Adjust max bitrate SNR floors

These values were defined in commit a1b790eb9d75 ("Select AP based on
estimated maximum throughput") with no justification. Other sources
[0,1,2] give a different (consistent) set of SNR floors per MCS index.
Adjust the values accordingly.

[0] http://www.revolutionwifi.net/revolutionwifi/2014/09/wi-fi-snr-to-mcs-data-rate-mapping.html
[1] https://higher-frequency.blogspot.com/2016/10/80211n-80211ac-data-rates-and-snr.html
[2] https://www.wlanpros.com/resources/mcs-index-802-11ac-vht-chart/

Signed-off-by: Matthew Wang <matthewmwang@chromium.org>

diff --git a/wpa_supplicant/scan.c b/wpa_supplicant/scan.c
index db1f6e1fa679e6ea5a391dc16ff9965e5d52a95d..98b0408d8f60927c0d809eef51f1320c93c89391 100644 (file)
--- a/wpa_supplicant/scan.c
+++ b/wpa_supplicant/scan.c
@@ -2185,67 +2185,77 @@ void scan_snr(struct wpa_scan_res *res)
 }
 
 
-static unsigned int max_ht20_rate(int snr)
+static unsigned int max_ht20_rate(int snr, int vht)
 {
-       if (snr < 6)
+       if (snr < 2)
+               return 0;
+       if (snr < 5)
                return 6500; /* HT20 MCS0 */
-       if (snr < 8)
+       if (snr < 9)
                return 13000; /* HT20 MCS1 */
-       if (snr < 13)
+       if (snr < 11)
                return 19500; /* HT20 MCS2 */
-       if (snr < 17)
+       if (snr < 15)
                return 26000; /* HT20 MCS3 */
-       if (snr < 20)
+       if (snr < 18)
                return 39000; /* HT20 MCS4 */
-       if (snr < 23)
+       if (snr < 20)
                return 52000; /* HT20 MCS5 */
-       if (snr < 24)
+       if (snr < 25)
                return 58500; /* HT20 MCS6 */
-       return 65000; /* HT20 MCS7 */
+       if (snr < 29 || !vht)
+               return 65000; /* HT20 MCS7 */
+       return 78000; /* VHT20 MCS8 */
 }
 
 
-static unsigned int max_ht40_rate(int snr)
+static unsigned int max_ht40_rate(int snr, int vht)
 {
-       if (snr < 3)
+       if (snr < 5)
+               return 0;
+       if (snr < 8)
                return 13500; /* HT40 MCS0 */
-       if (snr < 6)
+       if (snr < 12)
                return 27000; /* HT40 MCS1 */
-       if (snr < 10)
+       if (snr < 14)
                return 40500; /* HT40 MCS2 */
-       if (snr < 15)
+       if (snr < 18)
                return 54000; /* HT40 MCS3 */
-       if (snr < 17)
+       if (snr < 21)
                return 81000; /* HT40 MCS4 */
-       if (snr < 22)
+       if (snr < 23)
                return 108000; /* HT40 MCS5 */
-       if (snr < 24)
+       if (snr < 28)
                return 121500; /* HT40 MCS6 */
-       return 135000; /* HT40 MCS7 */
+       if (snr < 32 || !vht)
+               return 135000; /* HT40 MCS7 */
+       if (snr < 34)
+               return 162000; /* VHT40 MCS8 */
+       return 180000; /* VHT40 MCS9 */
 }
 
 
 static unsigned int max_vht80_rate(int snr)
 {
-       if (snr < 1)
+       if (snr < 8)
                return 0;
-       if (snr < 2)
+       if (snr < 11)
                return 29300; /* VHT80 MCS0 */
-       if (snr < 5)
+       if (snr < 15)
                return 58500; /* VHT80 MCS1 */
-       if (snr < 9)
+       if (snr < 17)
                return 87800; /* VHT80 MCS2 */
-       if (snr < 11)
+       if (snr < 21)
                return 117000; /* VHT80 MCS3 */
-       if (snr < 15)
+       if (snr < 24)
                return 175500; /* VHT80 MCS4 */
-       if (snr < 16)
+       if (snr < 26)
                return 234000; /* VHT80 MCS5 */
-       if (snr < 18)
+       if (snr < 31)
                return 263300; /* VHT80 MCS6 */
-       if (snr < 20)
+       if (snr < 35)
                return 292500; /* VHT80 MCS7 */
-       if (snr < 22)
+       if (snr < 37)
                return 351000; /* VHT80 MCS8 */
        return 390000; /* VHT80 MCS9 */
 }
@@ -2285,7 +2295,7 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
        if (capab == CAPAB_HT || capab == CAPAB_HT40 || capab == CAPAB_VHT) {
                ie = get_ie(ies, ies_len, WLAN_EID_HT_CAP);
                if (ie) {
-                       tmp = max_ht20_rate(snr);
+                       tmp = max_ht20_rate(snr, 0);
                        if (tmp > est)
                                est = tmp;
                }
@@ -2295,7 +2305,7 @@ 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)) {
-                       tmp = max_ht40_rate(snr);
+                       tmp = max_ht40_rate(snr, 0);
                        if (tmp > est)
                                est = tmp;
                }
@@ -2305,7 +2315,7 @@ unsigned int wpas_get_est_tpt(const struct wpa_supplicant *wpa_s,
                /* Use +1 to assume VHT is always faster than HT */
                ie = get_ie(ies, ies_len, WLAN_EID_VHT_CAP);
                if (ie) {
-                       tmp = max_ht20_rate(snr) + 1;
+                       tmp = max_ht20_rate(snr, 1) + 1;
                        if (tmp > est)
                                est = tmp;
 
@@ -2313,7 +2323,7 @@ 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)) {
-                               tmp = max_ht40_rate(snr) + 1;
+                               tmp = max_ht40_rate(snr, 1) + 1;
                                if (tmp > est)
                                        est = tmp;
                        }