[PATCH usteer] Add band-steering signal threshold with adaption

[Nils Hendrik Rottgardt]

Avoid ping-pong between bands by adding a dynamic signal threshold.
If 5Ghz band is below roaming threshold (e.g. -70) and 2,4Ghz over
band-steering threshold (e.g. -50) this adds a dynamic threshold
depends on the signal level when station has connected. It adapts to
worser signal slowly.

- band_steering: added dynamic signal threshold
- main: added config option

Signed-off-by: Nils Hendrik Rottgardt <n.rottgardt at gmail.com>
---
 band_steering.c                        | 19 ++++++++++++++++++-
 main.c                                 |  1 +
 openwrt/usteer/files/etc/config/usteer |  4 ++++
 openwrt/usteer/files/etc/init.d/usteer |  6 +++---
 usteer.h                               |  2 ++
 5 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/band_steering.c b/band_steering.c
index 7fce1df..8577caf 100644
--- a/band_steering.c
+++ b/band_steering.c
@@ -20,7 +20,24 @@
 
 void usteer_band_steering_sta_update(struct sta_info *si)
 {
-	if (si->signal < usteer_snr_to_signal(si->node, config.band_steering_min_snr))
+	if (si->connected == STA_NOT_CONNECTED) {
+		if (si->band_steering.signal_threshold != NO_SIGNAL) {
+			si->band_steering.signal_threshold = NO_SIGNAL;
+		}
+		return;
+	}
+	if (si->connected != STA_NOT_CONNECTED && si->band_steering.signal_threshold == NO_SIGNAL) {
+		si->band_steering.signal_threshold = si->signal;
+		MSG(DEBUG, "band steering station " MAC_ADDR_FMT " (%s) set threshold (signal threshold %u)\n", MAC_ADDR_DATA(si->sta->addr), usteer_node_name(si->node), si->band_steering.signal_threshold);
+		return;
+	}
+
+	/* Adapt signal threshold to actual signal quality */
+	if (si->signal < si->band_steering.signal_threshold) {
+		si->band_steering.signal_threshold--;
+		MSG(DEBUG, "band steering station " MAC_ADDR_FMT " (%s) reduce threshold (signal: %d, signal threshold: %u)\n", MAC_ADDR_DATA(si->sta->addr), usteer_node_name(si->node), si->signal, si->band_steering.signal_threshold);
+	}
+	if (si->signal < usteer_snr_to_signal(si->node, config.band_steering_min_snr) || si->signal < si->band_steering.signal_threshold + config.band_steering_signal_threshold)
 		si->band_steering.below_snr = true;
 }
 
diff --git a/main.c b/main.c
index 99aa6ad..4a9253c 100644
--- a/main.c
+++ b/main.c
@@ -101,6 +101,7 @@ void usteer_init_defaults(void)
 
 	config.band_steering_interval = 120000;
 	config.band_steering_min_snr = -60;
+	config.band_steering_signal_threshold = 5;
 
 	config.link_measurement_interval = 30000;
 
diff --git a/openwrt/usteer/files/etc/config/usteer b/openwrt/usteer/files/etc/config/usteer
index f53c338..58d1f44 100644
--- a/openwrt/usteer/files/etc/config/usteer
+++ b/openwrt/usteer/files/etc/config/usteer
@@ -128,6 +128,10 @@ config usteer
 	# steered to a higher frequency band
 	#option band_steering_min_snr -60
 
+	# Difference that the signal must be better compared to signal was on connection to node.
+	# Avoids conflicts between roaming and band-steering policies.
+	# option band_steering_signal_threshold 5
+
 	# Interval (ms) the device is sent a link-measurement request to help assess
 	# the bi-directional link quality. Setting the interval to 0 disables link-measurements.
 	#option link_measurement_interval 30000
diff --git a/openwrt/usteer/files/etc/init.d/usteer b/openwrt/usteer/files/etc/init.d/usteer
index 07fd99e..965aa0a 100755
--- a/openwrt/usteer/files/etc/init.d/usteer
+++ b/openwrt/usteer/files/etc/init.d/usteer
@@ -83,9 +83,9 @@ uci_usteer() {
 		min_connect_snr min_snr min_snr_kick_delay signal_diff_threshold \
 		initial_connect_delay steer_reject_timeout roam_process_timeout\
 		roam_kick_delay roam_scan_tries roam_scan_timeout \
-		roam_scan_snr roam_scan_interval \
-		roam_trigger_snr roam_trigger_interval \
-		band_steering_interval band_steering_min_snr link_measurement_interval \
+		roam_scan_snr roam_scan_interval roam_trigger_snr roam_trigger_interval \
+		link_measurement_interval \
+		band_steering_interval band_steering_min_snr band_steering_signal_threshold \
 		load_kick_threshold load_kick_delay load_kick_min_clients \
 		load_kick_reason_code
 	do
diff --git a/usteer.h b/usteer.h
index f692fb8..f354282 100644
--- a/usteer.h
+++ b/usteer.h
@@ -191,6 +191,7 @@ struct usteer_config {
 
 	uint32_t band_steering_interval;
 	int32_t band_steering_min_snr; 
+	uint32_t band_steering_signal_threshold;
 
 	uint32_t link_measurement_interval;
 
@@ -265,6 +266,7 @@ struct sta_info {
 
 	struct {
 		bool below_snr;
+		int signal_threshold;
 	} band_steering;
 
 	uint64_t kick_time;
-- 
2.39.5