A Survey of Blind Modulation Classification Techniques for OFDM Signals

Blind modulation classification (MC) is an integral part of designing an adaptive or intelligent transceiver for future wireless communications. Blind MC has several applications in the adaptive and automated systems of sixth generation (6G) communications to improve spectral efficiency and power efficiency, and reduce latency. It will become a integral part of intelligent software-defined radios (SDR) for future communication. In this paper, we provide various MC techniques for orthogonal frequency division multiplexing (OFDM) signals in a systematic way. We focus on the most widely used statistical and machine learning (ML) models and emphasize their advantages and limitations. The statistical-based blind MC includes likelihood-based (LB), maximum a posteriori (MAP) and feature-based methods (FB). The ML-based automated MC includes k-nearest neighbors (KNN), support vector machine (SVM), decision trees (DTs), convolutional neural networks (CNNs), recurrent neural networks (RNNs), and long short-term memory (LSTM) based MC methods. This survey will help the reader to understand the main characteristics of each technique, their advantages and disadvantages. We have also simulated some primary methods, i.e., statistical- and ML-based algorithms, under various constraints, which allows a fair comparison among different methodologies. The overall system performance in terms bit error rate (BER) in the presence of MC is also provided. We also provide a survey of some practical experiment works carried out through National Instrument hardware over an indoor propagation environment. In the end, open problems and possible directions for blind MC research are briefly discussed

Blind Demodulation of Pass Band OFDMA Signals and Jamming Battle Damage Assessment Utilizing Link Adaptation

This research focuses on blind demodulation of a pass band OFDMA signal so that jamming effectiveness can be assessed; referred to in this research as BDA. The research extends, modifies and collates work within literature to perform a new method of blindly demodulating of a passband OFDMA signal, which exhibits properties of the 802.16 Wireless MAN OFDMA standard, and presents a novel method for performing BDA via observation of SC LA. Blind demodulation is achieved by estimating the carrier frequency, sampling rate, pulse shaping filter roll off factor, synchronization parameters and CFO. The blind demodulator\u27s performance in AWGN and a perfect channel is evaluated where it improves using a greater number OFDMA DL symbols and increased CP length. Performance in a channel with a single multi-path interferer is also evaluated where the blind demodulator\u27s performance is degraded. BDA is achieved via observing SC LA modulation behavior of the blindly demodulated signal between successive OFDMA DL sub frames in two scenarios. The first is where modulation signaling can be used to observe change of SC modulation. The second assumes modulation signaling is not available and the SC\u27s modulation must be classified. Classification of SC modulation is performed using sixth-order cumulants where performance increases with the number of OFDMA symbols. The SC modulation classi er is susceptible to the CFO caused by blind demodulation. In a perfect channel it is shown that SC modulation can be classified using a variety of OFDMA DL sub frame lengths in symbols. The SC modulation classifier experienced degraded performance in a multi-path channel and it is recommended that it is extended to perform channel equalization in future work

Handover analysis over mobile WiMAX technology.

As new mobile devices and mobile applications continue to growth, so does the data traffic demand for broadband services access and the user needs toward mobility, thereby, wireless application became today the fastest solution and lowest cost implementation unlike traditional wired deployment such as optical fibers and digital lines. WiMAX technology satisfies this gap through its high network performance over the air interface and high data rates based on the IEEE 802.16-2004 standards, this original specification does not support mobility. Therefore, the IEEE introduces a new standard that enables mobility profiles under 802.16e-2005, from which three different types of handovers process are introduced as hard handover (HHO), macro diversity handover (MDHO) and fast base station switching (FBSS) handover. The objective of this master thesis is to analyze how the handover process affects network performance. The analysis propose three scenarios, built over OPNET simulator to measure the most critical wireless parameter and performance indicator such as throughput, handover success rate, packet drop, delay and network usage.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Non-linear echo cancellation - a Bayesian approach

Echo cancellation literature is reviewed, then a Bayesian model is introduced and it is shown how how it can be used to model and fit nonlinear channels. An algorithm for cancellation of echo over a nonlinear channel is developed and tested. It is shown that this nonlinear algorithm converges for both linear and nonlinear channels and is superior to linear echo cancellation for canceling an echo through a nonlinear echo-path channel

Assessment and Real Time Implementation of Wireless Communications Systems and Applications in Transportation Systems

Programa Oficial de Doutoramento en Tecnoloxías da Información e das Comunicacións en Redes Móbiles. 5029V01[Resumo] Os sistemas de comunicación sen fíos de cuarta e quinta xeración (4G e 5G) utilizan unha capa física (PHY) baseada en modulacións multiportadora para a transmisión de datos cun gran ancho de banda. Este tipo de modulacións proporcionan unha alta eficiencia espectral á vez que permiten corrixir de forma sinxela os efectos da canle radio. Estes sistemas utilizan OFDMA como mecanismo para a repartición dos recursos radio dispoñibles entre os diferentes usuarios. Este repartimento realízase asignando un subconxunto de subportadoras a cada usuario nun instante de tempo determinado. Isto aporta unha gran flexibilidade ó sistema que lle permite adaptarse tanto ós requisitos de calidade de servizo dos usuarios como ó estado da canle radio. A capa de acceso ó medio (MAC) destes sistemas encárgase de configurar os diversos parámetros proporcionados pola capa física OFDMA, ademais de xestionar os diversos fluxos de información de cada usuario, transformando os paquetes de capas superiores en paquetes da capa física. Neste traballo estúdase o deseño e implementación das capas MAC e PHY de sistemas de comunicación 4G ademais da súa aplicabilidade en sistemas de transporte ferroviarios. Por unha parte, abórdase o deseño e implementación en tempo real do estándar WiMAX. Estúdanse os mecanismos necesarios para establecer comunicacións bidireccionais entre unha estación base e múltiples dispositivos móbiles. Ademais, estúdase como realizar esta implementación nunha arquitectura hardware baseada en DSPs e FPGAs, na que se implementan as capas MAC e PHY. Dado que esta arquitectura ten uns recursos computacionais limitados, tamén se estudan as necesidades de cada módulo do sistema para poder garantir o funcionamento en tempo real do sistema completo. Por outra parte, tamén se estuda a aplicabilidade dos sistemas 4G a sistemas de transporte públicos. Os sistemas de comunicacións e sinalización son unha parte vital para os sistemas de transporte ferroviario e metro. As comunicacións sen fíos utilizadas por estes sistemas deben ser robustas e proporcionar unha alta fiabilidade para permitir a supervisión, control e seguridade do tráfico ferroviario. Para levar a cabo esta avaliación de viabilidade realízanse simulacións de redes de comunicacións LTE en contornos de transporte ferroviarios, comprobando o cumprimento dos requisitos de fiabilidade e seguridade. Realízanse diferentes simulacións do sistema de comunicacións para poder ser avaliadas e seleccionar a configuración e arquitectura do sistema máis axeitada en función do escenario considerado. Tamén se efectúan simulacións de redes baseadas en Wi-Fi, dado que é a solución máis utilizada nos metros, para confrontar os resultados cos obtidos para LTE. Para que os resultados das simulacións sexan realistas débense empregar modelos de propagación radio axeitados. Nas simulacións utilízanse tanto modelos deterministas como modelos baseados nos resultados de campañas de medida realizadas nestes escenarios. Nas simulacións empréganse os diferentes fluxos de información destes escenarios para comprobar que se cumpren os requisitos de calidade de servicio (QoS). Por exemplo, os fluxos críticos para o control ferroviario, como European Train Control System (ETCS) ou Communication-Based Train Control (CBTC), necesitan unha alta fiabilidade e un retardo mínimo nas comunicacións para garantir o correcto funcionamento do sistema.[Resumen] Los sistemas de comunicación inalámbricos de cuarta y quinta generación (4G y 5G) utilizan una capa física (PHY) basada en modulaciones multiportadora para la transmisión de datos con un gran ancho de banda. Este tipo de modulaciones han demostrado tener una alta eficiencia espectral a la vez que permiten corregir de forma sencilla los efectos del canal radio. Estos sistemas utilizan OFDMA como mecanismo para el reparto de los recursos radio disponibles entre los diferentes usuarios. Este reparto se realiza asignando un subconjunto de subportadoras a cada usuario en un instante de tiempo determinado. Esto aporta una gran flexibilidad al sistema que le permite adaptarse tanto a los requisitos de calidad de servicio de los usuarios como al estado del canal radio. La capa de acceso al medio (MAC) de estos sistemas se encarga de configurar los diversos parámetros proporcionados por la capa física OFDMA, además de gestionar los diversos flujos de información de cada usuario, transformando los paquetes de capas superiores en paquetes de la capa física. En este trabajo se estudia el diseño e implementación de las capas MAC y PHY de sistemas de comunicación 4G además de su aplicabilidad en sistemas de transporte ferroviarios. Por una parte, se aborda el diseño e implementación en tiempo real del estándar WiMAX. Se estudian los mecanismos necesarios para establecer comunicaciones bidireccionales entre una estación base y múltiples dispositivos móviles. Además, se estudia cómo realizar esta implementación en una arquitectura hardware basada en DSPs y FPGAs, en la que se implementan las capas MAC y PHY. Dado que esta arquitectura tiene unos recursos computacionales limitados, también se estudian las necesidades de cada módulo del sistema para poder garantizar el funcionamiento en tiempo real del sistema completo. Por otra parte, también se estudia la aplicabilidad de los sistemas 4G a sistemas de transporte públicos. Los sistemas de comunicaciones y señalización son una parte vital para los sistemas de transporte ferroviario y metro. Las comunicaciones inalámbricas utilizadas por estos sistemas deben ser robustas y proporcionar una alta fiabilidad para permitir la supervisión, control y seguridad del tráfico ferroviario. Para llevar a cabo esta evaluación de viabilidad se realizan simulaciones de redes de comunicaciones LTE en entornos de transporte ferroviarios, comprobando si se cumplen los requisitos de fiabilidad y seguridad. Se realizan diferentes simulaciones del sistema de comunicaciones para poder ser evaluados y seleccionar la configuración y arquitectura del sistema más adecuada en función del escenario planteado. También se efectúan simulaciones de redes basadas en Wi-Fi, dado que es la solución más utilizada en los metros, para comparar los resultados con los obtenidos para LTE. Para que los resultados de las simulaciones sean realistas se deben utilizar modelos de propagación radio apropiados. En las simulaciones se utilizan tanto modelos deterministas como modelos basados en los resultados de campañas de medida realizadas en estos escenarios. En las simulaciones se utilizan los diferentes flujos de información de estos escenarios para comprobar que se cumplen sus requisitos de calidad de servicio. Por ejemplo, los flujos críticos para el control ferroviario, como European Train Control System (ETCS) o Communication-Based Train Control (CBTC), necesitan una alta fiabilidad y un retardo bajo en las comunicaciones para garantizar el correcto funcionamiento del sistema.[Abstract] The fourth and fifth generation wireless communication systems (4G and 5G) use a physical layer (PHY) based on multicarrier modulations for data transmission using high bandwidth. This type of modulations has shown to provide high spectral efficiency while allowing low complexity radio channel equalization. These systems use OFDMA as a mechanism for distributing the available radio resources among different users. This allocation is done by assigning a subset of subcarriers to each user in a given instant of time. This provides great flexibility to the system that allows it to adapt to both the quality of service requirements of users and the radio channel state. The media access layer (MAC) of these systems is in charge of configuring the multiple OFDMA PHY layer parameters, in addition to managing the data flows of each user, transforming the higher layer packets into PHY layer packets. This work studies the design and implementation of MAC and PHY layers of 4G communication systems as well as their applicability in rail transport systems. On the one hand, the design and implementation in real time of the WiMAX standard is addressed. The required mechanisms to establish bidirectional communications between a base station and several mobile devices are also evaluated. Moreover, a MAC layer and PHY layer implementation is presented, using a hardware architecture based in DSPs and FPGAs. Since this architecture has limited computational resources, the requirements of each processing block of the system are also studied in order to guarantee the real time operation of the complete system. On the other hand, the applicability of 4G systems to public transportation systems is also studied. Communications and signaling systems are a vital part of rail and metro transport systems. The wireless communications used by these systems must be robust and provide high reliability to enable the supervision, control and safety of rail traffic. To carry out this feasibility assessment, LTE communications network simulations are performed in rail transport environments to verify that reliability and safety requirements are met. Several simulations are carried out in order to evaluate the system performance and select the most appropriate system configuration in each case. Simulations of Wi-Fi based networks are also carried out, since it is the most used solution in subways, to compare the results with those obtained for LTE. To perform the simulations correctly, appropriate radio propagation models must be used. Both deterministic models and models based on the results of measurement campaigns in these scenarios are used in the simulations. The simulations use the different information flows present in the railway transportation systems to verify that its quality of service requirements are met. For example, critical flows for railway control, such as the European Train Control System (ETCS) or Communication-Based Train Control (CBTC), require high reliability and low delay communications to ensure the proper functioning of the system

Algorithm-Architecture Co-Design for Digital Front-Ends in Mobile Receivers

The methodology behind this work has been to use the concept of algorithm-hardware co-design to achieve efficient solutions related to the digital front-end in mobile receivers. It has been shown that, by looking at algorithms and hardware architectures together, more efficient solutions can be found; i.e., efficient with respect to some design measure. In this thesis the main focus have been placed on two such parameters; first reduced complexity algorithms to lower energy consumptions at limited performance degradation, secondly to handle the increasing number of wireless standards that preferably should run on the same hardware platform. To be able to perform this task it is crucial to understand both sides of the table, i.e., both algorithms and concepts for wireless communication as well as the implications arising on the hardware architecture. It is easier to handle the high complexity by separating those disciplines in a way of layered abstraction. However, this representation is imperfect, since many interconnected "details" belonging to different layers are lost in the attempt of handling the complexity. This results in poor implementations and the design of mobile terminals is no exception. Wireless communication standards are often designed based on mathematical algorithms with theoretical boundaries, with few considerations to actual implementation constraints such as, energy consumption, silicon area, etc. This thesis does not try to remove the layer abstraction model, given its undeniable advantages, but rather uses those cross-layer "details" that went missing during the abstraction. This is done in three manners: In the first part, the cross-layer optimization is carried out from the algorithm perspective. Important circuit design parameters, such as quantization are taken into consideration when designing the algorithm for OFDM symbol timing, CFO, and SNR estimation with a single bit, namely, the Sign-Bit. Proof-of-concept circuits were fabricated and showed high potential for low-end receivers. In the second part, the cross-layer optimization is accomplished from the opposite side, i.e., the hardware-architectural side. A SDR architecture is known for its flexibility and scalability over many applications. In this work a filtering application is mapped into software instructions in the SDR architecture in order to make filtering-specific modules redundant, and thus, save silicon area. In the third and last part, the optimization is done from an intermediate point within the algorithm-architecture spectrum. Here, a heterogeneous architecture with a combination of highly efficient and highly flexible modules is used to accomplish initial synchronization in at least two concurrent OFDM standards. A demonstrator was build capable of performing synchronization in any two standards, including LTE, WiFi, and DVB-H

PROCESS FOR BREAKING DOWN THE LTE SIGNAL TO EXTRACT KEY INFORMATION

The increasingly important role of Long Term Evolution (LTE) has increased security concerns among the service providers and end users and made security of the network even more indispensable. The main thrust of this thesis is to investigate if the LTE signal can be broken down in a methodical way to obtain information that would otherwise be private; e.g., the Global Positioning System (GPS) location of the user equipment/base station or identity (ID) of the user. The study made use of signal simulators and software to analyze the LTE signal to develop a method to remove noise, breakdown the LTE signal and extract desired information. From the simulation results, it was possible to extract key information in the downlink like the Downlink Control Information (DCI), Cell-Radio Network Temporary Identifier (C-RNTI) and physical Cell Identity (Cell-ID). This information can be modified to cause service disruptions in the network within a reasonable amount of time and with modest computing resources.Defence Science and Technology Agency, SingaporeApproved for public release; distribution is unlimited