all_PPT_ch07.pdf

Guide to Wireless Communications, Fourth Edition Chapter 7 Enhancing WLAN Performance  Objectives After completing this chapter, you will be able to: Explain how IEEE 802.11g enhances 802.11b networks Outline how IEEE 802.11a works and how...

Guide to Wireless Communications, Fourth Edition Chapter 7 Enhancing WLAN Performance  Objectives After completing this chapter, you will be able to: Explain how IEEE 802.11g enhances 802.11b networks Outline how IEEE 802.11a works and how it differs from 802.11 networks Discuss IEEE 802.11n and how it functions in both 2.4 GHz and 5 GHz bands Describe the 802.11ac and 802.11ad amendments List other important current and future amendments to 802.11 Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 2  IEEE 802.11g Main drivers for development of 802.11g: – Demand for higher Internet access speeds – Significantly higher throughput of wired networks Operates in the same frequency band as 802.11b – But supports data rates of 6, 9, 12, 18, 24, 36, and 54 Mbps in additions to 802.11b rates 802.11g amendment is called Extended Rate PHY (ERP) Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 3  802.11g PHY Layer Orthogonal Frequency Division Multiplexing (OFDM) – Splits a high-speed digital signal into several slower signals running in parallel – Sends the transmission in parallel across several lower-speed, narrower frequency channels OFDM uses 48 of the 52 subchannels for data – Extra four are used to monitor the strength and quality of the RF signal Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 4  802.11g PHY Layer Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 5  802.11g PHY Layer Multipath distortion – Receiving device gets the signal from several different directions at different times Must wait until all reflections are received OFDM avoids problems caused by multipath distortion by sending the bits slowly enough that any delayed copies are late by a much smaller amount of time Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 6  802.11g PHY Layer Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 7  Transmission Modes Mandatory transmission modes – Same mode used by 802.11b and must support the rates of 1, 2, 5.5, and 11 Mbps – Uses OFDM mode and supports 802.11g only Optional transmission modes – PBCC (Packet Binary Convolutional Coding) and can transmit at 22 or 33 Mbps – DSSS-OFDM, which uses the standard DSSS preamble of 802.11b Transmits the data portion of the frame using OFDM Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 8  Transmission Modes Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 9  Transmission Modes Signal timing differences – When device transmits at a higher rate than 802.11b A 6-microsecond quiet time of no transmission is added – At the end of the data portion of every frame – Short interframe space (SIFS) timing Affected by the addition of the quiet time Overall performance is lower than that of 802.11a due to the added ‘quiet time’ when 802.11b devices are present An all-80211.g network does not require the quiet time Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 10  Transmission Modes PLCP frame formats used in 802.11g are the same as for 802.11b Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 11  802.11g MAC Layer The 802.11g amendment includes a change to the MAC layer for compatible devices – To slightly increase performance by transmitting the entire PLCP frame using OFDM – While still preventing collisions To accomplish: – A CTS-to-Self frame is transmitted with destination MAC address of the transmitting station – Purpose is to act as a protection mechanism notifying legacy devices to not attempt to “understand” or transmit during frame exchange Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 12  IEEE 802.11a 802.11a standard maintains the same medium access control (MAC) layer functions as 802.11g WLANs – Differences are confined to the physical layer 802.11a achieves its increase in speed and flexibility over 802.11b through: – Use of OFDM – A more efficient error-correction scheme Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 13  U-NII Frequency Band IEEE 802.11a uses the Unlicensed National Information Infrastructure (U-NII) band – Intended for devices that provide short-range, high- speed wireless digital communications U-NII spectrum is segmented into four bands – Each band has a maximum power limit Total bandwidth available for IEEE 802.11a WLANs using U-NII is almost seven times that which is available for 802.11b Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 14  U-NII Frequency Band Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 15  Channel Allocation in 802.11a Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 16  Channel Allocation in 802.11a Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 17  Channel Allocation in 802.11a Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 18  802.11a PHY Layer Modulation techniques – At 6 Mbps, phase shift keying (PSK) – At 12 Mbps, quadrature phase shift keying (QPSK) – At 24 Mbps, 16-level quadrature amplitude modulation (16-QAM) – At 54 Mbps, 64-level quadrature amplitude modulation (64-QAM) Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 19  802.11a PHY Layer Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 20  802.11a PHY Layer Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 21  802.11a PHY Layer Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 22  802.11a PHY Layer Hardware designers cannot increase the complexity of the modulation on the subcarriers beyond the maximum 54 Mbps rate The IEEE made only minor changes to the PCLP frame format in 802.11a Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 23  Error Correction in 802.11a/g IEEE 802.11g and 802.11a handle errors differently than 802.11b Because transmissions are sent over parallel subcarriers – Radio interference from outside sources is minimized Forward Error Correction (FEC) transmits extra bits per byte of data – Eliminates the need to retransmit if an error occurs, which saves time, increases throughput Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 24  IEEE 802.11n The 802.11n amendment is called high throughput (HT) – Ratified end of 2009 802.11n uses multiple antennas along multiple radios in each device – Allows it to take advantage of multipath interference to increase the SNR – Results in an increase in range and reliability Works in 2.4 and 5 GHz bands; backward compatible with 802.11a Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 25  MIMO and Beamforming Based on using multiple radios and antennas – Prior to 802.11n, two antennas were used for antenna diversity – antenna with the strongest signal is used 802.11n MIMO devices employ beamforming to direct transmissions to the device from which a frame was received 802.11n MIMO also uses spatial multiplexing - frames are broken up and sent in multiple parts from different radios Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 26  MIMO and Beamforming Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 27  MIMO and Beamforming 802.11n specifies radio configurations using multiple transmitters and receivers called radio chains – Using up to four transmitters and four receivers – Max transmission speed of 600 Mbps – Configurations such as 2x3 (2 transmitters and 3 receivers) and 3x3 (3 of each) exist Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 28  MIMO and Beamforming Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 29  MIMO and Beamforming Spatial multiplexing and beamforming can be combined to increase both the range and reliability of transmission – Both rely on feedback information from the receiver Information about spatial multiplexing capabilities is usually advertised by devices during association with the WLAN Beamforming capability can be learned by the devices monitoring the pilot carriers – Or by an exchange of information using sounding frames Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 30  Channel Configuration 802.11n – Uses more bandwidth than other standards Can use 20 or 22 MHz to communicate with 802.11b or 802.11g devices Uses 40 MHz for high throughput (HT); 300 to 600 Mbps – Support DSSS and OFDM – 802.11n supports channel bonding – two channels are combined into on 40 MHz channel Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 31  Channel Configuration Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 32  Channel Configuration Guard Interval – In non-HT transmissions, delay is required at the end of each frame to allow reflected signals to arrive The delay is called the guard interval Prevents intersymbol interference (ISI) Modulation and Coding Sets – 802.11n uses a combination of nine different factors define the data rates – There are eight mandatory MCSs supporting data rates of up to 72.2 Mbps Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 33  Channel Configuration HT PHY Layer – Supports three frame formats 1 – when communicating with 802.11a/g devices 2 – when used in mixed HT and legacy devices 3 – 802.11n only (greenfield mode) – Not compatible with non-HT devices – Most efficient way to communicate with other HT devices – Also not possible when there are legacy devices either present or within range of the WLAN Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 34  Channel Configuration HT MAC Sublayer – Enhancements to increase throughput and power management Frame aggregation – combines multiple MAC frames into one PHY frame to reduce overhead Two new power management methods – Spatial multiplexing power save mode (SMPS) » A MIMO device can shut down all but one of its radios – Power save multi-poll (PSMP) » Devices can turn off all but one radio Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 35  Channel Configuration Reduced Interframe Space (RIFS) – Allowed only in greenfield mode A shorter 2-microsecond interframe space can be used instead of a SIFS at the end of each transmitted frame Less timing overhead (normal SIFS interval is 10 microseconds) Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 36  Channel Configuration HT Operation Modes – Allows 802.11n to coexist with non-HT devices – Mode 0 – greenfield mode, supports only HT- capable devices using 20 or 40 MHz channels – Mode 1 – an HT mode but prevents interference from non-HT devices by using protection mechanisms – Mode 2 – supports either 20 or 40 MHz channels – Mode 3 – non-HT mixed mode; supports devices at 20 or 40 MHz Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 37  IEEE 802.11ac In 802.11ac – Transmissions are limited to the 5 GHz band – Offers more bandwidth and uses even wider channels with more subcarriers to transmit more data than 802.11n Increased data rates possible through the use of 80 and 160 MHz channels – Includes 80 MHz channels divided into 242 subcarriers with 8 pilot subcarriers – A 160 MHz channel is divided into 484 subcarriers with 16 pilot subcarriers Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 38  IEEE 802.11ac Data rates are increased from 433 Mbps to around 6.9 Gbps 802.11ac is named very high throughput (VHT) – Can use between two and eight radios to transmit a maximum of eight spatial streams per AP If all eight radios are present in AP, but all are not being used to communicate with a single device – Additional spatial streams can be used to communicate with multiple client devices – Feature is called multi-user MIMO (MU-MIMO) Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 39  IEEE 802.11ac Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 40  IEEE 802.11ad 802.11ad amendment – Spawned by the Wireless Gigabit (WiGig) Alliance specification – Goal was to expand the 802.11 standard to work in the 60 GHz portion of the ISM band – Has a limited range of an average of about 6 feet Maximum range is about 33 feet but would require few obstructions or other energy-absorbing items Advantage of the 60 GHz band – Has approximately 2 GHz of spectrum available – Can support very wide channels Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 41  IEEE 802.11e Approved for publication in November 2005 Defines enhancements to the MAC layer of 802.11 – To expand support for LAN applications that require Quality of Service (QoS) 802.11e allows the receiving device to acknowledge after receiving a burst of frames Enables prioritization of frames in distributed coordinated function (DCF) mode Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 42  IEEE 802.11e Figure 7-16 802.11e frame acknowledgement Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 43  IEEE 802.11e Implements two new coordination functions – Enhanced DCF (EDCF) Station with higher priority traffic waits less to transmit – Hybrid coordination function (HCF) Combination of DCF and point coordination function (PCF) Supports traffic prioritization based on QoS (quality-of-service); improves security features for mobile and nomadic users A nomadic user moves frequently but does not use the equipment while in motion Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 44  IEEE 802.11r Amount of time required by 802.11 devices to associate and disassociate – It is in the order of hundreds of milliseconds Support voice over WLAN (VoWLAN) in a business environment with multiple access points – 802.11 standard needs a way to provide quicker handoffs 802.11 MAC protocol – Does not allow a device to find out if the necessary QoS resources are available at a new AP Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 45  IEEE 802.11r 802.11r is designed to resolve these issues – In addition to security concerns regarding the handoff 802.11r is designed to enhance the convergence of wireless voice, data, and video Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 46  IEEE 802.11s Imagine you had to: – Deploy a wireless network over the entire downtown area of a medium-sized city – Provide seamless connectivity to all city employees Ideal solution – Connect the wireless APs to each other over the wireless communications channels 802.11s provides the solution – wireless mesh network Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 47  IEEE 802.11s Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 48  Other Amendments and Amendments Currently Under Development 802.11af – Uses the recently released analog over-the-air television frequency spectrum to transmit at sub-1 GHz frequency At lower data rates but at greater distances 802.11ah – Developing a standard for wireless communications in other sub-1 GHz frequency bands to support Internet connectivity for low-duty-cycle devices Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 49  Other Amendments and Amendments Currently Under Development 802.11ax – An enhancement that will enable simultaneous communication with multiple devices (multiple access) within a single OFDM transmission – Under development 802.11ay – An improvement of 802.11ad – Expected to enable 60 GHz transmissions at 20 to 40 Gbps at distances between 300 and 500 meters – Expected to be completed in 2017 Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 50  Summary IEEE 802.11g provided significant improvement in performance over 802.11b and sparked an expansion in WLANs IEEE 802.11a networks use the Unlicensed National Information Infrastructure (U-NII) band The 802.11n amendment increases the data rate up to 450 Mbps using either the 2.4 GHz ISM or the 5 GHz U-NII band The 802.11ac amendment boosts the speed of WLANs up to nearly 7 Gbps Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 51  Summary The IEEE 802.11ad amendment works in the 60 GHz portion of the ISM band and supports data rates of 7+ Gbps 802.11e standard adds QoS to 802.11 standards The 802.11r amendment enables fast roaming and reduces the time required for a device to associate with a new AP The 802.11s amendment enables APs to communicate and pass traffic from one to the other Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 52  Summary The IEEE continues to work on further enhancements to the 802.11 standard – One of them is 802.11ax, which will allow independent communications with multiple devices within a single frame transmission Guide to Wireless Communications, Fourth Edition © Cengage Learning 2017 53