These days, every home and office uses a plethora of electronic devices that employ some form of wireless data communications, for example mobile
and cordless phones, wireless mouse and keyboard, etc.
Wireless data communications permits computers and other computer-controlled devices (after all, your mobile phone is nothing more than a special type of computer) to communicate with each other and/or with their associated networks without the need for interconnecting cables.
For example, wireless modems are used by internet service providers (ISPs) as a low cost means of linking customers to their servers.
These links often span several kilometres. As another example, Bluetooth is a form of data communications commonly used with suitably enabled mobile phones (often called smartphones). Functionality includes taking and sending video and still pictures, email connectivity, downloading and playing music and even web browsing.
Of interest for this article are computer networks that employ wireless communications for LAN connectivity, and in particular by making use of a technology known as WiFi.
WiFi permits WiFi-enabled devices such as personal computers, gaming consoles and smartphones to communicate over a LAN fitted with WiFi access points without the use of interconnecting cables.
Clearly, all WiFi enabled devices must be compatible in order for the system to work. The WiFi standards that ensure this interoperability were originally developed by members of an organisation known as the WiFi Alliance (WFA).
The WFA is an association of electronics manufacturers whose aim is to promote the use of WiFi technology. One of their functions is to certify devices that conform to their standards of interoperability, and devices that have this certification are tagged with the WFA logo, which is a registered trademark.
Today, the WFA has over 500 member companies worldwide.
However, WiFi technology is based on the US IEEE 802.11 series of standards, and the fact that a particular device is not certified by the WFA does not necessarily mean that it is not compatible.
The IEEE 802.11 series sets the rules for wireless LAN (WLAN) communications.
The first IEEE 802.11 standard was released back in 1997. IEEE 802.11a was the first widely accepted version (1999), and it was soon followed by
802.11b (1999), ‘g’ (2003), ‘n’ (2009) and now ‘ac’ (2012). These performance enhancing variants off ered improvements in speed, range and encryption technology.
WLANs in use today mainly use 802.11g and 802.11n, and I discuss the salient features of these in detail below.
THE NATURE OF WIFI
WiFi uses half duplex transmission. This means that at any particular moment, a WiFi device can either receive or transmit, but not do both.
All WiFi communications have to go through a wireless access point or WiFi hub. The WiFi hub is connected to the cabled part of the LAN by a normal, wired network connection. It serves as the interface between the wireless and the wired LAN devices. All wireless traffi c must pass through
a WiFi hub. Direct wireless device-to-device communications is not permitted.
WiFi technology makes use of the 2.4, 3.6, 5.8 and (in the future) the 60HGz bands in the microwave part of the RF spectrum.
Signal bandwidth for current generation WiFi technology is up to 40MHz. This will increase with the proposed higher speed 60GHz versions.
WiFi technology is intended to be short range, with typical maximum access point to indoor device range being around 35m. This relatively short range limit was set on purpose, so that adjacent WLANs can co-exist without undue mutual interference.
To restrict transmissions to this short range, low power transmitters and inefficient antennas are employed on the RF interfaces, with transmit lower being a low 0.1W. Compare this with the typical GSM phone running in the 1.8GHz band – it has a maximum transmit power of 1.0W.
The WiFi spectrum allocations are often shared with other low power wireless technology devices in the same premises (e.g. DECT cordless phones, wireless keyboardand mouse). Mutual interference is a fairly common problem. In addition, microwave ovens operate at very high power levels at
2.4GHz and can cause interference, despite being well shielded.
The nature of microwave signals is such that they are severely attenuated when passing through solid obstructions such as brick walls. In addition, metal objects reflect microwave signals. This can cause multipath interference at the receiver.
Consequently, ensuring adequate signal strength at each WiFi node and eliminating sources of interference can be a major issue when setting up a WLAN.
For a typical domestic application, particularly where the coverage area is restricted to single level premises, a single wireless hub will usually provide adequate coverage. For larger sites, ensuring satisfactory connectivity everywhere is not so straightforward. The easiest solution is to use two or more WiFi hubs, suitably spread over the intended coverage area. Judicious use of directional antennas can also help.
The fixed networking interconnections are done using Category 5e LAN cable, with each hub connected with a normal wired LAN connection back a network router.
For commercial applications, coverage oflarge areas in a multi-storey environment is often required. In such applications, the WLAN will contain many networked WiFi hubs.
In shopping centres, airports, university campuses, etc, WLAN services are often provided free as a courtesy to potential clients or simply to facilitate LAN and/or internet access for staff. Sites where free WiFi internet access is available are commonly known as WiFi hotspots.
The nature of the RF environment in such locations can be quite hostile to WiFi. To ensure complete coverage, many WiFi hubs are usually required.
The very first WiFi devices operated under 802.11 on the 2.4GHz band. They had woeful throughput by today’s standards, as well as interoperability problems. Link speed was limited to 1Mbps or 2Mbps (depending on version) under optimum conditions.
The first popularly accepted implementation of WiFi technology appeared in early 2000 using IEEE 802.11b on 2.4GHz, and providing 11Mbps link
speed. The actual throughput is much less than this due to error correction and other overheads.
This was followed by 802.11g in 2003, with a respectable 54Mbps theoretical maximum link speed. Again, actual throughput is realistically about half this.
In 2009, 802.11n made an appearance.
This offered twice the range and up to three times the link speed of 802.11g. In addition, it can work on both 2.4GHz and 5.8GHz. When running at 5.8GHz, it is far removed from (in terms of spectrum use) and relatively immune to the many sources of interference that plague 2.4GHz WiFi implementations.
The next jump in WLAN technology is to 802.11ac. The standard for this is currently still under development. It is designed to run only in the 5.8GHz band and purports a further large increase in throughput. Some product using this technology was already available back in 2012, even though the standard is still in draft form.
In the future, IEEE 802.ad promises to offer very high throughput (up to 7Gbps link speed), running in the 60GHz band. The IEEE workgroup for this standard first met in 2009 and target completion for the standard is sometime in 2014.
INTRODUCING SUPER WIFI
Super WiFi (also known as ‘white-fi’ for reasons that will become apparent) is a technology recently proposed in the US by the Federal Communications Commission (FCC – the authority charged with regulating RF spectrum in the US). The FCC wants to make available for WiFi and other similar low power applications narrow segments of unlicensed and presently unused RF spectrum in the UHF TV band.
These ‘white’ spectrum spaces presently act as guard bands between licensed sections of spectrum used by TV stations. They could, theoretically, be used for low power data communications without causing undue interference to existing spectrum users.
One idea is to develop a massive, nationwide, public access WiFi network using this spectrum space.
This would have major ramifications for anyone in the communications business as well as for users of communications services. It could imply, among other things, free phone calls via the internet and free internet access.
Clearly, the throughput would be limited and congestion in heavily populated areas is likely to be a problem, but for those people who cannot afford present day telco and ISP charges, such a free public WiFi network would represent a means of gaining access to communications facilities that were
previously beyond their means.
SUPER WIFI TECHNOLOGY
The IEEE has set up working group 802.11af to study and prepare a standard to implement this new WiFi technology. Because of the proposed frequency band (470 to 710MHz in the UHF band), it would be incompatible with all other existing and proposed WiFi technologies.
It does have some advantages however, when compared to existing WiFi. The lower frequency has much better obstacle penetration and signal propagation characteristics than the existing 2.4GHz and higher frequency band WiFi networks.
Even though the same output power is proposed in the new IEEE standard (0.1W), the use of lower frequencies would extend the reach well beyond the maximum 70m of current and proposed 802.11 WiFi technologies.
The proposed speeds for Super WiFi are something like 20Mbps downloads and 6Mbps uploads – hardly record breaking by today’s standards.
Notwithstanding this, the establishment of a free, public Super WiFi network, particularly in rural and regional areas could provide a boon to people who are otherwise unable to afford or do not have access broadband internet services.