A decentralized protocol for mobile control access

In this paper we use the Diffie–Hellman key exchange protocol to introduce a decentralized key agreement protocol based on elliptic curves. We do not use any public key infrastructure, which makes it suitable for light devices with low computational and storage capabilities. Thus mobile devices can directly authorize other mobile devices to exchange keys in order to get access to a service or system, in a secure and efficient manner.     

Optimal decentralized control of dynamic systems

In this paper, several aspects of decentralized control theory applied to dynamic systems are studied. First of all, some classical definitions about matricial functions and new results on gradient calculations are presented. In the following we generalize to matricial problems the method of gradient projection of Rosen. Finally, some aspects of stability, initialization and initial condition independence are studied in detail, and two numerical examples are considered in order to emphasize the advantages of the given procedure: the decentralized Kalman filter and the optimal power-frequency control.     

Optimal decentralized control of large scale systems

This paper presents a new optimized decentralized controller design method for solving the tracking and disturbance rejection problems for large-scale linear time-invariant systems, using only low-order decentralized controllers. To illustrate the type of results which can be obtained using the new optimized decentralized control design method, the control of a large flexible space structure is studied and compared with the standard centralized LQR-observer controller. The order of the resultant decentralized controller is much smaller than that of the standard centralized LQR-observer controller. The proposed controller also has certain fail-safe properties and, in addition, it can be five orders of magnitude more robust than the standard LQR-observer controller based on their real stability radii. The new decentralized controller design method is applied to a large flexible space structure system with 5 inputs and 5 outputs and of order 24.     

Revocable,dynamic and decentralized data access control in cloud storage

The Journal of Supercomputing - Attribute-based encryption(ABE) can enable user-centered data sharing in untrusted cloud scenario where users usually lack control on their outsourced data. However,...     

Optimal decentralized control in a multiaccess channel with partial information

We consider two transmission stations sharing a single communication channel. For different values of the input message ratesr_{i}, i = 1,2, a simple open-loop control policy is shown to be optimal for the long-run average throughput criterion.     

Optimal arrivals in a two-server random access system with loss

This paper considers a two-server random access system with loss that receives requests on a time interval [0, T]. The users (players) send their requests to the system, and then the system provides a random access to one of its two servers with some known probabilities. We study the following non-cooperative game for this service system. As his strategy, each player chooses the time to send his request to the system, trying to maximize the probability of servicing. The symmetric Nash equilibrium acts as the optimality criterion. Two models are considered for this game. In the first model the number of players is deterministic, while in the second it obeys the Poisson distribution. We demonstrate that there exists a unique symmetric equilibrium for both models. Finally, some numerical experiments are performed to compare the equilibria under different values of the model parameters.     

A trusted decentralized access control framework for the client/server architecture

This paper proposes a trusted decentralized access control (TDAC) framework for the client/server architecture. As the fundamental principle, TDAC enforces access control policies at the client side and protects sensitive objects at the server side by leveraging trusted computing technologies. Compared with the previous work of Sandhu and Zhang (2005), TDAC uses fewer requirements for trusted components. To implement TDAC, we design a private trusted reference monitor that runs at the client side, evaluates an access control request, and signs a temporary access control credential for a client application trustworthily; we also design a master reference monitor that runs at the server side, evaluates the request from the client application only according to the temporary access control credential. As a typical application, TDAC can protect client's private context data in subject-context aware access control.     

Optimal observations in decentralized systems

We study here the problem of improving the performance of decentralized regulators by optimizing the constrained observation matrices. A numerical example illustrates the solution.     

Optimal economic stabilization policies under decentralized control and conflicting objectives

This paper derives methods for the calculation of optimal stabilization policies under the assumption that monetary and fiscal control are exercised by separate authorities who may have different objectives. Each authority minimizes its own quadratic cost functional subject to the constraint of a linear econometric model. Nash solution strategies are calculated for this discrete-time differential game, both in the context of open-loop and closed-loop behavior (in the closed-loop framework each authority can continually revise his policy in response to the evolving strategy of the other authority). The results are applied to a small econometric model, and show how the degree of fiscal or monetary, control depends on the particular conflict situation, and how conflicting policies are "suboptimal" in comparison with coordinated policies.     

A stochastic control approach to Slotted-ALOHA random access protocol

ALOHA random access protocols are distributed protocols based on transmission probabilities, that is, each node decides upon packet transmissions according to a transmission probability value. In the literature, ALOHA protocols are analysed by giving necessary and sufficient conditions for the stability of the queues of the node buffers under a control vector (whose elements are the transmission probabilities assigned to the nodes), given an arrival rate vector (whose elements represent the rates of the packets arriving in the node buffers). The innovation of this work is that, given an arrival rate vector, it computes the optimal control vector by defining and solving a stochastic control problem aimed at maximising the overall transmission efficiency, while keeping a grade of fairness among the nodes. Furthermore, a more general case in which the arrival rate vector changes in time is considered. The increased efficiency of the proposed solution with respect to the standard ALOHA approach is evaluated by means of numerical simulations.     

Overload control of massive random access for machine-type communications

Traditional cellular systems may not be appropriate to support machine-type communications (MTC) due to a large number of devices and relatively small, infrequent data transmissions. The 3GPP has identified the MTC as an important area of the LTE system and has discussed several mechanisms that control random access (RA) overload caused by massive MTC devices. In this paper, we show that a retransmission mechanism of RA may lead to performance degradation in an overload situation, and propose two RA solutions that relieve the RA overload. Since the RA success probability is closely related with the number of simultaneous RA attempts, the first solution adjusts the maximum number of RA retransmissions to control the amount of RA attempts. The second solution separates the RA resources into two subsets that MTC devices can access according to the number of consecutive RA failures and distributes the RA traffic over the two subsets. The two proposed solutions are analyzed by a mathematical model assuming a simplified operation, and a more realistic environment is considered by protocol-level simulations. Since the performance of the proposed solutions depends on the system configurations and parameters, the base station may adaptively adjust them for an optimal operation.     

随机接入移动无线传感器网络快速组网媒体访问控制

基于非时隙CSMA/CA随机接入机制的IEEE802.15.4MAC协议组网耗时过长,不能满足自组网实时通信应用需求。针对这一问题,分析了MAC组网流程中各步骤所耗时间,提出一种新的快速组网策略,采用预分配信道,将关联过程从间接传输简化为直接传输,改进CSMA/CA冲突避免机制以减少冲突。仿真实验和现场测试结果均表明,与IEEE 802.15.4协议相比,提出的快速组网策略使得信道冲突降低,组网时间更快,更符合实时通信需求。     

Optimal control of linear plants with random parameters

The subject of this paper is the optimal control of linear plants whose coefficients and whose reference signals are random processes. The discrete-time as well as the continuous-time problems are treated and some fairly deep-seated distinctions between the two are pointed out. Special emphasis is placed on control over long periods of time. A set of assumptions is laid down under which the transition to infinitely long periods of operation is tractable. It is shown that a discrete-time plant is controllable, in the sense that the rate of the mean-squared error remains finite, only when certain necessary and sufficient conditions are fulfilled by the statistics of the plant parameters.     

Optimal design parameters in a multihop packet radio network using random access techniques

Takagi and Kleinrock studied the problem of optimal transmission ranges in a packet radio network with mobile terminals, assuming that each terminal is equipped with an omidirectional antenna. The purpose of this paper is to examine the possible improvement gained by directional antennas. The protocols considered include slotted ALOHA (with and without capture) and non-persistent CSMA. Results show throughput performance can be greatly enhanced by proper directional antennas. Two routing strategies, most-forward-routing and point-to-destination, are investigated and compared. The study shows both strategies posses roughly the same degree of performance. However the latter is attractive for its simplicity of system operation.     

Optimal non‐blocking decentralized supervisory control with unobservable controllable events

Paranormality is an observation property of a language, in which the occurrence of unobservable events never exits the closure of the language. In this paper, a synthesis method is proposed to construct a paranormal supervisor. We propose a method to construct a controllable language such that the occurrence of unobservable events does not exit the closure of the controllable language. Moreover, a new observation property, that is, Quasi Output Control Consistency (QOCC) is defined to construct the optimal (least restrictive) non‐blocking decentralized supervisory control in the presence of unobservable controllable events. Using QOCC and natural observer properties, we propose a method to construct a normal supervisor such that an arbitrary pair of lookalike strings are initiated and terminated with identical observable and uncontrollable events. It is assumed that one of these strings has unobservable controllable events. An OCC property is defined in the literature as a special case of QOCC property, where none of the lookalike strings has unobservable controllable events.     

Access granularity control of multichannel random access in next-generation wireless LANs

As the next-generation Wireless LANs (WLANs) will provide the ubiquitous high-data-rate network coverage, the traditional contention-based Medium Access Control (MAC) scheme may be unable to fulfill the requirement of efficient channel access. To address this problem, several research works have proposed the random access systems combined with Orthogonal Frequency Division Multiplex Access (OFDMA) technology. Access granularity control is a crucial issue in this combination. Specifically, this issue focuses on how to tune the subchannel bandwidth and the number of accessible subchannels towards the maximum channel utilization. This paper analyzes access granularity control in an OFDMA system that adopts a multichannel Carrier Sensing Multiple Access (CSMA) MAC and resolves contention by the frequency-domain backoff. The theoretical analysis verifies the significance of access granularity control. In addition, the simulation experiments demonstrate that the proposed dynamic access granularity control algorithms notably outperform the traditional ones that divide channel band statically and adjust the number of accessible subchannels empirically.     

Maximum lifetime rate control and random access in multi-hop wireless networks

Network lifetime and transmission quality are of paramount importance for rate control in an energy constrained multi-hop wireless network. It is known that they depend on mechanisms that span several protocol layers due to the existing interference across collision links and the energy constrained nature of wireless nodes. Although separate consideration of these issues simplifies the system design, it is often insufficient for wireless networks when the overall system performance is required. In this paper, we present a framework for cross-layer rate control towards maximum network lifetime and collision avoidance. The main contributions of this paper are twofold. First, although the link attainable rate is typically a non-convex and non-separable function of persistent probabilities, we prove the convergence of this cross-layer algorithm to the global optimum of joint congestion control and random access algorithm under the framework of nonlinear programming. Second, by adjusting a parameter in the objective function, we achieve the tradeoff between transmission quality and network lifetime. Simulations illustrate the desirable properties of the proposed algorithm, including convergence to the global optimum, better performance than the layered scheme, desirable tradeoff between transmission quality and network lifetime.     

Utility-optimal random access control in wireless multi-hop networks with queuing constraints

In this paper, a model of network utility maximization （NUM） is presented for random access control in multi-hop wireless networks. Different from the classical NUM framework, our model considers the queueing stability. We propose a distributed iterative prices and link probabilities adaption algorithm by using dual decomposition techniques, which only requires limited message passing, but converges to the global optimum of the total network utility. Numerical results and simulation comparison validate our conclusion.     

Performance limitations in decentralized control

In decentralized control of multivariable systems, the system is decomposed into a number of subsystems and individual controllers are designed for each subsystem. Advantages of such decomposition include reduced modelling requirements and ease of implementation. However, a potential disadvantage is a reduction in achievable control performance due to restricted controller structure. In this paper we consider performance limitations from non-minimum phase transmission zeros in decentralized control. In particular, we derive conditions on when closing the loop around one subsystem moves transmission zeros of other subsystems across the imaginary axis. Such zero crossings may occur regardless of the existence of non-minimum phase behavior in the open-loop system, and may, therefore, represent performance limitations specific to the use of decentralized controllers.     

Asynchronous decentralized event-triggered control

In this paper we propose an approach to the implementation of controllers with decentralized strategies triggering controller updates. We consider set-ups with a central node in charge of the computation of the control commands, and a set of not co-located sensors providing measurements to the controller node. The solution we propose does not require measurements from the sensors to be synchronized in time. The sensors in our proposal provide measurements in an aperiodic way triggered by local conditions. Furthermore, in the proposed implementation (most of) the communication between nodes requires only the exchange of one bit of information (per controller update), which could aid in reducing transmission delays and as a secondary effect result in fewer transmissions being triggered.