There is a dearth of information on community radio in South Africa; although much attention has been given to the role of community radio in development, education and community representation, there has been very little focus on community radio’s functioning within South Africa’s current broadcast system. The researcher explored the viability of the current conception of community radio by means of a literature review, as well as an examination of the South African Advertising Research Foundation’s listener figures for community radio stations across South Africa. The researcher then investigated how conducive the present broadcasting climate is to the growth of this medium through the use of a campus radio station as case-study. Semi-structured interviews were held with the management staff of a campus radio station; a thematic analysis was then conducted on the completed interviews so as to extract the meanings inherent in the participant’s experience. As such, the question of whether community radio can continue to survive within South Africa’s three-tier system of broadcasting without a radical re-conceptualization of the broadcasting system itself, was addressed. The researcher explored what community radio gives to the world of broadcasting that commercial and public radio does not, and how these contributions can be compounded to ensure the long term sustainability of this medium. These arguments were then put forth in the creation of a hypothetical re-conceptualization of a new broadcasting system. / Dissertation (M (Research Psychology))--University of Pretoria, 2007. / Psychology / M (Research Psychology) / unrestricted

A converse method is developed for the source broadcast problem. Specifically, it is shown that the separation architecture is optimal for a variant of the source broadcast problem and the associated source-channel separation theorem can be leveraged, via a reduction argument, to establish a necessary condition for the original problem, which uni es several existing results in the literature. Somewhat surprisingly, this method, albeit based on the source-channel separation theorem, can be used to prove the optimality of non-separation based schemes and determine the performance limits in certain scenarios where the separation architecture is suboptimal. / Thesis / Master of Applied Science (MASc)

Suppose there is a transmitter located at each vertex of a graph G. A k-limited broadcast on G is an assignment of the integers 0,1,...,k to the vertices of G. The integer assigned to the vertex x represents the strength of the broadcast from x, where strength 0 means the transmitter at x is not broadcasting. A broadcast of positive strength s from x is heard by all vertices at distance at most s from x. A k-limited broadcast is called dominating if every vertex assigned 0 is within distance d of a vertex whose transmitter is broadcasting with strength at least d. The k-limited broadcast domination number of G is the minimum possible value of the sum of the strengths of the broadcasts in a k-limited dominating broadcast of G. We establish upper and lower bounds for the 2-limited broadcast domination number of various grid graphs, in particular the Cartesian products of two paths, a path and a cycle, and two cycles. The upper bounds are derived by explicit broadcast constructions for these graphs. The lower bounds are obtained via linear programming duality by finding lower bounds for the fractional 2-limited multipacking number of these graphs. Finally, we present an algorithm to improve the lower bound for the 2-limited broadcast domination number of special sub-families of grids. We conclude this thesis with suggested open problems in broadcast domination and multipackings. / Graduate

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / The Broadcast Scheduling Problem (BSP) is a well known NP-complete problem that arises in the study of wireless networks. In the BSP, a finite set of stations are to be scheduled in a time division multiple access (TDMA) frame. The objective is a collision free transmission schedule with the minimum number of TDMA slots and maximal slot utilization. Such a schedule will minimize the total system delay. We present variations of a Greedy Randomized Adaptive Search Procedure (GRASP) for the BSP. Path-relinking, a post-optimization strategy is applied. Also, a reactivity method is used to balance GRASP parameters. Numerical results of our research are reported and compared with other heuristics from the literature.

This thesis investigates four FEC (forward error correction) coding schemes for their suitability for a broadcast system where there is one energy-rich transmitter and many energy-constrained receivers with a variety of channel conditions. The four coding schemes are: repetition codes (the baseline scheme); Reed-Solomon (RS) codes; Luby-Transform (LT) codes; and a type of RS and LT concatenated codes. The schemes were tested in terms of their ability to achieve both high average data reception success probability and short data reception time at the receivers (due to limited energy). The code rate (Rc) is fixed to either 1/2 or 1/3. Two statistical channel models were employed: the memoryless channel and the Gilbert-Elliott channel. The investigation considered only the data-link layer behaviour of the schemes. During the course of the investigation, an improvement to the original LT encoding process was made, the name LTAM (LT codes with Added Memory) was given to this improved coding method. LTAM codes reduce the overhead needed for decoding short-length messages. The improvement can be seen for decoding up to 10000 number of user packets. The maximum overhead reduction is as much as 10% over the original LT codes. The LT-type codes were found to have the property that can both achieve high success data reception performance and flexible switch off time for the receivers. They are also adaptable to different channel characteristics. Therefore it is a prototype of the ideal coding scheme that this project is looking for. This scheme was then further developed by applying an RS code as an inner code to further improve the success probability of packet reception. The results show that LT&RS code has a significant improvement in the channel error tolerance over that of the LT codes without an RS code applied. The trade-off is slightly more reception time needed and more decoding complexity. This LT&RS code is then determined to be the best scheme that fulfils the aim in the context of this project which is to find a coding scheme that both has a high overall data reception probability and short overall data reception time. Comparing the LT&RS code with the baseline repetition code, the improvement is in three aspects. Firstly, the LT&RS code can keep full success rate over channels have approximately two orders of magnitude more errors than the repetition code. This is for the two channel models and two code rates tested. Secondly, the LT&RS code shows an exceptionally good performance under burst error channels. It is able to maintain more than 70% success rate under the long burst error channels where both the repetition code and the RS code have almost zero success probability. Thirdly, while the success rates are improved, the data reception time, measured in terms of number of packets needed to be received at the receiver, of the LT&RS codes can reach a maximum of 58% reduction for Rc = 1=2 and 158% reduction for Rc = 1=3 compared with both the repetition code and the RS code at the worst channel error rate that the LT&RS code maintains almost 100% success probability.

The pervasiveness of wireless communications in modern society is unprecedent. Using numerous wireless technologies, including cellular, WiFi, WiMax and others, users gain ubiquitous access to a wealth of information services relevant to their everyday lives. These include communication services (voice, email, text), commercial transactions (e-banking, e-trading), location-based services (points of interest, navigation), social networking, web access, and others. Further proliferation of mobile services and applications provided via wireless communications is contingent upon the network's reliability and security. As this wireless revolution continues to unfold, users have grown increasingly concerned with the amount of sensitive information that leaks to unauthorized parties. They have also become more skeptical to the abilities of current technologies in providing a reliable and secure environment. The problem of ensuring network reliability and security is particularly challenging in the wireless domain. The open nature of the wireless medium leaves it accessible to any device equipped with a transceiver. Wireless networks remain vulnerable to numerous attacks, including eavesdropping, packet modification and injection, replay, impersonation, and jamming. Moreover, the poor physical security of the majority of wireless stations (mobile devices, sensor, etc.) makes them susceptible to physical compromise. Such compromised devices become a launchpad for internal attacks from adversaries with intimate knowledge of network secrets and protocol specifications. Internal attacks are much harder to counter than external ones since the adversary can bypass typical cryptographic methods that authorize user access. In this dissertation, we investigate attacks on wireless communications launched by internal adversaries. In particular, we are concerned with sophisticated intentional interference (jamming) attacks against broadcast communications. Such attacks have been shown to be detrimental to network operation. We further consider the problem of distributed node coordination in dynamic spectrum networks. To address these problems, we design novel communication protocols that protect broadcast communications from internal attacks via a combination of randomization, redundancy and cryptographic techniques. We propose new security metrics to quantify the ability of the adversary to deny access to the broadcast channel. We introduce a randomized distributed scheme that allows nodes to establish and maintain the broadcast channel in the presence of the jammer. Also this scheme uniquely identifies the set of compromised nodes, both when nodes are acting independently and when they are colluding. To protect broadcast communication performed on control channel, we propose a secure broadcast scheme called TDBS, which implements the broadcast operation as a series of unicast transmissions, distributed in frequency and time. Finally, we address the problem of dynamically assigning the control channel in CRNs based on time- and space-varying spectrum opportunities. We propose a cluster-based architecture that allocates different channels for control at various clusters in the network. The clustering problem is formulated as a bipartite graph problem, for which we develop a class of algorithms to implement. Extensive simulations are conducted to verify the validity of the proposed mechanisms.

In a world that is increasingly relying on digital technologies, the ability to securely communicate and distribute information is of crucial importance. Cryptography plays a key role in this context and the research presented in this thesis focuses on developing cryptographic primitives whose properties address more closely the needs of users. We start by considering the notion of robustness in public-key encryption, a property which models the idea that a ciphertext should not decrypt to a valid mes- sage under two different keys. In contexts where anonymity is relevant, robustness is likely to be needed as well, since a user cannot tell from the ciphertext if it is intended for him or not. We develop and study new notions of robustness, relating them to one another and showing how to achieve them. We then consider the important issue of protecting users' privacy in broadcast encryption. Broadcast encryption (BE) is a cryptographic primitive designed to efficiently broadcast an encrypted message to a target set of users that can decrypt it. Its extensive real-life application to radio, television and web-casting renders BE an extremely interesting area. However, all the work so far has striven for efficiency, focusing in particular on solutions which achieve short ciphertexts, while very little attention has been given to anonymity. To address this issue, we formally define anonymous broadcast encryption, which guarantees recipient-anonymity, and we provide generic constructions to achieve it from public-key, identity-based and attribute-based encryption. Furthermore, we present techniques to improve the efficiency of our constructions. Finally, we develop a new primitive, called time-specific encryption (TSE), which allows us to include the important element of time in the encryption and decryption processes. In TSE, the sender is able to specify during what time interval a ciphertext can be decrypted by a receiver. This is a relevant property since information may become useless after a certain point, sensitive data may not be released before a particular time, or we may wish to enable access to information for only a limited period. We define security models for various flavours of TSE and provide efficient instantiations for all of them. These results represent our efforts in developing public-key encryption schemes with enhanced properties, whilst maintaining the delicate balance between security and efficiency.

Master of Science / Department of Agronomy / Dorivar Ruiz Diaz / Corn (Zea mays) response to fertilization and placement methods has been studied extensively; however studies on soybean [Glycine max (L.) Merr.] response to placement have been limited. Three studies were completed to evaluate different aspects of crop response. The objective of the first study was to evaluate the effect of starter and broadcast fertilizer application on corn and soybean, in a typical corn-soybean rotation in Kansas. Treatments were unfertilized control, starter (N, P and K), broadcast P and K using mono ammonium phosphate (MAP) and potassium chloride (KCl) and the combination of starter and broadcast. Corn and soybean yield generally was not affected by starter and broadcast treatments. Thus fertilization may be recommended only under specific conditions. The objectives of the second study were (i) to evaluate the effect of residual and direct fertilization on soybeans after corn under a corn-soybean rotation system, and (ii) study the effect of fertilizer P and K application on soil test P (STP) and soil test K (STK) changes over time. Direct fertilization increased soybean yield while residual fertilizer did not. Therefore maintenance rates may be effective to improve soybean yield and likely maintain STP and STK levels. Application of P and K fertilizer generated significant increases in STP and STK after one year of application. The rate of P and K fertilizer required to increase 1 mg kg-1 yr-1 was between 2.8 - 5.1 kg ha-1 for P and between 1.0- 2.5 kg ha-1 for K, respectively. The objective of the third study evaluate both corn and soybean response to direct P fertilization including starter and broadcast. The treatments were a control, two starter fertilizers (with N-P and N only), five P rates (9.8, 19.6, 29.3, 39.1, 48.9 kg P ha-1) and one treatment with starter fertilizer in addition to the broadcast fertilizer application. Corn grain yield was not significantly affected by any broadcast or starter treatments. Broadcast application rates significantly increased soybean yield on low STP levels. Results of this study show that large corn or soybean yield response to starter and broadcast P application are likely with low STP levels.

This thesis is about the relationship between Hurricane Katrina and the television news industry. My goal was to record the experiences of my fellow co-workers at WWL-TV, which was the only local television station to remain on the air throughout the hurricane. I also wanted to perform a review of the news industry up until the point of the storm, in order to analyze any affects the hurricane may have had on news coverage in general.

Understanding the effects of quality metrics on the user behavior is important for the increasing number of content providers in order to maintain a competitive edge. The two data sets used are gathered from a provider of live streaming and a provider of video on demand streaming. The important quality and non quality features are determined by using both correlation metrics and relative importance determined by machine learning methods. A model that can predict and simulate the user behavior is developed and tested. A time series model, machine learning model and a combination of both are compared. Results indicate that both quality features and non quality features are important in understanding user behavior, and the importance of quality features are reduced over time. For short prediction times the model using quality features is performing slightly better than the model not using quality features.