Joint Adaptive Modulation and Power Allocation for Variable-Rate Space-Time Block Codes

Variable-rate space-time block codes (vr-STBCs) without any feedback can support different transmission rates and unequal error protection (UEP) which are needed for multimedia communications. Assuming necessary feedback, in this letter, we introduce a joint adaptive modulation and power allocation (AMP) for vr-STBCs so as to maximize the total throughput under constraints of transmit power limit and error requirements. Based on a Lagrangian multiplier method, optimum modulation orders and power levels are provided for the transmitter. Numerical results show that the proposed AMP enhances the throughput of existing vr-STBCs up to 20% with very limited feedback, e.g., at most 3-5 bits feedback.