Simplified ordering for fixed-complexity sphere decoder

This paper proposes a simplified ordering algorithm for the fixed-complexity sphere decoder (FSD). The new algorithm is developed from the analysis of the ordering for FSD from a geometrical point of view. Computer simulation is used to assess the improvements in bit-error rate (BER) performances of MIMO systems using the FSD with the original and the simplified ordering. Simulation results show that the new ordering method can achieve nearly the same BER as the original ordering method but with much less complexity. Copyright © 2010 ACM.postprintThe 6th International Wireless Communications and Mobile Computing Conference (IWCMC 2010), Caen, France, 28 June-2 July 2010. In Proceedings of the 6th International Wireless Communications and Mobile Computing Conference, 2010, p. 804-80

A new family of linear dispersion code for fast sphere decoding

In this paper, a new family of Linear Dispersion Codes (LDCs) that can be decoded using a fast Sphere Decoding (SD) algorithm in MIMO systems is proposed. The basic principle of this structure is to make the LDC to have as many as possible the rows orthogonal in the dispersion matrices. Monte Carlo simulation results show that the optimum LDCs with this orthogonal structure have nearly identical bit-error-rate (BER) performances as other optimal LDCs. We develop a simplified Sphere Decoding (SD) algorithm that can significantly reduce the decoding complexity in decoding the new LDCs with proposed orthogonal structure. Simulation results show that the complexity reduction is more significant for MIMO system transmitting higher level modulation. For 2×4 MIMO systems transmitting 4 64QAM and 256QAM symbols in a block length of 4, the reductions are about 71-83% and 76-88%, respectively. ©2009 IEEE.published_or_final_versionThe 22nd IEEE Canadian Conference on Electrical and Computer Engineering (CCECE 2009), St. John's, NL., 3-6 May 2009. In Proceedings of the 22nd CCECE, 2009, p. 314-31

A fast-decodable code structure for linear dispersion codes

This paper proposes the design of a new family of fast-decodable, full-rank, flexible-rate linear dispersion codes (LDCs) for MIMO systems with arbitrary numbers of transmit and receive antennas. The codewords of LDCs can be expressed as a linear combination of certain dispersion matrices and, in this new family of LDCs, we propose to have orthogonal rows in as many dispersion matrices as possible. We show that, with the proposed code, the number of levels in the tree search and hence the complexity of the sphere decoder (SD) at the receiver can be substantially reduced. Monte Carlo computer simulation has shown that the LDCs with and without the orthogonal structure have nearly identical bit-error-rate (BER) performances. However, the complexity of the SD used for decoding the proposed family of LDCs is substantially reduced. © 2009 IEEE.published_or_final_versio

Evaluation of union bounds for space-time codes based on a common function

Error-rate evaluation of Space-Time codes using Union bounds sometimes requires very heavy computational loads and so is impractical to use. In this paper, a Common function shared by different Union bounds is derived and used to develop a modified Union bound (MUB) for error-rate evaluation. Results of numerical evaluations and Monte-Carlo simulation on two 2x2 rotation-based S-T codes show that the MUB provides a good compromise between the required computational load and the accuracy for error-rate evaluation. ©2009 IEEE.published_or_final_versionThe 22nd IEEE Canadian Conference on Electrical and Computer Engineering (CCECE 2009), St. John's, NL., 3-6 May 2009. In Proceedings of the 22nd CCECE, 2009, p. 89-9

Difficulties in using the exact closed-form PEP formula for BER calculation of S-T codes

The formula for the exact union bound (EUB) on BER based on the exact closed-form Pair-wise Error Probability (PEP) is most accurate for calculating the bit-error-rates (BERs) of Space-Time (S-T) codes in Multiple-Input Multiple Output (MIMO) systems. In this paper, it is shown that using the exact closed-form PEP formula for numerical calculations of the PEP or the EUB on BER could produce negative results. The formula for the exact closed-form PEP is therefore re-examined and explanations for the problem are given. A simple trick is suggested to reduce the effect of the problem. A new upper bound on PEP derived using the Hölder Inequality is proposed to replace the exact closed-form PEP formula. Numerical calculation results show that the union bound based on the proposed new upper bound on PEP is a very tight bound to the EUB and doesn't have the problem of negative results. ©2009 IEEE.published_or_final_versionThe 2009 IEEE Radio and Wireless Symposium (RWS) 2009, San Diego, CA., 18-22 January 2009. In Proceedings of RWS, 2009, p. 292-29

Development of a special multi-wavelength pyrometer for temperature distribution measurements in rocket engines

Previously a fast multi-wavelength pyrometer was developed in a collaboration between the Harbin Institute of Technology of China and Rome University of Italy. The main features of the instrument include the use of a dispersing prism and a photodiode array to cover the entire spectral band. Following this experience, a new type of six-target eight-wavelength pyrometer for solid propellant rocket engine plume temperature distribution measurements has been developed. The instrument can record the radiation fluxes of eight wavelengths for six different uniformly distributed points on the target surface, which are well defined by holes on a field stop. The fast pyrometer with a specially designed synchronous data acquisition system can assure that the recorded thermal radiation fluxes of different spectral regions are at the same time and the same true temperature, even with dramatically changed targets

Effect of Al addition on the microstructure and electronic structure of HfO₂film

Author name used in this publication: P. F. LeeAuthor name used in this publication: J. Y. Dai2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Effects of Al addition on the native defects in hafnia

Author name used in this publication: P. F. LeeAuthor name used in this publication: J. Y. Dai2005-2006 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Graphene on hexagonal boron nitride as a tunable hyperbolic metamaterial

Hexagonal boron nitride (h-BN) is a natural hyperbolic material1, in which the dielectric constants are the same in the basal plane (ε[superscript t] ≡ ε[superscript x] = ε[superscript y]) but have opposite signs (ε[superscript t] ε[superscript z ]< 0) in the normal plane (ε[superscript z]). Owing to this property, finite-thickness slabs of h-BN act as multimode waveguides for the propagation of hyperbolic phonon polaritons—collective modes that originate from the coupling between photons and electric dipoles in phonons. However, control of these hyperbolic phonon polaritons modes has remained challenging, mostly because their electrodynamic properties are dictated by the crystal lattice of h-BN. Here we show, by direct nano-infrared imaging, that these hyperbolic polaritons can be effectively modulated in a van der Waals heterostructure composed of monolayer graphene on h-BN. Tunability originates from the hybridization of surface plasmon polaritons in graphene with hyperbolic phonon polaritons in h-BN so that the eigenmodes of the graphene/h-BN heterostructure are hyperbolic plasmon–phonon polaritons. The hyperbolic plasmon–phonon polaritons in graphene/h-BN suffer little from ohmic losses, making their propagation length 1.5–2.0 times greater than that of hyperbolic phonon polaritons in h-BN. The hyperbolic plasmon–phonon polaritons possess the combined virtues of surface plasmon polaritons in graphene and hyperbolic phonon polaritons in h-BN. Therefore, graphene/h-BN can be classified as an electromagnetic metamaterial as the resulting properties of these devices are not present in its constituent elements alone