Complex Mobile Environments Research Articles

Biolocomotion and Premelting in Ice

Biota are found in glaciers, ice sheets and permafrost. Ice bound micro-organisms evolve in a complex mobile environment facilitated or hindered by a range of bulk and surface interactions. When a particle is embedded in a host solid near its bulk melting temperature, a melted film forms at the surface of the particle in a process known as interfacial premelting. Under a temperature gradient, the particle is driven by a thermomolecular pressure gradient toward regions of higher temperatures in a process called thermal regelation. When the host solid is ice and the particles are biota, thriving in their environment requires the development of strategies, such as producing exopolymeric substances (EPS) and antifreeze glycoproteins (AFP) that enhance the interfacial water. Therefore, thermal regelation is enhanced and modified by a process we term bio-enhanced premelting. Additionally, the motion of bioparticles is influenced by chemical gradients influenced by nutrients within the icy host body. We show how the overall trajectory of bioparticles is controlled by a competition between thermal regelation and directed biolocomotion. By re-casting this class of regelation phenomena in the stochastic framework of active Ornstein-Uhlenbeck dynamics, and using multiple scales analysis, we find that for an attractive (repulsive) nutrient source, that thermal regelation is enhanced (suppressed) by biolocomotion. This phenomena is important in astrobiology, the biosignatures of extremophiles and in terrestrial paleoclimatology.

Capture-Aware Identification of Mobile RFID Tags With Unreliable Channels

Radio frequency identification (RFID) has been widely applied in large-scale applications such as logistics, merchandise and transportation. However, it is still a technical challenge to effectively estimate the number of tags in complex mobile environments. Most of existing tag identification protocols assume that readers and tags remain stationary throughout the whole identification process and ideal channel assumptions are typically considered between them. Hence, conventional algorithms may fail in mobile scenarios with unreliable channels. In this paper, we propose a novel RFID anti-collision algorithm for tag identification considering path loss. Based on a probabilistic identification model, we derive the collision, empty and success probabilities in a mobile RFID environment, which will be used to define the cardinality estimation method and the optimal frame length. Both simulation and experimental results of the proposed solution show noticeable performance improvement over the commercial solutions.

Channel Estimation and Combining Orthogonal Pilot Design in MIMO-OFDM System

The current technology of high speed wireless communication exist the following weaknesses, limited bandwidth, bad transmitted channel, complex mobile environment and the quality of service under limited service time. The dispersing pilot pattern and the method of channel estimation using in MIMO-OFDM system couldn’t eliminate the same frequency interference caused by the OFDM frequency among different transmit-receive antenna couples. Aiming at these problems, we proposed a method of MIMO-OFDM channel estimation combining orthogonal pilot design. The data format of pilot is designed. It can retain the orthogonality of different sub-carriers of OFDM which are produced by different transmit-receive antenna couples or transmit-receive antenna couple. In wireless mobile environment, it can better estimate the channel parameters without any prior channel information. This method proposed in the paper has finished the design of the completely orthogonal pilot data symbol among the different subcarriers position of different transmitting-receiving antenna pair. And the pilot data symbols are distributed in the entire time-frequency grid of the channel reasonably, therefore this paper uses a FFT unit whose points are equal to the number of the OFDM subcarriers to realize the least-square channel estimation algorithm. In the process of channel estimation, the channel parameters estimation precision has increased because of the noise getting better inhibition, which reduces the least squares estimate noise sensitivity to the requirements