The interplay between mapping/demapping and non-binary LDPC coding in MIMO wireless communication systems

Recently, the need for innovative services available for the end users has led to an increasing demand of higher throughputs of wireless systems. On the other hand higher throughput means wider bandwidth, so that channel selectivity and fading might be a severe challenge to combat in order to ensure high level of Quality of Service (QoS). In this scenario one of the possible approach to increase the system throughput is the use of multiple antennas, both at the transmitter and the receiver side. Instead the typical manner to combat channel effects is to employ powerful channel coding schemes, which target the mitigation of these propagation effects. This work follows this approach combining the MIMO techniques jointly with the powerful channel coding scheme of non-binary LDPC. The expression "non-binary" refers to the fact that these codes are defined over high order Galois Field. These codes have been researched in the literature to achieve higher error protection than conventional binary codes for transmission over different noisy channels. The main novelty of this work is related to the mapping and demapping of the non-binary information. Typically the main contributions in the literature focus on the low complexity decoders, whilst the demapping complexity is neglected. However, the demapping complexity might become a real bottleneck in the global receiver complexity, so that we decide to investigate this topic. A strategy is devised to guarantee an efficient mapping at the transmitter, together with an algorithm for low complexity soft demapping at the receiver. The proposed solutions target the best trade-off between performance and complexity, for any combination of the Galois field order, QAM constellation order, and MIMO scheme

Rivelazione e Sincronizzazione di tempo per un segnale multiportante UMTS-LTE

Questo elaborato si occupa per prima cosa di illustrare brevemente le reti cellulari di terza generazione (UMTS), prima di introdurre gli obiettivi e lo standard downlink 3GPP – Long Term Evolution (LTE), che rappresenta il futuro delle comunicazioni mobili cellulari. In seguito viene presentata la catena di trasmissione downlink implementata, soffermandosi poi sul ricevitore LTE, in particolare sul filtro di ricezione e sull’equalizzatore. Successivamente l’attenzione di questo elaborato di tesi si concentra sulla procedura di sincronizzazione, che rappresenta la parte principale delle simulazioni effettuate; vengono illustrati nel dettaglio tutti i passi dell’algoritmo di sincronizzazione scelto, con una trattazione analitica là dove è stato ritenuto opportuno. Infine vengono presentate le curve di probabilità d’errore (BER), che consentono una valutazione delle prestazioni del ricevitore in analisi, ed eventuali possibili evoluzioni dello stesso

NAVIGATION MESSAGE AUTHENTICATION FOR NEXT GENERATION GNSS

Since the early days of GNSS, one of the main issues has been the need to protect the final user from attackers trying to emulate the data sent by the real system, the so-called spoofers. This can be done in particular adding the system the function of navigation message authentication, that represents the subject of this paper. The paper introduces a general approach to the problem, to come to a detailed real-world in-orbit case, that is the Galileo Navigation System. This kind of authentication feature is in fact foreseen for the evolution of the system towards its own second generation, evolution that is currently ongoing. Recent research (performed by Wiser and TASI in the frame of internal R&D activities) within the GNSS evolution study for Galileo Second Generation as well as GPS evolution, are investigating the possibility to have a more robust and reliable signal through the broadcasting of navigation message authentication bits. The paper describes a possible solution to the problems wherein the authentication bits are included in a dedicated channel that is added on top of the current signal-in-space format using IBOC multiplexing. This represents an alternative solution to the standard idea of reserving some bits of the current navigation message for authentication. The advantage of the dedicated channel is relatively clear: the bit-rate dedicated to authentication is considerably larger than that resulting from the reserved bits in the current message, thus providing a higher security level, and lower time to first authenticated fix (TTFA)/time between authentication (TBA). This allows in particular to easily meet the latest recommendations stating that (at least) a security equivalent to a symmetric algorithm with 128-bit key is needed. Concerning the authentication algorithm, the present study proposes a combination of the TESLA protocol with a public-key protocol (such as ECDSA). This allows to improve on a weakness of TESLA that requires time synchronization: albeit loos, it cannot guaranteed at receiver start-up, and in addition the TESLA root key shall be authenticated anyway. The optimal combination is found based on a trade-off between security strength, bandwidth overhead, authentication error rate, and time between authentication. Our proposal may pave the way towards an Open Service Navigation Message Authentication (NMA) solution to be broadcast on future GNSS signal channel using IBOC multiplexing solution. The proposed NMA criteria are based on the mutual combination of Elliptic Curve Digital Signature Algorithm (ECDSA) and TESLA authentication protocol. NAVITEC 2018 The solution foresee the use of ECDSA in a first phase when time synchronization between the sender and the recipient is not available, to switch afterwards TESLA when time synchronization is achieved. The paper concentrates on a specific solution wherein iBOC multiplexing on the E1 channels is supplemented with NMEA. This feasibility assessment is just a case study to show the generality of the approach and does not preclude any other implementation for future GNSS signals. The paper is organized as follows: first a summary of the authentication protocols are provided, focusing on the TESLA one, and the IBOC multiplexing scheme for GNSS evolution signals. Then a proposed solution is detailed, together with associated performance, and finally the conclusions are draw