Throughout this work, channel estimation techniques have been analyzed and proposed for moderate and very high mobility DVB (digital video broadcasting) receivers, focusing on the DVB-T2 (Digital Video Broadcasting - Terrestrial 2) framework and the forthcoming DVB-NGH (Digital Video Broadcasting - Next Generation Handheld) standard. Mobility support is one of the key features of these DVB specifications, which try to deal with the challenge of enabling HDTV (high definition television) delivery at high vehicular speed. In high-mobility scenarios, the channel response varies within an OFDM (orthogonal frequency-division multiplexing) block and the subcarriers are no longer orthogonal, which leads to the so-called ICI (inter-carrier interference), making the system performance drop severely. Therefore, in order to successfully decode the transmitted data, ICI-aware detectors are necessary and accurate CSI (channel state information), including the ICI terms, is required at the receiver. With the ...

This PhD dissertation analyzes the behavior of multi-antenna diversity techniques in broadcasting scenarios of TDT (terrestrial digital television) systems and proposes a low-complexity detection and decoding design for their practical implementation. For that purpose, the transmission-reception chains of the European DVB-T (Digital Video Broadcasting - Terrestrial) and DVB-T2 standards have been implemented over which diversity and MIMO (multiple-input multiple-output) techniques have been assessed through Monte Carlo simulations. On one hand, the most important multi-antenna diversity techniques such as CDD (cyclic delay diversity), Alamouti code-based SFBC (space-frequency block coding) and MRC (maximum ratio combining), have been evaluated in a DVB-T system over both fixed and mobile Rayleigh and Ricean channels. With the DVB-T2 standard release, multi-antenna processing has actually been introduced in digital television systems. The distributed SFBC configuration proposed in DVB-T2 is analyzed from a performance point of view considering ...

Broadband wireless communication is a very fast growing communication area. Multicarrier modulation techniques like Orthogonal Frequency Division Multiplexing (OFDM), Biorthogonal Frequency Division Multiplexing (BFDM), Pulse Shaping (PS) and Multi-Carrier Spread Spectrum (MCSS) have recently been introduced as robust techniques against intersymbol interference (ISI) and noise, compared to single carrier communication systems over fast fading multipath communication channels. Therefore, multicarrier modulation techniques have been considered as a candidate for new generation, high data rate broadband wireless communication systems and have been adopted as the related standards. Several examples are the European digital audio broadcasting (DAB) and digital video broadcasting (DVB), the IEEE standands for wireless local area networks (WLAN), 802.11a, and wireless metropolitan area networks (WMAN), 802.16a. However, Doppler frequency shifts, phase offset, local oscillator frequency shifts, and multi-path fading severely degrade the performance of multicarrier communication systems. For fast-varying channels, ...

The widespread use of mobile internet and smart applications has led to an explosive growth in mobile data traffic. With the rise of smart homes, smart buildings, and smart cities, this demand is ever growing since future communication systems will require the integration of multiple networks serving diverse sectors, domains and applications, such as multimedia, virtual or augmented reality, machine-to-machine (M2M) communication / the Internet of things (IoT), automotive applications, and many more. Therefore, in the future, the communication systems will not only be required to provide Gbps wireless connectivity but also fulfill other requirements such as low latency and massive machine type connectivity while ensuring the quality of service. Without significant technological advances to increase the system capacity, the existing telecommunications infrastructure will be unable to support these multi-dimensional requirements. This poses an important demand for suitable waveforms with ...

Error control coding is an essential part of modern communications systems. LDPC codes have been demonstrated to offer performance near the fundamental limits of channels corrupted by random noise. Optimal maximum likelihood decoding of LDPC codes is too complex to be practically useful even at short block lengths and so a graph-based message passing decoder known as the belief propagation algorithm is used instead. In fact, on graphs without closed paths known as cycles the iterative message passing decoding is known to be optimal and may converge in a single iteration, although identifying the message update schedule which allows single-iteration convergence is not trivial. At finite block lengths graphs without cycles have poor minimum distance properties and perform poorly even under optimal decoding. LDPC codes with large block length have been demonstrated to offer performance close to that predicted for ...

Wireless broadband communications for users moving at vehicular speed is a cor- nerstone of future fourth generation (4G) mobile communication systems. We inves- tigate a multi-carrier (MC) code division multiple access (CDMA) system which is based on orthogonal frequency division multiplexing (OFDM). A spreading sequence is used in the frequency domain in order to distinguish individual users and to take advantage of the multipath diversity of the wireless channel. The transmission is block oriented. A block consists of OFDM pilot and OFDM data symbols. At pedestrian velocities the channel can be modelled as block fading. We ap- ply iterative multi-user detection and channel estimation. In iterative receivers soft symbols are derived from the output of an soft-input soft-output decoder. These soft symbols are used in order to reduce the interference from other users and to enhance the channel estimates. We ...

This thesis represents a significant part of the research activity conducted during the PhD program in Information Technologies, supported by Selta S.p.A, Cadeo, Italy, focused on the analysis and design of a Power Line Communications (PLC) system. In recent times the PLC technologies have been considered for integration in Smart Grids architectures, as they are used to exploit the existing power line infrastructure for information transmission purposes on low, medium and high voltage lines. The characterization of a reliable PLC system is a current object of research as well as it is the design of modems for communications over the power lines. In this thesis, the focus is on the analysis of a full-duplex PLC modem for communication over high-voltage lines, and, in particular, on the design of the echo canceller device and innovative channel coding schemes. The first part ...

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 ...

This dissertation presents a general method and eight algebraic methods for constructing high performance and efficiently encodable non-binary quasi-cyclic LDPC codes based on arrays of special circulant permutation matrices. Two design techniques, array masking and array dispersion, for constructing both regular and irregular LDPC codes with desired specifications are also proposed. Codes constructed based on these methods perform very well over the AWGN channel and flat fading channels. With iterative decoding using a Fast Fourier Transform based sum-product algorithm, they achieve significantly large coding gains over Reed-Solomon codes of the same lengths and rates decoded with either algebraic hard-decision Berlekamp- Massey algorithm or algebraic soft-decision K¨otter-Vardy algorithm. Also presented is a class of asymptotically optimal LDPC codes for correcting bursts of erasures. Due to their quasi-cyclic structure, these non-binary LDPC codes can be encoded using simple shift-registers with linear complexity. ...

The aim of this dissertation is the investigation of the key issues encountered in the development of wideband radio air-interfaces. Orthogonal frequency-division multiplexing (OFDM) is considered as the enabling technology for transmitting data at extremely high rates over time-dispersive radio channels. OFDM is a transmission scheme, which splits up the data stream, sending the data symbols simultaneously at a drastically reduced symbol rate over a set of parallel sub-carriers. The first part of this thesis deals with the modeling of the time-dispersive and frequency-selective radio channel, utilizing second order Gaussian stochastic processes. A novel channel measurement technique is developed, in which the RMS delay spread of the channel is estimated from the level-crossing rate of the frequency-selective channel transfer function. This method enables the empirical channel characterization utilizing simplified non-coherent measurements of the received power versus frequency. Air-interface and multiple ...

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 ...

In a communication system it results undoubtedly of great interest to compress the information generated by the data sources to its most elementary representation, so that the amount of power necessary for reliable communications can be reduced. It is often the case that the redundancy shown by a wide variety of information sources can be modelled by taking into account the probabilistic dependance among consecutive source symbols rather than the probabilistic distribution of a single symbol. These sources are commonly referred to as single or multiterminal sources "with memory" being the memory, in this latter case, the existing temporal correlation among the consecutive symbol vectors generated by the multiterminal source. It is well known that, when the source has memory, the average amount of information per source symbol is given by the entropy rate, which is lower than its entropy ...

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 ...

Efficient decoding techniques for LDPC codes are in demand, since these codes are included in many standards nowadays. Although the theoretical performance of LDPC codes is impressive, their practical implementation leads to problems like numerical inaccuracy, limited memory resources, etc. We investigate methods that are suited to reduce the decoding complexity while still keeping the loss in performance small. We aim to reduce the complexity using three approaches: simplification of the component decoders, restricting the message passing algorithm to binary variables and combining the LDPC decoder with other receiver tasks like demapping or multi-user detection. For the simplification of the component decoders, we analyze the min-sum algorithm and derive a theoretical framework which is used to explain previous heuristic approaches to improve the performance of this algorithm. Using this framework, we are able to modify the algorithm in order to ...

Mobile communication networks of the third and future generations are designed to offer high-data rate services like video-telephony and data-transfer. The current Rake receiver architecture will create a shortage in available bandwidth offered to the users. This is not due to a shortage in spectrum but results from inefficient receiver architectures. Spectral efficiency can be increased considerably through multi-user detection techniques in the receiver algorithms. The present thesis investigates iterative re- ceivers for encoded CDMA transmission in the uplink. The iterative receiver is a suboptimal receiver algorithm with manageable complexity. It consists of an inter- ference mitigating multi-user detector, a bank of single-user decoders, and a channel estimator. Instead of deciding on the transmitted symbols right after the first decod- ing, the receiver feeds back tentative decision symbols to mitigate multiple-access interference in the next iteration. Similarly, soft decision symbols ...