MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

Compressive Random Access Using A Common Overloaded Control Channel

We introduce a "one shot" random access procedure where users can send a message without a priori synchronizing with the network. In this procedure a common overloaded control channel is used to jointly detect sparse user activity and sparse channel profiles. The detected information is subsequently used to demodulate the data in dedicated frequency slots. We analyze the system theoretically and provide a link between achievable rates and standard compressing sensing estimates in terms of explicit expressions and scaling laws. Finally, we support our findings with simulations in an LTE-A-like setting allowing "one shot" sparse random access of 100 users in 1ms.Comment: 6 pages, 3 figures, published at Globecom 201

Facilitating Flexible Link Layer Protocols for Future Wireless Communication Systems

This dissertation addresses the problem of designing link layer protocols which are flexible enough to accommodate the demands offuture wireless communication systems (FWCS).We show that entire link layer protocols with diverse requirements and responsibilities can be composed out of reconfigurable and reusable components.We demonstrate this by designing and implementinga novel concept termed Flexible Link Layer (FLL) architecture.Through extensive simulations and practical experiments, we evaluate a prototype of the suggested architecture in both fixed-spectrumand dynamic spectrum access (DSA) networks. FWCS are expected to overcome diverse challenges including the continual growthin traffic volume and number of connected devices.Furthermore, they are envisioned to support a widerange of new application requirements and operating conditions.Technology trends, including smart homes, communicating machines, and vehicularnetworks, will not only grow on a scale that once was unimaginable, they will also become the predominant communication paradigm, eventually surpassing today's human-produced network traffic. In order for this to become reality, today's systems have to evolve in many ways.They have to exploit allocated resources in a more efficient and energy-conscious manner.In addition to that, new methods for spectrum access and resource sharingneed to be deployed.Having the diversification of applications and network conditions in mind, flexibility at all layers of a communication system is of paramount importance in order to meet the desired goals. However, traditional communication systems are often designed with specific and distinct applications in mind. Therefore, system designers can tailor communication systems according to fixedrequirements and operating conditions, often resulting in highly optimized but inflexible systems.Among the core problems of such design is the mix of data transfer and management aspects.Such a combination of concerns clearly hinders the reuse and extension of existing protocols. To overcome this problem, the key idea explored in this dissertation is a component-based design to facilitate the development of more flexible and versatile link layer protocols.Specifically, the FLL architecture, suggested in this dissertation, employs a generic, reconfigurable data transfer protocol around which one or more complementary protocols, called link layer applications, are responsible for management-related aspects of the layer. To demonstrate the feasibility of the proposed approach, we have designed andimplemented a prototype of the FLL architecture on the basis ofa reconfigurable software defined radio (SDR) testbed.Employing the SDR prototype as well as computer simulations, thisdissertation describes various experiments used to examine a range of link layerprotocols for both fixed-spectrum and DSA networks. This dissertation firstly outlines the challenges faced by FWCSand describes DSA as a possible technology component for their construction.It then specifies the requirements for future DSA systemsthat provide the basis for our further considerations.We then review the background on link layer protocols, surveyrelated work on the construction of flexible protocol frameworks,and compare a range of actual link layer protocols and algorithms.Based on the results of this analysis, we design, implement, and evaluatethe FLL architecture and a selection of actual link layer protocols. We believe the findings of this dissertation add substantively to the existing literature on link layer protocol design and are valuable for theoreticians and experimentalists alike

On the feasibility of unlicensed communications in the TV white space: Field measurements in the UHF band

In practical unlicensed communications in TV band, radio devices have to identify, at first, the transmission opportunities, that is, the portion of the spectrum licensed for broadcasting services unoccupied in a certain region at certain time, that is, the so-called TV white space. In this paper the outcome of field measurements in the UHF TV band (470-860 MHz) conducted in EU is presented. To obtain empirical values for the parameters upon which unlicensed radio devices are able to distinguish in a real scenario between empty and occupied TV channels, signal power measurements have been performed in Italy, Spain, and Romania on rural, suburban, and urban sites, at different heights over the ground by using different analysis bandwidths. The aim of this work is to provide a set of practical parameters upon which harmless unlicensed communication in the UHF TV white space is feasible. The results have been analyzed with respect to the hidden node margin problem, spectrum sensing bandwidth, and occupancy threshold

Fusion of Smartphone Motion Sensors for Physical Activity Recognition

For physical activity recognition, smartphone sensors, such as an accelerometer and a gyroscope, are being utilized in many research studies. So far, particularly, the accelerometer has been extensively studied. In a few recent studies, a combination of a gyroscope, a magnetometer (in a supporting role) and an accelerometer (in a lead role) has been used with the aim to improve the recognition performance. How and when are various motion sensors, which are available on a smartphone, best used for better recognition performance, either individually or in combination? This is yet to be explored. In order to investigate this question, in this paper, we explore how these various motion sensors behave in different situations in the activity recognition process. For this purpose, we designed a data collection experiment where ten participants performed seven different activities carrying smart phones at different positions. Based on the analysis of this data set, we show that these sensors, except the magnetometer, are each capable of taking the lead roles individually, depending on the type of activity being recognized, the body position, the used data features and the classification method employed (personalized or generalized). We also show that their combination only improves the overall recognition performance when their individual performances are not very high, so that there is room for performance improvement. We have made our data set and our data collection application publicly available, thereby making our experiments reproducible

Steady-State Performance of an Adaptive Combined MISO Filter Using the Multichannel Affine Projection Algorithm

The combination of adaptive filters is an effective approach to improve filtering performance. In this paper, we investigate the performance of an adaptive combined scheme between two adaptive multiple-input single-output (MISO) filters, which can be easily extended to the case of multiple outputs. In order to generalize the analysis, we consider the multichannel affine projection algorithm (APA) to update the coefficients of the MISO filters, which increases the possibility of exploiting the capabilities of the filtering scheme. Using energy conservation relations, we derive a theoretical behavior of the proposed adaptive combination scheme at steady state. Such analysis entails some further theoretical insights with respect to the single channel combination scheme. Simulation results prove both the validity of the theoretical steady-state analysis and the effectiveness of the proposed combined scheme.The work of Danilo Comminiello, Michele Scarpiniti and Aurelio Uncini has been supported by the project: “Vehicular Fog energy-efficient QoS mining and dissemination of multimedia Big Data streams (V-FoG and V-Fog2)”, funded by Sapienza University of Rome Bando 2016 and 2017. The work of Michele Scarpiniti and Aurelio Uncini has been also supported by the project: “GAUChO – A Green Adaptive Fog Computing and networking Architectures” funded by the MIUR Progetti di Ricerca di Rilevante Interesse Nazionale (PRIN) Bando 2015, grant 2015YPXH4W_004. The work of Luis A. Azpicueta-Ruiz is partially supported by the Spanish Ministry of Economy and Competitiveness (under grant DAMA (TIN2015-70308-REDT) and grants TEC2014-52289-R and TEC2017-83838-R), and by the European Union