Improving the Performance of Wireless LANs

This book quantifies the key factors of WLAN performance and describes methods for improvement. It provides theoretical background and empirical results for the optimum planning and deployment of indoor WLAN systems, explaining the fundamentals while supplying guidelines for design, modeling, and performance evaluation. It discusses environmental effects on WLAN systems, protocol redesign for routing and MAC, and traffic distribution; examines emerging and future network technologies; and includes radio propagation and site measurements, simulations for various network design scenarios, numerous illustrations, practical examples, and learning aids

Holistic and efficient link adaptation for 802.11x wireless LANs

Wireless LANs (WLANs), based on the IEEE 802.11 standard, have become the standard means for indoor wireless connectivity. At the same time, the rising number of smart mobile devices, broadband access speeds, and bandwidth hungry applications (e.g., high definition video streaming) have led to an increase not only of usage but also of demand for higher data-rates. This demand for higher rates is being met with newer IEEE 802.11 standards (e.g., 802.11n/ac) that introduce new features and also increase the different possible settings for each feature. Inherent channel variations and the possible interference conditions when operating in unlicensed spectrum necessitate adaptation of the various medium access control (MAC) and physical (PHY) layer features to ensure high performance. Selecting the values of those features to optimise a criterion such as throughput is the link adaptation problem. Link adaptation, the focus of this thesis, can play a key role in improving the performance of 802.11 WLANs. Increasing number of features and feature setting combinations with newer 802.11 standards is not only making link adaptation even more important but also more challenging. The contributions made in this thesis significantly advance the state of the art on link adaptation for 802.11 WLANs along three dimensions. First, we show that not knowing the exact cause of loss is not an impediment to effective link adaptation. Nevertheless, actions taken in response to losses are more crucial and they ought to be holistic and not solely dependent on the exact cause of loss. Second, we make significant methodological contributions for analysing the impact of multiple parameters on a given criterion, based on comprehensive experimental measurements. The application of this methodology on 802.11n measurements, examining the interaction of the protocols various parameters on performance under varying conditions, has lead to several valuable findings on how to perform efficient link adaptation in a complex WLAN scenario like 802.11n and future 802.11 standards. Adaptation should be holistic, based on the channel quality instead of the interference scenario, and independent of loss differentiation. Based on these insights, lastly and most importantly, we propose two novel holistic link adaptation schemes for legacy 802.11a/b/g and 802.11n WLANs, termed Themis and SampleLite, respectively. Both Themis and SampleLite take a hybrid approach relying on easily accessed channel quality information at the sender side to perform holistic adaptation. The hypothesis that adaptation should be holistic is validated by our results, with both Themis and SampleLite outperforming the current state of the art

Design of Low Latency and High Reliable Industrial Wireless Lan System

Industrial wireless system, particularly Factory Automation (FA) system has been recognized as one of potential applications in machine type communication. A wireless system for an industrial network is preferable due to its primary advantages: flexibility for controlling mobile clients, low-complexity installation and low-cost maintenance by reducing physical connectivity in factory environment, and also applicable for hazardous sites. Several existing wireless technologies have been deployed for industrial wireless system, including Zigbee, WirelssHART and WLAN based system. However, the existing technologies have several limitations in terms of low throughput, poor reliability, as well as non deterministic. These drawbacks restrict the deployment of these technologies in critical industrial control system where low latency and high reliability are the primary requirements. In order to overcome the limitations of current technology, this thesis proposes low latency and high reliable industrial wireless LAN system, particularly for FA system. Specifically, two main topics are presented: (1) Design of high throughput of WLAN PHY transceiver for industrial wireless system. The first topic is presented to deal with fast transmission requirements. Typically, a WLAN system is deployed for home or office network scenarios. Since this scenario incorporates large data payload, throughput metric is higher priority than latency metric. Hence, to adopt WLAN based PHY transceiver for industrial wireless network, the issue of latency should be addressed as the top priority with respect to maintain reliability performance as well as low-complexity implementation. Therefore, as a first step, cross layer design approach is carried out in order to achieve optimum trade-off between QoS performance, implementation complexity, as well as lower power consumption. Later, the obtained PHY system parameters from cross layer design stage are employed for designing PHY transceiver system. In addition, several design optimizations are also incorporated during designing transceiver system that was conducted based on Model based RTL design. (2) Retransmission diversity based on channel selectivity scheme. The second part discusses performance improvement, specifically reliability performance in regard to low latency communication. The proposed work leverages frequency diversity that is available in the employed transmission bandwidth. A low complexity sub channel selection method by utilizing adjacent channel selection is considered. To confirm the effectiveness of this proposal, the performance results in terms of latency and reliability are evaluated, covering link level and system level performance of the FAWLAN system. Hardware implementation and verification result confirms that the designed PHY system achieves processing latency for about 13μs, corresponding to total transmission delay for about 85μs. This performance could satisfy the performance target in terms of FA WLAN protocol which requires transmission delay less than 100μs. Furthermore, the proposed PHY design also offers better normalize power consumption per transmitted bit (e.g. energy efficiency performance) for around 6.76 mJ/Mb. Moreover, the proposed retransmission scheme could also offer control duration per user (cycle time) from 52-63μs, improving the control duration per user for approximately 36% from the conventional system. Therefore, the proposed retransmission scheme is an sub-optimum method in terms of low complexity and low latency, as compared to CSI based retransmission. This could be potentially applied in industrial wireless system.九州工業大学博士学位論文 学位記番号:情工博甲第350号 学位授与年月日:令和2年9月25日1 Introduction|2 Overview of Low Latency and High Reliable Industrial Wireless System|3 Cross Layer Design|4 Low Latency and High Throughput PHY Design|5 High Reliable Transceiver System|6 Conclusion and Future Work九州工業大学令和2年

Algorithm-Architecture Co-Design for Digital Front-Ends in Mobile Receivers

The methodology behind this work has been to use the concept of algorithm-hardware co-design to achieve efficient solutions related to the digital front-end in mobile receivers. It has been shown that, by looking at algorithms and hardware architectures together, more efficient solutions can be found; i.e., efficient with respect to some design measure. In this thesis the main focus have been placed on two such parameters; first reduced complexity algorithms to lower energy consumptions at limited performance degradation, secondly to handle the increasing number of wireless standards that preferably should run on the same hardware platform. To be able to perform this task it is crucial to understand both sides of the table, i.e., both algorithms and concepts for wireless communication as well as the implications arising on the hardware architecture. It is easier to handle the high complexity by separating those disciplines in a way of layered abstraction. However, this representation is imperfect, since many interconnected "details" belonging to different layers are lost in the attempt of handling the complexity. This results in poor implementations and the design of mobile terminals is no exception. Wireless communication standards are often designed based on mathematical algorithms with theoretical boundaries, with few considerations to actual implementation constraints such as, energy consumption, silicon area, etc. This thesis does not try to remove the layer abstraction model, given its undeniable advantages, but rather uses those cross-layer "details" that went missing during the abstraction. This is done in three manners: In the first part, the cross-layer optimization is carried out from the algorithm perspective. Important circuit design parameters, such as quantization are taken into consideration when designing the algorithm for OFDM symbol timing, CFO, and SNR estimation with a single bit, namely, the Sign-Bit. Proof-of-concept circuits were fabricated and showed high potential for low-end receivers. In the second part, the cross-layer optimization is accomplished from the opposite side, i.e., the hardware-architectural side. A SDR architecture is known for its flexibility and scalability over many applications. In this work a filtering application is mapped into software instructions in the SDR architecture in order to make filtering-specific modules redundant, and thus, save silicon area. In the third and last part, the optimization is done from an intermediate point within the algorithm-architecture spectrum. Here, a heterogeneous architecture with a combination of highly efficient and highly flexible modules is used to accomplish initial synchronization in at least two concurrent OFDM standards. A demonstrator was build capable of performing synchronization in any two standards, including LTE, WiFi, and DVB-H

Strategies That Mitigate IT Infrastructure Demands Produced by Student BYOD Usa

The use of bring your own devices (BYOD) is a global phenomenon, and nowhere is it more evident than on a college campus. The use of BYOD on academic campuses has grown and evolved through time. The purpose of this qualitative multiple case study was to identify the successful strategies used by chief information officers (CIOs) to mitigate information technology infrastructure demands produced by student BYOD usage. The diffusion of innovation model served as the conceptual framework. The population consisted of CIOs from community colleges within North Carolina. The data collection process included semistructured, in-depth face-to-face interviews with 9 CIOs and the analysis of 25 documents, all from participant case organizations. Member checking was used to increase the validity of the findings. During the data analysis phase, the data were coded, sorted, queried, and analyzed obtained from semistructured interviews and organizational documentation with NVivo, a qualitative data analysis computer software package. Through methodological triangulation, 3 major themes emerged from the study: the importance of technology management tools, the importance of security awareness training, and the importance of BYOD security policies and procedures. These themes highlight successful strategies employed by CIOs. The implications for positive social change as a result of this study include creating a more positive experience for students interacting with technology on campus. Effects on social change will also arise by increasing a student\u27s mindfulness through security awareness programs, which will empower the student to take more control of their online presence and as they pass that information along to family and friends

A comparative investigation on the application and performance of Femtocell against Wi-Fi networks in an indoor environment

Due to the strenuous demands on the available spectrum and bandwidth, alongside the ever increasing rate at which data traffic is growing and the poor quality of experience QoE) faced with indoor communications, in order for cellular networks to remain dominant in areas pertaining to voice and data services, cellular service providers have to reform their marketing and service delivery strategies together with their overall network rchitecture. To accomplish this leap forward in performance, cellular service operators need to employ a network topology, which makes use of a mix of macrocells and small cells, effectively evolving the network, bringing it closer to the end-­‐user. This investigation explores the use of small cell technology, specifically Femtocell technology in comparison to the already employed Wi-­‐Fi technology as a viable solution to poor indoor communications.The performance evolution is done by comparing key areas in the every day use of Internet communications. These include HTTP testing, RTP testing and VoIP testing. Results are explained and the modes of operation of both technologies are compared

Performance Optimization in Wireless Local Area Networks

Wireless Local Area Networks (WLAN) are becoming more and more important for providing wireless broadband access. Applications and networking scenarios evolve continuously and in an unpredictable way, attracting the attention of academic institutions, research centers and industry. For designing an e cient WLAN is necessary to carefully plan coverage and to optimize the network design parameters, such as AP locations, channel assignment, power allocation, MAC protocol, routing algorithm, etc... In this thesis we approach performance optimization in WLAN at di erent layer of the OSI model. Our rst approach is at Network layer. Starting from a Hybrid System modeling the ow of tra c in the network, we propose a Hybrid Linear Varying Parameter algorithm for identifying the link quality that could be used as metric in routing algorithms. Go down to Data Link, it is well known that CSMA (Carrier Sense Multiple Access) protocols exhibit very poor performance in case of multi-hop transmissions, because of inter-link interference due to imperfect carrier sensing. We propose two novel algorithms, that are combining Time Division Multiple Access for grouping contending nodes in non-interfering sets with Carrier Sense Multiple Access for managing the channel access behind a set. In the rst solution, a game theoretical study of intra slot contention is introduced, in the second solution we apply an optimization algorithm to nd the optimal degree between contention and scheduling. Both the presented solutions improve the network performance with respect to CSMA and TDMA algorithms. Finally we analyze the network performance at Physical Layer. In case of WLAN, we can only use three orthogonal channels in an unlicensed spectrum, so the frequency assignments should be subject to frequent adjustments, according to the time-varying amount of interference which is not under the control of the provider. This problem make necessary the introduction of an automatic network planning solution, since a network administrator cannot continuously monitor and correct the interference conditions su ered in the network. We propose a novel protocol based on a distributed machine learning mechanism in which the nodes choose, automatically and autonomously in each time slot, the optimal channel for transmitting through a weighted combination of protocols