Wifi is very slow on my Macbook Air 13" mid 2012

I'm experiencing very slow speeds on my new Macbook Air 13" mid 2012. For example when I'm transferring files from my NAS, a Qnap TS-259 Pro+, wirelessly through my D-Link DIR 855 router. I barely reach speeds around 1MB/s. If I use my Windows 7 laptop, that sits right next to my Mac, to transfer the exact same file I get constant speeds around 6MB/s. That's six times faster.

Is there a known issue with the wifi that I've missed?

I did some further testing to try and identify the cause of the wifi problem. I installed Windows 7 in Parallels and transferred the exact the same files once again. Here's where it becomes interesting. Transferring those same files on my Macbook, using Windows 7 under Parallels, the speed was the same as it was on my physical Windows 7 machine, i.e. a constant speed of around 6MB/s. I then switched back to Mac OSX again and the speed once again decreased to around 1MB/s.

I think its fair to say that the problem is caused by the software rather than the hardware. Don't you agree?

Any help is appreciated!

//Fred