Spread Spectrum and Wi-Fi Basics Syed Masud Mahmud, Ph.D
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Transmission Media Transmission Media Are Actually Located Below the Physical Layer and Are Directly Controlled by the Physical Layer
SYBScIT /Sem III / Computer networks UNIT II • MULTIPLEXING Multiplexing is the set of technique that allow the simultaneous transmission of multiple signals across a single data link.In a multiplexed system, n lines share the bandwidth of one link. The lines on the left direct their transmission streams to a multiplexer (MUX), which combines them into a single stream (many-to-one). At the receiving end, that stream is fed into a demultiplexer (DEMUX), which separates the stream back into its component transmissions (one- to-many) and directs them to their corresponding lines. In the figure, the word link refers to the physical path. The word channel refers to the portion of a link that carries a transmission between a given pair of lines. One link can have many (n) channels. There are three basic multiplexing techniques: frequency-division multiplexing, wavelength- division multiplexing, and time-division multiplexing. • Frequency-Division Multiplexing(FDM) Frequency-division multiplexing (FDM) is an analog technique that can be applied when the bandwidth of a link (in hertz) is greater than the combined bandwidths of the signals to be transmitted. In FDM, signals generated by each sending device modulate different carrier frequencies. These modulated signals are then combined into a single composite signal that can be transported by the link. Carrier frequencies are separated by sufficient bandwidth to accommodate the modulated signal. These bandwidth ranges are the channels through which the various signals travel chapter SYBScIT /Sem III / Computer networks Channels can be separated by strips of unused bandwidth—guard bands—to prevent signals from overlapping. FDM is an analog multiplexing technique that combines analog signals. -
Analysis of FHSS-CDMA with QAM-64 Over AWGN and Fading Channels Prashanth G S1
International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p-ISSN: 2395-0072 Analysis of FHSS-CDMA with QAM-64 over AWGN and Fading Channels Prashanth G S1 Assistant Professor, Dept. of ECE, JNNCE, Shivamogga, Karnataka, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract – CDMA is a type of channel access method in huge amount of power which result in implementation of which users using the same channel will use the same extra hardware to normalize the power requirement. [2] frequency band and also can access the channel at the same Frequency-hopping spread spectrum (FHSS) is a time. Using CDMA, more users can be allocated in the channel method of transmitting radio signals by rapidly compared to TDMA and FDMA. CDMA can be achieved using switching a carrier among many frequency channels Direct sequence spread spectrum(DSSS) and Frequency using a pseudo random sequence known to both transmitter hopping spread spectrum(FHSS). FHSS-CDMA consumes less and receiver. FHSS-CDMA consumes less power compared to power compared to DSSS-CDMA. High data rate modulation DSSS-CDMA. High data rate modulation schemes are used schemes are used along with FHSS-CDMA to deliver high along with FHSS-CDMA to deliver high quality multimedia quality multimedia content. High data rate modulation content. QAM-64 modulation technique as good bandwidth techniques have good bandwidth efficiency in FHSS-CDMA. In efficiency with wideband FHSS-CDMA. Author in [4], wireless communication, QAM is one of the most commonly discusses about broadband wireless access techniques. used modulation technique. Due to noise and interference, For 4G systems data rates up to 100 Mbps will be high data rate modulation techniques are prone to errors. -
F. Circuit Switching
CSE 3461: Introduction to Computer Networking and Internet Technologies Circuit Switching Presentation F Study: 10.1, 10.2, 8 .1, 8.2 (without SONET/SDH), 8.4 10-02-2012 A Closer Look At Network Structure: • network edge: applications and hosts • network core: —routers —network of networks • access networks, physical media: communication links d. xuan 2 1 The Network Core • mesh of interconnected routers • the fundamental question: how is data transferred through net? —circuit switching: dedicated circuit per call: telephone net —packet-switching: data sent thru net in discrete “chunks” d. xuan 3 Network Layer Functions • transport packet from sending to receiving hosts application transport • network layer protocols in network data link network physical every host, router network data link network data link physical data link three important functions: physical physical network data link • path determination: route physical network data link taken by packets from source physical to dest. Routing algorithms network network data link • switching: move packets from data link physical physical router’s input to appropriate network data link application router output physical transport network data link • call setup: some network physical architectures require router call setup along path before data flows d. xuan 4 2 Network Core: Circuit Switching End-end resources reserved for “call” • link bandwidth, switch capacity • dedicated resources: no sharing • circuit-like (guaranteed) performance • call setup required d. xuan 5 Circuit Switching • Dedicated communication path between two stations • Three phases — Establish (set up connection) — Data Transfer — Disconnect • Must have switching capacity and channel capacity to establish connection • Must have intelligence to work out routing • Inefficient — Channel capacity dedicated for duration of connection — If no data, capacity wasted • Set up (connection) takes time • Once connected, transfer is transparent • Developed for voice traffic (phone) g. -
Next-Generation Secure, Scalable Communication Network for the Smart Grid an Advanced Radio Technology That Is Inherently Secure and Robust for Utility Environments
Next-Generation Secure, Scalable Communication Network for the Smart Grid An advanced radio technology that is inherently secure and robust for utility environments Background Project Description Benefits Spread spectrum techniques are used in This project involves developing a Addresses latency, jitter and security communication systems to disperse wireless technology that is robust, secure issues signals, creating a wider bandwidth. This and scalable for smart grid applications, Uses adaptive hybrid spread-spectrum can establish more secure with advanced radio technology capable modulation format communications and resist interferences of high reliability in utility environments. Suits high quality-of-service or jamming. applications The project team will use Oak Ridge There is a significant gap between National Laboratory’s Hybrid Spread Provides superior resistance to multipath, noise, interference and commercially available communications Spectrum (HSS) waveform to develop jamming systems and those needed to satisfy the code division multiple access (CDMA)- requirements associated with the electric based wireless mesh networks. These sector. These requirements include networks are primarily used in the Partners noise/interference resistance, scalability, context of closed-loop and open-loop latency and data security. Several control systems such as advanced Oak Ridge National Laboratory spread-spectrum wireless signal metering infrastructure (AMI) and Pacific Northwest National Laboratory transmission protocols that are adequate -
Module # 7 Spread Spectrum and Multiple Access Techniques
Module 7 Spread Spectrum and Multiple Access Technique Version 2 ECE IIT, Kharagpur Lesson 38 Introduction to Spread Spectrum Modulation Version 2 ECE IIT, Kharagpur After reading this lesson, you will learn about ¾ Basic concept of Spread Spectrum Modulation; ¾ Advantages of Spread Spectrum (SS) Techniques; ¾ Types of spread spectrum (SS) systems; ¾ Features of Spreading Codes; ¾ Applications of Spread Spectrum; Introduction Spread spectrum communication systems are widely used today in a variety of applications for different purposes such as access of same radio spectrum by multiple users (multiple access), anti-jamming capability (so that signal transmission can not be interrupted or blocked by spurious transmission from enemy), interference rejection, secure communications, multi-path protection, etc. However, irrespective of the application, all spread spectrum communication systems satisfy the following criteria- (i) As the name suggests, bandwidth of the transmitted signal is much greater than that of the message that modulates a carrier. (ii) The transmission bandwidth is determined by a factor independent of the message bandwidth. The power spectral density of the modulated signal is very low and usually comparable to background noise and interference at the receiver. As an illustration, let us consider the DS-SS system shown in Fig 7.38.1(a) and (b). A random spreading code sequence c(t) of chosen length is used to ‘spread’(multiply) the modulating signal m(t). Sometimes a high rate pseudo-noise code is used for the purpose of spreading. Each bit of the spreading code is called a ‘chip’. Duration of a chip ( Tc) is much smaller compared to the duration of an information bit ( T). -
Uhf Radio Alternative - Spread Spectrum Radios
By: Robert J. Reese, PLS UHF RADIO ALTERNATIVE - SPREAD SPECTRUM RADIOS any of us surveyors using radio links for data transfer are familiar with UHF radios and their limita- Mtions. UHF radios are used for many types of data transfer, but in this article I am primarily concerned with the application of radio links to RTK GPS. If you are using cell phones for data links from your own base stations, or from Continuously Operating Reference Stations (CORS), or are using correction signals from other proprietary subscrip- tion services, this article doesn’t apply. But if you work in places that may not have cell coverage, or you need a local base for your rover control, the info below might help. First, let’s get my disclaimer out of the way. If I mention products or manufacturers by name, it is not an endorsement or a criticism. There are many other products and manufacturers of radios and data link equipment. I mention any products by name only because I have experience with them. In fact, all the radios I use operate very well. But they all have advantages that can be exploited for different field conditions. You’ll have to do your own research on radio types and manufacturers that will work for you. The UHF (Ultra-High Frequency) band of the radio spectrum covers several frequency ranges that are assigned by the Federal Communications Commission (FCC) to various user groups for different purposes (http://www.jneuhaus.com/fccindex/spectrum.html). The UHF frequencies used, generally, by the land surveying and geodetic control community in the US are between 460 MHz to 470 MHz. -
Wi-Fi/Bluetooth Coexistence Issues
Bluetooth and Wi-Fi Coexistence Originally Published: November 2011 Updated: October 2012 A White Paper from Bluetooth and Wi-Fi transmit in different ways using Laird Technologies differing protocols. When Wi-Fi operates in the 2.4 GHz band, Wi-Fi transmissions can interfere with Bluetooth transmissions, and Bluetooth transmissions can interfere with Wi-Fi transmissions. Because Bluetooth and Wi-Fi radios often operate in the same physical area and many times in the same device, interference between Bluetooth and Wi-Fi can impact the performance and reliability of both wireless interfaces. Americas: +1-800-492-2320 Option 3 Europe: +44-1628-858-940 Hong Kong: +852-2268-6567 x026 www.lairdtech.com/wireless White Paper Bluetooth and Wi-Fi Coexistence Contents Overview....................................................................................................................................................... 3 Spread Spectrum .......................................................................................................................................... 3 Frequency Hopping Spread Spectrum ......................................................................................................... 3 Direct Sequence Spread Spectrum .............................................................................................................. 4 Mutual Interference .................................................................................................................................... 4 Temporal Isolation: Time Division -
MIMO Technology in Wifi Systems
MIMO in WiFi Systems Rohit U. Nabar Smart Antenna Workshop Aug. 1, 2014 WiFi • Local area wireless technology that allows communication with the internet using 2.4 GHz or 5 GHz radio waves per IEEE 802.11 • Proliferation in the number of devices that use WiFi today: smartphones, tablets, digital cameras, video-game consoles, TVs, etc • Devices connect to the internet via wireless network access point (AP) Advantages • Allows convenient setup of local area networks without cabling – rapid network connection and expansion • Deployed in unlicensed spectrum – no regulatory approval required for individual deployment • Significant competition between vendors has driven costs lower • WiFi governed by a set of global standards (IEEE 802.11) – hardware compatible across geographical regions WiFi IC Shipment Growth 1.25x 15x Cumulative WiFi Devices in Use Data by Local Access The IEEE 802.11 Standards Family Standard Year Ratified Frequency Modulation Channel Max. Data Band Bandwidth Rate 802.11b 1999 2.4 GHz DSSS 22MHz 11 Mbps 802.11a 1999 5 GHz OFDM 20 MHz 54 Mbps 802.11g 2003 2.4 GHz OFDM 20 MHz 54 Mbps 802.11n 2009 2.4/5 GHz MIMO- 20,40 MHz 600 Mbps OFDM 802.11ac 2013 5 GHz MIMO- 20, 40, 80, 6.93 Gbps OFDM 160 MHz 802.11a/ac PHY Comparison 802.11a 802.11ac Modulation OFDM MIMO-OFDM Subcarrier spacing 312.5 KHz 312.5 KHz Symbol Duration 4 us (800 ns guard interval) 3.6 us (400 ns guard interval) FFT size 64 64(20 MHz)/512 (160 MHz) FEC BCC BCC or LDPC Coding rates 1/2, 2/3, 3/4 1/2, 2/3, 3/4, 5/6 QAM BPSK, QPSK, 16-,64-QAM BPSK, QPSK, 16-,64-,256- QAM Factors Driving the Data Rate Increase 6.93 Gbps QAM 802.11ac (1.3x) FEC rate (1.1x) MIMO (8x) 802.11a Bandwidth (8x) 54 Mbps 802.11 Medium Access Control (MAC) Contention MEDIUM BUSY DIFS PACKET Window • Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) • A wireless node that wants to transmit performs the following sequence 1. -
Multiple Access Techniques for 4G Mobile Wireless Networks Dr Rupesh Singh, Associate Professor & HOD ECE, HMRITM, New Delhi
International Journal of Engineering Research and Development e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com Volume 5, Issue 11 (February 2013), PP. 86-94 Multiple Access Techniques For 4G Mobile Wireless Networks Dr Rupesh Singh, Associate Professor & HOD ECE, HMRITM, New Delhi Abstract:- A number of new technologies are being integrated by the telecommunications industry as it prepares for the next generation mobile services. One of the key changes incorporated in the multiple channel access techniques is the choice of Orthogonal Frequency Division Multiple Access (OFDMA) for the air interface. This paper presents a survey of various multiple channel access schemes for 4G networks and explains the importance of these schemes for the improvement of spectral efficiencies of digital radio links. The paper also discusses about the use of Multiple Input/Multiple Output (MIMO) techniques to improve signal reception and to combat the effects of multipath fading. A comparative performance analysis of different multiple access schemes such as Time Division Multiple Access (TDMA), FDMA, Code Division Multiple Access (CDMA) & Orthogonal Frequency Division Multiple Access (OFDMA) is made vis-à-vis design parameters to highlight the advantages and limitations of these schemes. Finally simulation results of implementing some access schemes in MATLAB are provided. I. INTRODUCTION 4G (also known as Beyond 3G), an abbreviation of Fourth-Generation, is used for describing the next complete evolution in wireless communications. A 4G system will be a complete replacement for current networks and will be able to provide a comprehensive and secure IP solution. Here, voice, data, and streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and at much higher data rates than the previous generations [1], [2], [3]. -
Multiplexing and Sampling Theory
Multiplexing and Sampling Theory THE ECONOMY OF MULTIPLEXING contact type determine its current carrying capacity. For instance, laboratory instrument relays typically switch Sampled-Data Systems up to 3A, while industrial applications use larger relays An ideal data acquisition system uses a single ADC for to switch higher currents, often 5 to 10A. each measurement channel. In this way, all data are captured in parallel and events in each channel can be Solid-state switches, on the other hand, are much faster compared in real time. But using a multiplexer, Figure than relays and can reach sampling rates of several MHz. 3.01, that switches among the inputs of multiple chan- However, these devices can’t handle inputs higher than nels and drives a single ADC can substantially reduce 25V, and they are not well suited for isolated applica- the cost of a system. This approach is used in so-called tions. Moreover, solid-state devices are typically limited sampled-data systems. The higher the sample rate, the to handling currents of only one mA or less. closer the system mimics the ideal data acquisition system. But only a few specialized data acquisition Another characteristic that varies between mechani- systems require sample rates of extraordinary speed. cal relays and solid-state switches is called ON resis- Most applications can cope with the more modest tance. An ideal mechanical switch or relay contact sample rates typically offered by mainstream data pair has zero ON resistance. But real devices such acquisition systems. as common reed-relay contacts are 0.010 W or less, a quality analog switch can be 10 to 100 W, and an Solid State Switches vs. -
Wi-Fi Data Rates, Channels and Capacity
WHITE PAPER Wi-Fi Data Rates, Channels and Capacity By Cees Links, GM of Qorvo Wireless Connectivity Business Unit Formerly CEO & Founder of GreenPeak Technologies Introduction Considerable confusion exists about the performance that Wi-Fi at 5 GHz and at 60 GHz (WiGig) actually deliver. The “Over the past 20 cause of this confusion stems mostly from the complexity of the interplay of the technical factors involved, as well as years, the IEEE the widely different Wi-Fi transmission environments – especially in indoor environments. Another reason is the 802.11 standard has not uncommon but facile assumption that faster is better. If you asked a road traffic expert whether faster meant provided increased better, he would tell you that faster driving means reduced road capacity. Data communications in a shared medium transmission speeds.” is not very different. Over the 20 years of its development, the IEEE 802.11 standard has provided for increasing levels of transmission speeds, but disappointing results in practical use have led to more emphasis on capacity. This paper attempts to clarify some of the complexities and to derive, given reasonable assumptions, what capacity consumers in dense residential settings can expect. December 2017 | Subject to change without notice. 1 of 8 www.qorvo.com WHITE PAPER: Wi-Fi Data Rates, Channels and Capacity IEEE 802.11ac and 802.11ax Transmission rates Marketing brochures usually give the maximum theoretically possible data rates that can only be realized in the lab under carefully controlled conditions. Table 1 lists the theoretical rates obtainable with the various protocol versions of the IEEE 802.11 standard. -
DATA COMMUNICATION Multiplexing
CS311: DATA COMMUNICATION Multiplexing by Dr. Manas Khatua Assistant Professor Dept. of CSE IIT Jodhpur E-mail: [email protected] Web: http://home.iitj.ac.in/~manaskhatua http://manaskhatua.github.io/ Outline of the Lecture • What is Multiplexing and why is it used ? • Basic concepts of Multiplexing • Types of Multiplexing: Frequency Division Multiplexing (FDM) Wavelength Division Multiplexing (WDM) Time Division Multiplexing (TDM) . Synchronous . Asynchronous Inverse TDM 24-09-2017 Dr. Manas Khatua 2 Introduction • To make efficient use of high-speed telecommunications lines, some form of multiplexing is used. • Multiplexing allows several transmission sources to share a larger transmission capacity. • Most individual data communicating devices typically require modest data rate, but the media usually has much higher bandwidth. • Two communicating stations do not utilize the full capacity of a data link. • The higher the data rate, the most cost effective is the transmission facility. 24-09-2017 Dr. Manas Khatua 3 Cont… • When the bandwidth of a medium is greater than individual signals to be transmitted through the channel, a medium can be shared by more than one channel of signals by using Multiplexing. • For efficiency, the channel capacity can be shared among a number of communicating stations. • Most common use of multiplexing is in long-haul communication using coaxial cable, microwave and optical fibre. 24-09-2017 Dr. Manas Khatua 4 Basic Concept • A device known as Multiplexer (MUX) combines ‘n’ channels for transmission through a single medium or link. • At the other end a De-multiplexer (DEMUX) is used to separate out the ‘n’ channels. 24-09-2017 Dr.