/**************************************************************************
*
* ROUTINE
*               smoothpgain
*
* FUNCTION
*
*               smooth pgain values when two errors detected in
*		Hamming block
*
* SYNOPSIS
*               smoothpgain(pgain,twoerror,syndavg,pgains,subframe)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*       pgain		float	i/o	input pgain
*	twoerror	int	i	two error flag
*	syndavg		float	i	error rate estimation parameter
*	pgains		float	i	vector of pgains to calculate variance
*	subframe	int	i	subframe number
*
*   external
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*       frame           int     i
*
***************************************************************************
*
* DESCRIPTION
*
*	Smoothing routine to smooth pgain (alpha) when errors are detected:
*
*	Due to the range of PGAIN, statistical variance is not appropriate.
*	Pseudovariance is used and calculated as: 
*		sum of delta oldpgains/# of deltas
*
*	If this variance of past pgain values is within the range VARLIMIT, 
*	the validity of the current pgain value is tested.  If the current 
*	value of pgain is within the range PGAINLIMIT, PGAIN is passed.  
*	If PGAIN is not within that range it is reset to the average
*	value of surrounding pgain values.
*
*	The array OLDPGAIN contains past values of pgain.  The array
*	PGAINS contains current and future values of pgain.  The array 
*	VECTOR is constructed from the arrays OLDPGAIN and PGAINS 
*	depending on the current subframe.  PGAIN is smoothed based on 
*	the statistics of VECTOR, which contains the nearest four 
*	surrounding pgain values, both past and future values, except 
*	where future values are not available (subframes 3 and 4).
*
*	Absolute values of pgain are used in averaging and reassigning
*	pgain.  All reassigned pgains are limited to the range 0.0-1.0.
*
*	Note:  The smoothing parameters should be capable of adapting
*	to various bit error rate estimates. For example, different
*	values of SYNDAVG should select different levels of PGAINLIMIT,
*	VARLIMIT, and SYNDLIMIT.
*
*
***************************************************************************
*
* CALLED BY
*
*       celp
*
* CALLS
*
*
*
**************************************************************************/
#define PGAINHISTORY	4
#define PGAINLIMIT	0.9
#define VARLIMIT	0.2
#define SYNDLIMIT	0.04
#define TRUE		1
#define FALSE		0
#include <math.h>
extern int frame;
smoothpgain(pgain, twoerror, syndavg, pgains, subframe)
int twoerror, subframe;
float *pgain, syndavg, pgains[];

{
  int i;
  static int enable;
  float abspgain, avg, var, sum1, sum2, vector[4];
  static float oldpgain[PGAINHISTORY];

  abspgain = fabs(*pgain);
  if (subframe != 4)
    enable = TRUE;
  if ((twoerror || syndavg > SYNDLIMIT) && enable)
  {
    if (subframe == 1)
    {
      vector[0] = oldpgain[0];
      vector[1] = oldpgain[1];
      vector[2] = fabs(pgains[1]);
      vector[3] = fabs(pgains[2]);
    }
    else if (subframe == 2)
    {
      vector[0] = oldpgain[0];
      vector[1] = oldpgain[1];
      vector[2] = fabs(pgains[2]);
      vector[3] = fabs(pgains[3]);
    }
    else if (subframe == 3)
    {
      vector[0] = oldpgain[0];
      vector[1] = oldpgain[1];
      vector[2] = oldpgain[2];
      vector[3] = fabs(pgains[3]);
    }
    else if (subframe == 4)
    {
      vector[0] = oldpgain[0];
      vector[1] = oldpgain[1];
      vector[2] = oldpgain[2];
      vector[3] = oldpgain[3];
    }
    else
      printf("smoothpgain: Error in subframe number\n");

    for (sum1 = 0.0, i = 0; i < PGAINHISTORY; i++)
    {
      sum1 += vector[i];
    }
    avg = sum1 / PGAINHISTORY;
    for (sum2 = 0.0, i = 0; i < PGAINHISTORY - 1; i++)
      sum2 += fabs(vector[i] - vector[i + 1]);
    var = sum2 / (PGAINHISTORY - 1);
    if (var < VARLIMIT && enable &&
	(abspgain > avg + PGAINLIMIT || abspgain < avg - PGAINLIMIT))
    {
      *pgain = avg;
      if (*pgain > 1.0)
	*pgain = 1.0;
      if (*pgain < -1.0)
	*pgain = -1.0;
      printf("smoothpgain:  pgain value reset to avg at frame %d subframe %d\n",
	      frame, subframe);
      if (subframe == 3)
      {
	enable = FALSE;
	printf("smoothpgain:  smoothing disabled for subframe 4\n");
      }
    }
  }

  for (i = PGAINHISTORY - 1; i > 0; i--)
    oldpgain[i] = oldpgain[i - 1];
  oldpgain[0] = abspgain;
}