Using Shannon's Theorem, Calculate The Maximum Bit Rate
Using Shannons theorem,calculate the maximum bit rate that
Using Shannon's theorem, calculate the maximum data transmission rate (bit rate) on a fiber optic link with a signal-to-noise ratio (SNR) of 40 dB. The central wavelength of the light used is 850 nm, with a bandwidth of 10 nm on either side.
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Shannon's theorem provides a fundamental limit on the maximum data rate (channel capacity) that can be transmitted over a communication channel without error, given the bandwidth and the signal-to-noise ratio (SNR). The theorem states that:
\[ C = B \times \log_{2}(1 + \text{SNR}) \]
where:
- \( C \) is the channel capacity in bits per second (bps),
- \( B \) is the bandwidth in Hertz (Hz),
- \( \text{SNR} \) is the linear signal-to-noise ratio (not in decibels).
In this context, we are asked to determine the maximum bit rate achievable over a fiber optic link using Shannon's theorem, given specific parameters.
Step 1: Convert the SNR from decibels to a linear ratio
Given SNR in dB: 40 dB
\[
\text{SNR}_{\text{linear}} = 10^{\frac{\text{SNR}_{dB}}{10}} = 10^{\frac{40}{10}} = 10^{4} = 10,000
\]
Step 2: Determine the bandwidth \( B \)
The bandwidth of the optical signal is derived from the central wavelength of 850 nm and a bandwidth of 10 nm on either side, making a total spectral bandwidth of \( 20 \) nm.
The spectral bandwidth in frequency terms can be computed by:
\[
B = \frac{\Delta \lambda}{\lambda^{2}} \times c
\]
where:
- \( \Delta \lambda \) is the spectral bandwidth in meters,
- \( \lambda \) is the central wavelength in meters,
- \( c \) is the speed of light (\( \approx 3 \times 10^{8} \) m/s).
Converting wavelengths to meters:
\[
\lambda = 850\, \text{nm} = 850 \times 10^{-9}\, \text{m}
\]
\[
\Delta \lambda = 20\, \text{nm} = 20 \times 10^{-9}\, \text{m}
\]
Calculating the bandwidth:
\[
B = \frac{20 \times 10^{-9}}{(850 \times 10^{-9})^{2}} \times 3 \times 10^{8}
\]
Calculating denominator:
\[
(850 \times 10^{-9})^{2} = 850^{2} \times 10^{-18} = 722,500 \times 10^{-18} = 7.225 \times 10^{-13}
\]
Now, substitute into \( B \):
\[
B = \frac{20 \times 10^{-9}}{7.225 \times 10^{-13}} \times 3 \times 10^{8}
\]
Simplify numerator:
\[
20 \times 10^{-9} = 2 \times 10^{-8}
\]
Division:
\[
\frac{2 \times 10^{-8}}{7.225 \times 10^{-13}} \approx \frac{2}{7.225} \times 10^{5} \approx 0.277 \times 10^{5} = 2.77 \times 10^{4}
\]
Multiply by \( 3 \times 10^{8} \):
\[
B \approx 2.77 \times 10^{4} \times 3 \times 10^{8} = 8.31 \times 10^{12}\, \text{Hz}
\]
So, the spectral bandwidth \( B \) is approximately \( 8.31 \times 10^{12} \) Hz or 8.31 THz.
Step 3: Calculate the channel capacity \( C \)
Applying Shannon's theorem:
\[
C = B \times \log_{2}(1 + \text{SNR}_{\text{linear}})
\]
\[
C \approx 8.31 \times 10^{12} \times \log_{2}(1 + 10,000)
\]
Calculate \( \log_{2}(10,001) \):
\[
\log_{2}(10,001) \approx \frac{\ln(10,001)}{\ln 2}
\]
Using approximations:
\[
\ln(10,001) \approx 9.210, \quad \ln 2 \approx 0.693
\]
Therefore:
\[
\log_{2}(10,001) \approx \frac{9.210}{0.693} \approx 13.28
\]
Finally, compute the capacity:
\[
C \approx 8.31 \times 10^{12} \times 13.28 \approx 1.105 \times 10^{14}\, \text{bps}
\]
This corresponds to approximately 110.5 Terabits per second (Tbps).
Conclusion
Using Shannon's theorem, with a spectral bandwidth derived from the wavelength parameters and a signal-to-noise ratio of 40 dB (linear ratio 10,000), the maximum data transmission rate on this fiber optic link is approximately 110.5 Tbps. This theoretical limit demonstrates the potential of high-capacity optical communication systems but does not account for practical implementation constraints such as modulation formats, coding schemes, dispersion, and other physical limitations.
References
- Shannon, C. E. (1948). "A Mathematical Theory of Communication." Bell System Technical Journal, 27(3), 379–423.
- G. P. Agrawal, "Fiber-Optic Communication Systems," 4th Edition, Wiley, 2010.
- J. M. Kahn, J. R. Barry, "Wireless Infrared Communications," Proceedings of the IEEE, Vol. 85, No. 2, 1997.
- H. G. Weber, A. Peña, "Multimode Fiber Optics," Wiley, 2012.
- J. B. Keller, "Optical Fiber Communications," Springer, 2007.
- M. K. Simon, J. K. Omura, "Spread Spectrum Communications," 3rd Edition, McGraw-Hill, 2004.
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