Normalised Least Mean Squares - C Implemetation

ironclaw

Hi Everyone,

I'm looking to implement the Normalised Least Mean Squares (NLMS) in C. My issue is in the weight update (I think) As I'm running it against a standard MATLAB library. This is the MATLAB code (That works):

function [e,w,y]=nlmsFunc(mu,M,u,d,a);
% Normalized LMS
% Call:
% [e,w]=nlms(mu,M,u,d,a);
%
% Input arguments:
% mu = step size, dim 1x1
% M = filter length, dim 1x1
% u = input signal, dim Nx1
% d = desired signal, dim Nx1
% a = constant, dim 1x1
%
% Output arguments:
% e = estimation error, dim Nx1
% w = final filter coefficients, dim Mx1
%intial value 0

w=zeros(M,1); %This is a vertical column

%input signal length
N=length(u);
%make sure that u and d are colon vectors
u=u(:);
d=d(:);
%NLMS
for n=M:N %Start at M (Filter Length) and Loop to N (Length of Sample)
uvec=u(n:-1:n-M+1); %Array, start at n, decrement to n-m+1
e(n)=d(n)-w'*uvec;
w=w+mu/(a+uvec'*uvec)*uvec*conj(e(n));
y(n) = w'*uvec; %In ALE, this will be the narrowband noise.
end

My issue is translating this to C, and this is what I have so far:

float mu = 0.05; //Set up mu
    int a = 1; //Constant
    
    int inputSigSize = numSamples;
    float outputYSignal[inputSigSize];
    float desiredSignal[inputSigSize];
    float error[inputSigSize];
    
    
    float inputSignal[inputSigSize];
    
    //Initialise Weights to Zero
    if (weights[0] == 0) {

        for (int k = 0; k<=filterLength; k++) {
            weights[k]=0;
        }
    }
    
    float X[filterLength+1];
    float Y = 0;
    float E = 0;
    
    //Start NLMS Loop
    for (int t = 0; t<numSamples; t++) {
        
        X[0] = inputSignal[t];
        
        for (int i = 0; i<=filterLength; i++) {
            Y += (weights[i]*X[i]);
        }
        
        E = desiredSignal[t] - Y;
        
        for (int i = filterLength; i>=0; i--) {
            weights[i] = weights[i] + (mu*E*X[i]);
            
            if (i!=0) {
                X[i]=X[i-1];
            }
        }
        
        outputYSignal[t] = Y;
        error[t] = E;
    }
    //END NLMS Loop

Can anyone shed some light? This isn't homework / assignment. I have a feeling its a way I'm handling the weight updates

eddyc

I've only had a brief look at the code there, but whenever I am translating Matlab to C, I try to use functions as much as possible to make the structure of the main C function as close to the Matlab one. Things like vector/matrix multiplication, dot product etc., if you can make these functions and you know that the functions are accurate it will make it easier to debug than a function with a load of nested for loops and the like.

Or you can of course use a library, armadillo is a C++ one so I don't know if that would be suitable, but it manages to get very close to Matlab syntax http://arma.sourceforge.net/