11 research outputs found
Symbol-Level Precoding Through the Lens of Zero Forcing and Vector Perturbation
Symbol-level precoding (SLP) has recently emerged as a new paradigm for
physical-layer transmit precoding in multiuser multi-input-multi-output (MIMO)
channels. It exploits the underlying symbol constellation structure, which the
conventional paradigm of linear precoding does not, to enhance symbol-level
performance such as symbol error probability (SEP). It also allows the precoder
to take a more general form than linear precoding. This paper aims to better
understand the relationships between SLP and linear precoding, subsequent
design implications, and further connections beyond the existing SLP scope.
Focused on the quadrature amplitude modulation (QAM) constellations, our study
is built on a basic signal observation, namely, that SLP can be equivalently
represented by a zero-forcing (ZF) linear precoding scheme augmented with some
appropriately chosen symbol-dependent perturbation terms, and that some
extended form of SLP is equivalent to a vector perturbation (VP) nonlinear
precoding scheme augmented with the above-noted perturbation terms. We examine
how insights arising from this perturbed ZF and VP interpretations can be
leveraged to i) substantially simplify the optimization of certain SLP design
criteria, namely, total or peak power minimization subject to SEP quality
guarantees; and ii) draw connections with some existing SLP designs. We also
touch on the analysis side by showing that, under the total power minimization
criterion, the basic ZF scheme is a near-optimal SLP scheme when the QAM order
is very high -- which gives a vital implication that SLP is more useful for
lower-order QAM cases. Numerical results further indicate the merits and
limitations of the different SLP designs derived from the perturbed ZF and VP
interpretations
FPGA Acceleration for Computationally Efficient Symbol-Level Precoding in Multi-User Multi-Antenna Communication Systems
In this paper, we demonstrate an FPGA accelerated design of the computationally efficient Symbol-Level Precoding (SLP) for high-throughput communication systems. The SLP technique recalculates optimal beam-forming vectors by solving a non-negative least squares (NNLS) problem per every set of transmitted symbols. It exploits the advantages of constructive inter-user interference to minimize the total transmitted power and increase service availability. The benefits of using SLP come with a substantially increased computational load at a gateway. The FPGA design enables the SLP technique to perform in realtime operation mode and provide a high symbol throughput for multiple receive terminals. We define the SLP technique in a closed-form algorithmic expression and translate it to Hardware Description Language (HDL) and build an optimized HDL core for an FPGA. We evaluate the FPGA resource occupation, which is required for high throughput multiple-input-multiple-output (MIMO) systems with sizeable dimensions. We describe the algorithmic code, the I/O ports mapping and the functional behavior of the HDL core. We deploy the IP core to an actual FPGA unit and benchmark the energy efficiency performance of SLP. The synthetic tests demonstrate a fair energy efficiency improvement of the proposed closed-form algorithm, also compared to the best results obtained through MATLAB numerical simulations
SYMBOL LEVEL PRECODING TECHNIQUES FOR HARDWARE AND POWER EFFICIENT WIRELESS TRANSCEIVERS
Large-scale antennas are crucial for next generation wireless communication
systems as they improve spectral efficiency, reliability and coverage compared to
the traditional ones that are employing antenna arrays of few elements. However,
the large number of antenna elements leads to a big increase in power
consumption of conventional fully digital transceivers due to the one Radio
Frequency (RF) chain / per antenna element requirement. The RF chains include
a number of different components among which are the Digital-to-Analog
Converters (DACs)/Analog-to-Digital Converters (ADCs) that their power consumption
increases exponential with the resolution they support. Motivated by
this, in this thesis, a number of different architectures are proposed with the
view to reduce the power consumption and the hardware complexity of the
transceiver. In order to optimize the transmission of data through them, corresponding
symbol level precoding (SLP) techniques were developed for the proposed
architectures. SLP is a technique that mitigates multi-user interference
(MUI) by designing the transmitted signals using the Channel State Information
and the information-bearing symbols. The cases of both frequency flat and
frequency selective channels were considered.
First, three different power efficient transmitter designs for transmission over
frequency flat channels and their respective SLP schemes are considered. The
considered systems tackle the high hardware complexity and power consumption
of existing SLP techniques by reducing or completely eliminating fully digital
RF chains. The precoding design is formulated as a constrained least squares
problem and efficient algorithmic solutions are developed via the Coordinate
Descent method.
Next, the case of frequency selective channels is considered. To this end,
Constant Envelope precoding in a Multiple Input Multiple Output Orthogonal
Frequency Division Multiplexing system (CE MIMO-OFDM) is considered.
In CE MIMO-OFDM the transmitted signals for each antenna are designed
to have constant amplitude regardless of the channel realization and the information
symbols that must be conveyed to the users. This facilitates the
use of power-efficient components, such as phase shifters and non-linear power
amplifiers. The precoding problem is firstly formulated as a least-squares problem
with a unit-modulus constraint and solved using an algorithm based on
the coordinate descent (CCD) optimization framework and then, after reformulating
the problem into an unconstrained non-linear least squares problem,
a more computationally efficient solution using the Gauss-Newton algorithm is
presented.
Then, CE MIMO-OFDM is considered for a system with low resolution
DACs. The precoding design problem is formulated as a mixed discrete- continuous
least-squares optimization one which is NP-hard. An efficient low complexity
solution is developed based also on the CCD optimization framework.
Finally, a precoding scheme is presented for OFDM transmission in MIMO
systems based on one-bit DACs and ADCs at the transmitter’s and the receiver’s
end, respectively, as a way to reduce the total power consumption. The objective
of the precoding design is to mitigate the effects of one-bit quantization and
the problem is formulated and then is split into two NP hard least squares optimization problems. Algorithmic solutions are developed for the solution of the latter problems, based on the CCD framework
Symbol-Level Noise-Guessing Decoding with Antenna Sorting for URLLC Massive MIMO
Supporting ultra-reliable and low-latency communication (URLLC) is a
challenge in current wireless systems. Channel codes that generate large
codewords improve reliability but necessitate the use of interleavers, which
introduce undesirable latency. Only short codewords can eliminate the
requirement for interleaving and reduce decoding latency. This paper suggests a
coding and decoding method which, when combined with the high spectral
efficiency of spatial multiplexing, can provide URLLC over a fading channel.
Random linear coding and high-order modulation are used to transmit information
over a massive multiple-input multiple-output (mMIMO) channel, followed by
zero-forcing detection and guessing random additive noise decoding (GRAND) at a
receiver. A variant of GRAND, called symbol-level GRAND, originally proposed
for single-antenna systems that employ high-order modulation schemes, is
generalized to spatial multiplexing. The paper studies the impact of the
orthogonality defect of the underlying mMIMO lattice on symbol-level GRAND, and
proposes to leverage side-information that comes from the mMIMO channel-state
information and relates to the reliability of each receive antenna. This
induces an antenna sorting step, which further reduces decoding complexity by
over 80\% when compared to bit-level GRAND
Trellis coding with Continuous Phase Modulation (CPM) for satellite-based land-mobile communications
This volume of the final report summarizes the results of our studies on the satellite-based mobile communications project. It includes: a detailed analysis, design, and simulations of trellis coded, full/partial response CPM signals with/without interleaving over various Rician fading channels; analysis and simulation of computational cutoff rates for coherent, noncoherent, and differential detection of CPM signals; optimization of the complete transmission system; analysis and simulation of power spectrum of the CPM signals; design and development of a class of Doppler frequency shift estimators; design and development of a symbol timing recovery circuit; and breadboard implementation of the transmission system. Studies prove the suitability of the CPM system for mobile communications
Clustering techniques for base station coordination in a wireless cellular system
A lo largo de este Proyecto Fin de Carrera, propondremos mejoras para futuros sistemas de comunicaciones móviles mediante un estudio detallado de la coordinación entre estaciones base en sistemas celulares basados en MIMO. Este proyecto se compone de dos partes fundamentales. Por un lado, nos centraremos en técnicas de procesado de señal para MIMO como filtrado y precodificación lineales en el dominio espacial. Partiendo de los últimos desarrollos en dicho ámbito, se han desarrollado precodificadores de mínimo error cuadrático medio que incluyen restricciones de máxima potencia transmitida por celda. Además, se ha propuesto un concepto novedoso consistente en la introducción de una nueva formulación que, además de minimizar el error cuadrático medio en el interior de cada agrupación de celdas (cluster ), trata de mantener la interferencia entre clusters en niveles suficientemente bajos. Durante la segunda parte, analizaremos el impacto que la agrupación de celdas en clusters, que define qué estaciones base pueden ser coordinadas entre sí , tiene en el rendimiento global del sistema. Se ha estudiado la aplicabilidad de técnicas de agrupamiento dentro del aprendizaje máquina, dando como resultado un conjunto de nuevos algoritmos que han sido desarrollados adaptando algoritmos de agrupamiento de propósito general ya existentes al problema de crear una partición del conjunto de celdas de acuerdo a las condiciones de propagación de señal existentes en el sistema en un determinado instante. Todas nuestras contribuciones se han verificado mediante la simulación de un sistema de comunicaciones móviles basado en modelos de propagación de señal del 3GPP para LTE. De acuerdo a los resultados obtenidos, las técnicas propuestas a lo largo de este proyecto proporcionan un aumento considerable de la media y la mediana de las tasas por usuario respecto a soluciones ya existentes. La idea de introducir la reducción de interferencia entre clusters en la formulación de los precodifiadores MMSE mejora dramáticamente el rendimiento en sistemas celulares MIMO al ser comparados con precodifiadores de Wiener tradicionales. Por otro lado, nuestros algoritmos de agrupamiento dinámico de estaciones base exhiben un notable aumento de las tasas por usuario a la vez que emplean clusters de menor tamaño con respecto a soluciones existentes basadas en particiones estáticas del conjunto de celdas en el sistema. _______________________________________________________________________________________________________________________________In this project, we attempt to provide enhancements for future mobile communications systems by carrying out a throughout study of base-station coordination in cellular MIMO systems. Our work can be divided in two main blocks. During the first part, we focus our attention on linear MIMO signal processing techniques such as linear spatial precoding and linear spatial ltering. Starting from the state-of-the-art in that area of knowledge, we have developed novel MMSE precoders which include per-cell power constraints and a new formulation which, apart from minimizing the intra-cluster MSE, tries to keep inter-cluster interference at low levels. In the second part, we focus on the study of the impact the particular mapping of cells to clusters in the cellular system has on the overall performance of the mobile communication radio access network. The applicability of existing clustering algorithms in the fi eld of machine learning has been studied, resulting in a set of novel algorithms that we developed by adapting existing general-purpose clustering solutions for the problem of dynamically partitioning a set of cells according to the instantaneous signal propagation conditions. All our contributions have been exhaustively tested by simulation of a cellular mobile communication system based on 3GPP signal propagation models for LTE. According to the results obtained, the techniques proposed along this project provide a remarkable increase of both the average and median user rates in the system with respect to previous existing solutions. The inter-cluster interference-awareness we introduced in the formulation of MMSE precoders dramatically increases the performance in cellular coordinated MIMO when comparing it with traditional Wiener precoders. On the other hand, our dynamic base-station clustering has been shown to signi catively enhance the user rates while using smaller clusters that existing solutions based on static partitions of the base-station deployment.Ingeniería de Telecomunicació
Cooperative Radio Communications for Green Smart Environments
The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin
Cooperative Radio Communications for Green Smart Environments
The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin