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Faster than Nyquist (FTN) signaling is a nonorthogonal transmission scheme, in which the pulses appear faster than the rate known from the Nyquist criterion. The FTN signaling offers a higher data rate compared to Nyquist signaling but results in intersymbol interference due to the violation of the Nyquist theorem. In this paper, we investigate the FTN system performance in terms of bit error rate (BER), peakto-average power ratio (PAPR), spectral efficiency and compare these with Nyquist signaling given that both systems have the same pulse shape and data rate. Simulation results confirm that FTN signaling system has higher spectral efficiency than the Nyquist signaling system. Furthermore, FTN signaling offers benefits in terms of BER and PAPR by using a pulse shaping filter with a large excess bandwidth factor. The PAPR and BER gains achieved by FTN increase with rising the excess bandwidth factor of the applied pulse shape. In the case of using appropriate pulse shape with high energy concentration in time domain, the PAPR and BER gains given by FTN can be achieved more than 2 dB and 3 dB, respectively.

To achieve the full multiplexing gains or the degrees of freedom of the K-multiuser MIMO interference channel, the interference alignment technique has been proposed and investigated. The main idea of interference alignment is to design the pre-coder at each transmitter, so that each receiver can align all interference from undesired transmitters in interference subspaces by exploiting knowledge of the channel state information (CSI) of all transmission links. Currently, a closed-form solution for the pre-coding filters exists only for the case of up to three users and provides poor sum-rate performance compared to iterative algorithms. Furthermore, all available algorithms for interference alignment were investigated only for the case, where each transmitter sends only one data stream. In this paper, the MMSE-based interference alignment is exploited to improve the BER and sum-rate performance of the system especially in the low SNR regime. This paper focuses on a multiuser MIMO UWB system based on MB-OFDM with arbitrary number of independent data streams per user. The simulation results confirm that the MMSE-based interference alignment provides sum-rate and BER superior to Orthogonal Frequency-Division Multiple Access (OFDMA) at marginal performance degradation.

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