Circularly Shifted Block QAM-FBMC System with Two-Stage Detector

A block quadrature amplitude modulation based filter bank multi-carrier (QAM-FBMC) system with circularly shifted prototype filters is proposed. Since the circularly shifted prototype filters do not satisfy the complex orthogonality, the intrinsic interference occurs in the block QAM-FBMC system. Additionally, the inter-block interference (IBI) and inter-carrier interference (ICI) occur in the multipath fading channels since the circularly shifted prototype filters degrade the localization in the time domain. In order to reduce the intrinsic interference, we adopt a frequency domain minimum mean-squared error receiver which is derived from an effective channel matrix which is represented by the transceiver structure and channels. Then, the two-stage detector is applied to reduce IBI from the preceding block and suppress ICI which occurs from the loss of signal in the current block. Numerical results show that the proposed block QAM-FBMC system achieves low out-of-band emission similar to the conventional offset QAM-FBMC (OQAM-FBMC) system and almost the same bit error rate performances as the orthogonal frequency division multiplexing with a cyclic prefix (CP-OFDM) in the multipath fading channels. Also, the block QAM-FBMC system obtains higher spectral efficiency by eliminating the transition time compared to the QAM-FBMC and OQAM-FBMC systems.