This paper investigates the adaptive subcarrier and bit allocation algorithmfor OFDMA systems. To minimize overall transmitted power, we propose a noveladaptive subcarrier and bit allocation algorithm based on channel stateinformation (CSI) and quality state information (QSI). A suboptimal approachthat separately performs subcarrier allocation and bit loading is proposed. Itis shown that a near optimal solution is obtained by the proposed algorithmwhich has low complexity compared to that of other conventional algorithm. Wewill study the problem of finding an optimal sub-carrier and power allocationstrategy for downlink communication to multiple users in an OFDMA basedwireless system. Assuming knowledge of the instantaneous channel gains for allusers, we propose a multiuser OFDMA subcarrier, and bit allocation algorithm tominimize the total transmit power. This is done by assigning each user a set ofsubcarriers and by determining the number of bits and the transmit power levelfor each subcarrier. The objective is to minimize the total transmitted powerover the entire network to satisfy the application layer and physical layer. Weformulate this problem as a constrained optimization problem and presentcentralized algorithms. The simulation results will show that our approachresults in an efficient assignment of subcarriers and transmitter power levelsin terms of the energy required for transmitting each bit of information, toaddress this need, we also present a bit loading algorithm for allocatingsubcarriers and bits in order to satisfy the rate requirements of the links.
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