The Tech Blog

Back to Basics: Bit Rate and Bandwidth

Posted under Back to Basics, Educational on October 23rd, 2022 by Amaldev

After the last week’s post, a few of you had doubts pertaining to bitrate and bandwidth. This by itself is not a confusing topic but it’s made confusing by the use of the same word in different contexts to mean different things. The word “Bandwidth” refers to different things in different fields (I don’t why, but it’s just the way it is).

From a network & digital communication engineer’s POV, bandwidth actually refers to the maximum amount of bit rate(bits per sec) a communication channel can transmit at a time. Each communication channel can have inherent restrictions on how much data it can transmit. Think of a home internet optical fibre link. This channel can potentially physically transfer let’s say 1Giga bit per sec. But let’s say you are subscribed to a 100Mbps plan with your vendor, so even though your overall bandwidth is large, the max bit rate you can transfer based on the limits is 100Mbps. Bandwidth in this context(it can be 100Mbps or 1Gbps based on how you want to define it) is just the upper limit of the information bit rate in a communication system.

From an analog communication engineer’s POV, bandwidth refers to the frequency range in Hz. It represents the range of frequencies that a signal occupies in the frequency domain. Take Bluetooth for example, It operates in the 2400 – 2483.5 MHz range with an overall bandwidth of 83.5MHz. This range simply says that whatever signals you send in BLE should lie in this range. This range is again divided into 40channels with each having a bandwidth 2MHz so that multiple people can communicate in this same band at the same time. 40 X 2 = 80MHz. The remaining 3.5MHz range is used as a guard band on the lower and upper side so that it wouldn’t interfere with other communication systems.

Now to tie these two domains together, Shannon defined an equation which is shown in the images. It defines the maximum upper bound data bit rate that you transfer using a signal with a particular bandwidth. The overall rate of info transfer depends on the analog bandwidth (larger bandwidth means more data can be pushed). It also introduces the Signal to Noise factor which limits this rate. All its saying is if the noise is high, the meaningful data rate will be low.

I hope this clears up the confusion about using the same term for different things. The problem is not with the terms, but mostly with how we pick these up in colleges. You have different Profs teaching you analog and digital communication courses and each defines in their own way. As a student, you wouldn’t be able to put the two together unless you abstract this infos out and start seeing how these are implemented in real life. Always be curious and ask questions. Understand that your learning should never ever stop for you to keep growing.

If you liked the post, Share it with your friends!

Back to Basics: Bit Rate vs Baud Rate

Posted under Back to Basics, Educational, Technology on October 16th, 2022 by Amaldev

This is one of the most confusing questions out there. Folks use these interchangeably without really knowing what is what. Definitions first.

Bit Rate means the number of bits transmitted per sec.

Baud Rate means the number of symbols transmitted per sec.

Now, what the heck is a symbol? The symbol is just a way to wrap information. One signal block can be represented by let’s say 2bits, 5 bits, 6 bits or 32bits depending on how the receiver and transmitter agree. Think of this like a secret communication protocol which you and your friend use to communicate.

Electrically let’s say you want to send 4 voltage levels from 0-3V. I will use 0V – 00, 1V – 01, 2V – 10, 3V – 11. Here each information symbol is encoded by 2 bits. So now if I transmit 1 symbol per second, my baud rate is 1 but my bit rate is 2 bits per second as each symbol contains 2 bits.

Now, where does all the confusion arise from? In let’s say serial communication between embedded devices, you use binary signalling, meaning 1 symbol = 1 bit(either 0 or 1). In this case, the baud rate is always the same as the bit rate. This is one of the reasons you see baud rates and bit rates used interchangeably. Take UART, usually on Windows, the default bit rate is kept as 9600, which is equivalent to 9600 bits per sec. This means 1 bit has a time length of 1/9600 = 104us.

But now to confuse this further, this is not the actual data transfer because UART needs a start bit and a stop bit for every 8bits of actual data. For every 8bit data takes 104us *10 = 1.04ms to transfer. This is the UART protocol overhead. So actual meaningful information bit rate(avoiding protocols) = 8bits every 1.04ms = 7692 bits per second.

Hoping this can clear up most doubts out there on the topic.

If you liked the post, Share it with your friends!