A Novel Channel Access Scheme for Full-Duplex Wireless Networks Based on Contention in Time and Frequency Domains
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Vision-Based Mobile Free-Space Optical Communications Kyle Cavorley, Wayne Chang, Jonathan Giordano, Taichi Hirao Advisor: Prof
Vision-Based Mobile Free-Space Optical Communications Kyle Cavorley, Wayne Chang, Jonathan Giordano, Taichi Hirao Advisor: Prof. Daut Abstract Methodology The implementation of a free-space optical (FSO) communication system capable of interfacing with moving receivers such as unmanned ground or aerial vehicles. Two way communication Inexpensive laser diodes are used to transmit data at rates of up to 1 Mbps. A computer vision and tracking system controls a pan-tilt platform for target Transmit side Receive side acquisition and tracking. Complex package components, suchs as a laser driver and photo receiver, are avoided when possible to study the design of low-level system components. A two way communication system is made possible utilizing a reflective optical chopper (ROC) at the receiver end. Motivations and Objectives Motivations: -High power efficiency with high throughput Fig. 2: Photodiode Amplifier and Comparator Circuit. Fig. 4: Laser Diode Driver Circuit. -Increased security Objectives: -Construct optical communication link capable of 1 Mbps at thirty feet range -Form and maintain two way optical communication channel -Build computer vision tracking system and platform Fig. 6: Boston Micromachines Reflective Optical Chopper (ROC); used in two-way communication Fig. 3: Output Response of photodiode Fig. 5: Schmitt Trigger Circuit. Only one end of the communication link amplifier/comparator. requires a visual tracking/laser targeting system. Results ❑ 2 Mhz signal successfully transmitted 14 feet using 5 mW 670 nm laser. ❑ AD8030 Op-amp used to amplify photodiode response signal from a range [60 mV, 1 V] to 5V before entering comparator that generates a TTL output. Fig. 1: Vision Based FSO Communication Block Diagram. -
Unit 7: Choosing Communication Channels
UNIT 7: CHOOSING COMMUNICATION CHANNELS Unit 7 highlights the importance of selecting an appropriate channel mix for a communication response and describes five categories of communication channels: mass media, mid media, print media, social and digital media and interpersonal communication (IPC). For each of these channels, advantages and disadvantages have been listed, as well as situations in which different channels may be used. Although this Unit has attempted to differentiate the channels and their uses for simplicity, there is recognition that channels frequently overlap and may be effective for achieving similar objectives. This is why the match between channel, audience and communication objective is important. This unit provides some tools to help assess available and functioning channels during an emergency, as well as those that are more appropriate for reaching specific audience segments. Once you have completed this unit, you will have the following tools to support the development of your SBCC response: • Worksheet 7.1: Assessing Available Communication Channels • Worksheet 7.2: Matching Communication Channels to Primary and Influencing Audiences What Is a Communication Channel? A communication channel is a medium or method used to deliver a message to the intended audience. A variety of communication channels exist, and examples include: • Mass media such as television, radio (including community radio) and newspapers • Mid media activities, also known as traditional or folk media such as participatory theater, public talks, announcements through megaphones and community-based surveillance • Print media, such as posters, flyers and leaflets • Social and digital media such as mobile phones, applications and social media • IPC, such as door-to-door visits, phone lines and discussion groups Different channels are appropriate for different audiences, and the choice of channel will depend on the audience being targeted, the messages being delivered and the context of the emergency. -
Modeling and Simulation of an Asynchronous Digital Subscriber Line Transceiver Data Transmission Subsystem
Modeling and Simulation of an Asynchronous Digital Subscriber Line Transceiver Data Transmission Subsystem Elmustafa Erwa ABSTRACT Recently, there has been an increase in demand for digital services provided over the public telephone line network. Asymmetric digital subscriber line (ADSL) transmit high bit rate data in the forward direction to the subscriber, and lower bit rate data in the reverse direction to the central office, both on a single copper telephone loop. I implemented a Synchronous Dataflow (SDF) model for an ADSL transceiver’s data transmission subsystem in LabVIEW. My implementation enables designers to simulate and optimize different ADSL transceiver designs. The overall implementation is compliant with the European Telecommunications Standards Institute’s ADSL specification. 1. INTRODUCTION With the emergence of the Internet as the cornerstone of communications in this age, the demand for high speed Internet access has only been increasing. Asymmetric digital subscriber lines (ADSL) is one of the technologies that provide high-speed Internet access in residences and offices [1]. It facilitates the use of normal telephone services, Integrated Services Digital Network (ISDN), and high-speed data transmission simultaneously. Hence, bandwidth-demanding technologies, such as video-conferencing and video-on-demand, are enabled over ordinary telephone lines. ADSL standards use discrete multi-tone (DMT) modulation [2]. DMT divides the effectively bandlimited communication channel into a larger number of orthogonal narrowband subchannels. This allows for maximizing the transmitted bit rate and adapting to changing line conditions. Designing ADSL systems is inherently complex. However, advances in the digital signal processor (DSP) technology allowed programmable DSP based solutions to replace application-specific integrated circuit based implementations. -
MAC Protocols for IEEE 802.11Ax: Avoiding Collisions on Dense Networks Rafael A
MAC Protocols for IEEE 802.11ax: Avoiding Collisions on Dense Networks Rafael A. da Silva1 and Michele Nogueira1;2 1Department of Informatics, Federal University of Parana,´ Curitiba, PR, Brazil 2Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, PA, USA E-mails: [email protected] and [email protected] Wireless networks have become the main form of Internet access. Statistics show that the global mobile Internet penetration should exceed 70% until 2019. Wi-Fi is an important player in this change. Founded on IEEE 802.11, this technology has a crucial impact in how we share broadband access both in domestic and corporate networks. However, recent works have indicated performance issues in Wi-Fi networks, mainly when they have been deployed without planning and under high user density. Hence, different collision avoidance techniques and Medium Access Control protocols have been designed in order to improve Wi-Fi performance. Analyzing the collision problem, this work strengthens the claims found in the literature about the low Wi-Fi performance under dense scenarios. Then, in particular, this article overviews the MAC protocols used in the IEEE 802.11 standard and discusses solutions to mitigate collisions. Finally, it contributes presenting future trends arXiv:1611.06609v1 [cs.NI] 20 Nov 2016 in MAC protocols. This assists in foreseeing expected improvements for the next generation of Wi-Fi devices. I. INTRODUCTION Statistics show that wireless networks have become the main form of Internet access with an expected global mobile Internet penetration exceeding 70% until 2019 [1]. Wi-Fi Notice: This work has been submitted to the IEEE for possible publication. -
2 the Wireless Channel
CHAPTER 2 The wireless channel A good understanding of the wireless channel, its key physical parameters and the modeling issues, lays the foundation for the rest of the book. This is the goal of this chapter. A defining characteristic of the mobile wireless channel is the variations of the channel strength over time and over frequency. The variations can be roughly divided into two types (Figure 2.1): • Large-scale fading, due to path loss of signal as a function of distance and shadowing by large objects such as buildings and hills. This occurs as the mobile moves through a distance of the order of the cell size, and is typically frequency independent. • Small-scale fading, due to the constructive and destructive interference of the multiple signal paths between the transmitter and receiver. This occurs at the spatialscaleoftheorderofthecarrierwavelength,andisfrequencydependent. We will talk about both types of fading in this chapter, but with more emphasis on the latter. Large-scale fading is more relevant to issues such as cell-site planning. Small-scale multipath fading is more relevant to the design of reliable and efficient communication systems – the focus of this book. We start with the physical modeling of the wireless channel in terms of elec- tromagnetic waves. We then derive an input/output linear time-varying model for the channel, and define some important physical parameters. Finally, we introduce a few statistical models of the channel variation over time and over frequency. 2.1 Physical modeling for wireless channels Wireless channels operate through electromagnetic radiation from the trans- mitter to the receiver. -
Migrating Backoff to the Frequency Domain
No Time to Countdown: Migrating Backoff to the Frequency Domain Souvik Sen Romit Roy Choudhury Srihari Nelakuditi Duke University Duke University University of South Carolina Durham, NC, USA Durham, NC, USA Columbia, SC, USA [email protected] [email protected] [email protected] ABSTRACT 1. INTRODUCTION Conventional WiFi networks perform channel contention in Access control strategies are designed to arbitrate how mul- time domain. This is known to be wasteful because the chan- tiple entities access a shared resource. Several distributed nel is forced to remain idle while all contending nodes are protocols embrace randomization to achieve arbitration. In backing off for multiple time slots. This paper proposes to WiFi networks, for example, each participating node picks a break away from convention and recreate the backing off op- random number from a specified range and begins counting eration in the frequency domain. Our basic idea leverages the down. The node that finishes first, say N1, wins channel con- observation that OFDM subcarriers can be treated as integer tention and begins transmission. The other nodes freeze their numbers. Thus, instead of picking a random backoff duration countdown temporarily, and revive it only after N1’s trans- in time, a contending node can signal on a randomly cho- mission is complete. Since every node counts down at the sen subcarrier. By employing a second antenna to listen to same pace, this scheme produces an implicit ordering among all the subcarriers, each node can determine whether its cho- nodes. Put differently, the node that picks the smallest ran- sen integer (or subcarrier) is the smallest among all others. -
Designing Asymmetric Digital Subscriber Line with Discrete Multitone Modulator
ISSN (Online) 2321-2004 IJIREEICE ISSN (Print) 2321-5526 International Journal of Innovative Research in Electrical, Electronics, Instrumentation and Control Engineering Vol. 7, Issue 11, November 2019 Designing Asymmetric Digital Subscriber Line with Discrete Multitone Modulator Attiq Ul Rehman1, Maninder Singh2 M. Tech., Student, ECE Department, Haryana Engineering College, Jagadhri, Haryana, India1 Assistant Professor, ECE Department, Haryana Engineering College, Jagadhri, Haryana, India2 Abstract: The objective of Digital Subscriber Line (DSL) is to propagate signal from the transmitter to the receiver over telephone lines. In communication industry Asymmetric Digital Subscriber Line (ADSL) is widely used because it can handle both phone services and internet access services at same time. As the communication industry develops, its main concern is to maximize the user handling capacity of communication systems. For this purpose, ADSL uses Discrete Multitone (DMT) modulator with QAM bank. But as the number of users increases the system complexity and interference also increases. The communication channel is not free from the effects of channel impairments such as noise, interference and fading. These channel impairments caused signal distortion and Signal to Ratio (SNR) degradation. One method that can be implemented to overcome this problem is by introducing channel coding. Channel encoding is applied by adding redundant bits to the transmitted data. The redundant bits increase raw data used in the link and therefore, increase the bandwidth requirement. So, if noise or fading occurred in the channel, some data may still be recovered at the receiver. While at the receiver, channel decoding is used to detect or correct errors that are introduced to the channel. -
Collision Detection
Computer Networking Michaelmas/Lent Term M/W/F 11:00-12:00 LT1 in Gates Building Slide Set 3 Evangelia Kalyvianaki [email protected] 2017-2018 1 Topic 3: The Data Link Layer Our goals: • understand principles behind data link layer services: (these are methods & mechanisms in your networking toolbox) – error detection, correction – sharing a broadcast channel: multiple access – link layer addressing – reliable data transfer, flow control • instantiation and implementation of various link layer technologies – Wired Ethernet (aka 802.3) – Wireless Ethernet (aka 802.11 WiFi) • Algorithms – Binary Exponential Backoff – Spanning Tree 2 Link Layer: Introduction Some terminology: • hosts and routers are nodes • communication channels that connect adjacent nodes along communication path are links – wired links – wireless links – LANs • layer-2 packet is a frame, encapsulates datagram data-link layer has responsibility of transferring datagram from one node to adjacent node over a link 3 Link Layer (Channel) Services • framing, physical addressing: – encapsulate datagram into frame, adding header, trailer – channel access if shared medium – “MAC” addresses used in frame headers to identify source, dest • different from IP address! • reliable delivery between adjacent nodes – we see some of this again in the Transport Topic – seldom used on low bit-error link (fiber, some twisted pair) – wireless links: high error rates 4 Link Layer (Channel) Services - 2 • flow control: – pacing between adjacent sending and receiving nodes • error control: – error -
The Wireless Communication Channel Objectives
9/9/2008 The Wireless Communication Channel muse Objectives • Understand fundamentals associated with free‐space propagation. • Define key sources of propagation effects both at the large‐ and small‐scales • Understand the key differences between a channel for a mobile communications application and one for a wireless sensor network muse 1 9/9/2008 Objectives (cont.) • Define basic diversity schemes to mitigate small‐scale effec ts • Synthesize these concepts to develop a link budget for a wireless sensor application which includes appropriate margins for large‐ and small‐scale pppgropagation effects muse Outline • Free‐space propagation • Large‐scale effects and models • Small‐scale effects and models • Mobile communication channels vs. wireless sensor network channels • Diversity schemes • Link budgets • Example Application: WSSW 2 9/9/2008 Free‐space propagation • Scenario Free-space propagation: 1 of 4 Relevant Equations • Friis Equation • EIRP Free-space propagation: 2 of 4 3 9/9/2008 Alternative Representations • PFD • Friis Equation in dBm Free-space propagation: 3 of 4 Issues • How useful is the free‐space scenario for most wilireless syst?tems? Free-space propagation: 4 of 4 4 9/9/2008 Outline • Free‐space propagation • Large‐scale effects and models • Small‐scale effects and models • Mobile communication channels vs. wireless sensor network channels • Diversity schemes • Link budgets • Example Application: WSSW Large‐scale effects • Reflection • Diffraction • Scattering Large-scale effects: 1 of 7 5 9/9/2008 Modeling Impact of Reflection • Plane‐Earth model Fig. Rappaport Large-scale effects: 2 of 7 Modeling Impact of Diffraction • Knife‐edge model Fig. Rappaport Large-scale effects: 3 of 7 6 9/9/2008 Modeling Impact of Scattering • Radar cross‐section model Large-scale effects: 4 of 7 Modeling Overall Impact • Log‐normal model • Log‐normal shadowing model Large-scale effects: 5 of 7 7 9/9/2008 Log‐log plot Large-scale effects: 6 of 7 Issues • How useful are large‐scale models when WSN lin ks are 10‐100m at bt?best? Fig. -
Telecommunication Through Broadband Services of Bsnl: a Bird’S Eye View
International Journal of Technical Research and Applications e-ISSN: 2320-8163, www.ijtra.com Volume 1, Issue 2 (may-june 2013), PP. 37-41 TELECOMMUNICATION THROUGH BROADBAND SERVICES OF BSNL: A BIRD’S EYE VIEW Dr Shilpi Verma Assistant Professor Deptt. of Library & information Science (School for Information Science & Technology) Babasaheb Bhimrao Ambedkar University (A Central University) Vidya Vihar, Rai-bareli Road Lucknow-226025 (UP) Abstract: In the cut throat competition every country telecommunication technologies are playing very vital want to be information equipped, the role. The consumers or users are demanding for faster and telecommunication is helping a lot in achieving the reliable bandwidth for purpose of e-commerce, same. Integrated communication is emerged as a boom videoconferencing, information retrieval and such other in communication world. The growth of data, applications. Broadband seems as a answer to these communication market and the networking questions. Broadband provides means of accessing technology trend has amplified the importance of technologies to bridge the customer & the service telecommunication in the field of information provider throughout the world. It basically provides high communication. Telecommunication has become one speed internet access, whereas the dial up connections of the very important part that is very essential to the was having their limitations and low speed. These socio-economic well being of any nation. The paper broadband services allow the user to send or receive video deals with concept of Broad band services of BSNL, or audio digital content and having real time features also. technology options for broadband services. Bharat It is able to provide interactive services. -
How Computers Share Data
06 6086 ch03 4/6/04 2:51 PM Page 41 HOUR 3 Getting Data from Here to There: How Computers Share Data In this hour, we will first discuss four common logi- cal topologies, starting with the most common and ending with the most esoteric: . Ethernet . Token Ring . FDDI . ATM In the preceding hour, you read a brief definition of packet-switching and an expla- nation of why packet switching is so important to data networking. In this hour, you learn more about how networks pass data between computers. This process will be discussed from two separate vantage points: logical topologies, such as ethernet, token ring, and ATM; and network protocols, which we have not yet discussed. Why is packet switching so important? Recall that it enables multiple computers to send multiple messages down a single piece of wire, a technical choice that is both efficient and an elegant solution. Packet switching is intrinsic to computer network- ing—without packet switching, no network. In the first hour, you learned about the physical layouts of networks, such as star, bus, and ring technologies, which create the highways over which data travels. In the next hour, you learn about these topologies in more depth. But before we get to them, you have to know the rules of the road that determine how data travels over a network. In this hour, then, we’ll review logical topologies. 06 6086 ch03 4/6/04 2:51 PM Page 42 42 Hour 3 Logical Topologies Before discussing topologies again, let’s revisit the definition of a topology. -
Listen Before You Talk but on the Frequency Domain
1 Listen Before You Talk But On The Frequency Domain Souvik Sen Romit Roy Choudhury Srihari Nelakuditi Duke University Duke University University of South Carolina Abstract Access control strategies are designed to arbitrate how multiple entities access a shared resource. Several dis- tributed protocols embrace randomization to achieve arbitration. In WiFi networks, for example, each participating node picks a random number from a specified range and begins counting down. The device that reaches zero first wins the contention and initiates transmission. This core idea – called backoff – is known to be inherently wasteful because the channel must remain idle while all contending nodes are simultaneously counting down. This wastage has almost been accepted as a price for decentralization. In this paper, we ask whether the entire backoff operation can be migrated to the frequency domain, thereby eliminating a long-standing source of channel inefficiency. Our core idea draws on OFDM subcarriers in modern WiFi radios, treating each subcarrier as an integer number. By transmitting a signal on a random subcarrier frequency, and using a second antenna to listen for all active frequencies, each node may be able to detect its rank among all contenders. Since signaling on subcarriers is almost instantaneous, the wastage from backoff can become negligible. We design such an unconventional backoff scheme called Back2F, implement it on a software- radio testbed, and demonstrate its feasibility with real-world experiments. A natural next step would be to revisit today’s protocols, and ask what other operations may be similarly migrated to the frequency domain. I. PROBLEM &MOTIVATION Accessing a shared resource in a decentralized manner has been studied for several decades.