How to config network in host (wireless network) for QEMU guest os

The host os is connected into network by wireless one so how to let its guest os connect network.

Take [1] as a reference. I run it successfully with following steps.
1, create /etc/qemu-ifup script and chmod it.
2, start a qemu guest os with command sudo ./qemu/qemu-system-x86_64 -enable-kvm -m 1024 -drive file=marss_dram.qcow2 -vnc 127.0.0.1:0 -net tap -net nic

[1] http://wiki.qemu.org/Documentation/Networking/NAT