Application of Superposition Coding for Subcarrier and Bit Allocation in Downlink OFDM Systems

Abstract

Orthogonal frequency division multiplexing (OFDM) is well known for multicarrier modulation technique in which a high data rate stream is divided into different parallel lower data stream. In this paper, we study the margin adaptive - superposition coding (MA-SC) algorithm and rate adaptive - superposition coding (RA-SC) algorithm, where at most two user can share each subcarrier as compared to MA and RA algorithm, where each subcarrier is shared by only single user without SC scheme. We apply SC scheme over MA and RA to achieve maximum system throughput with separate power constraint for real and non real time users, ensuring that QoS requirement for real time and proportional fairness among non real time users is satisfied. The overall computational complexity of proposed modified RA-SC algorithm is same as RA algorithm. In the modified proposed MA-SC, complexity increases in some of the steps due to addition of SC scheme over MA algorithm, but overall complexity remains the same. Monte-Carlo simulations are being carried out to show that the proposed algorithm improves the performance in terms of power required and throughput.