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path: root/cesar/ce/rx/bitloading/src/ber.c
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/* Cesar project {{{
 *
 * Copyright (C) 2009 Spidcom
 *
 * <<<Licence>>>
 *
 * }}} */
/**
 * \file    ce/rx/bitloading/src/ber.c
 * \brief   Functions to compute BER.
 * \ingroup ce_rx
 *
 * This module contains some sets of functions to compute the BER from a given
 * NSR and modulation.
 */
#include "common/std.h"

#include "ce/rx/bitloading/inc/ber.h"
#include "ce/rx/bitloading/inc/poly.h"

/**
 * Default value of margin to apply to BER target.
 * This value is apparently quantified on 53 bits.
 *
 * By default, we do not want any BER margin.
 */
u64 ce_rx_bl_ber_margin_[] = { 0ull, 0ull };

/* Imported from
 * http://stestephe/svn/spidcom_digital_svn/projects/DSP_350/DSP_chain/SW/Bit_Loading/BER_vs_NSR/Polynomes_BERinq_vs_NSRq_normalises.m
 * Revision: 11785.
 */
ce_rx_bl_ber_poly_coef_t ce_rx_bl_ber_poly_coef[PHY_FEC_RATE_NB][CE_MOD_COUNT - 1] =
{
    {
        {
            1,
            { 3 },
            {
                { 2ll, -614142ll, 69770329856ll, -362383471042474ll },
            },
            { 5461, 131070 },
        },
        {
            1,
            { 3 },
            {
                { 21ll, -3182001ll, 154673115663ll, -388385849742766ll },
            },
            { 2654, 35212 },
        },
        {
            1,
            { 3 },
            {
                { 445ll, -19298713ll, 343639234529ll, -279649449376397ll },
            },
            { 854, 29538 },
        },
        {
            1,
            { 3 },
            {
                { 2204ll, -55355989ll, 564885755970ll, -264069612527883ll },
            },
            { 491, 17534 },
        },
        {
            1,
            { 4 },
            {
                { -20ll, 212913ll, -854282799ll, 1912250068949ll, -188500565548306ll },
            },
            { 104, 4107 },
        },
        {
            1,
            { 5 },
            {
                { 1ll, -4119ll, 8965279ll, -9491962383ll, 5894366772316ll, -106995737728260ll },
            },
            { 19, 1516 },
        },
        {
            1,
            { 5 },
            {
                { 2ll, -9622ll, 20100982ll, -19509283504ll, 9585633818678ll, 143328708605390ll },
            },
            { 0, 1436 },
        },
    },
    {
        {
            1,
            { 3 },
            {
                { 2ll, -614142ll, 69770329856ll, -362383471042474ll },
            },
            { 5461, 131070 },
        },
        {
            1,
            { 3 },
            {
                { 21ll, -3182001ll, 154673115663ll, -388385849742766ll },
            },
            { 2654, 35212 },
        },
        {
            1,
            { 3 },
            {
                { 445ll, -19298713ll, 343639234529ll, -279649449376397ll },
            },
            { 854, 29538 },
        },
        {
            1,
            { 3 },
            {
                { 2204ll, -55355989ll, 564885755970ll, -264069612527883ll },
            },
            { 491, 17534 },
        },
        {
            1,
            { 4 },
            {
                { -10ll, 134707ll, -659991499ll, 1736969891776ll, -177145201462823ll },
            },
            { 107, 4225 },
        },
        {
            1,
            { 5 },
            {
                { 1ll, -3453ll, 7709283ll, -8478165747ll, 5556178345777ll, -134510842708508ll },
            },
            { 26, 1423 },
        },
        {
            1,
            { 5 },
            {
                { 30ll, -86185ll, 92863876ll, -48024691156ll, 13632579799234ll, -24445679596716ll },
            },
            { 2, 792 },
        },
    },
};

static const s64
ce_rx_bl_ber_consign_coefs[PHY_FEC_RATE_NB][CE_RX_BL_BER_POLY_MAX_DEGREE] = {
    { -106541828252ll, 841188148187808ll },
    { -5639041049ll, 127893477397182ll },
};
static const u8 ce_rx_bl_ber_consign_degrees[PHY_FEC_RATE_NB] = { 1, 1, };

const u64 ce_rx_bl_initial_bpt[PHY_FEC_RATE_NB] = {
    10 * CE_RX_BL_BPT_QUANT_FACTOR,
    10 * CE_RX_BL_BPT_QUANT_FACTOR
};

u64
ce_rx_bl_ber_for_mod (ce_rx_bl_ber_poly_coef_t *poly, u32 nsr, u8 mod_index)
{
    /* Check parameters. */
    dbg_assert (poly);
    dbg_assert (mod_index <= CE_MOD_COUNT);

    /* If modulation is 0 or NSR under first range. */
    if (!mod_index || nsr < poly[mod_index - 1].range[0])
        return CE_RX_BL_BER_DEFAULT_UNDER;
    /* Go through each range. */
    uint i;
    for (i = 0; i < poly->poly_count; i++)
    {
        /* If under range, compute polynomial. */
        if (nsr <= poly[mod_index - 1].range[i + 1])
            return ce_rx_bl_poly (poly[mod_index - 1].degree[i],
                                  poly[mod_index - 1].coef[i],
                                  nsr);
    }
    return CE_RX_BL_BER_DEFAULT_OVER;
}

void
ce_rx_bl_ber_vs_nsr (ce_rx_bl_ber_poly_coef_t *poly, u32 nsr, u64 ber_pt,
                     u8 *mod_lower, u64 *ber_lower, u64 *ber_upper)
{
    /* Check parameters. */
    dbg_assert (poly);
    dbg_assert (ber_pt < CE_RX_BL_BER_DEFAULT_OVER);
    dbg_assert (mod_lower);
    dbg_assert (ber_lower);
    dbg_assert (ber_upper);

    /* Let's do a dichotomy search. */
    uint lm = 1, um = 8, m;
    u64 ber_index[CE_MOD_COUNT] = { 0, -1, -1, -1, -1, -1, -1, -1 };

    /* Dichotomy search. */
    while (lm != um)
    {
        m = (lm + um) / 2;
        ber_index[m] = ce_rx_bl_ber_for_mod (poly, nsr, m);
        /* Index to high? */
        if (ber_index[m] > ber_pt)
        {
            um = m;
        }
        else
        {
            lm = m + 1;
        }
    }
    m = lm;

    dbg_assert (m);
    *mod_lower = m - 1;
    *ber_lower = ber_index[m - 1];
    /* Lower BER must respect consign. */
    dbg_assert (*ber_lower < ber_pt);
    *ber_upper = ber_index[m];
}

u64
ce_rx_bl_ber_pt_bpt (phy_fecrate_t fec_rate, u64 bpt)
{
    /* Check parameters. */
    dbg_assert (fec_rate < PHY_FEC_RATE_NB);
    dbg_assert (bpt >= (CE_BIT_PER_MOD[1] * CE_RX_BL_BPT_QUANT_FACTOR)
                && bpt <= (CE_BIT_PER_MOD[CE_MOD_COUNT - 1]
                           * CE_RX_BL_BPT_QUANT_FACTOR));

    return ce_rx_bl_poly (ce_rx_bl_ber_consign_degrees[fec_rate],
                          ce_rx_bl_ber_consign_coefs[fec_rate], bpt);
}

void
ce_rx_bl_ber_margin_set (u64 margin_q[PHY_FEC_RATE_NB])
{
    /* Check parameter. */
    dbg_assert (margin_q);

    /* Store margin values. */
    phy_fecrate_t i;
    for (i = PHY_FEC_RATE_1_2; i < PHY_FEC_RATE_NB; i++)
        ce_rx_bl_ber_margin_[i] = margin_q[i];
}