Add some notes on which channels can be used with HT40- and HT40+

This is not a complete list, but at least it can provide some help for
whoever is trying to configure hostapd for 802.11n HT40 operation.

diff --git a/hostapd/hostapd.conf b/hostapd/hostapd.conf
index 8df35c8..f8771b7 100644 (file)
--- a/hostapd/hostapd.conf
+++ b/hostapd/hostapd.conf
@@ -384,6 +384,14 @@ wme_ac_vo_acm=0
 #      channel below the primary channel; [HT40+] = both 20 MHz and 40 MHz
 #      with secondary channel below the primary channel
 #      (20 MHz only if neither is set)
+#      Note: There are limits on which channels can be used with HT40- and
+#      HT40+. Following table shows the channels that may be available for
+#      HT40- and HT40+ use per IEEE 802.11n Annex J:
+#      freq            HT40-           HT40+
+#      2.4 GHz         5-13            1-7 (1-9 in Europe/Japan)
+#      5 GHz           40,48,56,64     36,44,52,60
+#      (depending on the location, not all of these channels may be available
+#      for use)
 # Spatial Multiplexing (SM) Power Save: [SMPS-STATIC] or [SMPS-DYNAMIC]
 #      (SMPS disabled if neither is set)
 # HT-greenfield: [GF] (disabled if not set)