Comparing IDMA and NOMA with Superimposed Pilots based Channel Estimation in Uplink

In this paper, we compare two potential multiple access schemes, namely Non-Orthogonal Multiple Access (NOMA) and Interleave Division Multiple Access (IDMA). Especially, we focus on their performance in uplink with a real channel estimator, by exploiting superimposed pilots. The utilized superimposed pilots are the cyclically repeated spreading sequence, a priori known by the transmitter and receiver, and are assigned a marginal fraction of the total transmit power. The superimposed pilots help to generate the initial channel estimation with respect to the code-division orthogonality and exhibit robustness against asynchronicity as well. Furthermore, iterative channel estimation is considered, by introducing a trellis-based channel estimator, which can significantly enhance the channel estimation during the iterations, by reusing the superimposed pilots. The behaviors of Bit Error Rate (BER) and channel estimation Mean Square Error (MSE) will be investigated for NOMA and IDMA system.