Constellation Rotation Assisted Uplink NOMA With OFDM-IM

In this paper, an uplink non-orthogonal multiple access (NOMA) with orthogonal frequency division multiplexing-index modulation (OFDM-IM) is proposed by exploiting the constellation rotation to enhance the spectral efficiency (SE) while achieving an improved level of error performance. The users transmit information with index modulation to activate certain sub-carriers. Then the active sub-carriers carry <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$M$</tex-math></inline-formula>-ary modulation with orthogonal constellation rotation based on the channel condition. Hence, successive interference cancellation is not required at the base station to separate the superimposed signal, resulting in reduced computational complexity and increased user connectivity. The proposed scheme is compared with the existing techniques in terms of bit-error rate and SE.