Delay Adaptation Method for Relay Assisted Optical Wireless Systems
2020 22nd International Conference on Transparent Optical Networks (ICTON)
In this paper, we investigate optical wireless repeaters as relay terminals between a transmitter and a user in an Infrared Optical Wireless Communication (IROWC) system. A delay adaptation method is introduced to solve the problem of irregular signal arrival time from different relay terminals. Three different relay terminal deployment scenarios were investigated in a typical two-phase relay IROWC system with the proposed delay adaptation method. The simulation results indicate that the
... d system has better impulse response compared to the conventional system and that the root-mean-square delay spread of the relay system with the delay adaptation method is on average 30% less than the conventional system. INTRODUCTION Relay communication techniques can be attractive in Infrared Optical Wireless Communication (IROWC) systems. IROWC systems are a kind of indoor OWC systems that are not affected by dimming control and illumination requirement -. Such systems can be considered a s complementary to conventional radio frequency communication (RFC) systems or as independent systems to provide wireless communication in indoor environment -. Conventional diffuse systems (CDS) are a form of IROWC system that contain a diffuse transmitter and wide field of view (FOV) receiver at the user device. Due to Inter Symbol Interference (ISI) distortion, intense ambient noise, and relatively low received power, a CDS cannot archive high data rate communication . In order to overcome this drawback of CDS, relay communication techniques common in RFC systems can be considered in IROWC systems - . The signal from the transmitter can be enhanced by some relay terminals and forwarded to the user. Moreover, the relay terminals can enhance the received optical power at the user in situations where link blockage occurs between the transmitter and the user. Figure 1 shows a typical two-phase relay mode used in the IROWC system. In this relay IROWC mode, a communication is divided into two phases. In the first phase, the infrared transmitter on the ceiling sends a signal to several relay terminals. In the second phase, the relay terminals send the signal to the users on the communication plane. However, for different relay terminals, the link distance from the transmitter via relay terminals to user are different causing dspersed signal arrival time at the receiver. This multipath spread caused by multiple relay terminals can result in serious pulse spread and ISI. In this paper, we propose a delay adaptation method to address this problem. This method balances the arrival time of the signals from different relay terminals by adding a pre-calculated (derived through a pre-distortion equalizer) delay to different relay terminals. In order to study the effectiveness of this method, we consider three different relay terminal deployment scenarios. The rest of the paper is organized as follows: The delay adaptation method is introduced in Section 2, while the simulation configuration and the results are provided in Section 3. Finally, the conclusions are presented in Section 4.