Two-Way Relaying for Orbital Angular Momentum LOS Transmission

Wireless communications based on orbital angular momentum (OAM) is an important line-of-sight scheme for next generation limited range networks. In this paper, we first investigate low-complexity near-maximum-likelihood (near-ML) detectors, which are independent of amplitude and/or phase modulation constellation size for both OAM-based mode division multiplexing (OAM-MDM) and OAM-based index modulation (OAM-IM). Second, we investigate infrastructure-based two-way relaying (TWR) for these OAM-based schemes. A network of two source/destination nodes with a single relay node placed between these nodes and employing decode-and-forward is considered. The transmission interval is partitioned into two transmission phases. In the first phase, the two source nodes transmit message blocks to the relay node. On receiving these message blocks, the relay node decodes the message blocks and encodes them into a single message block via the use of network coding. In the second transmission phase, the relay node forwards the single message block to the destination nodes, where the intended message block is decoded via network coding. The theoretical average bit error probability (ABEP) for a message block at the destination is derived and analyzed for the proposed TWR schemes, with validation provided by comprehensive simulation results.