Efficient implementation of filter bank multicarrier systems using circular fast convolution

In this paper, filter bank-based multicarrier systems using a fast convolution approach are investigated. We show that exploiting offset quadrature amplitude modulation enables us to perform FFT/IFFT-based convolution without overlapped processing, and the circular distortion can be discarded as a part of orthogonal interference terms. This property has two advantages. First, it leads to spectral efficiency enhancement in the system by removing the prototype filter transients. Second, the complexity of the system is significantly reduced as the result of using efficient FFT algorithms for convolution. The new scheme is compared with the conventional waveforms in terms of out-of-band radiation, orthogonality, spectral efficiency, and complexity. The performance of the receiver and the equalization methods are investigated and compared with other waveforms through simulations. Moreover, based on the time variant nature of the filter response of the proposed scheme, a pilot-based channel estimation technique with controlled transmit power is developed and analyzed through lower-bound derivations. The proposed transceiver is shown to be a competitive solution for future wireless networks

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing

To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation. This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed. The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms. In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels

Filter Bank-based Multicarrier Modulation for Multiple Access in Next Generation Satellite Uplinks: A DVB-RCS2-based Experimental Study

In the context of the ongoing evolution of satellite communication systems to their next generation, involving higher data rates and increased flexibility, it is of interest to study in depth the applicability of multiple access (MA) multi-carrier modulation (MCM) schemes that have shown promise to meet the requirements of the future terrestrial networks. A comparative study of MA schemes employing offset quadrature amplitude modulation (OQAM)-based filter bank multicarrier (FBMC/OQAM) and classical orthogonal frequency division multiplexing (OFDM) is presented in this paper. The considered air-interface follows the latest Digital Video Broadcasting (DVB) family of standards for the satellite return link. Considering a high-power amplifier (HPA) of a very small aperture terminal (VSAT), the performance of the two MA schemes is evaluated in an asynchronous multiuser satellite environment involving time and frequency synchronization errors. Our results indicate that while FBMC-based MA (FBMA) is more sensitive near saturation and in the presence of timing errors, it is more robust to frequency offset errors not only in terms of the Total Degradation (TD) but also in terms of the Spectral Efficiency (SE), since it only needs minimal guard bands among the different users. This is a preliminary study of the potential gains from the integration of the FBMA technology in the satellite infrastructures and standards. Future work will include results on single-carrier modulation (SCM) FBMA as well

Combined Pilot-Aided and Decision-Directed Carrier Synchronization for Filtered Multitone Wireless Systems

This paper focuses on the issue of carrier frequency synchronization for filtered multitone wireless transmission over time-frequency selective fading channels. Rather than either relying only on known pilot symbols multiplexed within the transmitted burst or exploiting the specific signal structure in a blind mode, the estimation algorithm we pursue is derived from the maximum likelihood principle and takes advantage of both pilot symbols and also the unknown information-bearing symbols through specific differential decision-directed processing. When compared to conventional pilot-based methods, the proposed approach improves the frequency acquisition range without degrading estimation accuracy at even lower cost in terms of computational complexity