This project took place for the course of Intergrated Communication Systems in 2018.
Using MATLAB we simulated a digital communication system using the Alternate Mark Inversion (AMI) encoding technique. Our goal was to test the bit-error-rate(BER) performance on the receiver and compare it with the ΒΕR-SNR theoretical curve.
AMI is a synchronous clock encoding technique that uses bipolar pulses to represent logical 1. The next logic 1 is represented by a pulse of the opposite polarity. Hence a sequence of logical 1s are represented by a sequence of pulses of alternating polarity.
Bit error rate (BER) is defined as the percentage of bits that have errors relative to the total number of bits received in a transmission. BER is usually expressed as 10 to a negative power. The BER is calculated by comparing the transmitted sequence of bits to the received bits and counting the number of errors.
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise.
Additive white Gaussian noise (AWGN) is a basic noise model used in information theory to mimic the effect of many random processes that occur in nature. The modifiers denote specific characteristics:
Additive because it is added to any noise that might be intrinsic to the information system.
White refers to the idea that it has uniform power across the frequency band for the information system. It is an analogy to the color white which has uniform emissions at all frequencies in the visible spectrum.
Gaussian because it has a normal distribution in the time domain with an average time domain value of zero.
A root-raised-cosine filter (RRC), sometimes known as square-root-raised-cosine filter (SRRC), is frequently used as the transmit and receive filter in a digital communication system to perform matched filtering. This helps in minimizing intersymbol interference (ISI). The combined response of two such filters is that of the raised-cosine filter. To have minimum ISI (Intersymbol interference), the overall response of transmit filter, channel response and receive filter has to satisfy Nyquist ISI criterion. Raised-cosine filter is the most popular filter response satisfying this criterion.
- SNR = 6
- SNR = 9
3.SNR = 12
The BER-SNR diagram satisfyingly approaches the theoretical BER-SNR diagram .