Všechny publikace

Linear precoding for asynchronous WPNC 2-source hierarchical multiple access channel

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper addresses the problem of asynchronous reception in a 2-source Hierarchical MAC (H-MAC) in the context of a Wireless Physical Layer Network Coded (WPNC) system with a Hierarchical Decode and Forward (HDF) relaying strategy. This work is motivated by the difficulty of precise synchronization among different sources of an H-MAC stage. Because of the non-orthogonal nature of the H-MAC even when the individual delays are known to the receiver a simple compensation is not possible. Compensation at the transmitters would require a channel state feedback channel which is not always available. In some scenarios with varying distances between individual nodes even the knowledge of the delays to the transmitter, a simple time base adjustment would not solve the problem w.r.t. all participating receivers. In this work, we assume delays of a fraction of the symbol time duration and propose a delay-independent transmitter-side linear precoding together with symbol-spaced and fractionally-spaced processing at the receiver. For each approach, we derive an equivalent channel model and analyze its properties in the case of an root-raised-cosine (RRC) modulation pulse. The proposed techniques are numerically evaluated in terms of Hierarchical Bit Error Rate (H-BER). We show that in some cases the asynchronous reception can lead to a performance boost.

Noncoherent WPNC 2-source MAC channel demodulation methods

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper addresses the problem of differential demodulation in a 2-source Hierarchical MAC (H-MAC) in the context of a Wireless Physical Layer Network Coded system with Hierarchical Decode and Forward relaying strategy. We consider a parametric H-MAC with known attenuation values but unknown phases. Component phases have generally a strong impact on the resulting superposed constellation and need to be accurately estimated to facilitate a coherent demodulation. The use of a differentially encoded modulation eliminates the need of precise channel phase tracking, which is a nontrivial problem in the WPNC scenario. At the same time it can operate with the same 3dB penalty as in a differential single user case. In this paper we summarize several differential demodulation procedures and additionally introduce new ad hoc methods, which can substantially reduce the computation complexity of the demodulation. We compare the various demodulation algorithms by means of evaluating the hierarchical bit error rate performance for different channel states. Additionally we analyze the robustness of differential demodulation w.r.t. channel phase noise.

Closed-Form Differential Hierarchical Demodulator of 2-source Hierarchical-MAC Channel

  • DOI: 10.1109/LCOMM.2021.3105814
  • Odkaz: https://doi.org/10.1109/LCOMM.2021.3105814
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper addresses a problem of differential demodulation in a 2-source Hierarchical MAC (H-MAC) in the context of a Wireless Physical Layer Network Coded system with Hierarchical Decode and Forward strategy. We assume a parametric H-MAC with known attenuations but unknown phases. Component phases have generally strong impact on the resulting superposed constellation which poses high demands on the accuracy of their estimation. In this paper we propose multiple suboptimal closed-form differential demodulation methods which do not require explicit phase estimation and thus substantially simplify the receiver processing. We analyze and compare their performance. Particularly we measure the resulting hierarchical bit error rate for all proposed demodulation methods for different scenarios of a particular symbol alphabet and channel attenuation values. For comparison we include a reference scenario of a fully coherent demodulation.

SDR verification of noncoherent WPNC 2-source MAC channel reception

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper considers a noncoherent reception in a parametrized hierarchical MAC (H-MAC) stage in Wireless Physical Layer Network Coding (WPNC) networks with Hierar- chical Decode and Forward (HDF) relay strategy. We employ a differential PSK modulation on two source node transmitters and perform a hierarchical target symbol demodulation at a relay without the need of an explicit estimation of channel phases. Relative channel phase parametrization has generally a nonlinear impact on the resulting constellation, which poses high demands on its estimation accuracy in coherent reception settings. In this paper we present the results of an over-the-air verification of proposed differential demodulation algorithms together with a comparison with respect to results obtained by a computer simulation.

SDR verification of Hierarchical Decision Aided 2-Source BPSK H-MAC CSE with Feed-Back Gradient Solver for WPNC Networks

  • DOI: 10.13164/re.2020.0573
  • Odkaz: https://doi.org/10.13164/re.2020.0573
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper considers a channel state estimation (CSE) pro- blem in a parametrized Hierarchical MAC (H-MAC) stage in Wireless Physical Layer Network Coding (WPNC) networks with Hierarchical Decode and Forward (HDF) relay strategy. The primary purpose is to present the results of a non-pilot based phase estimator performance evaluation. In particular, the performance comparison of a Matlab simulation and an over the air transmission using USRP N210 transceivers in terms of mean square error (MSE) and bit error rate (BER). Also, we analyze the properties of the Cramer Rao Lower Bound (CRLB) w.r.t. different channel parametrizations.

Update-Based Machine Learning Classification of Hierarchical Symbols in a Slowly Varying Two-Way Relay Channel

  • DOI: 10.3390/math8112007
  • Odkaz: https://doi.org/10.3390/math8112007
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    This paper presents a stochastic inference problem suited to a classification approach in a time-varying observation model with continuous-valued unknown parameterization. The utilization of an artificial neural network (ANN)-based classifier is considered, and the concept of a training process via the backpropagation algorithm is used. The main objective is the minimization of resources required for the training of the classifier in the parametric observation model. To reach this, it is proposed that the weights of the ANN classifier vary continuously with the change of the observation model parameters. This behavior is then used in an update-based backpropagation algorithm. This proposed idea is demonstrated on several procedures, which re-use previously trained weights as prior information when updating the classifier after a channel phase change. This approach successfully saves resources needed for re-training the ANN. The new approach is verified via a simulation on an example communication system with the two-way relay slowly fading channel.

Performance analysis of hierarchical decision aided 2-source BPSK H-MAC CSE with feed-back gradient solver for WPNC networks

  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    The paper addresses a problem of channel phase estimation in a 2-source Hierarchical MAC channel in a Wireless Physical Layer Coded (WPNC) system with Hierarchical Decode and Forward strategy. We assume a non-pilot based estimator, a pilot based one would require orthogonal pilot signal resources which are not available in WPNC system. In such a system, the receiving relay node does not have the individual source data available and the only data related estimator aid is a many-to-one network coded data function. We analyze the performance of estimator with feed-back gradient solver. Particularly we analyze: (1) mean square error (MSE) performance including its relation to Cramer-Rao Lower Bound (CRLB), and (2) we analyze properties of ambiguity modes of the estimator.

Performance analysis of hierarchical decision aided 2-source BPSK H-MAC CSE with feed-back gradient solver for WPNC networks

  • Autoři: Ing. Petr Hron, prof. Ing. Jan Sýkora, CSc.,
  • Publikace: Proceedings of 2019 IEEE Microwave Theory and Techniques in Wireless Communications MTTW 2019. IEEE (Institute of Electrical and Electronics Engineers), 2019. p. 72-75. ISBN 978-1-7281-4473-3.
  • Rok: 2019
  • DOI: 10.1109/MTTW.2019.8897247
  • Odkaz: https://doi.org/10.1109/MTTW.2019.8897247
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    The paper addresses a problem of channel phase estimation in a 2-source Hierarchical MAC channel in a Wireless Physical Layer Coded (WPNC) system with Hierarchical Decode and Forward strategy. We assume a non-pilot based estimator, a pilot based one would require orthogonal pilot signal resources which are not available in a WPNC system. In such a system,the receiving relay node does not have the individual source data available and the only data related estimator aid is a many-to-one network coded data function. We analyze the properties of the estimator metric and the performance of the estimator with a feed-back gradient solver. Particularly we analyze: (1) mean square error (MSE) performance including its relation to Cramer-Rao Lower Bound (CRLB), and (2) we analyze properties of ambiguity modes of the estimator.

Achievable Rates for HDF WPNC Strategy with Hierarchical Bit-Wise Network Coding Maps for Higher-Order Constellations in H-MAC Channel with Relative Fading

  • Autoři: prof. Ing. Jan Sýkora, CSc., Ing. Petr Hron,
  • Publikace: 2018 European Conference on Networks and Communications, EuCNC 2018. IEEE (Institute of Electrical and Electronics Engineers), 2018. p. 11-15. ISSN 2475-6490. ISBN 978-1-5386-1478-5.
  • Rok: 2018
  • DOI: 10.1109/EuCNC.2018.8443240
  • Odkaz: https://doi.org/10.1109/EuCNC.2018.8443240
  • Pracoviště: Katedra radioelektroniky
  • Anotace:
    The paper addresses Wireless Physical Layer Network Coding (WPNC) with Hierarchical Decode and Forward (HDF) strategy. We analyze achievable hierarchical rates in one stage hierarchical MAC (H-MAC) channel for higher order component constellations with bit-wise Hierarchical Network Code (HNC) maps. This is motivated by a possible application of state-of-the-art binary (e.g. LDPC) codes over higher order constellations. We show that the bit-mapped binary codes do not have the same achievable rates as direct higher-order codes. On top of this, the individual bits in the HNC map might provide very uneven performance and it strongly depends on the combination of component alphabets. The results are supported by a validation with practical LDPC codes.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk