  A wideband fading channel is considered with causal channel state information
(CSI) at the transmitter and no receiver CSI. A simple orthogonal code with
energy detection rule at the receiver (similar to [6]) is shown to achieve the
capacity of this channel in the limit of large bandwidth. This code transmits
energy only when the channel gain is large enough. In this limit, this capacity
without any receiver CSI is the same as the capacity with full receiver CSI--a
phenomenon also true for dirty paper coding. For Rayleigh fading, this capacity
(per unit time) is proportional to the logarithm of the bandwidth. Our coding
scheme is motivated from the Gel'fand-Pinsker [2,3] coding and dirty paper
coding [4]. Nonetheless, for our case, only causal CSI is required at the
transmitter in contrast with dirty-paper coding and Gel'fand-Pinsker coding,
where non-causal CSI is required.
  Then we consider a general discrete channel with i.i.d. states. Each input
has an associated cost and a zero cost input "0" exists. The channel state is
assumed be to be known at the transmitter in a causal manner. Capacity per unit
cost is found for this channel and a simple orthogonal code is shown to achieve
this capacity. Later, a novel orthogonal coding scheme is proposed for the case
of causal transmitter CSI and a condition for equivalence of capacity per unit
cost for causal and non-causal transmitter CSI is derived. Finally, some
connections are made to the case of non-causal transmitter CSI in [8].
