This paper presents a well-structured, mixed-criticality, system that exhibits rich spatio-temporal behaviors that arise from the interactions of mobile conveying units. The system-level objective is for the collection of decentralized, autonomous, mobile units to transport entities from some input port to an output port when each entity has its own destination, deadline and Quality of Service constraints. Entities move by riding on the mobile units and transfer from one unit to another when two units rendezvous. We propose a systematic approach to transform the spatio-temporal patterns of interactions to a graph from which we can obtain the shortest paths that can help to address the system objective. In the future, such systems can be used to investigate a variety of intelligent, embedded, mechatronic systems issues. This system can also be integrated with other models for processes and systems to investigate some of the challenges envisaged in Industry 4.0.

In this paper, we propose an effective method to calculate the average achievable rate and outage probability of a practical cognitive radio (CR) link with finite-alphabet inputs under imperfect spectrum sensing in fast and slow Rayleigh fading, respectively. In the considered CR system, the secondary user (SU) senses and dynamically exploits the spectrum pool via dynamic frequency hopping. Since spectrum sensing is not perfect, miss-detection occurs. Under this event, the interference emerged from collisions due to the simultaneous spectrum access of both primary and cognitive users leads to a non-Gaussian CR link. This makes it very challenging to evaluate the information theoretical limits, especially when finite-alphabet inputs are used. To overcome such challenge, we first introduce a simple method to calculate the instantaneous differential entropy of the channel output for a given fading gain using Laguerre-Gauss quadrature formulas. Using this result, we propose a piece-wise linear curve fitting (PLCF)-based method to calculate the average output entropy and outage probability, respectively. It is then demonstrated that the average achievable rate in fast fading and the outage probability in slow fading of the considered CR channel can be calculated effectively to achieve any predetermined accuracy level for a given finite-alphabet input.

This paper studies a wire-tap channel in which a source node wants to communicate securely to a destination node in the presence of an eavesdropper and under the aid of an amplify-and-forward (AF) relay operating in full-duplex (FD) mode. The residual self-interference due to FD transmission is explicitly taken into account. The secrecy capacity and the respective optimal power allocation schemes for this system are examined under both individual and joint power constraints. At first, the related optimization problems are shown to be quasi-concave. As such, the globally optimal solution exists and is unique. Due to the non-linearity of the derivative, we apply a simple bisection method for root finding and obtain a simple expression for the optimal power allocation scheme. To further provide some insight on the solutions, we apply the method of dominant balance to analyze the capacity and power allocations in different high power regions. It is then demonstrated that full relay power is only needed when the power at the relay is sufficiently small compared to the power at the source. Comparisons with half-duplex (HD) relaying also revealed that FD can achieve a significantly higher secrecy capacity. Finally, numerical results are presented to confirm the optimality of the solutions.

We study the feasibility of cognitive radio (CR) communication in the presence of a K-user multi-input multi-output (MIMO) interference channel as the primary network. Assuming that the primary interference network has unused spatial degrees of freedom (DoFs) , we first investigate the sufficient condition on the number of antennas at the secondary transmitter under which the secondary system can communicate while causing no interference to the primary receivers. We show that, to maximize the benefit, the secondary transmitter should have at least the same number of antennas as the spatial DoFs of the primary system. We then derive the secondary precoding and decoding matrices to have zero interference leakage into the primary network while the signal-to-interference plus noise ratio (SINR) at the secondary receiver is maximized. As the success of the secondary communication depends on the availability of unused DoFs, we then propose a fast sensing method based on the eigenvalue analysis of the received signal covariance matrix to determine the availability of unused DoFs or equivalently spatial holes. Since the proposed fast sensing method cannot identify the indices of inactive primary streams, we also provide a fine sensing method based on the generalized likelihood ratio test (GLRT) to decide the absence of individual primary streams. Simulation results show that the proposed CR sensing and transmission scheme can, in practice, provide a significant throughput while causing no interference to the primary receivers, and that the sensing detects the spatial holes of the primary network with high detection probability.

Emerging applications in areas such as advanced manufacturing and healthcare systems demand predictable delivery of prioritized message streams over multihop wireless systems. The dominance protocol is an important approach in which transmitting nodes use priority identifiers to dynamically regulate access to the shared medium. This protocol, however, has an unresolved problem called the Multihop Competing Problem (MCP). Despite recognizing that the problem could occur, the current literature offers no characterization of the problem or when it can occur. Because MCP could occur, it was not possible to analytically determine the end-to-end latency bounds of the message streams. When MCP occurred, the end-to-end latency of the message streams was affected adversely. We characterize MCP and show that it is an exposed terminal problem that occurs when the nodes use certain priority identifiers in adjacent two-hop neighborhoods of a transmitting node. Using a random disk graph model, we show that MCP occurs often in such systems. We utilize our characterization of MCP to derive priority identifiers that guarantee that MCP will not occur. The MCP free labels propose enable the predictable delivery of multihop message streams, improve end-to-end latency of the streams, and improve throughput in well-engineered and ad hoc networks.

This paper investigates the achievable rate and ergodic capacity of a non-orthogonal amplify-and-forward (NAF) half-duplex multi-relay network where multiple relays exploit channel state information (CSI) to cooperate with a pair of source and destination. In the first step, for a given input covariance matrix at the source, we derive an optimal power allocation scheme among the relays via optimal instantaneous power amplification coefficients to maximize the achievable rate. Given the nature of broadcasting and receiving collisions in NAF, the considered problem in this step is non-convex. To overcome this drawback, we propose a novel method by evaluating the achievable rate in different sub-domains of the vector channels. It is then demonstrated that the globally optimal solution can be derived in closed-form. In the next step, we establish the ergodic channel capacity by jointly optimizing the input covariance matrix at the source and the power allocation among the relays. We show that this is a bi-level non-convex problem and solve it using Tammer decomposition method. This approach allows us to transform the original optimization problem into an equivalent master problem and a set of sub-problems having closed-form solutions derived in the first step. The channel capacity is then obtained using an iterative water-filling-based algorithm. Finally, we analyze the capacity-achieving input covariance matrix at the source in high and low signal-to-noise ratio (SNR) regimes. At sufficiently high SNRs, it is shown that the transmit power at the source should be equally distributed in all broadcasting and cooperative phases. On the other hand, in low SNR regions, the source should spend all its power in the broadcasting phase associated with a relay having the strongest cascaded source-relay and relay-destination channels.

This paper investigates the achievable rate and ergodic capacity of an orthogonal amplify-and-forward (OAF) half-duplex multiple-relay network with direct link where multiple relays use channel state information (CSI) to cooperate with the source and destination. The relays are subject to two types of power constraint: the total average power constraint (TAPC) and the individual average power constraint (IAPC). In the first step, by assuming a fixed input covariance matrix at the source, we derive an optimal power allocation (OPA) scheme among the relays via optimal instantaneous power amplification coefficients to maximize the achievable rate. The closed-form optimal solutions are obtained for the considered system under either the TAPC or both the TAPC and IAPC. Next, we derive the ergodic capacity by jointly optimizing the input covariance matrix and the power allocation at the relays. We show that this is a bi-level non-convex problem and solve this using Tammer decomposition method. This approach allows us to convert the original optimization problem to a master problem and a set of sub-problems that have closed-form solutions as obtained in the first step. The ergodic capacity is then obtained using an iterative water-filling-based algorithm.

Mesh topologies are important for large-scale peer-to-peer systems that use low-power transceivers. The quality of service (QoS) in such systems is known to decrease as the scale increases. We present a scalable approach for dissemination that exploits all the shortest paths between a pair of nodes and improves the QoS. Despite the presence of multiple shortest paths in a system, we show that these paths cannot be exploited by spreading the messages over the paths in a simple round-robin manner; nodes along one of these paths will always handle more messages than the nodes along the other paths. We characterize the set of shortest paths between a pair of nodes in regular mesh topologies and derive rules, using this characterization, to effectively spread the messages over all the available paths. These rules ensure that all the nodes that are at the same distance from the source handle roughly the same number of messages. By modeling the multihop propagation in the mesh topology as a multistage queuing network, we present simulation results from a variety of scenarios that include link failures and propagation irregularities to reflect real-world characteristics. Our method achieves improved QoS in all these scenarios.

We present a systematic approach to selecting cluster heads in regular mesh topologies based on the idea of k- Domination in graphs. Given a graph, G=(V,E), a subset D of V is said to be a 1-dominating set if every node v in V is either in D or is adjacent to a node in D. A subset D is said to be a k- dominating set if every node v, not in D, is connected to a node in D via a path of length less than or equal to k. Using regular mesh topologies that are obtained by embedding a collection of nodes in a two dimensional grid, where each node has q neighbors, we show how k-dominating sets impact the energy consumed and the quality of service of the data aggregation. We present simulation results that validate the results.

Testing graphical user interfaces (GUI) is difficult, involving many states, inputs and events. Another serious problem is that in testing GUI, not all effects created by the testing are observable. We have previously reported a scalable method for testing GUIs based on complete interactions sequences (CIS). A CIS is a sequence of GUI objects and selections that collaborate to produce a response for the user called the responsibility. In this paper we use the CIS foundation to develop a new firewall method for GUI regression testing. This new method is an inherently selective regression approach in which only GUI objects in the firewall need be regression tested. An empirical study of a commercial GUI system is used to illustrate this new method.