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Frequency error, non-ideal channel estimation (CE) and inefficient seamless road side unit (RSU) service are critical issues occurring in conventional systems that are completely specified by current IEEE 802.11p standards. This study investigates novel techniques for achieving accurate frequency offset compensation and effective CE and RSU selection for handover in signal-overlapping areas. Recently, communications using data-aided orthogonal frequency-division multiplexing (DA-OFDM), such as pseudo-random-postfix OFDM and time-domain-synchronous OFDM (TDS-OFDM), have been actively studied because of their higher effectiveness, efficiency and better transmission quality. This study consists of three parts: (i) derivation of the maximum likelihood estimation for DA-OFDM, (ii) design of an accurate RSU selection scheme and (iii) implementation of a superior TD CE technique. Performance comparisons between the conventional and the proposed techniques are conducted through comprehensive computer simulations.

Wireless network authentication schemes have been researched forabout a decade, and associated security problems explored by manyresearchers. In 2004, Zhu and Ma proposed an authentication schemefor wireless environments. Afterwards other researchers proposedimprovements according to Zhu-Ma scheme. Mutual authentication isone of the most important issues. To the best of our knowledge,there is no scheme that allows a foreign agent to authenticate thehome agent and mobile user at the same time. Towards this purpose,we propose a simultaneous authentication scheme based on chaoticmaps, and describe how our proposed scheme addresses varioussecurity problems while maintain anonymity. DOI: http://dx.doi.org/10.5755/j01.itc.45.2.8875

Next-generation telematics solutions are being driven by the maturation of recently deployed intelligent transportation systems, assisted by the integration of and rapid collaboration with information communication technology markets and the automotive industry. Examples of this trend can be found in DSRC contexts in which Wi-Fi and WiMAX have become very relevant in vehicular environments. Comprehensive field trials were conducted and relevant measurements were collected in physical environments to investigate the possible environmental factors that occur in roadside-unit-to-vehicle communication scenarios. In these carefully controlled automobile experiments, the most representative parameters are measured and analyzed for DSRC in dynamic environments (e.g., packet loss, latency, and delay spread). Using a systematic testing procedure and through measurement analysis, the communication performance and the operating reliability of wireless communications can be effectively verified; insightful improvements and helpful suggestions and contributions may thus be achieved for telematics system designs. Furthermore, a practical, reasonable, and standardized testing procedure is proposed, and it can be utilized in equipment verification and product certification.

Operating up to 5.5 GHz with 1-mW power consumption, a 90-nm CMOS programmable frequency divider with eight stages of new static D-flip-flop-based (2/1) divider cells is presented, where the supply voltage of 1.0 V is employed. The divider achieves a full modulus range from 1 to 256 and operates over a wide range maintaining up to 4 GHz with -30-dBm input power. The divider also accomplishes a power efficiency of 12.8 GHz/mW with 0.5-V supply voltage. It is favorable for advanced processes.

Drawing on both social exchange theory and impression management theory, this study sought to explain how perception of organizational politics (POP) influences organizational citizenship behaviour (OCB) through two contrary psychological processes. We proposed that through the mediation of job satisfaction, POP has an inhibiting effect on OCB; through the mediation of careerism, POP has a nourishing effect on OCB. Data were obtained from 393 police officers and their colleagues from a city police department in northern Taiwan. Results from structural equation modelling (SEM) revealed that the relationship between POP and OCB was negatively mediated by job satisfaction and positively mediated by careerism. Such antithetical psychological processes imply that employees may experience psychological dilemmas over the performance of OCB when they perceive their organization as political. Implications for theory and future research are discussed.

The ultra-long period Cepheids (ULPCs) are classical Cepheids with pulsation periods exceeding $\approx 80$ days. The intrinsic brightness of ULPCs are ~1 to ~3 mag brighter than their shorter period counterparts. This makes them attractive in future distance scale work to derive distances beyond the limit set by the shorter period Cepheids. We have initiated a program to search for ULPCs in M31, using the single-band data taken from the Palomar Transient Factory, and identified eight possible candidates. In this work, we presented the VI-band follow-up observations of these eight candidates. Based on our VI-band light curves of these candidates and their locations in the color-magnitude diagram and the Period-Wesenheit diagram, we verify two candidates as being truly ULPCs. The six other candidates are most likely other kinds of long-period variables. With the two confirmed M31 ULPCs, we tested the applicability of ULPCs in distance scale work by deriving the distance modulus of M31. It was found to be $\mu_{M31,ULPC}=24.30\pm0.76$ mag. The large error in the derived distance modulus, together with the large intrinsic dispersion of the Period-Wesenheit (PW) relation and the small number of ULPCs in a given host galaxy, means that the question of the suitability of ULPCs as standard candles is still open. Further work is needed to enlarge the sample of calibrating ULPCs and reduce the intrinsic dispersion of the PW relation before re-considering ULPCs as suitable distance indicators., Comment: 13 pages, with 14 Figures and 4 Tables (one online table). AJ accepted

The star 1SWASP J022727.03+115641.7 was reported as a contact binary with a period shorter than the empirical limit of such systems. Our study shows the star not to be variable. Instead, it is the nearby star, 2MASS 02272637 +1156494, that exhibits variability. The BRI CCD light curves of 2MASS 02272637+1156494 show the system to be a moderate mass ratio (2.154(-0.008)(+0.074)), and shallow contact (10.4(-1.9)(+1.4)%) W-type contact binary. The masses, radii, and luminosities of the binary components are, respectively, M-1 = 0.25(-0.01)(+0.05), M-circle dot, M-2 = 0.54(-0.04)(+0.11) M-circle dot, R-1 = 0.45(-0.01)(+0.02) R-circle dot, R-2 = 0.063(-0.02)(+0.04) R-circle dot, L-1 = 0.038(-0.005)(+0.018) L-circle dot, and L-2 = 0.071(-0.010)(+0.037) L-circle dot, with an estimated distance 326(-46)(+127) pc. These uncertainties mainly come from the errors of the colors used to estimate the temperature of the primary star. A dark spot was introduced on the massive component in the final solution.