Byeongjae Kim

Design of W-OFDM and nonlinear performance comparison for 5G waveform

For the spectrum efficiency improvement of 5G mobile communication, a new waveform based on multi-carrier are important. In this paper, we like to suggest a W-OFDM(weighted orthogonal frequency division multiplex) system design and compare the nonlinear system performance with the already existing OFDM, UFMC(universal filtered multicarrier), FBMC(filter bank multicarrier) systems. At first, we describe OFDM, UFMC, FBMC, and W-OFDM(weighted OFDM). Then, we evaluate and compare the spectrum characteristics of these systems in the nonlinear HPA environment. As simulation results, OOB power of FBMC is the lowest under the linear HPA condition. But, OOB power of UFMC, FBMC, and W-OFDM is similar under the nonlinear HPA environment. In the real HPA nonlinearity, W-OFDM with low-complexity and simple structure is advantageous than the well-known strong candidates for 5G mobile system such as FBMC and UFMC.

WR-OFDM system and OOB spectrum comparison

The most important figure-of-merit for the 5G waveform is the spectrum efficiency. Especially, OOB (out-of-band) spectrum must be reduced to increase the spectrum efficiency and decrease the guard band between the channels. In the filtering methods, UFMC (universal filtered multi-carrier) and FBMC (filter bank multi-carrier) were suggested for the new waveform for 5G mobile communication system. Similar to OFDM system, they are based on the multi-carrier, but they have sharper OOB spectrum. Due to the very complicated process and some serious 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 famous and representative windowing method among the many possible conventional windowing methods. 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 WR (windowing and restructuring)-OFDM system that shows competitive OOB spectrum characteristics and is designed by simple some modification 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. From the simulation results, it is confirmed that OOB power spectrum of WR-OFDM is quite comparable with the existing waveforms.

Design and Performance Evaluation of W-OFDM System for 5G Mobile Communication

본 논문에서는 5세대 이동통신을 위한 OFDM(Orthogonal Frequency Division Multiplexing)을 기반으로 하고 Window 함수을 적용한 W-OFDM 시스템 모델을 제시하고 그 성능을 평가한다. 제안하는 시스템은 기존의 OFDM 시스템의 높은 OOB 전력을 가지는 문제점을 해결하기 위해 CP를 추가하는 부분에 Window 함수를 함께 적용한다. 이는 시간영역에서 연속성을 갖게 만들고 OOB 전력을 저감시킨다. 그리고 수신기에서는 Window 함수를 적용함으로써 생긴 데이터 손실을 CP의 일부를 이용하여 재구성함으로써 데이터 손실을 막는다. 이로 인해서 Window 함수의 길이는 CP길이의 절반이하로 정한다. 제안하는 시스템 모델을 Window 함수의 종류와 길이의 따라 시뮬레이션을 진행하였다. 비교한 Window 함수 중에서는 Kaiser Window 함수가 가장 OOB 저감 효과가 컸다. 또한 Window 함수의 길이를 늘일수록 OOB 전력 저감 효과가 더 크게 나타났으며 동일한 BER성능을 얻으면서 기존 OFDM 시스템 대비 OOB전력을 저감시킬 수 있는 것을 확인 하였다. 즉 제안하는 시스템은 다가올 5세대 이동통신에 적합하다고 할 수 있다.

WF-OFDM (windowing and filtering OFDM) system for the 5G new radio waveform

The 2 approaches for the 5G new radio waveform design are the filtering and windowing for the spectrum efficiency improvement by reducing the OOB(out-of-band) power spectrum. As filtering method, UFMC (universal filtered multicarrier), FBMC (filter bank multicarrier) and f-OFDM (filtered orthogonal frequency division multiplexing) waveforms are the potential candidates for a new waveform for 5G system. Another possible approach is to use the windowing in the conventional CP-OFDM system in order to reduce the OOB power spectrum. W-OFDM (window orthogonal frequency division multiplexing) is typical and show comparable performance. Each approach has some advantages and disadvantages together. The best OOB reduction performance can be shown in FBMC system. However, FBMC system is the most complicated and cannot support the general M-QAM (M-ary quadrature amplitude modulation) format. So, it is very important to design a novel OFDM-based waveform that has the similar OOB power spectrum to the FBMC and support the general M-QAM modulation as well. In this paper, we like to propose a WF-OFDM System for the 5G and 5G beyond mobile system waveform design. This WF-OFDM system uses a combination method of the filtering and windowing to get the synergy effect, so that the spectrum efficiency may be increased by reducing the OOB (out-of-band) power spectrum. 4 kinds of WF-OFDM systems are devised depending on the filtering and windowing positions for the OOB performance improvement. Simulations results show that the proposed WF-OFDM system has comparable or better OOB spectrum reduction characteristics to FBMC system. Especially, the proposed system WF-OFDM # 3 and #4 show the remarkable OOB reduction performance even in the short window length of 6 or 8.