Wireless Interference Coverage Area Speed and Capacity
 


Although we use the term wireless network loosely, there are in fact three different types of network.

  • Wide area networks that the cellular carriers create,
  • Wireless local area networks, that you create, and
  • Personal area networks, that create themselves.

They all have a part to play in developing wireless solutions, separately or in various combinations. This article describes these different types of network, and explains where each can add value.

Wide Area Networks 

Wide Area Networks include the networks provided by the cell phone carriers such as Bell Mobility, Telus Mobility and Rogers Wireless. Originally providing cellular voice services, the carriers added data services as well, at first by overlaying digital data services on top of the early analogue voice services, and later by building out brand new generation voice-plus-data networks. Suffice it to say, wireless data services are available just about everywhere you can use a voice cell phone (Another article describes the types of service that are available).

The carriers determine where to provide coverage based on their business strategy, and they also control Quality of Service (QoS). If you are a very large, powerful organization, the carriers may add additional network resources in your corporate tower, especially if you buy a large number of cell phones from them.

Where would you use WANs? You would use WANs when reach is the most important aspect of your solution, and speed is less important. Reach is important if you are providing wireless solutions to the public at large, for example, or you want to give your employees wireless access to your corporate data, whether they are in the office, across town, out of town, or (in some cases) in other countries.

You can't get too far in your study of wireless without running into technical terms. Here are some to start with:

  • GSM/GPRS - the voice plus data network technology offered by Rogers Wireless, updated to EDGE in 2004
  • 1XRTT (usually called 1X) - the latest voice plus data network technology offered by Bell Mobility and Telus Mobility

Both of these networks are completely incompatible with one another.

Wireless Local Area Networks 

Wireless LANs are networks are set up to provide wireless connectivity within a finite coverage area. Typical coverage areas might be a hospital (for patient care systems), a university, the airport, or a gas plant. They usually have a well-known audience in mind, for example health care providers, students, or field maintenance staff. You would use WLANS when high data-transfer rate is the most important aspect of your solution, and reach is restricted. For example, in a hospital setting, you would require a high data rate to send patient X-rays wirelessly to a doctor, provided he is on the hospital premises.

Wireless LANS work in an unregulated part of the spectrum, so anyone can create their own wireless LAN, say in their home or office. In principle, you have complete control over where coverage is provided. In practice, coverage spills over into the street outside exposing you to a particular range of vulnerabilities. Deliberately seeking WLAN vulnerabilities is called wardriving. Our region has its share of wardrivers, and a later article will describe our adventures during an International Wardriving Day. 

Wireless LANs have their own share of terminology, including:

  • 802.11 - this is the network technology used in wireless LANs. In fact, it is a family of technologies such as 802.11a. 802.11b, etc., differing in speed and other attributes
  • WiFi - a common name for the early 802.11b standard.

In addition to creating your own private WLAN, some organizations (Starbucks) and some carriers (Telus Mobility) are providing high speed WLAN internet access to the public at certain locations. These locations are called hotspots, and for a price you can browse the internet at speeds about 20 times greater than you could get over your cell phone.

Personal Area Networks 

These are networks that provide wireless connectivity over distances of up to 10m or so. At first this seems ridiculously small, but this range allows a computer to be connected wirelessly to a nearby printer, or a cell phone's hands-free headset to be connected wirelessly to the cell phone. The most talked about (and most hyped) technology is called Bluetooth. 

Personal Area Networks are a bit different than WANs and WLANs in one important respect. In the WAN and WLAN cases, networks are set up first, which devices then use. In the Personal Area Network case, there is no independent pre-existing network. The participating devices establish an ad-hoc network when they are within range, and the network is dissolved when the devices pass out of range. If you ever use Infrared (IR) to exchange data between laptops, you will be doing something similar. This idea of wireless devices discovering each other is a very important one, and appears in many guises in the evolving wireless world.

PAN technologies add value to other wireless technologies, although they wouldn't be the primary driver for a wireless business solution. For example, a wireless LAN in a hospital may allow a doctor to see a patient's chart on a handheld device. If the doctor's handheld was also Bluetooth enabled, he could walk to within range of the nearest Bluetooth enabled printer and print the chart.

 


802.11 network standards

 

 
802.11 network standards
802.11
protocol
Release Freq.
(GHz)
Bandwidth
(MHz)
Data rate per stream
(Mbit/s)
Allowable
MIMO streams
Modulation Approximate indoor range Approximate outdoor range
(m) (ft) (m) (ft)
Jun 1997 2.4 20 1, 2 1 DSSS, FHSS 20 66 100 330
a Sep 1999 5 20 6, 9, 12, 18, 24, 36, 48, 54 1 OFDM 35 115 120 390
3.7 5,000 16,000[A]
b Sep 1999 2.4 20 1, 2, 5.5, 11 1 DSSS 35 115 140 460
g Jun 2003 2.4 20 6, 9, 12, 18, 24, 36, 48, 54 1 OFDM, DSSS 38 125 140 460
n Oct 2009 2.4/5 20 7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2[B] 4 OFDM 70 230 250 820
40 15, 30, 45, 60, 90, 120, 135, 150[B] 70 230 250 820
ac (DRAFT) ~Feb 2014 5 20 up to 87.6 8        
40 up to 200        
80 up to 433.3        
160 up to 866.7        
ad (DRAFT) ~Dec 2012 60   up to 7000            

802.11-1997 (802.11 legacy)

The original version of the standard IEEE 802.11 was released in 1997 and clarified in 1999, but is today obsolete. It specified two net bit rates of 1 or 2 megabits per second (Mbit/s), plus forward error correction code. It specified three alternative physical layer technologies: diffuse infrared operating at 1 Mbit/s; frequency-hopping spread spectrum operating at 1 Mbit/s or 2 Mbit/s; and direct-sequence spread spectrum operating at 1 Mbit/s or 2 Mbit/s. The latter two radio technologies used microwave transmission over the Industrial Scientific Medical frequency band at 2.4 GHz. Some earlier WLAN technologies used lower frequencies, such as the U.S. 900 MHz ISM band.

Legacy 802.11 with direct-sequence spread spectrum was rapidly supplanted and popularized by 802.11b.

802.11a

The 802.11a standard uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface (physical layer). It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net achievable throughput in the mid-20 Mbit/s.

Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively unused 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: the effective overall range of 802.11a is less than that of 802.11b/g. In theory, 802.11a signals are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength and, as a result, cannot penetrate as far as those of 802.11b. In practice, 802.11b typically has a higher range at low speeds (802.11b will reduce speed to 5 Mbit/s or even 1 Mbit/s at low signal strengths). 802.11a also suffers from interference, but locally there may be fewer signals to interfere with, resulting in less interference and better throughput.

802.11b

802.11b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.

802.11b devices suffer interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include microwave ovens, Bluetooth devices, baby monitors, cordless telephones and some amateur radio equipment.

802.11g

In June 2003, a third modulation standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b), but uses the same OFDM based transmission scheme as 802.11a. It operates at a maximum physical layer bit rate of 54 Mbit/s exclusive of forward error correction codes, or about 22 Mbit/s average throughput. 802.11g hardware is fully backward compatible with 802.11b hardware and therefore is encumbered with legacy issues that reduce throughput when compared to 802.11a by ~21%.

The then-proposed 802.11g standard was rapidly adopted by consumers starting in January 2003, well before ratification, due to the desire for higher data rates as well as to reductions in manufacturing costs. By summer 2003, most dual-band 802.11a/b products became dual-band/tri-mode, supporting a and b/g in a single mobile adapter card or access point. Details of making b and g work well together occupied much of the lingering technical process; in an 802.11g network, however, activity of an 802.11b participant will reduce the data rate of the overall 802.11g network.

Like 802.11b, 802.11g devices suffer interference from other products operating in the 2.4 GHz band, for example wireless keyboards.

802.11-2007

In 2003, task group TGma was authorized to "roll up" many of the amendments to the 1999 version of the 802.11 standard. REVma or 802.11ma, as it was called, created a single document that merged 8 amendments (802.11a, b, d, e, g, h, i, j) with the base standard. Upon approval on March 8, 2007, 802.11REVma was renamed to the then-current base standard IEEE 802.11-2007.

802.11n

802.11n is an amendment which improves upon the previous 802.11 standards by adding multiple-input multiple-output antennas (MIMO). 802.11n operates on both the 2.4 GHz and the lesser used 5 GHz bands. It operates at a maximum net data rate from 54 Mbit/s to 600 Mbit/s. The IEEE has approved the amendment and it was published in October 2009. Prior to the final ratification, enterprises were already migrating to 802.11n networks based on the Wi-Fi Alliance's certification of products conforming to a 2007 draft of the 802.11n proposal.

802.11-2012

In 2007, task group TGmb was authorized to "roll up" many of the amendments to the 2007 version of the 802.11 standard. REVmb or 802.11mb, as it was called, created a single document that merged ten amendments (802.11k, r, y, n, w, p, z, v, u, s) with the 2007 base standard. In addition much cleanup was done, including a reordering of many of the clauses. Upon publication on March 29, 2012, the new standard was referred to as IEEE 802.11-2012.

802.11ac

IEEE 802.11ac is a standard under development which will provide high throughput in the 5 GHz band. This specification will enable multi-station WLAN throughput of at least 1 gigabits per second and a maximum single link throughput of at least 500 megabits per second, by using wider RF bandwidth (80 or 160 MHz), more streams (up to 8), and high-density modulation (up to 256 QAM).

802.11ad

IEEE 802.11ad "WiGig" is a new proposed standard that is already seeing a major push from hardware manufacturers. On 24 July 2012 Marvell and Wilocity announced a new partnership to bring a new tri-band Wi-Fi solution to market. Using 2.4 GHz, 5 GHz and 60 GHz, the new standard can achieve a theoretical maximum throughput of up to 7Gbit/s. This standard is expected to reach the market sometime in early 2014.

 

--wikipedia