dl_start.m

一个WCDMA接收机的matlab程序

function [size, crc, chCode, C, control] = dl_start(nCode, c_type, Kindex, nFrames,tx_ch)
%
%
% FUNCTION:     dl_start      
% AUTHOR:       Maarit Melvasalo
% DATE:         April 21, 1999
%
% DESC:         This fuction set values for downlink transport channels
%               defined in Simulink library:  utra_lib 
%               These values have been obtained from ETSI UTRA 
%               for ITU-R RTT.  
%
% NOTE:         Parameter value may be changed, but be carefully!
%               Do not change the calcutions.   
%
% HISTORY:      June 17,1999 Maarit Melvasalo
%                   Comments added
% Copyright disclaimer:
%   This software was developed at the National Institute of Standards
%   and Technology by employees of the Federal Government in the course
%   of their official duties. Pursuant to title 17 Section 105 of the
%   United States Code this software is not subject to copyright
%   protection and is in the public domain.
%
%   We would appreciate acknowledgement if the software is used.
%
% *******************************************************************
%
% INPUTS:
%
%  nCode =[code_length, index ] = 
%            spreading factor and index (NOTE index is not required!!) 
%            If the code has been pre set i.e nCode = C, nothing is done
% c_type = mode indicating the channel coding scheme
%      1 = Convolutional coding with   
%      3 = Turbo coding (NOT YET)
% K_index = Coding ratio (input values: (1,2)
% nFrames = number of frames in each block interleaver
% tx_ch = transport channel type
%         1 = Dedicated transport channel			  
%         2 = Primarly common control physical cahnnel (NO CRC)
%         3 = Secondary common control physical channel (FACH or PCH)			  
%
% OUTPUTS: 
%
% size = [N = input_block_size bits_in_frame nFrames N_offset nSlot]
%             input_block_size= number of bits in each input block (calculated)
%             bits_in_frame   = number of coded bits in frame (calculated)
%                               Note that this does not include contorl bits
%             nFrames         = number of frames in each block (calculated) 
%             N_offset        = offset required to obtain correct blocksize (calculated)
%                               after channel coding (and before interleaving)
%             nSlot           = number of slots in frame (set by user)
%             chips_in_slot   = number of slots in frame (constant for given bit bandwidth)
%
% crc = [nCRC poly] 
%             nCRC  = number of CRC bits  (set by user) different for different 
%                     physical channels
%             poly  = generating polynomial for CRC (set by user)
%
% chCode = [c_type K tail poly]
%             c_type  = channel type (given in function call = set by user) 
%             K       = Coding gain  (given in function call = set by user) 
%             tail    = Coding tail length  (set by user)
%             poly    = Generating polynomials for channel coding (set by user)
%
% C = spreading code
%             spreading code depends on given parameters (calculated / given by user)
%
% control = [nPilot TPC TFI] 
%             nPilot  = number of Pilot bits (given by user) 
%             TPC     = number of Power control bits (given by user) 
%             TFI     = number of Transport Format Indicator bits (given by user)  
% 
%
%
%
% ***************************************************************
%
% Common parameters to all Downlink transport channels
%
% ***************************************************************

       R = 4096000;        % chips rate  1/s
       nSlot = 16;         % Number of slots per frame same as 
                           %  wcdma_config.h = SLOTS_IN_FRAME
       tFrame = 1/100;     % 10 ms = frame time 
                           % Simulink s-functions use TD_FRAME = 1 
                           % defined in wcdma_config.h
       chips_in_slot = R/nSlot*tFrame; 
                           % Number of chips in each slot (constant) 

% ***************************************************************
    % If only only one argument is given at the function call
    % only the basic parameters are returned to the user

    if(nargin == 1)

    size = [nSlot,chips_in_slot];
    crc =0;
    C = 0;
    chCode = 0;
    control =0;
    return
    end;

% ***************************************************************
%
%        CRC Basic settings 
%
% *************************************************************** 

    nCRC = 16 ;                     % Number of CRC bits;  
    crc_q = '1021';                 % ARIB  in decimal presentation  4129
    CRCQ = base2dec(crc_q,16);      % same in decimal representation
    crc = [nCRC CRCQ]; 


% ***************************************************************
%
%       CONVOLUTIONAL CODING PARAMETERS
%
% *************************************************************** 
if (c_type == 1)

     % CODING RATIO
     % Kindex == 1 -> K = 2; 
     % Kindex == 2 -> K = 3;

     K = Kindex + 1 ;  tail = 8;  

     %*****************************************

% The Generator polynomials for convolutional coding and decoding
% see UTRA specification chapter 5.2.1.1.1 

     Base = 8;  % indicates the base in which the numbers are given/**/

     if (K == 3)
         p1_o = '557';  % desimal: 367;
         p2_o = '663';  % desimal: 435;
	 p3_o = '711';  % desimal: 457; 
     else 
         p1_o = '561';  % desimal: 367;
	 p2_o = '753';  % desimal: 435;
	 p3_o = '0';    % desimal: N/A; 
     end;


     poly = [base2dec(p1_o,Base) base2dec(p2_o,Base) base2dec(p3_o,Base)];


% ***************************************************************
%
%      NUMBER OF CONTROL BITS
%
% *************************************************************** 

     nPilot = 8;  TPC = 3;    TFI = 2;

     % If not Dedicated transport channel update the following parameters:
     if(tx_ch == 3)
          TPC = 0;    TFI = 0;                 % Secondary common control
     end;
     if (tx_ch == 2)
          TPC = 0;    TFI = 0;  nCRC = 0;       % Primary common control
	  crc = [nCRC CRCQ];
	  if (nCode(1) < 256) 
	       disp('Only Spreading ratio 256 allowed for Primary common control channel');
	       nCode(1)=256;
	       end;
     end;

     % *************************************************************** 
     % Update return values

     chCode = [c_type  K tail poly];
     control = [nPilot TPC TFI];

% *************************************************************** 
%
%      SPREADING CODE
%
% *************************************************************** 

     % if the spreading code has not been assigned

     if ( length(nCode)  < 3)
     
           % set the code index for a inital value 
           index = nCode(1) / 2 ;

           % If the code index has been defined by the use 
	   % in thefunction call check that is valid index

           if ((length(nCode) == 2) & ((index <= nCode) & (index >0) ))  
               index = nCode(2);     end;

	   % Call a matalb mex function which returns the code      
	   C = get_ovsf_code(nCode(1),index);                 
     end; 

     
     if ( length(nCode) > 2) % if the spreading code has already been assigned 
           C = nCode;
           nCode = length(C);
     end;

% *************************************************************** 
%
%      NUMBER OF BITS IN BLOCK, FRAME AND SLOT ETC 
%           
%              DO NOT CHANGE!!!!!!!!
%
% *************************************************************** 

     total_bits = R/nCode(1) * 2 ;
     bits_in_slot = total_bits * tFrame / nSlot ; 
     coded_bits_frame = (bits_in_slot - nPilot -TPC - TFI) * nSlot  ;

     % NOTE:
     % Size of the inputblock to CRC must be * 8 

     N_total = nFrames * coded_bits_frame - tail  ;
     N_tmp = floor(N_total / K);
     if( nCRC > 0)
         N_tmp = 8 * floor(N_tmp / 8)  ;
     end;
     N = N_tmp - nCRC ;
     N_offset = N_total - N_tmp*K;

     size =[N coded_bits_frame nFrames N_offset nSlot chips_in_slot];


     return;
end;

% ***************************************************************
%       END of CONVOLUTIONAL CODING
% ***************************************************************


% ***************************************************************
%
%       TURBO CODING PARAMETERS
%
%       NOT IMPLEMENTED YET
%
% *************************************************************** 

if (c_type > 1)
    disp('Only the convolutiona channel coding (1/3, 9) is implemented currently');
size = 0;
crc =0;
C = 0;
chCode = 0;
control =0;

    return;
end;