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Introduction to Wireless LAN Measurements From 802.11a to 802.11ac Introduction to Wireless LAN Measurements From 802.11a to 802.11ac 1 Visit www.ni.com/rf-academy Introduction to Wireless LAN Measurements From 802.11a to 802.11ac Table of Contents 1. History of Wireless LAN ....................................................................................................... 3 2. WLAN Physical Layer Characteristics ................................................................................ 5 Bands and Channels ...............................................................................................................................................5 Bandwidth Configurations .....................................................................................................................................5 Key WLAN Enabling Technologies ........................................................................................................................7 DSSS ......................................................................................................................................................................8 OFDM ....................................................................................................................................................................9 MIMO ..................................................................................................................................................................11 Theoretical Data Rate Calculation ........................................................................................................................16 Instrument Configuration for WLAN Measurements ........................................................................................20 3. Transmit Measurements ..................................................................................................... 22 Maximum Transmit Power ...................................................................................................................................22 Average Power .....................................................................................................................................................23 Peak Power ...........................................................................................................................................................23 Power Versus Time ..............................................................................................................................................24 Cross Power (MIMO) ..........................................................................................................................................25 Power-On and Power-Down Ramp ......................................................................................................................25 Modulation Quality ................................................................................................................................................25 Error Vector Magnitude .......................................................................................................................................26 Spectrum Measurements .......................................................................................................................................30 Spectrum Mask ....................................................................................................................................................30 DSSS Spectrum Mask ..........................................................................................................................................31 OFDM, HT, and VHT Spectrum Mask ................................................................................................................31 Carrier Suppression (DSSS) .................................................................................................................................33 Center Frequency Leakage (OFDM, HT and VHT) ............................................................................................34 4. Receiver Measurements ....................................................................................................... 37 Minimum Input Sensitivity ..................................................................................................................................37 Maximum Input Level .........................................................................................................................................38 Adjacent Channel Rejection .................................................................................................................................39 Nonadjacent Channel Rejection ...........................................................................................................................41 Received Channel Power Indicator ......................................................................................................................42 2 Visit www.ni.com/rf-academy Introduction to Wireless LAN Measurements From 802.11a to 802.11ac 1. History of Wireless LAN A basic Wireless Local Area Network (WLAN) network design uses the idea of an access point and clients. The access point or router is the equivalent of a base station in a cellular network. It acts as a bridge between the wired backbone and the wireless client traffic. Examples of client devices include desktops, laptops, smart phones, game consoles and printers. In 1997, the IEEE 802.11 Working Group approved IEEE 802.11 as the world’s first WLAN standard, which supported data rates of 1 Mb/s and 2 Mb/s. In 1999, two important amendments to the original 802.11 standard were ratified. • IEEE 802.11a-1999, known as 802.11a, allowed data rates of up to 54 Mb/s in the 5 GHz band using OFDM technology. • IEEE 802.11b-1999, known as 802.11b, allowed for up to 11 Mb/s in the 2.4 GHz unlicensed band by extending the use of direct sequence spread spectrum (DSSS) technology. 802.11a was the basis for the 802.11g amendment released in 2003, which used an identical orthogonal frequency division multiplexing (OFDM) physical layer structure but in the 2.4 GHz band. The need for 802.11g was driven by the slow adoption of 802.11a in the 5 GHz band, which contained limited channels for commercial use. The Wi-Fi Alliance (WFA), a consortium of industry-leading companies, was formed in 1999 to facilitate better interoperability, quality, and user experience for IEEE 802.11 devices from a broad range of vendors. Manufacturers of such devices can pursue the Wi-Fi certification with the alliance, which allows them to use the Wi-Fi logo, shown in Figure 1.1, on WLAN devices. Figure 1.1. Wi-Fi Logo Since the late 1990s, the IEEE 802.11 family of standards has continued to evolve to serve consumers with increasingly higher data rates. IEEE 802.11n was officially released in 2009, though products based on the draft specification were available as early as 2006. This standard marked a substantial data rate increase over the existing 802.11a, b, and g amendments. IEEE 802.11n allowed for wider channel bandwidths (40 MHz versus 20 MHz) and was the first WLAN standard to use multiple antennas for data streams: up to 4x4 multiple input, multiple output (MIMO). As a result, 802.11n increased the theoretical data throughput from 54 Mb/s to 300 Mb/s in a 20 MHz channel, and 600 Mb/s in a 40 MHz channel. In January 2012, a finalized 802.11ac draft amendment was released, outlining substantial improvements in data rates over 802.11n. The 802.11ac amendment provides a maximum theoretical data throughput of 6.93 Gb/s using channel bandwidths of up to 160 MHz, higher order modulation schemes, such as 256-QAM, and MIMO configurations of up to 8x8. Table 1.1 illustrates a brief summary of the evolution of the 802.11 standard. 3 Visit www.ni.com/rf-academy Introduction to Wireless LAN Measurements From 802.11a to 802.11ac Year Amendment Throughput1 Purpose 1997 802.11 2 Mb/s Original release. Included 1 Mb/s and 2Mb/s data rates in the 2.4GHz ISM band based on a physical layer (PHY). 1999 802.11a 54 Mb/s Added an OFDM-based PHY in the 5 GHz band. 1999 802.11b 11 Mb/s Extended the DSSS PHY from the original standard in the ISM band to a maximum of 11 Mb/s. 2003 802.11g 54 Mb/s Implemented the ODFM-based PHY (up to 54 Mb/s) introduced in 802.11a in the 2.4GHz ISM band. 2007 802.11-2007 Consolidated the 802.11 amendments with the base standard. 2009 802.11n 600 Mb/s Added MIMO options in both 2.4GHz and 5GHz bands. The maximum data rate can range from 54 Mb/s (mandatory) to 600 Mb/s (optional). 2012 802.11-2012 Consolidated the 802.11 amendments with the base standard. TBD 802.11ac 6.93 Gb/s Extended the HT (802.11n) specification in the 5GHz band to offer increased throughput through wider channel bandwidths, higher density modulation, and additional MIMO streams. Using an aggregate of stations, in conjunction with optional specifications, a theoretical throughput of 6.77 Gb/s is achievable. TDB 802.11ad 7 Gb/s A new standard to offer incredibly high theoretical throughput (7 Gb/s) in a 60 GHz band. Table 1.1 History of WLAN Standard Introduction 802.11 Naming Conventions Although engineers have long referred to the specific IEEE 802.11 amendments such as 802.11a,b, g, n, and ac to identify the specific technology they were using, the 2012 revision of the 802.11 specifications established specific naming criteria for each amendment. Table 1.2 lists the alternate name for each
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