A high-performance data structure for mobile information systems

Mobile information systems can now be provided on small form-factor computers. Dictionary-based data compression extends the capabilities of systems with limited processing and memory to enable data intensive applications to be supported in such environments. The nature of judicial sentencing decisions requires that a support system provides accurate and up-to-date data and is compatible with the professional working experience of a judge. The difficulties caused by mobility and the data dependence of the decision-making process are addressed by an Internet-based architecture for collecting and distributing system data.We describe an approach to dictionary-based data compression and the structure of an information system that makes use of this technology

High-rate codes that are linear in space and time

Multiple-antenna systems that operate at high rates require simple yet effective space-time transmission schemes to handle the large traffic volume in real time. At rates of tens of bits per second per hertz, Vertical Bell Labs Layered Space-Time (V-BLAST), where every antenna transmits its own independent substream of data, has been shown to have good performance and simple encoding and decoding. Yet V-BLAST suffers from its inability to work with fewer receive antennas than transmit antennas-this deficiency is especially important for modern cellular systems, where a base station typically has more antennas than the mobile handsets. Furthermore, because V-BLAST transmits independent data streams on its antennas there is no built-in spatial coding to guard against deep fades from any given transmit antenna. On the other hand, there are many previously proposed space-time codes that have good fading resistance and simple decoding, but these codes generally have poor performance at high data rates or with many antennas. We propose a high-rate coding scheme that can handle any configuration of transmit and receive antennas and that subsumes both V-BLAST and many proposed space-time block codes as special cases. The scheme transmits substreams of data in linear combinations over space and time. The codes are designed to optimize the mutual information between the transmitted and received signals. Because of their linear structure, the codes retain the decoding simplicity of V-BLAST, and because of their information-theoretic optimality, they possess many coding advantages. We give examples of the codes and show that their performance is generally superior to earlier proposed methods over a wide range of rates and signal-to-noise ratios (SNRs)

An unequal modulation scheme for the transmission of compressed multimedia data over MIMO-OFDM systems

Modern video/image source coders employ data compression techniques which encode information that are not equally important. Transform based or subband coders, compress data into their respective low-frequency and high-frequency components. In wireless/mobile communication systems, data representing the low-frequency components are more sensitive to the time-varying nature of channel conditions and propagation environments. To deal with this problem, we propose an optimum transceiver structure for a combined source-modulation coded MIMO-OFDM system with adaptive eigen-beamforming. Using an unequal adaptive modulator, we maximize the channel-to-noise ratio (CNR) based on a lookup matrix-adaptive bit and power allocation (LM-ABPA) scheme to sort and allocate subcarriers with the highest SNR to the low-frequency components of the compressed data, and adjusting the signal constellation/modulation type respectively. In comparison to other transmission systems, simulation results based on the application of compressed images showed that the proposed unequal adaptive modulation scheme achieves significant performance gains under a constant data rate loa

Enhancing diversity and multiplexing gains in multi-user wireless relay systems

The demand for higher transmission rates and better quality of service in modern wireless communications is endless. The use of multiple transmit or /and receive antennas has been considered as one of the most powerful approaches to facilitate high -speed and high -quality communications. However, in practical cellular systems, mobile terminals may not be able to support a multiple- antenna setup. Thus an emerging technique called cooperative diversity is under consideration to utilize the multi -hop relay concept to realize the advantages of multiple - antenna systems in multi -user single- antenna networks. Cooperative diversity has attracted much interest in recent years as a very promising direction for future wireless communication evolution.Due to the fact that in practice terminals cannot transmit and receive simultaneously (i.e. the half -duplex limitation), the diversity improvement brought by the standard cooperative diversity transmission protocols is in general accompanied by a multiplexing loss (equivalent to a reduction in transmission data rate in high signal -to -nose ratio (SNR)). The purpose of this thesis is to use advanced transmission protocols to provide both good diversity and multiplexing performance when using the practical repetition -coded decode - and -forward (DF) relaying strategy in uplink mobile -to -base station transmission of cellular systems.The task is fulfilled by relaxing the orthogonal channel allocation requirement of the standard protocols and by using two relays to take turns forwarding source information to destination. We start our analysis from an M- source two -relay one -destination network. Through diversity -multiplexing tradeoff (DMT) analysis, we prove that for an isolated -relay scenario and a strong -interference scenario, the considered approach effectively recovers the multiplexing loss induced by the standard protocols while still obtaining diversity improvement over direct source -destination transmission without considering relaying.In addition, since the optimal multiplexing gain of the considered system can be achieved by the above approach, we study further improving diversity performance for a two -source network. We analyze taking full advantage of the multiple- source structure, multiple -relay structure, and the capability of affording complex signal processing at the destination (base station). For all three cases, we prove that the diversity performance of the above approach can be enhanced without a significant loss of multiplexing performance or using complex coding strategies at relays. Since the good DMT performance is not affected by source -relay channel conditions, the protocols discussed in this thesis make relaying more beneficial

Low-resolution ADC receiver design, MIMO interference cancellation prototyping, and PHY secrecy analysis.

This dissertation studies three independent research topics in the general field of wireless communications. The first topic focuses on new receiver design with low-resolution analog-to-digital converters (ADC). In future massive multiple-input-multiple-output (MIMO) systems, multiple high-speed high-resolution ADCs will become a bottleneck for practical applications because of the hardware complexity and power consumption. One solution to this problem is to adopt low-cost low-precision ADCs instead. In Chapter II, MU-MIMO-OFDM systems only equipped with low-precision ADCs are considered. A new turbo receiver structure is proposed to improve the overall system performance. Meanwhile, ultra-low-cost communication devices can enable massive deployment of disposable wireless relays. In Chapter III, the feasibility of using a one-bit relay cluster to help a power-constrained transmitter for distant communication is investigated. Nonlinear estimators are applied to enable effective decoding. The second topic focuses prototyping and verification of a LTE and WiFi co-existence system, where the operation of LTE in unlicensed spectrum (LTE-U) is discussed. LTE-U extends the benefits of LTE and LTE Advanced to unlicensed spectrum, enabling mobile operators to offload data traffic onto unlicensed frequencies more efficiently and effectively. With LTE-U, operators can offer consumers a more robust and seamless mobile broadband experience with better coverage and higher download speeds. As the coexistence leads to considerable performance instability of both LTE and WiFi transmissions, the LTE and WiFi receivers with MIMO interference canceller are designed and prototyped to support the coexistence in Chapter IV. The third topic focuses on theoretical analysis of physical-layer secrecy with finite blocklength. Unlike upper layer security approaches, the physical-layer communication security can guarantee information-theoretic secrecy. Current studies on the physical-layer secrecy are all based on infinite blocklength. Nevertheless, these asymptotic studies are unrealistic and the finite blocklength effect is crucial for practical secrecy communication. In Chapter V, a practical analysis of secure lattice codes is provided

BEHAVIOURAL MODELLING FOR THE DESIGN OF HIGH SPEED PHYSICAL LAYERS

This thesis work is the result of a 9 months activity at the IP&Reuse Division - Physical Layer team - of Intel Mobile Communications GmbH in Munich, Germany; the work has been sponsored by the company itself and by an Erasmus grant in the context of ‘LifeLongLearning Program’, academic year 2011-2012. It has been developed a high-level simulation environment to support the concept, architectural exploration and system-level performance analysis of High Speed Serial Interfaces’ Physical Layer. Equivalent representation using Analogue Mixed Signal - Hardware Description Languages (HDLs-AMS) have been also implemented to speed-up full chip transistor-level transient simulations. In Chapter 1 is presented an overview of the state of the art on methodologies, styles, implementation languages and simulation tools used in the design of mixed-signal systems and in the creation of behavioural models. Practical rules for trading off accuracy and speed are also discussed. In Chapter 2, a high-level description of a generic Physical Layer structure is introduced and all the basic building blocks are analyzed; for each of them it has been implemented a model: the realization methodology is presented and discussed in detail. The focus is put on the analysis of the Transmitter, the PCB interconnection, the Receiver, the Phased Locked Loops (PLLs) and the Clock and Data Recovery (CDR). Chapter 3 analyzes the fundamental parameters that determine the performances of a Physical Layer; the construction and the use of the Eye diagram are presented together with the actions to extract timing information and, then, to perform a budget. The various types of jitter and the corresponding causes are discussed. A statistical abstraction is introduced toward the computation of the Bit Error Rate (BER). In Chapter 4, it is illustrated the theory behind a MATLAB script that analyzes the channel pulse response to extract worst-case scenarios and to study the impact of a simple equalizer stage on the overall PHY’s performances; the design key-parameters of this block are then extracted and used in a VHDL-AMS implementation

The Design of a System Architecture for Mobile Multimedia Computers

This chapter discusses the system architecture of a portable computer, called Mobile Digital Companion, which provides support for handling multimedia applications energy efficiently. Because battery life is limited and battery weight is an important factor for the size and the weight of the Mobile Digital Companion, energy management plays a crucial role in the architecture. As the Companion must remain usable in a variety of environments, it has to be flexible and adaptable to various operating conditions. The Mobile Digital Companion has an unconventional architecture that saves energy by using system decomposition at different levels of the architecture and exploits locality of reference with dedicated, optimised modules. The approach is based on dedicated functionality and the extensive use of energy reduction techniques at all levels of system design. The system has an architecture with a general-purpose processor accompanied by a set of heterogeneous autonomous programmable modules, each providing an energy efficient implementation of dedicated tasks. A reconfigurable internal communication network switch exploits locality of reference and eliminates wasteful data copies

Blind equalization based on spatial and temporal diversity in block coded modulations

Linear block codes can be applied in spatial and/or temporal diversity receivers in order to develop high performance schemes for blind equalization in mobile communications. The proposed technique uses the structure of the encoded transmitted information (with redundancy) to achieve equalization schemes based on a deterministic criterion. Simulations show that the proposed technique is more efficient than other schemes that follow similar equalizer structures. The result is an algorithm that provides the design of blind channel equalizers in low EbNo scenarios.Peer ReviewedPostprint (published version

Wireless Communications in the Era of Big Data

The rapidly growing wave of wireless data service is pushing against the boundary of our communication network's processing power. The pervasive and exponentially increasing data traffic present imminent challenges to all the aspects of the wireless system design, such as spectrum efficiency, computing capabilities and fronthaul/backhaul link capacity. In this article, we discuss the challenges and opportunities in the design of scalable wireless systems to embrace such a "bigdata" era. On one hand, we review the state-of-the-art networking architectures and signal processing techniques adaptable for managing the bigdata traffic in wireless networks. On the other hand, instead of viewing mobile bigdata as a unwanted burden, we introduce methods to capitalize from the vast data traffic, for building a bigdata-aware wireless network with better wireless service quality and new mobile applications. We highlight several promising future research directions for wireless communications in the mobile bigdata era.Comment: This article is accepted and to appear in IEEE Communications Magazin