission times need to be reliably decoded at the single receiver. We show that for Kn= enνwith ν > α, not even synchronization is possible when transmitting a single message per user. We also show that for Kn= eνwith ν = o(n), each user can achieve its point-to-point asynchronous capacity, which is a trivial upper bound for the capacity of the MAC. Finally, achievable rates for Kn= enν. with 0 <; ν <; α/2 are derived.