The data rate is the number of bits transmitted from one device to another or over a network per second.
Data rates are usually expressed in bits per second or bytes per second.
The maximum data transmission rate of a wireless communication channel is dependent on the bandwidth of the channel, the number of discrete levels in the digital signal, and the level of noise in the signal.
When I was a postgraduate student living in a hostel, I accessed the internet via Bluetooth LAN. However, it was not possible to send or download a large amount of data with that connection. I learned this was due to the slow internet connection, as the maximum data rate over the air interface was limited in the connectivity access via Bluetooth LAN.
This experience clearly illustrated for me that data rate is a key performance metric in wireless communication systems. To achieve the maximum data rate, wireless technology must be optimized. In this article, we will learn a little more about data rates in wireless communication systems and how the bandwidth of communication channels relates to these rates.
Data Rates in Wireless Communication
Data rates define the speed of data transmission in wireless communication. The data rate can be referred to as the number of bits transmitted from one device to another or over a network per second. Data rates are usually expressed in bits per second or bytes per second. In most wireless communication networks, along with the useful data bits, additional data is transmitted for signaling, error correction, and addresses. This makes the useful data rate less than the actual data rate.
Bandwidth vs. Data Rate
The data rate of communication links is often confused with the term bandwidth. The data rate and bandwidth are two different entities of a wireless communication channel. The bandwidth refers to the data transmission capacity of a communication network. In short, bandwidth is the maximum amount of data that can be transmitted by a communication channel in a specified time.
Bandwidth is associated with maximum data transmission speed, whereas the data rate gives the actual data transmission speed. From the bandwidth specifications, one gets to know the capacity of the communication channel, and the data rate gives the present data transmission speed in the channel.
As we distinguish the data rate and bandwidth, it's worth mentioning the dependency between the two. The upcoming section reveals how data rate is related to bandwidth.
The Dependency of the Data Rate on the Bandwidth of Communication Channels
There is a finite bandwidth associated with any wireless communication channel. The maximum data transmission rate of a wireless communication channel is dependent on the bandwidth of the channel, the number of discrete levels in the digital signal, and the level of noise in the signal. The noise level or the quality of the signal influences the data transmission speed. There are two theorems governing the maximum data rate in noiseless and noisy communication channels—the Nyquist theorem for noiseless communication channels and Shannon’s theorem for noisy communication channels.
According to the Nyquist theorem, the maximum data rate achieved (bits per second) by a noiseless communication channel of bandwidth ‘B’ that sends data with ‘M’ number of discrete levels is given by:
For a given communication channel with fixed bandwidth, the only variable in the equation is the discrete levels of signal. Increasing the number of levels of the signal improves the data rate. However, the higher number of discrete levels in the signal threatens the reliability of the communication channel.
Practically, it is impossible to design a noiseless communication channel. Communication channels are always noisy, and Shannon’s theorem addresses the highest data rate in noisy communication channels. According to Shannon’s theorem, the maximum data transmission rate possible in bits per second is given by the following equation:
Note that S is the signal power and N is the noise power. The ratio SN gives the signal-to-noise ratio. According to the above equation, there are three ways to increase the data rate in noisy wireless communication channels. They are:
- Increase the bandwidth of the wireless communication channel.
- Increase signal power.
- Decrease noise power.
As the power of the signal increases above noise power, the data rate of the noisy communication channel builds up. However, increasing the bandwidth of the wireless communication channel is more effective than increasing the signal power.
The data rate is one of the benchmarks for assessing the performance of a wireless communication channel. There are various developments happening in wireless technology to achieve higher data rates, including 5G to achieve Gigabits per second or terabits per second data rates in wireless communication technology.
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