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Now showing items 1 - 16 of 22

  • Optimal Symbol-by-Symbol Costa Precoding for a Relay-Aided Downlink Channel

    Jinfeng Du   Larsson, E.G.   Ming Xiao   Skoglund, M.  

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  • Cooperative Network Coding Strategies for Wireless Relay Networks with Backhaul

    Jinfeng Du   Ming Xiao   Skoglund, M.  

    We investigate cooperative network coding strategies for relay-aided two-source two-destination wireless networks with a backhaul connection between the source nodes. Each source multicasts information to all destinations using a shared relay. We study cooperative strategies based on different network coding schemes, namely, finite field and linear network coding, and lattice coding. To further exploit the backhaul connection, we also propose network coding based beamforming. We measure the performance in term of achievable rates over Gaussian channels, and observe significant gains over benchmark schemes. We derive the achievable rate regions for these schemes and find the cut-set bound for our system. We also show that the cut-set bound can be achieved by network coding based beamforming when the signal-to-noise ratios lie in the sphere defined by the source-relay and relay-destination channel gains.
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  • Interaction of aloe-emodin with human serum albumin

    JinFeng Du   Ying Li   Qi Zhang   XiaoJun Yao  

    The presence of several high affinity binding sites on human serum albumin (HSA) makes it a possible target for many drugs. This study is designed to examine the effect of aloe-emodin on HSA by fluorescence, CD spectroscopy and molecular modeling. The results of fluorescence measurements suggested that the hydrophobic interaction was the predominant intermolecular force stabilizing the AE-HSA complex, which was in good agreement with the result of molecular modeling study. And the enthalpy change Delta H-0 and the entropy change Delta S-0 were calculated to be -7.041 KJ.mol(-1) and 76.619 J.mol(-1).K-1 according to the Van't Hoff equation. The alterations of protein secondary structure in the presence of AE in aqueous solution were quantitatively calculated from CD spectra, and the content of a-helices obviously increased.
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  • Research on Microstructure and Mechanical Property of S30432 Supreheater Pipe Aged at 700°C

    Jinfeng Du   Jun Liang   Huichuan Zhao and Biao Sun  

    The microstructure and performance of S30432 supreheater pipe were investigated before and after it is aged 3000 h at 700°C. A lot of twins disappeared after aging, M23C6 particles precipitated along the grain boundary and MX particles precipitated near the dislocation. After the endurance experiment of the aged pipe, M23C6 precipitations with the size of about 50 nm pinned dislocations and the cavity appeared on the grain boundary. The aged S30432 supreheater pipe showed the ductile fracture. Increasing temperature made the inter-granular fracture transfer the quasi-cleavage fracture and the equiaxed morphology change the parabola morphology. The strength of the untreated specimen decreased with the temperature increasing. The hardness and the impact energy of the aged specimen were larger than those of the untreated specimen. Tensile strength and elongation of untreated specimen were larger than that of aged specimen.
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  • Research on Microstructure and Mechanical Property of S30432 Supreheater Pipe Aged at 700°C

    Jinfeng Du   Jun Liang   Huichuan Zhao   Biao Sun  

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  • Land pricing and its impact on land use efficiency in post-land-reform China: A case study of Beijing

    Jinfeng Du   Jean-Claude Thill   Richard B. Peiser  

    a r t i c l e i n f o Keywords: Land use efficiency Land use productivity Land pricing Beijing China This paper analyzes how the newly introduced land pricing system affects urban land productivity in China, taking post-land-reform Beijing as an example. China has been developing its urban land market by building an effective pricing system. This study indicates that the effects of such pricing system on urban land productivity have evolved with the progress of land reform. It is only since 2004, when land granting by negotiation was at last totally prohibited for profit-oriented developments, that the land pricing system has started to positively and significantly improve urban land productivity; the land pricing system also promotes more productive urban land usage by stimulating more intensive investment and better business management. Improving the efficient use of land is commonly recognized as of paramount importance in balancing the protection of farmland and the accommodation of socioeconomic development, especially for a country like China with intense human-land relationship and rapid urbanization (Choy, Lai, and Lok, 2013; Meng et al., 2008). During the planned economy era, land was free of charge for development in China. Land users tended to occupy more land than they actually needed, leading to massive loss of cultivated land in rural areas and inefficient land usage in urban areas. From 1956 to 1978, the area of cultivated land shrank 12.44 million ha nationwide and the annual loss amounted to 5652 km 2 (Li, 2000). An urban land reform based on the paid-to-use 1 principle was initiated in the late 1980s with the expectation that land pricing would improve the cost of land use. More accurate land use cost would compel land users to utilize land more economically, and therefore, help improve urban land use efficiency, 2 preserve cultivated land, and raise capital for development it remains unclear whether the market mechanism has helped improve land use efficiency as anticipated. With the expansion of urban land, land use efficiency can increase or decrease depending upon the relative rates of change between land consumption and socioeconomic output. Existing studies have looked critically at the massive magnitude of urban development by analyzing the dynamics of urban expansion and the institutional roots of " losing control " of urban sprawl in China (Zhou, 2006). However, incorporating more land to accommodate a growing population and to support urban economic growth is inherent …
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  • Bandwidth occupancy of non-coherent wideband fading channels

    Felipe Gómez-Cuba   Jinfeng Du   Muriel Médard   Elza Erkip  

    Peaky and non-peaky signaling schemes have long been considered species apart in non-coherent wideband fading channels, as the first approaches asymptotically the linear-in-power capacity of a wideband AWGN channel with the same SNR, whereas the second reaches a nearly power-limited peak rate at some finite critical bandwidth and then falls to zero as bandwidth grows to infinity. In this paper it is shown that this distinction is in fact an artifact of the limited attention paid in the past to the product between the bandwidth and the fraction of time it is in use. This fundamental quantity, that is termed bandwidth occupancy, measures average bandwidth usage over time. The two types of signaling in the literature are harmonized to show that, for any type of signals, there is a fundamental limit-a critical bandwidth occupancy. All signaling schemes with the same bandwidth occupancy approach the capacity of wideband AWGN channels with the same asymptotic behavior as the bandwidth occupancy grows to its critical value. For a bandwidth occupancy above the critical, rate decreases to zero as the bandwidth occupancy goes to infinity.
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  • Costa Precoding in One Dimension

    Jinfeng Du   Erik G. Larsson   Mikael Skoglund  

    We design an optimum modulator for the Costa (dirty-paper) precoding problem under the constraint of a binary signaling alphabet, and assuming the interference symbols belong to a binary constellation. We evaluate the performance of our technique in terms of the mutual information between the channel input and output, and compare it to that of Tomlinson-Harashima precoding (THP) with optimized parameters. We show that our optimal modulator is always better than THP. In many relevant scenarios, the performance difference is significant
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  • Costa Precoding in One Dimension

    Jinfeng Du   Erik G. Larsson   Mikael Skoglund  

    We design an optimum modulator for the Costa (dirty-paper) precoding problem under the constraint of a binary signaling alphabet, and assuming the interference symbols belong to a binary constellation. We evaluate the performance of our technique in terms of the mutual information between the channel input and output, and compare it to that of Tomlinson-Harashima precoding (THP) with optimized parameters. We show that our optimal modulator is always better than THP. In many relevant scenarios, the performance difference is significant.
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  • Classic OFDM Systems and Pulse Shaping OFDM/OQAM Systems

    Jinfeng Du   Svante Signell  

    In this report; we provide a comparative study of state-of-the-art in Orthogonal Frequency Division Multiplexing (OFDM) techniques with orthonormal analysis and synthesis basis. Two main categories; OFDM/QAM which adopts baseband Quadrature Amplitude Modulation (QAM) and rectangular pulse shape; and OFDM/OQAM which uses baseband offset QAM and various pulse shapes; are intensively reviewed. OFDM/QAM can provide high data rate communication and effectively remove intersymbol interference (ISI) by employing guard interval; which costs a loss of spectral efficiency and increases power consumption. Meanwhile it remains very sensitive to frequency offset which causes intercarrier interference (ICI). In order to achieve better spectral efficiency and reducing combined ISI/ICI; OFDM/OQAM using well designed pulses with proper Time Frequency Localization (TFL) is of great interest. Various prototype functions; such as rectangular; half cosine; Isotropic Orthogonal Transfer Algorithm (IOTA) function and Extended Gaussian Functions (EGF) are discussed and simulation results are provided to illustrate the TFL properties by the ambiguity function and the interference function.
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  • How Much Spectrum is Too Much in Millimeter Wave Wireless Access

    Jinfeng Du   Reinaldo A. Valenzuela  

    Great increase in wireless access rates might be attainable using the large amount of spectrum available in the millimeter wave (mmWave) band. However, higher propagation losses inherent in these frequencies must be addressed, especially at ranges beyond 100 meters and in non-line-of-sight (NLOS) settings. In contrast to the interference limited legacy cellular systems where using more bandwidth is favorable, , to use wider bandwidth for mmWave channels in noise limited settings may be ineffective or even counterproductive when accounting for channel estimation penalty. In this paper we quantify the maximum beneficial bandwidth for mmWave transmission in some typical deployment scenarios where pilot-based channel estimation penalty is taken into account assuming a minimum mean square error (MMSE) channel estimator at the receiver. We find that, under I.I.D. block fading model with coherence time Tc and coherence bandwidth Bc, for transmitters and receivers equipped with a single antenna, the optimal (rate maximizing) signal-to-noise-ratio (SNR) is a constant that only depends on the product BcTc, which measures the channel coherence and equals the average number of orthogonal symbols per each independent channel coefficient. That is, for fixed channel coherence BcTc, the optimal bandwidth scales linearly with the received signal power. Under 3GPP Urban Micro NLOS path loss model with coherence time Tc = 5 ms and coherence bandwidth Bc = 10 MHz, using 52 dBm Equivalent Isotropic Radiated Power (EIRP) at the transmitter and 11 dBi antenna gain at the receiver, the maximum beneficial bandwidth at 28 (resp. 39) GHz is less than 1 GHz at a distance beyond 210 (resp. 170) meters with maximum throughput about 200 Mbps, and less than 100 MHz beyond 400 (resp. 310) meters with maximum throughput about 20 Mbps. At EIRP of 85 dBm, corresponding to the FCC limit of 75 dBm per 100 MHz, 1 Gbps rate can be delivered using 1 GHz bandwidth up to 860 (resp. 680) meters.
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  • Unified Capacity Limit of Non-coherent Wideband Fading Channels

    Felipe Gómez-Cuba   Jinfeng Du   Muriel Médard   Elza Erkip  

    In non-coherent wideband fading channels where energy rather than spectrum is the limiting resource, peaky and non-peaky signaling schemes have long been considered species apart, as the first approaches asymptotically the capacity of a wideband AWGN channel with the same average SNR, whereas the second reaches a peak rate at some finite critical bandwidth and then falls to zero as bandwidth grows to infinity. In this paper it is shown that this distinction is in fact an artifact of the limited attention paid in the past to the product between the bandwidth and the fraction of time it is in use. This fundamental quantity, that is termed bandwidth occupancy, measures average bandwidth usage over time. As it turns out, a peaky signal that transmits in an infinite bandwidth but only for an infinitesimal fraction of the time may only have a small bandwidth occupancy, and so does a non-peaky scheme that limits itself to the critical bandwidth even though more spectrum is available, so as to not degrade rate. The two types of signaling in the literature are harmonized to show that, for all signaling schemes with the same bandwidth occupancy, rates converge to the wideband AWGN capacity with the same asymptotic behavior as the bandwidth occupancy approaches its critical value, and decrease to zero as the occupancy goes to infinity. This unified analysis not only recovers previous results on capacity bounds for (non-)peaky signaling schemes, but also reveals the fundamental tradeoff between precision and accuracy when characterizing the maximal achievable rate.
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  • Network-Coding-Aware Link Adaptation for Wireless Broadcast Transmission

    Jawad Manssour   Jinfeng Du  

    We present a network-coding-aware link adaptation scheme for wireless broadcast transmission; which can achieve significantly higher throughput compared to schemes which always ensure correct decoding by the weakest link receiver. We evaluate the performance for the broadcast phase of a twoway relay channel based on average SNR feedback. If dynamic switch between the bit-wise XOR network coding scheme and the generalized multiplicative network coding is allowed; a less than 1% throughput loss compared to ideal network coding can be achieved in most SNR regions; and a less than 6% throughput loss can be guaranteed regardless of link asymmetry.
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  • Cooperative Network Coding Strategies for Wireless Relay Networks with Backhaul

    Jinfeng Du   Ming Xiao   Mikael Skoglund  

    We investigate cooperative network coding strategies for relay-aided two-source two-destination wireless networks with a backhaul connection between the source nodes. Each source multicasts information to all destinations using a shared relay. We study cooperative strategies based on different network coding schemes, namely, finite field and linear network coding, and lattice coding. To further exploit the backhaul connection, we also propose network coding based beamforming. We measure the performance in term of achievable rates over Gaussian channels, and observe significant gains over benchmark schemes. We derive the achievable rate regions for these schemes and find the cut-set bound for our system. We also show that the cut-set bound can be achieved by network coding based beamforming when the signal-to-noise ratios lie in the sphere defined by the source-relay and relay-destination channel gains.
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  • Urban land market and land-use changes in post-reform China: A case study of Beijing

    Jinfeng Du   Jean-Claude Thill   Richard B. Peiser   Changchun Feng  

    Highlights • Land use changed dramatically in post-reform Beijing from 1992 to 2008. • Cultivated land more than halved while two types of urban built land doubled. • Land price, cultivated land availability and location are significant dynamic factors. • Land reforms affected the spatial–temporal dynamics of land use changes. • Conformity of land price mechanism with reform goals depends on land use types. Abstract China launched an ambitious urban land-use reform to improve land-use efficiency, raise funds for infrastructure construction, and facilitate foreign investment in the late 1980s. Few studies have systematically evaluated the effects of the market mechanisms on land-use changes in Chinese cities. This paper takes the city of Beijing as a case study to quantify the magnitude of land-use changes and model it in relation to spatial and market drivers through time and across the metropolitan region. The analysis uses unique district-level land survey data from 1992, 1996, 2001, 2004 and 2008, as well as land granting records. Analysis reveals that, since the urban land market was established in 1992, the spatial pattern of land uses has changed dramatically in Beijing, land price has exerted a significantly influence on land-use conversion, and the municipal recognition of an open market for land assets has set the spatial–temporal pattern of land uses on a course that sharply differs from past trends in Beijing.
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  • Cross-layer design of network-coded transmission with a delay constraint

    Jinfeng Du   David C. Adams   Muriel Médard  

    We investigate the cross-layer design of wireless networks where end-to-end data transmission is subject to delay constraint and there is no end-to-end feedback. The transmission is coded by random linear network coding (RLNC) on packet level to recover from packet erasures and by forward error-correction coding (FEC) on bit level to combat channel distortions. Based on the two-layer model developed by Adams et al. where the end-to-end coded transmission is characterized by a throughput-reliability function, we formulate the cross-layer design as a goodput optimization problem relax the integrality constraint. We show that for single-hop transmissions there exists a globally optimal operating point for the relaxed problem. For multiple-hop transmissions, the goodput function is component-wise concave with respect to the physical layer data rate over each individual link.
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