Replace two-way propagation channel with two one-way propagation channels

Hello,

I am using the Phased Array System Toolbox and I want to replace a two-way propagation channel by two one-way propagation channels, so I can add more signals to the receive path.

Why are the receive signals rxsig and yt not the same even though I am reusing the same radiator/collector?

Am I using the target relection in the correct way?

% Two-way channel
channel = phased.FreeSpace('PropagationSpeed',c,'OperatingFrequency',fc,'SampleRate',fs,'TwoWayPropagation',true);

% Two way propagation
sig = waveform(); % waveform
[~,txang] = rangeangle(tgtPos,radarParams.OriginPosition,radarParams.Orientation);
txsig = transmitter(sig);                                   % transmit
txsig = radiator(txsig,txang);                              % radiate
txsig = channel(txsig,radarParams.OriginPosition,tgtPos,... % propagate in two-way channel
    radarParams.OriginVelocity,tgtVel);
tgtsig = pointTgts(txsig,tgtAngs);                          % pointTgts of type phased.BackscatterRadarTarget
rxsig = collector(tgtsig,txang);                            % collect
rxsig = receiver(rxsig);                                    % receive


% Two one-way channels
envout = phased.FreeSpace('TwoWayPropagation',false,'SampleRate', fs,'OperatingFrequency',fc,'PropagationSpeed',c);
envin  = phased.FreeSpace('TwoWayPropagation',false,'SampleRate', fs,'OperatingFrequency',fc,'PropagationSpeed',c);

% One way propagation (from FrequencyAgilityExample)
xt = transmitter(sig);                                      % transmit
xtarray = radiator(xt, txang);                              % radiate
yp = envout(xtarray,radarParams.OriginPosition,tgtPos,...   % propagate
    radarParams.OriginVelocity,tgtVel);
yr = pointTgts(yp,tgtAngs);                                 % reflect
ye = envin(yr,tgtPos,radarParams.OriginPosition,...         % propagate
    tgtVel,radarParams.OriginVelocity);
yt = collector(ye,txang);                                   % collect
yt = receiver(yt);                                          % receive

Answer 1

[Honglei Chen]

This may have to do with your target location. The channel delays signal based on the distance. However, when the travel time is not a multiple of sampling time, then the signal arrives between the samples. In this case, a fractional delay filter is applied to the signal. Thus, when you change one two-way channel with two one-way channel, the signal may go through one more filter and therefore the result may be slightly different.

HTH