New converses in the theory of identification via channels

New converses for identification via arbitrary finite alphabet single-user and multiple-access channels, with finite first- and second-type probabilities of error, are presented. For the arbitrary single-user channel, it is shown that (λ₁, λ ₂)-identification capacity is upper bounded by λ-capacity, for any λ>λ₁+λ₂. An outer bound on the (λ₁, λ₂)-identification capacity region of an arbitrary multiple-access channel is developed. A consequence of this bound is that the identification capacity region is equal to the transmission capacity region for any stationary, finite-memory multiple-access channel