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iwd/src/band.c

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/*
*
* Wireless daemon for Linux
*
* Copyright (C) 2021 Intel Corporation. All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
*/
#include <stdbool.h>
#include <stdint.h>
#include <errno.h>
#include <ell/ell.h>
#include "ell/useful.h"
#include "band.h"
void band_free(struct band *band)
{
l_free(band);
}
/*
* Rates are stored as they are encoded in the Supported Rates IE.
* This data was taken from 802.11 Section 17.3.10.2 Table 17-18 and
* Table 17-4. Together we have minimum RSSI required for a given data rate.
*/
static const struct {
int32_t rssi;
uint8_t rate;
} rate_rssi_map[] = {
{ -90, 2 }, /* Make something up for 11b rates */
{ -88, 4 },
{ -86, 11 },
{ -84, 22 },
{ -82, 12 },
{ -81, 18 },
{ -79, 24 },
{ -77, 36 },
{ -74, 48 },
{ -70, 72 },
{ -66, 96 },
{ -65, 108 },
};
static bool peer_supports_rate(const uint8_t *rates, uint8_t rate)
{
int i;
if (rates && rates[1]) {
for (i = 0; i < rates[1]; i++) {
uint8_t r = rates[i + 2] & 0x7f;
if (r == rate)
return true;
}
}
return false;
}
int band_estimate_nonht_rate(const struct band *band,
const uint8_t *supported_rates,
const uint8_t *ext_supported_rates,
int32_t rssi, uint64_t *out_data_rate)
{
int nrates = L_ARRAY_SIZE(rate_rssi_map);
uint8_t max_rate = 0;
int i;
if (!supported_rates && !ext_supported_rates)
return -EINVAL;
/*
* Start at the back of the array. Rates are generally given in
* ascending order, starting at 11b rates, then 11g rates. More often
* than not we'll pick the highest rate and avoid unneeded processing
*/
for (i = band->supported_rates_len - 1; i >= 0; i--) {
uint8_t rate = band->supported_rates[i];
int j;
if (max_rate >= rate)
continue;
/* Can this rate be used at the peer's RSSI? */
for (j = 0; j < nrates; j++)
if (rate_rssi_map[j].rate == rate)
break;
if (j == nrates)
continue;
if (rssi < rate_rssi_map[j].rssi)
continue;
if (peer_supports_rate(supported_rates, rate) ||
peer_supports_rate(ext_supported_rates, rate))
max_rate = rate;
}
if (!max_rate)
return -ENETUNREACH;
*out_data_rate = max_rate * 500000;
return 0;
}
/*
* Base RSSI values for 20MHz (both HT and VHT) channel. These values can be
* used to calculate the minimum RSSI values for all other channel widths. HT
* MCS indexes are grouped into ranges of 8 (per spatial stream) where VHT are
* grouped in chunks of 10. This just means HT will not use the last two
* index's of this array.
*/
static const int32_t ht_vht_base_rssi[] = {
-82, -79, -77, -74, -70, -66, -65, -64, -59, -57
};
/*
* Data Rate for HT/VHT is obtained according to this formula:
* Nsd * Nbpscs * R * Nss / (Tdft + Tgi)
*
* Where Nsd is [52, 108, 234, 468] for 20/40/80/160 Mhz respectively
* Nbpscs is [1, 2, 4, 6, 8] for BPSK/QPSK/16QAM/64QAM/256QAM
* R is [1/2, 2/3, 3/4, 5/6] depending on the MCS index
* Nss is the number of spatial streams
* Tdft = 3.2 us
* Tgi = Long/Short GI of 0.8/0.4 us
*
* Short GI rate can be easily obtained by multiplying by (10 / 9)
*
* The table was pre-computed using the following python snippet:
* rfactors = [ 1/2, 1/2, 3/4, 1/2, 3/4, 2/3, 3/4, 5/6, 3/4, 5/6 ]
* nbpscs = [1, 2, 2, 4, 4, 6, 6, 6, 8, 8 ]
* nsds = [52, 108, 234, 468]
*
* for nsd in nsds:
* rates = []
* for i in xrange(0, 10):
* data_rate = (nsd * rfactors[i] * nbpscs[i]) / 0.004
* rates.append(int(data_rate) * 1000)
* print('rates for nsd: ' + nsd + ': ' + rates)
*/
static const uint64_t ht_vht_rates[4][10] = {
[OFDM_CHANNEL_WIDTH_20MHZ] = {
6500000ULL, 13000000ULL, 19500000ULL, 26000000ULL,
39000000ULL, 52000000ULL, 58500000ULL, 65000000ULL,
78000000ULL, 86666000ULL },
[OFDM_CHANNEL_WIDTH_40MHZ] = {
13500000ULL, 27000000ULL, 40500000ULL, 54000000ULL,
81000000ULL, 108000000ULL, 121500000ULL, 135000000ULL,
162000000ULL, 180000000ULL, },
[OFDM_CHANNEL_WIDTH_80MHZ] = {
29250000ULL, 58500000ULL, 87750000ULL, 117000000ULL,
175500000ULL, 234000000ULL, 263250000ULL, 292500000ULL,
351000000ULL, 390000000ULL, },
[OFDM_CHANNEL_WIDTH_160MHZ] = {
58500000ULL, 117000000ULL, 175500000ULL, 234000000ULL,
351000000ULL, 468000000ULL, 526500000ULL, 585000000ULL,
702000000ULL, 780000000ULL,
}
};
/*
* Both HT and VHT rates are calculated in the same fashion. The only difference
* is a relative MCS index is used for HT since, for each NSS, the formula
* is the same with relative index's. This is why this is called with index % 8
* for HT, but not VHT.
*/
bool band_ofdm_rate(uint8_t index, enum ofdm_channel_width width,
int32_t rssi, uint8_t nss, bool sgi,
uint64_t *data_rate)
{
uint64_t rate;
int32_t width_adjust = width * 3;
if (rssi < ht_vht_base_rssi[index] + width_adjust)
return false;
rate = ht_vht_rates[width][index];
if (sgi)
rate = rate / 9 * 10;
rate *= nss;
*data_rate = rate;
return true;
}
static bool find_best_mcs_ht(const struct band *band,
const uint8_t *tx_mcs_set,
uint8_t max_mcs, enum ofdm_channel_width width,
int32_t rssi, bool sgi,
uint64_t *out_data_rate)
{
int i;
/*
* TODO: Support MCS values 32 - 76
*
* The MCS values > 31 use an unequal modulation, and the number of
* supported MCS indexes per NSS differs. We do not consider them
* here for now to keep things simple(r).
*/
for (i = max_mcs; i >= 0; i--) {
if (!test_bit(band->ht_mcs_set, i))
continue;
if (!test_bit(tx_mcs_set, i))
continue;
if (band_ofdm_rate(i % 8, width, rssi,
(i / 8) + 1, sgi, out_data_rate))
return true;
}
return false;
}
int band_estimate_ht_rx_rate(const struct band *band,
const uint8_t *htc, const uint8_t *hto,
int32_t rssi, uint64_t *out_data_rate)
{
uint8_t channel_offset;
int max_mcs = 31;
bool sgi;
uint8_t unequal_tx_mcs_set[16];
const uint8_t *tx_mcs_set;
if (!band->ht_supported)
return -ENOTSUP;
if (!htc || !hto)
return -ENOTSUP;
memset(unequal_tx_mcs_set, 0, sizeof(unequal_tx_mcs_set));
tx_mcs_set = htc + 5;
/*
* Check 'Tx MCS Set Defined' at bit 96 and 'Tx MCS Set Unequal' at
* bit 97 of the Supported MCS Set field. Also extract 'Tx Maximum
* Number of Spatial Streams Supported' field at bits 98 and 99.
*
* Note 44 on page 1662 of 802.11-2016 states:
* "How a non-AP STA determines an AP's HT MCS transmission support,
* if the Tx MCS Set subfield in the HT Capabilities element
* advertised by the AP is equal to 0 or if he Tx Rx MCS Set Not Equal
* subfield in that element is equal to 1, is implementation dependent.
* The non-AP STA might conservatively use the basic HT-MCS set, or it
* might use knowledge of past transmissions by the AP, or it might
* use other means.
*/
if (test_bit(tx_mcs_set, 96)) {
if (test_bit(tx_mcs_set, 97)) {
uint8_t max_nss = bit_field(tx_mcs_set[12], 2, 2);
max_mcs = max_nss * 4 + 7;
/*
* For purposes of finding the best MCS below, assume
* the AP can send any MCS up to max_nss (i.e 0-7 for
* 1 nss, 0-15 for 2 nss, 0-23 for 3 nss, 0-31 for 4
*/
memset(unequal_tx_mcs_set, 0xff, max_nss + 1);
tx_mcs_set = unequal_tx_mcs_set;
}
} else
max_mcs = 7;
/* Test for 40 Mhz operation */
channel_offset = bit_field(hto[3], 0, 2);
if (test_bit(hto + 3, 2) &&
(channel_offset == 1 || channel_offset == 3)) {
sgi = test_bit(band->ht_capabilities, 6) &&
test_bit(htc + 2, 6);
if (find_best_mcs_ht(band, tx_mcs_set, max_mcs,
OFDM_CHANNEL_WIDTH_40MHZ,
rssi, sgi, out_data_rate))
return 0;
}
sgi = test_bit(band->ht_capabilities, 5) && test_bit(htc + 2, 5);
if (find_best_mcs_ht(band, tx_mcs_set, max_mcs,
OFDM_CHANNEL_WIDTH_20MHZ,
rssi, sgi, out_data_rate))
return 0;
return -ENETUNREACH;
}
static bool find_best_mcs_vht(uint8_t max_index, enum ofdm_channel_width width,
int32_t rssi, uint8_t nss, bool sgi,
uint64_t *out_data_rate)
{
int i;
/*
* Iterate over all available MCS indexes to find the best one
* we can use. Note that band_ofdm_rate() will return false if a
* given combination cannot be used due to rssi being too low.
*
* Also, Certain MCS/Width/NSS combinations are not valid,
* refer to IEEE 802.11-2016 Section 21.5 for more details
*/
for (i = max_index; i >= 0; i--)
if (band_ofdm_rate(i, width, rssi,
nss, sgi, out_data_rate))
return true;
return false;
}
/*
* IEEE 802.11 - Table 9-250
*
* For simplicity, we are ignoring the Extended BSS BW support, per NOTE 11:
*
* NOTE 11-A receiving STA in which dot11VHTExtendedNSSCapable is false will
* ignore the Extended NSS BW Support subfield and effectively evaluate this
* table only at the entries where Extended NSS BW Support is 0.
*
* This also allows us to group the 160/80+80 widths together, since they are
* the same when Extended NSS BW is zero.
*/
int band_estimate_vht_rx_rate(const struct band *band,
const uint8_t *vhtc, const uint8_t *vhto,
const uint8_t *htc, const uint8_t *hto,
int32_t rssi, uint64_t *out_data_rate)
{
uint32_t nss = 0;
uint32_t max_mcs = 7; /* MCS 0-7 for NSS:1 is always supported */
const uint8_t *rx_mcs_map;
const uint8_t *tx_mcs_map;
int bitoffset;
uint8_t chan_width;
uint8_t channel_offset;
bool sgi;
if (!band->vht_supported || !band->ht_supported)
return -ENOTSUP;
if (!vhtc || !vhto || !htc || !hto)
return -ENOTSUP;
if (vhto[2] > 3)
return -EBADMSG;
/*
* Find the highest NSS/MCS index combination. Since this is used by
* STAs, we try to estimate our 'download' speed from the AP/peer.
* Hence we look at the TX MCS map of the peer and our own RX MCS map
* to find an overlapping combination that works
*/
rx_mcs_map = band->vht_mcs_set;
tx_mcs_map = vhtc + 2 + 8;
for (bitoffset = 14; bitoffset >= 0; bitoffset -= 2) {
uint8_t rx_val = bit_field(rx_mcs_map[bitoffset / 8],
bitoffset % 8, 2);
uint8_t tx_val = bit_field(tx_mcs_map[bitoffset / 8],
bitoffset % 8, 2);
/*
* 0 indicates support for MCS 0-7
* 1 indicates support for MCS 0-8
* 2 indicates support for MCS 0-9
* 3 indicates no support
*/
if (rx_val == 3 || tx_val == 3)
continue;
/* 7 + rx_val/tx_val gives us the maximum mcs index */
max_mcs = minsize(rx_val, tx_val) + 7;
nss = bitoffset / 2 + 1;
break;
}
if (!nss)
return -EBADMSG;
/*
* There is no way to know whether a peer would send us packets using
* the short guard interval (SGI.) SGI capability is only used to
* indicate whether the peer can accept packets that we send this way.
* Here we make the assumption that if the peer has the capability to
* accept packets using SGI and we have the capability to do so, then
* SGI will be used
*
* Also, we assume that the highest bandwidth will result in the
* highest rate for any given rssi. Even accounting for invalid
* MCS/Width/NSS combinations, the higher channel width results
* in better data rate at [mcs index - 2] compared to [mcs index] of
* a next lower bandwidth.
*/
/* See if 160 Mhz operation is available */
chan_width = bit_field(band->vht_capabilities[0], 2, 2);
if (chan_width != 1 && chan_width != 2)
goto try_vht80;
/*
* Channel Width is set to 2 or 3, or 1 and
* channel center frequency segment 1 is non-zero
*/
if (vhto[2] == 2 || vhto[2] == 3 || (vhto[2] == 1 && vhto[4])) {
sgi = test_bit(band->vht_capabilities, 6) &&
test_bit(vhtc + 2, 6);
if (find_best_mcs_vht(max_mcs, OFDM_CHANNEL_WIDTH_160MHZ,
rssi, nss, sgi, out_data_rate))
return 0;
}
try_vht80:
if (vhto[2] == 1) {
sgi = test_bit(band->vht_capabilities, 5) &&
test_bit(vhtc + 2, 5);
if (find_best_mcs_vht(max_mcs, OFDM_CHANNEL_WIDTH_80MHZ,
rssi, nss, sgi, out_data_rate))
return 0;
} /* Otherwise, assume 20/40 Operation */
channel_offset = bit_field(hto[3], 0, 2);
/* Test for 40 Mhz operation */
if (test_bit(hto + 3, 2) &&
(channel_offset == 1 || channel_offset == 3)) {
sgi = test_bit(band->ht_capabilities, 6) &&
test_bit(htc + 2, 6);
if (find_best_mcs_vht(max_mcs, OFDM_CHANNEL_WIDTH_40MHZ,
rssi, nss, sgi, out_data_rate))
return 0;
}
sgi = test_bit(band->ht_capabilities, 5) && test_bit(htc + 2, 5);
if (find_best_mcs_vht(max_mcs, OFDM_CHANNEL_WIDTH_20MHZ,
rssi, nss, sgi, out_data_rate))
return 0;
return -ENETUNREACH;
}
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