lect8a_Ross_09spg

lect8a_Ross_09spg - Detection, Noise, SNR and BER Lecture...

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Elec 300u Energy and Noise Slide 1 Detection, Noise, SNR and BER Lecture 8a Signal-to Noise Ratio (SNR) Bit error rate (BER) versus SNR Some content taken with permission from material developed for the course EECS6.02 by C. Sodini, M. Perrot and H. Balakrishnan
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Noise in digital communications • The discrete nature of digital communications means that two adjacent pulses of information can interfere with each other and corrupt the data being transmitted. This is known as inter-symbol interference (ISI) • A data bit can also be corrupted by channel noise , similar to the distortions that occur to analog message signals over a noisy channel • The rate at which interference and noise corrupt a transmission is the bit error rate (BER) • ISI and the effects of channel noise can be minimized if the binary information is properly encoded and decoded during transmission (channel coding next week)
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Optimal pulse shaping to minimize the BER Optimal pulse shaping minimizes the BER. Rectangular pulse x(t) T A -T X(t) T -T f 1/2T -1/2T TA “Ideal” pulse Raised cosine pulse
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Bit errors 0 2 4 6 8 10 12 14 16 18 20 0 0.5 1 Data In dmin=1 0 2 4 6 8 10 12 14 16 18 20 -1 0 1 2 Received Signal 0 2 4 6 8 10 12 14 16 18 20 0 0.5 1 sliced output at dmin/2 0 2 4 6 8 10 12 14 16 18 20 0 0.5 1 Bit Errors Slicing level samples
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Definition of Signal-to-Noise Ratio Signal-to-Noise ratio (SNR) indicates impact of noise on system performance (ratio of signal power to noise power) We often like to use units of dB to express SNR: A signal[n] n n noise[n] rx[n]
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A signal[n] n n noise[n] rx[n] n n n SNR = 20.4 dB SNR = 10.7 dB SNR = 0.4 dB SNR Example Scaling the gain factor A leads to different SNR values Lower A results in lower SNR Signal quality steadily degrades with lower SNR
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• SNR influenced by transmitted power, distance between transmitter and receiver, and noise • Increase in received signal power leads to increased SNR if noise level unchanged Impact of SNR on Receiver
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n noise[n] (Trial = 1) sample value Histogram of 100 samples Histogram of 1,000 samples Histogram of 10,000 samples Histogram of 1,000,000 samples sample value sample value sample value
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This note was uploaded on 01/28/2011 for the course ELEC 300U taught by Professor Rossmurchandaminebermak during the Fall '08 term at HKUST.

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lect8a_Ross_09spg - Detection, Noise, SNR and BER Lecture...

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