/etc/systemd/system/wpa_supplicant@wlan0.service :
[Unit]
Description=Mein-WPA-Service
Wants=network.target
Before=network.target
BindsTo=sys-subsystem-net-devices-wlan0.device
After=sys-subsystem-net-devices-wlan0.device
After=system-resolved.service

[Service]
Type=oneshot
RemainAfterExit=yes

ExecStart=/sbin/ip l set wlan0 up
ExecStart=/sbin/wpa_supplicant -B -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant-wlan0.conf
ExecStart=/usr/bin/dhcpcd -r 192.168.16.10 wlan0

ExecStop=/sbin/ip l set wlan0 down

[Install]
WantedBy=multi-user.target