The Discrete Fourier Transform (DFT) algorithm is widely used in signal processing and communication systems to transform the signal to the frequency-domain. As real-time signal analysis is required for fast processing, several recursive algorithms were proposed to perform the calculation with overlapping sequences in a sliding manner. One Sliding DFT (SDFT) method is the Hopping DFT (HDFT), where the DFT calculations are not evaluated sample-by-sample but with longer steps, thus further reducing the computational complexity compared to the other SDFT algorithms. This paper analyses the effect of fixed-point roundoff error in the HDFT algorithm, including the Updating Vector Transform (UVT) block. A closed-form expression for the resulting quantization noise power at the output of the HDFT algorithm is provided, which is validated through simulations. The results show that the roundoff error can be determined based on the number and size of the hops, the window size, and the number of fractional bits used in the quantization process.

Filter Bank Multi-Carrier (FBMC) modulation is a promising modulation technique that is expected to play an important role in future 5G systems alongside Orthogonal Frequency Division Multiplexing (OFDM). In spite of its attractive properties, mainly the signal is well localized in frequency and time, a major drawback to FBMC is the high signal processing load compared with OFDM. Although FBMC using PolyPhase Network (PPN) requires lower computational complexity compared with Frequency Spreading (FS) implementations, FS-FBMC receivers have shown better performance compared with PPN-FBMC, especially when equalization is also considered. In this paper, we focus on reducing the complexity of FS-FBMC receivers by applying Hopping Discrete Fourier Transform (HDFT) instead of Fast Fourier Transform (FFT). Furthermore, we derive an improved HDFT based on the split radix method and analyze the resulting structure in terms of computational complexity. We show that the proposed HDFT based FS-FBMC receiver has a lower complexity and introduces a smaller delay in processing time compared to the conventional FFT based FS-FBMC receiver.

With the opening up of white spaces, efficient use of the fragmented spectrum - TV white space in particular - has become an extremely important focus of research. Apart from efficient spectrum usage, special care needs to be taken to maintain low out-of-band radiation to avoid harmful interference to incumbent services like TV signals and wireless microphones. For this reason, a flexible digital radio with multicarrier modulation scheme is the only solution. In this paper, we show the performance of two innovative multicarrier systems, Filter Bank Multi Carrier (FBMC) and Generalized Frequency Division Multiplexing (GFDM). A simple interference cancellation technique called serial inter-carrier interference cancellation scheme has been used to improve performance of the GFDM system. Channel equalization techniques have been implemented for FBMC.

Cognitive radio (CR) is one of the promising future possibilities for wireless broadcasting and communication. One of the key issues is the physical layer, where the modulation waveform best suitable for the CRs has to be chosen. In this paper we present the most promising modulation schemes with their advantages and disadvantages. Orthogonal frequency division multiplexing (OFDM) is the most favored modulation nowadays for high speed digital communications, but many other modulation techniques show advantages over it. Notably DFT-spread OFDM (DFTS-OFDM), Constant Envelope OFDM (CE-OFDM) and Filter Bank Multicarrier (FBMC).We give an overview of these schemes to see which is the most suitable with a given set of parameters or in a specific scenario. We compare these methods via spectral characteristics, signal metrics and system performance in the presence of non-linear distortions.

In this paper, we briefly describe four modulation schemes (Orthogonal Frequency Division Multiplexing (OFDM), DFT-spread OFDM, Constant Envelope OFDM (CEOFDM)and Filter Bank Multicarrier (FBMC)) for Cognitive Radios (CR) in white space. In the first part, we give a short overview of the main signal processing blocks and signal properties. Then, we compare them by means of sensitivity to various synchronization errors such as timing error, frequency mismatch, phase noise and IQ-imbalance. These errors can be caused by either non-ideal analog components, movement of the transceiver or imperfect synchronization. Each synchronization error is examined separately; the performance is verified by means of bit error rates. Each modulation has a different sensitivity for a given type of synchronization error, which has to be taken into account when choosing the most suitable modulation scheme for a given application.