Cooperative spectrum sensing using adaptive quantization mapping for mobile cognitive radio networks

Sparsity in spectrum is the result of spectrum underutilization. Cognitive radio (CR) technology has been proposed to address inefficiency of spectrum utilisation through dynamic spectrum access technique. CR in general allows secondary node (SN) users to access the licensed or primary users’ (PU) band without disrupting their activities. In CR cooperative spectrum sensing (CSS), a group of SNs share their spectrum sensing information to provide a better picture of the spectrum usage over the area where the SNs are located. In centralised CCS approach, all the SNs report their sensing information to a master node (MN) through a control reporting channel before the MN decides the spectrum bands that can be used by the SNs. To reduce unnecessary reporting information by the cooperating nodes, orthogonal frequency division multiplexing (OFDM) Subcarrier Mapping (SCM) spectrum exchange information was proposed. In this technique, the detection power level from each secondary SN user is quantized and mapped into a single OFDM subcarrier number before delivering it to the MN. Most researches in cooperative spectrum sensing often stated that the SNs are absolutely in stationary condition. So far, the mobility effect on OFDM based SCM spectrum exchange information has not been addressed before. In this thesis, the benchmarking of SCM in mobility environment is carried out. The results showed that during mobility, the performance of OFDM-based SCM spectrum exchange information degraded significantly. To alleviate the degradation, OFDM-based spectrum exchange information using adaptive quantization is proposed, which is known as Dynamic Subcarrier Mapping (DSM). The method is proposed to adapt to changes in detected power level during mobility. This new nonuniform subcarrier mapping considers the range of received power, threshold level and dynamic subcarrier width. The range of received power is first compressed or expanded depending on the intensity of the received power against a pre-determined threshold level before the OFDM subcarrier number is computed. The results showed that OFDM-based DSM spectrum exchange information is able to enhance the probability of detection for cooperative sensing by up to 43% and reduce false alarm by up to 28%. The DSM spectrum exchange information method has the potential to improve cooperative spectrum sensing for future CR mobile wireless networks

무선랜 비디오 멀티캐스트의 문제 발견 및 성능 향상 기법

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 최성현.Video multicast, streaming real-time videos via multicast, over wireless local area network (WLAN) has been considered a promising solution to share common venue-specific videos. By virtue of the nature of the wireless broadcast medium, video multicast basically enables scale-free video delivery, i.e., it can deliver a common video with the fixed amount of wireless resource regardless of the number of receivers. However, video multicast has not been widely enjoyed in our lives due to three major challenges: (1) power saving-related problem, (2) low reliability and efficiency, and (3) limited coverage. In this dissertation, we consider three research topics, i.e., (1) identification of practical issues with multicast power saving, (2) physical (PHY) rate and forward erasure correction code (FEC) rate adaptation over a single-hop network, and (3) multi-hop multicast, which deal with the three major challenges, respectively. Firstly, video multicast needs to be reliably delivered to power-saving stations, given that many portable devices are battery-powered. Accordingly, we investigate the impact of multicast power saving, and address two practical issues related with the multicast power saving. From the measurement with several commercial WLAN devices, we observe that many devices are not standard compliant, thus making video multicast performance severely degraded. We categorize such standard incompliant malfunctions that can result in significant packet losses. We also figure out a coexistence problem between video multicast and voice over Internet protocol (VoIP) when video receivers runs in power saving mode (PSM). The standard-compliant power save delivery of multicast deteriorates the VoIP performance in the same WLAN. We analyze the VoIP packet losses due to the coexistence problem, and propose a new power save delivery scheme to resolve the problem. We further implement the proposed scheme with an open source device driver, and our measurement results demonstrate that the proposed scheme significantly enhances the VoIP performance without sacrificing the video multicast performance. Second, multi-PHY rate FEC-applied wireless multicast enables reliable and efficient video multicast with intelligent selection of PHY rate and FEC rate. The optimal PHY/FEC rates depend on the cause of the packet losses. However, previous approaches select the PHY/FEC rates by considering only channel errors even when interference is also a major source of packet losses.We propose InFRA, an interference-aware PHY/FEC rate adaptation framework that (1) infers the cause of the packet losses based on received signal strength indicator (RSSI) and cyclic redundancy check (CRC) error notifications, and (2) determines the PHY/FEC rates based on the cause of packet losses. Our prototype implementation with off-the-shelf chipsets demonstrates that InFRA enhances the multicast delivery under various network scenarios. InFRA enables 2.3x and 1.8x more nodes to achieve a target video packet loss rate with a contention interferer and a hidden interferer, respectively, compared with the state-of-theart PHY/FEC rate adaptation scheme. To the best of our knowledge, InFRA is the first work to take the impact of interference into account for the PHY/FEC rate adaptation. Finally, collaborative relaying that enables selected receiver nodes to relay the received packets from source node to other nodes enhances service coverage, reliability, and efficiency of video multicast. The intelligent selection of sender nodes (source and relays) and their transmission parameters (PHY rate and the number of packets to send) is the key to optimize the performance. We propose EV-CAST, an interference and energy-aware video multicast system using collaborative relays, which entails online network management based on interference-aware link characterization, an algorithm for joint determination of sender nodes and transmission parameters, and polling-based relay protocol. In order to select most appropriate set of the relay nodes, EV-CAST considers interference, battery status, and spatial reuse, as well as other factors accumulated over last decades. Our prototype-based measurement results demonstrate that EV-CAST outperforms the state-of-the-art video multicast schemes. In summary, from Chapter 2 to Chapter 4, the aforementioned three pieces of the research work, i.e., identification of power saving-related practical issues, InFRA for interference-resilient single-hop multicast, and EV-CAST for efficient multi-hop multicast, will be presented, respectively.1 Introduction 1 1.1 Video Multicast over WLAN 1 1.2 Overview of Existing Approaches 4 1.2.1 Multicast Power Saving 4 1.2.2 Reliability and Efficiency Enhancement 4 1.2.3 Coverage Extension 5 1.3 Main Contributions 7 1.3.1 Practical Issues with Multicast Power Saving 7 1.3.2 Interference-aware PHY/FEC Rate Adaptation 8 1.3.3 Energy-aware Multi-hop Multicast 9 1.4 Organization of the Dissertation 10 2 Practical Issues with Multicast Power Saving 12 2.1 Introduction 12 2.2 Multicast & Power Management Operation in IEEE 802.11 14 2.3 Inter-operability Issue 15 2.3.1 Malfunctions of Commercial WLAN Devices 17 2.3.2 Performance Evaluation 20 2.4 Coexistence Problem of Video Multicast and VoIP 21 2.4.1 Problem Statement 21 2.4.2 Problem Identification: A Measurement Study 23 2.4.3 Packet Loss Analysis 27 2.4.4 Proposed Scheme 32 2.4.5 Performance Evaluation 33 2.5 Summary 37 3 InFRA: Interference-Aware PHY/FEC Rate Adaptation for Video Multicast over WLAN 39 3.1 Introduction 39 3.2 Related Work 42 3.2.1 Reliable Multicast Protocol 42 3.2.2 PHY/FEC rate adaptation for multicast service 44 3.2.3 Wireless Video Transmission 45 3.2.4 Wireless Loss Differentiation 46 3.3 Impact of Interference on Multi-rate FEC-applied Multicast 46 3.3.1 Measurement Setup 47 3.3.2 Measurement Results 47 3.4 InFRA: Interference-aware PHY/FEC Rate Adaptation Framework 49 3.4.1 Network Model and Objective 49 3.4.2 Overall Architecture 50 3.4.3 FEC Scheme 52 3.4.4 STA-side Operation 53 3.4.5 AP-side Operation 61 3.4.6 Practical Issues 62 3.5 Performance Evaluation 65 3.5.1 Measurement Setup 66 3.5.2 Small Scale Evaluation 67 3.5.3 Large Scale Evaluation 70 3.6 Summary 74 4 EV-CAST: Interference and Energy-aware Video Multicast Exploiting Collaborative Relays 75 4.1 Introduction 75 4.2 Factors for Sender Node and Transmission Parameter Selection 78 4.3 EV-CAST: Interference and Energy-aware Multicast Exploiting Collaborative Relays 80 4.3.1 Network Model and Objective 80 4.3.2 Overview 81 4.3.3 Network Management 81 4.3.4 Interference and Energy-aware Sender Nodes and Transmission Parameter Selection (INFER) Algorithm 87 4.3.5 Assignment, Polling, and Re-selection of Relays 93 4.3.6 Discussion 95 4.4 Evaluation 96 4.4.1 Measurement Setup 96 4.4.2 Micro-benchmark 98 4.4.3 Macro-benchmark 103 4.5 Related Work 105 4.5.1 Multicast Opportunistic Routing 105 4.5.2 Multicast over WLAN 106 4.6 Summary 106 5 Conclusion 108 5.1 Research Contributions 108 5.2 Future Research Directions 109 Abstract (In Korean) 121Docto

Achieving reliable and enhanced communication in vehicular ad hoc networks (VANETs)

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirement for the degree of Doctor of PhilosophyWith the envisioned age of Internet of Things (IoTs), different aspects of Intelligent Transportation System (ITS) will be linked so as to advance road transportation safety, ease congestion of road traffic, lessen air pollution, improve passenger transportation comfort and significantly reduce road accidents. In vehicular networks, regular exchange of current position, direction, speed, etc., enable mobile vehicle to foresee an imminent vehicle accident and notify the driver early enough in order to take appropriate action(s) or the vehicle on its own may take adequate preventive measures to avert the looming accident. Actualizing this concept requires use of shared media access protocol that is capable of guaranteeing reliable and timely broadcast of safety messages. This dissertation investigates the use of Network Coding (NC) techniques to enrich the content of each transmission and ensure improved high reliability of the broadcasted safety messages with less number of retransmissions. A Code Aided Retransmission-based Error Recovery (CARER) protocol is proposed. In order to avoid broadcast storm problem, a rebroadcasting vehicle selection metric η, is developed, which is used to select a vehicle that will rebroadcast the received encoded message. Although the proposed CARER protocol demonstrates an impressive performance, the level of incurred overhead is fairly high due to the use of complex rebroadcasting vehicle selection metric. To resolve this issue, a Random Network Coding (RNC) and vehicle clustering based vehicular communication scheme with low algorithmic complexity, named Reliable and Enhanced Cooperative Cross-layer MAC (RECMAC) scheme, is proposed. The use of this clustering technique enables RECMAC to subdivide the vehicular network into small manageable, coordinated clusters which further improve transmission reliability and minimise negative impact of network overhead. Similarly, a Cluster Head (CH) selection metric ℱ(\u1d457) is designed, which is used to determine and select the most suitably qualified candidate to become the CH of a particular cluster. Finally, in order to investigate the impact of available radio spectral resource, an in-depth study of the required amount of spectrum sufficient to support high transmission reliability and minimum latency requirements of critical road safety messages in vehicular networks was carried out. The performance of the proposed schemes was clearly shown with detailed theoretical analysis and was further validated with simulation experiments

Multicast MAC extensions for high rate real-time traffic in wireless LANs

Nowadays we are rapidly moving from a mainly textual-based to a multimedia-based Internet, for which the widely deployed IEEE 802.11 wireless LANs can be one of the promising candidates to make them available to users anywhere, anytime, on any device. However, it is still a challenge to support group-oriented real-time multimedia services, such as video-on-demand, video conferencing, distance educations, mobile entertainment services, interactive games, etc., in wireless LANs, as the current protocols do not support multicast, in particular they just send multicast packets in open-loop as broadcast packets, i.e., without any possible acknowledgements or retransmissions. In this thesis, we focus on MAC layer reliable multicast approaches which outperform upper layer ones with both shorter delays and higher efficiencies. Different from polling based approaches, which suffer from long delays, low scalabilities and low efficiencies, we explore a feedback jamming mechanism where negative acknowledgement (NACK) frames are allowed from the non-leader receivers to destroy the acknowledgement (ACK) frame from the single leader receiver and prompts retransmissions from the sender. Based on the feedback jamming scheme, we propose two MAC layer multicast error correction protocols, SEQ driven Leader Based Protocol (SEQ-LBP) and Hybrid Leader Based Protocol (HLBP), the former is an Automatic Repeat reQuest (ARQ) scheme while the later combines both ARQ and the packet level Forward Error Correction (FEC). We evaluate the feedback jamming probabilities and the performances of SEQ-LBP and HLBP based on theoretical analyses, NS-2 simulations and experiments on a real test-bed built with consumer wireless LAN cards. Test results confirm the feasibility of the feedback jamming scheme and the outstanding performances of the proposed protocols SEQ-LBP and HLBP, in particular SEQ-LBP is good for small multicast groups due to its short delay, effectiveness and simplicity while HLBP is better for large multicast groups because of its high efficiency and high scalability with respect to the number of receivers per group.Zurzeit vollzieht sich ein schneller Wechsel vom vorwiegend textbasierten zum multimediabasierten Internet. Die weitverbreiteten IEEE 802.11 Drahtlosnetzwerke sind vielversprechende Kandidaten, um das Internet für Nutzer überall, jederzeit und auf jedem Gerät verfügbar zu machen. Die Unterstützung gruppenorientierter Echtzeit-Dienste in drahtlosen lokalen Netzen ist jedoch immer noch eine Herausforderung. Das liegt daran, dass aktuelle Protokolle keinen Multicast unterstützen. Sie senden Multicast-Pakete vielmehr in einer "Open Loop"-Strategie als Broadcast-Pakete, d. h. ohne jegliche Rückmeldung (feedback) oder Paketwiederholungen. In der vorliegenden Arbeit, anders als in den auf Teilnehmereinzelabfragen (polling) basierenden Ansätzen, die unter langen Verzögerungen, geringer Skalierbarkeit und geringer Effizienz leiden, versuchen wir, Multicast-Feedback bestehend aus positiven (ACK) und negativen Bestätigungen (NACK) auf MAC-Layer im selben Zeitfenster zu bündeln. Die übrigen Empfänger können NACK-Frames senden, um das ACK des Leaders zu zerstören und Paketwiederholungen zu veranlassen. Basierend auf einem Feedback-Jamming Schema schlagen wir zwei MAC-Layer-Protokolle für den Fehlerschutz im Multicast vor: Das SEQ-getriebene Leader Based Protocol (SEQ-LBP) und das Hybrid Leader Based Protocol (HLBP). SEQ-LBP ist eines Automatic Repeat reQuest (ARQ) Schema. HLBP kombiniert ARQ und paketbasierte Forward Error Correction (FEC). Wir evaluieren die Leistungsfähigkeit von ACK/NACK jamming, SEQ-LBP und HLBP durch Analysis, Simulationen in NS-2, sowie Experimenten in einer realen Testumgebung mit handelsüblichen WLAN-Karten. Die Testergebnisse bestätigen die Anwendbarkeit der Feedback-Jamming Schemata und die herausragende Leistungsfähigkeit der vorgestellten Protokolle SEQ-LBP und HLBP. SEQ-LBP ist durch seine kurze Verzögerung, seine Effektivität und seine Einfachheit für kleine Multicast-Gruppen nützlich, während HLBP auf Grund seiner hohen Effizienz und Skalierbarkeit im Bezug auf die Größe der Empfänger eher in großen Multicast-Gruppen anzuwenden ist

Reliable Multicast transport of the video over the WiFi network

Le transport multicast est une solution efficace pour envoyer le même contenu à plusieurs récepteurs en même temps. Ce mode est principalement utilisé pour fournir des flux multimédia en temps réel. Cependant, le multicast classique de l IEEE 802.11 n'utilise aucun mécanisme d acquittement. Ainsi, l échec de réception implique la perte définitive du paquet. Cela limite la fiabilité du transport multicast et impact la qualité des applications vidéo. Pour résoudre ce problème, 802.11v et 802.11aa sont définis récemment. Le premier amendement propose Direct Multicast Service (DMS). D'autre part, le 802.11aa introduit GroupCast with Retries (GCR). GCR définit deux nouvelles politiques de retransmission : Block Ack (BACK) et Unsolicited Retry (UR).Dans cette thèse, nous évaluons et comparons les performances de 802.11v/aa. Nos résultats montrent que tous les nouveaux protocoles multicast génèrent un overhead de transmission important. En outre, DMS a une scalabilité très limitée, et GCR-BACK n'est pas approprié pour des grands groupes multicast. D autre part, nous montrons que DMS et GCR-BACK génèrent des latences de transmission importantes lorsque le nombre de récepteurs augmente. Par ailleurs, nous étudions les facteurs de pertes dans les réseaux sans fil. Nous montrons que l'indisponibilité du récepteur peut être la cause principale des pertes importantes et de leur nature en rafales. En particulier, nos résultats montrent que la surcharge du processeur peut provoquer un taux de perte de 100%, et que le pourcentage de livraison peut être limité à 35% lorsque la carte 802.11 est en mode d économie d'énergie.Pour éviter les collisions et améliorer la fiabilité du transport multicast, nous définissons le mécanisme Busy Symbol (BS). Nos résultats montrent que BS évite les collisions et assure un taux de succès de transmission très important. Afin d'améliorer davantage la fiabilité du trafic multicast, nous définissons un nouveau protocole multicast, appelé Block Negative Acknowledgement (BNAK). Ce protocole opère comme suit. L AP envoi un bloc de paquets suivi par un Block NAK Request (BNR). Le BNR permet aux membres de détecter les données manquantes et d envoyer une demande de retransmission, c.à.d. un Block NAK Response (BNAK). Un BNAK est transmis en utilisant la procédure classique d accès au canal afin d'éviter toute collision avec d'autres paquets. En plus, cette demande est acquittée. Sous l'hypothèse que 1) le récepteur est situé dans la zone de couverture du débit de transmission utilisé, 2) les collisions sont évitées et 3) le terminal a la bonne configuration, très peu de demandes de retransmission sont envoyées, et la bande passante est préservée. Nos résultats montrent que BNAK a une très grande scalabilité et génère des délais très limités. En outre, nous définissons un algorithme d'adaptation de débit pour BNAK. Nous montrons que le bon débit de transmission est sélectionné moyennant un overhead très réduit de moins de 1%. En plus, la conception de notre protocole supporte la diffusion scalable de lavvidéo. Cette caractéristique vise à résoudre la problématique de la fluctuation de la bande passante, et à prendre en considération l'hétérogénéité des récepteurs dans un réseau sans fil.The multicast transport is an efficient solution to deliver the same content to many receivers at the same time. This mode is mainly used to deliver real-time video streams. However, the conventional multicast transmissions of IEEE 802.11 do not use any feedback policy. Therefore missing packets are definitely lost. This limits the reliability of the multicast transport and impacts the quality of the video applications. To resolve this issue, the IEEE 802.11v/aa amendments have been defined recently. The former proposes the Direct Multicast Service (DMS). On the other hand, 802.11aa introduces Groupcast with Retries (GCR) service. GCR defines two retry policies: Block Ack (BACK) and Unsolicited Retry (UR).In this thesis we evaluate and compare the performance of 802.11v/aa. Our simulation results show that all the defined policies incur an important overhead. Besides, DMS has a very limited scalability, and GCR-BACK is not appropriate for large multicast groups. We show that both DMS and GCR-BACK incur important transmission latencies when the number of the multicast receivers increases. Furthermore, we investigate the loss factors in wireless networks. We show that the device unavailability may be the principal cause of the important packet losses and their bursty nature. Particularly, our results show that the CPU overload may incur a loss rate of 100%, and that the delivery ratio may be limited to 35% when the device is in the power save mode.To avoid the collisions and to enhance the reliability of the multicast transmissions, we define the Busy Symbol (BS) mechanism. Our results show that BS prevents all the collisions and ensures a very high delivery ratio for the multicast packets. To further enhance the reliability of this traffic, we define the Block Negative Acknowledgement (BNAK) retry policy. Using our protocol, the AP transmits a block of multicast packets followed by a Block NAK Request (BNR). Upon reception of a BNR, a multicast member generates a Block NAK Response (BNAK) only if it missed some packets. A BNAK is transmitted after channel contention in order to avoid any eventual collision with other feedbacks, and is acknowledged. Under the assumption that 1) the receiver is located within the coverage area of the used data rate, 2) the collisions are avoided and 3) the terminal has the required configuration, few feedbacks are generated and the bandwidth is saved. Our results show that BNAK has a very high scalability and incurs very low delays. Furthermore, we define a rate adaptation scheme for BNAK. We show that the appropriate rate is selected on the expense of a very limited overhead of less than 1%. Besides, the conception of our protocol is defined to support the scalable video streaming. This capability intends to resolve the bandwidth fluctuation issue and to consider the device heterogeneity of the group members.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF