Planning wi-fi systems in buildings

Photo © BigStockPhoto/Michel Aubry

By Bob Chomycz, P.Eng.
Wi-Fi is a popular communication medium used for wirelessly connecting computers, laptops, smart phones, and surveillance cameras to the Internet or a local area network (LAN). In order to provide ubiquitous and reliable Wi-Fi coverage in a given area, proper planning of access points (AP) deployed throughout a building is essential. The AP is the gateway device connecting wireless Wi-Fi devices to the building’s wired data and Internet network. Poorly planned deployment within buildings can result in significant problems including spotty coverage, unreliable communication, and security risks.

In 1999, the Institute of Electrical and Electronics Engineers (IEEE) introduced the first Wi-Fi standards to provide manufacturers with the necessary details to build interoperable equipment. These are:

  • IEEE 802.11a, Wireless LAN Medium Access Control and Physical Layer Specifications High-speed Physical Layer in the 5 GHz Band; and
  • IEEE 802.11b, Wireless LAN Medium Access Control and Physical Layer Specifications: Higher-Speed Physical Layer Extension in the 2.4 GHz Band.

IEEE 802.11b allows for a transmission rate of up to 11 Mbps—a realistic maximum data throughput
6 Mbps—in the 2.4-GHz frequency band. IEEE 802.11a allows for transmission rate of up to 54 Mbps—a realistic maximum data throughput 24 Mbps—in the 5-GHz frequency band. Both standards are commonly used today, even though the transmission speed is slow compared to the current IEEE 802.11ac, Wireless LAN Medium Access Control and Physical Layer Specifications Amendment 4: Enhancements for Very High Throughput for Operation in Bands Below 6 GHz.

In 2003, IEEE 802.11g, Wireless LAN Medium Access Control and Physical Layer Specifications Amendment 4: Further Higher Data Rate Extension in the 2.4 GHz Band, was introduced and provides up to 54 Mbps transmission in the 2.4-GHz band. This allows for faster communications in 2.4-GHz band than IEEE 802.11b, and better range than communications in the 5 GHz band. A further improvement in transmission rate standard was released in 2009 with IEEE 802.11n, Wireless LAN Medium Access Control and Physical Layer Specifications Amendment 5: Enhancements for Higher Throughput, providing up to 144 Mbps rates in the 2.4-MHz band or 450 Mbps in the 5-GHz band.

The latest standard is IEEE 802.11ac, which provides for a transmission rate up to 6.77 Gbps. Current commercially available IEEE 802.11ac equipment transmission rate is 1.3 Gbps—a realistic maximum data throughput 910 Mbps. These rates are maximum transmission rates for one Wi-Fi mobile device communicating with an AP radio. If more than one mobile device is communicating with an access point, then the AP shares the channel with all mobile devices and the data throughput is divided among the mobile devices. Consequently, each device has a much lower data throughput.

Access point
The AP is a data radio transceiver permanently and securely mounted high up on room ceilings, walls, and other building structures. It converts wireless signals from one or many Wi-Fi mobile devices operating in the 2.4-GHz and/or 5-GHz radio frequency (RF) bands to electrical data signals. It then funnels these electrical data signals into an Ethernet cable, which is connected to a LAN or Internet router. This allows Wi-Fi mobile devices to connect to the Internet, or to other LAN computers or servers.

WiFi_ap_collection r1
This shows typical access points (AP) for Wi-Fi connections allowing Wi-Fi mobile devices to connect to the Internet, or to other local area network (LAN) computers or servers. Images courtesy Telecom Engineering Inc.

The AP can be a small, standalone device—typically about 180 mm (7 in.) in diameter—or it can be integrated into a router. Often for residential applications, the AP with the integrated router is used for simplifying Internet deployment. For commercial applications, one or more standalone APs are located throughout a facility to provide wireless coverage for mobile devices.

Wi-Fi communication is also used in industrial applications to communicate with mobile devices. However, it should be noted Wi-Fi uses half-duplex communication (i.e. only one device transmits at any one time), therefore quality of services (QoS) and data latency can suffer due to contention for the wireless channel from multiple devices or interference. If a high level of QoS and low latency is important to an application, then an Ethernet or fibre-optic cable is considered instead of Wi-Fi.

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