Fast Resource Allocation for OFDMA Downlink Utilizing An Efficient Bit Loading

In this paper, bit loading for orthogonal frequency division multiplexing (OFDM) is studied first. The continuous water-filling is modified to take the maximal rate constraint on each subcarrier into account. Its continuous outputs are optimally quantized by a non-iterative algorithm. By iteratively utilizing bit loading for OFDM, a class of resource allocation methods with low complexity for orthogonal frequency division multiple access (OFDMA) downlink is proposed. Subcarrier assignments for users are initialized independently, which may cause conflicts on arbitrary subcarriers. We suggest a method for conflict cancellation, which may be improved by using appropriate sorting criteria. The proposed method is compared to a newly suggested reference method by simulation. Within the simulation the performance loss is limited by about 5% whereas the complexity reduction is up to 95%.