internet sharing is slow but with usb modem is very fast

[Guest kuoching]

Hi,I have noticed that the internet sharing shows a slower speed as compared with usb modem, why ?I used htc 8525 and now omnia..both devices cannot fetch the speed that if i use usb modem(both using same sim card to try). The speed with internet sharing is around 50KB whilst with usb modem is around 140KB...why is this happens and any tweaks for it?