/* CHANNEL.C - Procedures and variables regarding channels. */ /* Copyright (c) 2001 by Radford M. Neal * * Permission is granted for anyone to copy, use, modify, or distribute this * program and accompanying programs and documents for any purpose, provided * this copyright notice is retained and prominently displayed, along with * a note saying that the original programs are available from Radford Neal's * web page, and note is made of any changes made to the programs. The * programs and documents are distributed without any warranty, express or * implied. As the programs were written for research purposes only, they have * not been tested to the degree that would be advisable in any important * application. All use of these programs is entirely at the user's own risk. */ #include #include #include #include #include "channel.h" /* GLOBAL VARIABLES. Declared in channel.h. */ channel_type channel; /* Type of channel */ double error_prob; /* Error probability for BSC */ double std_dev; /* Noise standard deviation for AWGN */ double lwidth; /* Width of noise distribution for AWLN */ /* PARSE A COMMAND-LINE SPECIFICATION OF A CHANNEL. Takes a pointer to an argument list and an argument count; returns the number of arguments that make up a channel specification at this point in the command line. Returns zero if the argument list does not start with a channel specification. Returns -1 if there seems to be a channel specification here, but it's invalid. Sets the variables declared in channel.h to the type and parameters of the channel. */ int channel_parse ( char **argv, /* Pointer to argument list */ int argc /* Number of arguments in list */ ) { char junk; if (argc==0) return 0; if (strcmp(argv[0],"bsc")==0 || strcmp(argv[0],"BSC")==0) { channel = BSC; if (argc<2 || sscanf(argv[1],"%lf%c",&error_prob,&junk)!=1 || error_prob<=0 || error_prob>=1) { return -1; } else { return 2; } } else if (strcmp(argv[0],"awgn")==0 || strcmp(argv[0],"AWGN")==0) { channel = AWGN; if (argc<2 || sscanf(argv[1],"%lf%c",&std_dev,&junk)!=1 || std_dev<=0) { return -1; } else { return 2; } } else if (strcmp(argv[0],"awln")==0 || strcmp(argv[0],"AWLN")==0) { channel = AWLN; if (argc<2 || sscanf(argv[1],"%lf%c",&lwidth,&junk)!=1 || lwidth<=0) { return -1; } else { return 2; } } else { return 0; } } /* PRINT USAGE MESSAGE REGARDING CHANNEL SPECIFICATIONS. */ void channel_usage(void) { fprintf(stderr, "Channel: bsc error-probability | awgn standard-deviation | awln width\n"); }