Multicarrier faster-than-Nyquist transceivers: hardware architecture and performance analysis

This paper evaluates the hardware aspects of multicarrier faster-than-Nyquist (FTN) signaling transceivers. The choice of time-frequency spacing of the symbols in an FTN system for improved bandwidth efficiency is targeted towards efficient hardware implementation. This work proposes a hardware architecture for the realization of iterative decoding of FTN multicarrier modulated signals. Compatibility with existing systems has been considered for smooth switching between the faster-than-Nyquist and orthogonal signaling schemes. One such being the use of FFTs for multicarrier modulation. The performance of the fixed point model is very close to that of the floating point representation. The impact of system parameters such as number of projection points, time-frequency spacing, finite wordlengths and their design trade-offs for reduced complexity iterative decoders in FTN systems have been investigated. The FTN decoder has been designed and synthesized in both 65nm CMOS and FPGA. From the hardware resource usage numbers it can be concluded that FTN signaling can be used to achieve higher bandwidth efficiency with acceptable complexity overhead

Faster-than-Nyquist system design for next generation fixed transmission networks

Monumental growth of traffic load in the communication networks has heavily strained the existing fixed transmission network infrastructure. Such enormous surge of traffic warrants enabling higher data rates in these networks, where predominantly optical fibers and microwave radio links are deployed. With bandwidth becoming an expensive resource, and owing to the practical constraints of the electronic components, employing high baud rates alone may be insufficient to accomplish such high throughputs in these optical fiber communication (OFC) and microwave communication (MWC) systems. Hence, increasing the spectral efficiency (SE) is a key requirement for these networks. For this pursuit, this thesis investigates the application of Faster-than-Nyquist (FTN) signaling in fixed transmission networks, with an objective to achieve high SE and data rates. FTN is an enabling technology that offers SE improvements by allowing controlled overlap of the transmitted symbols in time or frequency or both. OFC and MWC systems are suitable platforms for the introduction of FTN signaling, since FTN can moderate the need for higher order modulation formats, which are sensitive to phase noise and fiber nonlinearity. In this thesis, we combine the concept of FTN signaling with other conventional throughput increasing techniques, such as polarization multiplexing and multicarrier transmission, to further the data rate improvements. However, FTN introduces inter-symbol-interference and/or inter-carrier interference. Moreover, integrating FTN signaling with polarization multiplexing and multicarrier transmission complicates the realistic implementation. OFC and MWC systems also pose additional practical challenges stemming from the specific communication channel environments and the transceiver components. If not successfully mitigated, all of these impairments and non-idealities significantly deteriorate the performance of the communication links. In this thesis, we address each of these unique challenges through suitable mitigation algorithms, to facilitate an efficient FTN transmission. For this, we present sophisticated system designs equipped with powerful digital signal processing tools. We numerically evaluate the performance of our proposed methods by simulating realistic OFC and MWC systems. The simulation results indicate that our proposed spectrally efficient designs offer significant performance advantages over existing competitive schemes.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Improving Spectral Efficiency While Reducing PAPR Using Faster-Than-Nyquist Multicarrier Signaling

International audienceMulticarrier modulations are widely used in mobile radio applications due to their adaptability to the time-frequency characteristics of the channel, thus enabling low-complexity equalization. However, their intrinsically high peak-to-average power ratio (PAPR) is a major drawback with regard to implementation issues (e.g., power amplification efficiency, regulatory constraints...). In this paper, we confirm that the PAPR can be decreased as the signal-ing density (i.e., spectral efficiency at fixed constellation size) increases, even in the case where symbols cannot be perfectly reconstructed using a linear system. In such a two-dimensional generalization of faster-than-Nyquist (FTN) systems, PAPR distribution models from the literature are confirmed by simulation results. Furthermore, for a fixed number of subcarriers, we show that a sufficient condition to yield the optimal PAPR distribution at the output of a critically sampled transmitter is to specify pulse shapes as tight frames. Finally, simulation are performed in the more realistic case of an oversampled transmitted signal

Improving spectral efficiency using hybrid system solutions

As frequency bands become increasingly crowded, one of the major research challenges for future wireless communication networks is how to use the radio frequency bands more efficiently. In wireless communication networks, spectral efficiency can be improved either through frequency reuse technologies such as cognitive radio and multi-user techniques or by using technologies to increase the data rate. However, in this regard there is still room for further improvements, and thus, development of novel hybrid solution approaches to enhance spectral efficiency for future wireless communication networks is put into the focus of this dissertation. In this thesis, a multi-tier heterogeneous network with macro cells, small cells and relays is addressed. In order to improve spectral efficiency in a single carrier system, the non-orthogonal transmission scheme Faster-than Nyquist (FTN) signaling is investigated. Furthermore, novel hybrid interference mitigation approaches to achieve a spectral efficiency improvement in multi-user multicarrier Multiple-Input and Multiple-Output (MIMO) systems by using cognitive radio and relay technology are proposed

Analysis of the optimal linear system for multicarrier FTN communications

National audienceFaster-than-Nyquist signalization allows for a better spectral efficiency at the expense of an increased complexity. Regarding multicarrier communications, previous work mainly relied on the study of non-linear systems exploiting coding and/or equalization techniques, with no particular optimization regarding the linear part of the system. In this paper, we analyse the behavior of the optimal linear multicarrier system when used with non-linear receiving structures (iterative decoding and direct feedback equalization), or in a standalone fashion. We also investigate the limits of the assumptions commonly made for the implementation of such non-linear systems. The use of this optimal linear system allows for a closed-form expression of the bit-error probability which can be used to predict the performances and help the design of coded systems. Our work also highlights the great performance/complexity trade-off offered by decision feedback equalization in a faster-than-Nyquist context.Les communications au delà de la cadence de Nyquist permettent une augmentation de l'efficacité spectrale en contre-partie d'une complexité plus élevée. Concernant les communications multiporteuses, les travaux menés jusque là se sont principalement focalisés sur l'étude des systèmes non-linéaires exploitant des techniques de codage et/ou d'égalisation, sans considération ou optimisation particulière de la partie linéaire du système. Dans cet article, nous analysons le compor-tement du système linéaire multiporteuse optimal lorsqu'il est utilisé seul ou avec des structures de réception non-linéaires (décodage itératif et égalisation à retour de décision). Nous nous intéressons également aux limites des hypothèses com-munément utilisées lors de l'implémentation de ces systèmes non-linéaires. L'utilisation du système linéaire optimal permet une expression analytique de la probabilité d'erreur qui peut être utilisée pour prédire les performances et aider la conception de systèmes codés. Ce travail met aussi en avant le bon compromis performances/complexité offert par l'égaliseur à retour de décision dans le contexte des communications au-delà de la cadence de Nyquist