Timing and Carrier Synchronization with Channel Estimation in AF Two-Way Relaying Networks

Two-way relaying networks (TWRNs) allow for more bandwidth efficient use of the available spectrum since they allow for simultaneous information exchange between two users with the assistance of an intermediate relay node. However, due to superposition of signals at the relay node, the received signal at the user terminals is affected by multiple impairments, i.e., channel gains, timing offsets, and carrier frequency offsets, that need to be jointly estimated and compensated. This paper presents the system model for amplify-and-forward (AF) TWRNs in the presence of multiple impairments and proposes least squares and differential evolution based algorithms for joint estimation of these impairments. The Cramér-Rao lower bounds (CRLBs) for the joint estimation of multiple impairments are derived. A minimum mean-square error based receiver is then proposed to compensate the effect of multiple impairments and decode each user’s signal. Simulation results show that the performance of the proposed estimators is very close to the derived CRLBs at moderate-to-high signal-to-noise-ratios. It is also shown that the bit-error rate performance of the overall AF TWRN is close to a TWRN that is based on assumption of perfect knowledge of the synchronization parameters

Reversal in time order of interactive events: Collision of inclined rods

In the rod and hole paradox as described by Rindler (1961 Am. J. Phys. 29 365-6), a rigid rod moves at high speed over a table towards a hole of the same size. Observations from the inertial frames of the rod and slot are widely different. Rindler explains these differences by the concept of differing perceptions in rigidity. Gron and Johannesen (1993 Eur. J. Phys. 14 97-100) confirmed this aspect by computer simulation where the shapes of the rods are different as observed from the co-moving frames of the rod and slot. Lintel and Gruber (2005 Eur. J. Phys. 26 19-23) presented an approach based on retardation due to speed of stress propagation. In this paper we consider the situation when two parallel rods collide while approaching each other along a line at an inclination with their axis. The collisions of the top and bottom ends are reversed in time order as observed from the two co-moving frames. This result is explained by the concept of extended present derived from the principle of relativity of simultaneity

The relationship between adolescents’ civic knowledge, civic attitude, and civic behavior and their self-reported future likelihood of voting

A long-standing objective of American public education is fostering civically engaged youth. Identifying characteristics associated with likelihood of future voting, a measure of democratic participation that predicts future voting behavior, might yield targets for education programs to increase civic participation. Survey data from urban adolescents were analyzed to elucidate how civic knowledge, civic attitudes, and civic behaviors are associated with self-reported likelihood of future voting. In a multivariable ordered logistic regression model with latent constructs for civic knowledge, attitudes, and behavior, two civic knowledge constructs and two civic attitude constructs maintained a positive, statistically significant independent association with future voting likelihood after adjusting for race/ethnicity and advanced coursework: knowledge of American governance, current events knowledge, general self-efficacy, and skill-specific self-efficacy. Further research is necessary to determine whether education programs can intervene upon these civic knowledge and civic attitude factors to increase voting participation later in life