Analysis of OAM Modes and OFDM Modulation for Outdoor Conditions

Abstract

Signals transporting orbital angular momentum (OAM) have gained significant interest due to their unique structure and capability for increasing the channel capacity. OAM beams are orthogonal and can be multiplexed to increase link capacity in different scenarios. The collective combination of radio OAM modes and OFDM modulations in outdoor conditions has not been extensively explored. This paper depicts an analysis of multiple OAM modes transmitted as narrowband subcarriers using orthogonal frequency division multiplexing (OFDM) modulation with outdoor free space optical channel measurements based on OAM modes. OAM-OFDM simulations were conducted to investigate the performance of QPSK, 16QAM, and 64QAM baseband modulation and demodulation mechanisms, with code rates ½ and ¾ respectively. Four outdoor OAM free space optical channel characteristics parameters were applied. The throughput, bit error rate (BER), and packet error rate (PER) were evaluated. The results show that OAM +4 Mode outperforms other OAM modes in terms of BER and PER. In terms of the throughput, 64 QAM at code rate ¾ outperforms other coding schemes and code rates, for all OAM modes.