  Classical communication through quantum channels may be enhanced by sharing
entanglement. Superdense coding allows the encoding, and transmission, of up to
two classical bits of information in a single qubit. In this paper, the maximum
classical channel capacity for states that are not maximally entangled is
derived. Particular schemes are then shown to attain this capacity, firstly for
pairs of qubits, and secondly for pairs of qutrits.
