  We consider the Gaussian Dirty Tape Channel (DTC) Y=X+S+Z, where S is an
additive Gaussian interference known causally to the transmitter. The general
expression [max]\_top(P_U,f(.),X=f(U,S))I(U;Y) is presented for the capacity of
this channel. For linear assignment to f(.), i.e. X=U-{\beta}S, this expression
leads to the compensation strategy proposed previously by Willems to obtain an
achievable rate for the DTC. We show that linear assignment to f(.) is optimal,
under the condition that there exists a real number {\beta}^* such that the
pair (X+{\beta}^* S,U) is independent of interference S. Furthermore, by
applying a time-sharing technique to the achievable rate derived by linear
assignment to f(.), an improved lower bound on the capacity of DTC is obtained.
We also consider the Gaussian multiple access channel with additive
interference, and study two different scenarios for this system. In the first
case, both transmitters know interference causally while in the second, one
transmitter has access to the interference noncausally and the other causally.
Achievable rate regions for these two scenarios are then established.
