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The noise covariance matrices Q and R are set as constant values in the traditional extended Kalman filter (TEKF). They are determined by trial and error. This process is very complicated and the optimal matrices are difficult to determine. In addition, when the characteristic of noise changes, the matrices cannot be adjusted correspondingly, and the performance of the TEKF deteriorates. Therefore, an adaptive EKF algorithm based on the maximum likelihood estimation criterion with limited memory exponential weighting (EW-MLE-AEKF) is proposed in this paper. In the proposed EW-MLE-AEKF algorithm, the windowing method is adopted to save the posterior residual sequences in the previous N calculation periods. Then, these sequences are used to estimate and update the process noise covariance matrix Q in real time. To speed up the convergence speed of the estimation, a limited memory exponential weighting algorithm is added to the windowing method, which can increase the importance of recent data. Through real-time experiments, the superiority of the proposed EW-MLE-AEKF algorithm is verified.

The paper studies two moving vehicles exchanging messages assisted by another vehicle which is used as a relay. All the vehicle-to-vehicle (V2V) links are modeled as flat double-Rayleigh fading. Based on this particular channel model, the OPA (optimal power allocation) solutions are derived through maximizing source-to-destination channel capacity on the assumptions of amplify-and-forward relaying strategy. Then, the outage probability is discussed and the lower bound on it is acquired. Simulation results manifest that the OPA method improves the average throughput of the IVC (inter-vehicular communication) system by about 2 dB at low SNR (signal-to-noise ratio) and has no less than 2 dB gains on outage probability at medium to high SNR over equal power allocation (EPA) scheme. They also show that the lower bound on outage probability approximates to the Monte Carlo numerical calculations at low to medium SNR region and, as the exact outage probability is not easy to obtain, it can be used to estimate the outage performance of the relay-assisted IVC system roughly.

This paper studies the inter-vehicular communication (IVC) system where a vehicle transmits information to another vehicle assisted by an access point (AP), which may be mounted along a street or on a rooftop. The paper first presents the double-Rayleigh fading vehicle-to-vehicle (V2V) channel model and the amplify-and-forward (AF) relaying system. And then the optimal power allocation (OPA) solutions are derived through maximizing source-to-destination channel capacity. Based on mathematic analysis, the closed-form expression on outage probability is concluded finally. Simulation results show that the OPA scheme improves the average throughput by about 2 dB at low to high SNR (signal-to-noise ratio) and has no less than 2 dB gains on outage probability at medium to high SNR over equal power allocation (EPA) method. They also manifest that the theoretical analysis on average outage probability coincides very well with the Monte Carlo numerical calculations. The diversity order can be achieved as large as 2.7 dB in the relay-assisted IVC system when the relay approaches to the source and under EPA solution.

This paper explores the relay-assisted transmission system with mobile-to-mobile links undergo cascaded Rayleigh fading. The BER (bit error rate) bounds of the system are derived through mathematic analysis assuming amplify-and-forward relaying. And the OPA (optimal power allocation) method is discussed which is based on minimizing Chernoff bound on BER performance. The paper presents two classical cases based on geometrical topology and gets optimized power distribution parameters by numerical calculations. It further emphasizes useful insights which are as bellows: when the relay is closer to destination terminal (e.g., d R2 ≤d 12 /10), it should spend more than 97% power to source terminal for the first phase transmission, whereas the relay approaches to the source, an equal power method (EPA) is adopted between the source and the relay during two transmissions. Simulation results manifest that through OPA power savings can be achieved as large as 3dB.