Narrowband Interference Suppression in MIMO Systems

Multiple Input Multiple Output (MIMO) communication technology has received recently significant attention triggered by the rapid development of Orthogonal Frequency Division Multiplexing (OFDM) broad-band wireless and high speed wireline communication systems. Such systems are very sensitive to Narrowband Interferences (NBI) due to their relatively low transmission power. This type of signal interference can be found in the new unlicensed frequency bands, e.g., the Industrial Scientific Medical (ISM) band, coming from systems such as Bluetooth or microwave ovens which interfere with OFDM based Wireless Local Area Networks (WLAN), like Hiperlan II. Other examples of NBI, typical for Digital Subscriber Line (DSL) communications, are strong Radio Frequency Interferences (RFI) from short-wave radio, Citizen's Band (CB) radio and amateur “ham” radio which interfere with Hybrid Fiber Coaxial (HFC) networks and high speed DSL. Ineffective shielding of a cable network may also cause the ingress from external home electrical devices, such as cordless phones, TVs and computers. Let’s consider a strong NBI signal which resides within the same frequency band as a wideband OFDM signal. In this case, severe Signal to Noise Ratio (SNR) degradation is likely to occur across all OFDM subcarriers due to spectral leakage of the NBI signal from block processing in the OFDM receiver. In Fig. 1, the magnitude-squared of the received