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IEEE Transactions on Wireless Communications. 01/2012; 11:397-407.
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IEEE Communications Letters. 01/2012; 16:92-94.
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IEEE Transactions on Wireless Communications. 01/2011; 10:1721-1724.
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IEEE Transactions on Information Theory. 01/2010; 56:5796-5804.
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ABSTRACT: A MIMO system with finite-bit feedback based on fixed constellations is considered. For this system, an optimal operating system with maximum-likehood (ML)-decoding is demonstrated, and furthermore, to reduce encoding complexity, an asymptotic optimal operating system is also proposed. Theoretical analysis and simulations show that our encoding method has much less complexity than existing encoding methods.
Wireless Communications, Networking and Mobile Computing, 2009. WiCom '09. 5th International Conference on; 10/2009
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ABSTRACT: By applying Anderson-Darling test in statistics into spectrum sensing, this paper gives a new sensing of existence of unknown signals. Both theoretical analysis and simulations show that the proposed sensing method has much higher probability of detection than energy detector-based sensing, especially in a low SNR region and a case with a small sampling number.
Wireless Communications, Networking and Mobile Computing, 2009. WiCom '09. 5th International Conference on; 10/2009
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ABSTRACT: In this paper, design of a distributed differential space time code is considered. To satisfy the commuting property required in the design, Weyl reciprocity is hired. Introducing methods and illustrating examples show that the proposed methods have more flexible, and more easy to get codes than existing methods, especially in a case with high dimensional unitary matrices and a large number of relays.
Information Theory, 2009. ISIT 2009. IEEE International Symposium on; 08/2009
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ABSTRACT: Orthogonal space-time block codes (OSTBC) from orthogonal designs have both advantages of complex symbol-wise maximum-likelihood (ML) decoding and full diversity. However, their symbol rates are upper bounded by 3/4 for more than two antennas for complex symbols. To increase the symbol rates, they have been generalized to quasi-orthogonal space-time block codes (QOSTBC) in the literature but the diversity order is reduced by half and the complex symbol-wise ML decoding is significantly increased to complex symbol pair-wise (pair of complex symbols) ML decoding. The QOSTBC has been modified by rotating half of the complex symbols for achieving the full diversity while maintaining the complex symbol pair-wise ML decoding. The optimal rotation angles for any signal constellation of any finite symbols located on both square lattices and equal-literal triangular lattices have been found by Su-Xia, where the optimality means the optimal diversity product (or product distance). QOSTBC has also been modified by Yuen-Guan-Tjhung by rotating information symbols in another way such that it has full diversity and in the meantime it has real symbol pair-wise ML decoding (the same complexity as complex symbol-wise decoding) and the optimal rotation angle for square and rectangular QAM constellations has been found. In this paper, we systematically study general linear transformations of information symbols for QOSTBC to have both full diversity and real symbol pair-wise ML decoding. We present the optimal transformation matrices (among all possible linear transformations not necessarily symbol rotations) of information symbols for QOSTBC with real symbol pair-wise ML decoding such that the optimal diversity product is achieved for both general square QAM and general rectangular QAM signal constellations. Furthermore, our newly proposed optimal linear transformations for QOSTBC also work for general QAM constellations in the sense that QOSTBC have full diversity with good diversit-
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y product property and real symbol pair-wise ML decoding. Interestingly, the optimal diversity products for square QAM constellations from the optimal linear transformations of information symbols found in this paper coincide with the ones presented by Yuen-Guan-Tjhung by using their optimal rotations. However, the optimal diversity products for (nonsquare) rectangular QAM constellations from the optimal linear transformations of information symbols found in this paper are better than the ones presented by Yuen-Guan-Tjhung by using their optimal rotations. In this paper, we also present the optimal transformations for the co-ordinate interleaved orthogonal designs (CIOD) proposed by Khan-Rajan for rectangular QAM constellations.
IEEE Transactions on Information Theory 04/2009; · 3.01 Impact Factor
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ABSTRACT: In this paper, we first present two tight upper bounds for the normalized diversity products (or product distances) of 2 × 2 diagonal space-time block codes from quadratic extensions on BBQ ( i ) and BBQ ( mmbzeta<sub>6</sub>) , where i =radic{-1} and mmbzeta<sub>6</sub>=exp( i 2pi/6) . Two such codes are shown to reach the tight upper bounds and therefore have the maximal normalized diversity products. We present two new diagonal space-time block codes from higher order algebraic extensions on BBQ ( i ) and BBQ ( mmbzeta<sub>6</sub>) for three and four transmit antennas. We also present a nontight upper bound for normalized diversity products of 2 × 2 diagonal space-time block codes with QAM information symbols, i.e., in BBZ [ i ] , from general 2 × 2 complex-valued generating matrices. We then present an n × n -diagonal space-time code design method directly from 2 n real integers based on extended complex lattices (of generating matrix size n × 2 n ) that are shown to have better normalized diversity products than the optimal diagonal cyclotomic codes do. We finally use the optimal 2 × 2 diagonal space-time codes from the optimal quadratic extensions to construct two 2 × -
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2 full-rate space-time block codes and find that both of them have better normalized diversity products than the Golden code does.
IEEE Transactions on Information Theory 03/2009; · 3.01 Impact Factor
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ABSTRACT: Differential space-time modulation (DSTM) has been recently proposed by Hughes, and Hochwald and Sweldens when the channel information is not known at the receiver, where the demodulation is in fact the same as the coherent demodulation of space-time block coding by replacing the channel matrix with the previously received signal matrix. On the other hand, the DSTM also needs a recursive memory of a matrix block at the encoder and therefore provides a trellis structure when the channel information is known at the receiver, which is the interest of this paper. This recursive structure of the DSTM has been adopted lately by Schlegel and Grant in joint with a conventional binary code and joint iterative decoding/demodulation with a superior performance. The number of states of the trellis from the recursive structure depends on both the memory size, which is fixed in this case, and the unitary space-time code (USTC). When a USTC for the DSTM forms a group, the number of states is the same as the size of the USTC, otherwise the number of the states is the size of the semi-group generated by the USTC from all the multiplications of the matrices in the USTC. It is well known in the conventional convolutional coding (CC) or the trellis coded modulation (TCM), the free (Hamming or Euclidean) distance (or the performance) increases when the number of states increases by adding more memory with a properly designed CC or TCM. In this paper, we systematically study and design the USTC/DSTM for the recursive space-time trellis modulation and show that the diversity product increases when the number of states increases, which is not because of the memory size but because of the different USTC designs that generate different sizes of semi-groups. We propose a new USTC design criterion to ensure that the trellis structure improves the diversity product over the USTC as a block code. Based on the new criterion, we propose a new class of USTC design for an arbitrary number of transmi-
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t antennas that has an analytical diversity product formula for two transmit antennas. We then follow Schlegel and Grant's approach for joint encoding and iterative decoding of a binary coded DSTM (turbo space-time coding) and numerically show that our new USTC designs for the recursive space-time trellis modulation outperforms the group USTC used by Schlegel and Grant.
IEEE Transactions on Information Theory 03/2009; · 3.01 Impact Factor
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ABSTRACT: This paper proposes a designing framework for down-sampling compressed images/video with arbitrary ratio in the discrete cosine transform (DCT) domain. In this framework, we first derive a set of DCT-domain down-sampling methods which can be represented by a linear transform with double-sided matrix multiplication (LTDS) in the DCT domain and show that the set contains a wide range of methods with various complexity and visual quality. Then, for a preselected spatial-domain down-sampling method, we formulate an optimization problem for finding an LTDS to approximate the given spatial-domain down-sampling method for a trade-off between the visual quality and the complexity. By modeling LTDS as a multiple layer network, a so-called structural learning with forgetting algorithm is then applied to solve the optimization problem. The proposed framework has been applied to discover optimal LTDSs corresponding to a spatial down-sampling method with Butterworth low-pass filtering and bicubic interpolation. Experimental results show that the resulting LTDS achieves a significant reduction on the complexity when compared with other methods in the literature with similar visual quality.
IEEE Transactions on Image Processing 02/2009; · 3.04 Impact Factor
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IEEE Transactions on Information Theory. 01/2009; 55:1104-1130.
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IEEE Transactions on Wireless Communications. 01/2009; 8:5427-5430.
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IEEE Transactions on Information Theory. 01/2009; 55:569-583.
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ABSTRACT: This paper studies the design of vector quantization (VQ) on noisy channels and its asymptotic performance analysis. Given a tandem source-channel coding system with VQ and block channel coding, we derive a closed-form formula of the average end-to-end distortion (EED), which reveals a structural factor called the scatter factor for noisy channel quantizers. Based on this formula, an iterative algorithm is developed for jointly designing optimal quantizers with channel conditions. Simulations show that quantizers that are jointly designed with channel conditions significantly reduce the EED when compared with quantizers that are designed separately from channel conditions. Indeed, our asymptotic analyses show that the infimum of the mean squared EED over all possible quantizers with joint quantization design is p<sub>err</sub>sigma<sup>2</sup>, where p<sub>err</sub> is the average transmission error probability of the channel and sigma<sup>2</sup> is the component variance of the source. This is 4.77dB better than that with separate quantization design for an i.i.d. Guassian source.
Information Theory, 2008. ISIT 2008. IEEE International Symposium on; 08/2008
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ABSTRACT: In this correspondence, we prove that the optimal normalized diversity product of lattice-based diagonal space-time block codes with Gaussian integer (or QAM) signal constellations, i.e., , and any generating matrices of complex entries (not necessarily algebraic extensions of as commonly used) is . This result implies that lattice-based diagonal space-time block codes with Gaussian integer signal constellations and generating matrices of entries from quadratic algebraic extensions of have already reached the optimal normalized diversity product.
IEEE Transactions on Information Theory 05/2008; · 3.01 Impact Factor
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Proceedings of the IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2008, March 30 - April 4, 2008, Caesars Palace, Las Vegas, Nevada, USA; 01/2008
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ABSTRACT: In this letter, we propose a new family of space-time trellis codes, which are constructed by combining a super set of quasi-orthogonal space-time block codes with minimum decoding complexity with an outer multiple trellis coded modulation encoder. A systematic set-partitioning method for quadratic amplitude modulation constellations is given. The proposed scheme can be used for systems with four or more than four transmit antennas. Furthermore, its decoding complexity is low because its branch metric calculation can be implemented in a symbolwise way. Simulation results demonstrate that the proposed scheme has a comparable performance as super quasi-orthogonal space-time trellis codes proposed by Jafarkhani and Hassanpour while providing a lower decoding complexity.
IEEE Transactions on Communications 09/2007; · 1.68 Impact Factor
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ABSTRACT: Space time coding for a multiple input, multiple output (MIMO) system with finite-bit feedback and maximum-likehood (ML)-decoding is considered. Based on the analysis of union bound of error probability of the system, it is shown that designing the system with good performance can be divided into the following three steps: (1) efficiently packing finite points into a dynamic ellipsoid in a finite dimensional real Euclidean space; (2) effectively quantizing a Stiefel manifold; (3) optimally quantizing a cone in a real Euclidean space. Furthermore, criteria and methods to implement the above steps are given. A design example for a system, which has 2 transmit and 2 receive antennas, 2 time slot delay and 4 bits transmission rate, shows that 5 bits feedback can derive 1.8 dB gain over the system without feedback.
Information Theory, 2007. CWIT '07. 10th Canadian Workshop on; 07/2007
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ABSTRACT: In this paper, a recursive space-time trellis coding (RSTTC) from general differential encoding is proposed for multiple antenna systems, where general differential encoding is implemented separately from the space-time matrix modulation. The general differential encoding is achieved by introducing a new multiplication on a set of symbols (called trellis codewords) such that the corresponding RSTTC has its minimum error event length 3 or above and in the meantime it has the minimum number of states. The space-time matrix modulation is the mapping of the differentially encoded symbols to a set of space-time matrices (called modulation codewords). Due to the separation of differential encoding and space-time matrix modulation, more freedom on the design of modulation codewords (or a space-time code) exists, which may result in a larger diversity product (or determinant distance or product distance or coding advantage) than that the existing combined differential encoding and space-time matrix modulation can achieve in the concatenation with an outer binary channel encoder proposed by Schlegel and Grant. A new design of modulation codewords is then proposed for the RSTTC with larger diversity products than the existing schemes. Simulation results are finally presented to show that our new design significantly outperforms the existing schemes.
Information Theory Workshop, 2006. ITW '06 Punta del Este. IEEE; 11/2006
