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Articles 1 - 14 of 14
Full-Text Articles in Physical Sciences and Mathematics
A Method For Evaluating Bias In Global Measurements Of Co2 Total Columns From Space, D Wunch, P O. Wennberg, G C. Toon, B J. Connor, B Fisher, G B. Osterman, C Frankenberg, L Mandrake, C O'Dell, P Ahonen, S C. Biraud, R Castano, Noel Cressie, D Crisp, N M. Deutscher, A Eldering, M L. Fisher, David W. Griffith, M Gunson, P Heikkinen, G Keppel-Aleks, E Kyro, R Lindemaier, Ronald Macatangay, J Mendonca, J Messerschmidt, C E. Miller, I Morino, J Notholt, F A. Oyafuso, M Rettinger, J Robinson, C M. Roehl, R J. Salawitch, V Sherlock, K Strong, R Sussmann, T Tanaka, D R. Thompson, O Uchino, Thorsten Warneke, Steven C. Wofsy
A Method For Evaluating Bias In Global Measurements Of Co2 Total Columns From Space, D Wunch, P O. Wennberg, G C. Toon, B J. Connor, B Fisher, G B. Osterman, C Frankenberg, L Mandrake, C O'Dell, P Ahonen, S C. Biraud, R Castano, Noel Cressie, D Crisp, N M. Deutscher, A Eldering, M L. Fisher, David W. Griffith, M Gunson, P Heikkinen, G Keppel-Aleks, E Kyro, R Lindemaier, Ronald Macatangay, J Mendonca, J Messerschmidt, C E. Miller, I Morino, J Notholt, F A. Oyafuso, M Rettinger, J Robinson, C M. Roehl, R J. Salawitch, V Sherlock, K Strong, R Sussmann, T Tanaka, D R. Thompson, O Uchino, Thorsten Warneke, Steven C. Wofsy
Faculty of Informatics - Papers (Archive)
We describe a method of evaluating systematic errors in measurements of total column dry-air mole fractions of CO2 (XCO2) from space, and we illustrate the method by applying it to the v2.8 Atmospheric CO2 Observations from Space retrievals of the Greenhouse Gases Observing Satellite (ACOS-GOSAT) measurements over land. The approach exploits the lack of large gradients in XCO2 south of 25S to identify large-scale offsets and other biases in the ACOS-GOSAT data with several retrieval parameters and errors in instrument calibration. We demonstrate the effectiveness of the method by comparing the ACOS-GOSAT data …
The Path Space Of A Higher-Rank Graph, Samuel B. Webster
The Path Space Of A Higher-Rank Graph, Samuel B. Webster
Faculty of Informatics - Papers (Archive)
We construct a locally compact Hausdorff topology on the path space of a finitely aligned k -graph Λ . We identify the boundary-path space ∂Λ as the spectrum of a commutative C ∗ -subalgebra D Λ of C ∗ (Λ) . Then, using a construction similar to that of Farthing, we construct a finitely aligned k -graph Λ ˜ with no sources in which Λ is embedded, and show that ∂Λ is homeomorphic to a subset of ∂Λ ˜ . We show that when Λ is row-finite, we can identify C ∗ (Λ) with a full corner of C ∗ …
Initial Values In Estimation Procedures For State Space Models (Ssms), Raed Alzghool, Yan-Xia Lin
Initial Values In Estimation Procedures For State Space Models (Ssms), Raed Alzghool, Yan-Xia Lin
Faculty of Informatics - Papers (Archive)
In this paper, we will focus on State Space Models(SSMs), especially the stochastic volatility model, and lookfor a standard approach for assigning initial values in theQuasi-Likelihood (QL) and Asymptotic Quasi-Likelhood (AQL)estimation procedures.
Quasi-Orthogonal Space-Time-Frequency Codes In Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins, Tadeusz A. Wysocki
Quasi-Orthogonal Space-Time-Frequency Codes In Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins, Tadeusz A. Wysocki
Faculty of Informatics - Papers (Archive)
Quasi-Orthogonal Space-Time-Frequency Codes (QOSTFCs) will be examined in this paper to advance either data rate or error performance in recently proposed Space-Time-Frequency Coded Multiband OFDM Ultra-Wideband (STFC MB-OFDM UWB) communication systems. It is shown that QOSTFCs can provide signi¯cantly better error performance, compared to the conventional MB-OFDM UWB (without STFCs) and to the Orthogonal STFCs (OSTFCs) of the same order, at the same data rate, without increasing the total transmission power. Another form of the enhancement would be that QOSTFCs can provide higher data rates with the same error performance, compared to OSTFCs.
Differential Space-Time-Frequency Codes For Mb-Ofdm Uwb With Dual Carrier Modulation, Alfred Mertins, Le Chung Tran
Differential Space-Time-Frequency Codes For Mb-Ofdm Uwb With Dual Carrier Modulation, Alfred Mertins, Le Chung Tran
Faculty of Informatics - Papers (Archive)
In a multiple-input multiple-output (MIMO) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system, coherent detection where the channel state information (CSI) is assumed to be exactly known at the receiver requires the transmission of a large number of symbols for channel estimation, thus reducing the bandwidth efficiency. This paper examines the use of unitary differential space-time frequency codes (DSTFCs) in MB-OFDM UWB, which increases the system bandwidth efficiency due to the fact that no CSI is required for differential detection. The proposed DSTFC MB-OFDM system would be useful when the transmission of multiple channel estimation symbols is impractical or …
Unitary Differential Space-Time-Frequency Codes For Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins, E. Dutkiewicz, Xiaojing Huang
Unitary Differential Space-Time-Frequency Codes For Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins, E. Dutkiewicz, Xiaojing Huang
Faculty of Informatics - Papers (Archive)
In a multiple-input multiple-output (MIMO) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system, coherent detection where the channel state information (CSI) is assumed to be exactly known at the receiver requires the transmission of a large number of symbols for channel estimation, thus reducing the bandwidth efficiency. This paper examines the use of unitary differential space-time frequency codes (DSTFCs) in MB-OFDM UWB, which increases the system bandwidth efficiency due to the fact that no CSI is required for differential detection. The proposed DSTFC MB-OFDM system would be useful when the transmission of multiple channel estimation symbols is impractical or …
Space-Time-Frequency Code Implementation In Mb-Ofdm Uwb Communications: Design Criteria And Performance, Alfred Mertins, Le Chung Tran
Space-Time-Frequency Code Implementation In Mb-Ofdm Uwb Communications: Design Criteria And Performance, Alfred Mertins, Le Chung Tran
Faculty of Informatics - Papers (Archive)
This paper proposes a general framework of Space-Time-Frequency Codes (STFCs) for Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) communications systems. A great similarity between the STFC MB-OFDM UWB systems and conventional wireless Complex Orthogonal Space-Time Block Code (CO STBC) Multiple-Input Multiple-Output (MIMO) systems is discovered. This allows us to quantify the pairwise error probability (PEP) of the proposed system and derive the general decoding method for the implemented STFCs. Based on the theoretical analysis results of PEP, we can further quantify the diversity order and coding gain of MB-OFDM UWB systems, and derive the design criteria for STFCs, …
Novel Cooperative Communication Schemes For Space-Time-Frequency Coded Mb-Ofdm Uwb, Le Chung Tran, Xiaojing Huang, Alfred Mertins, Eryk Dutkiewicz
Novel Cooperative Communication Schemes For Space-Time-Frequency Coded Mb-Ofdm Uwb, Le Chung Tran, Xiaojing Huang, Alfred Mertins, Eryk Dutkiewicz
Faculty of Informatics - Papers (Archive)
Cooperative communication has been intensively considered for general wireless and sensor networks. However, it has been almost untouched in Space-Time-Frequency Coded Multi-band OFDM Ultra-Wideband (STFC MB-OFDM UWB) systems. This paper thus proposes two cross-layer designs for cooperative communication, namely Simple Cooperative Communication Scheme (SCCS) and Advanced Cooperative Communication Scheme (ACCS), in slow fading scenarios. In the former, nodes always cooperate with one another despite the possibly erroneous reception at the partner nodes, while in the latter, nodes cooperate only in the case of successful reception. Simulations show that these schemes may considerably improve the performance of STFC MB-OFDM UWB without …
Mitagation Against Mai In A Space Time Spreading Software Defined Radio, Shinhan Wee, Montse Ros, Peter James Vial
Mitagation Against Mai In A Space Time Spreading Software Defined Radio, Shinhan Wee, Montse Ros, Peter James Vial
Faculty of Informatics - Papers (Archive)
A Software Defined Radio test bed using the Gnu Radio project was installed on Unix boxes and modified so that estimates of the channel state coefficients were taken for a Multiple Input Multiple output (MIMO) system to take advantage of space time transmission at a frqeuency of 2.4GHz. This system was modified to provide a Space Time Spreading test bed. The test bed was modified so that multiple access interference was experienced by off-setting different users data streams. The Walsh-Hadamard and Wysocki (low correlation) spreading sequences were deployed in the test bed to compare their Bit Error Rate performance. We …
On The Use Of Quasi-Orthogonal Space-Time-Frequency Codes In Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins
On The Use Of Quasi-Orthogonal Space-Time-Frequency Codes In Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins
Faculty of Informatics - Papers (Archive)
Space-Time-Frequency Codes (STFCs), which haverecently been proposed in the literature for Multiband OFDMUltra-Wideband (MB-OFDM UWB) systems to improve thesystem capacity, error performance and wireless communicationrange, are all constructed based on orthogonal structures. Thispaper examines the application of Quasi-Orthogonal STFCs(QOSTFCs) to enhance further either data rate or error performancein the recently proposed STFC MB-OFDM UWB systems.It will be shown that QOSTFCs can provide significantly bettererror performance, compared to the conventional MB-OFDMUWB (without STFCs) as well as to the Orthogonal STFCs(OSTFCs) of the same order, at the same data rate, withoutincreasing the total transmission power. Equivalently, QOSTFCscan provide higher data rates with …
Cooperative Communication In Space-Time-Frequency Coded Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins, Tadeusz A. Wysocki
Cooperative Communication In Space-Time-Frequency Coded Mb-Ofdm Uwb, Le Chung Tran, Alfred Mertins, Tadeusz A. Wysocki
Faculty of Informatics - Papers (Archive)
Though cooperative communication has been intensively examined for general wireless systems, such as mobile and ad-hoc networks, it has been almost unexplored in the case of Space-Time-Frequency Coded Multi-band OFDM Ultra-Wideband (STFC MB-OFDM UWB). This paper proposes a framework of cooperative communication in such systems where nodes are equipped with only one antenna. Simulation results show that cooperative communication might, in some cases, provide better error performance than non-cooperative communication without any additional transmission power.
Application Of Quasi-Orthogonal Space-Time-Frequency Codes In Mb-Ofdm Uwb, Alfred Mertins, Le Chung Tran
Application Of Quasi-Orthogonal Space-Time-Frequency Codes In Mb-Ofdm Uwb, Alfred Mertins, Le Chung Tran
Faculty of Informatics - Papers (Archive)
This paper examines the application of Quasi-Orthogonal Space-Time-Frequency Codes (QOSTFCs) to advance either data rate or error performance in recently proposed Space-Time-Frequency Coded Multiband OFDM Ultra-Wideband (STFC MB-OFDM UWB) communications systems. It is shown that QOSTFCs can provide significantly better error performance, compared to the conventional MB-OFDM UWB (without STFCs) and to the Orthogonal STFCs (OSTFCs) of the same order, at the same data rate, without increasing the total transmission power. In other words, QOSTFCs can provide higher data rates with the same error performance, compared to OSTFCs.
A Simple Orthogonal Space-Time-Polarization Block Code, Beata J. Wysocki, Tadeusz A. Wysocki, Jennifer R. Seberry, Sarah S. Adams, Hamid Sharif
A Simple Orthogonal Space-Time-Polarization Block Code, Beata J. Wysocki, Tadeusz A. Wysocki, Jennifer R. Seberry, Sarah S. Adams, Hamid Sharif
Faculty of Informatics - Papers (Archive)
This letter proposes a simple but highly efficient technique to jointly utilize space, time, and polarization diversities. The technique is based on extending orthogonal space-time block codes into the quaternion domain and utilizing a description of the dual-polarized signal by means of quaternions, which are a generalization of complex numbers. In the given example, the achievable performance gain for two transmit and one receive antennas is approximately 6 dB at a bit error rate of 10-4 when compared with the Alamouti code.
A Spatial-Temporal Statistical Approach To Command And Control Problems In Battle-Space Digitization, David A. Wendt, Noel A. Cressie, Gardar Johannesson
A Spatial-Temporal Statistical Approach To Command And Control Problems In Battle-Space Digitization, David A. Wendt, Noel A. Cressie, Gardar Johannesson
Faculty of Informatics - Papers (Archive)
There are considerable difficulties in the integration, visualization, and overall management of battle-space information for the purpose of Command and Control (C2). One problem that we see as being important is the timely combination of digital information from multiple (possibly disparate) sources in a dynamically evolving environment. That is, there is a need to assimilate incoming data rapidly, so as to provide the battle commander with up-to-date knowledge about the battle-space and thereby to facilitate the command-decision process. In this paper, we present a spatial-temporal approach to obtaining accurate estimates of the constantly changing battlefield, based on noisy data from …