Data_Com_L5.pdf - Lecture 5 DATA RATE LIMITS Data Rate \u2022 A very important consideration in data communications is how fast we can send data in bits

Data_Com_L5.pdf - Lecture 5 DATA RATE LIMITS Data Rate •...

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DATA RATE LIMITS Lecture 5
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Data Rate A very important consideration in data communications is how fast we can send data, in bits per second over a channel. Data rate depends on three factors: 1. The bandwidth available 2. The level of the signals we use 3. The quality of the channel (the level of noise) Two theoretical formulas were developed to calculate the data rate: 1. Nyquist for a noiseless channel. 2. Shannon for a noisy channel.
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Noiseless Channel: Nyquist Bit Rate For a noiseless channel, the Nyquist bit rate formula defines the theoretical maximum bit rate 𝐵𝑖𝑡𝑅?𝑡? = 2 ? ?????𝑖?𝑡ℎ ? 𝑙?𝑔 2 𝐿 Where, bandwidth is the bandwidth of the channel, L is the number of signal levels used to represent data. and BitRate is the bit rate in bits per second.
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Noiseless Channel: Nyquist Bit Rate According to the formula, we might think that, given a specific bandwidth, we can have any bit rate we want by increasing the number of signal levels. Although the idea is theoretically correct, practically there is a limit. When increase the number of signal levels, we impose a burden on the receiver. If the number of levels in a signal is just 2, the receiver can easily distinguish between a 0 and a 1. If the level of a signal is 64, the receiver must be very sophisticated to distinguish between 64 different levels. So, increasing the levels of a signal reduces the reliability of the system.
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Examples
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Examples
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Noisy Channel: Shannon Capacity In reality, we cannot have a noiseless channel; the channel is always noisy. In 1944, Claude Shannon introduced a formula, called the Shannon capacity, to
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