The goal of this Ph.D. dissertation is to address a number of challenges encountered in the digital baseband design of modern and future wireless communication systems. The fast and continuous evolution of wireless communications has been driven by the ambitious goal of providing ubiquitous services that could guarantee high throughput, reliability of the communication link and satisfy the increasing demand for efficient re-utilization of the heavily populated wireless spectrum. To cope with these ever-growing performance requirements, researchers around the world have introduced sophisticated broadband physical (PHY)-layer communication schemes able to accommodate higher bandwidth, which indicatively include multiple antennas at the transmitter and receiver and are capable of delivering improved spectral efficiency by applying interference management policies. The merging of Multiple Input Multiple Output (MIMO) schemes with the Orthogonal Frequency Division Multiplexing (OFDM) offers a flexible signal processing substrate to implement ...

Nowadays, the design of embedded systems is confronted with the combination of complex signal processing algorithms on the one hand and a variety of computational intensive multimedia applications on the other hand, while time to product launch has been extremely reduced. Especially in the wireless domain those challenges are stacked with tough requirements on power consumption and chip size. Unfortunately, design productivity did not undergo a similar progression and therefore fails to cope with the heterogeneity of modern hardware architectures. Until now, electronic design automation do not provide for complete coverage of the design ow. In particular crucial design tasks as high level characterisation of algorithms, oating-point to xed-point conversion, automated hardware/software partitioning, and automated virtual prototyping are not suciently supported or completely absent. In recent years a consistent design framework named Open Tool Integration Environment (OTIE) has been established ...

In the last two decades, multicarrier modulations have emerged as a low complexity solution to combat the effects of the multipath in wireless communications. Among them, Orthogonal Frequency Division Multiplexing (OFDM) is possibly the most studied modulation scheme, and has also been widely adopted as the foundation of industry standards such as WiMAX or LTE. However, OFDM is sensitive to time-selective channels, which are featured in mobility scenarios, due to the appearance of Inter-Carrier Interference (ICI). Implementation of hardware equipment for the end user is usually implemented in dedicated chips, but in research environments, more flexible solutions are preferred. One popular approach is the so-called Software Defined Radio (SDR), where the signal processing algorithms are implemented in reconfigurable hardware such as Digital Signal Processors (DSPs) and Field Programmable Gate Arrays (FPGAs). The aim of this work is two-fold. On the ...

Cellular Neural Networks are characterized by simplicity of operation. The network consists of a large number of nonlinear processing units; called cells; that are equally spread in the space. Each cell has a simple function (sequence of multiply-add followed by a single discrimination) that takes an element of a topographic map and then interacts with all cells within a specified sphere of interest through direct connections. Due to their intrinsic parallel computing power, CNNs have attracted the attention of a wide variety of scientists in, e.g., the fields of image and video processing, robotics and higher brain functions. Simplicity of operation together with the local connectivity gives CNNs first-hand advantages for tiled VLSI implementations with very high speed and complexity. The first VLSI implementation has been based on analogue technology but was small and suffered from parasitic capacitances and resistances ...

Designing energy-efficient multiprocessing hardware for applications such as video decoding or MIMO-OFDM baseband processing is challenging because these applications require high throughput, as well as flexibility for efficient use of the processing resources. Application specific hardwired accelerator circuits are the most energy-efficient processing resources, but are inflexible by nature. Furthermore, designing an application specific circuit is expensive and time-consuming. A solution that maintains the energy-efficiency of accelerator circuits, but makes them flexible as well, is to make the accelerator circuits fine-grained. Fine-grained application specific processing elements can be designed to implement general purpose functions that can be used in several applications and their small size makes the design and verification times reasonable. This thesis proposes an efficient method for orchestrating the use of heterogeneous fine-grained processing elements in dynamic applications without introducing tremendous orchestration overheads. Furthermore, the thesis presents a ...

Since their inception, energy dissipation has been a critical issue for mobile computing systems. Although a large research investment in low-energy circuit design and hardware level energy management has led to more energy-efficient architectures, even then, there is a growing realization that the contribution to energy conservation should be more rigorously considered at higher levels of the systems, such as operating systems and applications. This dissertation puts forth the claim that energy-aware compilation to improve appli- cation quality both in terms of execution time and energy consumption is essential for a high performance mobile computing embedded system design. Our work is a design paradigm shift from the logic gate being the basic silicon computation unit, to an in- struction running on an embedded processor. Multimedia DSP processors are the most lucrative choice to a mobile computing system design for their ...

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 ...

Bit-rate and quality of service demands of new wireless communication standards are pushing signal theory and algorithm implementation to their limits. One of the main strategies which are being used to achieve the demanded rates is the multiple input-multiple output (MIMO) technique, which employs multiple antennas, both at transmission and reception. This PhD dissertation concentrates on the analysis of the effects of channel estimation, specially complex due to the number of parameters to estimate, on the performance of MIMO detectors, focusing on both practical and theoretical aspects. The practical analysis has been addressed by designing and developing a real-time wireless MIMO communication platform. A whole 2 X 2 system has been implemented which has allowed to evaluate the eects of a real hardware implementation on the performance of the MIMO receiver. A zero-forcing (ZF) detector and a sphere decoder (SD) ...

The importance of power reduction of embedded systems has continuously increased in the past years. Recently, reducing power dissipation and energy consumption of a program have become optimization goals in their own right, no longer considered a side-effect of traditional performance optimizations which mainly target program execution time and/or program size. Nowadays, there is an increasing demand for developing power-optimizing compilers for embedded systems. This thesis is a step towards such important goal. In this thesis, we develop functional-level power models and investigate several software optimization techniques for embedded-processor systems. As a specific example, we consider the powerful Texas Instruments C6416T DSP processor. We analyze the power consumption contributions of the different functional units of this DSP. We assess the effect of the compiler performance optimizations on the energy and power consumption. Moreover, we explore the impact of two special ...

In nowadays communication systems, error correction provides robust data transmission through imperfect (noisy) channels. Error correcting codes are a crucial component in most storage and communication systems – wired or wireless –, e.g. GSM, UMTS, xDSL, CD/DVD. At least as important as the data integrity issue is the recent realization that error correcting codes fundamentally change the trade-offs in system design. High-integrity, low redundancy coding can be applied to increase data rate, or battery life time or by reducing hardware costs, making it possible to enter mass market. When it comes to the design of error correcting codes and their properties, there are two main theories that play an important role in this work. Classical coding theory aims at finding the best code given an available block length. This thesis focuses on the ubiquitous Reed-Solomon codes, one of the major ...

Since Marconi succeeded in carrying out the first wireless transmission in 1894, experimental research has been always linked with wireless communications. Today, most wireless communications research relies only on computer simulations. Although computer simulations are necessary and recommendable for wireless systems evaluation, they only reflect the simulation environment rather than the actual scenarios in which wireless systems operate. Consequently, it is desirable to assess wireless communications systems in real-world scenarios while, at the same time, keeping the required effort within reasonable terms. Among the different strategies suitable for undertaking such assessment, the testbed approach constitutes a simple and flexible enough solution based on the software-defined radio concept in which only the fundamental operations (usually the transmission and the acquisition) are carried out in real- time, while the remaining tasks are implemented off-line in high-level programming languages (e.g. MATLAB) and using ...

The unprecedented processing demand, posed by the explosion of big data, challenges researchers to design efficient and adaptive machine learning algorithms that do not require persistent retraining and avoid learning redundant information. Inspired from learning techniques of intelligent biological agents, identifying transferable knowledge across learning problems has been a significant research focus to improve machine learning algorithms. In this thesis, we address the challenges of knowledge transfer through embedding spaces that capture and store hierarchical knowledge. In the first part of the thesis, we focus on the problem of cross-domain knowledge transfer. We first address zero-shot image classification, where the goal is to identify images from unseen classes using semantic descriptions of these classes. We train two coupled dictionaries which align visual and semantic domains via an intermediate embedding space. We then extend this idea by training deep networks that ...

This doctoral thesis aims at optimising the floating-point implementations of signal processing algorithms on reconfigurable hardware with respect to accuracy, hardware resource and execution time. It is known that reduced precision in floating-point arithmetic operations on reconfigurable hardware directly translates into increased parallelism and peak performance. As a result, efficient implementations can be obtained by choosing the minimal acceptable precision for floating-point operations. Furthermore, custom-precision floating-point operations allow for trading accuracy with parallelism and performance. We use Affine Arithmetic (AA) for modeling the rounding errors of floating-point computations. The derived rounding error bound by the AA-based error model is then used to determine the smallest mantissa bit width of custom-precision floating-point number formats needed for guaranteeing the desired accuracy of floating-point applications. In this work, we implement the first Matlab-based framework for performing rounding error analysis and numerical range evaluation ...

Multi-antenna processing is widely adopted as one of the key enabling technologies for current and future cellular networks. Particularly, multiuser downlink beamforming (also known as space-division multiple access), in which multiple users are simultaneously served with spatial transmit beams in the same time and frequency resource, achieves high spectral efficiency with reduced energy consumption. To harvest the potential of multiuser downlink beamforming in practical systems, optimal beamformer design shall be carried out jointly with network resource allocation. Due to the specifications of cellular standards and/or implementation constraints, resource allocation in practice naturally necessitates discrete decision makings, e.g., base station (BS) association, user scheduling and admission control, adaptive modulation and coding, and codebook-based beamforming (precoding). This dissertation focuses on the joint optimization of multiuser downlink beamforming and discrete resource allocation in modern cellular networks. The problems studied in this thesis involve ...

In the world of Information and communications technology (ICT), strategies for innovation and development are increasingly focusing on applications that require spatial representation and real-time interaction with and within 3D-media environments. One of the major challenges that such applications have to address is user-centricity, reflecting e.g. on developing complexity-hiding services so that people can personalize their own delivery of services. In these terms, multimodal interfaces represent a key factor for enabling an inclusive use of new technologies by everyone. In order to achieve this, multimodal realistic models that describe our environment are needed, and in particular models that accurately describe the acoustics of the environment and communication through the auditory modality are required. Examples of currently active research directions and application areas include 3DTV and future internet, 3D visual-sound scene coding, transmission and reconstruction and teleconferencing systems, to name but ...