63,137 research outputs found

    Multi-Round Contention in Wireless LANs with Multipacket Reception

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    Multi-packet reception (MPR) has been recognized as a powerful capacity-enhancement technique for random-access wireless local area networks (WLANs). As is common with all random access protocols, the wireless channel is often under-utilized in MPR WLANs. In this paper, we propose a novel multi-round contention random-access protocol to address this problem. This work complements the existing random-access methods that are based on single-round contention. In the proposed scheme, stations are given multiple chances to contend for the channel until there are a sufficient number of ``winning" stations that can share the MPR channel for data packet transmission. The key issue here is the identification of the optimal time to stop the contention process and start data transmission. The solution corresponds to finding a desired tradeoff between channel utilization and contention overhead. In this paper, we conduct a rigorous analysis to characterize the optimal strategy using the theory of optimal stopping. An interesting result is that the optimal stopping strategy is a simple threshold-based rule, which stops the contention process as soon as the total number of winning stations exceeds a certain threshold. Compared with the conventional single-round contention protocol, the multi-round contention scheme significantly enhances channel utilization when the MPR capability of the channel is small to medium. Meanwhile, the scheme automatically falls back to single-round contention when the MPR capability is very large, in which case the throughput penalty due to random access is already small even with single-round contention

    A Different Look at Inward FDI into Mainland China

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    This paper aims to find out the relationship between inward FDI into China and China's economic development. According to the descriptive analysis of FDI data from 1980 till 2007, we firstly found that there is a sectoral and regional biased distribution with regard to the inward FDI into China; we saw that the contribution of inward FDI to China's economic development exhibits a reversed U shape (the turning point locates in the year of 2001). In order to figure out the main reason and the causal-effect relationship between inward FDI into China and China's economic growth, we used ECM and Granger Causality Test based on the data between 1978 and 2001 in the second part. We found that within this period the causal-effect relationship between China's economic development and inward FDI was bidirectional and the causal impact of China's economic development on FDI was larger than the impact of FDI on China's economic development. To discover the reason of reduced FDI contribution to China's economic development since 2001 onwards, we used the fixed-effect panel analysis based on a panel dataset consisting 31 provinces in China from 2001 to 2005. We found that inward FDI in China since 2001 onwards has negative spillover effect on China's economic development. We argue that the reason might be the duplication effect of foreign firms, negative externalities of backward, forward and horizontal relationships between foreign and domestic firms, increased welfare loss, and China's regional economic disparity.Foreign direct investment, economic growth, externalities, spillovers, China

    Alliance-based Network View on Chinese Firms' Catching-up: Case Study of Huawei Technologies Co.Ltd

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    With China's rapid economic growth in recent years, many Chinese firms especially in high-tech industries have started to technically lead in the international market. In this study, we aim to uncover the root causes that lead to Chinese firms' catching up from network perspective. By taking Huawei Technologies Co. Ltd. as a case, we integrate absorptive capacity development and firm-level catching up into an alliances-based network framework. We found that network alliances with firms and universities complement each other at different catching up stages; and alliances-based network provides a springboard for Chinese firms to shorten catching up path. We argue that in Chinese context, impact of FDI on firms' performance comes into effect only if partnership is carried out; alliances with universities facilitate development of absorptive capacity at an early stage; Partnering with leading players stimulate R&D investment at a late stage and simultaneously enhance firm's innovation performance as well.Strategic alliances, Network, Chinese firms, absorptive capacity, catching up
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