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802.11ac Technology Introduction - Rohde & Schwarz

TechnologyIntroductionWhite PaperThis white paper provides a brieftechnology Introduction on the to the successful standard. providesmechanisms to increase throughput anduser experience of existing WLAN and willbuild on of Contents1MA192_7eRohde & Technology Introduction2 Table of Contents1 Introduction .. Core Documents .. Key .. to OFDMS ubcarriers .. Preamble fields in detail .. SIG-A .. SIG-B .. Data Field for Single User with BCC .. Transmitter Specification .. Spectral Flatness .. Center frequency and Symbol Clock Tolerance .. modulation Accuracy .. Center frequency Leakage .. Constellation Error .. Receiver Specification .. MinimumInput and Nonadjacent Channel MaximumInput Channel Assessment (CCA)..266 Abbreviations/Acronyms/Initialisms .. 27 IntroductionChannelization1MA192_7eRohde & Technology Introduction31 IntroductionIEEE is the IEEE working group developing Wireless Local Area Networkspecifications.

requirements. For example, the 11ac PHY is based on the well known OFDM (Orthogonal Frequency Division Multiplexing) PHY used for 11a and 11n and will maintain the same modulation, interleaving and coding architecture of 11n. However, some modifications and new 11ac features/parameters are necessary to meet 11ac™s goals.

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Transcription of 802.11ac Technology Introduction - Rohde & Schwarz

1 TechnologyIntroductionWhite PaperThis white paper provides a brieftechnology Introduction on the to the successful standard. providesmechanisms to increase throughput anduser experience of existing WLAN and willbuild on of Contents1MA192_7eRohde & Technology Introduction2 Table of Contents1 Introduction .. Core Documents .. Key .. to OFDMS ubcarriers .. Preamble fields in detail .. SIG-A .. SIG-B .. Data Field for Single User with BCC .. Transmitter Specification .. Spectral Flatness .. Center frequency and Symbol Clock Tolerance .. modulation Accuracy .. Center frequency Leakage .. Constellation Error .. Receiver Specification .. MinimumInput and Nonadjacent Channel MaximumInput Channel Assessment (CCA)..266 Abbreviations/Acronyms/Initialisms .. 27 IntroductionChannelization1MA192_7eRohde & Technology Introduction31 IntroductionIEEE is the IEEE working group developing Wireless Local Area Networkspecifications.

2 The group began work in the late 1990s and since then has createdseveral successful standards/amendments including , b and g. WLAN is nowubiquitous, with one or more of these WLAN technologies included as standardcapabilities on most laptops and many smartphones. The IEEE group hascontinued to build and improve on the earlier a/b and g with the official approval in 2009 and other enhancements such as , 11k, etc. An IEEES tandards in Communications and Networking article, "The IEEE Universe" [1]provides a very good overview of past and current projects. For more insightinto Technology and test solutions, please see application note WLAN :FromSISO to MIMO [2] and application note Measurement of WLAN acsignals [15].Late in 2008, two new task groups, TGad for the amendment and TGac forthe amendment, were started with the goal of significantly improving the datathroughput of so that performance of a wireless network can be equivalent to awired network.

3 Will use very wide bandwidths in the 60 GHz band will use frequencies in the 5 GHz. Both amendments are scheduled forcompletion at the end of Technology Introduction paper covers the (also known as VHT, VeryHigh Throughput) amendment and is divided into several main topics: documents, key requirements, and the PHY which is further brokeninto sections describing the channel structure, frame formats, preamble fields, and datafields. This is followed by a description of PHY layer test Core Documents TGac Usage Models R2 [4], approved during May 2010 working groupmeeting. This document contains 6 usage models that are expected to beused for 11ac . TGac Feature Requirements and Evaluation Methodology Document v16[5],approved during the January 2011 meeting: The main purpose is to definethe functional requirements that the amendment must meet.

4 TGac Channel Model Addendumv12 [6], approved during the March 2010meeting: This document defines the channel models that 11ac will use. Theyare primarily modifications to the channel models. These models areused in simulations (along with other parameters specified in the EvaluationMethodology Document) to show that inputs to the amendment meetthe feature requirements. Specification Framework Document, currently at v21 [7].ApprovedJanuary, 2011. Members of TGac have developed the higher levelrequirements in this document and it is used as the framework or outline ofthe Key RequirementsChannelization1MA192_7eRohde & Technology Introduction4 TGac Draft Amendment [16]. Draft version of the 11ac document contains the necessary changes to draft v9 to meetthe requirements. ( is the revision project of the standard. It incorporates all approved amendments since therelease of and fixes any ambiguities found since the release ofthese standards.)

5 These changes include a new clause for the PHYspecifications and modifications to the MAC specifications. Version was released August, 2011. The expected completion datefor the final amendment version is in early to mid Key RequirementsThe main requirements/goals for the amendment are (see [5]): Backwards Compatibility: 11ac shall provide backwards compatibility and devices operating in the 5 GHz band. This means that11ac must interwork with 11a and 11n and care is being taken in the 11ac todefine frame structures to accommodate the 11a and 11n devices. Coexistence: 11ac will provide mechanisms to ensure coexistence with 11aand 11n devices operating in the 5 GHz band. Single-STA (station) throughput:A station (a device compliant PHY and MAC) shall be capable of throughput greater than500 Mbps as measured at the MAC Service Access Point (SAP) while using nomore than an 80 MHz channel.

6 Multi-STA throughput(measured at the MAC SAP): The throughput when the11ac systemhas multiple stations shall be greater than 1 Gbps while using nomore than an 80 MHz will use the higher throughput and data rates to address several categoriesof usage models (see [4]) home distribution of HDTV and other upload/download of large files traffic (mesh, point to point, etc.) and floor automationIt is anticipated that the top three markets/usage models of very high throughputdevices shipping in 2012 will be: In roomgaming (category 1), Rapid sync-n-go filetransfer (category 3) and Projection to TV or projector in conference room(category 1). PHYC hannelization1MA192_7eRohde & Technology plans to re-use 11n (&11a) details where possible. This is advantageous forensuring backwards compatibility and co-existence and also allows the 11acdevelopers to focus on the new features that are needed to achieve the throughputrequirements.

7 For example, the 11ac PHY is based on the well known ofdm ( orthogonal frequency division multiplexing ) PHY used for 11a and 11n and willmaintain the same modulation , interleaving and coding architecture of 11n. However,some modifications and new 11ac features/parameters are necessary to meet 11ac (aka VHT, Very High Throughput) devices are required to support 20, 40,and 80 MHz channels and 1 spatial stream. Several optional features are also definedin : Wider channel bandwidths (80+80 MHz and 160 MHz) Higher modulation support (optional 256 QAM) 2 or more spatial streams (up to 8) MU-MIMO (Multi-User MIMO) 400 ns short guard interval STBC (Space Time Block Coding) LDPC (Low Density Parity Check)An 11ac device making use of only the mandatory parameters (80 MHz bandwidth, 1spatial stream, and 64 QAM 5/6) will be capable of a data rate of ~293 Mbps while adevice that implements all optional parameters (8 spatial streams and 256 QAM5/6with a short guard interval) will be able to achieve almost the OFDMPHY was introduced to , the channel bandwidth was 20 MHzwith later amendments adding support for 5 and 10 MHz bandwidths.

8 The added support for an optional 40 MHz channel. will includesupport for 80 MHz bandwidth as well as an optional 160 MHz bandwidth. The 11acdevice is required to support 20, 40, and 80 MHz channel bandwidth reception andtransmission. The 80 MHz channel will consist of two adjacent, non-overlapping 40 MHzchannels. The 160 MHz channels will be formed by two 80 MHz channels which maybe adjacent (contiguous) or non-contiguous. Channelization for 11ac (See [8]) provides a nice background of the 11ac channelallocation for the US (Figure 1) and for Europe and Japan (Figure 2). Since therelease of that contribution, the FCC has approved the use of channel 144 in the US.(See Annex E of [16].) Figure 1 reflects this additional 20 MHz channel and theresulting additional 40 MHz channel and 80 MHz channel for 11ac for US and for theglobal operating PHYC hannelization1MA192_7eRohde & Technology Introduction6 Figure 1: US and Global Operating Class Channel Allocation140136132128124120116112108104 1006460565248444036 IEEE channel #20 MHz40 MHz80 MHz5170 MHz5330 MHz5490 MHz5710 MHz160 MHzFigure 2: Europe and Japan Class Channel AllocationTo signal the VHT bandwidth and operating frequencies 4 fields are used: Current Channel Bandwidth: Provides the channel bandwidth and could be20 MHz, 40 MHz, 80 MHz, 160 MHz, and 80+80 MHz.

9 Current Channel Center frequency Index 1:oFor 20, 40, 80 or 160 MHz bandwidths, this provides the channelcenter frequencyoFor 80+80 MHz, this provides the center frequency of the primarysegment. Current Channel Center frequency Index 2:oFor 20, 40, 80 or 160 MHz bandwidths, this is 80+80 MHz, this provides the center frequency of the secondarysegment. Current Primary 20 MHz Channel: Provides the location of the primary 20 MHzchannel. All channel bandwidths will have a primary 20 MHz parameters are sent in the PLME MIB (Physical Layer Management EntityManagement Information Base) and are used along with thechannel startingfrequencygiven in the Country Information and Regulatory Classes Annex of standard [13] in the following equations to determine channel center frequencyand the frequency for the 20 MHz primary subchannel:Channel center frequency [MHz]=Channel starting frequency 5 * Current Channel Center frequency IndexPrimary 20 MHz channel center frequency [MHz] Channel starting frequency 5 * Current Primary 20 MHz PHYFromBandwidth to ofdm Subcarriers1MA192_7eRohde & Technology Introduction7A few examples (from[9]) will help to illustrate how these parameters work to providethe center frequency and bandwidth.

10 (Since a VHT STA operates in 5 GHz band, theexamples will assume a regulatory class that has a channel starting frequency = 5 GHz.)Example 1:A channel specified byCurrentChannelBandwidth= 80 MHzCurrentChannelCenterFrequencyIndex1= 42 CurrentPrimary20 MHzChannel= 36is an 80 MHz channel withChannel center frequency = 5 GHz + 5 * 42= 5210 MHzPrimary 20 MHz center freq=5 GHz + 5 * 36= 5180 MHzExample 2:A channel specified byCurrentChannelBandwidth= 80+80 MHzCurrentChannelCenterFrequencyIndex1=1 55 CurrentChannelCenterFrequencyIndex2= 106 CurrentPrimary20 MHzChannel= 161is an 80+80 MHz channel withChannel center freq (Primary)= 5 GHz + 5 * 155= 5775 MHzChannel center freq (Secondary)= 5 GHz + 5 * 106= 5530 MHzPrimary 20 MHz channel center freq= 5 GHz + 5 * 161= 5805 to ofdm uses ofdm ( orthogonal frequency division multiplexing ) just as do. (In fact 11ac reuses much of the existing (legacy) specifications modifying where necessary to achieve the 11ac goals.)


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