Filtered-OFDM for Visible Light Communications

In visible light communications (VLCs), adaptive Orthogonal Frequency Division Multiplexing (OFDM) systems can adjust the transmission parameters according to channel estimation results to improve the system performance. Filtered-OFDM (F-OFDM) is a new flexible and adaptive technology based on OFDM systems and can further improve the system performance. In F-OFDM scheme, the out-of-band emission of OFDM signal is greatly inhibited by using the filter and the guard interval of the two subbands is reduced to save the spectrum resources. In this paper, we creatively apply the F-OFDM technology to visible light OFDM systems and derive the specific signal expression. Simulation results show that as the number of quadrature amplitude modulation (QAM) increases, the bit error rate (BER) performance of the F-OFDM system gets worse. Compared with asymmetrically clipped optical OFDM (ACO-OFDM) and direct current biased OFDM (DCO-OFDM) in VLCs, F-OFDM has better BER performance in 4QAM, 16QAM, and 64QAM schemes.

I. Introduction

The concept of F-OFDM was re-proposed by Huawei at the Mobile World Congress in 2015 [1]. F-OFDM is a kind of adaptive air interface waveform modulation technique with variable subcarrier bandwidth, which is based on the improved scheme of OFDM [2] [3]. The basic idea of F-OFDM technology is to divide OFDM carrier bandwidth into several subbands with different parameters, and to filter the subbands. The guard band consumption between two subbands can be designed as small as possible [4]. For example, in order to realize the Internet-of-Things (IoT) with low power consumption, the single carrier waveform can be adopted in the selected subband. Smaller subcarrier intervals and longer cyclic prefixes(CPs) can be used to combat multi-path channels. In order to achieve a lower air interface delay, a smaller transmission symbol length can be adopted.