Analysis of asymmetry of traffic in full-duplex wireless local area network

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáThe standard commodity wireless hardware is half-duplex because there are challenges in full-duplex wireless that need attention and improvement. The self-interference in radios is one of the big challenges, but, even though there is no standard yet, there are several proposals that cancel enough self-interference that it is possible for communication to be successfully made. The standard half-duplex rules of the media access control (MAC) protocol contained on wireless cards do not accept simultaneous transmissions, because simultaneous transmissions are likely to collide with each other. Therefore, full-duplex wireless networks need a new MAC protocol to be able to handle the different full-duplex transmissions, namely, symmetric and asymmetric. Symmetric full-duplex transmissions ocurr between just two stations, which can be managed trivially by a suitable MAC protocol. On the other hand, asymmetric transmissions occur in communications involving three stations, and those transmissions are likely to produce collisions if one station receives simultaneously signals from the two others. From the different difficulties of each transmission type, emerges the doubt about how many opportunities are there for a full-duplex wireless network to make each type of transmission. With the focus on this question, this research proposes a method to collect traffic data from a real half-duplex wireless local area network (WLAN) to measure the amount of full-duplex symmetric and asymmetric transmission opportunities. The proposed method relies on: the brcmfmac driver, to collect the traffic data in kernel space; the Ftrace tracing utility framework, to send the data from kernel to user space; a Raspberry Pi 3 B+, in which is installed the modified driver and tracing utility; and an estimate of the travel time of frames between the kernel and firmware. The results of this research include a method to collect traffic data with the goal of measuring the amount of full-duplex transmissions opportunities and their types in a real half-duplex WLAN. It is also presented the analysis of a small amount of data collected during four days as an example of the proposed method, which shows that 4.096% of the frames presented the proper conditions to symmetric transmissions, while only 0.025% in the case of asymmetric transmissions.Os dispositivos sem fio padrão são half-duplex, pois o full-duplex sem fio apresenta desafios que precisam receber atenção e melhorias. A auto-interferência presente é um dos desafios, mas, ainda que não haja padrão, existem algumas propostas que cancelam a auto-interferência a ponto de comunicações serem realizadas com sucesso. As regras padrão do protocolo de controle de acesso ao meio (MAC) half-duplex contido nas placas sem fio não permitem transmissões simultâneas, já que são propensas a causar colisões. Portanto, redes full-duplex sem fio precisam de um novo protocolo MAC para que os diferentes tipos de transmissão full-duplex (simétrico e assimétrico) sejam utilizados. As transmissões simétricas ocorrem em comunicações entre apenas duas estações, o que pode ser gerido de forma trivial por um protocolo MAC apropriado. Por outro lado, as transmissões assimétricas envolvem comunicações entre três estações, e estas transmissões são propensas a gerar colisões no caso de uma das estações receber sinal das outras duas, simultaneamente. Devido às diferentes dificuldades de cada tipo de transmissão, surge a dúvida sobre quantas oportunidades existem para comunicação full-duplex de cada tipo de transmissão. Com foco nessa questão, esta pesquisa propõe um método para coleta de dados de tráfego de uma rede de área local sem fio (WLAN) half-duplex com o objetivo de calcular a quantidade de oportunidades de transmissões full-duplex simétricas e assimétricas. O método proposto conta com: o driver brcmfmac, para coleta de dados de tráfego em ambiente de kernel; o Ftrace, ferramenta utilitária de rastreamento, usado para enviar os dados do kernel para o ambiente do usuário; um Raspberry Pi 3 B+, no qual é instalado o driver modificado e o utilitário de rastreamento; e, um cálculo para estimar o tempo de viagem de pacotes entre o kernel e o firmware. Os resultados desta pesquisa incluem um método de coleta de dados de tráfego com o objetivo de quantificar as oportunidades de transmissões full-duplex e seus tipos em uma WLAN real. Também é apresentado uma coleta feita por quatro dias como um exemplo do mesmo. A análise mostra que 4.096% dos pacotes apresentam condições adequadas para transmissões simétricas, e apenas 0.025% para transmissões assimétricas

Link Scheduling Algorithms For In-Band Full-Duplex Wireless Networks

In the last two decades, wireless networks and their corresponding data traffic have grown significantly. This is because wireless networks have become an indispens- able and critical communication infrastructure in a modern society. An on-going challenge in communication systems is meeting the continuous increase in traffic de- mands. This is driven by the proliferation of electronic devices such as smartphones with a WiFi interface along with their bandwidth intensive applications. Moreover, in the near future, sensor devices that form the Internet of Things (IoTs) ecosystem will also add to future traffic growth. One promising approach to meet growing traffic demands is to equip nodes with an In-band-Full-Duplex (IBFD) radio. This radio thus allows nodes to transmit and receive data concurrently over the same frequency band. Another approach to in- crease network or link capacity is to exploit the benefits of Multiple-Input-Multiple- Output (MIMO) technologies; namely, (i) spatial diversity gain, which improves Signal-to-Noise Ratio (SNR) and thus has a direct impact on the data rate used by nodes, and (ii) spatial multiplexing gain, whereby nodes are able to form concurrent links to neighbors

Traffic integration in personal, local and geograhical wireless networks

Currently, users identify wireless networks with the first and second generation of cellular-telephony networks. Although voice and short messaging have driven the success of these networks so far, data and more sophisticated applications are emerging as the future driving forces for the extensive deployment of new wireless technologies. In this chapter we will consider future wireless technologies that will provide support to different types of traffic including legacy voice applications, Internet data traffic, and sophisticated multimedia applications. In the near future, wireless technologies will span from broadband wide-area technologies (such as satellite-based network and cellular networks) to local and personal area networks. Hereafter, for each class of networks, we will present the emerging wireless technologies for supporting service integration. Our overview will start by analyzing the Bluetooth technology that is the de-facto standard for Wireless Personal Area Networks (WPANs), i.e. networks that connect devices placed inside a circle with radius of 10 meters. Two main standards exist for Wireless Local Area Networks (WLANs): IEEE 802. and HiperLAN. In this chapter we focus on the IEEE 802.11 technology, as it is the technology currently available on the market. In this chapter, after a brief description of the IEEE 802.11 architecture, we will focus on the mechanisms that have been specifically designed to support delay sensitive traffics

AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing

The enormous success of advanced wireless devices is pushing the demand for higher wireless data rates. Denser spectrum reuse through the deployment of more access points per square mile has the potential to successfully meet the increasing demand for more bandwidth. In theory, the best approach to density increase is via distributed multiuser MIMO, where several access points are connected to a central server and operate as a large distributed multi-antenna access point, ensuring that all transmitted signal power serves the purpose of data transmission, rather than creating "interference." In practice, while enterprise networks offer a natural setup in which distributed MIMO might be possible, there are serious implementation difficulties, the primary one being the need to eliminate phase and timing offsets between the jointly coordinated access points. In this paper we propose AirSync, a novel scheme which provides not only time but also phase synchronization, thus enabling distributed MIMO with full spatial multiplexing gains. AirSync locks the phase of all access points using a common reference broadcasted over the air in conjunction with a Kalman filter which closely tracks the phase drift. We have implemented AirSync as a digital circuit in the FPGA of the WARP radio platform. Our experimental testbed, comprised of two access points and two clients, shows that AirSync is able to achieve phase synchronization within a few degrees, and allows the system to nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC and higher layer aspects of a practical deployment. To the best of our knowledge, AirSync offers the first ever realization of the full multiuser MIMO gain, namely the ability to increase the number of wireless clients linearly with the number of jointly coordinated access points, without reducing the per client rate.Comment: Submitted to Transactions on Networkin

Robust distributed resource allocation for cellular vehicle-to-vehicle communication

Mit Release 14 des LTE Standards unterstützt dieser die direkte Fahrzeug-zu-Fahrzeug-Kommunikation über den Sidelink. Diese Dissertation beschäftigt sich mit dem Scheduling Modus 4, einem verteilten MAC-Protokoll ohne Involvierung der Basisstation, das auf periodischer Wiederverwendung von Funkressourcen aufbaut. Der Stand der Technik und eine eigene Analyse des Protokolls decken verschiedene Probleme auf. So wiederholen sich Kollisionen von Paketen, wodurch manche Fahrzeuge für längere Zeit keine sicherheitskritischen Informationen verbreiten können. Kollisionen entstehen vermehrt auch dadurch, dass Hidden-Terminal-Probleme in Kauf genommen werden oder veränderliche Paketgrößen und -raten schlecht unterstützt werden. Deshalb wird ein Ansatz namens "Scheduling based on Acknowledgement Feedback Exchange" vorgeschlagen. Zunächst wird eine Funkreservierung in mehrere ineinander verschachtelte Unter-Reservierungen mit verschiedenen Funkressourcen unterteilt, was die Robustheit gegenüber wiederholenden Kollisionen erhöht. Dies ist die Grundlage für eine verteilte Staukontrolle, die die Periodizitätseigenschaft nicht verletzt. Außerdem können so veränderliche Paketgrößen oder -raten besser abgebildet werden. Durch die periodische Wiederverwendung können Acknowledgements für Funkressourcen statt für Pakete ausgesendet werden. Diese können in einer Bitmap in den Padding-Bits übertragen werden. Mittels der Einbeziehung dieser Informationen bei der Auswahl von Funkressourcen können Hidden-Terminal-Probleme effizient vermieden werden, da die Acknowledgements auch eine Verwendung dieser Funkressource ankündigen. Kollisionen können nun entdeckt und eine Wiederholung vermieden werden. Die Evaluierung des neuen MAC-Protokolls wurde zum großen Teil mittels diskreter-Event-Simulationen durchgeführt, wobei die Bewegung jedes einzelnen Fahrzeuges simuliert wurde. Der vorgeschlagene Ansatz führt zu einer deutlich erhöhten Paketzustellrate. Die Verwendung einer anwendungsbezogenen Awareness-Metrik zeigt, dass die Zuverlässigkeit der Kommunikation durch den Ansatz deutlich verbessert werden kann. Somit zeigt sich der präsentierte Ansatz als vielversprechende Lösung für die erheblichen Probleme, die der LTE Modus 4 mit sich bringt.The LTE Standard added support for a direct vehicle-to-vehicle communication via the Sidelink with Release 14. This dissertation focuses on the scheduling Mode 4, a distributed MAC protocol without involvement of the base station, which requires the periodic reuse of radio resources. The state of the art and a own analysis of this protocol unveil multiple problems. For example, packet collisions repeat in time, so that some vehicles are unable to distribute safety-critical information for extended periods of time. Collisions also arise due to the hidden-terminal problem, which is simply put up with in Mode 4. Additionally, varying packet sizes or rates can hardly be supported. Consequently, an approach called "Scheduling based on Acknowledgement Feedback Exchange" is proposed. Firstly, a reservation of radio resources is split into multiple, interleaved sub-reservations that use different radio resources. This increases the robustness against repeating collisions. It is also the basis for a distributed congestion control that does not violate the periodicity. Moreover, different packet rates or sizes can be supported. The periodic reuse of radio resources enables the transmission of acknowledgements for radio resources instead of packets. These can be transmitted in a bitmap inside the padding bits. Hidden-terminal problems can be mitigated by considering the acknowledgements when selecting radio resources as they announce the use of these radio resources. Collisions can also be detected and prevented from re-occurring. The evaluation of the MAC protocol is mostly performed using discrete-event simulations, which model the movement of every single vehicle. The presented approach leads to a clear improvement of the packet delivery rate. The use of an application-oriented metric shows that the communication robustness can be improved distinctly. The proposed approach hence presents itself as a promising solution for the considerable problems of LTE Mode 4

Wireless body sensor networks for health-monitoring applications

This is an author-created, un-copyedited version of an article accepted for publication in Physiological Measurement. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://dx.doi.org/10.1088/0967-3334/29/11/R01