The major contribution of this thesis is on the problem of transmit beamforming to multiple cochannel multicast groups. Two viewpoints are considered: i) minimizing total transmission power while guaranteeing a prescribed minimum signal-to-interference-plus-noise ratio (SINR) at each receiver; and ii) a "fair" approach maximizing the overall minimum SINR under a total power budget. The core problem is a multicast generalization of the multiuser downlink beamforming problem; the difference is that each transmitted stream is directed to multiple receivers, each with its own channel. Such generalization is relevant and timely, e.g., in the context of the emerging WiMAX and UMTS-LTE wireless networks. The joint multicast beamforming problem is in general NP-hard, motivating the pursuit of computationally efficient quasi-optimal solutions. In chapter 1, it is shown that semidefinite relaxation coupled with suitable randomization / cochannel multicast power control yield computationally efficient high-quality ...

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 ...

Source coding concerns the representation of information in a source signal using as few bits as possible. In the case of lossy source coding, it is the encoding of a source signal using the fewest possible bits at a given distortion or, at the lowest possible distortion given a specified bit rate. Channel coding is usually applied in combination with source coding to ensure reliable transmission of the (source coded) information at the maximal rate across a channel given the properties of this channel. In this thesis, we consider the coding of auto-regressive (AR) sources which are sources that can be modeled as auto-regressive processes. The coding of AR sources lends itself to linear predictive coding. We address the problem of joint source/channel coding in the setting of linear predictive coding of AR sources. We consider channels in which individual ...

Multiple-input multiple-output (MIMO) technology promises significant capacity improvements in order to more efficiently utilise the radio frequency spectrum. To achieve its anticipated multiplexing gain as well as meet the requirements for high data rate services, proposed broadband systems are based on OFDM or similar block based techniques, which are afflicted by poor design freedom at low redundancy, and are known to suffer badly from co-channel interference (CCI) in the presence of synchronisation errors. Non-block based approaches are scarce and use mostly decision feedback equalisation (DFE) or V-BLAST approaches adopted for the broadband case, as well as Tomlinson-Harashima precoding (THP). These methods do not require a guard interval and can therefore potentially achieve a higher spectral efficiency. The drawback of these schemes is the large effort in determining the optimum detection order in both space and time, often motivating the adoption ...

In multi-user (MU) downlink beamforming, a high spectral efficiency along with a low transmit power is achieved by separating multiple users in space rather than in time or frequency using spatially selective transmit beams. For streaming media applications, multi-group multicast (MGM) downlink beamforming is a promising approach to exploit the broadcasting property of the wireless medium to transmit the same information to a group of users. To limit inter-group interference, the individual streams intended for different multicast groups are spatially separated using MGM downlink beamforming. Spatially selective downlink beamforming requires the employment of an array of multiple antennas at the base station (BS). The hardware costs associated with the use of multiple antennas may be prohibitive in practice. A way to avoid the expensive employment of multiple antennas at the BS is to exploit user cooperation in wireless networks where ...

High compression ratio, scalability and reliability are the main issues for transmitting multimedia content over best effort networks. Scalable image and video coding meets the user requirements by truncating the scalable bitstream at different quality, resolution and frame rate. However, the performance of scalable coding deteriorates rapidly over packet networks if the base layer packets are lost during transmission. Multiple description coding (MDC) has emerged as an effective source coding technique for robust image and video transmission over lossy networks. In this research problem of incorporating scalability in MDC for robust image and video transmission over best effort network is addressed. The first contribution of this thesis is to propose a strategy for generating more than two descriptions using multiple description scalar quantizer (MDSQ) with an objective to jointly decoded any number of descriptions in balanced and unbalanced manner. The ...

In the last years, research has focused on multiple-input multiple-output (MIMO) wireless technology due to the capacity and performance improvement it provides, offering a higher spectral efficiency. In addition, when multiple users take part in the network, the scenario becomes much more complex, since resources like bandwidth, time or transmission power must be shared. Furthermore, the performance of the system is degraded as a consequence of the noise and multiuser interference (MUI). When the transmission is conducted from a base station (BS) to multiple users, a pre-equalization stage called precoding is applied. By means of this, each user will be able to interpret the signal independently, without the knowledge of the channel. Precoding techniques are classified into linear and non-linear. In fact, the non-linear Tomlinson-Harashima precoding (THP) and vector precoding (VP) techniques have been shown to achieve very good results ...

In this thesis, we investigate the following three fields on multi-input multi-output (MIMO) systems with limited feedback. End-to-end distortion: The first part of the thesis presents the joint impact of antenna numbers, source-to-channel bandwidth ratio, spatial correlation and time diversity on the optimum expected end-to-end distortion in an outage-free MIMO system. In particular, based on the analytical expression for any signal-to-noise ratio (SNR), the closed-form expression of the asymptotic optimum expected end-to-end distortion at a high SNR is derived, comprised of the optimum distortion exponent and the optimum distortion factor. The simulation results illustrate that, at a practical high SNR, the analysis on the impacts of the optimum distortion exponent and the optimum distortion factor explains the behavior of the optimum expected end-to-end distortion. The results in this part could be the performance objectives for analog-source transmission systems as well ...

An important specificity of wireless communication channels are the rapid fluctuations of propagation coefficients. This effect is called fading and is caused by the motion of obstacles, scatterers and reflectors standing along the different paths of electromagnetic wave propagation between the transmitting and the receiving terminal. These changes in the geometry of the wireless channel prompt the attenuation coefficients and the relative phase shifts between the multiple propagation paths to vary. This suggests to model the channel coefficients (the transfer matrix) as random variables. The present thesis studies information rates for reliable transmission of information over fading channels under the realistic assumption that the receiver has only imperfect knowledge of the random fading state. While the over-idealized assumption of perfect channel-state information at the receiver (CSIR) gives rise to many simple expressions and is fairly well understood, the settings with ...

Wyner-Ziv (WZ) video coding is a particular case of distributed video coding, a new video coding paradigm based on the Slepian-Wolf and Wyner-Ziv theorems which mainly exploit the source correlation at the decoder and not only at the encoder as in predictive video coding. Therefore, this new coding paradigm may provide a flexible allocation of complexity between the encoder and the decoder and in-built channel error robustness, interesting features for emerging applications such as low-power video surveillance and visual sensor networks among others. Although some progress has been made in the last eight years, the rate-distortion performance of WZ video coding is still far from the maximum performance attained with predictive video coding. The WZ video coding compression efficiency depends critically on the capability to model the correlation noise between the original information at the encoder and its estimation generated ...

In this thesis we construct and analyze index-assignment based multiple-description coding schemes.

Multi-input multi-output (MIMO) wireless networks and distributed MIMO relaying wireless networks have attracted significant attention in current generation of wireless communication networks, and will play a key role in the next generation of wireless net- works. The improvement of network capacity, data rate and reliability can be achieved at the cost of increasing computational complexity of employing space-time coding (STC) and distributed STC (DSTC) in MIMO and distributed MIMO relaying networks, respectively. Efficient designs and algorithms to achieve high diversity and coding gains with low computational complexity in encoding and decoding of STC and DSTC schemes are essential. In this thesis, DSTC designs with high diversity and coding gains and efficient detection and code matrices optimization algorithms in cooperative MIMO networks are proposed. Firstly, adaptive power allocation (PA) algorithms with different criteria for a coop- erative MIMO network equipped with ...

Multi-antenna processing is widely adopted as one of the key enabling technologies for current and future cellular networks. Particularly, multiuser downlink beamforming (also known as space-division multiple access), in which multiple users are simultaneously served with spatial transmit beams in the same time and frequency resource, achieves high spectral efficiency with reduced energy consumption. To harvest the potential of multiuser downlink beamforming in practical systems, optimal beamformer design shall be carried out jointly with network resource allocation. Due to the specifications of cellular standards and/or implementation constraints, resource allocation in practice naturally necessitates discrete decision makings, e.g., base station (BS) association, user scheduling and admission control, adaptive modulation and coding, and codebook-based beamforming (precoding). This dissertation focuses on the joint optimization of multiuser downlink beamforming and discrete resource allocation in modern cellular networks. The problems studied in this thesis involve ...

In 1948, the Shannon’s work titled ”A mathematical theory of communication” completely revolutionized the way to understand the problem of the reliable communications. He showed that any communications system is able to transmit with an arbitrarily low error probability as long as the transmission rate is kept below a certain limit. The separation between the source and channel coding was also shown as the optimal strategy to achieve the theoretical limits. Those ideas inspire the development of a whole digital communication theory focused on building more and more sophisticated coding schemes. It leads to most of communication systems were designed according to a digital approach and the separation principle from that moment, whereas other alternatives were set aside. However, in the last years, communication systems based on a jointly optimization of the source and channel encoder has aroused the interest ...

The aim of this dissertation is the study of cooperative communications in wireless networks. In cooperative networks, each user transmits its own data and also aids the communication of other users. User cooperation is particularly attractive for the wireless medium, where every user listens to the transmission of other users. The main benefit of user cooperation in wireless networks is, probably, its efficacy to combat the wireless channel impairments. Path loss and shadowing effects are overcome using intermediate nodes, with better channel conditions, to retransmit the received signal to the estination. Further, the channel fading effect can be also mitigated by means of cooperative spatial diversity (the information arrives at the destination through multiple independent paths). These benefits result in an increase of the users spectral efficiency and/or savings on the overall network power resource. Besides these gains, the simple ...