http://dspace.cityu.edu.hk:80/handle/2031/20 2013-06-17T12:06:14Z 2013-06-17T12:06:14Z Wang, Hao (汪浩) http://dspace.cityu.edu.hk:80/handle/2031/7013 2013-06-13T02:39:28Z 2012-01-01T00:00:00Z

Title: Impact of antenna correlation on multi-user MIMO systems Authors: Wang, Hao (汪浩) Abstract: Multiple-input multiple-output (MIMO) techniques provide a promising solution to enhance the performance of wireless communication systems. Antenna correlation exists in practical MIMO systems for two reasons. First, there may be no sufficient space to separate antenna elements due to the limited physical sizes of the transmitters and/or the receivers. Second, the practical propagation environments may not provide sufficient scatters. In a conventional single-user MIMO system, since antenna correlation results in reduced degrees of freedom (DOF) and may severely degrade the system capacity, it has been generally regarded as a negative factor. However, the impact of antenna correlation in multi-user environments is still limited explored. In this thesis, we make a comprehensive study on theoretical and practical aspects of multi-user MIMO systems with correlated fading. In the first contribution, the capacity of correlated MIMO systems with full channel state information (CSI) at both the transmitters and the receiver over multiple access channels (MACs) (i.e. uplink multi-user MIMO systems) is analyzed. In contrast to the common views, we show that antenna correlation is potentially beneficial in a multi-user environment. The key is that the spatial diversity related to user locations (i.e., multi-user diversity) can compensate the loss of DOF due to antenna correlation. More specifically, it is shown numerically that there is a cross point between the capacity curves for systems with and without correlation. Below this point, correlation is advantageous and vice versa. Moreover, such a point occurs at a rate increasing with the number of mobile units (MUs) (denoted by K in this thesis), which implies that the range where antenna correlation is beneficial increases with K. We also quantify this advantage analytically in the limiting case of K → ∞. In the meanwhile, it is shown numerically and analytically that there is a similar advantage from antenna correlation for MIMO MACs with rate constraints. (We call this advantage correlation gain in this thesis.) In the second contribution, we study the impact of antenna correlation on the capacity of MIMO MACs with imperfect CSI at the transmitter (CSIT). We first consider the case of no CSIT.We prove that isotropic inputs (i.e., the covariance of transmitted signal for each MU is identity matrix) are the most robust and optimal ones, and therefore achieve the capacity of such systems. Both numerical results and theoretical analysis show that although antenna correlation is detrimental in all rate or power range, the capacity degradation decreases with K increasing and vanishes when K → ∞. These results imply that besides multi-user diversity, CSIT also plays an important role in exploiting correlation gain. We then study the systems with partial CSIT in form of channel covariance information (CCI). Our major finding is that, similar to the scenario of perfect CSIT, antenna correlation is potentially beneficial in a multi-user environment. We also prove that, when antennas at MUs are fully correlated, systems with CCI at transmitters can obtain exact the same correlation gain as that in systems with perfect CSIT. This indicates that CCI may be enough to exploit the potential benefit of antenna correlation. In the third contribution, we extend the results from the MAC scenario to the broadcast channel (BC) scenario (i.e., downlink multi-user MIMO systems). Numerical results show that, similar to MIMO MACs, antenna correlation can potentially improve the capacity of MIMO BCs. We point out that, besides multiuser diversity and power focusing effect, such a gain mainly comes from the fact that antenna correlation can increase the variance of the channel gain, which has already been regarded as a advantageous factor in systems with user scheduling. We also quantify the correlation gain in BCs for the limiting case of K → ∞ when antennas at the base station (BS) and/or MUs are fully correlated. Theoretical analysis shows that the asymptotic correlation gain for the case of full correlation at both the BS and MUs grows linearly and logarithmically with the antenna number at the BS, and logarithmically with the antenna number at each MU. In the final contribution, we consider the practical implementation aspects of correlation gain in coded MIMO multiple-access systems. To decrease the complexity of MIMO transmission under imperfect CSIT, we propose two types of low-cost but asymptotically optimal strategies, i.e. the instantaneous maximum eigenmode beamforming (MEB) and statistical MEB strategy. Interleave-division multiple-access (IDMA) technique, as a low-cost iterative multi-user detection (MUD) approach, is adopted to alleviate inter-user interference resulting from multi-user concurrent transmission. Simulation results demonstrate that our proposed transceiver (i.e., MEB-based IDMA system) is an effective platform in practice to obtain the aforementioned correlation gain. In summary, this thesis presents a comprehensive study on antenna correlation in multi-user MIMO systems. Both numerical and analytical results show that antenna correlation is potential advantageous in a multi-user environment. Such an advantage mainly comes from three aspects. First, the loss of the spatial DOF due to antenna correlation is compensated by multi-user diversity. Second, antenna correlation enables focusing power. Third, the variance of the channel gain is enlarged by antenna correlation, which is beneficial in systems with user scheduling. The finding in this thesis is useful in practice as minimizing the physical size of MUs and/or the BS is highly desirable, but it may result in antenna correlation. Notes: CityU Call Number: TK5103.4836 .W36 2012; xi, 91, iii leaves : ill. 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2012.; Includes bibliographical references (leaves [83]-91)

2012-01-01T00:00:00Z Jiang, Feng (姜峰) http://dspace.cityu.edu.hk:80/handle/2031/7012 2013-06-13T02:39:26Z 2012-01-01T00:00:00Z

Title: Culture and experience : Chinese and Americans judgment about experience-related issues Authors: Jiang, Feng (姜峰) Abstract: Human experience is the crucial connection of the outer world and inner world, as well as the important foundation of human existence. Although experience happens almost every day, it has been overlooked by psychologists for a long time. Regarding this issue, a series questions can be asked for psychologists: Do we prefer to cope with new situations by consulting prior experience or depending upon exploratory approach? What is the reason for adopting certain strategies? Is our cultural background involved? In this dissertation, Chinese and American psychological approaches to experience were differentiated in terms of reflective orientation versus exploratory orientation. Chinese ways of understanding experience - considering it as a rigid or closed entity that should always be obeyed and abided by, result in a reflective approach. In contrast, American ways of understanding experience - regarding it as a tool or method to explore the unknown world and to obtain knowledge, result in an exploratory approach. This dissertation builds on four studies conducted to test our contention and results are as follows. Chinese preferred reflective proverbs that emphasize the importance of experiences whereas Americans preferred exploratory proverbs that stress on the importance of exploration (Study 1). Chinese were more likely to attribute their success or achievement to experiences whereas Americans were more likely to attribute it to their exploration (Study 2). Chinese tended to evaluate the reflective-oriented values more important whereas American tended to evaluate the exploratory-oriented values more important (Study 3). Chinese prediction was more easily influenced by prior information whereas Americans prediction was immune to prior information (Study 4). Implications and future direction about the reflective-exploratory orientations are discussed. Notes: CityU Call Number: BF637.E97 J63 2012; vi, 118 leaves 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2012.; Includes bibliographical references (leaves 88-103)

2012-01-01T00:00:00Z Hu, Kang (胡康) http://dspace.cityu.edu.hk:80/handle/2031/7011 2013-06-13T02:39:23Z 2012-01-01T00:00:00Z

Title: The effect of social capital on civic engagement in urban China Authors: Hu, Kang (胡康) Abstract: Against a backdrop of weakening social solidarity, inadequate government efficiency, and widening economic inequality that might have emerged in China urban society after Deng Xiaoping's economic reforms since late 1970s, the present study proposed three types of civic engagement that may contribute to understand and tackle these issues. First, the Durkheimian civic engagement refers to the kinds of civic engagement that may strengthen social solidarity. Second, the Weberian civic engagement refers to the kinds of civic engagement that may facilitate the rationalisation of government. Third, the Marxian civic engagement refers to the kinds of civic engagement that may potentially reduce economic inequality of a society. Specifically, two forms of Durkheimian civic engagement are identified: citizen cooperation and generalised altruism. Citizen cooperation refers to the cooperative behaviours among citizens to resolve public problems in their community, while generalised altruism refers to a citizen's altruistic behaviours, such as charitable donations and volunteering, that are oriented to the less fortunate in society. A form of Weberian civic engagement is identified: influencing government. This refers to those actions that are intended to resolve public problems by influencing government. A form of Marxian civic engagement is identified: voting participation. This refers to citizen's voting participation in institutionalised elections. The mechanisms of these three types of civic engagement were investigated by a survey with 867 respondents and supplementary in-depth interviews with 17 urban residents. The findings reveal an indigenised view of the effect of social capital on civic engagement in urban China, with three major findings. First, social capital was a robust predictor of all three types of civic engagement; however, social capital's effect on Durkheimian type was more prominent than its effects on Weberian and Marxian type. Second, the specific means social capital motivated the three types of civic engagement varied across each other. For instance, while the public affairs discussion increased by social capital was effective in inducing Durkheimian and Weberian types of civic engagement, it was irrelevant to Marxian civic engagement. In addition, while the generalised norm of reciprocity strengthened by social capital was effective in inducing Durkheimian and Marxian types of civic engagement, it was irrelevant to Weberian civic engagement. Third, it is revealed that the two Chinese cultural values - Confucian moral progression value and socialist collectivism value - that the present study investigated did not impact individual-level social capital's effect on civic engagement. However, endorsement of the Confucian moral progression value was able to reinforce the contextual effects of community-level social capital on Durkheimian and Weberian types of civic engagement, and endorsement of the socialist collectivism value was able to reinforce the contextual effects of community-level social capital on Durkheimian civic engagement. This study argues the variations exist across social capital's effects on the three types of civic engagement might be due to some institutional arrangement of current urban society of China. As for Durkheimian type, various institutions such as local governments, Community Residents' Committee, workplace, and schools all are able to induce people to engage. However, the channels for Weberian type are quite limited due to constraints exerted by the current political regime. In addition, the paternalistic government-governed relationship arising from China's Confucian cultural tradition may also make people avoid addressing public problems through Weberian civic engagement. As for Marxian civic engagement, barriers exist for urban residents, who do not have a local residential status, to participate in the election of Community Residents' Committee and the election of local level People's Congress. The present study concluded that, to address the declining social solidarity, inadequate government efficiency, and widening economic inequality in the post-reform urban society, not only should public policy makers pay attention to the importance of social capital, but also need to reform the institutional constraints that potentially weakened the motivational power of social capital. Notes: CityU Call Number: HN733.5 .H798 2012; xv, 327 leaves 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2012.; Includes bibliographical references (leaves 274-289)

2012-01-01T00:00:00Z Liu, Suet Yee (廖雪怡) http://dspace.cityu.edu.hk:80/handle/2031/7010 2013-06-13T02:39:21Z 2012-01-01T00:00:00Z

Title: Augmented reality display of three-dimensional impossible objects in real time Authors: Liu, Suet Yee (廖雪怡) Abstract: The first impression of three-dimensional impossible object often fools viewer's perception to believe that this object exists physically in the real world. However, on a second though, viewer will recognize that the shape of the object is impossible indeed. There are many ways to create impossible object. The simplest form of impossible object can be created from two-dimensional drawing. Besides two-dimensional drawing, people construct other kinds of impossible objects by different approaches, such as using curved edges to built a physical object in order to swap the overlapping parts; construct the object in a special way and take photograph of it from a specific angle; take a photograph of a real object and post-edit it with image editing tools, etc. Generally speaking, object created in these ways need to be viewed from a very special vantage point to have an impossible effect. If the object is not viewed from that specific vantage point, the illusion of the impossible object will not be possible. Apart from that, computer graphics researchers also introduced a way to generate impossible object on computer which could be viewed from different angles; however, this method only applied to certain kinds of object which have volume inside its framework. This thesis will first introduce a way to identify the types of impossible objects. Then it explores a new way for creating different impossible objects on a computer display in real time, using the so-called Augmented Reality (AR) technology. AR is a novel technology which brings a new visual experience to the viewer. Different from Virtual Reality (VR), the virtual objects display on the computer can be overlay on real objects or physical environment in real time in order to create an augmented experience. With the use of tracking technology, we can place a fiduciary marker in front of the camera to give a signal to the computer's program where we plan to generate the impossible object. Using a special design of real-time shading algorithm, impossible object can be created in real-time on the fiduciary marker. Viewer can then orient the fiduciary marker so as to rotate the three-dimensional impossible object. This can give a better experience for the viewer on how the impossible object is formed. Two categories of impossible object generating techniques will be introduced in this thesis: 1) the depth impossible object and 2) the impossible vanishing boundaries object. Notes: CityU Call Number: TA1637 .L584 2012; v, 88 leaves : ill. (some col.) 30 cm. + 1 CD-ROM (4 3/4 in.); Thesis (M.Phil.)--City University of Hong Kong, 2012.; Includes bibliographical references (leaves 85-87)

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