CDMA/CDMA.java at master · Michaelo0/CDMA · GitHub

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package cdma;
import java.util.*;


/**
 *
 * @author Mike
 */
public class CDMA {

    private int[][] wtable;
    private int[][] copy;
    private int[] channel_sequence;

    private void setUp(int[] data, int num_stations) {
        wtable = new int[num_stations][num_stations];
        copy = new int[num_stations][num_stations];

        buildWalshTable(num_stations, 0, num_stations - 1, 0, num_stations - 1, false);

        showWalshTable(num_stations);

        for (int i = 0; i < num_stations; i++) {
            for (int j = 0; j < num_stations; j++) {
                //Making a opy of walsh table
                //to be used later
                copy[i][j] = wtable[i][j];

                // each row in table is code for one station.
                // So we multiply each row with station data
                wtable[i][j] *= data[i];
            }
        }

        channel_sequence = new int[num_stations];

        for (int i = 0; i < num_stations; i++) {
            for (int j = 0; j < num_stations; j++) {
                // Adding all sequances to get channel sequance
                channel_sequence[i] += wtable[j][i];
            }
        }
    }

    public void listenTo(int sourceStation, int num_stations) {
        int innerProduct = 0;

        for (int i = 0; i < num_stations; i++) {

            // multiply channel sequance and source station code
            innerProduct += copy[sourceStation][i] * channel_sequence[i];
        }

        System.out.println("The data received is: " + (innerProduct / num_stations));
    }

    public int buildWalshTable(int len, int i1, int i2, int j1, int j2, boolean isBar) {
        // len = size of matrix. (i1, j1), (i2, j2) are
        // starting and ending indices of wtable.

        // isBar represents whether we want to add simple entry
        // or complement(southeast submatrix) to wtable.
        if (len == 2) {
            if (!isBar) {
                wtable[i1][j1] = 1;
                wtable[i1][j2] = 1;
                wtable[i2][j1] = 1;
                wtable[i2][j2] = -1;
            } else {
                wtable[i1][j1] = -1;
                wtable[i1][j1] = -1;
                wtable[i1][j1] = -1;
                wtable[i1][j1] = 1;
            }
            return 0;
        }
        int midi = (i1 + i2) / 2;
        int midj = (j1 + j2) / 2;

        buildWalshTable(len / 2, i1, midi, j1, midj, isBar);
        buildWalshTable(len / 2, i1, midi, midj + 1, j2, isBar);
        buildWalshTable(len / 2, midi + 1, i2, j1, midj, isBar);
        buildWalshTable(len / 2, midi + 1, i2, midj + 1, j2, !isBar);

        return 0;
    }

    public void showWalshTable(int num_stations)
    {

        System.out.print("\n");

        for (int i = 0; i < num_stations; i++) {
            for (int j = 0; j< num_stations; j++) {
                System.out.print(wtable[i][j] + " ");
            }
            System.out.print("\n");
        }
        System.out.println("-----------------------");
        System.out.print("\n");
    }


    public static void main(String[] args)
    {
       int num_stations = 4;
       int [] data = new int[num_stations];

       //data bits corresponding to each station
       data[0] = -1;
       data[1] = -1;
       data[2] = 0;
       data[3] = 1;

       CDMA channel = new CDMA();
       channel.setUp(data, num_stations);

       // station you want to listen to
       int sourceStation = 3;
       channel.listenTo(sourceStation, num_stations);
    }

}