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# Documentation

### Contents

Bit error rate (BER) for Rayleigh and Rician fading channels

## Alternatives

As an alternative to the berfading function, invoke the BERTool GUI (bertool), and use the Theoretical tab.

## Description

### For All Syntaxes

The first input argument, EbNo, is the ratio of bit energy to noise power spectral density, in dB. If EbNo is a vector, the output ber is a vector of the same size, whose elements correspond to the different Eb/N0 levels.

Most syntaxes also have an M input that specifies the alphabet size for the modulation. M must have the form 2k for some positive integer k.

berfading uses expressions that assume Gray coding. If you use binary coding, the results may differ.

For cases where diversity is used, the Eb/N0 on each diversity branch is EbNo/divorder, where divorder is the diversity order (the number of diversity branches) and is a positive integer.

### For Specific Syntaxes

ber = berfading(EbNo,'pam',M,divorder) returns the BER for PAM over an uncoded Rayleigh fading channel with coherent demodulation.

ber = berfading(EbNo,'qam',M,divorder) returns the BER for QAM over an uncoded Rayleigh fading channel with coherent demodulation. The alphabet size, M, must be at least 4. When $k={\mathrm{log}}_{2}M$ is odd, a rectangular constellation of size $M=I×J$ is used, where $I={2}^{\frac{k-1}{2}}$ and $J={2}^{\frac{k+1}{2}}$.

ber = berfading(EbNo,'psk',M,divorder) returns the BER for coherently detected PSK over an uncoded Rayleigh fading channel.

ber = berfading(EbNo,'depsk',M,divorder) returns the BER for coherently detected PSK with differential data encoding over an uncoded Rayleigh fading channel. Only M = 2 is currently supported.

ber = berfading(EbNo,'oqpsk',divorder) returns the BER of coherently detected offset-QPSK over an uncoded Rayleigh fading channel.

ber = berfading(EbNo,'dpsk',M,divorder) returns the BER for DPSK over an uncoded Rayleigh fading channel. For DPSK, it is assumed that the fading is slow enough that two consecutive symbols are affected by the same fading coefficient.

ber = berfading(EbNo,'fsk',M,divorder,coherence) returns the BER for orthogonal FSK over an uncoded Rayleigh fading channel. coherence should be 'coherent' for coherent detection, or 'noncoherent' for noncoherent detection.

ber = berfading(EbNo,'fsk',2,divorder,coherence,rho) returns the BER for binary nonorthogonal FSK over an uncoded Rayleigh fading channel. rho is the complex correlation coefficient. See Nonorthogonal 2-FSK with Coherent Detection for the definition of the complex correlation coefficient and how to compute it for nonorthogonal BFSK.

ber = berfading(EbNo,...,K) returns the BER over an uncoded Rician fading channel, where K is the ratio of specular to diffuse energy in linear scale. For the case of 'fsk', rho must be specified before K.

ber = berfading(EbNo,'psk',2,1,K,phaserr) returns the BER of BPSK over an uncoded Rician fading channel with imperfect phase synchronization. phaserr is the standard deviation of the reference carrier phase error in radians.

[BER,SER] = berfading(EbNo, ...) returns both the BER and SER.

## Examples

The following example computes and plots the BER for uncoded DQPSK (differential quaternary phase shift keying) modulation over a flat Rayleigh fading channel for several diversity order values.

```EbNo = 8:2:20;
M = 16; % Use 16 QAM
semilogy(EbNo,ber);
text(18.5, 0.02, sprintf('L=%d', L))
hold on
% Loop over diversity order, L, 2 to 20
for L=2:20
semilogy(EbNo,ber);
end
text(18.5, 1e-11, sprintf('L=%d', L))
title('QAM over fading channel with diversity order 1 to 20')
xlabel('E_b/N_o (dB)')
ylabel('BER')
grid on```

## Limitations

The numerical accuracy of this function's output is limited by approximations related to the numerical implementation of the expressions

You can generally rely on the first couple of significant digits of the function's output.

## References

[1] Proakis, John G., Digital Communications, 4th ed., New York, McGraw-Hill, 2001.

[2] Modestino, James W., and Mui, Shou Y., Convolutional code performance in the Rician fading channel, IEEE Trans. Commun., 1976.

[3] Cho, K., and Yoon, D., "On the general BER expression of one- and two-dimensional amplitude modulations", IEEE Trans. Commun., Vol. 50, Number 7, pp. 1074-1080, 2002.

[4] Lee, P. J., "Computation of the bit error rate of coherent M-ary PSK with Gray code bit mapping", IEEE Trans. Commun., Vol. COM-34, Number 5, pp. 488-491, 1986.

[5] Lindsey, W. C., "Error probabilities for Rician fading multichannel reception of binary and N-ary signals", IEEE Trans. Inform. Theory, Vol. IT-10, pp. 339-350, 1964.

[6] Simon, M. K , Hinedi, S. M., and Lindsey, W. C., Digital Communication Techniques – Signal Design and Detection, Prentice-Hall, 1995.

[7] Simon, M. K., and Alouini, M. S., Digital Communication over Fading Channels – A Unified Approach to Performance Analysis, 1st ed., Wiley, 2000.

[8] Simon, M. K , "On the bit-error probability of differentially encoded QPSK and offset QPSK in the presence of carrier synchronization", IEEE Trans. Commun., Vol. 54, pp. 806-812, 2006.