An spectrum efficient WO-OFDM using windowing and overlapping on the cyclic prefix and postfix

Abstract

In this paper, we like to propose an WO-OFDM (windowing and overlapping — orthogonal frequency division multiplexing) which is an improved version of conventional OFDM system. For the new radio waveform of the 5G and the beyond mobile system, the spectrum efficiency is the most important factor. Especially, OOB (out-of-band) power spectrum must be reduced to increase the spectrum efficiency and to save the frequency resources. Filtering is the one way to get the sharp OOB spectrum. But, due to the very complicated process and some difficulty to the realization of the filtering method, windowing method has been enlightened more. WOLA-OFDM (weighted overlap and add — orthogonal frequency division multiplexing) system is the most representative windowing method. However, the WOLA-OFDM system has some serious problem. The first problem is the time loss because of the copy and extensions in the right and left part in the conventional CP-OFDM (cyclic prefix — orthogonal frequency division multiplexing). There must be the extension in the right and left ends of the CP-OFDM even though there are overlapped in the consecutive symbols. This is the obvious loss problem of the time resource. The second problem is that when the consecutive symbols are overlapped keeping the same CP-OFDM period in order not to lose the time resource, the sharpened OOB spectrum of single WOLA-OFDM symbol cannot exist any longer because of the waveform change due to the overlapping of the consecutives symbols. The last is the data collision, which is very serious problem even before the transmission. Due to the overlap of the 2 extensions of copy and addition processes, the left part of the copied and added parts invades into the right part of the previous OFDM symbol. So, in this paper, to improve the WOLA-OFDM system and to avoid these problems of WOLA-OFDM, we like to propose an WO-OFDM. In this WO-OFDM system there are WO1-OFDM system and WO2-OFDM system, whether the overlapping between the consecutive OFDM symbols is allowed or not. Compared with the conventional WOLA-OFDM system, the proposed WO-OFDM system is an simple and solve the problems. Simulations results show that the proposed WO-OFDM system has comparable OOB spectrum reduction characteristics and can be designed by simple some modification from the conventional OFDM system.