Fifth generation (5G) communication systems include enhanced mobile broadband, massive machine-type communication, and ultra-reliable low-latency communication. To support various 5G applications, researchers have considered multiple scalable subcarrier spacing and transmission time interval (TTI). In this paper, we introduce a concept of waveform multiplexing for frequency multiplexing of numerologies. Waveform multiplexing consists of different waveforms on subbands with scalable subcarrier spacing and TTI operating on one frequency band. The Waveform multiplexing also possesses dynamic cyclic prefix and minimum guard band, which are the key features for the high spectral efficiency. We verify the performance and the potential of the waveform multiplexing using 3-dimensional (3D) ray-tracing based system-level evaluation in a realistic environment and a 3D channel.