# Bandwidth and data rate relationship

### Nyquist formula: relating data rate and bandwidth

The bit rate fb is related to the bandwidth by the bandwidth efficiency eta. Eta itself depends on the modulation technique. For QAM modulation the bandwidth . Relationship between Data Rate and Bandwidth. Consider a square wave. • Data rate R = 2 x f. • Double the bandwidth ⇒ double the data rate. (other things. This posts describes the relationship between signal bandwidth, channel bandwidth and maximum achievable data rate. Before, going into detail, knowing the.

We expect to see that there are two ways to increase the speed of data transmission: Results When we send 5 megabytes 40 Mbits of data at a rate of 0.

### Relationship between Bandwidth, Data Rate and Channel Capacity | Computer Networking Demystified

However, if we change the bitrate to 2 Mbps, 2 MHz of bandwidth is used and the transmission takes about 20 seconds. To reduce the speed of data transfer by a factor of 4, we had to increase the bandwidth by a factor of 4: Finally, on changing the constellation size to 4 points squaring the number of signal levels relative to the first transmissionthe transmission also takes about 20 seconds, but uses only 1 MHz, when transmitting at 2 Mbps: You will have to make your reservation in advance.

To reserve WITest, visit http: Then, use the reservation calendar to reserve one or two consecutive hours for this experiment. For further information, refer to this tutorial on the reservation system. Then, click on "Control Panel". Use the calendar interface to request time on sb2, sb3 or sb7.

## Nyquist formula: relating data rate and bandwidth

Set up testbed At your reserved time, open a terminal and log in to the console of the testbed that you have reserved. This is usually your regular GENI username with a geni- prefix, e.

If you are using WITest, log in to witestlab. Then, you must load a disk image onto the testbed nodes. From the testbed console, run: If you are using WITest note that there is no space around the comma: This process can take minutes. Don't interrupt it in middle - you'll just have to start again, and it will only take longer.

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If it's been successful, then once the process finishes running completely you should see output similar to: Then, turn on your nodes with the following command: Prepare your receiver Open a new terminal window, and run the following command to tunnel the ShinySDR ports between your laptop and the receiver node: If you are using WITest note: Then, in that terminal window which should now be logged in to your testbed consolelog on to the receiver node: If you are using WITest: Configure your Shiny window as follows: Click on the "hamburger" icon in the top left corner to open the menu, if it isn't already open.

Apart from this, there are standard transmission constraints in the form of different channel noise sources that strictly limit the signal bandwidth to be used. Nyquist and Shannon have given methods for calculating the channel capacity C of bandwidth limited communication channels. Nyquist Criteria for maximum data rate for noiseless channels Given a noiseless channel with bandwidth B Hz.

The converse is also true, namely for achieving a signal transmission rate of 2B symbols per second over a channel, it is enough if the channel allows signals with frequencies upto B Hz. Another implication of the above result is the sampling theorem, which states that for a signal whose maximum bandwidth is f Hz. This is because, even if the signals are sampled at a higher rate than 2f and thereby including the higher harmonic componentsthe channel would anyway filter out those higher frequency components.

## Relationship between Bandwidth, Data Rate and Channel Capacity

In such cases, each symbol value could represent more than 1 digital bit. For example, assume a noiseless 3-kHz channel.

Thus, theoritically, by increasing the number of signalling values or symbols, we could keep on increasing the channel capacity C indefinitely. But however, in practise, no channel is noiseless and so we cannot simply keep increasing the number of symbols indefinitely, as the receiver would not be able to distinguish between different symbols in the presence of channel noise.

Using the previous examples of Nyquist criteria, we saw that for a channel with bandwidth 3 KHz, we could double the data rate from bps to bps.