IEEE 802.11 based Wireless Local Area Networks (WLANs) are becoming popular in home, enterprise and public access areas primarily due to their low cost, simplicity of installation and high data rates. While WLANs continue to be predominantly data centric, there is growing interest in using WLANs for voice and text data especially in enterprise markets. This paper will present the comparison of different WLAN technologies analytically and theoretically. In this I consider IEEE 802.11a, 802.11b and 802.11g systems and compare their basic structure bandwidths, frequency, data rate, user access points, maximum available channels cost, modulation encoding technique, density and backward compatibility. I show that the analytical results are in close agreement with those from simulations and conclude the paper by highlighting some key factors that dictate the capacity of WLANs.
802.11a operates in the 5-GHz frequency band. This frequency band, called the Universal Networking Information Infrastructure (UNII) band, is divided into three parts. UNII-1 is for indoor use, and the antenna must be fixed to the radio; UNII-2 is for indoor or outdoor use, with either a fixed or remote antenna; and UNII-3 is for outdoor bridging only. 802.11a’s bandwidth and frequency is 5GHz and speed is of 54 Mbps (Effective speed - 50% rated speed), it use OFDM for the modulation.
802.11b operates in 2.4GHz band. Its speed is 11 Mbps (Effective speed - half of rated speed). It covers up to 300 feet distance. Its capacity is 32 users per Access Point. Its range is quite large and used where range matters rather then the density. It normally installed in both business and homes for easiest migration between the two locations, also being deployed in “hot spots” such as hotels, airports and Starbucks.
802.11g operates in 2.4GHz band same as that of 802.11b but it increases the speed of 802.11b up to 22 Mbps. Its Poor range (although better than that of 802.11a). An Apple technical note describes the peak performance range of its 802.11g equipment as 50 feet or less. Its speed decreases dramatically as the distance increase.
In this paper we will compare the performances of IEEE 802.11a, IEEE 802.11b and IEEE 802.11g in aspects.
- Data Rate (speed)
- Frequency and modulation Technique
- Range &Density Comparison
- Number of Users per access point
- Comparison Summary Chart
802.11 systems divide the spectrum into channels so that multiple access points can each be set to a different channel and operate close by without interference. However, 802.11b and 11g use overlapping channels, which means that out of the 11 channels used in the U.S., only channels 1, 6 and 11 can be used, effectively allowing only three access points to operate without interference. With 802.11a, 12 access points can operate in the same vicinity because it uses 12 channels that do not overlap.
Data Rate (Speed)
The data rate of IEEE 802.11a is 54 Mbps. The data rate of IEEE 802.11b is 11 Mbps. The data rate of IEEE 802.11g is 54 Mbps. Moreover the data rate is distance dependent. As the distance increase the data rate is decreases. In the graph the data rate of IEEE 802.11g falls to 6Mbps as the distance increase to 180feet. IEEE 802.11a requires access point at every 50 feet while 802.11b requires the access points after every 300 feet in each direction.
Frequency and Modulation Technique
The frequency of IEEE 802.11a is 5GHz, the frequency of IEEE 802.11b is 2.4GHz and same is of IEEE 802.11g. That is the reason IEEE 802.11b and IEEE 802.11g can work in the same network without making any trouble. The modulation encoding technique used by IEEE 802.11a is OFDM (orthogonal frequency division Multiplexing), IEEE 802.11b use DSSS and CCK while IEEE 802.11g uses DSSS and PBCC. The difference in modulation encoding technique also make the IEEE 802.11a incompatible with IEEE 802.11b and IEEE 802.11g networks. 802.11a and 802.11g use common 802.11 medium access control (MAC) layer functions. As a result, protocols responsible for operation of the network, including security, power management and fragmentation, are essentially the same. 802.11a and 802.11g only implement physical layer functions, such as modulation and demodulation, not the higher layer stuff.
IEEE 802.11b and IEEE 802.11g both are compatible with each other because of two reasons. Both use the same frequency band i.e. 2.4GHz and same frequency modulation encoding technique i.e. DSSS although IEEE 802.11b use CKK and IEEE 802.11g use PBCC. As the IEEE 802.11g and IEEE 802.11b are compatible to each other. That’s why the customers who don’t need to send data frequently (where speed is not a issue.) and are using IEEE 802.11b are not upgrading their systems to IEEE 802.11g. The speed is time delay is occur if IEEE 802.11b is using CKK and IEEE 802.11g is using PBCC (due to conversion) but Details of making b and g work well together occupied much of the lingering technical process. In older networks, however, the presence of an 802.11b participant significantly reduces the speed of an 802.11g network. As the data rate of IEEE 802.11g is 54Mbps and data rate of IEEE 802.11b is 11Mbps so it cause the 802.11g device to reduce the data rate to effectively the same rates used by 802.11b. 802.11a and 802.11g use common 802.11 medium access control (MAC) layer functions. As a result, protocols responsible for operation of the network, including security, power management and fragmentation, are essentially the same.
Compatibility chart of IEEE 802.11a, IEEE 802.11b with IEEE 802.11g is shown below.
Physical Layer protocol
Maximum Users per Access Point
IEEE 802.11a supports the 64 users per access point. IEEE 802.11b supports 32 users per access point. IEEE 802.11g also supports the 64 users per access point. But as the range of b is more as compared to that of IEEE 802.11a and IEEE 802.11g that’s why in a particular “cell” IEEE 802.11b support more users as compare to that of IEEE 802.11a and IEEE 802.11g. IEEE 802.11b (often called Wi-Fi) the ability to serve up to four to five times more users than they now do. It also opens the possibility for using IEEE 802.11 networks in more demanding applications, such as wireless multimedia video transmission and broadcast MPEG.
IEEE 802.11a is costly. IEEE 802.11b is of low price. But if we compare IEEE 802.11a and IEEE 802.11b with IEEE 802.11g, we find that IEEE 802.11g is less expensive then IEEE 802.11a but expensive then that of IEEE 802.11b. The appliances of IEEE 802.11g may interfere on the unregulated signal frequency. But reports shown that that prices will lose rapidly as the time passed. Specially the prices of the devices that supports the IEEE 802.11g.
Range and Density Comparison
The range of IEEE 802.11g is greater then IEEE 802.11a and almost same as that of IEEE 802.11g but its density is much poor as compare to IEEE 802.11a but quite better then that of IEEE 802.11b.
We prefer to use IEEE 802.11g where the range coverage is hard issue and environment is less populated (mean the density is not an issue).
Comparison Summary Chart
I have summarized the entire measuring units of IEEE 802.11a; IEEE 802.11b, IEEE 802.11g in the chart shown below and you will get a clear idea of these standards.
Following results can be extracted from the above material.
- Consider waiting for 802.11g products if you have a relatively large installed base of 802.11b. You'll be able to upgrade to 802.11g rather easily.
- Implement 802.11a now within existing 802.11b networks if you have specific areas needing high performance (e.g., conference and computer rooms). As with the point above, however, end-users will need 802.11a/b NICs to ensure interoperability.
- If cost is issue then use IEEE 802.11b which are low in price, but IEEE 802.11a is more costly.
- If range is issue then use IEEE 802.11a. it cover more as compare to IEEE 802.11b and IEEE 802.11a (about 4 times greater then IEEE 802.11b).
- If the network is populated (i.e. the number of users per access point are greater in number) then use IEEE 802.11b or IEEE 802.11g(but preference should be given to IEEE 802.11g as it has more data rate 54 Mbps as compare to IEEE 802.11b which has 11 Mbps).
Following are the articles, websites and books are consulted.
- Voice Capacity of IEEE 802.11b, 802.11a and 802.11g: Wireless LANs by Kamesh Medepalli.S. Garg and M. Kappes, “A New Admission Control Metric for VoIP Traffic in 802.11 Networks,” Avaya Labs Tech Report, May 2002.