A Low Complexity Transmitter Structure for OFDM-FDMA Uplink Systems
The Orthogonal Frequency Division Multiplex (OFDM) transmission technique can efficiently deal with the effects of multi-path propagation in the broadband radio channel. It also has a high system inherent flexibility for designing a multiple access scheme by combining the conventional TDMA, FDMA and CDMA approaches with the OFDM modulation scheme. The FDMA multiple access schemes are especially interesting for an uplink of a communication system since it can completely avoid any Multiple Access Interferences (MAI). Moreover, the Peak-to-Average Ratio (PAR) of the uplink OFDM transmit signal can be greatly reduced if this OFDM-FDMA multiple access scheme is additionally combined with a data spreading technique based on a Discrete Fourier Transform (DFT) spreading matrix using only the user specific subcarriers.