This study proposes an analytical model and an effective scheme for the periodic broadcast on the control channel in vehicular ad hoc networks (VANETs). An improved Markov model for analysing the performance of the periodic broadcast in VANETs is established. Compared with the traditional two-dimensional Markov chain models, the improvement of our proposed model is achieved by the considerations of the unsaturated traffic conditions with the deterministic message generation at each node, modelled by a discrete-time D/M/1 queue and the control mechanism of freezing the backoff-time counter. In adapting to the change of the vehicle densities, the authors propose to use the dynamic contention window (DCW), instead of the fixed contention window (CW), for the broadcast in the IEEE 802.11p medium access control in VANETs. For a certain vehicle density, a best CW size is chosen to achieve a more effective broadcast. Simulation results show that the proposed DCW-based broadcast performs better than the traditional fixed-CW-size broadcast in terms of the packet collision probability. The results also validate our proposed Markov model and its performance improvement than the scheme without the consideration of freezing the backoff-time counter.

To rapidly determine the pollution extent of wastewater, the calibration models were established for deter-mination of Chemical Oxygen Demand and Biological Oxygen Demand in wastewater by partial least squares and near infrared spectrometry of 120 samples. Spectral data preprocessing and outliers’ diagnosis were also discussed. Correlation coefficients of the models were 0.9542 and 0.9652, and the root mean square error of prediction (RMSEP) were 25.24 mg?L-1 and 12.13 mg?L-1 in the predicted range of 28.40~528.0 mg?L-1 and 16.0~305.2 mg?L-1 for Chemical Oxygen Demand and Biological Oxygen Demand, respectively. By statistical significance test, the results of determination were compared with those of stan-dard methods with no significant difference at 0.05 level. The method has been applied to simultaneous de-termination of Chemical Oxygen Demand and Biological Oxygen Demand in wastewater with satisfactory results

No abstract

In this paper, an algorithm called DPB (Distributed Probabilistic Broadcasting) is proposed to increase the reliability of the emergent message transmission for safety applications in VANETs (Vehicular Ad Hoc Networks). In DPB which is based on probabilistic broadcasting, vehicles compute their own relay probability according to their own states at first, and then retransmit the message on basis of the adaptive probability. An analysis model combined with the model of headway in traffic theory is presented, and the performance shows that DPB does well in both low and high density networks. Keywords-Distributed Probabilistic Broadcasting (DPB); Vehicular Ad Hoc Network (VANET); broadcast; safety applicationsI.

No abstract