Closed-Form Expressions for Channel Shortening Receivers Using A Priori Information

Channel shortening has been studied in the context of ISI and MIMO channels as a means to compute a posteriori probabilities with a BCJR algorithm at a reduced computational complexity. This is done by considering an approximate channel response of reduced length. In a turbo receiver, soft a priori information can be linearly combined with the received sequence to form a new input to the BCJR trellis-based processing. In this letter, we provide closed-form expressions for the channel shortening filters using a generalized mutual information objective function. The proposed receiver allows a complexity reduction with respect to numerical optimization approaches which may also present stability, precision and convergence issues

Blind Symbol Rate Estimation of Faster-than-Nyquist Signals Based on Higher-Order Statistics

Both faster-than-Nyquist (FTN) and cognitive radio go towards an efficient use of spectrum in radio communications systems at the cost of an added computational complexity at the receiver side. To gain the maximum potential from these techniques, non-data-aided receivers are of interest. In this paper, we use fourth-order statistics to perform blind symbol rate estimation of FTN signals. The estimator shows good performance results for moderate system's densities beyond the Nyquist rate and for a reasonable number of received samples

Faster-than-Nyquist Signaling: on Linear and Non-Linear Reduced-Complexity Turbo Equalization

In the framework of digital video broadcasting by satellite - second generation (DVB-S2), we analyze a faster-than-Nyquist (FTN) system based on turbo equalization and low-density parity-check (LDPC) codes. Truncated maximum a posteriori (MAP) and minimum mean square error (MMSE) equalizers provide a reduced-complexity implementation of the FTN system. On the other hand, LDPC codes allow us to demonstrate attractive performance results over an additive white Gaussian noise (AWGN) channel while increasing spectral efficiency beyond the Nyquist rate and keeping a complexity comparable to that of a current DVB-S2 mode

Transmission au-delà de la cadence de Nyquist pour les liaisons vidéo pour drones

Les techniques de transmission au-delà de la cadence de Nyquist ou Faster-Than-Nyquist (FTN) constituent une alternative prometteuse pour améliorer l'efficacité spectrale des systèmes de transmission au prix d'une augmentation de la complexité de décodage des données. Dans le contexte de la diffusion vidéo en temps réel pour drones, le FTN présente plusieurs avantages : (i) une augmentation de la capacité des systèmes proche de la limite de Shannon par rapport à des techniques de transmission orthogonales, (ii) une protection de la forme d'onde contre l'interception grâce à la rupture de la relation entre rythme symbole et bande occupée. Au cours de cet exposé, un schéma de réalisation efficace basé sur un turbo égaliseur (MMSE-MAP)/LDPC sera présenté. Afin de satisfaire la contrainte de délai imposée par l'application, les performances du système seront évaluées en utilisant des trames courtes. De plus, une mise en perspective du standard DVB-RCS2 permettra d'évaluer l'apport du système FTN dans un contexte de transmission à longue portée

Performance Evaluation of a Faster-than-Nyquist System Based on Turbo Equalization and LDPC Codes

In the frame of digital video broadcasting by satellite - second generation (DVB-S2), a faster-than-Nyquist (FTN) system based on turbo equalization and low-density parity-check (LDPC) codes is proposed. Truncated maximum a posteriori (MAP) and minimum mean square error (MMSE) equalizers provide a reduced complexity implementation of the FTN system. On the other hand, LDPC codes allow us to demonstrate attractive performance results over an additive white Gaussian noise (AWGN) channel while increasing spectral efficiency beyond the Nyquist rate up to 60 % and keeping a complexity comparable to a current DVB-S2 modem