Alzaq and Ustundag EURASIP Journal on Wireless Communications and Networking (2017) 2017:120 DOI 10.1186/s13638-017-0902-7 RESEARCH Open Access Very-low-SNR cognitive receiver based on wavelet preprocessed signal patterns and neural network Husam Y. Alzaq * and B. Berk Ustundag Abstract A pattern-based cognitive communication system (PBCCS) that optimizes non-periodic RF waveforms for security applications is proposed. PBCCS is a cross-layer approach that merges the channel encoding and modulation. The transmitter encodes sequences of bits into continuous signal patterns by selecting the proper symbol glossaries. The cognitive receiver preprocesses the received signal by extracting a limited set of wavelet features. The extracted features are fed into an artificial neural network (ANN) to recover the digital data carried by the distorted symbol. The PBCCS system offers a flexible management for robustness against a high noise level and increases the spectral efficiency. In this study, the spectral efficiency and robustness of a PBCCS scheme for an additive white Gaussian noise (AWGN) channel is investigated. The results show that at an SNR of -5 dB, a 3-bit glossary achieves a bit error rate (BER) of 10 -5 . Also, the link spectral efficiency (LSE) of the proposed system is 2.61 bps/Hz. Keywords: Cognitive radio (CR), Pattern-based cognitive communication system (PBCCS), Artificial neural network, Wavelet decomposition, Digital signal processing (DSP), Very-low-SNR 1 Introduction The efficiency of bandwidth utilization takes an impor- tant role in spectrum management [1, 2]. Due to fixed spectrum assignment policies and its inadequate to meet an unexpected increase in the number of higher-data- rate devices, the spectrum is inefficiently used. Cognitive radio (CR) [3–6] was proposed as a promising solution to alleviate the spectrum scarcity problem through dynamic management of the available spectrum. The pioneer work of Mitola et al. [3] led to an efficient utilization of the spec- tral bandwidth by allowing the secondary user (SU), who is not serviced, to detect and access the primary network spectrum gaps. CR allows detection of the state of the spectrum to adjust its own system parameters (transmis- sion power, frequency band, throughput and modulation scheme) in real time [7]. The result is that the utilization of the spectral bandwidth is performed with the soft- ware flexibility in an adaptive manner with respect to the system parameters. *Correspondence: alzaq@itu.edu.tr Department of Computer Engineering, Faculty of Computer Engineering, Istanbul Technical University, Maslak, Ayazaga, 34469 Istanbul, Turkey However, efficient spectral bandwidth usage under the influence of higher noise is not the major consideration of CR. Claude Shannon [8] showed that the SNR is a lead- ing factor that influences the link spectral efficiency (LSE), η = C/B, (in bps/Hz). SNR also limits the channel capac- ity. Therefore, the utilization of spectral bandwidth and the robustness to high SNR level are the keys to maximize the channel capacity. Thus, a pattern-based cognitive communication system (PBCCS) was introduced to optimize the overall spec- tral efficiency with respect to SNR [9, 10]. It is inspired by the recognition capability of humans to concentrate on a single conversation irrespective of the surround- ing loudness. If human ears hear sounds from different sources, the brain chooses to pay attention to a particu- lar voice amongst a whole range of sound streams in an environment. Similar to human cognitive capabilities, the communication system in PBCCS selectively recognizes and recovers the communication signal(s) a into known symbol(s), even within the same frequency range. © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.