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Sponsored Contributed Article Using 802.11 in Industrial Applications By Jack Ganssle, Mouser Electronics The IEEE 802.11 wireless networking standard dates to 1997 and was rapidly adopted in homes and offices. It is eminently suitable for industrial environments as well, such as warehouses and factories. But those facilities are much more inhospitable to electronics and RF than a home. Ranges are greater as well. The IEEE 802.11 standard has evolved dramatically, and is now a collection of standards with downward compatibility. From the original 1 Mbit per second requirements it now (or, soon with a new version that is in draft form) will stream data at 7 Gbit per second. Frequencies are migrating to 60 GHz, which means antennas are much more complex and walls absorb much of the signal. This article will explore these issues and dig into problems engineers must face when outfitting an industrial plant with 802.11 wireless networks. For instance, multipath reception can completely null out a signal. Interference in an RF-rich environment can cut data rates Figure 1: Microchip’s SST11CP16 RF power amplifier (Courtesy substantially. And consider that of Microchip). much of 802.11 communication shares the same band as Bluetooth, and it is likely many employees carry a Bluetooth transmitter. Quality of service and security can both be major concerns. With careful forethought, an 802.11 network can reduce wiring and bring high-speed communications to any facility. In a factory, it is a bit harder to get it right. Setting the standard IEEE 802.11 is a set of standards for wireless data transmission that is in many cases replacing Ethernet and other wired networks. Though first deployed in home and office environments, it is increasingly used in hospitals, factories, and other industrial facilities. In the past most of the latter applications involved data logging and machine control, which require relatively low data rates. But data rates are going up, driven by machine vision, video surveillance, and other streaming services. The IEEE 802.11 standard provides for both “stations” – devices connected only to the wireless LAN (WLAN) such as a programmable logic controller transmitting logging data and “access points” that bridge the WLAN to another, typically wired, network (e.g., a Wi-Fi router). The standard permits wireless peer-to-peer communications as well. 802.11b/g/n are the most widely used variants, though 802.11ac (expected early in 2014) and 802.11ad (currently in draft form) are expected to become important since they support very high data rates and are compatible with the older, slower versions. 802.11ad will support transmissions up to 7 Gbit per second, but at that rate it operates at 60 GHz, which cannot penetrate walls. 802.11ac can operate up to 867 Mbit per second at 5 GHz, and 802.11b/g /n operates to 11, 54, and 150 Mbit per second respectively using the 2.4 and (802.11n) 5 GHz bands. None of these standards typically support a range greater than a hundred meters indoors. As the range and attenuation (often due to walls) increases, data rates drop off. As of this writing, 802.11ad is uncharacterized for range, but the free-space path loss is roughly proportional to the square of the frequency, so the jump to 60 GHz will have a significant negative impact. In big buildings like factories and warehouses, the only real solution will be to distribute more access points about the facility. At 60 GHz, antenna design becomes a significant issue. 802.11ad requires a phased array antenna so the routers can use beam forming to direct the signal towards a receiver. A training sequence is part of each transmission to insure that the array is properly phased so the beam is always directed properly, for example, to devices in motion. Peaceful coexistence The 2.4 GHz spectrum is designated for the industrial, scientific and medical (ISM) band. As such, electronics-rich facilities such as factories are likely to have many transmitters vying for a slice of that spectrum. Microwave ovens share the band, as do amateur radio operators, who may operate in a number of digital modes that can cause interference. Bluetooth, too, operates in this band, and though it is of low power (100 mW or less) it frequency hops 1600 times per second, and nearly every employee can be expected to have a Bluetooth transmitter in his or her cell phone. While in many cases the RF babble may be a problem, some vendors see an opportunity to provide products that bridge networks. For instance, Microchip’s SST12LF03 RF front-end module supports both 802.11b/g/n as well as Bluetooth in a single QFN-20 package. Similarly, Murata’s LBEE5ZSTNC-523 is a complete module that supports the IEEE 802.11b/g/n standards as well as Bluetooth. All of the IEEE 802.11 standards use a variety of spread spectrum approaches to share spectrum. They employ the carrier sense multiple access with collision avoidance (CSMA/ CD) protocol, wherein transmitting stations first listen for a clear channel, transmit, and then await an acknowledgement from the receiver. They generally employ much smaller packet sizes than those used by protocols on Ethernet, so retransmissions 10 Electronic Engineering Times Europe October 2013 www.electronics-eetimes.com


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