Towards Fully Optimized BICM Transceivers

Bit-interleaved coded modulation (BICM) transceivers often use equally spaced constellations and a random interleaver. In this paper, we propose a new BICM design, which considers hierarchical (nonequally spaced) constellations, a bit-level multiplexer, and multiple interleavers. It is shown that this new scheme increases the degrees of freedom that can be exploited in order to improve its performance. Analytical bounds on the bit error rate (BER) of the system in terms of the constellation parameters and the multiplexing rules are developed for the additive white Gaussian Noise (AWGN) and Nakagami-$m$ fading channels. These bounds are then used to design the BICM transceiver. Numerical results show that, compared to conventional BICM designs, and for a target BER of $10^{-6}$, gains up to 3 dB in the AWGN channel are obtained. For fading channels, the gains depend on the fading parameter, and reach 2 dB for a target BER of $10^{-7}$ and $m=5$.Comment: Submitted to the IEEE Transactions on Communication

Small enterprise development in Bangladesh : a study of nature and effectiveness of support services

This thesis examines empirically the demand for as well as the supply, design and the effects of small enterprise support services in Bangladesh. Recognition of the role of small enterprises in economic growth and development has resulted in promoting institutions for providing support services to these enterprises in most developing countries. From the very beginning, expectations have been very high on the effectiveness of this supply-side intervention in fostering healthy growth of the small enterprises sector. As a result, there now exist numerous agencies, both in the public and private sector, for providing support services. However, the initial high expectations about the effectiveness of these services now seem somewhat over optimistic or, as in some cases, even unrealistic, giving rise to a re-examination of the effectiveness of these services and the institutions involved, particularly between the public and private sector organisations. In the literature, apart from the question of the nature and need for support services from small enterprises, there is also the issue of how these services can be evaluated. To address the issues of evaluation, a framework is developed, bringing together major influences on the evaluation process. The framework was applied to a sample of predominantly manufacturing small enterprises, located in the district of Dhaka - the capital city of Bangladesh. Data were gathered through interviews with owner-managers of the small firms. The study also surveyed major public and private support agencies involved in the small enterprise sector. The findings support a view that, overall, the effect of assistance is low, in terms of growth in sales, employment and value added. Financial assistance, however, seems to have a considerable effect on survival, start-up process, production and sales turnover of small firms. Here, the study underlines the importance of extensive support, comprising financial and non financial components. It uncovered that most firms do not receive the services they need and want. The study confirms the view that an agency - which is private, small, autonomous, closer to its clients in terms of people, processes and structures employed, and provider of financial and non financial assistance - can effectively meet the needs of small firms. Thus, private support agencies are well suited in terms of design and are more effective, perhaps due to their pre-selection of few viable small firms, unlike the public agencies. There is evidence, however, to conclude that public support organisations play a major role in the survival of small firms, usually less attractive to private support agencies. Overall, the study underpins the view that assistance can be a trigger to the development of small enterprises, if it is selective. Evaluation of support services, as the findings suggest, can be done by an exploration of the supply-demand interaction, viewing supply-inputs through a process to ultimate outputs. Finally, the study recommends, among others, a restructuring by formation of partnership between the public and private support agencies for the promotion and development of small enterprises in Bangladesh

Throughput Maximization in Cloud Radio Access Networks using Network Coding

This paper is interested in maximizing the total throughput of cloud radio access networks (CRANs) in which multiple radio remote heads (RRHs) are connected to a central computing unit known as the cloud. The transmit frame of each RRH consists of multiple radio resources blocks (RRBs), and the cloud is responsible for synchronizing these RRBS and scheduling them to users. Unlike previous works that consider allocating each RRB to only a single user at each time instance, this paper proposes to mix the flows of multiple users in each RRB using instantly decodable network coding (IDNC). The proposed scheme is thus designed to jointly schedule the users to different RRBs, choose the encoded file sent in each of them, and the rate at which each of them is transmitted. Hence, the paper maximizes the throughput which is defined as the number of correctly received bits. To jointly fulfill this objective, we design a graph in which each vertex represents a possible user-RRB association, encoded file, and transmission rate. By appropriately choosing the weights of vertices, the scheduling problem is shown to be equivalent to a maximum weight clique problem over the newly introduced graph. Simulation results illustrate the significant gains of the proposed scheme compared to classical coding and uncoded solutions.Comment: 7 pages, 7 figure