where can i find settings for wifi internal scan period I have already found some guide related to this. But my experience is that if wifi.supplicant_scan_interval = 15
my device scans for wifi with 60s period
so I dont think that this is the right parameter for that. Any suggestions?
Edited: here is my build.prop:

# begin build properties
# autogenerated by buildinfo.sh
ro.build.id=GRK39F
ro.build.display.id=GRK39F
ro.build.version.incremental=eng.paul.30092011.041430
ro.build.version.sdk=10
ro.build.version.codename=REL
ro.build.version.release=2.3.6
ro.build.date=Fri Aug 30 04:14:55 EDT 2011
ro.build.date.utc=0
ro.build.type=user
ro.build.user=paul
ro.build.host=paul-VM
ro.build.tags=test-keys
ro.product.model=U20i
ro.product.brand=Sony Ericsson
ro.product.name=mimmi
ro.product.device=mimmi
ro.product.board=mimmi
ro.product.cpu.abi=armeabi-v6l
ro.product.cpu.abi2=armeabi
ro.product.manufacturer=Sony Ericsson
ro.product.locale.language=en
ro.product.locale.region=US
ro.wifi.channels=14
ro.board.platform=msm7k
# ro.build.product is obsolete; use ro.product.device
ro.build.product=mimmi
# Do not try to parse ro.build.description or .fingerprint
ro.build.description=passion-user 2.3.6 GRK39F 189904 release-keys
ro.build.fingerprint=google/passion/passion:2.3.6/GRK39F/189904:user/release-keys
# end build properties

#
# ADDITIONAL_BUILD_PROPERTIES
#
keyguard.no_require_sim=true
ro.ril.hsxpa=2
ro.ril.hsupa.category=5
ro.ril.def.agps.mode=2
ro.media.dec.jpeg.memcap=20000000
rild.libpath=/system/lib/libril-qc-1.so
rild.libargs=-d /dev/smd0
wifi.interface=wlan0
wifi.supplicant_scan_interval=15
ro.ril.def.agps.mode=2
ro.ril.def.agps.feature=1
ro.opengles.version=131072
ro.com.google.locationfeatures=1
ro.com.google.networklocation=1
ro.ril.enable.a52=1
ro.ril.enable.a53=1
ro.media.enc.file.format=3gp,mp4
ro.media.enc.vid.codec=m4v,h263
ro.media.enc.vid.h263.width=176,640
ro.media.enc.vid.h263.height=144,480
ro.media.enc.vid.h263.bps=64000,1600000
ro.media.enc.vid.h263.fps=1,30
ro.media.enc.vid.m4v.width=176,640
ro.media.enc.vid.m4v.height=144,480
ro.media.enc.vid.m4v.bps=64000,1600000
ro.media.enc.vid.m4v.fps=1,30
ro.media.dec.aud.wma.enabled=1
ro.media.dec.vid.wmv.enabled=1
ro.media.dec.aud.divx.enabled=1
ro.media.dec.vid.xvid.enabled=1
settings.display.autobacklight=0
media.stagefright.enable-player=true
media.stagefright.enable-meta=true
media.stagefright.enable-scan=true
media.stagefright.enable-http=true
keyguard.no_require_sim=true

#MT and LCD
ro.sf.lcd_density=120
qemu.sf.lcd_density=120
ro.product.multi_touch_enabled=true
ro.product.max_max_num_touch=2

dalvik.vm.execution-mode=int:jit
dalvik.vm.heapsize=32m
ro.compcache.default=0
ro.rommanager.developerid=cyanogenmod
ro.url.legal=http://www.google.com/intl/%s/mobile/android/basic/phone-legal.html
ro.url.legal.android_privacy=http://www.google.com/intl/%s/mobile/android/basic/privacy.html
ro.com.google.clientidbase=android-sonyericsson
ro.com.android.wifi-watchlist=GoogleGuest
ro.setupwizard.enterprise_mode=1
ro.com.android.dateformat=MM-dd-yyyy
ro.com.android.dataroaming=false
ro.config.ringtone=MiniCM7Pro.mp3
ro.config.notification_sound=DontPanic.ogg
ro.config.alarm_alert=alarm.ogg
ro.modversion=MiniCM7 Pro V16 Pre-Final
ro.setupwizard.mode=OPTIONAL
net.bt.name=Android
dalvik.vm.stack-trace-file=/data/anr/traces.txt

#SEMC
persist.service.xloud.enable=1
persist.service.swiqi.enable=1
ro.semc.timescape_keys=Sony_Ericsson_Xperia
ro.semc.sound_effects_enabled=true
ro.semc.xloud.supported=true
ro.service.swiqi.supported=true
ro.semc.batt.capacity=950
ro.semc.batt.test.consumption=150
ro.semc.batt.test.z_threshold=50
ro.semc.batt.test.min_level=60


Edit2: The scanning period is depending on the connectivity as well. Means if the phone establishes a WI-FI connection, then the scanning period will be different from the wifi.supplicant_scan_interval. Also when the phone get into idle state (around 10 mins of inactivity) the scanning period will be 10 min.
This property comes from during build-time and is extremely, dependant on the wifi driver, for each and every device tree that gets integrated into the build of Android, there's what's called an overlay, this overlay may contain extras pertaining to the said device in question. 

In fact, its rather, an XML document that gets parsed during build and "overlays" or "overwrites" the standard Android defaults, such as animation speed, etc.

This pertinent information of this comes from the device's overlay/frameworks/base/core/res/res/values/config.xml which contains the very exact line:

&lt;!-- Boolean indicating whether the wifi chipset has background scan support --&gt;
&lt;bool translatable="false" name="config_wifi_background_scan_support"&gt;true&lt;/bool&gt;


From that, that is telling the build, to say, that the property wifi.supplicant_scan_interval is supported and can be used dynamically from the build.prop file found in the /system directory, which in turn, is read from the Android's native binary executable wpa_supplicant. 

However, it must be said, it depends on the Wifi Driver to support that, and how much integration of the Wifi functionality is within the frameworks. To find the exact source can be found in external/wpa_supplicant/wpa_supplicant.c, around lines 2459:

#ifdef ANDROID
    char scan_prop[PROPERTY_VALUE_MAX];
    char *endp;
    if (property_get("wifi.supplicant_scan_interval", scan_prop, "5") != 0) {
        wpa_s-&gt;scan_interval = (int)strtol(scan_prop, &amp;endp, 0);
        if (endp == scan_prop) {
            wpa_s-&gt;scan_interval = 5;
        }
    }
#endif


default here on Gingerbread is 5secs, again the mileage will vary depending on the version of wpa_supplicant used, there was two versions, wpa_supplicant_6 which was broken under ICS, and the newer version wpa_supplicant_8, despite saying that, it may no longer be supported now with the newer releases.