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

Union bounds for BER evaluation and code optimization of space-time codes in 2-by-2 MIMO systems

In this paper, an exact closed-form formula for the Pair-wise Error Probability (PEP) is derived for two transmit and two receive antennas MIMO systems using the probability density function (PDF) of the modified Euclidean distance. An exact Union Bound formed by this formula, together with the Asymptotic Union Bound, are studied for optimization and biterror rate (BER) evaluation of Space-Time (S-T) codes. Numerical calculations and Monte Carlo computer simulation have been used to study these two Union Bounds on a 2-by-2 MIMO system using a rotation-based diagonal S-T code (D code) in a block fading channel. Results show that the exact Union Bound is a very tight Bound for BER evaluation while the Asymptotic Union Bound is very accurate for code optimization. © 2006 IEEE.published_or_final_versionIEEE 63rd Vehicular Technology Conference (VTC 2006-Spring), Melbourne, Australia, 7-10 May 2006. In Proceedings of the 63rd IEEE VTC Spring 2006, v. 3, p. 1506-151

A new fast sub-optimal search method for closed-loop transmit diversity system with limited number of feedback bits

IEEE Radio and Wireless Conference, Atlanta, Georgia, USA, 19-22 September 2004In this paper, we present a fast sub-optimal searching algorithm for the closed-loop transmit diversity scheme used in wireless system. Under the low mobility condition and with perfect channel knowledge at the receiving end, our proposed searching algorithm can use a limited number of feedback bits to provide a sub-optimal solution that can achieve the SNR values close to the optimal solution with a greatly reduced complexity and outperform other sub-optimal schemes. The scheme also works well under the presence of feedback errors. © 2004 IEEE.published_or_final_versio

Novel search algorithm for closed-loop transmit diversity system with limited number of feedback bits

We propose two simple closed-loop transmit diversity schemes with a fixed number of feedback bits being allocated for each transmit antenna. Under a low mobility condition and with perfect channel knowledge at the receiver, we show that our proposed schemes can achieve signal-to-noise ratio (SNR) values close to the optimal solution but with greatly reduced complexity. We also show that our methods outperform other suboptimal schemes such as the co-phasing method. © 2004 IEEE.published_or_final_versionIEEE 60th Vehicular Technology Conference 2004-Fall (VTC2004-Fall), "Wireless Technologies for Global Security", Los Angeles, CA, USA, 26-29 September 2004. In IEEE - VTS Vehicular Technology Conference Proceedings, 2004, v. 60 n. 3, p. 1849-185

Clinical and histopathological observations of autologous bone marrow stromal cells implantation on the regeneration of sciatic nerve neurotmesis in rabbit

The peripheral nerve injuries (PNI) is due to stretching and laceration. Therefore, the epineural repair technique is currently accepted as a standard method for peripheral nerve repair. Thirty-two (32) rabbits were divided equally into perineural nerve sutures as control group (CG) and bone marrow stromal cells (BMSCs) as the treatment group (TG). The aim of this study was to investigate the effect of the autologous BMSCs implantation on the regeneration of sciatic nerve neurotmesis in rabbits. There was significant improvement (p<0.05) of the motor and sensory functions in the TG animals as compared to the CG. Histopathological examinations of the proximal nerve stump in the CG showed mild adherence surrounding an anastomosed area, few vacuolation and plenty of collagen at the peri and epineurium. The anastomosed site showed the degeneration, disorientation and giant cell surrounding the stitches, while intraneurial scar tissues were seen in the distal segment at the 112th post operation day (POD). The histopathology of TG showed the activated Schwann cells, good myelination, minimum scar tissue, good orientation and remarkable angiogenesis at the 112th POD. BMSCs are capable of improving the motor and sensory functions and significantly promote the regeneration of sciatic nerve neurotmesis in rabbits.Key words: Clinical, histopathological, bone marrow stromal cells (BMSCs), neurotmesis, sciatic nerve, rabbit

Distribution of Craniofacial Variables in South Dalmatian and Middle Croatian Populations

The objective of the present work was to determine some relevant craniofacial parameters, particularly in relation to sex, for the study of the distribution of basic head and face types, and to investigate craniofacial and morphological differences between two population samples. The study sample comprised 100 subjects of both sex aged 18 to 30 from South Dalmatia and 200 subjects from Middle Croatia. Eight basic craniofacial variables were measured to obtain head, forehead and face indexes. The data indicate that average values of all variables can be used as standard craniofacial parameters for the examined population groups. All the craniofacial variables are considerably higher in men than in women (p < 0.05). In the South Dalmatian population mesocephalia (48.0%) and leptoprosopia (82.0%) prevail, while in the Middle Croatian population the brachycephalia (62.0%), and euriprosopia (73.5%) are present to a greater degree. The most significant craniofacial and morphological differences between the examined study samples are head width (Eu–Eu), face width (Zy–Zy), and forehead height (Tr–N). They were found to be statistically significant in the examined Middle Croatian population (p < 0.05). The presented measurements are highly relevant to orthodontic diagnostics and therapy

Evaluation of Craniometric Methods for Determination of Vertical Dimension of Occlusion

In clinical practice, fully precise method for exact determination of vertical relation of occlusion still does not exist. This study examines the relationship between different craniofacial distances and the distance subnasale– gnathion (Sn–Gn), which represents the lower third of the face in vertical relation determination. The highest coefficient of correlation was (r = 0.8678, p < 0.05) between the distance eye–ear (E–E = lateral border of the ocular orbit–medial opening of the meatus of the external auditory canal) and Sn–Gn. The prediction of the distance Sn–Gn could be determined through the formula: Sn–Gn = E–E / 1.08 or through the regression analysis: Sn–Gn = 1.9197 + 0.6449 x E–E. None of the calculated coefficients of correlation was 1, but was < 1, so that the prediction of the distance Sn–Gn by craniometric distances is not absolutely reliable, although it is considerably helpful. Our results point at the variations of craniofacial distances in the Croatian population. Yet, craniometry could still be recommended in everyday clinical practice for prediction of vertical relation of occlusion, as it is a simple, economic and non-invasive method, however in combination with some other methods, which have proved to be helpful

The Dichotomy between Nodal and Antinodal Quasiparticles in Underdoped (La2−x_{2-x}Srx_x)CuO4_4 Superconductors

High resolution angle-resolved photoemission measurements on underdoped (La$_{2-x}$Sr$_x$)CuO$_4$ system show that, at energies below 70 meV, the quasiparticle peak is well defined around the ($\pi$/2,$\pi$/2) nodal region and disappears rather abruptly when the momentum is changed from the nodal point to the ($\pi$,0) antinodal point along the underlying ``Fermi surface''. It indicates that there is an extra low energy scattering mechanism acting upon the antinodal quasiparticles. We propose that this mechanism is the scattering of quasiparticles across the nearly parallel segments of the Fermi surface near the antinodes.Comment: to appear in Phys. Rev. Let