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In recent years, there has been much attention on software defined radio (SDR) schemes for high speed multimedia applications. It is required that the SDR system is flexible enough to support multiple air interfaces and signal processing functions at the same time. Also digital signal processors and FPGAs are widely used for implementation of these adaptive and flexible functions of a baseband modem for SDR applications. Meanwhile, it is known that the modulation schemes OCQPSK (orthogonal complex QPSK) and HPSK (hybrid PSK) are used for IMT-2000 services of synchronous systems and asynchronous systems, respectively. Thus, we designed and implemented an OCQPSK/HPSK modem using a DSP chip with consideration of SDR concepts. One modulation scheme is operated by adaptive selection between the two schemes, and 5 physical traffic channels differentiated by orthogonal codes are implemented in one DSP chip. Each channel has 1 Mbps data rates and 8 Mcps chip rates.