When you think about boosting the performance of your wireless network, 5-GHz wireless 802.11n routers are probably what come to mind. But the higher frequency used in the draft-n routers is only half the story. The "n" specification also allows wireless devices to use multiple antennas and MIMO (multiple input–multiple output) technology, also referred to as spatial multiplexing. With spatial multiplexing, operating systems have to coordinate higher volumes of TCP data streams at constant round-trip times between the router or access point and laptop. For years our connection and network bandwidth limited our download speeds. With 802.11n networks, it might just be our local operating systems that throttle the pipe.
Because the throughput of 802.11n is wider, more bits can flow between your wireless notebook and the router, but that means a legacy operating system like Windows XP requires more time to assemble and process the data. There is an option called Receive Window Scaling to optimize the performance of Windows XP, but the option is turned off by default in the Registry.
For this tweak to work, your laptop's wireless network adapter must use either an internal "n" wireless chipset or an "n" PC card. Just add a few entries in the Registry:
1. Open the Windows XP Registry (Click Start and then Run, type regedit, and press Enter)
2. Back up the current Registry (File | Export…)
3. Find the values in the folder path HKey_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\
Parameters and add a DWORD entry with the name Tcp1323Opts. Right-click on the entry, then choose New | DWORD value. Give it a hexadecimal value of 3.
Add a DWORD entry with the name TcpWindowSize and give it a hexadecimal value of 40000.
You must reboot your system so that the changes can take effect. The tweak tells the driver that the OS has turned on the Windows Scaling option. Windows Scaling improves the data stream's round-trip time in the TCP stack, so your laptop will perform faster with 802.11n routers in 5-GHz mode. There isn't a nice, neat dialog box you can call up to tell you how much your throughput has improved, but you should see a real difference in download times.
http://www.pcmag.com/article2/0,2817,2330471,00.asp