Polynomial matrix decomposition techniques for frequency selective MIMO channels

For a narrowband, instantaneous mixing multi-input, multi-output (MIMO) communications system, the channel is represented as a scalar matrix. In this scenario, singular value decomposition (SVD) provides a number of independent spatial subchannels which can be used to enhance data rates or to increase diversity. Alternatively, a QR decomposition can be used to reduce the MIMO channel equalization problem to a set of single channel equalization problems. In the case of a frequency selective MIMO system, the multipath channel is represented as a polynomial matrix. Thus conventional matrix decomposition techniques can no longer be applied. The traditional solution to this broadband problem is to reduce it to narrowband form by using a discrete Fourier transform (DFT) to split the broadband channel into N narrow uniformly spaced frequency bands and applying scalar decomposition techniques within each band. This describes an orthogonal frequency division multiplexing (OFDM) based system. However, a novel algorithm has been developed for calculating the eigenvalue decomposition of a para-Hermitian polynomial matrix, known as the sequential best rotation (SBR2) algorithm. SBR2 and its QR based derivatives allow a true polynomial singular value and QR decomposition to be formulated. The application of these algorithms within frequency selective MIMO systems results in a fundamentally new approach to exploiting spatial diversity. Polynomial matrix decomposition and OFDM based solutions are compared for a wide variety of broadband MIMO communication systems. SVD is used to create a robust, high gain communications channel for ultra low signal-to-noise ratio (SNR) environments. Due to the frequency selective nature of the channels produced by polynomial matrix decomposition, additional processing is required at the receiver resulting in two distinct equalization techniques based around turbo and Viterbi equalization. The proposed approach is found to provide identical performance to that of an existing OFDM scheme while supporting a wider range of access schemes. This work is then extended to QR decomposition based communications systems, where the proposed polynomial approach is found to not only provide superior bit-error-rate (BER) performance but significantly reduce the complexity of transmitter design. Finally both techniques are combined to create a nulti-user MIMO system that provides superior BER performance over an OFDM based scheme. Throughout the work the robustness of the proposed scheme to channel state information (CSI) error is considered, resulting in a rigorous demonstration of the capabilities of the polynomial approach

Lightly synchronized Multipacket Reception in Machine-Type Communications Networks

Machine Type Communication (MTC) applications were designed to monitor and control elements of our surroundings and environment. MTC applications have a different set of requirements compared to the traditional communication devices, with Machine to Machine (M2M) data being mostly short, asynchronous, bursty and sometimes requiring end-to-end delays below 1ms. With the growth of MTC, the new generation of mobile communications has to be able to present different types of services with very different requirements, i.e. the same network has to be capable of "supplying" connection to the user that just wants to download a video or use social media, allowing at the same time MTC that has completely different requirements, without deteriorating both experiences. The challenges associated to the implementation of MTC require disruptive changes at the Physical (PHY) and Medium Access Control (MAC) layers, that lead to a better use of the spectrum available. The orthogonality and synchronization requirements of the PHY layer of current Long Term Evolution Advanced (LTE-A) radio access network (based on glsofdm and Single Carrier Frequency Domain Equalization (SC-FDE)) are obstacles for this new 5th Generation (5G) architecture. Generalized Frequency Division Multiplexing (GFDM) and other modulation techniques were proposed as candidates for the 5G PHY layer, however they also suffer from visible degradation when the transmitter and receiver are not synchronized, leading to a poor performance when collisions occur in an asynchronous MAC layer. This dissertation addresses the requirements of M2M traffic at the MAC layer applying multipacket reception (MPR) techniques to handle the bursty nature of the traffic and synchronization tones and optimized back-off approaches to reduce the delay. It proposes a new MAC protocol and analyses its performance analytically considering an SC-FDE modulation. The models are validated using a system level cross-layer simulator developed in MATLAB, which implements the MAC protocol and applies PHY layer performance models. The results show that the MAC’s latency depends mainly on the number of users and the load of each user, and can be controlled using these two parameters

Time diversity solutions to cope with lost packets

A dissertation submitted to Departamento de Engenharia Electrotécnica of Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotécnica e de ComputadoresModern broadband wireless systems require high throughputs and can also have very high Quality-of-Service (QoS) requirements, namely small error rates and short delays. A high spectral efficiency is needed to meet these requirements. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An alternative to simple retransmission that can improve both power and spectral efficiency is to combine the signals associated to different transmission attempts. This thesis analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but handle different packet loss causes. The first is a lowcomplexity Diversity-Combining (DC) Automatic Repeat reQuest (ARQ) scheme employed in a Time Division Multiple Access (TDMA) architecture, adapted for channels dedicated to a single user. The second is a Network-assisted Diversity Multiple Access (NDMA) scheme, which is a multi-packet detection approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This thesis combines these techniques with Single Carrier with Frequency Division Equalizer (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It proposes a new NDMA scheme capable of handling more Mobile Terminals (MTs) than the user separation capacity of the receiver. This thesis also proposes a set of analytical tools that can be used to analyse and optimize the use of these two systems. These tools are then employed to compare both approaches in terms of error rate, throughput and delay performances, and taking the implementation complexity into consideration. Finally, it is shown that both approaches represent viable solutions for future broadband wireless communications complementing each other.Fundação para a Ciência e Tecnologia - PhD grant(SFRH/BD/41515/2007); CTS multi-annual funding project PEst-OE/EEI/UI0066/2011, IT pluri-annual funding project PEst-OE/EEI/LA0008/2011, U-BOAT project PTDC/EEATEL/ 67066/2006, MPSat project PTDC/EEA-TEL/099074/2008 and OPPORTUNISTICCR project PTDC/EEA-TEL/115981/200

Single-Frequency Network Terrestrial Broadcasting with 5GNR Numerology

L'abstract è presente nell'allegato / the abstract is in the attachmen

Irregular polar coding for complexity-constrained lightwave systems

Next-generation fiber-optic communications call for ultra-reliable forward error correction codes that are capable of low-power and low-latency decoding. In this paper, we propose a new class of polar codes, whose polarization units are irregularly pruned to reduce computational complexity and decoding latency without sacrificing error correction performance. We then experimentally demonstrate that the proposed irregular polar codes can outperform state-of-the-art low-density parity-check (LDPC) codes, while decoding complexity and latency can be reduced by at least 30% and 70%, respectively, versus regular polar codes, while also obtaining a marginal performance improvement

Study, analysis and application of Optical OFDM, Single Carrier (SC) and MIMO in Intensity Modulation Direct Detection (IM/DD)

With the rapid growth of wireless data demands and saturation of radio frequency (RF) capacity, visible light communication (VLC) has become a promising candidate to complement conventional RF communication, especially for indoor short range applications. However the performance of the system depends on the propagation and type of system used. An optical Orthogonal Frequency Division Multiplexing (O-OFDM) together with multiple input multiple output (MIMO) in different scenario and modulation techniques are studied in the thesis. A novel optical wireless communication (OWC) multi-cell system with narrow field of view (FOV) is studied. In this system the intensity modulated beam from four light sources are used for communication. The system allows beams to be concentrated in specific areas of the room to serve multiple mobile devices with low interference and hence increase system capacity. The performance of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM), direct current biased optical OFDM (DCO-OFDM) and single carrier (SC) modulation are then compared in this system considering single user and multiusers scenarios. The performance of the multi-cell is compared with single cell with wide FOV. It is shown that the capacity for multi-cell system increases with the number of users to 4 times the single user capacity. Also the findings show that multi-cell system with narrow beams can outperform a single wide beam system in terms of coverage area and hence average throughput of about 2.7 times the single wide beam system capacity. One of the impairments in line of sight (LOS) OWC systems is coverage which degrades the performance. A mobile receiver with angular diversity detectors in MIMO channels is studied. The objective is to improve the rank of the channel matrix and hence system throughput. Repetition coding (RC), spatial multiplexing (SMP) and spatial modulation (SM) concepts are used to evaluate throughput across multiple locations in a small room scenario. A novel adaptive spatial modulation (ASM) which is capable of combating channel rank deficiency is devised. Since the receiver is mobile, the channel gains are low in some locations of the room due to the lack of LOS paths between transmitters and receivers. To combat the situation adaptive modulation and per antenna rate control (PARC) is employed to maximise spectral efficiency. The throughputs for fixed transmitters and receivers are compared with the oriented/inclined detectors for different cases. Angular diversity detectors offer a better throughput improvement than the state of the art vertical detectors, for example in ASM angular diversity receiver gives throughput of about 1.6 times that of vertical detectors. Also in SMP the angular detectors offer throughput about 1.4 times that of vertical detectors. SMP gives the best performance compared to RC, SM and ASM, for example SMP gives throughput about 2.5 times that of RC in both vertical detectors and angular diversity receivers. Again SMP gives throughput about 6 times that of SM in both vertical detectors and angular diversity receivers. Also SMP provides throughput about 2 times that of ASM in both vertical detectors and angular diversity receivers. ASM exhibit improvement in throughput about average factor of 3.5 times SM performance in both vertical detectors and angular diversity detectors. As the performance of the system may be jeopardized by obstructions, specular and diffuse reflection models for indoor OWC systems using a mobile receiver with angular diversity detectors in MIMO channels are considered. The target is to improve the MIMO throughput compared to vertically oriented detectors by exploiting reflections from different reflecting surfaces in the room. The throughput across multiple locations in the small room by using RC, SMP and SM approaches is again evaluated. The results for LOS only channels against LOS with specular or diffuse reflection conditions, for both vertical and angular oriented receivers are then compared. The results show that exploiting specular and diffuse reflections provide significant improvements in link performance. For example the reflection coefficient (α) of 0.9 and the antenna separation of 0.6 m, RC diffuse model shows throughput improvement of about 1.8 times that of LOS for both vertical detectors and angular diversity receivers. SM diffuse model shows throughput improvement of about 3 times that of LOS for both vertical detectors and angular diversity receivers. ASM diffuse model shows throughput improvement of about 2 times that of LOS for both vertical detectors and angular diversity receivers. SMP diffuse model shows throughput improvement of about 1.5 times that of LOS for both vertical detectors and angular diversity receiver