java实现LDPC码(附完整源码)

以下是Java实现LDPC码的完整源码：

public class LDPC {
    private int[][] H;
    private int N;
    private int K;
    private int[] perm;
    private int[] invPerm;
    private int[] rowWeight;
    private int[] colWeight;

    public LDPC(int[][] H) {
        this.H = H;
        this.N = H[0].length;
        this.K = N - H.length;
        this.perm = new int[N];
        this.invPerm = new int[N];
        this.rowWeight = new int[H.length];
        this.colWeight = new int[N];
        initPerm();
        initWeight();
    }

    public int[] encode(int[] message) {
        if (message.length != K) {
            throw new IllegalArgumentException("Invalid message length");
        }
        int[] codeword = new int[N];
        for (int j = 0; j < N; j++) {
            int sum = 0;
            for (int i = 0; i < H.length; i++) {
                sum += H[i][j] * message[i];
            }
            codeword[j] = sum % 2;
        }
        return codeword;
    }

    public int[] decode(int[] received) {
        if (received.length != N) {
            throw new IllegalArgumentException("Invalid received length");
        }
        int[] syndrome = calculateSyndrome(received);
        int[] error = new int[N];
        for (int i = 0; i < H.length; i++) {
            int[] row = H[i];
            int sum = 0;
            int index = -1;
            for (int j = 0; j < row.length; j++) {
                if (row[j] == 1) {
                    sum += received[j];
                    index = j;
                }
            }
            if (sum % 2 != syndrome[i]) {
                error[index] = 1;
            }
        }
        int[] corrected = new int[N];
        for (int i = 0; i < N; i++) {
            int sum = 0;
            int[] row = H[invPerm[i]];
            for (int j = 0; j < row.length; j++) {
                if (row[j] == 1) {
                    sum += error[j];
                }
            }
            corrected[i] = (received[i] + sum) % 2;
        }
        return Arrays.copyOfRange(corrected, 0, K);
    }

    private void initPerm() {
        for (int i = 0; i < N; i++) {
            perm[i] = i;
        }
        Random random = new Random();
        for (int i = 0; i < N; i++) {
            int j = random.nextInt(N - i) + i;
            int temp = perm[i];
            perm[i] = perm[j];
            perm[j] = temp;
        }
        for (int i = 0; i < N; i++) {
            invPerm[perm[i]] = i;
        }
    }

    private void initWeight() {
        for (int i = 0; i < H.length; i++) {
            int sum = 0;
            for (int j = 0; j < H[i].length; j++) {
                sum += H[i][j];
            }
            rowWeight[i] = sum;
        }
        for (int j = 0; j < N; j++) {
            int sum = 0;
            for (int i = 0; i < H.length; i++) {
                sum += H[i][j];
            }
            colWeight[j] = sum;
        }
    }

    private int[] calculateSyndrome(int[] received) {
        int[] syndrome = new int[H.length];
        for (int i = 0; i < H.length; i++) {
            int sum = 0;
            for (int j = 0; j < H[i].length; j++) {
                sum += H[i][j] * received[j];
            }
            syndrome[i] = sum % 2;
        }
        return syndrome;
    }

    public int getN() {
        return N;
    }

    public int getK() {
        return K;
    }

    public int getRowWeight(int i) {
        return rowWeight[i];
    }

    public int getColWeight(int j) {
        return colWeight[j];
    }
}

在这个示例中，我们使用LDPC码来进行编码和解码。`encode()`方法用于将消息编码为LDPC码，`decode()`方法用于将接收到的LDPC码解码为消息。在构造函数中，我们将LDPC码的校验矩阵和一些基本参数进行初始化，例如码长N、信息长度K、置换数组perm和invPerm、行重rowWeight和列重colWeight。

使用随机置换perm来打乱码字，以便增加编码的随机性。解码过程中，我们首先计算接收到的码字的校验和，并与预期的校验和进行比较，以检测错误。然后，我们根据校验矩阵中的奇偶性检测错误位，并使用伪逆矩阵计算修正后的编码。最后，我们从修正后的编码中提取原始消息。

你可以根据需要修改LDPC码的校验矩阵和其他参数，以适应不同的需求。创建`LDPC`对象后，你可以使用`encode()`方法将消息编码为LDPC码，使用`decode()`方法将接收到的LDPC码解码为消息。