This paper presents a radio transceiver architecture in mobile devices for coexistence of 4G-LTE and 5G systems, with fewer extra components and easier circuit implementations. The radio front-end is divided into two parts depending on the frequency bands, below 6 GHz or higher than 10 GHz even to millimeter-waves. Direct IQ modulation/demodulation blocks, baseband analog circuitries and frequency synthesizer are commonly used parts for both of low/high frequency operations where one-stage frequency up/down conversions are exploited for high frequency bands. Transmit/receive performance tests of a prototype using commercial-off-the-shelf components are demonstrated to validate the proposed radio transceiver design.