Quadrature product subcarrier modulation (QPSM)

Due to the limited availability of spectrum allocations for communications systems, it has become desirable to reuse existing spectrum by employing bandwidth efficient modulation methods to existing satellite communications systems. As the number of users of a given communication system increases, it often becomes necessary to augment the system with additional communication signals. One method that has been used to achieve this goal in Timing, Telemetry and Command (TT&C) links is conventional subcarrier phase modulation. In this work we present a new subcarrier modulation technique called Quadrature Product Subcarrier Modulation (QPSM) that enables the transmission of a quadrature multiplexed carrier modulation with single or multiple subcarrier signals in the same constant-envelope waveform. The general approach is applied to the addition of subcarrier signals to a quadrature multiplexed spread-spectrum system. The overall power efficiency is derived for each case under consideration. The modulation's spectral components are derived analytically and the analytical results are compared to results simulated using the Signal Processing WorkSystem simulation environment.