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CBOC signal modulation and demodulation simulation based on MATLAB, output its correlation, power spectrum and frequency offset tracking

2022-07-23 15:04:00 【I love c programming】

Catalog

1. Algorithm description

BOC－Binary Offset Carrier, Also known as binary offset carrier modulation , Is in Galileo A new carrier modulation method proposed in the process of system design . Its basic principle is based on the original BPSK Modulation basis , Add another binary subcarrier （ At present, subcarriers are mainly composed of sine or cosine symbol functions , I.e. similitude of form sgn(sin(t)) or sgn(cos(t)), A symbolic function with sine or cosine signals as parameters ）. The biggest feature of this modulation method is , The main lobe of its power spectrum is split into two symmetrical parts , And according to the selected parameters , The distance between the two main lobes can also vary . The commonly used expression is BOC(m,n) In the form of , among m Represents the subcarrier frequency ,n It represents the spreading code rate , The specific values are 1.023MHz Of m Times and n times .

MBOC－Multiplexed Binary Offset Carrier, It can be seen from the English name that this is BOC A multiplexing method of subcarrier modulated signals . This is from Guenter W.Hein The leadership of the GPS Signal design team and Jhon W.Betz The leadership of the Galileo A modulation method jointly proposed by the signal design team . Currently, it has been optimized , The main discussion and design application is BOC(1,1) and BOC(6,1) The combination of . According to the power distribution requirements of data channel and pilot channel , And adopt different specific modulation methods , There can be many combinations , For details, please refer to relevant literature . At present, they are basically from BOC(1,1) and BOC(6,1) From the perspective of power distribution .

MBOC It's just a general term for signal multiplexing , At present, there are mainly two specific implementations , namely CBOC（Composite BOC） and TMBOC（time-multiplexed BOC）.CBOC To put it simply , It's based on BOC(1,1) and BOC(6,1) Different power （ amplitude ） Weight composition 4 Modulation realized by level symbol , It is a compound implementation of amplitude . and TMBOC It is a method similar to time division multiplexing , That is, specify the length of a group of chips , Among the fixed positions in this group of chips are BOC(6,1), The other positions are BOC(1,1). Both methods can meet the requirements of power spectrum allocation , However, the power spectrum is different .

2. Partial procedure

f0            = 1.023e6;% Reference frequency 
BOCm          = 10;
BOCn          = 2;
% Subcarrier frequency 
fs            = BOCm*f0;
% Code rate 
fc            = BOCn*f0; 
fIF           = 2*fs;
fsamp         = 24*f0;% sampling frequency 
% Sampling point of one cycle 
n             = fsamp/1000;
KK            = 1000;
% Doppler frequency 
fd            = 0;
Nn            = n;
nn            = [0:Nn-1];
CAIndex       = floor(fsamp/fc);
% Satellite number of data channel 
Ndata         = 1;
% The satellite number of the pilot channel 
Npilot        = 2;
%BOC
[BOC_data,BOC_pilot] = func_BOC_Signal(Ndata,Npilot,Nn,CAIndex);
% Mobile chip 
BOC_data_code        = [BOC_data(n-KK:n),BOC_data(1:n-KK-1)]; 
BOC_pilot_code       = [BOC_pilot(n-KK:n),BOC_pilot(1:n-KK-1)];
t                    = [1:Nn]/fsamp;
% Input signal 
cosCarr              = cos(2*pi*(fIF + fd)*t);
sinCarr              = sin(2*pi*(fIF + fd)*t);
Signal_Boc           = 2*BOC_data_code .* cosCarr + 2*BOC_pilot_code .* sinCarr;
 
% Length of simulation data 
in_signal            = Signal_Boc;

figure,
plot(in_signal);
acf_cboc = xcorr(in_signal,in_signal);

figure,
plot(acf_cboc);
title('CBOC ACF');

psd_cboc = fftshift(fft(acf_cboc));
figure,
plot(abs(psd_cboc));
title('CBOC PSD');

% Add Gaussian white noise 
in_signal = awgn(in_signal,SNR,'measured');

% Compare algorithms BPSK like
[Y,Yi]    = BPSK_like(in_signal,n,Nn,fsamp,f0,fIF);