f=10e6; % signal's frequency
fs=1e9; % sampling frequency
t=0:1/fs:20/f1-1/fs; % time vector
x=sin(2*pi*f*t); % sinusoidal signal

% upsampling by a factor of 8
x1=upsample(x,8);
% filtering
filt=[1,2,1,2,1,2,1,2,1]/2; %triangular impulse response
foh=conv(x1,filt,'same');

%scale time axis
nt=0:1/(8*fs):20/f-1/(8*fs); % scaled time vector

%plot reconstructed signal
plot(nt,foh)