Rate adaptive hierarchical modulation assisted two-user opportunistic scheduling

We propose and study a two best user opportunistic scheduling algorithm using discrete rate adaptive hierarchical constellations (known also as embedded, multi-resolution, or asymmetrical constellations). The key idea is to rely on hierarchical constellations to transmit information to the two best users opportunistically. The newly proposed scheme transmits information to single or two best users jointly considering the channel qualities of these users. We present expressions for the information transmission probability and the overall average spectral efficiency [Bits/Sec/Hz] defined as the overall average transmitted data rate per unit bandwidth for a specified number of users, average carrier-to-noise ratio (CNR), and bit error rate (BER). Numerical results for an identical and independent (i.i.d.) fading environment, where the channel variation among the users is i.i.d., are presented. The results show that in such i.i.d. fading environment, our newly proposed discrete rate adaptive hierarchical modulation assisted two best user scheduling provides more frequent access to the information (almost double) without any average spectral efficiency degradation compared to the classical single best user opportunistic scheduling.