A Novel Uplink Multiple Access Technique Based on Index-Modulation Concept

Index Modulation (IM) concept is exploited to propose a novel uplink multiple access technique called, IM–multiple access (IMMA). In IMMA, part of the transmitted block for each user is used to modulate a complex symbol that is transmitted on a specific time slot determined by the remaining bits in that block. Concurrent transmissions from different users are probable in IMMA since the operating time slot for each user is individually selected and the scheme can be considered as a non–orthogonal multiple access (NOMA) technique. Yet, it is revealed that the error rate at the centralized receiver is better than other orthogonal multiple access schemes. Adopting a maximum likelihood detector to jointly decode all the transmitted blocks from various users is shown to be computationally complex. Hence, a reduced-complexity detection scheme is proposed where a substantial reduction in computational complexity of more than 50% is attained with a marginal performance penalty. Besides, an analytical upper bound of the average bit error rate (BER) and the probability of collision are derived in a closed form expression. It is also disclosed through simulation results that a significant enhancement in the BER is achieved for the proposed IMMA scheme as compared with the conventional TDMA system and to sparse code multiple access NOMA scheme.