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Adjust the SNR when comparing BSSes based on Tx power config

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The max transmit power of Standard Power (SP) Access Points (AP) on
6 GHz band and APs on 2.4 GHz and 5 GHz bands is limited by effective
isotropic radiated power (EIRP), while the max transmit power of Low
Power Indoor (LPI) APs on 6 GHz Band is limited by power spectral
density (PSD). Therefore the max transmit power of LPI APs grows as the
channel width increases, similar to the noise power which has constant
PSD.

Adjust the SNR of BSSes based on the transmit power config and max
channel width. EIRP limited APs usually have constant max transmit power
on different channel widths, their SNR decreases on larger channel width
because the noise power is higher, while PSD limited APs have constant
SNR over all channel widths.

Signed-off-by: Kaidong Wang <kaidong@chromium.org>
This commit is contained in:
Kaidong Wang 2023-11-08 03:58:05 +00:00 committed by Jouni Malinen
parent cab5f5fa7a
commit 790beb84ac
6 changed files with 216 additions and 9 deletions
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3
src/drivers/driver.h
View file

@ -334,6 +334,8 @@ struct hostapd_hw_modes {
* @flags: information flags about the BSS/IBSS (WPA_SCAN_*)
* @bssid: BSSID
* @freq: frequency of the channel in MHz (e.g., 2412 = channel 1)
* @max_cw: the max channel width of the connection (calculated during scan
* result processing)
* @beacon_int: beacon interval in TUs (host byte order)
* @caps: capability information field in host byte order
* @qual: signal quality
@ -370,6 +372,7 @@ struct wpa_scan_res {
unsigned int flags;
u8 bssid[ETH_ALEN];
int freq;
enum chan_width max_cw;
u16 beacon_int;
u16 caps;
int qual;

1
wpa_supplicant/bss.c
View file

@ -296,6 +296,7 @@ static void wpa_bss_copy_res(struct wpa_bss *dst, struct wpa_scan_res *src,
dst->flags = src->flags;
os_memcpy(dst->bssid, src->bssid, ETH_ALEN);
dst->freq = src->freq;
dst->max_cw = src->max_cw;
dst->beacon_int = src->beacon_int;
dst->caps = src->caps;
dst->qual = src->qual;

2
wpa_supplicant/bss.h
View file

@ -96,6 +96,8 @@ struct wpa_bss {
size_t ssid_len;
/** Frequency of the channel in MHz (e.g., 2412 = channel 1) */
int freq;
/** The max channel width supported by both the AP and the STA */
enum chan_width max_cw;
/** Beacon interval in TUs (host byte order) */
u16 beacon_int;
/** Capability information field in host byte order */

4
wpa_supplicant/events.c
View file

@ -2058,8 +2058,10 @@ wpas_get_est_throughput_from_bss_snr(const struct wpa_supplicant *wpa_s,
int rate = wpa_bss_get_max_rate(bss);
const u8 *ies = wpa_bss_ie_ptr(bss);
size_t ie_len = bss->ie_len ? bss->ie_len : bss->beacon_ie_len;
enum chan_width max_cw = CHAN_WIDTH_UNKNOWN;
return wpas_get_est_tpt(wpa_s, ies, ie_len, rate, snr, bss->freq);
return wpas_get_est_tpt(wpa_s, ies, ie_len, rate, snr, bss->freq,
&max_cw);
}

201
wpa_supplicant/scan.c
View file

@ -2213,6 +2213,160 @@ struct wpabuf * wpa_scan_get_vendor_ie_multi(const struct wpa_scan_res *res,
}
static int wpas_channel_width_offset(enum chan_width cw)
{
switch (cw) {
case CHAN_WIDTH_40:
return 1;
case CHAN_WIDTH_80:
return 2;
case CHAN_WIDTH_80P80:
case CHAN_WIDTH_160:
return 3;
case CHAN_WIDTH_320:
return 4;
default:
return 0;
}
}
/**
* wpas_channel_width_tx_pwr - Calculate the max transmit power at the channel
* width
* @ies: Information elements
* @ies_len: Length of elements
* @cw: The channel width
* Returns: The max transmit power at the channel width, TX_POWER_NO_CONSTRAINT
* if it is not constrained.
*
* This function is only used to estimate the actual signal RSSI when associated
* based on the beacon RSSI at the STA. Beacon frames are transmitted on 20 MHz
* channels, while the Data frames usually use higher channel width. Therefore
* their RSSIs may be different. Assuming there is a fixed gap between the TX
* power limit of the STA defined by the Transmit Power Envelope element and the
* TX power of the AP, the difference in the TX power of X MHz and Y MHz at the
* STA equals to the difference at the AP, and the difference in the signal RSSI
* at the STA. tx_pwr is a floating point number in the standard, but the error
* of casting to int is trivial in comparing two BSSes.
*/
static int wpas_channel_width_tx_pwr(const u8 *ies, size_t ies_len,
enum chan_width cw)
{
#define MIN(a, b) (a < b ? a : b)
int offset = wpas_channel_width_offset(cw);
const struct element *elem;
int max_tx_power = TX_POWER_NO_CONSTRAINT, tx_pwr = 0;
for_each_element_id(elem, WLAN_EID_TRANSMIT_POWER_ENVELOPE, ies,
ies_len) {
int max_tx_pwr_count;
enum max_tx_pwr_interpretation tx_pwr_intrpn;
enum reg_6g_client_type client_type;
if (elem->datalen < 1)
continue;
/*
* IEEE Std 802.11ax-2021, 9.4.2.161 (Transmit Power Envelope
* element) defines Maximum Transmit Power Count (B0-B2),
* Maximum Transmit Power Interpretation (B3-B5), and Maximum
* Transmit Power Category (B6-B7).
*/
max_tx_pwr_count = elem->data[0] & 0x07;
tx_pwr_intrpn = (elem->data[0] >> 3) & 0x07;
client_type = (elem->data[0] >> 6) & 0x03;
if (client_type != REG_DEFAULT_CLIENT)
continue;
if (tx_pwr_intrpn == LOCAL_EIRP ||
tx_pwr_intrpn == REGULATORY_CLIENT_EIRP) {
int offs;
max_tx_pwr_count = MIN(max_tx_pwr_count, 3);
offs = MIN(offset, max_tx_pwr_count) + 1;
if (elem->datalen <= offs)
continue;
tx_pwr = (signed char) elem->data[offs];
/*
* Maximum Transmit Power subfield is encoded as an
* 8-bit 2s complement signed integer in the range -64
* dBm to 63 dBm with a 0.5 dB step. 63.5 dBm means no
* local maximum transmit power constraint.
*/
if (tx_pwr == 127)
continue;
tx_pwr /= 2;
max_tx_power = MIN(max_tx_power, tx_pwr);
} else if (tx_pwr_intrpn == LOCAL_EIRP_PSD ||
tx_pwr_intrpn == REGULATORY_CLIENT_EIRP_PSD) {
if (elem->datalen < 2)
continue;
tx_pwr = (signed char) elem->data[1];
/*
* Maximum Transmit PSD subfield is encoded as an 8-bit
* 2s complement signed integer. -128 indicates that the
* corresponding 20 MHz channel cannot be used for
* transmission. +127 indicates that no maximum PSD
* limit is specified for the corresponding 20 MHz
* channel.
*/
if (tx_pwr == 127 || tx_pwr == -128)
continue;
/*
* The Maximum Transmit PSD subfield indicates the
* maximum transmit PSD for the 20 MHz channel. Suppose
* the PSD value is X dBm/MHz, the TX power of N MHz is
* X + 10*log10(N) = X + 10*log10(20) + 10*log10(N/20) =
* X + 13 + 3*log2(N/20)
*/
tx_pwr = tx_pwr / 2 + 13 + offset * 3;
max_tx_power = MIN(max_tx_power, tx_pwr);
}
}
return max_tx_power;
#undef MIN
}
/**
* Estimate the RSSI bump of channel width |cw| with respect to 20 MHz channel.
* If the TX power has no constraint, it is unable to estimate the RSSI bump.
*/
int wpas_channel_width_rssi_bump(const u8 *ies, size_t ies_len,
enum chan_width cw)
{
int max_20mhz_tx_pwr = wpas_channel_width_tx_pwr(ies, ies_len,
CHAN_WIDTH_20);
int max_cw_tx_pwr = wpas_channel_width_tx_pwr(ies, ies_len, cw);
return (max_20mhz_tx_pwr == TX_POWER_NO_CONSTRAINT ||
max_cw_tx_pwr == TX_POWER_NO_CONSTRAINT) ?
0 : (max_cw_tx_pwr - max_20mhz_tx_pwr);
}
int wpas_adjust_snr_by_chanwidth(const u8 *ies, size_t ies_len,
enum chan_width max_cw, int snr)
{
int rssi_bump = wpas_channel_width_rssi_bump(ies, ies_len, max_cw);
/*
* The noise has uniform power spectral density (PSD) across the
* frequency band, its power is proportional to the channel width.
* Suppose the PSD of noise is X dBm/MHz, the noise power of N MHz is
* X + 10*log10(N), and the noise power bump with respect to 20 MHz is
* 10*log10(N) - 10*log10(20) = 10*log10(N/20) = 3*log2(N/20)
*/
int noise_bump = 3 * wpas_channel_width_offset(max_cw);
return snr + rssi_bump - noise_bump;
}
/* Compare function for sorting scan results. Return >0 if @b is considered
* better. */
static int wpa_scan_result_compar(const void *a, const void *b)
@ -2224,6 +2378,7 @@ static int wpa_scan_result_compar(const void *a, const void *b)
struct wpa_scan_res *wb = *_wb;
int wpa_a, wpa_b;
int snr_a, snr_b, snr_a_full, snr_b_full;
size_t ies_len;
/* WPA/WPA2 support preferred */
wpa_a = wpa_scan_get_vendor_ie(wa, WPA_IE_VENDOR_TYPE) != NULL ||
@ -2245,10 +2400,21 @@ static int wpa_scan_result_compar(const void *a, const void *b)
return -1;
if (wa->flags & wb->flags & WPA_SCAN_LEVEL_DBM) {
snr_a_full = wa->snr;
snr_a = MIN(wa->snr, GREAT_SNR);
snr_b_full = wb->snr;
snr_b = MIN(wb->snr, GREAT_SNR);
/*
* The scan result estimates SNR over 20 MHz, while Data frames
* usually use wider channel width. The TX power and noise power
* are both affected by the channel width.
*/
ies_len = wa->ie_len ? wa->ie_len : wa->beacon_ie_len;
snr_a_full = wpas_adjust_snr_by_chanwidth((const u8 *) (wa + 1),
ies_len, wa->max_cw,
wa->snr);
snr_a = MIN(snr_a_full, GREAT_SNR);
ies_len = wb->ie_len ? wb->ie_len : wb->beacon_ie_len;
snr_b_full = wpas_adjust_snr_by_chanwidth((const u8 *) (wb + 1),
ies_len, wb->max_cw,
wb->snr);
snr_b = MIN(snr_b_full, GREAT_SNR);
} else {
/* Level is not in dBm, so we can't calculate
* SNR. Just use raw level (units unknown). */
@ -2701,7 +2867,7 @@ static unsigned int max_he_eht_rate(const struct minsnr_bitrate_entry table[],
unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
const u8 *ies, size_t ies_len, int rate,
int snr, int freq)
int snr, int freq, enum chan_width *max_cw)
{
struct hostapd_hw_modes *hw_mode;
unsigned int est, tmp;
@ -2754,6 +2920,7 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
if (hw_mode && hw_mode->ht_capab) {
ie = get_ie(ies, ies_len, WLAN_EID_HT_CAP);
if (ie) {
*max_cw = CHAN_WIDTH_20;
tmp = max_ht20_rate(snr, false);
if (tmp > est)
est = tmp;
@ -2765,6 +2932,7 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
ie = get_ie(ies, ies_len, WLAN_EID_HT_OPERATION);
if (ie && ie[1] >= 2 &&
(ie[3] & HT_INFO_HT_PARAM_SECONDARY_CHNL_OFF_MASK)) {
*max_cw = CHAN_WIDTH_40;
tmp = max_ht40_rate(snr, false);
if (tmp > est)
est = tmp;
@ -2777,6 +2945,8 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
if (ie) {
bool vht80 = false, vht160 = false;
if (*max_cw == CHAN_WIDTH_UNKNOWN)
*max_cw = CHAN_WIDTH_20;
tmp = max_ht20_rate(snr, true) + 1;
if (tmp > est)
est = tmp;
@ -2785,6 +2955,7 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
if (ie && ie[1] >= 2 &&
(ie[3] &
HT_INFO_HT_PARAM_SECONDARY_CHNL_OFF_MASK)) {
*max_cw = CHAN_WIDTH_40;
tmp = max_ht40_rate(snr, true) + 1;
if (tmp > est)
est = tmp;
@ -2811,6 +2982,7 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
}
if (vht80) {
*max_cw = CHAN_WIDTH_80;
tmp = max_vht80_rate(snr) + 1;
if (tmp > est)
est = tmp;
@ -2820,6 +2992,7 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
(hw_mode->vht_capab &
(VHT_CAP_SUPP_CHAN_WIDTH_160MHZ |
VHT_CAP_SUPP_CHAN_WIDTH_160_80PLUS80MHZ))) {
*max_cw = CHAN_WIDTH_160;
tmp = max_vht160_rate(snr) + 1;
if (tmp > est)
est = tmp;
@ -2853,6 +3026,8 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
}
}
if (*max_cw == CHAN_WIDTH_UNKNOWN)
*max_cw = CHAN_WIDTH_20;
tmp = max_he_eht_rate(he20_table, snr, is_eht) + boost;
if (tmp > est)
est = tmp;
@ -2862,6 +3037,9 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
if (cw &
(IS_2P4GHZ(freq) ? HE_PHYCAP_CHANNEL_WIDTH_SET_40MHZ_IN_2G :
HE_PHYCAP_CHANNEL_WIDTH_SET_40MHZ_80MHZ_IN_5G)) {
if (*max_cw == CHAN_WIDTH_UNKNOWN ||
*max_cw < CHAN_WIDTH_40)
*max_cw = CHAN_WIDTH_40;
tmp = max_he_eht_rate(he40_table, snr, is_eht) + boost;
if (tmp > est)
est = tmp;
@ -2869,6 +3047,9 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
if (!IS_2P4GHZ(freq) &&
(cw & HE_PHYCAP_CHANNEL_WIDTH_SET_40MHZ_80MHZ_IN_5G)) {
if (*max_cw == CHAN_WIDTH_UNKNOWN ||
*max_cw < CHAN_WIDTH_80)
*max_cw = CHAN_WIDTH_80;
tmp = max_he_eht_rate(he80_table, snr, is_eht) + boost;
if (tmp > est)
est = tmp;
@ -2877,6 +3058,9 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
if (!IS_2P4GHZ(freq) &&
(cw & (HE_PHYCAP_CHANNEL_WIDTH_SET_160MHZ_IN_5G |
HE_PHYCAP_CHANNEL_WIDTH_SET_80PLUS80MHZ_IN_5G))) {
if (*max_cw == CHAN_WIDTH_UNKNOWN ||
*max_cw < CHAN_WIDTH_160)
*max_cw = CHAN_WIDTH_160;
tmp = max_he_eht_rate(he160_table, snr, is_eht) + boost;
if (tmp > est)
est = tmp;
@ -2890,6 +3074,9 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
if (is_6ghz_freq(freq) &&
(eht->phy_cap[EHT_PHYCAP_320MHZ_IN_6GHZ_SUPPORT_IDX] &
EHT_PHYCAP_320MHZ_IN_6GHZ_SUPPORT_MASK)) {
if (*max_cw == CHAN_WIDTH_UNKNOWN ||
*max_cw < CHAN_WIDTH_320)
*max_cw = CHAN_WIDTH_320;
tmp = max_he_eht_rate(eht320_table, snr, true);
if (tmp > est)
est = tmp;
@ -2916,8 +3103,8 @@ void scan_est_throughput(struct wpa_supplicant *wpa_s,
if (!ie_len)
ie_len = res->beacon_ie_len;
res->est_throughput =
wpas_get_est_tpt(wpa_s, ies, ie_len, rate, snr, res->freq);
res->est_throughput = wpas_get_est_tpt(wpa_s, ies, ie_len, rate, snr,
res->freq, &res->max_cw);
/* TODO: channel utilization and AP load (e.g., from AP Beacon) */
}

14
wpa_supplicant/scan.h
View file

@ -30,6 +30,14 @@
*/
#define GREAT_SNR 25
/*
* IEEE Sts 802.11ax-2021, 9.4.2.161 (Transmit Power Envelope element) indicates
* no max TX power limit if Maximum Transmit Power field is 63.5 dBm.
* The default TX power if it is not constrained by Transmit Power Envelope
* element.
*/
#define TX_POWER_NO_CONSTRAINT 64
#define IS_2P4GHZ(n) (n >= 2412 && n <= 2484)
#define IS_5GHZ(n) (n > 4000 && n < 5895)
@ -88,12 +96,16 @@ void scan_est_throughput(struct wpa_supplicant *wpa_s,
struct wpa_scan_res *res);
unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
const u8 *ies, size_t ies_len, int rate,
int snr, int freq);
int snr, int freq, enum chan_width *max_cw);
void wpa_supplicant_set_default_scan_ies(struct wpa_supplicant *wpa_s);
int wpa_add_scan_freqs_list(struct wpa_supplicant *wpa_s,
enum hostapd_hw_mode band,
struct wpa_driver_scan_params *params,
bool is_6ghz, bool only_6ghz_psc,
bool exclude_radar);
int wpas_channel_width_rssi_bump(const u8 *ies, size_t ies_len,
enum chan_width cw);
int wpas_adjust_snr_by_chanwidth(const u8 *ies, size_t ies_len,
enum chan_width max_cw, int snr);
#endif /* SCAN_H */