REFERENCES CCRI Engineering and Technology Jbernardini 1 Introduction to Wireless Networking Module-5 Physical Layer Access Methods and Spread Spectrum CCRI ENGINEERING AND TECHNOLOGY Jerry Bernardini CCRI Engineering and Technology Jbernardini 1 1

REFERENCES CCRI Engineering and Technology Jbernardini 2 REFERENCES CCRI Engineering and Technology Jbernardini 2 2 CWTS Certified Wireless Technology Specialist Official Study Guide, Chapter-5 CWNA Certified Wireless Network Administration Official Study Guide (PWO-104), David Coleman, David Westcott, 2009, Chapter-6 The California Regional Consortium for Engineering Advances in Technological Education (CREATE) project Spread Spectrum Scene mag.com/primer.htmlhttp:// mag.com/primer.html

REFERENCES CCRI Engineering and Technology Jbernardini 3 Chapter Objectives CCRI Engineering and Technology Jbernardini 3 Define concepts which make up the functionality of RF and spread spectrum technology Define and differentiate between the following physical layer (PHY) wireless technologies

REFERENCES CCRI Engineering and Technology Jbernardini 4 IEEE CSMA/CD vs. IEEE CSMA/CA CCRI Engineering and Technology Jbernardini 4 CSMA/CD is for wired collision handling CSMA/CA is for wireless collision handling CSMA = Carrier Sense Multiple Access CD = Collision Detection CA = Collision Avoidance Why do collisions occur? – Answer = Two or more stations transmit at the same time Why is it important to detect or avoid collisions? – Answer = Because there is data loss and retransmission is necessary Wired networks are designed for the transmitting station to detect most collisions Many collisions will not be detected by Wireless networks – therefore avoid collisions

REFERENCES CCRI Engineering and Technology Jbernardini 5 IEEE Collision Handling CSMA/CA CCRI Engineering and Technology Jbernardini 5 In CSMA/CA a Wireless node that wants to transmit performs the following sequence: 1.Listen on the desired channel. 2.If channel is idle (no active transmitters) it sends a packet. 3.If channel is busy the node waits random time until transmission stops and then waits an additional time period. 4.If the channel is still idle at the end of the time period the node transmits its packet otherwise it repeats the process defined in 3 above until it gets a free channel. 5.Additional support mechanisms such as ACK, RTS/CTS can be used but increase overhead noticeably.

REFERENCES CCRI Engineering and Technology Jbernardini 6 CSMA/CA and ACK CCRI Engineering and Technology Jbernardini 6 CSMA/CA also reduces collisions via explicit frame acknowledgment Acknowledgment frame (ACK): Sent by receiving device to sending device to confirm data frame arrived intact If ACK not returned, transmission error assumed CSMA/CA does not eliminate collisions and does not solve hidden node problem

REFERENCES CCRI Engineering and Technology Jbernardini 7 Two Kinds of Carrier Sensing Mechanisms CCRI Engineering and Technology Jbernardini 7 Physical Carrier Sense – Uses Clear Channel Assessment (CCA) – Is the RF energy on the channel above a threshold? – If CCA>threshold --->wait for CCA< threshold before transmitting – Checks received signal strength using RSSI – RF energy from a hidden node could be missed Virtual Carrier Sense – Uses the Network Allocation Vector (NAV) in each station – NAV is a timer that determines if station can contend for RF medium – NAV >0 --->wait for count down to NAV=0 – NAV=0 --->use CCA to check for RF energy on medium – IF NAV=0 and CCA > threshold --->station resets NAV>0 and waits

REFERENCES CCRI Engineering and Technology Jbernardini 8 Network Access Methods CCRI Engineering and Technology Jbernardini 8 Reserving Time for Data Transmission Using Distributed Coordination Function (DCF) – Employs a contention period for devices competing to send data on the wireless network

REFERENCES CCRI Engineering and Technology Jbernardini 9 CSMA/CA Request to Send/Clear to Send CCRI Engineering and Technology Jbernardini 9 Request to Send/Clear to Send (RTS/CTS) protocol: Option used to solve hidden node problem –Significant overhead upon the WLAN with transmission of RTS and CTS frames Especially with short data packets –RTS threshold: Only packets that longer than RTS threshold transmitted using RTS/CTS

REFERENCES CCRI Engineering and Technology Jbernardini 10 IEEE Half Duplex Communication CCRI Engineering and Technology Jbernardini 10 Effects of Half Duplex on Wireless Throughput – Half Duplex: two way communication that occurs in only one direction at a time Effective halves the max bit rate

REFERENCES CCRI Engineering and Technology Jbernardini 11 Telecommunication Channel CCRI Engineering and Technology Jbernardini 11 Channel - a path along which information in the form of an electrical signal passes. Usually a range of contiguous frequencies involved in supporting information transmission Bandwidth Amplitude Frequency Channel Center Channel Frequency

REFERENCES CCRI Engineering and Technology Jbernardini 12 RF Bands for Wireless Networks CCRI Engineering and Technology Jbernardini 12 ISM- Industrial Scientific and Medical – Three Bands – 900 MHz band – 2.4 GHz band – 5 GHz Band UNII- Unlicensed National Information Infrastructure – 5 GHz band – UNII-1 (Lower) – UNII-2 (middle) – UNII2 Extended – UNII-3 (Upper)

REFERENCES CCRI Engineering and Technology Jbernardini 13 DSSS USA Channel Allocation CCRI Engineering and Technology Jbernardini Channels available 11 Channels in the United States GHz2.473 GHz Amplitude Freq. Channels

REFERENCES CCRI Engineering and Technology Jbernardini 14 DSSS 3 Non-overlap Channels CCRI Engineering and Technology Jbernardini GHz GHz Ch 1Ch 6Ch 11 (2.412 GHz)(2.437GHz)(2.462 GHz) Amplitude Freq MHz 22 MHz 3MHz 2426 MHz 2423 MHz

REFERENCES CCRI Engineering and Technology Jbernardini 15 5 GHz Band and Channels CCRI Engineering and Technology Jbernardini 15

REFERENCES CCRI Engineering and Technology Jbernardini 16 Introduction to Spread Spectrum CCRI Engineering and Technology Jbernardini 16 Spread Spectrum – a telecommunications technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. Frequency Amplitude Narrowband Wideband

REFERENCES CCRI Engineering and Technology Jbernardini 17 Narrow Band and Spread Spectrum Communications CCRI Engineering and Technology Jbernardini 17 Narrowband Vs. Spread Spectrum Communication – Narrowband and Spread Spectrum are two examples of how devices can communicate using radio frequency

REFERENCES CCRI Engineering and Technology Jbernardini 18 4-Types Spread Spectrum CCRI Engineering and Technology Jbernardini 18 Time Hopping, (THSS) Frequency Hopping, (FHSS) Direct Sequence Spread Spectrum, (DSSS) Hybrid, DSSS/FHSS Original IEEE wireless LAN standard: – Frequency-hopping spread spectrum (FHSS) – Direct-sequence spread spectrum (DSSS) High Rate/ Direct-Sequence Spread Spectrum (HR/DSSS) DSSS and HR/DSSS Channels

REFERENCES CCRI Engineering and Technology Jbernardini 19 Uses of Spread Spectrum CCRI Engineering and Technology Jbernardini 19 Military - For low probability of interception of telecommunications. Civil/Military - Range and positioning measurements. GPS – satellites. Civil Cellular Telephony. Civil Wireless Networks – and Bluetooth.

REFERENCES CCRI Engineering and Technology Jbernardini 20 Frequency Hopping Patent CCRI Engineering and Technology Jbernardini 20 Hedy Lamarr and composer George Antheil, patent number 2,292,387, circa 1942 A Hollywood cocktail party with Navy officers present

REFERENCES CCRI Engineering and Technology Jbernardini 21 Frequency Hopping Spread Spectrum (FHSS) CCRI Engineering and Technology Jbernardini 21 FHSS - Acronym for frequency-hopping spread spectrum , Bluetooth, & HomeRF. Freq. Amp Frequency Hop Sequence: 1, 3, 2, 4 Wide Band Channel

REFERENCES CCRI Engineering and Technology Jbernardini 22 Frequency Hopping Spread Spectrum – Simplistic View CCRI Engineering and Technology Jbernardini 22

REFERENCES CCRI Engineering and Technology Jbernardini 23 FHSS System Block Diagram CCRI Engineering and Technology Jbernardini 23 Frequency Synthesizer Carrier Frequency Data Buffer Sequence Generator Mixer Mod Antenna FHSS

REFERENCES CCRI Engineering and Technology Jbernardini 24 Direct Sequence Spread Spectrum (DSSS) CCRI Engineering and Technology Jbernardini 24 Freq. Amp DSSS Band Channel 1 Signal

REFERENCES CCRI Engineering and Technology Jbernardini 25 DSSS System Block Diagram CCRI Engineering and Technology Jbernardini 25 Carrier Frequency Data Buffer Pseudo – Noise Generator Antenna Carrier Generator 11-bit Barker Code Mixer Encoder DSSS Chipping Code Mod

REFERENCES CCRI Engineering and Technology Jbernardini 26 Comparing FHSS & DSSS CCRI Engineering and Technology Jbernardini 26 Frequency Hopping Spread Spectrum, FHSS Direct Sequence Spread Spectrum, DSSS b Dwell Time 400 mS Higher Cost No Dwell Time Lower Cost Lower Throughput (2 or 3 Mbps) Lower Interoperability Higher Throughput (11 Mbps) Higher Interoperability Better Immunity to Interference More User Density (79) Poorer Immunity to Interference Less User Density (3)

REFERENCES CCRI Engineering and Technology Jbernardini 27 Orthogonal Frequency Division Multiplexing (OFDM) CCRI Engineering and Technology Jbernardini 27 Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system. Orthogonal means to establish right angle relationships between frequencies OFDM spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies and null out of channel sidebands f1f3 f2 f4

REFERENCES CCRI Engineering and Technology Jbernardini 28 OFDM Features CCRI Engineering and Technology Jbernardini 28 Used in IEEE a (OFDM) and IEEE g (ERP-OFDM) and IEEE n (HT-OFDM) amendments Allows for much higher data rate transfers than DSSS and HR/DSSS Up to 54 Mbps for OFDM, ERP-OFDM and Mbps for HT-OFDM OFDM functions in either the 2.4 GHz ISM or the 5 GHz UNII bands The channel width is smaller than DSSS or HR/DSSS The width of an OFDM channel is only 20 MHz compared to 22 MHz for DSSS

REFERENCES CCRI Engineering and Technology Jbernardini 29 Orthogonal Frequency Division Multiplexing (OFDM) CCRI Engineering and Technology Jbernardini 29 OFDM operates in either the 2.4 GHz ISM or the 5 GHz UNII bands The width of an OFDM channel is only 20 MHz compared to 22 MHz for DSSS or HR/DSSS

REFERENCES CCRI Engineering and Technology Jbernardini 30 Multiple Input/Multiple Output (MIMO) Channels CCRI Engineering and Technology Jbernardini 30 MIMO networks can operate in both the 2.4 GHz ISM and 5 GHz UNII bands Capable of either 20 or 40 MHz–wide channels Wider channels mean more data can be transmitted over the RF medium simultaneously In the 2.4 GHz ISM band, there is only one 40 MHz– wide channel without any adjacent-channel overlap

REFERENCES CCRI Engineering and Technology Jbernardini 31 Multiple Input/Multiple Output (MIMO) CCRI Engineering and Technology Jbernardini 31 Used by IEEE n devices Wider channels mean more data can be transmitted over the RF medium simultaneously In the 2.4 GHz ISM band, there is only one 40 MHz–wide channel without any adjacent- channel overlap

REFERENCES CCRI Engineering and Technology Jbernardini 32 MIMO Throughput and Features CCRI Engineering and Technology Jbernardini 32 Allows for data rates up to 600 Mbps Current data rates up to 450 Mbps More throughput, reliable, predictable Lower latency for mobile communications More consistent coverage and throughput for mobile applications MIMO networks can operate in both the 2.4 GHz ISM and 5 GHz UNII bands Capable of either 20 MHz or 40 MHz–wide channels

REFERENCES CCRI Engineering and Technology Jbernardini 33 IEEE n Features CCRI Engineering and Technology Jbernardini 33 Uses three modes of OFDM – 20MHz and 40 MHz bands – Data rates up to 600 Mbps Non-HT mode – OFDM – Backward compatibility to a, b, g HT mixed mode – Supports OFDM and ERP-OFDM Greenfield mode – Only ERP-OFDM – Highest data rates Channel Bonding

REFERENCES CCRI Engineering and Technology Jbernardini 34 Co-Location WLAN systems CCRI Engineering and Technology Jbernardini 34 Co-location of IEEE b HR/DSSS and IEEE a/g/n OFDM Systems

REFERENCES CCRI Engineering and Technology Jbernardini 35 Co-Location WLAN systems CCRI Engineering and Technology Jbernardini 35 Adjacent-channel and Co-channel Interference – Adjacent-channel and co-channel interference WLAN/WPAN Coexistence – IEEE wireless LANs can be affected when co- located with WPAN devices

REFERENCES CCRI Engineering and Technology Jbernardini 36 Encoding and Modulation CCRI Engineering and Technology Jbernardini 36 Encoding - To change or translate one bit stream into another. Modulation – Appling information on a carrier signal by varying one or more of the signal's basic characteristics - frequency, amplitude and phase. DBPSK (Differential Binary Phase Shift Keying) DQPSK (Differential Quaternary PSK)

REFERENCES CCRI Engineering and Technology Jbernardini 37 Modulation CCRI Engineering and Technology Jbernardini 37 Carrier signal is a continuous electrical signal – Carries no information Three types of modulations enable carrier signals to carry information – Height of signal – Frequency of signal – Relative starting point Modulation can be done on analog or digital transmissions

REFERENCES CCRI Engineering and Technology Jbernardini 38 Analog vs. Digital Transmissions CCRI Engineering and Technology Jbernardini 38 Analog Signal = A signal that has continuously varying voltages, frequencies, or phases. All amplitude values are present from minimum to maximum signal levels. Digital Signal = A signal in which information is carried in a limited number of different discrete states or levels; High/Low, One/Zero, 1/0

REFERENCES CCRI Engineering and Technology Jbernardini 39 Analog and Digital Modulation CCRI Engineering and Technology Jbernardini 39 Analog Transmission use analog carrier signals and analog modulation. Digital Transmission use analog carrier signals and digital modulation. Modem (MOdulator/DEModulator): Used when digital signals must be transmitted over analog medium – On originating end, converts distinct digital signals into continuous analog signal for transmission – On receiving end, reverse process performed WLANs use digital modulation of analog signals (carrier signal)

REFERENCES CCRI Engineering and Technology Jbernardini 40 Frequency and Period CCRI Engineering and Technology Jbernardini 40

REFERENCES CCRI Engineering and Technology Jbernardini 41 Analog Modulation CCRI Engineering and Technology Jbernardini 41 Amplitude: Height of carrier wave Amplitude modulation (AM): Changes amplitude so that highest peaks of carrier wave represent 1 bit while lower waves represent 0 bit Frequency modulation (FM): Changes number of waves representing one cycle – Number of waves to represent 1 bit more than number of waves to represent 0 bit Phase modulation (PM): Changes starting point of cycle – When bits change from 1 to 0 bit or vice versa

REFERENCES CCRI Engineering and Technology Jbernardini 42 Analog Modulation CCRI Engineering and Technology Jbernardini 42 Amplitude modulation (AM) – Carrier frequency varies in amplitude Frequency modulation (FM) – Carrier frequency varies in frequency Phase modulation (PM) – Carrier varies in phase

REFERENCES CCRI Engineering and Technology Jbernardini 43 Digital Modulation CCRI Engineering and Technology Jbernardini 43 Advantages over analog modulation: – Better use of bandwidth – Requires less power – Better handling of interference from other signals – Error-correcting techniques more compatible with other digital systems Unlike analog modulation, changes occur in discrete steps using binary signals – Uses same three basic types of modulation as Amplitude shift keying (ASK)

REFERENCES CCRI Engineering and Technology Jbernardini 44 Frequency vs. Phase Shift Key Modulation CCRI Engineering and Technology Jbernardini 44 Frequency shift keying (FSK) Phase shift keying (PSK)

REFERENCES CCRI Engineering and Technology Jbernardini 45 Throughput vs. Data Rate CCRI Engineering and Technology Jbernardini 45 Data Rate = Total Data Rate through system Throughput = Data Payload Rate Data Rate = Data Payload Rate + Overhead Overhead = Coding + Modulation+ Bandwidth + Hardware + Software + Retransmission(errors) 5 Mbps Throughput11 Mbps Data Rate5 Mbps Throughput

REFERENCES CCRI Engineering and Technology Jbernardini 46 Analog vs. Digital Bandwidth CCRI Engineering and Technology Jbernardini 46 Analog Bandwidth – Frequency in Khz,Mhz (1 Mhz) Digital Bandwidth – bits per second (11 Mbps) Wireless Bandwidth – Frequency Space made available to network devices (22 Mhz) Frequency Amplitude Bandwidth Digital Bandwidth (Average Bit Rate)

REFERENCES CCRI Engineering and Technology Jbernardini 47 Quadrature phase shift keying (QPSK) CCRI Engineering and Technology Jbernardini 47

REFERENCES CCRI Engineering and Technology Jbernardini QAM Modulation CCRI Engineering and Technology Jbernardini 48

REFERENCES CCRI Engineering and Technology Jbernardini QAM - 64-level Quadrature Amplitude Modulation CCRI Engineering and Technology Jbernardini 49

REFERENCES CCRI Engineering and Technology Jbernardini 50 Spread Spectrum Comparisons CCRI Engineering and Technology Jbernardini 50 PHYData RatesFrequency Band StandardsMax Colocated WLANs Max Total Service Area Data Rate FHSS1 or 2 Mbps2.4 GHz ISMIEEE max, 12 practical 24 Mbps practical DSSS1 or 2 Mbps2.4 GHz ISMIEEE or 36 Mbps HR/ DSSS 1, 2, 5.5, or 11 Mbps 2.4 GHz ISMIEEE802.11b Mbps ERP1-54 Mbps2.4 GHz ISMIEEE g Mbps OFDM6-54 Mbps5 GHz U-NIIIEEE a Mbps

REFERENCES CCRI Engineering and Technology Jbernardini 51 Data Rates and Throughput Estimates CCRI Engineering and Technology Jbernardini 51 PHYStandardsData RateThroughput FHSSIEEE –2 Mbps0.7–1 Mbps DSSSIEEE –2 Mbps0.7–1 Mbps HR/DSSSIEEE b-19991, 2, 5.5, and 11 Mbps3–6 Mbps ERPIEEE g-20031, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48, 54 Mbps 3–29 Mbps OFDMIEEE a-19996, 9, 12, 18, 24, 36, 48, 54 Mbps3–29 Mbps HTIEEE n-20091–600 Mbps (with 4 spatial streams) ~ 100 Mbps

REFERENCES CCRI Engineering and Technology Jbernardini 52 Review CCRI Engineering and Technology Jbernardini 52 Access methods WLANs have no way of detecting collisions, so they use CSMA/CA Wireless LANs use half-duplex communication Physical Layer Specifications DSSS and HR/DSSS channels OFDM MIMO WLAN Co-location