From afe30ffc6e5755ee776c71c7d006d430d6565c5e Mon Sep 17 00:00:00 2001
From: Tim Wilkinson <tim.j.wilkinson@gmail.com>
Date: Sat, 25 Jun 2022 18:45:28 -0700
Subject: [PATCH] Graph in SNR + fixes (#412)

Feedback from Joe and others to adjust the noise floor (which is lower
for subchannels). Label with SNR because that's easier to compare to the
SNR values people are already familiar with.
---
 files/www/cgi-bin/scan | 60 ++++++++++++++++++++----------------------
 1 file changed, 29 insertions(+), 31 deletions(-)

diff --git a/files/www/cgi-bin/scan b/files/www/cgi-bin/scan
index 21ce1d0c..9657a55f 100755
--- a/files/www/cgi-bin/scan
+++ b/files/www/cgi-bin/scan
@@ -47,6 +47,7 @@ end
 local wifiiface = aredn.hardware.get_iface_name("wifi")
 local phy = iwinfo.nl80211.phyname(wifiiface)
 local rfband = aredn.hardware.get_rfband()
+local nf = iwinfo.nl80211.noise(wifiiface) or -95
 
 if not nixio.fs.stat("/tmp/web") then
     nixio.fs.mkdir("/tmp/web")
@@ -189,7 +190,7 @@ html.print("<button type=button onClick='window.location=\"status\"' title='Retu
 
 -- display scan
 html.print("<table class=sortable border=1 cellpadding=5>")
-html.print("<tr><th>Sig</th><th>Chan</th><th>Enc</th><th>SSID</th><th>Hostname</th><th>MAC/BSSID</th><th>802.11 Mode</th></tr>")
+html.print("<tr><th>SNR</th><th>Signal</th><th>Chan</th><th>Enc</th><th>SSID</th><th>Hostname</th><th>MAC/BSSID</th><th>802.11 Mode</th></tr>")
 
 -- load arp cache
 local arpcache = {}
@@ -248,7 +249,7 @@ do
     else
         html.print("<tr>")
     end
-    html.print("<td>" .. scan.signal .. "</td><td>" .. chan .. "</td><td>" .. scan.key .. "</td><td>" .. scan.ssid .. "</td><td align=center>" .. hostname .. "</td><td>" .. scan.mac:upper() .. "</td><td>" .. scan.mode .. "</td>")
+    html.print("<td>" .. (scan.signal - nf) .. "</td><td>" .. scan.signal .. "</td><td>" .. chan .. "</td><td>" .. scan.key .. "</td><td>" .. scan.ssid .. "</td><td align=center>" .. hostname .. "</td><td>" .. scan.mac:upper() .. "</td><td>" .. scan.mode .. "</td>")
     html.print("</tr>")
 end
 
@@ -260,7 +261,7 @@ local cheight = 400;
 html.print([[
     <center style="font-family: Arial">
     <div style="padding:8px">Spectral View</div>
-    <div style="position:relative;display:inline-block"><div style="position:absolute;left:-34px;top:-200px;transform:rotate(-90deg)">Signal</div></div>
+    <div style="position:relative;display:inline-block"><div style="position:absolute;left:-30px;top:-200px;transform:rotate(-90deg)">SNR</div></div>
     <canvas id="spectral" width="]] .. cwidth .. [[" height="]] .. cheight .. [[" style="border:1px solid grey;background-color:white"></canvas>
     <div style="padding:4px">Channel</div>
     </center>
@@ -273,7 +274,7 @@ function u8tos8(b)
     return b >= 128 and b - 256 or b
 end
 
-local nf = iwinfo.nl80211.noise(wifiiface) or -95
+local cnf = nf - 17.5 -- sub-carrier noise floor
 local start_freq
 local end_freq
 if rfband == "900" then
@@ -305,7 +306,7 @@ end
 bw = tonumber(bw) or 10
 
 local xscale = cwidth / (end_freq - start_freq)
-local min_sig = nf
+local min_sig = cnf
 local max_sig = -60
 local i = 1
 html.write("const p = [")
@@ -320,31 +321,29 @@ do
             local rssi = u8tos8(samples:byte(i + 6))
             local noise = u8tos8(samples:byte(i + 7))
             local datasqsum = 0
-            local dlen = l - 18
             local v = {}
-            for dptr = 0, dlen - 1
+            for dptr = 1,56
             do
-                local data = nixio.bit.lshift(samples:byte(dptr + i + 20), max_exp)
-                if data == 0 then
-                    data = 1
-                end
-                datasqsum = datasqsum + data * data
+                local data = nixio.bit.lshift(samples:byte(dptr + i + 19), max_exp)
+                data = data * data
+                datasqsum = datasqsum + data
                 v[dptr] = data
             end
-            datasqsum = math.log10(datasqsum) * 10
-            for dptr = 0, dlen - 1
+            for dptr = 1,56
             do
-                local data = v[dptr]
-                local sig = noise + rssi + 20 * math.log10(data) - datasqsum
-                local fr = freq + bw * (dptr / dlen - 0.5) - start_freq
-                if sig >= -125 then
-                    if sig < min_sig then
-                        min_sig = sig
+                local datasq = v[dptr]
+                if datasq ~= 0 then
+                    local sig = noise + rssi + 10 * math.log10(datasq / datasqsum)
+                    local fr = freq + bw * (dptr / 56 - 0.5) - start_freq
+                    if sig >= -125 then
+                        if sig < min_sig then
+                            min_sig = sig
+                        end
+                        if sig > max_sig then
+                            max_sig = sig
+                        end
+                        html.write(math.floor(fr * xscale) .. "," .. math.floor(-sig * 4) .. ",")
                     end
-                    if sig > max_sig then
-                        max_sig = sig
-                    end
-                    html.write(math.floor(fr * xscale) .. "," .. math.floor(-sig * 4) .. ",")
                 end
             end
         end
@@ -360,7 +359,7 @@ html.print([[
     for (let i = 0; i < p.length; i += 2) {
         const sig = p[i+1];
         const idx = 4 * (p[i] + ]] .. cwidth .. [[ * Math.floor(yscale * (ytran - sig)));
-        if (sig < ]] .. (-4 * nf) .. [[) {
+        if (sig < ]] .. (-4 * cnf) .. [[) {
             d[idx] = 0;
             d[idx+1] = 0;
             d[idx+2] = 255;
@@ -395,19 +394,18 @@ html.print([[
     ctx.textAlign = "left";
     ctx.strokeStyle = "lightblue";
     ctx.beginPath();
-    for (let signal = -30; signal >= -120; signal -= 10) {
-        const y = Math.floor(yscale * (ytran + signal * 4));
-        ctx.moveTo(30, y);
+    for (let snr = 60; snr >= 0; snr -= 10) {
+        const y = Math.floor(yscale * (ytran + ]] .. (cnf * 4) .. [[ + snr * 4));
+        ctx.moveTo(20, y);
         ctx.lineTo(]] .. cwidth .. [[, y);
-        ctx.fillText("" + signal, 2, y);
+        ctx.fillText("" + snr, 2, y);
     }
     ctx.stroke();
     ctx.strokeStyle = "blue";
     ctx.beginPath();
-    const y = Math.floor(yscale * (]] .. (nf * 4) .. [[ + ytran));
+    const y = Math.floor(yscale * (]] .. (cnf * 4) .. [[ + ytran));
     ctx.moveTo(30, y);
     ctx.lineTo(]] .. cwidth .. [[, y);
-    ctx.fillText("NF", 4, y);
     ctx.stroke();
     </script></form>
 ]])