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As the question , I don't really understand what is a wireless channel.
Supposed we have an access point with the standard 802.11b, it will use the frequency 2.4 GHz -->Is this the bandwith? And the transfer rate of this standard is 11 Mbps. What is the relationship between them? and why do we have to divide the bandwith into different channels?
Can anyone give me a briefly bottom-up concept about these concepts? Thanks in advanced.
When it says 2.4 GHz, it means the band between 2.4 GHz and 2.5 GHz (the exact range varies from one country to another). It's a similar idea to the allocation to CB radio of channels around 27 MHz.
Now, a single frequency just gives you a carrier; you need to modulate it to send information. If you looked at the signal with a spectrum analyzer, the sharp peak of the carrier will be broadened. This frequency spread is what analogue engineers call the bandwidth: 22 MHz in the case of 802.11b.
Networking people usually quote bandwidth in terms of bits/second; the exact relationship between frequency and bits/second depends on the encoding used. For 802.11b, divide by two: later standards tend to have more complex and efficient encodings.
The advantage of having multiple channels is that you can get aggregate performance of more than 11 Mbps by staggering the frequencies. In a corporate deployment with many APs, adjacent APs will operate on non-overlapping channels, as far as possible.
Stealing gio's link: en.wikipedia.org/wiki/List_of_WLAN_channels
Data transmission or reception happen through channels. Channel indicates the frequency range of operation. Typically its bandwidth will be +/- frequency range based on a operating frequency / center frequency. Here 2.4Ghz is the operating frequency / carrier frequency. The channel bandwidth for 802.11b is 22Mhz. This range is divided into 14 channels spaced 5 MHz apart. Channel contention shall occur if multiple AP operate in same channel.
The higher the channel bandwidth, the higher the amount of data that can be sent and higher the cost. So, Wide bandwidth channel will enable more data transfer, but in turn raises the chances of interference with other channels.
802.11b supports a max of only 11 Mbps data rate. Theoretical throughput is the maximum channel capacity of system that is equivalent to the maximum possible amount of data that can be transmitted in the channel in ideal conditions.
Presence of multiple channels provides choice of usage to avoid interference. Different countries have different policies in allowing the channel usage, number of users and power level within the operating frequency ranges.
To make a communication channel, a carrier frequency is selected (else you work on base band, which has greater loss and other problems). And on that carrier, a bandwidth for the signal is used.
In this case, your carrier frequency is 2.4GHz, which means the center frequency. and the 11MHz is the bandwidth of your channel, meaning that the channel is from 2400-5.5 MHz to 2400+5.5 Mhz (5.5 = 11/2, and central freq. is 2400MHz).
Channels are used to separate signals, for different usages.
For example on an FM radio, each channel is used for a radio provider (I dont know what they are called in english! sorry), so when you change frequency of a radio, you can hear different radio programs.
Multiple channels is the WAY to make a system available for multiple users, multiple streams of multimedia of multiple bandwidth options and multiple technologies Wireless is able to serve today 7 billion devices though the same devices are consumed by about 3.x billion people and world still needs to keep its energy and environment reachable to all humanity by 20XY year. Just like while light is of seven colors, and periodic table has multiple groups of blocks, the electromagnetic energy which is essentially from where our Radio Frequencies we use in all wireless come from is divided into several categories such as Infra-Red, Visible, Ultraviolet, Millimeter,X-Ray Gamma Ray,Ku band etc and each of these bands have some absorption band and some lucky bands like our visible band which is helping us to view this beautiful world because the visible spectrum of 7500 nano meters to 4000 nano meters of visible VIBGYOR not easily absorbed in nature in general and hence on a sunnny day we see every thing normally.The world of telecommunications is full of channels and various telecom Access technologies such as LTE, 3G, CDMA or GSM use several of these channels of different sizes in each of these technologies like 200 KHZ for eight time slots in GSM associated with a single Radio Transceiver and we have 124 of those to be divided amongst the telecommunication service providers in 900 MHz frequency range. In LTE the channel bandwidths are typically 1.4 Mhz, 3MHz,5 MHz, 10 MHz,15 and 20 MHz respectively of which 20 MHz is most widely deployed both in TDD and in FDD. There are multiple frequencies for multiple nations and you can look up more inputs in PREZI "LANDSCAPE OF ELECTROMAGNETIC SPECTRUM for a global perspective of end to end frequencies and their applications using various channels including details of each channel bandwidth
