Power Allocation for ACO-OFDM Systems With Upper Clipping and Limited Bandwidth

We investigate the relationship between transmission power and clipping distortion for asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) visible light communication (VLC) systems with light emitting diode (LED)'s limited bandwidth and upper clipping, which is modeled into the formulation of an achievable data rate problem. We formulate a unimodal function with respect to transmission power, which is proportional to the data rate on a single subcarrier. The local optimal transmission power on a single subcarrier is derived by the unimodal function. We formulate a data rate problem on all subcarriers with respect to transmission power optimization. By analyzing the derivative of data rate, the global optimal transmission power on all subcarriers exists in the range between the maximum and minimum local optimal transmission power over a number of single subcarriers, which is divided into a number of sub-ranges. The local optimal transmission power is used to derive the upper and lower bounds of the derivative of data rate in each sub-range, respectively. To maximize the data rate, the derivative of data rate must be zero, resulting in the target sub-range that the upper bound is higher than zero, and the lower bound is lower than zero, reducing the exhaustive searches into a small number of sub-ranges for the global transmission power optimization. We propose a scaling-based power allocation (SPA) approach, where the global transmission power optimization in the reduced range and the waterfilling algorithm are combined, requiring no exhaustive search, while providing near-optimal performance.