Several approaches for travel time data collection based on the reading of time-stamped media access control addresses fromBluetooth-enabled devices have been reported in the literature recently. This new approach offers a number of advantages over more conventional methods, including lower costs of hardware and software, the volume of data that can be collected over time, and ease of implementation. A fundamental component that may affect the quantity and the quality of the travel time samples collected with a Bluetooth-based system is the antenna type utilized. Antenna characteristics such as polarization and gain must be matched to specific application environments to optimize the performance of a Bluetooth reader unit. However, experimental data that focuses on antenna characterization as it relates to the use of Bluetooth technology to assess the performance of transportation facilities is lacking. In this study, five different types of antennas were characterized to assess their suitability to support a Bluetooth-based travel time data collection system. The results indicate that vertically polarized antennas with gains between 9dBi and 12dBi are good candidates for travel time data collection. Also, different antenna types are better suited to different uses of the Bluetooth-based system. If the main focus is the collection of travel time data, then an antenna with a lower sampling rate may provide more accurate travel time samples.
While fully opportunistic network coding is one of the pioneer works to successfully implement network coding in wireless networks, the analytical model of its performance is still not well understood. In particular, the end-to-end average bit error rate of the scheme is still unclear due to the complexity of the scheme. In this paper we provide a generalized model to analyze the performance of regenerative multi-hop wireless ad hoc networks where opportunistic network coding is applied. By using the model, a closed-form expression of the exact average end-to-end bit error rate of the system over Rayleigh fading channels can be derived. The results obtained in our work allow us to have a more complete understanding of the factors that affect performance, especially the error propagation when packets traverse the network.
In this study, the authors propose an improved version of the min-sum algorithm for low-density parity check code decoding, which the authors call 'adaptive normalised BP-based' algorithm. Their decoder provides a compromise solution between belief propagation and the min-sum algorithms by adding an exponent offset to each variable node's intrinsic information in the check node update equation. The extrinsic information from the min-sum decoder is then adjusted by applying a negative power of the two scale factor, which can be easily implemented by right shifting the min-sum extrinsic information. The difference between their approach and other adaptive normalised min-sum decoders is that the authors select the normalisation scale factor using a clear analytical approach based on the underlying principles. The simulation results show that the proposed decoder outperforms the min-sum decoder and performs very close to the BP decoder with lower complexity.
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