System Design Flow and Fixed-point Arithmetic - Digital Design of Signal Processing Systems: A Practical Approach - page 87

% BPSK = 1, QPSK = 2, 8PSK = 3, 16QAM = 4
% All-user defined parameters are set in structure USER_PARAMS
USER_PARAMS.MOD_SCH = 2; %select QPSK for current simulation
USER_PARAMS.CHUNK_SZ = 256; %set buffer size for chunk by chunk processing
USER_PARAMS.NO_CHUNKS = 100;% set no of chunks for simulation
% generate raw data for simulation
raw_data = randint(1, USER_PARAMS.NO_CHUNKS*USER_PARAMS.CHUNK_SZ)
% Initialize user defined, system defined parameters and states in respective
% Structures
PARAMS = MOD_Params_Init(USER_PARAMS);
STATES = MOD_States_Init(PARAMS);
mod_out = [];
% Code should be structured to process data on chunk-by-chunk basis
for iter = 0:USER_PARAMS.NO_CHUNKS-1
in_data = raw_data
(iter*USER_PARAMS.CHUNK_SZ+1:USER_PARAMS.CHUNK_SZ*(iter+1));
[out_sig,STATES]= Modulator(in_data,PARAMS,STATES);
mod_out = [mod_out out_sig];
end
The parameter initialization function sets all the parameters for the modulator.
% Initializing the user defined parameters and system design parameters
% In PARAMS
function PARAMS = MOD_Params_Init(USER_PARAMS)
% Structure for transmitter parameters
PARAMS.MOD_SCH = USER_PARAMS.MOD_SCH;
PARAMS.SPS = 4; % Sample per symbol
% Create a root raised cosine pulse-shaping filter
PARAMS.Nyquist_filter = rcosfir(.5 , 5, PARAMS.SPS, 1);
% Bits per symbol, in this case bits per symbols is same as mod scheme
PARAMS.BPS = USER_PARAMS.MOD_SCH;
% Lookup tables for BPSK, QPSK, 8-PSK and 16-QAM using gray coding
BPSK_Table = [(-1 + 0*j) (1 + 0*j)];
QPSK_Table = [(-.707 - .707*j) (-.707 + .707*j)...
(.707 - .707*j) (.707 + .707*j)];
PSK8_Table = [(1 + 0j) (.7071 + .7071i) (-.7071 + .7071i) (0 + i)...
(-1 + 0i) (-.7071 - .7071i) (.7071 - .7071i) (0 - 1i)];
QAM_Table = [(-3 + -3*j) (-3 + -1*j) (-3 + 3*j) (-3 + 1*j) (-1 + -3*j)...
(-1 + -1*j) (-1 + 3*j) (-1 + 1*j) (3 + -3*j) (3 + -1*j)...
(3 + 3*j) (3 + 1*j) (1 + -3*j) (1 + -1*j) (1 + 3*j) (1 + 1*j)];
% Constellation selection according to bits per symbol
if(PARAMS.BPS == 1)
PARAMS.const_Table = BPSK_Table;
elseif(PARAMS.BPS == 2)
PARAMS.const_Table = QPSK_Table;
elseif(PARAMS.BPS == 3)
PARAMS.const_Table = PSK8_Table;
elseif(PARAMS.BPS == 4)
PARAMS.const_Table = QAM_Table;