How to implement 8PSK modulation in Matlab?

clc, clear all, close all
N = 1e6-1;
M = 8;
k = log2(M);
SNR_db = 0:12;
max_b_sent = 3e7;

mapping =[1/sqrt(2) (1+1i)/2 (0+1i)/sqrt(2) (-1+1i)/2 -1/sqrt(2) (-1-1i)/(2) (0-1i)/sqrt(2) (1-1i)/(2)];
for m = 1:length(SNR_db)
    num_err = 0;
    num_tr = 0;
    num_symb_err = 0;
    num_symb_tr = 0;
    while (num_err<100) && (num_tr<max_b_sent)
          %Transmitter
          b = randi(2,1,N)-1;
          c = bi2de(reshape(b,k,N/k)','left-msb')';
          s = mapping(c+1);
          %AWGN Channel
          sigma = 10^(-SNR_db(m)/20);
          n = sigma*(1/sqrt(2))*(randn(1,N/k)+1i*randn(1,N/k));
          r = s+n;
          %Receiver
          Dist = [abs(r-mapping(1));abs(r-mapping(2));abs(r-mapping(3));abs(r-mapping(4));abs(r-mapping(5));abs(r-mapping(6));abs(r-mapping(7));abs(r-mapping(8))] ;
          [~,index] = min(Dist,[],1);
          c_est = index-1;
          b_est = reshape(de2bi(c_est,'left-msb')',1,N);
          num_err = num_err + sum(b~=b_est);
          num_tr = num_tr + N; 
          num_symb_err = num_symb_err + sum(c~=c_est);
          num_symb_tr = num_symb_tr + N/k;
    end
    ber(m) = num_err / num_tr ; 
    ser(m) = num_symb_err / num_symb_tr ; 
end
SNR_lin = 10.^(SNR_db/10);
% SER theory
ser_th = 2.*qfunc(sqrt(SNR_lin).*sin(pi/M));

% BER theory

ber_th = (1/M)*erfc(sqrt(SNR_lin*M)*sin(pi/M));
%ber_th = qfunc(sqrt(SNR_lin));

% SER drawing
figure
semilogy(SNR_db,ser,'*')
hold on
semilogy(SNR_db,ser_th,'r')

% BER drawing
figure
ebno = SNR_db-10*log10(k);
semilogy(ebno,ber,'*')
hold on
semilogy(ebno,ber_th,'r')