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Shilling attacks have been a significant vulnerability of collaborative filtering (CF) recommender systems, and trust in CF recommender algorithms has been proven to be helpful for improving the accuracy of system recommendations. As a few studies have been devoted to trust in this area, we explore the benefits of using trust to resist shilling attacks. Rather than simply using user-generated trust values, we propose the genre trust degree, which differ in terms of the genres of items and take both trust value and user credibility into consideration. This paper introduces different types of shilling attack methods in an attempt to study the impact of users' trust values and behavior features on defending against shilling attacks. Meanwhile, it improves the approach used to calculate user similarities to form a recommendation model based on genre trust degrees. The performance of the genre trust-based recommender system is evaluated on the Ciao dataset. Experimental results demonstrated the superior and comparable genre trust degrees recommended for defending against different types of shilling attacks. [ABSTRACT FROM AUTHOR]

This paper investigates coordinated multicast and unicast transmission for vehicle-to-vehicle (V2V) underlay massive multiple-input multiple-output (MIMO). First, the achievable ergodic multicast rate for the cellular link and the achievable ergodic unicast rate for all the V2V links are summed with weight to formulate the rate optimization problem, with the assumption that the statistical channel state information (CSI) is known at the base station and the transmitters of the V2V communication pairs. We then derive the optimal transmitting directions in closed-form for the cellular link and all the V2V links, respectively, which converts the original optimal problem to a simpler power allocation problem in the beam domain. Via invoking the concave-convex procedure, an efficient iterative algorithm with guaranteed convergence is proposed for the power allocation problem. Furthermore, we replace the objectives which contain high-complex expectation operations with their deterministic equivalents in each iteration of the proposed algorithm to achieve lower algorithm complexity. Simulation results show the fast convergence speed of the proposed power allocation algorithm and the significant performance gains of the proposed transmission design for V2V underlay massive MIMO. [ABSTRACT FROM AUTHOR]