This paper describes a combined modulation scheme for TH-UWB radio systems using on-off keying (OOK) and pulse shape modulation (PSM). For this scheme, a set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same time slot resulting in a composite pulse. The proposed transmission scheme can achieve higher data rate by using fewer number of pulses and receiver correlators than PSM. Due to the presence of OOK, the proposed scheme requires minimum energy and is applicable for energy constrained TH-UWB systems.