Out-of-band emission reduction and a unified framework for precoded OFDM

OFDM has been regarded as a promising candidate for use in cognitive radio systems with dynamic spectrum reuse capability. However, conventional OFDM has significant OOBE, which can cause severe interference to systems operating in adjacent frequency bands. In addition to conventional techniques such as spectral shaping filtering, guard band insertion, and time domain windowing, new OOBE reduction techniques, including cancellation carrier and spectral precoding, have been proposed in recent years. This article reviews various OOBE reduction techniques and proposes a generalized low-complexity OOBE reduction framework for discrete Fourier transform precoded OFDM. With the allocation of explicit frequency domain cancellation subcarriers and data domain cancellation symbols, the proposed framework enables various configurations to achieve significant OOBE reduction with low implementation complexity, and provides flexibility in balancing OOBE reduction and other performance metrics such as peak-to-average power ratio.