In this paper, a scheme was proposed to achieve microwave photonic real time Fourier transformation based on spectrally-discrete dispersion, which aimed for the time-frequency information analysis of microwave signals in the future 6G wireless communication. The discrete dispersion media showed periodic narrowband filtering in the intensity frequency response and discrete quadratic phase distribution in the phase frequency response. Real time frequency to time mapping of microwave signals was then obtained using the discrete dispersion media. Furthermore, the time and frequency information of a non-stationary signal could be analyzed. Since only discrete phase shifts rather than continuously-changed true time delay were required, huge equivalent dispersion could be achieved with compact device to reduce the delay. An implementation based on cascaded ring resonators was proposed in this paper to achieve discrete dispersion, where fiber loops of 4 cm were used. Highly linear FTM with a slope of 0.8 ps/MHz was obtained through numerical stimulation, which was equivalent to 5800 km standard single-mode fiber. The resolution of the FTM reached 50 MHz and the unambiguous bandwidth reached 5 GHz. Taking the linear frequency modulation (LFM) signal which was often used in the convergence of sensing and communication in 6G as an example, the short-time Fourier transform function of the system was simulated to analyze the time and frequency information of the signal. The time resolution reached 20 ns, and the speed of spectrum analysis was as high as $ 2.5\times {10}^{8} $ FTs/s, which was significantly better than the traditional DSP based schemes.