Identification of non-ideal receiver condition for orbital angular momentum transmission

Although orbital angular momentum (OAM) was first introduced for optical communications, it is drawing attention as a new transmission technique for millimeter wave communication. Due to the additional orthogonal transmit dimension by photon OAM, the theoretical throughput can increase dramatically with various OAM modes. In practice, since OAM by uniform circular arrays (UCAs) has the implementation problem such as twisted axis between transmitter and receiver, the performance degradation happens frequently. Hence, this paper investigates the imperfect receiver condition and the effect of this problem. In particular, the off-axis and non-parallel location problems are focused. Here, the capacity with inter-mode interference (IMI) of OAM is first considered and the receiver compensation method is proposed. Numerical results show that the throughput after compensation is better than that without compensation.