/* * * 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 #include #include #include #include "ell/useful.h" #include "band.h" void band_free(struct band *band) { l_free(band); } /* * 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_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 -EINVAL; }