Spectrum shaping in N-channel QPSK-OFDM systems

A compact time-domain treatment of a complete spectrum shaped N-channel orthogonal FDM system is presented, enabling practical DSP algorithms for modulation and demodulation to be clearly identified. The resulting DSP architecture is an alternative to previously described OQPSK-OFDM systems and directly provides the two complex samples per symbol required for symbol timing recovery. The paper also discusses parameter selection for the polyphase shaping filters and compares simulation results of power spectral density for shaped and unshaped systems. Simulation shows that shaped systems can closely approach the ideal transmission spectrum even for modest values of N.