www.pudn.com > WCDMA.rar > MpathChannel.m
function y=MpathChannel(SigLast,SigCurrent,SigNext,delays,amplitudes,TxPulseLength,SamplesPerChip)
%************************************************************************
%function y=MpathChannel(SigLast,SigCurrent,SigNext,delays,amplitudes,TxPulseLength,SamplesPerChip)
%
% Copyright 2002 The Mobile and Portable Radio Research Group
%
%This function simulates the behavior of a specular multhipath channel
%on the signal associated with the current frame (SigCurrent). The other
%two signals SigLast (the signal associated with the previous frame) and
%SigNext (the signal associated with the future frame) are included so
%that ther signal points can be included as needed when the delays are
%incorporated. They are also included to ensure that fading envelop, which
%is computed via interpolation, remains continuous from frame to frame.
%
%The number of multipath components is equal to the length of the vector,
%"delay". For each multipath component, SigCurrent is shifted by the
%amount specified in delay. SigLast is then used to fill the front
%part of the shifted version of SigCurrent, and SigNext is used to fill
%the rear of the shifted version of SigCurrent. This replica is then
%scaled by an fading signal. The fading signal is generated by taking
%the appropriate column in "amplitude" (the i^th column corresponds to
%the i^th multipath component) and inpterpolating that column in order
%to generate a fading vector whose length is equal to the replica.
%
%Once each replica is generated and the fading applied, they are then
%summed together to create the channel output.
%
%Parameters
% Input
% SigLast vector Contains the transmitted signal associated
% with the previous WCDMA radio frame
% SigCurrent vector Contains the transmitted signal associated
% with the currentWCDMA radio frame
% SigNext vector Contains the transmitted signal associated
% with the next WCDMA radio frame
% delays vector Contains the delays (in discrete time) of
% multipath channel. Its length determines
% the number of multipath components
% amplitudes matrix Contains the fading signal associated with
% or each delay. There is a one-to-one
% vector correspondence between the i^th element of
% "delay" and the i^th column of "amplitudes"
% Each column contains 60 elements. The first
% 20 corresponds to the fading in "SigLast",
% the next 20 corresponds to the fading in
% "SigCurrent", and the final 20 are associated
% with "SigNext".
% TxPulseLength Scalar Length of the transmitter filter pulse
% SamplesPerChip Scalar Number of samples per chip
% Output
% y vector Distorted version of the transmitted signal
% due to the multipath.
%************************************************************************
NumDelays=length(delays); %Number of Multipath Components
MaxDelay=max(delays); %Maximum Delay in the channel
FrameSampleLength=38400*SamplesPerChip; %Number of Samples for each frame duration
SigLength=length(SigCurrent); %Number of Samples for each signal associated frame
%This does not equal "FrameSampleLength" because
%"SigCurrent" contains the entire pulse contribution
%for each chip in the frame. Since the pulse shaping
%filter length is more than one chip duration,
%SigLength is typically longer
FrameBegin=(TxPulseLength+1)/2; %The index associated with the maximum value of the
%pulse associated with the first chip in the frame
FrameEnd=FrameBegin+SamplesPerChip*38400-1; %The index associated with the maximum
%value of the pulse associated with the
%last chip in the frame
%Initialize Output Vector
%The output vector must be long enough to support the "SigCurrent" when shifted by
%the maximum delay in the channel, "MaxDelay"
y=zeros(1,length(SigCurrent)+MaxDelay);
%Error Checking for "ampliutdes"
[nrow,ncol]=size(amplitudes);
if nrow ~= 60
error(' "amplitudes" must have 60 rows');
end
if ncol ~= NumDelays
error ('The number of columns in "amplitudes" must equal the length of "delays"')
end
%Determine the original abcissa values for the fading signal in "amplidues"
%Note that in amplutides, we have 20 samples of the fading signal per
%frame duration. Accordingly, we need to compute the abcissa values
%from 0 to FrameSampleLength-1 for one group of 20 signals. The abcissa
%values will be uniformly distributed across the frame duration
increment=FrameSampleLength/20;
x=0:increment:(FrameSampleLength-1);
for k=1:NumDelays
%Determine the number of fading Coefficient Data Points we need from the last frame
%At least two coefficients are needed because they will be interpolated to obtain
%a fading coefficient for each sample point. Further, a staged interpolation that
%initially involves cubic or cubic spline interpolation will be used. Therefore, to
%ensure that fading signal remains continuous from frame to frame (i.e., interation-to-
%iteration) it is necessary to include 2 coefficients from the previous frame, especially
%when cubic interpolation is employed
%
%This determines the number of fading coefficients that we needed from the last frame
PriorInterpPoints=fix(delays(k)/increment)+2;
%This extracts the indicies associated with the fading coefficients from the last frame
PriorAbcissa=20-PriorInterpPoints+1:20;
%This extracts frame sample positions associated with each coefficient
PriorIndex=x(PriorAbcissa);
%Get the appropriate Fading Coefficients associated with the previous frame
FadeLast=amplitudes(PriorAbcissa,k).';
%Determine the indicies of the signal points in the last frame that need to be included
%in order to ensure continuity in the interpolated fading signal and the associated
%faded signal on a frame-to-frame basis
PriorInterpIndex=ceil(x(20-PriorInterpPoints+1)):(FrameSampleLength-1);
%Get those signal points
PriorSig=SigLast(FrameBegin+PriorInterpIndex);
%Determine the number of fading Coefficient Data Points we need from the next frame
%At least two coefficients are needed because they will be interpolated to obtain
%a fading coefficient for each sample point. Further, a staged interpolation that
%initially involves cubic or cubic spline interpolation will be used. Therefore, to
%ensure that fading signal remains continuous from frame to frame (i.e., interation-to-
%iteration) it is necessary to include 2 coefficients from the next frame, especially
%when cubic interpolation is employed
%
%This determines the number of fading coefficients that we needed from the next frame
PostInterpPoints=ceil((MaxDelay-delays(k))/increment)+2;
%This extracts the indicies associated with the fading coefficients from the next frame
PostAbcissa=1:PostInterpPoints;
%This extracts the frame sample positions associated with each coeficient
PostIndex=x(PostAbcissa);
%Get the fading coefficients associated with the next frame
FadeNext=amplitudes(40+PostAbcissa,k).';
%Determin the indicies (Offset from "FrameBegin") of the signal points in the next frame
%that need to be included in order to ensure continuity in the interpolated fading
%signal and the associated fadied signal on a frame-to-frame basis
PostInterpIndex=0:x(PostInterpPoints);
%Get the signal points
PostSig=SigNext(FrameBegin+PostInterpIndex);
%Combine "PriorSig" with "PostSig" and the appropriate portion of "SigCurrent"
%The appropriate portion of "SigCurrent" is determined by "SigIndex"
SigIndex=FrameBegin+(0:FrameSampleLength-1);
%MComponent=[PriorSig,SigCurrent(SigIndex),PostSig];
MComponent=[PriorSig,SigCurrent(FrameBegin:(FrameBegin+FrameSampleLength-1)),PostSig];
%Compute abcissa for the data to be interpolated
xd=[PriorIndex-FrameSampleLength,x(1:20),FrameSampleLength+PostIndex];
%Concatenate the fading vector
FadeD=[FadeLast, amplitudes(21:40,k).', FadeNext];
%Create tne inperolated abcissa
xi=ceil(min(xd)):floor(max(xd));
index=(2-xi(1)-delays(k)-FrameBegin: 1-xi(1)-delays(k)-FrameBegin+length(y));
%Conduct Interpolation
%Fade=interp1(xd,FadeD,xi(index),'*cubic');
Fade=WCDMACubicInterp(xd,FadeD,xi(index)).';
%scale signal with fading signal at the appropriate abcissa points
%to create the multipath component
FadedMComponent=Fade.*MComponent(index);
%Combine multipath components
y=y+FadedMComponent;
end