ShiftFFT: An Efficient Approach to Mitigate Adjacent Channel Interference in OFDM Systems

Adjacent channel interference (ACI) in wireless systems is commonly mitigated through the use of guard bands and filters. Guard bands are not used for any transmissions and are therefore wasted spectrum. The use of sharp filters can reduce the size of required guard bands but they are costly and often not present in devices that are already deployed. We focus on OFDM wireless systems, which form the basis for almost all modern wireless networks, and pro- pose a novel technique called ShiftFFT that can be deployed at an OFDM receiver to mitigate ACI from legacy OFDM transmitters. ShiftFFT exploits the presence of over-provisioned cyclic prefixes in most OFDM wireless standards to optimize the starting time of the FFT operation at the receiver, which we show to have significant potential to reduce the amount of guard band required to avoid ACI and thereby enable efficient spectrum use. We evaluate ShiftFFT with a SDR testbed and using simulations across diverse settings, and show that using it can significantly reduce the guard band required by at least 10MHz in most cases while maintaining the same packet error rate performance.