A twisted modulation scheme for satellite communication

Twisted modulation schemes have recently been recognized as useful techniques to reduce the power and bandwidth requirements for transmitting sampled analog data. In geometrical terms, giving a twisted modulation scheme is equivalent to choosing a curve in n-dimensional space, and setting a one-to-one correspondence between its points and the values of the time samples of a band-limited process. When such a scheme is used to transmit over a satellite channel, a major source of impairment is the nonlinearity introduced by the traveling-wave tube located in the transponder; however, the performance impairment due to the nonlinearity can be avoided if the signal locus lies on the surface of a n-dimensional hypersphere. This paper proposes a twisted modulation scheme designed to avoid the performance degradation due to the nonlinearity. The scheme is evaluated in terms of output S/N ratio vs. input S/N ratio in the presence of additive noise and of an error in the recovery of the carrier phase.