The safety-message dissemination problem for vehicular ad hoc networks (VANETs) was investigated. Four novel techniques were contributed for the efficient and reliable routing of safety messages in the vehicular ad hoc networks. The instant-broadcast technique was proposed to improve the end-to-end dissemination delay. The lane-based sectoring mechanism was presented for the collision mitigation in the dense-urban traffic scenario. The negative acknowledgment with smart neighborhood (NSN) technique was proposed to ensure the reliability of reception through recovering the packet loss caused by interference. Finally, the negative acknowledgment with smart neighborhood - hole recovery (NSN-H) technique was presented to provide guaranteed reception of the safety message at each individual node in the VANET. The investigation of the safety message routing in VANET conducted in this research also revealed the significance of hitherto-neglected factors that influence the vehicular network. Significance of the small payload size of the VANET safety message, the effect of road width on the multi-hop relay, and the attenuation caused by vehicles in the propagation path were among the important revealed factors.

Employment of the multiple-antenna transmitters/receivers in communication systems is known as a promising solution to provide high-data-rate wireless links. In the multi-user environments, the problems of signaling and fairness for multi-antenna systems have emerged as challenging problems. This dissertation deals with these problems in several multi-antenna multi-user scenarios. In part one, a simple signaling method for the multi-antenna broadcast channels is proposed. This method reduces the MIMO broadcast system to a set of parallel channels. The proposed scheme has several desirable features in terms of: (i) accommodating users with different number of receive antennas, (ii) exploiting multi-user diversity, and (iii) requiring low feedback rate. The simulation results and analytical evaluations indicate that the achieved sum-rate is close to the sum-capacity of the underlying broadcast channel. In part two, for multiple-antenna systems with two transmitters and two receivers, a new non-cooperative scenario of data communication is studied in which each receiver receives data from both transmitters. For such a scenario, a signaling scheme is proposed which decomposes the system into two broadcast or two multi-access sub-channels. Using the decomposition scheme, it is shown that this signaling scenario outperforms the other known non-cooperative schemes in terms of the achievable multiplexing gain. In particular for some special cases, the achieved multiplexing gain is the same as the multiplexing gain of the system, where the full cooperation is provided between the transmitters and/or between the receivers. Part three investigates the problem of fairness for a class of systems for which a subset of the capacity region, which includes the sum-capacity facets, forms a polymatroid structure. The main purpose is to find a point on the sum-capacity facet which satisfies a notion of fairness among active users. This problem is addressed in the cases where the complexity of achieving interior points is not feasible, and where the complexity of achieving interior points is feasible. In part four, $K$-user memoryless interference channels are considered; where each receiver sequentially decodes the data of a subset of transmitters before it decodes the data of the designated transmitter. A greedy algorithm is developed to find the users which are decoded at each receiver and the corresponding decoding order such that the minimum rate of the users is maximized. It is proven that the proposed algorithm is optimal. The results of the parts three and four are presented for general channels which include the multiple-antenna systems as special cases.

Cell Broadcast is a relatively old technique within the GSM-network which makes it possible to broadcast text messages to one or more cells in the network. As efforts in Sweden have been made to develop both traffic safety and information technology, the automotive telematics market is predicted to grow rapidly in the near future. The characteristics of Cell Broadcast make it especially suitable for automotive telematics services. The main purpose of this thesis is to investigate possible automotive telematics services based on Cell Broadcast and how these services can affect traffic safety. The most important characteristics for Cell Broadcast in the automotive telematics market are close connection to the GSM/UMTS network, location-based information and information of push character. These characteristics allows the mobile operator to offer a number of automotive telematics services based on Cell Broadcast, some of them as service provider and some of them in joint ventures with car and mobile terminal manufacturers.

Employment of the multiple-antenna transmitters/receivers in communication systems is known as a promising solution to provide high-data-rate wireless links. In the multi-user environments, the problems of signaling and fairness for multi-antenna systems have emerged as challenging problems. This dissertation deals with these problems in several multi-antenna multi-user scenarios. In part one, a simple signaling method for the multi-antenna broadcast channels is proposed. This method reduces the MIMO broadcast system to a set of parallel channels. The proposed scheme has several desirable features in terms of: (i) accommodating users with different number of receive antennas, (ii) exploiting multi-user diversity, and (iii) requiring low feedback rate. The simulation results and analytical evaluations indicate that the achieved sum-rate is close to the sum-capacity of the underlying broadcast channel. In part two, for multiple-antenna systems with two transmitters and two receivers, a new non-cooperative scenario of data communication is studied in which each receiver receives data from both transmitters. For such a scenario, a signaling scheme is proposed which decomposes the system into two broadcast or two multi-access sub-channels. Using the decomposition scheme, it is shown that this signaling scenario outperforms the other known non-cooperative schemes in terms of the achievable multiplexing gain. In particular for some special cases, the achieved multiplexing gain is the same as the multiplexing gain of the system, where the full cooperation is provided between the transmitters and/or between the receivers. Part three investigates the problem of fairness for a class of systems for which a subset of the capacity region, which includes the sum-capacity facets, forms a polymatroid structure. The main purpose is to find a point on the sum-capacity facet which satisfies a notion of fairness among active users. This problem is addressed in the cases where the complexity of achieving interior points is not feasible, and where the complexity of achieving interior points is feasible. In part four, $K$-user memoryless interference channels are considered; where each receiver sequentially decodes the data of a subset of transmitters before it decodes the data of the designated transmitter. A greedy algorithm is developed to find the users which are decoded at each receiver and the corresponding decoding order such that the minimum rate of the users is maximized. It is proven that the proposed algorithm is optimal. The results of the parts three and four are presented for general channels which include the multiple-antenna systems as special cases.

The demand for wireless data services has been dramatically growing over the last decade. This growth has been accompanied by a significant increase in the number of users sharing the same wireless medium, and as a result, interference management has become a hot topic of research in recent years. In this dissertation, we investigate feedback and transmitter cooperation as two closely related tools to manage the interference and achieve high data rates in several wireless networks, focusing on additive white Gaussian noise (AWGN) interference, X, and broadcast channels. We start by a one-to-many network, namely, the three-user multiple-input multiple-output (MIMO) Gaussian broadcast channel, where we assume that the transmitter obtains the channel state information (CSI) through feedback links after a finite delay. We also assume that the feedback delay is greater than the channel coherence time, and thus, the CSI expires prior to being exploited by the transmitter for its current transmission. Nevertheless, we show that this delayed CSI at the transmitter (delayed CSIT) can help the transmitter to achieve significantly higher data rates compared to having no CSI. We indeed show that delayed CSIT increases the channel degrees of freedom (DoF), which is translated to an unbounded increase in capacity with increasing signal-to-noise-ratio (SNR). For the symmetric case, i.e. with the same number of antennas at each receiver, we propose different transmission schemes whose achievable DoFs meet the upper bound for a wide range of transmit-receive antenna ratios. Also, for the general non-symmetric case, we propose transmission schemes that characterize the DoF region for certain classes of antenna configurations. Subsequently, we investigate channels with distributed transmitters, namely, Gaussian single-input single-output (SISO) K-user interference channel and 2×K X channel under the delayed CSIT assumption. In these channels, in major contrast to the broadcast channel, each transmitter has access only to its own messages. We propose novel multiphase transmission schemes wherein the transmitters collaboratively align the past interference at appropriate receivers using the knowledge of past CSI. Our achievable DoFs are greater than one (which is the channel DoF without CSIT), and strictly increasing in K. Our results are yet the best available reported DoFs for these channels with delayed CSIT. Furthermore, we consider the K-user r-cyclic interference channel, where each transmitter causes interference on only r receivers in a cyclic manner. By developing a new upper bound, we show that this channel has K/r DoF with no CSIT. Moreover, by generalizing our multiphase transmission ideas, we show that, for r=3, this channel can achieve strictly greater than K/3 DoF with delayed CSIT. Next, we add the capability of simultaneous transmission and reception, i.e. full-duplex operation, to the transmitters, and investigate its impact on the DoF of the SISO Gaussian K-user interference and M×K X channel under the delayed CSIT assumption. By proposing new cooperation/alignment techniques, we show that the full-duplex transmitter cooperation can potentially yield DoF gains in both channels with delayed CSIT. This is in sharp contrast to the previous results on these channels indicating the inability of full-duplex transmitter cooperation to increase the channel DoF with either perfect instantaneous CSIT or no CSIT. With the recent technological advances in implementation of full-duplex communication, it is expected to play a crucial role in the future wireless systems. Finally, we consider the Gaussian K-user interference and K×K X channel with output feedback, wherein each transmitter causally accesses the output of its paired receiver. First, using the output feedback and under no CSIT assumption, we show that both channels can achieve DoF values greater than one, strictly increasing in K, and approaching the limiting value of 2 as K→∞. Then, we develop transmission schemes for the same channels with both output feedback and delayed CSIT, known as Shannon feedback. Our achievable DoFs with Shannon feedback are greater than those with the output feedback for almost all values of K.

This Master’s Thesis examines transnational conflicts and Christian-Muslim relations in Nigeria between the years 2001 and 2006. It focuses on two major transnational conflicts: The September 11, 2001 attacks in the United States and the Danish cartoon controversy of 2005/2006. It discusses the impact of these transnational conflicts on Christian-Muslim relations in Nigeria in the light of the implementation of the Sharia Law in some northern Nigerian states and the improved access to the broadcast media and mobile telephone communication in Nigeria. By underscoring the relationship between transnational conflicts and the local context, this study provides a new perspective for understanding Christian-Muslim relations in Nigeria

In a MIMO system, a transmitter with perfect knowledge of the underlying channel state information (CSI) can achieve a higher channel capacity compared to transmission without CSI. When reciprocity of the wireless channel does not hold, the identification and utilization of partial CSI at the transmitter are important issues. This thesis is focused on partial CSI acquisition and utilization techniques for MIMO channels. We propose a feedback algorithm for tracking the dominant channel subspaces for MIMO systems in a continuously time-varying environment. We exploit the correlation between channel states of adjacent time instants and quantize the variation of channel states. Specifically, we model a subspace as one point in a Grassmann manifold, treat the variations in principal right singular subspaces of the channel matrices as a piecewise-geodesic process in the Grassmann manifold, and quantize the velocity matrix of the geodesic. We design a complexity-constrained MIMO OFDM system where the transmitter has knowledge of channel correlations. The transmitter is constrained to perform at most one inverse Discrete Fourier Transform per OFDM symbol on the average. We show that in the MISO case, time domain beamforming can be used to do two-dimensional eigen-beamforming. For the MIMO case, we derive design criteria for the transmitter beamforming and receiver combining weighting vectors and show some suboptimal solutions. The feedback channel may have uncertainties such as unexpected delay or error. We consider channel mean feedback with an unknown delay and propose a broadcast approach that is able to adapt to the quality of the feedback. Having considered CSI feedback problems where the receiver tries to convey its attained CSI to the transmitter, we turn to noncoherent coding design for fast fading channels, where the receiver does not have reliable CSI. We propose a data-dependent superimposed training scheme to improve the performance of training based codes. The transmitter is equipped with multiple training sequences and dynamically selects a training sequence for each data sequence to minimize channel estimation error. The set of training sequences are optimized to minimize pairwise error probability between codewords.

Diversity methods are used to improve the reliability of the communication between transmitter and receiver. These methods use redundancy to reduce the errors in the communication link. Apart from the conventional diversity methods, multiuser diversity has an aim of maximizing the sum capacity of a multi-user system. To benefit from multiuser diversity, the opportunistic scheduling method grants the channel access to the user which has the best channel quality among all users. Therefore, the cumulative sum of the information sent to all users, which is the sum capacity, is maximized in the long term. Although the opportunistic scheduling maximizes the sum capacity, it has some drawbacks such as the feedback load growing with the number of users and the problem of fairness for the users which may have lower channel quality than some other users. In this thesis, these two issues are investigated for the broadcast channels. Feedback quantization, which gives partial information on the channel state, is studied to mitigate the feedback load with a goal of little loss in the sum capacity. The thresholds for the finite feedback quantization are determined to provide fairness and to reduce the feedback load at the same time. To provide fairness, users are grouped into clusters and thresholds are optimized for each cluster. A method is proposed by extending the one given by Floren et. al. to solve the mentioned problems and the proposed method is compared with some other scheduling methods in the literature.

In an energy harvesting communication system, energy is derived from outside sources and becomes partially available at different points in time. The constraints induced by this property on energy consumption plays an active role in the design of efficient communication systems. This thesis focuses on the optimal design of transmission and networking schemes for energy harvesting wireless communication systems. In particular, an energy harvesting transmitter broadcasting data to two receivers in an AWGN broadcast channel assuming that energy harvests and data arrivals occur at known instants is considered. In this system, optimal packet scheduling that achieves minimum delay is analyzed. An iterative algorithm, DuOpt, that achieves the same structural properties as the optimal schedule is proposed. DuOpt is proved to obtain the optimal solution when weaker user data is ready at the beginning. A dual problem is defined and shown to be strictly convex. Taking advantage of the dual problem, uniqueness of the solution of the main problem is proved. Finally, it is observed that DuOpt is almost two orders of magnitude faster than the SUMT (sequential unconstrained minimization technique) algorithm that solves the same problem.

This study examined the differences in reporting in Radio-Television of Serbia's (RTS) main newscast, Dnevnik 2, between the period of Slobodan Milosevic’s rule (1989-2000) and the period after the establishment of democracy in Serbia (2001-2009). The data were gathered by the content analysis of 63 RTS newscasts in the period 1989-2009. The research included quantitative analysis as well as additional observations of RTS newscasts noted at the time of coding. The major findings suggest that in the democratic period (2001-2009) RTS newscasts become shorter, more consistent in duration, less dedicated to coverage of state and ruling party officials’ activities, and more inclined to reporting about social issues and other political events. The number of voices in RTS newscasts became significantly higher. The overall reporting became more balanced and more diverse. At the same time RTS kept the old priority in news reporting which put Official Stories in leading positions and remained occasionally inclined to increase the number of Official Stories in times of important political events. Based on these results this study derived the following hypotheses for state/public service television stations in countries in transition: 1) consistency of duration of newscasts increases as the regime in the country becomes less controlling 2) the dominance of Official Stories decreases as the regime in the country becomes less controlling 3) the number of sound bites in newscasts increases as the regime becomes less controlling (the number of voices in newscasts increases as the democracy progresses), and 4) the coverage of Official Stories increases in times of important domestic political events, possibly those that have endangered national security, even if the regime becomes less controlling.