OFDM (Orthogonal Frequency Domain Multiplex) dominates modern communication systems, like 4G/5G, WiFi, DSL (Digital Subscriber Line), UWB (Ultra Wide Band) etc., as their base modulation scheme. Apart from numerous advantages of OFDM, one problem is its proneness to the in-band narrowband RFI (Radio Frequency Interference) such as a single carrier jammer, FM (Frequency Modulation) signal, AM (Amplitude Modulation) signal, etc. This is due to the spectral leakage from FFT (Fast Fourier Transform) operation in the OFDM receiver. The leakage spreads the energy of the narrowband interfering signal over the whole bandwidth of the desired signal, which could significantly interfere all subcarriers of the OFDM system. An OFDM system can thus get easily jammed by a strong narrowband signal source. For example, it is a well-known problem that a WiFi device can get totally jammed when it gets close to a microwave oven in operation.
Even in licensed spectrum bands, a wireless system like LTE (Long Term Evolution) can still suffer from intentional jammers, when someone generates deliberately strong interfering signals to jam the system around. Also, unintentional interference can occur in licensed spectrum bands e.g. from faulty equipment, local oscillator leakage, harmonics or intermodulation products from transmitters in other bands. Furthermore, in some systems, radio base stations are provided with a central digital processing unit (e.g. for baseband processing) and remote radio heads comprising antennas. The links to the remote radio heads carry RF (Radio Frequency) signals, but can be downconverted to intermediate frequency e.g. to be able to use Ethernet cabling. However, nearby strong analogue modulated signals on the same IF band, e.g. from walkie-talkie, may get a way to be coupled into the system through the cable or the cable connector and thereby interfere the downconverted RF signals received from the cable. In practice, many Ethernet cables are unshielded or insufficiently shielded, whereby RFI signals negatively affects the reception of the intended signal.
In C. De Frein, M. F. Flanagan and A. D. Fagan, “OFDM Narrowband Interference Estimation using Cyclic Prefix Based Algorithm”, 11th International OFDM Workshop, Hamburg, Germany, 30-31 Aug. 2006, http://ee.ucd.ie/˜mark/papers/OFDM_Workshop_NBI.pdf, a NBI (Narrowband Interference) cancellation algorithm for a wideband OFDM receiver is presented. The NBI is modelled as a single-tone sinusoid. The information bearing component of the received signal is removed prior to the estimation of NBI. However, this solution presents great limitations in the single-tone sinusoid modelling; in reality, interference comes in a great number of waveforms.