Design and evaluation of spectrum efficient WR-OFDM system for 5G and B5G mobile system

摘要

In this paper, we like to suggest a spectrum efficient WR (windowing and restructuring)-OFDM system for 5G and B5G (beyond 5th generation) mobile system. The figure-of-merit for the 5G and B5G waveform is the spectrum efficiency. Especially, OOB (out-of-band) power spectrum must be reduced to increase the spectrum efficiency. Filtering and windowing method have been used for the OOB power reduction. As filtering method, UFMC and FBMC have been famous as a new waveform for 5G system. Similar to OFDM system, these techniques use multi-carrier, but they have sharper OOB spectrum. Due to the very complicated process and some difficulty to the realization, windowing method has been enlightened. In the windowing method, WOLA-OFDM (weighted overlap and add - orthogonal frequency division multiplexing) system is the most representative windowing method. However, the WOLA-OFDM system has serious problems. Due to the copy and addition processes, time resource will be slightly sacrificed and the other is that the left part of the copied and added parts will invade into the right part of the previous OFDM symbol. This is very serious data damage even before the transmission. In this paper, we like to suggest a spectrum efficient WR-OFDM system that shows competitive OOB spectrum characteristics and is designed by simple some modifications of the conventional OFDM system. Basically this is similar to the conventional OFDM system, but windowing process has to be included after the CP (cyclic prefix) addition stage. By adding this windowing process, we can get the desirable OOB (Out-Of-Band) spectrum characteristics that are very important to save the frequency resources and competitively similar shape to the OOB spectra of FBMC and UFMC system. As simulation results, it is confirmed that OOB power spectrum of WR-OFDM is quite comparable with the existing waveforms. Also, different power spectral densities of the proposed WR-OFDM system are shown depending on the different windowing function. Among the several window functions, Kaiser window function is the best and Hamming window is the worst.