Heterogeneous Non-orthogonal Multiple Access with Distributed Alamouti Space-Time Coding

Full frequency reuse with nonorthogonal multiple access (NOMA) in heterogeneous networks (HetNets) can promisingly satisfy the fast-growing wireless transmission requirements, as the data of different users can be simultaneously delivered over the same frequency band. In HetNets, the transmissions from a micro base station (BS) to its cell-edge users often suffer from strong interference from the macro BS, which severely degrades the communication quality. The macro BS and the micro BS can transmit simultaneously to a common far-user using the distributed Alamouti coding technique to improve the communication robustness. Meanwhile, each BS also transmits data to a near-user using the NOMA protocol. The common far-user adopts the maximal ratio combining (MRC) technique to decode its desired data by treating the data of near users as interference. Each near-user decodes the data of far-user using the MRC technique and cancels it to decode its own data by treating the remaining undesired data as interference. Numerical results show that the Alamouti coding based NOMA transmission can greatly improve the throughput of HetNets.