Abstract : Index modulation multiple access (IMMA) is anefficient non–orthogonal multiple access (NOMA) technique thatwas proposed recently. IMMA exploits index modulation (IM) toallow simultaneous transmission of data from multiple users, andcreates an extra constellation diagram that conveys additionalinformation bits each channel use. In this paper, the theoreticalcapacity for index modulation multiple access (IMMA) systemis derived along with the mutual information assuming perfectand imperfect channel estimation at the receiver. Monte Carlosimulation results were obtained to corroborate the derivedformulas, where it is demonstrated that the derived theoreticalcapacity formula is the upper bound for the simulated mutualinformation curves. Besides, the conditions under which thederived capacity is achieved are deduced and verified. As well,IMMA system’s performance, in terms of mutual informationand capacity, is compared to sparse code multiple access (SCMA)systems, where the superiority of IMMA is revealed. Further,a bound on the number of users that can share the availableorthogonal resources is acquired. Finally, a comparison betweenIMMA systems and orthogonal multiple access (OMA) systems isrealized to investigate the impact of overloading on the scheme.
Index terms : Index Modulation Multiple Access (IMMA) , index modulation (IM) , multiple–input multiple–output (MIMO) , Sparse Code Multiple Access (SCMA) , orthogonal frequency division multiple access (OFDMA)