TopTechnical Dictionary802.11g - wireless network standard

802.11g - wireless network standard

802.11 is a set of wireless standards that regulate the transmission modes within the network. They are commonly used in 802.11a, 802.11b, 802.11g, 802.11n and 802.11ac to provide wireless connectivity to your home office and commercial facilities.

 

IEEE 802.11g has been developed in 2003 as an extension to 802.11b. It increases bandwidth to 54 Mbit/s using the same 2.4 GHz band as 802.11b.

 

It uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance - a protocol defining the method of multiple access to the link with carrier status monitoring and collision avoidance). Available bandwidth is distributed between the transmitting stations, including AP (Access Point) for traffic to and from the device.

 

802.11g devices are backwards compatible with 802.11b devices. The presence of a device operating at 802.11b significantly reduces the capacity of the entire network operating at 802.11g.

 

802.11g standard uses OFDM (Orthogonal Frequency-Division Multiplexing) modulation originating in 802.11a with bit rates of 6, 9, 12, 18, 24, 36, 48 and 54 Mb/s and returns CCK (Complementary Code Keying - as in 802.11b standard) for 5.5 and 11 Mb/s and DBPSK/DQPSK + DSSS modulation for 1 and 2 Mb/s. Although 802.11g operates at the same frequency band as 802.11b, it may reach higher bit rates due to its origins in 802.11a.

 

Out of 52 OFDM sub-carriers, 48 are reserved for data, 4 are pilot sub-carriers with 0.3125 MHz (20 MHz/64) carrier spacing. Symbol duration is 4 microseconds and includes a 0.6 microsecond interval. The actual orthogonal components are generated and decoded in the baseband using DSP. The components are converted in the transmitter to 2.4 GHz frequencies. The benefits of using OFDM include reduced multi-path signal propagation phenomena and improved spectral efficiency.

 

Despite good reception and quick implementation, 802.11g is characterized by interference levels similar to 802.11b in the overcrowded 2.4 GHz band. The devices operating in this band include microwaves, Bluetooth devices or digital wireless phones, often introducing major interferences. Also, the number of users and their density in urban areas can be a major issue.

 

To prevent interferences, three non-overlapping channels are available in the US and countries with similar regulations (channel 1, 6, 11 with 25 MHz separation) and four in Europe (channel 1, 5, 9, 13 with 20 MHz separation). However, the interferences may still occur, due to the side lobes of the transmitter radiation characteristics, however those are much weaker.

 

Table 1. List of frequencies and corresponding channels

 

Channel

Mid-band frequency

Channel width

Overlapping channels

GHz GHz
1 2.412 2.401 - 2.423 2,3,4,5
2 2.417 2.406 - 2.428 1,3,4,5,6
3 2.422 2.411 - 2.433 1,2,4,5,6,7
4 2.427 2.416 - 2.438 1,2,3,5,6,7,8
5 2.432 2.421 - 2.443 1,2,3,4,6,7,8,9
6 2.437 2.426 - 2.448 2,3,4,5,7,8,9,10
7 2.442 2.431 - 2.453 3,4,5,6,8,9,10,11
8 2.447 2.436 - 2.458 4,5,6,7,9,10,11,12
9 2.452 2.441 - 2.463 5,6,7,8,10,11,12,13
10 2.457 2.446 - 2.468 6,7,8,9,11,12,13
11 2.462 2.451 - 2.473 7,8,9,10,12,13
12 2.467 2.456 - 2.478 8,9,10,11,13,14
13 2.472 2.461 - 2.483 9,10,11,12,14
14 2.484 2.473 - 2.495 12,13

Not all channels are legal in all countries 

Fig. 1. Graphic representation of 14 channels and corresponding mid-band frequencies

 


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