Digital subscriber line (DSL) is a technology to provide broadband communications over the existing twisted pair telephone network. The signals received by a DSL modem are typically corrupted by channel induced noise, background noise, radio frequeny interference (RFI) and undesired echo. In this thesis we focus on the design of digital signal processing algorithms to improve the bit rate and/or the loop reach of current and future DSL systems. Furthermore, in the proposed algorithms we aim at keeping the hardware cost as low as possible. The transmission format of many DSL systems is based on discrete multitone modulation (DMT). To combat channel induced noise, DMT-based receivers perform an equalization step by means of a time domain equalizer (TEQ) and a one-tap frequency domain equalizer (FEQ) per used tone. Despite the variety of TEQ design methods presented in the literature, we ...

Broadband communications over the local telephone loop has become feasible nowadays by means of Digital Subscriber Line (DSL) technologies. Asymmetric DSL and one proposal for Very high bit rate DSL adopt Discrete Multitone (DMT) as modulation scheme. In this thesis we develop new equalization and echo cancellation structures for DMT-based receivers. Our main motivation is the application to DMT-based DSL-modems. In literature, a DMT-based receiver containing a multitap time domain equalizer (TEQ) and a 1-taps frequency domain equalizer per tone, has been presented. The TEQ is usually initialized by means of the so-called channel shortening algorithm. This does however not correspond to bit rate optimization, which is a major disadvantage. In part I, we aim at improving upon the channel shortening algorithm. In a first attempt, we maintain the receiver structure and only change the TEQ-initialization algorithm. In a second ...

The wireless communication industry has experienced rapid growth in recent years, and digital cellular systems are currently designed to provide high data rates at high terminal speeds. High data rates give rise to intersymbol interference (ISI) due to so-called multipath fading. Such an ISI channel is called frequency selective. On the other hand, due to terminal mobility and/or receiver frequency offset the received signal is subject to frequency shifts (Doppler shifts). Doppler shift induces time-selectivity characteristics. The Doppler effect in conjunction with ISI gives rise to a so-called doubly selective channel (frequency- and time-selective). In addition to the channel effects, the analog front-end may suffer from an imbalance between the I and Q branch amplitudes and phases as well as from carrier frequency offset. These analog front-end imperfections then result in an additional and significant degradation in system performance, especially ...

Digital subscriber line (DSL) technology is a very popular broadband access technology. It uses the existing telephone infrastructure to provide broadband access. In order to cope with the increased bandwidth demand to support broadband services, such as, Video on Demand (VoD), real time multimedia streaming, it is important to further improve the DSL. The main performance degradation of the DSL system is caused by channel impairments, such as, crosstalk and inter-symbol interference (ISI). Furthermore, the discrete Fourier transform (DFT) based discrete multitone (DMT) system has very poor spectral properties, which prohibit the use of tones at the band edges in order to meet the power spectral density (PSD) constraints of the system, thus reducing the achievable bit rate. In order to mitigate the channel impairments as well as to combat the poor spectral properties of the DFT based DMT, sophisticated ...

The ability to easily exchange and access data has transformed the way we work, study, inform and entertain ourselves. In particular, the Internet has had an effect on people’s lives in the past two decades that is profound. Profound as this effect may be, people seem not to grow tired of it. On the contrary: as of today, the Internet revolution is far from over. The thirst for bigger amounts of data at higher speeds and biquitous connectivity seem not to abate. This thirst for more, faster and better quality data is both a huge challenge and a huge opportunity for the broadband access industry. The opportunity lies on the fact that, as of the end of 2012, there were 600 million subscribers to broadband services around the world. Plus, even though the market is already enormous, it still has ...

Fourier transform (DFT). In the case of MCM, the transmitted data is encoded into blocks in the frequency domain, by using an inverse DFT (IDFT) at the transmitter. The receiver then consists of a DFT, followed by a one-tap complex equalizer for each tone. In SC-FDE the information is encoded into blocks in the time domain. At the receiver, the DFT and one-tap equalizer are followed by an extra IDFT. To avoid the loss of orthogonality between the tones, a guard interval (GI) is inserted between each two blocks. If the channel order doesn’t exceed the GI length, zero-forcing equalization is possible. For longer channels, a Per-Tone equalizer (PTEQ) can be used, which minimizes the mean square error of the received symbols. In practice, the individual bands are orthogonal but overlap, due to the slow roll-off of the DFT’s side ...

In xDSL technology, high-speed data are transferred between the central office and the customers, or between two or more central offices using unshielded telephone lines. A major impairment that hinders the increase in data-rate through the twisted-pair line is near-end crosstalk (NEXT) between the adjacent twisted pairs. DSL systems with overlapping transmit and receive spectra are susceptible to NEXT which significantly increases the interference noise in the received signal and also reduces the reliability and availability of the system. One way to cancel the NEXT in the received signal is to deploy adaptive filters. However, if adaptive filters are deployed to cancel every possible NEXT signal from the other twisted pairs, the computational complexity increases in proportion to N^2 where N is the number of twisted pairs in the bundle and, therefore, it becomes prohibitive even for small values of ...

The increasing number of simultaneous input and output channels utilized in immersive audio configurations primarily in broadcasting applications has renewed industrial requirements for efficient audio coding schemes with low bit-rate and complexity. This thesis presents a comprehensive review and extension of conventional approaches for perceptual coding of arbitrary multichannel audio signals. Particular emphasis is given to use cases ranging from two-channel stereophonic to six-channel 5.1-surround setups with or without the application-specific constraint of low algorithmic coding latency. Conventional perceptual audio codecs share six common algorithmic components, all of which are examined extensively in this thesis. The first is a signal-adaptive filterbank, constructed using instances of the real-valued modified discrete cosine transform (MDCT), to obtain spectral representations of successive portions of the incoming discrete time signal. Within this MDCT spectral domain, various intra- and inter-channel optimizations, most of which are of ...

Multi-Carrier (MC) modulation has various advantages that make it useful for a wide variety of digital communication systems. Actually, it has been chosen as the physical layer standard for a diversity of basic systems such as digital transmission over telephone lines, applications in broadcasting and in wireless networks. The most important advantage of the MC system is its robustness against interferences. In fact, the cyclic prefix (CP) insertion through MC symbols provides higher immunity against delay spread and interferences. Therefore, as long as channel dispersion is not longer than the CP, system performance does not degrade and the need of time-domain equalization is not usually immediate. However, highly time dispersive channel leads to a significant reduction of the transmission data rate since the received signal is corrupted by both inter-carrier and inter symbol interferences. To avoid such a performance degradation, ...

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 ...

When data is transmitted over the wireless communication channel, the transmit signal experiences distortion depending on the channel¢s fading characteristics. On the one hand, this calls for efficient processing at the receiver to mitigate the detrimental effects of the channel and maximize data throughput. On the other hand, the diversity inherently present in these channels can be leveraged with appropriate transmit processing in order to increase the reliability of the transmission link. Recently, in [1] it was shown that the channel characteristics can be exploited to maximize the total data throughput in the interference channel where multiple user pairs rely on the same resource to communicate among themselves. In this PhD dissertation, we first propose novel equalizer designs for frequency selective channels. We then present new results on the diversity gain of equalizers in fading channels when appropriate precoding is ...

The appetite amongst consumers for ever higher data-rates seems insatiable. This booming market presents a huge opportunity for telephone and cable operators. It also presents a challenge: the delivery of broadband services to millions of customers across sparsely populated areas. Fully bre-based networks, whilst technically the most advanced solution, are prohibitively expensive to deploy. Digital subscriber lines (DSL) provide an alternative solution. Seen as a stepping-stone to a fully bre-based network, DSL operates over telephone lines that are already in place, minimizing the cost of deployment. The basic principle behind DSL technology is to increase data-rate by widening the transmission bandwidth. Unfortunately, operating at high frequencies, in a medium originally designed for voice-band transmission, leads to crosstalk between the di erent DSLs. Crosstalk is typically 10-15 dB larger than the background noise and is the dominant source of performance degradation ...

In recent years, we have assisted to the dawn of many wireless and wireline communication technologies that have adopted multi-carrier modulation (MCM) at the physical layer. The basic idea ofMCMs is to transmit a high rate data stream by dividing it into low rate streams that are used to generate low rate signals each modulated at a given carrier frequency. The use ofMCMs allows for dividing the frequency selective channel into a set of narrow-band sub-channels. Consequently, the transmitted signal experiences, in each sub-channel, a quasi flat frequency response, so that, the equalization task simplifies to a sub-channel filtering. In addition to the simplification of the equalization task, there are several benefits deriving from the use of MCMs that, in general, depend upon the considered transmission medium. The most important ones are the low complexity digital implementation, and the possibility ...

Power reduction in digital communication systems can be achieved in many ways. Re- duction of the wordlengths used to represent data and control variables in the digital circuits comprising a communication system is an efective strategy, as register power consumption increases with wordlength. Another strategy is the reduction of the required data trans- mission rate, and hence speed of the digital circuits, by efficient source encoding. In this dissertation, applications of both of these power reduction strategies are investigated. The LMS adaptive filter, for which a myriad of applications exists in digital communi- cation systems, is optimized for performance with a power consumption constraint. This optimization is achieved by an analysis of the effects of wordlength reduction on both perfor- mance -transient and steady-state- as well as power consumption. Analytical formulas for the residual steady-state mean square error (MSE) due ...

In multiuser ultra-wideband (UWB) systems, a large number of multipath components (MPCs) are introduced by the channel. One of the main challenges for the receiver is to effectively suppress the interference with affordable complexity. In this thesis, we focus on the linear adaptive interference suppression algorithms for the direct-sequence ultrawideband (DS-UWB) systems in both time-domain and frequency-domain. In the time-domain, symbol by symbol transmission multiuser DS-UWB systems are considered. We first investigate a generic reduced-rank scheme based on the concept of joint and iterative optimization (JIO) that jointly optimizes a projection vector and a reduced-rank filter by using the minimum mean-squared error (MMSE) criterion. A low-complexity scheme, named Switched Approximations of Adaptive Basis Functions (SAABF), is proposed as a modification of the generic scheme, in which the complexity reduction is achieved by using a multi-branch framework to simplify the structure ...