Modeling Volatility Using GARCH Models: Evidence from Vietnam

We explore the relevance of GARCH models in explaining stock return dynamics and volatility on the Vietnamese stock market. Although the evidence suggests that volatility is prevalent on this market, the effects of shocks on volatility are symmetric. The standard GARCH(0,1) model provides the best description of return dynamics. The results of GARCH-M do not show any relation between expected returns and expected risk. There exists only Bull effect, one characteristic of the emerging market. However, we could not find Friday, and low_transaction effects on Vietnamese stock market.Keywords: Vietnamese stock markets, GARCH, volatility, return.

Dynamic Radio Cooperation for Downlink Cloud-RANs with Computing Resource Sharing

A novel dynamic radio-cooperation strategy is proposed for Cloud Radio Access Networks (C-RANs) consisting of multiple Remote Radio Heads (RRHs) connected to a central Virtual Base Station (VBS) pool. In particular, the key capabilities of C-RANs in computing-resource sharing and real-time communication among the VBSs are leveraged to design a joint dynamic radio clustering and cooperative beamforming scheme that maximizes the downlink weighted sum-rate system utility (WSRSU). Due to the combinatorial nature of the radio clustering process and the non-convexity of the cooperative beamforming design, the underlying optimization problem is NP-hard, and is extremely difficult to solve for a large network. Our approach aims for a suboptimal solution by transforming the original problem into a Mixed-Integer Second-Order Cone Program (MI-SOCP), which can be solved efficiently using a proposed iterative algorithm. Numerical simulation results show that our low-complexity algorithm provides close-to-optimal performance in terms of WSRSU while significantly outperforming conventional radio clustering and beamforming schemes. Additionally, the results also demonstrate the significant improvement in computing-resource utilization of C-RANs over traditional RANs with distributed computing resources.Comment: 9 pages, 6 figures, accepted to IEEE MASS 201

Understanding the Computational Requirements of Virtualized Baseband Units using a Programmable Cloud Radio Access Network Testbed

Cloud Radio Access Network (C-RAN) is emerging as a transformative architecture for the next generation of mobile cellular networks. In C-RAN, the Baseband Unit (BBU) is decoupled from the Base Station (BS) and consolidated in a centralized processing center. While the potential benefits of C-RAN have been studied extensively from the theoretical perspective, there are only a few works that address the system implementation issues and characterize the computational requirements of the virtualized BBU. In this paper, a programmable C-RAN testbed is presented where the BBU is virtualized using the OpenAirInterface (OAI) software platform, and the eNodeB and User Equipment (UEs) are implemented using USRP boards. Extensive experiments have been performed in a FDD downlink LTE emulation system to characterize the performance and computing resource consumption of the BBU under various conditions. It is shown that the processing time and CPU utilization of the BBU increase with the channel resources and with the Modulation and Coding Scheme (MCS) index, and that the CPU utilization percentage can be well approximated as a linear increasing function of the maximum downlink data rate. These results provide real-world insights into the characteristics of the BBU in terms of computing resource and power consumption, which may serve as inputs for the design of efficient resource-provisioning and allocation strategies in C-RAN systems.Comment: In Proceedings of the IEEE International Conference on Autonomic Computing (ICAC), July 201

Farmland Acquisition and Household Livelihoods in Hanoi's Peri-Urban Areas

While farmland loss (due to urbanisation and industrialisation) causes job losses for a huge number of farmers and threatens food security, it can bring about a wide range of new job opportunities for local people through which they can change their livelihoods and improve their welfare. The literature in Vietnam and some other countries reveals that although there has been much discussion about the mixed impacts of farmland loss on rural household livelihoods, none of these impacts has been quantified thus far. This thesis is the first study to use econometric methods for quantifying the various impacts of farmland loss on households' livelihood strategies and outcomes. Using survey data from 477 randomly sampled households in 6 communes in a peri-urban district of Hanoi, several regression models were used to examine how and to what extent farmland loss has affected rural household livelihoods in Vietnam. Specifically, three key relationships were considered and tested: (i) the relationship between farmland loss and household livelihood strategies; (ii) the relationship between farmland loss and household livelihood outcomes (income and consumption expenditure); and (iii) the relationship between farmland loss and household income shares by source. It was found that farmland loss has a positive impact on the choice of non-farm work-based strategies, notably the informal wage work-based strategy. Given the impact of farmland loss, households' income shares actually diversified into non-farm sources, especially informal wage income. Interestingly, the results indicate that farmland loss, coupled with compensation, has no negative impact on livelihood outcomes (neither income nor consumption expenditure per capita). Possibly this can be explained by the fact that a number of households used part of their compensation money for smoothing consumption. In addition, income earned from jobs outside of farming might compensate for or even exceed the loss of farm income due to the loss of farmland. This suggests that farmland loss can have an indirect positive effect on livelihood outcomes (through its positive effect on non-farm participation). This thesis makes several key contributions. Firstly, with a combination of an adapted analytical framework and appropriate econometric models, this study provides a proper approach for studies of the relationship between farmland loss and rural household livelihoods. Secondly, it provides the first econometric evidence for the links between farmland loss and household livelihood strategies and outcomes. Finally, based on the empirical results, this study proposes valuable policy recommendations for mitigating negative impacts of farmland loss on rural households and helping them achieve better livelihood outcomes

Nonfarm employment and household income among ethnic minorities in Vietnam

This study examines the determinants of nonfarm participation and the effect of nonfarm employment on household income among ethnic minorities in the Northwest Mountains, Vietnam. The logistic regression analysis shows that education and the availability of local enterprises or trade villages, notably among other factors, have a significantly increasing impact on the likelihood of taking up wage employment, while the presence of paved roads gives households more chance to engage in nonfarm self-employment. Using a propensity score matching analysis, the study found that households that participated in wage or nonfarm self-employment have higher levels of per capita income than those without nonfarm employment. The findings imply that nonfarm employment offers a pathway out of poverty for ethnic minorities

Government financial support and firm productivity in Vietnam

Using the Färe-Primont index and instrumental variable fixed effect estimation for the data of small and medium-sized enterprises (SMEs), this study considers if receiving government financial support enables SMEs in Vietnam to become more productive. The paper discovers no evidence of linkage between financial support and firm productivity. However, access to financial support improves technological progress and growth in firm scale but has a negative effect on improvement in technical efficiency. The estimation results reveal that the use of productivity as an aggregated index in previous studies may hide the real effect of government support on firm productivity

Heterogeneous effects of livelihood strategies on household well-being: An analysis using unconditional quantile regression with fixed effects

Using a household panel dataset for the 2008-2016 period, we analyze the heterogeneous effects of livelihood change on household well-being in rural Vietnam. We use an unconditional quantile regression (UQR) model with fixed effects to control for unobservable time-invariant household characteristics. We find that when a fixed-effects estimator is employed, households switching from a crop livelihood to any non-crop livelihood (e.g., livestock, wage-earning, nonfarm or private transfer livelihoods) increase their per capita income and food consumption. However, the results from the UQR with fixed effects reveal a significant variation in the effect of such a switch in livelihood across various quantiles of well-being distribution, with a larger effect for poorer households. The income effect, however, tends to decline with higher quantiles and even turns negative with a switch to a wage-earning or public transfer livelihood for the better off. Notably, our study confirms the advantage for the poor of changing livelihood from crop to non-crop activities in rural Vietnam. Our research results also suggest that a mean regression approach, that often assumes a homogeneous/mean effect of livelihoods on well-being, may miss some heterogeneity that is useful to researchers and policy makers

Duality Theory on Vector Spaces

In this paper, we study the Fenchel-Rockafellar duality and the Lagrange duality in the general frame work of vector spaces without topological structures. We utilize the geometric approach, inspired from its successful application by B. S. Mordukhovich and his coauthors in variational and convex analysis (see \cite{CBN21,CBNC,CBNG22,CBNG,m-book,mn-book}). After revisiting coderivative calculus rules and providing the subdifferential maximum rule in vector spaces, we establish conjugate calculus rules under qualifying conditions through the algebraic interior of the function's domains. Then we develop sufficient conditions which guarantee the Fenchel-Rockafellar strong duality. Finally, after deriving some necessary and sufficient conditions for optimal solutions to convex minimization problems, under a Slater condition via the algebraic interior, we then obtain a sufficient condition for the Lagrange strong duality.Comment: 21 pages. arXiv admin note: text overlap with arXiv:2106.1577