Subcarrier and power allocation for QoS-aware OFDMA systems using embedded modulation

A low-complexity, suboptimal algorithm to distribute subcarriers and transmit power among multiple users according to their individual QoS requirements in an OFDMA system employing embedded modulation is proposed. Application of embedded modulation allows to increase the system capacity in the downlink by stacking K independent, QAM modulated signals on each of the N available OFDM subcarriers. In this way, the maximum number of independent links is N·K compared to N when no subcarrier sharing is allowed. The larger number of links can be used for serving more users or increasing the users´ data rates. Simulation results show that signal stacking is more power efficient than addressing users with a higher order modulation and applying time sharing (TDMA). The performance of the proposed algorithm expressed in total transmit power is very close to the optimal solution found by exhaustive search.