A new approach to cooperative NOMA using distributed space time block coding

This paper presents a novel approach to cooperative non orthogonal multiple access (NOMA) using distributed space time block coding (STBC) known as STBC-NOMA. In conventional NOMA, the strong users detect the messages of weak users through successive interference cancellation (SIC). In cooperative NOMA, these copies are then forwarded by strong users to weak users at the expense of extra time slots. However, the proposed scheme exploits this feature of cooperation using STBCs to enable cooperation among the users. The STBC-NOMA renders less complexity as lesser number of SICs are performed at each user. To this end, we derive the outage probability of the STBC-NOMA scheme which involves finding the distribution of signal-to-interference ratio at the receiving terminals. The numerical results show that STBC-NOMA outperforms conventional NOMA and conventional cooperative NOMA in terms of outage probability and average sum rate.