Quadrature NOMA-ALOHA: Throughput Bounds

This letter studies cross-layer physical (PHY) and medium access control (MAC) contention-based random access for uplink non-orthogonal multiple access assisted by slotted ALOHA (NOMA-ALOHA). In addition, an improved NOMA-ALOHA is proposed by exploiting signal space diversity using π/4-rotated M-ary amplitude shift keying (MASK) with coordinate interleaving (CI), known as quadrature NOMA-ALOHA (QNOMA-ALOHA). In QNOMA-ALOHA, the PHY layer creates a new transmission resource based on two quadrature carriers (cosine and sine) and generates a virtual subslot in the MAC layer. The throughput bounds of QNOMA-ALOHA are derived based on the Poisson model. The numerical results show that the improved NOMA-ALOHA with QNOMA in the PHY layer significantly outperforms the existing NOMA-ALOHA in terms of throughput. The improvement of QNOMA-ALOHA is two times the square root of the power level to slotted ALOHA and two times to NOMA-ALOHA.