A THEORY OF DIGITAL DIVIDE: WHO GAINS AND LOSES FROM TECHNOLOGICAL CHANGES?

This paper attempts to answer the question: How does the income gap between workers and capitalists evolve over time in the period of ITC and globalization increasing international technology creation and transfers? The model bases on a Romer¡¯s type of variety expansion of intermediate goods. We assume that there are two types of agents supplying two different types of factors. Workers supply specific skill weighted labor by accumulating their specific skills that depreciate with an introduction of new intermediate goods. The other type of agents, R&D agents, produce and sell new varieties of intermediate goods monopolistically after inventing them. The model yields: Depending on the elasticity of substitution between the two factors and on the value of the factor share, an increase in the efficiency of technology creation (or lowering the barriers on the imports of intermediate goods) affects the growth rates of workers¡¯ and R&D agents¡¯ average income differently. First, if the elasticity of substitution is greater than one, in a certain stage of development, an advance in ITC or ¡®globalization¡¯ increases the growth rate of R&D agents¡¯ average income, while it decreases that of workers¡¯. Thus, the ¡®Digital Divide¡¯ happens. Conversely, if the elasticity of substitution is less than one, the result will be reversed. These results are intuitively obvious. Second, if an economy develops from a higher factor share of the workers to a sufficiently lower one, the growth rates of GNP, and the average incomes of both workers and R&D agents increase over time.Romer¡¯s Model, R&D, Specific Skill, Digital Divide

Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems

We study optimal delivery strategies of one common and $K$ independent messages from a source to multiple users in wireless environments. In particular, two-layered superposition of broadcast/multicast and unicast signals is considered in a downlink multiuser OFDMA system. In the literature and industry, the two-layer superposition is often considered as a pragmatic approach to make a compromise between the simple but suboptimal orthogonal multiplexing (OM) and the optimal but complex fully-layered non-orthogonal multiplexing. In this work, we show that only two-layers are necessary to achieve the maximum sum-rate when the common message has higher priority than the $K$ individual unicast messages, and OM cannot be sum-rate optimal in general. We develop an algorithm that finds the optimal power allocation over the two-layers and across the OFDMA radio resources in static channels and a class of fading channels. Two main use-cases are considered: i) Multicast and unicast multiplexing when $K$ users with uplink capabilities request both common and independent messages, and ii) broadcast and unicast multiplexing when the common message targets receive-only devices and $K$ users with uplink capabilities additionally request independent messages. Finally, we develop a transceiver design for broadcast/multicast and unicast superposition transmission based on LTE-A-Pro physical layer and show with numerical evaluations in mobile environments with multipath propagation that the capacity improvements can be translated into significant practical performance gains compared to the orthogonal schemes in the 3GPP specifications. We also analyze the impact of real channel estimation and show that significant gains in terms of spectral efficiency or coverage area are still available even with estimation errors and imperfect interference cancellation for the two-layered superposition system