endfunction
-% Returns the most likely place for the start of a frame, as a
-% a candidate for coarse frame sync. Combines two frames pilots
-% so we need at least Nsamperframe+M+Ncp samples in rx
-
-function [ct_est foff_est] = coarse_sync(states, rx, rate_fs_pilot_samples)
- Nsamperframe = states.Nsamperframe; M = states.M; Ncp = states.Ncp; Fs = states.Fs;
+% Correlates the OFDM pilot symbol samples with a window of received
+% samples to determine the most likely timing offset. Combines two
+% frames pilots so we need at least Nsamperframe+M+Ncp samples in rx.
+% Also determines frequency offset at maximimum correlation. Can be
+% used for acquisition (coarse timing a freq offset), and fine timing
+
+function [t_est foff_est] = coarse_sync(states, rx, rate_fs_pilot_samples)
+ Nsamperframe = states.Nsamperframe; Fs = states.Fs;
+ Npsam = length(rate_fs_pilot_samples);
verbose = states.verbose;
- Ncorr = length(rx) - (Nsamperframe+M+Ncp) + 1;
+ Ncorr = length(rx) - (Nsamperframe+Npsam) + 1;
assert(Ncorr > 0);
corr = zeros(1,Ncorr);
for i=1:Ncorr
- corr(i) = abs(rx(i:i+M+Ncp-1) * rate_fs_pilot_samples');
- corr(i) += abs(rx(i+Nsamperframe:i+Nsamperframe+M+Ncp-1) * rate_fs_pilot_samples');
+ corr(i) = abs(rx(i:i+Npsam-1) * rate_fs_pilot_samples');
+ corr(i) += abs(rx(i+Nsamperframe:i+Nsamperframe+Npsam-1) * rate_fs_pilot_samples');
end
- [mx ct_est] = max(abs(corr));
+ [mx t_est] = max(abs(corr));
- C = abs(fft(rx(ct_est:ct_est+M+Ncp-1) .* conj(rate_fs_pilot_samples), Fs));
- C += abs(fft(rx(ct_est+Nsamperframe:ct_est+Nsamperframe+M+Ncp-1) .* conj(rate_fs_pilot_samples), Fs));
+ C = abs(fft(rx(t_est:t_est+Npsam-1) .* conj(rate_fs_pilot_samples), Fs));
+ C += abs(fft(rx(t_est+Nsamperframe:t_est+Nsamperframe+Npsam-1) .* conj(rate_fs_pilot_samples), Fs));
fmax = 30;
[mx_pos foff_est_pos] = max(C(1:fmax));
end
if verbose
- %printf("ct_est: %d\n", ct_est);
- figure(6); clf;
+ %printf("t_est: %d\n", t_est);
+ figure(7); clf;
plot(abs(corr))
- figure(7)
+ figure(8)
plot(C)
axis([0 200 0 0.4])
end
% channel simulation ---------------------------------------------------------------
+ tx = resample(tx, 2000, 2000);
+ tx = [tx zeros(1,Nsam-length(tx))];
+ tx = tx(1:Nsam);
rx = tx;
if hf_en
% some spare samples at end to allow for timing est window
- rx = [rx zeros(1,M)];
+ rx = [rx zeros(1,Nsamperframe)];
% pilot based phase est, we use known tx symbols as pilots ----------
phase_est_stripped_log = 10*ones(Nrp,Nc+2);
phase_est_log = 10*ones(Nrp,Nc+2);
timing_est_log = [];
- timing_est = Ncp/2;
+ timing_est = 1;
+ if timing_en
+ sample_point = timing_est;
+ else
+ sample_point = Ncp/2;
+ end
for r=1:Ns:Nrp-Ns
% update timing every frame
if (mod(r-1,Ns) == 0) && (r != 1) && (r != Nrp)
- %st = (r-1)*(M+Ncp) - ceil(window_width/2);
st = (r-1)*(M+Ncp) + 1 - floor(window_width/2) + (timing_est-1);
- en = st + Nsamperframe-1 + length(rate_fs_pilot_samples) + window_width-1;
+ en = st + Nsamperframe-1 + M+Ncp + window_width-1;
ft_est = coarse_sync(tstates, rx(st:en), rate_fs_pilot_samples);
timing_est += ft_est - ceil(window_width/2);
- %if verbose
- % printf("ft_est: %d timing_est %d\n", ft_est, timing_est);
- %end
+ if verbose
+ printf("ft_est: %2d timing_est: %2d sample_point: %2d\n", ft_est, timing_est, sample_point);
+ end
delta_t = [delta_t ft_est - ceil(window_width/2)];
+ sample_point = max(timing_est+Ncp/4, sample_point);
+ sample_point = min(timing_est+Ncp, sample_point);
end
end
if r > Ns+1
rr = r-Ns;
- st = (rr-1)*(M+Ncp) + 1 + timing_est; en = st + M - 1;
+ st = (rr-1)*(M+Ncp) + 1 + sample_point; en = st + M - 1;
for c=1:Nc+2
acarrier = rx(st:en) .* conj(W(c,:));
rx_sym(rr,c) = sum(acarrier);
for rr=r:r+Ns
- st = (rr-1)*(M+Ncp) + 1 + timing_est; en = st + M - 1;
+ st = (rr-1)*(M+Ncp) + 1 + sample_point; en = st + M - 1;
for c=1:Nc+2
acarrier = rx(st:en) .* conj(W(c,:));
rx_sym(rr,c) = sum(acarrier);
if r < Nrp - 2*Ns
rr = r+2*Ns;
- st = (rr-1)*(M+Ncp) + 1 + timing_est; en = st + M - 1;
+ st = (rr-1)*(M+Ncp) + 1 + sample_point; en = st + M - 1;
for c=1:Nc+2
acarrier = rx(st:en) .* conj(W(c,:));
rx_sym(rr,c) = sum(acarrier);
if verbose
figure(1)
plot(real(tx))
+
figure(2)
- Tx = abs(fft(tx.*hanning(Nsam)'));
+ Tx = abs(fft(tx(1:Nsam).*hanning(Nsam)'));
Tx_dB = 20*log10(Tx);
dF = Fs/Nsam;
plot((1:Nsam)*dF, Tx_dB);
figure(3); clf;
plot(rx_np,'+');
axis([-2 2 -2 2]);
-
+ title('Scatter');
if hf_en
figure(4); clf;
%hold on; plot(abs(spread2(1:Nsam)),'g'); hold off;
subplot(212)
plot(angle(spread1(1:Nsam)));
+ title('spread1 amp and phase');
end
plot(phase_est_log(:,2:Nc+1),'+', 'markersize', 10);
hold on;
plot(phase_est_pilot_log(:,2:Nc+1),'g+', 'markersize', 5);
+ title('Phase est');
#{
% todo, work out a way to plot rate Fs hf model phase
stem(delta_t)
subplot(212)
plot(timing_est_log);
+ title('Timing');
end
sim_out.ber(nn) = sum(Nerrs)/Nbits;
%sim_in.Nsec = 3*(sim_in.Ns+1)/sim_in.Rs; % one frame
sim_in.Nsec = 30;
- sim_in.EbNodB = 6;
+ sim_in.EbNodB = 3;
sim_in.verbose = 1;
sim_in.hf_en = 1;
sim_in.foff_hz = 0;
- sim_in.timing_en = 0;
+ sim_in.timing_en = 1;
run_sim(sim_in);
end
% Run an acquisition test, returning vectors of estimation errors
-function [delta_t delta_foff] = acquisition_test(Ntests=10, EbNodB=100, foff_hz=0, hf_en=0, fine_en)
+function [delta_t delta_foff] = acquisition_test(Ntests=10, EbNodB=100, foff_hz=0, hf_en=0, fine_en=0)
% generate test signal at a given Eb/No and frequency offset
sim_in.EbNodB = EbNodB;
sim_in.verbose = 0;
sim_in.hf_en = hf_en;
- sim_in.foff_hz = foff_hz;
-
- [sim_out rate_fs_pilot_samples rx] = run_sim(sim_in);
+ sim_in.foff_hz = foff_hz; sim_in.timing_en = 0;
% set up acquistion
projects / freetel-svn-tracking.git / commitdiff