reconnect repeatly, connection time less than 20s. hostapd built wifi AP.

[Gaofeng Zeng]

Hi, every one!
I'm Chinese, and I'm not good at English. Please forgive me.
I built a wifi AP for my Android phone using. But have a problem:
Android wifi-client can connect to this AP, but connection will be break
at soon(about 20 seconds), and then reconnect to AP.  It's repeatedly, 
connect, disconnect, connect, disconnect ...
Any one have solutions?
Thanks!

platform:
fedora17-64bit. hostapd-0.7.3
connect internet mode: PPPOE

net-card(USB)
Bus 001 Device 014: ID 0bda:8178 Realtek Semiconductor Corp. 
driver: rtl8192cu


# /etc/hostapd/hostadp.conf (just post modified)
 interface=wlan1
 driver=nl80211
 ssid=vlad_is_here
 channel=6
 hw_mode=g
 ignore_broadcast_ssid=0
 auth_algs=1
 wpa=2
 wpa_passphrase=xxxxxxxx
 wpa_key_mgmt=WPA-PSK
 wpa_pairwise=TKIP
 rsn_pairwise=CCMP


start wifi-AP:
$sudo hostapd /etc/hostapd/hostapd.conf
.......
wlan0: STA c4:6a:b7:54:f2:b1 RADIUS: starting accounting session
50A71B31-00000131
wlan0: STA c4:6a:b7:54:f2:b1 WPA: pairwise key handshake completed (RSN)
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: authenticated
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: associated (aid 1)
wlan0: STA c4:6a:b7:54:f2:b1 RADIUS: starting accounting session
50A71B31-00000132
wlan0: STA c4:6a:b7:54:f2:b1 WPA: pairwise key handshake completed (RSN)
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: authenticated
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: associated (aid 1)
wlan0: STA c4:6a:b7:54:f2:b1 RADIUS: starting accounting session
50A71B31-00000133
wlan0: STA c4:6a:b7:54:f2:b1 WPA: pairwise key handshake completed (RSN)
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: authenticated
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: associated (aid 1)
wlan0: STA c4:6a:b7:54:f2:b1 RADIUS: starting accounting session
50A71B31-00000134
wlan0: STA c4:6a:b7:54:f2:b1 WPA: pairwise key handshake completed (RSN)
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: authenticated
wlan0: STA c4:6a:b7:54:f2:b1 IEEE 802.11: associated (aid 1)
............


"staring accounting session ..... " print repeatedly, and reconnect
repeatedly.