说明：   Additionally, LTE supports operation both in paired and unpaired spectrum (FDD and TDD) using channel bandwidths of approximately 1.4MHz up to 20MHz. The frequency domain scheduling can be done in OFDMA. One of the main challenges in OFDMA is the high peak-to-average radio of the transmitted signal, which requires linearity in the transmitter. The linear amplifiers have low efficiency therefore, OFDMA is not an optimized solution for a mobile uplink where the