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This paper describes a combined modulation scheme for time-hopping ultra-wideband (TH-UWB) radio systems by using on-off keying (OOK) and pulse-shape modulation (PSM). A set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same pulse repetition interval resulting in a composite pulse. This scheme transmits the same number of bits by using fewer orthogonal pulses and receiver correlators than those used in PSM and biorthogonal PSM (BPSM). The proposed scheme reduces multiple-access interference and multipulse interference considerably by using crosscorrelation properties of orthogonal pulses. Since each bit is individually received by OOK, the proposed scheme requires less power. Hence, it is applicable for energy constrained and low-cost TH-UWB systems. The bit-error-rate (BER) performance is analyzed both mathematically and through computer simulations under the different channel environments. The performance of this scheme is compared with that of existing PSM and its combined modulation schemes by using two sets of orthogonal pulses.