%HW # 3
%computes the BER and plots the BER vs. SNR (dB) for 50, 100, 200,
% 500 km/h. Observe the error floors at higher speeds.

% looks like the error floor begins emerge even at 100 km/h so
% I am looking at lower speeds 50 km/h as well.

clear all;

freq=1900e6; %Hz
lambda=3e8/freq;
sample_freq=24000; % symbol rate 24 ksymbols/s
NF=10000; % frame length in bits
NUM_FRAMES = 10; %number of frames each of length NF
SNR_POINTS = 11; % number of SNR points 

speed=50 % km/h 
speed=speed*1000/3600; 
max_doppler=speed/lambda;

[avg_ber, snr_db] = DPSK_fading(max_doppler, sample_freq, ...
    NF, NUM_FRAMES, SNR_POINTS);
ber50=avg_ber;
snr50=snr_db;


speed=100 % km/h 
speed=speed*1000/3600; 
max_doppler=speed/lambda;

[avg_ber, snr_db] = DPSK_fading(max_doppler, sample_freq, ...
    NF, NUM_FRAMES, SNR_POINTS);
ber100=avg_ber;
snr100=snr_db;

speed=200 % km/h 
speed=speed*1000/3600; 
max_doppler=speed/lambda;

[avg_ber, snr_db] = DPSK_fading(max_doppler, sample_freq, ...
    NF, NUM_FRAMES, SNR_POINTS);
ber200=avg_ber;
snr200=snr_db;

semilogy(snr50, ber50, 'r', snr100, ber100, 'k', snr200, ber200, 'g');
grid;
legend('50 km/h', '100 km/h', '200 km/h');
xlabel('SNR -- dB');
ylabel('Bit-Error-Rate');
title('4-DPSK Performance for Different Mobile Speeds');