Csdrhrt

We know that the 20MHz/40MHz width channels are present in Wifi. For transmitter or receiver cab be tuned for a single frequency at a time,
for example: Transmitter is tuned for 2.437GHz if channel 6 being used. But I'm confusing with the term bandwidth.

In Bluetooth, uses 1MHz channels. Does Bandwidth matters in data rate?

Why do we need 20MHz/40MHz for Wifi and 1MHz for bluetooth for channels even though antennas are tuning for particular frequency? (If i am wrong here, please correct me).

Thanks

The channel width is, quite literally, the "band width". It has an effect because in many transmission schemes, such as FSK (frequency shift keying), the data is encoded in the pattern by which the signal frequency changes.

There are many other ways to encode digital data on analogue since wave carriers but it demonstrates a case where the transmission of one signal needs more than one specific frequency.

Wifi uses OFDM. It uses multiple carriers to transmit data and as such the wider the amount of frequency bandwidth that is available translates directly to an increase in the amount of data that can be transferred per unit time.

In any medium of communication, data exchange take place and when you talk about exchanging anything it has speed. If you imagine there is a group of people waiting at the lift area to use the lift and reach the top floor as soon as possible then the lift should have large space to carry maximum people at a time. Same way Bandwidth has to play this role in data transfer. It is the space allowing how much amount of data should be transferring. Higher the bandwidth more will data transfer and receiving rate.

I think you might have mistakenly thought that the center frequency of a channel is the only frequency that makes up the channel.

The reality is that although radio channels are referred to by their center frequency, they always make use of frequencies above and below their center frequency. This total range of frequencies used is called the channel bandwidth.

When you tune a Wi-Fi radio to channel 6, you don't tune it to the infinitely narrow channel at exactly 2,437,000,000.000 Hz. The center frequency of Wi-Fi channel 6 is 2.437 GHz, but typical 20 MHz-wide transmissions on channel 6 use frequencies from 10 MHz below to 10 MHz above the center frequency. So channel 6 is really the 20 MHz-wide range from 2.417 GHz to 2.447 GHz, which is centered on 2.437 GHz. So when you tune your Wi-Fi radio to channel 6, it endeavors to receive all those frequencies in that 20 MHz-wide range, while trying to ignore all frequencies outside of that 20 MHz-wide range.

Bluetooth uses 1MHz-wide channels. If there was a Bluetooth channel centered at 2.437 GHz, it would use from 2.4365 to 2.4375 GHz. That is, the 1MHz-wide channel centered at 2.437 GHz.

• Traditional North American broadcast TV channels are 6 MHz wide.


• Traditional North American "FM radio stations" (analog audio broadcast radio stations that use Frequency Modulation) transmit in 200 kHz-wide channels.


• Traditional North American "AM radio stations" (analog audio broadcast radio stations that use Amplitude Modulation) transmit in 10 kHz-wide channels.

So even the oldest transmission schemes most of us are familiar with use channels that have some width to them. They don't use a single infinitely-narrow frequency.

Yes, bandwidth matters in data rate. The channel width (bandwidth) affects how much data you can transmit per unit time. The formula for the limit of how much information per second can be transmitted with a single-carrier transmission with a fixed bandwidth and fixed noise level was discovered by Claude Shannon in 1948, and is known as the "Shannon Limit". Modern modulation schemes such as OFDM pack multiple separate subcarriers into the fixed-width channel, so they get more data per second out of a given width of channel than Shannon had theorized, because Shannon had limited his channel model to a single carrier.

Also note that those of us in computer networking have stolen the term "bandwidth" from the radio engineers and now we misuse it to mean "throughput" in the context of computer networking. To a radio engineer, bandwidth is just one of many factors in throughput (modulation scheme is another major factor). To a computer network engineer, "bandwidth" is pretty much just a synonym for throughput.