Mobile computing and wireless systems are becoming more common as wireless technology evolves. Many authors argue that wireless systems can provide advantages and value to organisations, such as increased efficiency and effectiveness. Literature also shows that wireless systems especially suits companies within the logistics industry. However, some authors also highlight disadvantages regarding these solutions, for example insufficient security. The purpose of this thesis is to present advantages and disadvantages for organisations regarding usage of wireless systems in a warehouse setting, and the factors that have an influence over these advantages and disadvantages. This purpose is fulfilled with the aid of a qualitative study at Maersk Logistics in Torsvik, Jönköping where a number of respondents were interviewed. The study began with a literature study covering different aspects of wireless systems. The literature study was used to construct an interview guide, and also as a foundation for the analysis. The empirical study shows that the wireless system at Maersk Logistics provides value to the organisation at both the operational and management level. The effectiveness and efficiency in the daily work increases and the system generates accurate information that forms a good foundation for the decision-making process. The study also shows that precautions need to be taken when using a wireless system, since the organisation becomes very dependent on the system. / Mobil datoranvändning och trådlösa system blir mer och mer vanliga i och med utvecklingen av trådlös teknik. Många författare hävdar att trådlösa system bidrar med fördelar och tillför värde till en organisation, exempelvis högre effek-tivitet. Litteraturen visar även att trådlösa system är speciellt lämpade inom logistikindustrin. Vissa författare belyser dock nackdelar relaterade till de här lösningarna, exempelvis bristande säkerhet. Syftet med denna uppsats är att presentera fördelar och nackdelar för organisa-tioner rörande användande av trådlösa system i lagermiljö, och de faktorer som påverkar dessa fördelar och nackdelar. Syftet uppfylls med hjälp av en kvalitativ studie på Maersk Logistics i Torsvik, Jönköping där ett antal respondenter har intervjuats. Studien inleddes med en litteraturstudie som omfattade olika aspekter av trådlösa system. Litteraturstudien låg sedan till grund för konstruktion av intervjuguide och genomförande av intervjuerna, och även som underlag för analysen. Den empiriska studien visar att det trådlösa systemet på Maersk Logistics tillför värde i en organisation både på driftsnivå och på managementnivå. Effektiviteten i det dagliga arbetet blir högre och systemet bidrar med korrekt information som bildar ett bättre underlag för beslutsprocessen. Studien visar också att försiktighetsåtgärder måste vidtas vid användandet av ett trådlöst system eftersom organisationen blir väldigt beroende av systemet.

Yes / Existing works on energy harvesting wireless systems often assume a constant conversion efficiency for the energy harvester. In practice, the conversion efficiency often varies with the input power. In this work, based on a review of existing energy harvesters in the literature, a heuristic expression for the conversion efficiency as a function of the input power is derived by curve fitting. Using this function, two example energy harvesters are used to analyze the realistic performances of wireless relaying and wireless energy transfer. Numerical results show that the realistic performances of the wireless systems could be considerably different from what predicted by the existing analysis.

As a result of rapid progress in research and development, today's wireless world exhibits several heterogeneous communication networks, such as cellular networks, satellite networks, wireless local area networks (WLAN), mobile ad hoc networks (MANET), and sensor networks. These networks are complementary to each other. Hence, their integration can realize a unified wireless system that has the best features of the individual networks. This has spurred much research interest in designing integrated next-generation of wireless systems (NGWS). While existing wireless networks have been extensively studied individually, the integrated wireless system brings new challenges in architecture design, system management, and protocol design. The different wireless networks use different communication technologies and are based on different networking paradigms. Therefore, it is challenging to integrate these networks such that their heterogeneities are hidden from each other and a harmonious inter-operation among them is achieved. The objective of this research is to design a scalable, secure, and robust architecture and to develop seamless mobility management protocols for NGWS. More specifically, an architecture that integrates the heterogeneous wireless systems is first proposed for NGWS. Next, a cross-layer (Layer 2 + 3) handoff management protocol is developed for NGWS. Afterward, analytical modeling is developed to investigate the handoff performance of the existing mobility management protocols for different types of applications. Finally, a framework for multi-layer mobility management is developed to support the seamless handoff support to all types of applications in NGWS.

The coding and feedback inaccuracies of the channel state information (CSI) in limited feedback multiple-input multiple-output (MIMO) wireless systems can severely impact the achievable data rate and reliability. The CSI is mathematically represented as a Grassmann manifold or manifold of unitary matrices. These are non-Euclidean spaces with special constraints that makes efficient and high fidelity coding especially challenging. In addition, the CSI inaccuracies may occur due to digital representation, time variation, and delayed feedback of the CSI. To overcome these inaccuracies, the manifold structure of the CSI can be exploited. The objective of this dissertation is to develop a new signal processing techniques on the manifolds to harvest the benefits of MIMO wireless systems. First, this dissertation presents the Kerdock codebook design to represent the CSI on the Grassmann manifold. The CSI inaccuracy due to digital representation is addressed by the finite alphabet structure of the Kerdock codebook. In addition, systematic codebook construction is identified which reduces the resource requirement in MIMO wireless systems. Distance properties on the Grassmann manifold are derived showing the applicability of the Kerdock codebook to beam-forming and spatial multiplexing systems. Next, manifold-constrained algorithms to predict and encode the CSI with high fidelity are presented. Two prominent manifolds are considered; the Grassmann manifold and the manifold of unitary matrices. The Grassmann manifold is a class of manifold used to represent the CSI in MIMO wireless systems using specific transmission strategies. The manifold of unitary matrices appears as a collection of all spatial information available in the MIMO wireless systems independent of specific transmission strategies. On these manifolds, signal processing building blocks such as differencing and prediction are derived. Using the proposed signal processing tools on the manifold, this dissertation addresses the CSI coding accuracy, tracking of the CSI under time variation, and compensation techniques for delayed CSI feedback. Applications of the proposed algorithms in single-user and multiuser systems show that most of the spatial benefits of MIMO wireless systems can be harvested. / text

We investigate in detail two multiuser opportunistic scheduling problems in centralized wireless systems: the scheduling of "delay-sensitive" flows with packet delay requirements of a few tens to few hundreds of milliseconds over the air interface, and the scheduling of "best-effort" flows with the objective of minimizing mean file transfer delay. Schedulers for delay-sensitive flows are characterized by a fundamental tradeoff between "maximizing total service rate by being opportunistic" and "balancing unequal queues (or delays) across users". In choosing how to realize this tradeoff in schedulers, our key premise is that "robustness" should be a primary design objective alongside performance. Different performance objectives -- mean packet delay, the tail of worst user's queue distribution, or that of the overall queue distribution -- result in remarkably different scheduling policies. Different design objectives and resulting schedulers are also not equally robust, which is important due to the uncertainty and variability in both the wireless environment and the traffic. The proposed class of schedulers offers low packet delays, less sensitivity to the scheduler parameters and channel characteristics, and a more graceful degradation of service in terms of the fraction of users meeting their delay requirements under transient overloads, when compared with other well-known schedulers. Schedulers for best-effort flows are characterized by a fundamental tradeoff between "maximizing the total service rate" and "prioritizing flows with short residual sizes". We characterize two regimes based on the "degree" of opportunistic gain present in the system. In the first regime -- where the opportunistic capacity of the system increases sharply with the number of users -- the use of residual flow-size information in scheduling will 'not' result in a significant reduction in flow-level delays. Whereas, in the second regime -- where the opportunistic capacity increases slowly with the number of users -- using flow-size information alongside channel state information 'may' result in a significant reduction. We then propose a class of schedulers which offers good performance in either regime, in terms of mean file transfer delays as well as probability of blocking for systems that enforce flow admission control. This thesis provides a comprehensive theoretical study of these fundamental tradeoffs for opportunistic schedulers, as well as an exploration of some of the practical ramifications to engineering wireless systems. / text

<p>Mobile computing and wireless systems are becoming more common as wireless technology evolves. Many authors argue that wireless systems can provide advantages and value to organisations, such as increased efficiency and effectiveness. Literature also shows that wireless systems especially suits companies within the logistics industry. However, some authors also highlight disadvantages regarding these solutions, for example insufficient security.</p><p>The purpose of this thesis is to present advantages and disadvantages for organisations regarding usage of wireless systems in a warehouse setting, and the factors that have an influence over these advantages and disadvantages.</p><p>This purpose is fulfilled with the aid of a qualitative study at Maersk Logistics in Torsvik, Jönköping where a number of respondents were interviewed. The study began with a literature study covering different aspects of wireless systems. The literature study was used to construct an interview guide, and also as a foundation for the analysis.</p><p>The empirical study shows that the wireless system at Maersk Logistics provides value to the organisation at both the operational and management level. The effectiveness and efficiency in the daily work increases and the system generates accurate information that forms a good foundation for the decision-making process. The study also shows that precautions need to be taken when using a wireless system, since the organisation becomes very dependent on the system.</p> / <p>Mobil datoranvändning och trådlösa system blir mer och mer vanliga i och med utvecklingen av trådlös teknik. Många författare hävdar att trådlösa system bidrar med fördelar och tillför värde till en organisation, exempelvis högre effek-tivitet. Litteraturen visar även att trådlösa system är speciellt lämpade inom logistikindustrin. Vissa författare belyser dock nackdelar relaterade till de här lösningarna, exempelvis bristande säkerhet.</p><p>Syftet med denna uppsats är att presentera fördelar och nackdelar för organisa-tioner rörande användande av trådlösa system i lagermiljö, och de faktorer som påverkar dessa fördelar och nackdelar.</p><p>Syftet uppfylls med hjälp av en kvalitativ studie på Maersk Logistics i Torsvik, Jönköping där ett antal respondenter har intervjuats. Studien inleddes med en litteraturstudie som omfattade olika aspekter av trådlösa system. Litteraturstudien låg sedan till grund för konstruktion av intervjuguide och genomförande av intervjuerna, och även som underlag för analysen.</p><p>Den empiriska studien visar att det trådlösa systemet på Maersk Logistics tillför värde i en organisation både på driftsnivå och på managementnivå. Effektiviteten i det dagliga arbetet blir högre och systemet bidrar med korrekt information som bildar ett bättre underlag för beslutsprocessen. Studien visar också att försiktighetsåtgärder måste vidtas vid användandet av ett trådlöst system eftersom organisationen blir väldigt beroende av systemet.</p>

[pt] A crescente demanda dos usuários por serviços de banda larga tais como dados a alta velocidade, vídeo, aúdio e multimídia, tem levado ao uso de sistemas rádio ponto- multiponto em freqüências superiores a 10 GHz, que além de menos utilizadas, permitem oferecer as grandes larguras de banda necessárias. Nessas freqüências, as perdas de propagação do sinal devem-se principalmente ao efeito de chuvas. A atenuação por chuvas afeta diretamente a cobertura e o desempenho dos sistemas que operam nestas faixas de freqüência. No presente trabalho é desenvolvido um modelo empírico para a previsão da distribuição cumulativa da atenuação por chuvas, utilizando a base oficial de ITU-R e resultados experimentais de medidas realizadas no Brasil. Este modelo fornece resultados mais precisos do que os atualmente propostos na literatura técnica e permite avaliar o impacto das chuvas na cobertura de sistemas ponto-multiponto tipo LMDS (Local Multipoint Distribution System). Além disto, foram desenvolvidos dois modelos para a previsão da distribuição da atenuação diferencial por chuvas, fator essencial para a determinação de efeitops de interferência e seu impacto das chuvas no desempenho de sistemas LMDS. Finalmente, foram desenvolvidos modelos para a previsão da duração total e média, de eventos de atenuação por chuvas, estatísticas também relevantes na análise de performance de sistemas LMDS. / [en] The growing demand for broadband services such as high- speed data, video, audio and multimedia, has lead to the use of point-multipoint radio systems operating in frequencies above of 10 GHz, that are not yet allocated for other services and allow the use of the large bandwidths required by these services. At these frequencies, the main contribution for the propagation losses is due to rain attenuation. The rain directly affects the area coverage and the performance of systems operating at these frequencies. In the present work, an empirical model is developed for predicting the cumulative distribution of rain attenuation prediction, using the ITU-R data base and results of propagation measurements campaigns performed in Brazil. The model provides better results than others currently found in the technical literature and allows the evaluation of the impact of rain attenuation in the coverage of LMDS (Local Multipoint Distribution System/Local Multipoint Communications System). Also, two models were developed for predicting distributions of differential rain attenuation, an essential factor for interference effects and its impact in LMDS performance. Finally, models were developed for the prediction of total and average duration of rain attenuation events, also relevant for systems performance assessment.

The current popularity of WLANs is a testament primarily to their convenience, cost efficiency and ease of integration. Even now the demand for high data rate wireless communications has increased fourfold as consumers demand better multimedia communications over the wireless medium. The next generation of high speed WLANs is expected to meet this increased demand for capacity coupled with high performance and spectral efficiency. The current generation of WLANs utilizes Orthogonal Frequency Division Multiplexing (OFDM) modulation. The next generation of WLAN standards can be made possible either by developing a different modulation technique or combining legacy OFDM with Multiple Input Multiple Output (MIMO) systems to create MIMO-OFDM systems. This dissertation presents two different basis technologies for the next generation of high speed WLANs: OWSS and MIMO-STC-OFDM. OWSS, or Orthogonal Wavelet Division Multiplexed - Spread Spectrum is a new class of wavelet pulses and a corresponding signaling system which has significant advantages over current signaling schemes like OFDM. In this dissertation, CSMA/CA is proposed as the protocol for full data rate multiplexing at the MAC layer for OWSS. The excellent spectral characteristics of the OWSS signal is also studied and simulations show that passband spectrum enjoys a 30-40% bandwidth advantage over OFDM. A novel pre-distortion scheme was developed to compensate for the passband PA non-linearity. Finally for OWSS, the fundamental limits of its system performance were also explored using a multi-level matrix formulation. Simulation results on a 108 Mbps OWSS WLAN system demonstrate the excellent effectiveness of this theory and prove that OWSS is capable of excellent performance and high spectral efficiency in multipath channels. This dissertation also presents a novel MIMO-STC-OFDM system which targets data rates in excess of 100 Mbps and at the same time achieve both high spectral efficiency and high performance. Simulation results validate the superior performance of the new system over multipath channels. Finally as channel equalization is critical in MIMO systems, a highly efficient time domain channel estimation formulation for this new system is also presented. In summary, both OWSS and MIMO-STC-OFDM appear to be excellent candidate technologies for next generation of high speed WLANs.

Data intensive applications, requiring reliability and strict delay constraints, have emerged recently and they necessitate a different approach to analyzing system performance. In my work, I establish a framework that relates physical channel parameters to the queueing performance for a single-user wireless system. I then seek to assess the potential benefits of multirate techniques, such as hybrid-ARQ (Automatic Repeat reQuest), in the context of delay-sensitive communications. Present methods of analysis in an information theoretic paradigm define capacity assuming that long codewords can be used to take advantage of the ergodic properties of the fading wireless channel. This definition provides only a limited characterization of the channel in the light of delay constraints. The assumption of independent and identically distributed channel realizations tends to over-estimate the system performance by not considering the inherent time correlation. A finite-state continuous time Markov channel model that I formulate enables me to partition the instantaneous data-rate received at the destination into a finite number of states, representing layers in a hybrid-ARQ scheme. The correlation of channel has been incorporated through level crossing rates as transition rates in the Markov model. The large deviation principle governing the buffer overflow of the Markov model, is very sensitive to channel memory, is tractable, and gives a good estimate of the system performance. Metrics such as effective capacity and probability of buffer overflow, that are obtained through large deviations have been related to the wireless physical layer parameters through the model. Using the above metrics under QoS constraints, I establish the quantitative performance advantage of using hybrid-ARQ over traditional systems. I conduct this inquiry by restricting attention to the case where the expected transmit power is fixed at the transmitter. The results show that hybrid-ARQ helps us in obtaining higher effective capacity, but it is very difficult to support delay sensitive communication over wireless channel in the absence of channel knowledge and dynamic power allocation strategies.

Next generation wireless systems will use multiple antenna technologies, also known as multiple-input multiple-output (MIMO), to provide high data rates and robustness against fading. MIMO communication strategies for single user communication systems and their practical application in wireless networks are by now well known. MIMO communication systems, however, can benefit from multiuser processing by coordinating the transmissions to multiple users simultaneously. For numerous reasons, work on the theory of multiuser MIMO communication has yet to see broad adoption in wireless communication standards. For example, global knowledge of channel state information is often required. Such an unrealistic assumption, however, makes it difficult in practice to implement precoding techniques. Furthermore, the achievable rates of the conventional multiuser MIMO techniques are far from the theoretical performance bounds. These and other factors motivate research on practical multiuser communication strategies for the MIMO broadcast channel (point to multi-point communication) and the analysis of those strategies. The primary contributions of this dissertation are i) the development of four novel low complexity coordinated MIMO transceiver design techniques to approach the theoretical performance bound and ii) the investigation of the optimality of the proposed coordinated wireless MIMO networks. Several coordinated beamforming algorithms are proposed, where each mobile station uses quantized combining vectors or each base station uses limited feedback from the MS. The asymptotic optimality of the proposed coordinated beamforming system for the MIMO Gaussian broadcast channel is next investigated. For multi-stream transmission, a novel block diagonalized vector perturbation is proposed and the achievable sum rate upper bound of the proposed system is derived. Finally, for multi-cell environments, linear and non-linear network CBF algorithms supporting multiple cell-boundary users are proposed. The optimality of network coordinated beamforming in terms of the number of receive antennas is also investigated. / text