17,286 research outputs found
On the Security of Millimeter Wave Vehicular Communication Systems using Random Antenna Subsets
Millimeter wave (mmWave) vehicular communica tion systems have the potential
to improve traffic efficiency and safety. Lack of secure communication links,
however, may lead to a formidable set of abuses and attacks. To secure
communication links, a physical layer precoding technique for mmWave vehicular
communication systems is proposed in this paper. The proposed technique
exploits the large dimensional antenna arrays available at mmWave systems to
produce direction dependent transmission. This results in coherent transmission
to the legitimate receiver and artificial noise that jams eavesdroppers with
sensitive receivers. Theoretical and numerical results demonstrate the validity
and effectiveness of the proposed technique and show that the proposed
technique provides high secrecy throughput when compared to conventional array
and switched array transmission techniques
An Optimal Medium Access Control with Partial Observations for Sensor Networks
We consider medium access control (MAC) in multihop sensor networks, where only partial information about the shared medium is available to the transmitter. We model our setting as a queuing problem in which the service rate of a queue is a function of a partially observed Markov chain representing the available bandwidth, and in which the arrivals are controlled based on the partial observations so as to keep the system in a desirable mildly unstable regime. The optimal controller for this problem satisfies a separation property: we first compute a probability measure on the state space of the chain, namely the information state, then use this measure as the new state on which the control decisions are based. We give a formal description of the system considered and of its dynamics, we formalize and solve an optimal control problem, and we show numerical simulations to illustrate with concrete examples properties of the optimal control law. We show how the ergodic behavior of our queuing model is characterized by an invariant measure over all possible information states, and we construct that measure. Our results can be specifically applied for designing efficient and stable algorithms for medium access control in multiple-accessed systems, in particular for sensor networks
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