14242473
An Experimental Investigation of Wideband MIMO Channel Based on Indoor Hotspot NLOS Measurements at 2.35GHz
In this paper, measurement data from wideband multiple-input multiple-output (MIMO) channel measurements at 2.35 GHz are presented. Measurements were preformed in indoor hotspot scenario with no line of sight (NLOS). Space-alternating generalized expectation (SAGE) algorithm was utilized to estimate angular domain parameters and powers of multipath components (MPCs), which are then used to compute the circular angular spread (CAS) and to construct the power azimuth spectrum (PAS) of transmitter and receiver sides. It is found that PASs of both sides follow multi-cluster truncated Laplacian distribution. The spatial correlation, capacity and multiplexing gain are also presented. Due to rich scatters in the indoor hotspot environment, the correlation space is Q.2lambda and the multiplexing gain is 15, which indicate indoor hotspot MIMO channels facilitate multiplexing and could achieve high capacity. The results provide important basis for future channel modeling and technique evaluation.
20797286
A Generic Validation Framework for Wideband MIMO Channel Models
In this paper, a generic framework for validating wideband MIMO channel models based on channel measurement results is proposed. The framework is formulated as a series of continuous functions (metrics) and a definition of distance of continuous function space (degree of approximation). The metrics characterize the MIMO channel from different perspectives, and the distance provides a quantitative measure of the degree of approximation for the specified model. Several fundamental metrics which reflect the spatial multiplexing gain, diversity capability, time and frequency variability, are derived for exploring the frequency-selective fading property. Based on an extensive measurement campaign at 5.25 GHz, the propagation channel is reconstructed by a WINNER-like model. The metrics are calculated from both the model generated channel realizations and the measured impulse response as a demonstration. The proposed framework can be applied to compare different channel models and to evaluate the simplified version of channel models.
1131898
A Novel Spatial Autocorrelation Model of Shadow Fading in Urban Macro Environments
In this paper, we propose a novel spatial autocorrelation model of the shadow fading process in urban macro environments. The proposed model is based on the empirical results obtained from extensive wideband radio channel measurement campaigns at 2.35 GHz in an urban area of a typical medium-sized Chinese city. The shadow fading component was extracted assuming a single-slope log-distance path loss model. The consistency with the level crossing theory of Gaussian processes is achieved by an implicit constraint on the parameters of the model. The proposed model gives a better fit to the empirical results in individual measurement routes than the widely reported exponential and double exponential models. An heuristic explanation of the proposed autocorrelation property is also presented.
41646301
A Comparison of Broadcast Strategy in MIMO Relay Networks
In this paper, the sum rate issue of a multiple-input multiple-output (MIMO) relay broadcast channel is studied, where the fixed relay station is used to support multiuser transmission in a downlink channel. With appropriate design, the sum rate can be expressed as a function of the processing units at the base station (BS) and relay, and the power allocation can be converted to a standard convex problem. We compared the sum rate of MIMO relay broadcast channel (BC) using time division multiple access (TDMA) to the strongest user, dirty paper coding (DPC) and beamforming (BF) when multiple antennas are deployed at each terminal in the system and separate power constraints at the BS and relay. Then, the sum rate bounds for each strategy and the sum capacity (achieved by DPC) gain over TDMA and BF are given, correspondingly. Finally, numerical results are presented to prove our discussions. With these results, we can easily obtain how far away TDMA and BF are from being optimal in terms of sum rate, and direct the practical system design.
8166991
On Destination Set in IP-Level Topology Measurement
We present a thorough investigation of four issues with the destination set in IP-level topology measurement. (1) To evaluate the completeness of the destination set, we measured by brute force and found that a half of edges will be missed by the uniform random selection (URS) method which was adopted by well-known CAIDA' skitter. (2) Two potential reasons for edge missing, the short-term routing dynamics and the subnetting technique, were investigated with the last-hop selection method and the bisection selection method respectively. And the results showed that the subnetting technique is the main reason. (3) To select destinations efficiently, we presented the minimum cover selection (MCS) method which performed better than the URS method on 75% of networks over three months. (4) Finally, to investigate the bias of topology characterization, we measured a destination set larger than before and discovered a Chinese topology whose size is 5 times as large as that discovered by skitter. The comparison between characteristics of skitter's topology and ours indicated that the small destination set trends to miss the information on marginal networks.
42969353
Impact of Randomized Cross-Polarization Discrimination on Channel Correlation Property of the 3GPP Spatial Channel Model
The use of cross-polarized antennas for multiple-input multiple-output (MIMO) systems is receiving attention as they are able to double the number of antenna for half antenna spacing needs. This paper presents the channel correlation property of the 3rd Generation Partner Project (3GPP)/3GPP2 spatial channel model (SCM) with the polarization propagation. The statistical average of the per path polarization correlation given random cross-polarization discrimination (XPD) with co-located ideal tilted dipole antennas is derived. The impact on the random behavior of the polarization correlation due to the slant offset angle, the per path angular spread (AS), and the random XPD is analyzed. The simulation results show that the variation of polarization correlation caused by the random XPD is maximized with a 58° slant offset angle under the assumptions of all predefined scenarios in SCM. The per path AS has minor impact on the statistics of the polarization correlations. The randomness of polarization correlation is negligible for an XPD with small standard deviation.
21919804
Logical Relations for Dynamic Name Creation
Pitts and Stark’s nu-calculus is a typed lambda-calculus which forms a basis for the study of interaction between higher-order functions and dynamically created names. A similar approach has received renewed attention recently through Sumii and Pierce’s cryptographic lambda-calculus, which deals with security protocols. Logical relations are a powerful tool to prove properties of such a calculus, notably observational equivalence. While Pitts and Stark construct a logical relation for the nu-calculus, it rests heavily on operational aspects of the calculus and is hard to be extended. We propose an alternative Kripke logical relation for the nu-calculus, which is derived naturally from the categorical model of the nu-calculus and the general notion of Kripke logical relation. This is also related to the Kripke logical relation for the name creation monad by Goubault-Larrecq et al. (CSL’2002), which the authors claimed had similarities with Pitts and Stark’s logical relation. We show that their Kripke logical relation for names is strictly weaker than Pitts and Stark’s. We also show that our Kripke logical relation, which extends the definition of Goubault-Larrecq et al., is equivalent to Pitts and Stark’s up to first-order types; our definition rests on purely semantic constituents, and dispenses with the detours through operational semantics that Pitts and Stark use.
6611945
Efficient Relay Beamforming Design With SIC Detection for Dual-Hop MIMO Relay Networks
In this paper, we consider a dual-hop multiple-input-multiple-output (MIMO) relay wireless network, in which a source-destination pair, which are both equipped with multiple antennas, communicates through a large number of half-duplex amplify-and-forward (AF) relay terminals. Two novel linear beamforming schemes based on the matched filter and regularized zero-forcing precoding techniques are proposed for the MIMO relay system. We focus on the linear process at the relay nodes and design the new relay beamformers by utilizing the channel-state information (CSI) of both backward and forward channels. The proposed beamforming designs are based on the QR decomposition filter at the destination node, which performs successive interference cancellation to achieve the maximum spatial-multiplexing gain. Simulation results demonstrate that the proposed beamformers that fulfil both the intranode array gain and distributed array gain outperform other relaying schemes under different system parameters in terms of the ergodic capacity.
32462907
Alignment of Optical Maps
We introduce a new scoring method for calculation of alignments of optical maps. Missing cuts, false cuts, and sizing errors present in optical maps are addressed by our alignment score through calculation of corresponding likelihoods. The size error model is derived through the application of Central Limit Theorem and validated by residual plots collected from real data. Missing cuts and false cuts are modeled as Bernoulli and Poisson events, respectively, as suggested by previous studies. Likelihoods are used to derive an alignment score through calculation of likelihood ratios for a certain hypothesis test. This allows us to achieve maximal descriminative power for the alignment score. Our scoring method is naturally embedded within a well known DP framework for finding optimal alignments.
45110732
Application of the Stress Waves to Extract Multi-fault Features of the Low-Speed Machinery Based on Blind Source Separation
This paper proposed a non-linear signal processing method to separate the stress wave signals from different sources for extracting the multi-fault features without any a priori knowledge. Firstly, stress wave theories of low-speed rotating machines are discussed. And then this paper described the basic principles of BSS, and a kind of non-linear neural network is used in consideration of the complex behavior of vibration, either nonlinear or random. After that BSS was applied to the experimental simulations for diagnosing the rubbing and looseness defects. Finally the processing results of a real process show that the new method based on non-linear blind source separation studied in this paper can simply and effectively remove the noise contained in the vibration signals and extract the multi-fault features to avoid the grand accidence.
35510017
A Link-Based Rank of Postings in Newsgroup
Discussion systems such as Usenet, BBS, Forum are important resources for information sharing, view exchanging, problem solving and product feedback, etc. on Internet. The postings in newsgroups on Usenet represents the judgments and choices of participators. The structure of postings could provide helpful information for the users. In this paper, we present a method called PostRank to rank the postings based on the structure of newsgroup. Its results correspond to the eigenvectors of the transition probability matrix and the stationary vectors of the Markov chains. It could provide useful global information for the newsgroup and it can be used to help the users access information in it more effectively and efficiently. This method can be also applied on other discussion systems. Some experimental results and discussions on real data sets collected by us are also provided.