Time-Frequency Warped Waveforms for Well-Contained Massive Machine Type Communications

This paper proposes a novel time-frequency warped waveform for short symbols, massive machine-type communication (mMTC), and internet of things (IoT) applications. The waveform is composed of asymmetric raised cosine (RC) pulses to increase the signal containment in time and frequency domains. The waveform has low power tails in the time domain, hence better performance in the presence of delay spread and time offsets. The time-axis warping unitary transform is applied to control the waveform occupancy in time-frequency space and to compensate for the usage of high roll-off factor pulses at the symbol edges. The paper explains a step-by-step analysis for determining the roll-off factors profile and the warping functions. Gains are presented over the conventional Zero-tail Discrete Fourier Transform-spread-Orthogonal Frequency Division Multiplexing (ZT-DFT-s-OFDM), and Cyclic prefix (CP) DFT-s-OFDM schemes in the simulations section.Comment: This paper has been accepted by IEEE JSAC special issue on 3GPP Technologies: 5G-Advanced and Beyond. Copyright may be transferred without notice, after which this version may no longer be accessibl

Centralized and Decentralized ML-Enabled Integrated Terrestrial and Non-Terrestrial Networks

Non-terrestrial networks (NTNs) are a critical enabler of the persistent connectivity vision of sixth-generation networks, as they can service areas where terrestrial infrastructure falls short. However, the integration of these networks with the terrestrial network is laden with obstacles. The dynamic nature of NTN communication scenarios and numerous variables render conventional model-based solutions computationally costly and impracticable for resource allocation, parameter optimization, and other problems. Machine learning (ML)-based solutions, thus, can perform a pivotal role due to their inherent ability to uncover the hidden patterns in time-varying, multi-dimensional data with superior performance and less complexity. Centralized ML (CML) and decentralized ML (DML), named so based on the distribution of the data and computational load, are two classes of ML that are being studied as solutions for the various complications of terrestrial and non-terrestrial networks (TNTN) integration. Both have their benefits and drawbacks under different circumstances, and it is integral to choose the appropriate ML approach for each TNTN integration issue. To this end, this paper goes over the TNTN integration architectures as given in the 3rd generation partnership project standard releases, proposing possible scenarios. Then, the capabilities and challenges of CML and DML are explored from the vantage point of these scenarios.Comment: This work was supported in part by the Scientific and Technological Research Council of Turkey (TUBITAK) under Grant No. 5200030 with the cooperation of Vestel and Istanbul Medipol Universit

An efficient joint channel estimation and decoding algorithm for turbo-coded space-time orthogonal frequency division multiplexing receivers

The challenging problem in the design of digital receivers of today's and future high-speed, high data-rate wireless communication systems is to implement the optimal decoding and channel estimation processes jointly in a computationally feasible way. Without realising such a critical function perfectly at receiver, the whole system will not work properly within the desired performance limits. Unfortunately, direct implementation of such optimal algorithms is not possible mainly due to their mathematically intractable and computationally prohibitive nature. A novel algorithm that reaches the performance of the optimal maximum a posteriori (MAP) algorithm with a feasible computational complexity is proposed. The algorithm makes use of a powerful statistical signal processing tool called the expectation?maximisation (EM) technique. It iteratively executes the MAP joint channel estimation and decoding for space?time block-coded orthogonal frequency division multiplexing systems with turbo channel coding in the presence of unknown wireless dispersive channels. The main novelty of the work comes from the facts that the proposed algorithm estimates the channel in a non-data-aided fashion and therefore except a small number of pilot symbols required for initialisation, no training sequence is necessary. Also the approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen?Loeve (KL) orthogonal expansion and finds MAP estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MAP estimator. Moreover, optimal rank reduction is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the iterative estimation approach

Space-Time Block Code Classification for MIMO Signals

22nd IEEE Signal Processing and Communications Applications Conference (SIU) -- APR 23-25, 2014 -- Karadeniz Teknik Univ, Trabzon, TURKEYWOS: 000356351400489Signal identification techniques developed for the purpose of blind and noncooperative identification of the transmission parameters of unknown communication signals have been employed both in military and civilian applications. Blind identification of the Space-Time Block Codes (STBC) used in a multiantenna transmisson can be regarded as one of the new and most significant challenges presented to the signal identification systems by the Multiple-Input-Multiple-Output (MIMO) transmission systems. In this work, we present novel STBC classification algorithms that exploit the cyclostationary characteristics of the coded transmit signals as discriminating features.IEEE, Karadeniz Tech Univ, Dept Comp Engn & Elect & Elect Eng

Over-the-Air OFDM-IM Through Frequency Mixing and Modulating Reconfigurable Intelligent Surfaces

Beyond fifth-generation (5G) wireless communication, reconfigurable intelligent surfaces (RIS) have emerged as a transformative technology that can redefine how we interact with and harness electromagnetic waves. Advancements in meta-materials and metasurfaces have brought about exceptional flexibility in controlling electromagnetic waves at scales smaller than the wavelength. The frequency-mixing RIS (FMx-RIS) has been introduced, considering the benefits of programmable metasurfaces. This method introduces additional frequencies into the original signal, making the communication environment non-linear. Among the different multicarrier transmission methods, orthogonal frequency division multiplexing (OFDM) has become the most commonly used option in wireless communications due to reducing intersymbol interference caused by the frequency selectivity of wireless channels. Upon examining the structure of FMx-RIS, it has been observed that signals similar to OFDM can be obtained at the receiver. This situation indicates the possibility of generating a signal in the air similar to OFDM using an RIS. Therefore, in this study, we propose a novel Over-the-Air OFDM system design by integrating frequency mixing and modulating RIS (FMMx-RIS) to exploit its ability to manipulate the incident wave’s magnitude and frequency. The most notable aspect of this innovative scheme is its ability to offer multi-carrier transmission with a straightforward transmitter structure rather than requiring the complex system design typical of OFDM. The novel concept of index modulation (IM), which leverages the spatial domain to transmit extra information more efficiently, enhancing energy and spectrum efficiency, has attracted considerable interest in both academic and industrial fields. Hence, we extend the system model into the Over-the-Air OFDM-IM system by toggling frequency-changing RIS on and off. Furthermore, we analytically assess the average bit error probability (ABEP) of the proposed Over-the-Air OFDM-IM system using the maximum likelihood (ML) decoder. Subsequently, we present comprehensive computer simulation results to demonstrate the significant improvement in bit error rate (BER) performance of the proposed Over-the-Air OFDM-IM system compared to reference systems employing RIS-aided OFDM

Identification of Distorted RF Components via Deep Multi-Task Learning

High-quality radio frequency (RF) components are imperative for efficient wireless communication. However, these components can degrade over time and need to be identified so that either they can be replaced or their effects can be compensated. The identification of these components can be done through observation and analysis of constellation diagrams. However, in the presence of multiple distortions, it is very challenging to isolate and identify the RF components responsible for the degradation. This paper highlights the difficulties of distorted RF components' identification and their importance. Furthermore, a deep multi-task learning algorithm is proposed to identify the distorted components in the challenging scenario. Extensive simulations show that the proposed algorithm can automatically detect multiple distorted RF components with high accuracy in different scenarios

A low-complexity time-domain MMSE channel estimator for space-time/frequency block-coded OFDM systems

Focusing on transmit diversity orthogonal frequency-division multiplexing (OFDM) transmission through frequency-selective channels, this paper pursues a channel estimation approach in time domain for both space-frequency OFDM (SF-OFDM) and space-time OFDM (ST-OFDM) systems based on AR channel modelling. The paper proposes a computationally efficient, pilot-aided linear minimum mean-square-error (MMSE) time-domain channel estimation algorithm for OFDM systems with transmitter diversity in unknown wireless fading channels. The proposed approach employs a convenient representation of the channel impulse responses based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Subsequently, optimal rank reduction is applied to obtain significant taps resulting in a smaller computational load on the proposed estimation algorithm. The performance of the proposed approach is studied through the analytical results and computer simulations. In order to explore the performance, the closed-form expression for the average symbol error rate (SER) probability is derived for the maximum ratio receive combiner (MRRC). We then consider the stochastic Cramer-Rao lower bound(CRLB) and derive the closed-form expression for the random KL coefficients, and consequently exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also analyze the effect of a modelling mismatch on the estimator performance. Simulation results confirm our theoretical analysis and illustrate that the proposed algorithms are capable of tracking fast fading and improving overall performance. Copyright (C) 2006 Hindawi Publishing Corporation. All rights reserved