Introduction: Nowadays firms must focus on maintaining healthy finished goods inventory stocks in order to be able to decrease inventory costs, meet customer requirements and to obtain competitive advantage. However large decentralized manufacturing companies often face the problem of sub-optimization in inventory management in subsidiaries due to several different reasons. As a result, company loses its competitiveness. Thus, there is a need to coordinate inventory activities of subsidiaries to prevent sub-optimization. Purpose: The purpose of this thesis is to investigate whether coordination mechanisms highlighted in academic literature are used in practice on the example of manufacturing company with decentralized decision-making structure for optimization finished goods inventory stocks. Frame of reference: This research is based on theoretical framework and empirical findings. Empirical data were collected through personal interviews and retrieved from organisational documents. Methodology: The research strategy for this paper is a single case study. This strategy allows investigating topic in its real life context. The deductive approach is used for this research based on qualitative data. The major source of data collection was semi-structured interviews and the company's documents. For analysing data categorisation approach was applied. Conclusion: The study found that most of coordination mechanisms presented in scientific literature are used in practice. To achieve better results these mechanisms should be applied simultaneously and consistently since they complement each other. We also observed that coordination mechanisms indeed give positive results and are able to optimize inventory management.

This thesis focuses on decentralized deadbeat output regulation of discrete-time nonlinear plants that are composed of multiple agents. These agents interact, via scalar-valued signals, in a known structured way represented with a graph. This work is motivated by applications where it is infeasible and/or undesirable to introduce control action within each plant agent; instead, control agents are introduced to interact with certain plant agents, where each control agent focuses on regulating a specific plant agent, called its target. Then, two analyses are carried out to determine if regulation is achieved: targeting analysis is used to determine if control laws can be found to regulate all target agents, then growing analysis is used to determine the effect of those control laws on non-target plant agents. The strength of this novel approach is the intuitively-appealing notion of each control agent focusing on the regulation of just one plant agent. This work goes beyond previous research by generalizing the class of allowable plant dynamics, considering not only arbitrary propagation times through plant agents, but also allowing for non-symmetrical influence between the agents. Moreover, new necessary and sufficient algebraic conditions are derived to determine when targeting succeeds. The main contribution of this work, however, is the development of new easily-verifiable conditions necessary for targeting and/or growing to succeed. These new conditions are valuable due to their simplicity and scalability to large systems. They concern the positioning of control agents and targets as well as the propagation time of signals through the plant, and they help significantly with design decisions. Various graph structures (such as queues, grids, spiders, rings, etc.) are considered and for each, these conditions are used to develop a control scheme with the minimum number of control agents needed.

Ad hoc networks and bluetooth systems operating over the unlicensed ISM band are in-stances of decentralized wireless networks. By definition, a decentralized network is com-posed of separate transmitter-receiver pairs where there is no central controller to assign the resources to the users. As such, resource allocation must be performed locally at each node. Users are anonymous to each other, i.e., they are not aware of each other's code-books. This implies that multiuser detection is not possible and users treat each other as noise. Multiuser interference is known to be the main factor that limits the achievable rates in such networks particularly in the high Signal-to-Noise Ratio (SNR) regime. Therefore, all users must follow a distributed signaling scheme such that the destructive effect of interference on each user is minimized, while the resources are fairly shared. In chapter 2 we consider a decentralized wireless communication network with a fixed number of frequency sub-bands to be shared among several transmitter-receiver pairs. It is assumed that the number of active users is a realization of a random variable with a given probability mass function. Moreover, users are unaware of each other's codebooks and hence, no multiuser detection is possible. We propose a randomized Frequency Hopping (FH) scheme in which each transmitter randomly hops over a subset of sub-bands from transmission slot to transmission slot. Assuming all users transmit Gaussian signals, the distribution of the noise plus interference is mixed Gaussian, which makes calculation of the mutual information between the transmitted and received signals of each user intractable. We derive lower and upper bounds on the mutual information of each user and demonstrate that, for large SNR values, the two bounds coincide. This observation enables us to compute the sum multiplexing gain of the system and obtain the optimum hopping strategy for maximizing this quantity. We compare the performance of the FH system with that of the Frequency Division (FD) system in terms of the following performance measures: average sum multiplexing gain and average minimum multiplexing gain per user. We show that (depending on the probability mass function of the number of active users) the FH system can offer a significant improvement in terms of the aforementioned measures. In the sequel, we consider a scenario where the transmitters are unaware of the number of active users in the network as well as the channel gains. Developing a new upper bound on the differential entropy of a mixed Gaussian random vector and using entropy power inequality, we obtain lower bounds on the maximum transmission rate per user to ensure a specified outage probability at a given SNR level. We demonstrate that the so-called outage capacity can be considerably higher in the FH scheme than in the FD scenario for reasonable distributions on the number of active users. This guarantees a higher spectral efficiency in FH compared to FD. Chapter 3 addresses spectral efficiency in decentralized wireless networks of separate transmitter-receiver pairs by generalizing the ideas developed in chapter 2. Motivated by random spreading in Code Division Multiple Access (CDMA), a signaling scheme is introduced where each user's code-book consists of two groups of codewords, referred to as signal codewords and signature codewords. Each signal codeword is a sequence of independent Gaussian random variables and each signature codeword is a sequence of independent random vectors constructed over a globally known alphabet. Using a conditional entropy power inequality and a key upper bound on the differential entropy of a mixed Gaussian random vector, we develop an inner bound on the capacity region of the decentralized network. To guarantee consistency and fairness, each user designs its signature codewords based on maximizing the average (with respect to a globally known distribution on the channel gains) of the achievable rate per user. It is demonstrated how the Sum Multiplexing Gain (SMG) in the network (regardless of the number of users) can be made arbitrarily close to the SMG of a centralized network with an orthogonal scheme such as Time Division (TD). An interesting observation is that in general the elements of the vectors in a signature codeword must not be equiprobable over the underlying alphabet in contrast to the use of binary Pseudo-random Noise (PN) signatures in randomly spread CDMA where the chip elements are +1 or -1 with equal probability. The main reason for this phenomenon is the interplay between two factors appearing in the expression of the achievable rate, i.e., multiplexing gain and the so-called interference entropy factor. In the sequel, invoking an information theoretic extremal inequality, we present an optimality result by showing that in randomized frequency hopping which is the main idea in the prevailing bluetooth devices in decentralized networks, transmission of independent signals in consecutive transmission slots is in general suboptimal regardless of the distribution of the signals. Finally, chapter 4 addresses a decentralized Gaussian interference channel consisting of two block-asynchronous transmitter-receiver pairs. We consider a scenario where the rate of data arrival at the encoders is considerably low and codewords of each user are transmitted at random instants depending on the availability of enough data for transmission. This makes the transmitted signals by each user look like scattered bursts along the time axis. Users are block-asynchronous meaning there exists a delay between their transmitted signal bursts. The proposed model for asynchrony assumes the starting point of an interference burst is uniformly distributed along the transmitted codeword of any user. There is also the possibility that each user does not experience interference on a transmitted codeword at all. Due to the randomness of delay, the channels are non-ergodic in the sense that the transmitters are unaware of the location of interference bursts along their transmitted codewords. In the proposed scheme, upon availability of enough data in its queue, each user follows a locally Randomized Masking (RM) strategy where the transmitter quits transmitting the Gaussian symbols in its codeword independently from symbol interval to symbol interval. An upper bound on the probability of outage per user is developed using entropy power inequality and a key upper bound on the differential entropy of a mixed Gaussian random variable. It is shown that by adopting the RM scheme, the probability of outage is considerably less than the case where both users transmit the Gaussian symbols in their codewords in consecutive symbol intervals, referred to as Continuous Transmission (CT).

Developing countries are facing a great challenge to collect, treat and dispose their waste in a more sustainable way. Today, most of the produced waste ends up on landfills, where they pose a great threat to the environment and human health. Kumasi, the second largest city in Ghana, faces the same issues as other cities in developing countries; waste management is run poorly and most waste ends up on the cities largest landfill, Dompoase, which will be full in a few years time. Issues such as low financial resources, bad urban planning and a growing population aggravate the implementation of a more sustainable development. Since most solid waste in developing countries is organic, composting is a good option towards a more sustainable waste management. There are numerous amounts of articles stating that decentralized composting is the best option for developed countries. Decentralized compost facilities are less costly to install and maintain, they require less technology and decrease the cost of waste transportation. Transportation poses a large expense when it comes  to waste management in developing countries. There is an advantage in integrating a more sustainable waste management in to the existing waste infrastructure since cities often are densely built up and there is a shortage of land. Therefore this thesis has investigated the possibilities of having waste sorting stations and decentralized compost facilities at public dumping sites in the Bantama area, one of ten sub--‐metros in Kumasi. Based on literature and observations during field visits in the Bantama area, a classification scheme was developed. The classification scheme was designed to simplify identification and differentiation of the sites. It contains thirteen criteria to consider when planning for organic waste sorting stations and decentralized compost facilities. Suitable sites for sorting stations and decentralized compost facilities were selected by a SQL analyzes in a Geographic Information System (GIS). The analyzes was based on the classification scheme. The result shows that of twenty--‐one public dumpingsites, seven were suitable as sorting stations and two sites were suitable for a decentralized compost facility. The expectation is that in due time and with infrastructure improvements, more than only seven communal sites can become sorting stations. When it comes to sites for composting the result reveals an issue in many cities  there is just not enough land to build as many decentralized facilities as would be necessary to recycle all organic waste. However, due to the advantages of having decentralized facilities, the recommendation is that Kumasi should start with a decentralized approach and as finance and technological skills exists the organic waste management can extend to also include larger facilities. Further this thesis shows the advantage of having decentralized composting when it comes totransportation costs. A transport analyzes was done in a GIS,  which showed the difference intransportation distances between having decentralized and centralized composting. The result showed that waste recycled close to its source, i.e. having decentralized waste management, is transported shorter distance compared to having centralized composting and  thus saving on cost for transportation.

Based on the Lyapunov stability theorem, a design methodology of adaptive block backstepping decentralized controller is proposed in this thesis for a class of large-scale systems with interconnections to solve regulation problems. Each subsystem contains m blocks¡¦ state variables, and m- 1 virtual input controllers are designed from the first block to the (m - 1)th block. Then the proposed robust controller is designed in accordance with the last block. Some adaptive mechanisms are embedded in the backstepping controllers as well as virtual input controllers in each subsystem, so that the upper bounds of interconnections as well as perturbations are not required. Furthermore, the dynamic equations of each subsystem do not need to strictly satisfy the block strict feedback form, and the resultant controlled system can achieve asymptotic stability. Finally, a numerical and a practical examples are given for demonstrating the feasibility of the proposed control scheme.

Based on the Lyapunov stability theorem, a decentralized adaptive backstepping tracking control scheme for a class of perturbed large-scale systems with non-strict feedback form is presented in this thesis to solve tracking problems. First of all, the dynamic equations of the plant to be controlled are transformed into other equations with semi-strict feedback form. Then a decentralized tracking controller is designed based on the backstepping control methodology so that the outputs of controlled system are capable of tracking the desired signals generated from a reference model. In addition, by utilizing adaptive mechanisms embedded in the backstepping controller, one need not acquire the upper bounds of the perturbations and the interconnections in advance. The resultant control scheme is able to guarantee the stability of the whole large-scale systems, and the tracking precision may be adjusted through the design parameters. Finally, one numerical and one practical examples are demonstrated for showing the applicability of the proposed design technique.

In this study, we analyze a decentralized supply chain with a single retailer and a single manufacturer where the retailer sells two products in a single period. The products offered by the retailer consist of families of closely related products, which differ from each other in terms of a limited number of features only. The retailer places initial orders based on preliminary demand forecasts at the beginning of the period and has an opportunity to modify his initial order after receiving perfect demand information. However, the final orders of the retailer are constrained by his initial orders. Furthermore, the manufacturer is obligated to fill the retailer&rsquo / s final order for each product. The manufacturer has two options for procurement. The first procurement option is regular delivery at the beginning of the period, after the initial orders of the retailer. The next one is expedited delivery, after the updated orders of the retailer are received. The expedited delivery is more expensive than regular. In this setting, our objective is to present an analytical model for this contract and characterize the optimal policies for the retailer and the manufacturer. We analyze three different levels of order adjustment flexibility settings: (i) no order adjustment, (ii) unlimited order adjustment and (iii) limited order adjustment.

Inventory management policies of two independent dealers in a service parts system with transshipment is studied in this thesis. Dealers can collaborate by pooling inventory or service. Revenue is shared in transshipment, can sometimes be contrary to profit maximization of one of the parties albeit sum of profits is increased. To assess the benefits of inventory pooling under equilibrium strategies, and the effect of competition on profits, a Markov Decision Process is formulated. A simpler variant of the optimal four-index threshold policy is used to characterize the production, service and transshipment related inventory decisions. A game theoretical approach as well as notions from policy iteration is taken to find the best response policy and equilibrium policies of the dealers. Numerical study is conducted to investigate the effect of cost, revenue and demand parameters, as well as dealer asymmetricities on benefit of pooling, service levels and transshipment flows. Analysis shows that commission schemes fairly allocating transshipment value to the players, high customer traffic intensities, and low transshipment costs are most suited environments for pooling. System centralization is beneficial when the inventory holding costs are high, transshipment costs are low, customer traffic intensities are high or the commission structure is distracting a party. Competition, within the experimental settings, dampens about 45% of the benefits of pooling.

Abstract In this dissertation, the eigenvalue analysis and decentralized robust controller design of uncertain multi-time-scale system with parametrical perturbations are considered. Because the eigenvalues of the multi-time-scale systems cluster in some difference regions of the complex plane, we can use the singular perturbation method to separate the systems into some subsystems. These subsystems are independent to each other. We can discuss the properties of eigenvalues and design controller for these subsystem respectively, then we composite these controllers to a decentralized controller. The eigenvalue positions dominate the stability and the performance of the dynamic system. However, we cannot obtain the precise position of the eigenvalues from the influence of parametrical perturbations. The sufficient conditions of the eigenvalues clustering for the multi-time-scale systems will be discussed. The uncertainties consider as unstructured and structured perturbations are taken into considerations. The design algorithm provides for designing a decentralized controller that can assign the poles to our respect regions. The specified regions are half-plane and circular disk. Furthermore, the concepts of decentralized control and optimal control are used to design the linear quadratic regulator (LQR) controller and linear quadratic Gaussian (LQG) controller for the perturbed multi-time-scale systems. That is, the system can get the optimal robust performance. The bound of the singular perturbation parameter would influence the robust stability of the multi-time-scale systems. Finally, the sufficient condition to obtain the upper bound of the singular perturbation parameter presented by the Lyapunov method and matrix norm. The condition also extends for the pole assignment in the specified regions of each subsystem respectively. The illustrative examples are presented behind each topic. They show the applicability of the proposed theorems, and the results are satisfactory.

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