41408712
Combined cross-layer design and HARQ for multiuser systems with outdated channel state information at transmitter (CSIT) in slow fading channels
Cross-layer scheduling and hybrid ARQ (HARQ) are effective means to improve the spectral efficiency of wireless systems. However, most of the existing works handle HARQ and cross-layer scheduling in a decoupled manner based on heuristic approaches. In this paper, we propose an integrated design framework for cross-layer scheduling and HARQ design in multiuser systems with slow fading channel and outdated knowledge of channel state information at the base station (CSIT). We consider both the chase combining and incremental redundancy in HARQ. We define the average system goodput (which measures the average bits successfully delivered to the receiver) as the measure of system performance. Based on information theoretical approach, we derive the asymptotically optimal cross-layer policy (power allocation, rate allocation and user selection policies) to optimize the average system goodput with HARQ. In addition, we derive analytically the closed-form expression of the average system goodput, from which we can obtain useful design insights such as the role of HARQ in the overall cross-layer gain, the tradeoff between the system goodput and the HARQ delay as well as the sensitivity of the average system goodput with respect to the CSIT quality.
26253657
Web mapping service on second life compatible virtual world system
Online virtual world such as second life becomes more and more popular nowadays. And way-finding in large-scale virtual worlds becomes important problem for both novices and experts. Similar to the physical world, a well-designed mapping system would play an important role in way-finding process. However, Second Life only supports thumbnail map system right now. The thumbnail map system could only provide an overview of the area and with no query support. There are several challenges to develop a better virtual mapping system. First, identify the virtual world geo-features and to develop proper criteria and algorithms to generate features from primitive which is the basic unit in virtual world. Second, provide web service for data access through the Internet from systems with different architectures. In this paper, we implemented a prototype map service system called VWMS conformed to OWS specification from OpenGIS consortium. The prototype includes an AJAX style map site and a feature generalization server-module extracting geo-feature from Open Simulator primitive database. Besides, the system also provides a Web Map Service interface for interoperability.1
3505472
Decentralized Fair Scheduling in Two-Hop Relay-Assisted Cognitive OFDMA Systems
In this paper, we consider a two-hop relay-assisted cognitive downlink Orthogonal frequency-division multiple access (OFDMA) system (named as secondary system) dynamically accessing a spectrum licensed to a primary network, thereby improving the efficiency of spectrum usage. A cluster-based relay-assisted architecture is proposed for the secondary system, where relay stations are employed for minimizing the interference to the users in the primary network and achieving fairness for cell-edge users in the secondary system. Based on this architecture, an asymptotically optimal solution is derived for jointly controlling data rates, transmission power, and subchannel allocation to optimize the average weighted sum goodput where the proportional fair scheduling (PFS) is included as a special case. This solution supports decentralized implementation, requires small communication overhead, and is robust against imperfect channel state information at the transmitter (CSIT) and imperfect sensing measurement. The proposed solution achieves significant throughput gain and better user-fairness compared with the existing designs. Finally, we derive a simple and asymptotically optimal scheduling solution as well as the associated closed-form performance under the proportional fair scheduling for a large number of users. The system throughput is shown to be O(N(1-qp)(1-qpN)lnlnKc), where Kc is the number of users in one cluster, N is the number of subchannels, and qp is the active probability of primary users.
7644449
A new scaling law on throughput and delay performance of wireless mobile relay networks over parallel fading channels
In this paper, utilizing the relay buffers, we propose an opportunistic decode-wait-and-forward relay scheme for a point-to-point communication system with a half-duplexing mobile relay network. The proposed scheme achieves the maximum throughput of Θ(log K) at a cost of O(1) total transmission power and O(K=q) average end-to-end packet delay, where 0 ≪ q ≤ ½ measures the speed of relays' mobility. It can be proved that this system throughput is unattainable for the existing designs with low relay mobility. Therefore, the proposed relay scheme can exploit the time diversity and relays' mobility more efficiently.
18276513
Decentralized Fair Resource Allocation for Relay-Assisted Cognitive Cellular Downlink Systems
In this paper, we consider a relay-assisted cognitive cellular downlink system dynamically accessing a spectrum licensed to a primary network, thereby improving the efficiency of spectrum usage. A cluster-based relay-assisted architecture is proposed, where relay stations are employed for minimizing the interference to users in the primary network and achieving fairness for cell-edge users. Based on this architecture, an optimal solution is derived for jointly controlling data rate, transmission power, and subband allocation to optimize the weighted sum goodput where proportional fair scheduling (PFS) is included as a special case. As shown by simulations, the proposed solution achieves significant throughput gains and better user fairness compared with existing designs.
9665993
Closed-loop cross-layer SDMA designs with outdated CSIT
In this paper, we propose a novel closed-loop approach for robust downlink multi-antenna cross-layer design with outdated channel state information at the transmitter (CSIT). Based on the ACK/NAK feedbacks from the mobiles, the proposed cross-layer design does not require the knowledge of CSIT error statistics. We formulate the cross-layer design as a mixed combinatorial search and Markov decision process (MDP). While it is well-known that general solutions for MDP are very complex, one important contribution of this paper is that we obtain simple closed-form power, rate and user allocation policies which are asymptotically optimal for small target frame error rate (FER). Simulation results illustrate that the performance of the proposed closed-loop cross-layer design is very robust with respect to the outdated CSIT, CSIT error model mismatch as well as channel variations due to Doppler.
17762507
Motivated learning agent model for distributed collaborative systems
The paper develops and discusses a conceptual model for a Mixed Reality-based remote collaborative system (MR-Collab) based on motivated learning Agents. The proposed MR-Collab system is described in details as well to help better understand this model. Self-Development Agent based on previous work is an intelligent Agent, which not only receives information from sensors in the environment, but also gives valuable suggestions that could help to improve the system. The model is not limited to this specific system, but could be adapted to other collaboration systems as well.
34764255
Mixed Reality-Mediated Collaborative Design System: Concept, Prototype, and Experimentation
This paper introduces a Mixed Reality-mediated Collaborative design system, named MR-Collab, which combines Mixed Reality (MR), Augmented Reality (AR) and various channels of communication technologies. The concept and system of MR-Collabare developed based on the Benford's Mixed-Reality boundaries theory. This paper presents how this theory is used as a tool to analyze the system framework and guide the design of the MR-Collabsystem. The technique details of prototype and application scenario of this system are also elaborated in the paper. The system, MR-Collab, is designed in the purpose of facilitating collaboration between distributed users through the Mixed Reality environment. Experimentation that can measure the correlations between the design performance/behaviors with the increased degree of co-presence is also planned in this paper.
9396741
DFKI-LT at QAST 2007: Adapting QA Components to Mine Answers in Speech Transcripts
The paper describes QAst-v1 a robust question answering system for answering factoid questions in manual and automatic transcriptions of speech. The system is an adaptation of our text---based crosslingual open---domain QA system that we used for the CLEF main tasks.
1701641
Precomputed Radiance Transfer Field for Rendering Interreflections in Dynamic Scenes
In this paper, we introduce a new representation – radiance transfer fields (RTF) – for rendering interreflections in dynamic scenes under low frequency illumination. The RTF describes the radiance transferred by an individual object to its surrounding space as a function of the incident radiance. An important property of RTF is its independence of the scene configuration, enabling interreflection computation in dynamic scenes. Secondly, RTFs naturally fit in with the rendering framework of precomputed shadow fields, incurring negligible cost to add interreflection effects. In addition, RTFs can be used to compute interreflections for both diffuse and glossy objects. We also show that RTF data can be highly compressed by clustered principal component analysis (CPCA), which not only reduces the memory cost but also accelerates rendering. Finally, we present some experimental results demonstrating our techniques.
10627177
Fast Omnidirectional 3D Scene Acquisition with an Array of Stereo Cameras
We present an omnidirectional 3D acquisition system based on a mobile array of high-resolution consumer digital SLR cameras that automatically capture high dynamic range stereo pairs across a full 360-degree panorama. The stereo pairs are augmented with a time-varying lighting pattern created using standard photographic flashes, lenses, and patterned slides. Spacetime stereo techniques are used to generate 3D range images with corresponding color data from the HDR photographs. The multiple range images are aligned with egomotion estimation and ICP registration techniques, and volumetric merging and color texturing algorithms allow the rapid creation of complete 3D models. The resulting system compares favorably with other state of the art 3D acquisition technologies in the resolution and quality of its output, and can be faster and less expensive than 3D laser scanners for digitizing large 3D scenes such as building interiors.