What DP master are you currently using in your stationary system? If you already have Labview working with one vendor’s master hardware, you probably can more easily adapt the Labview software to the portable version of your master. Look first at the vendor that provides your current hardware solution.
If you are starting from scratch, there are a lot of choices. Siemens has a USB PROFIBUS card CP5711; HelmHoltz has the NETlink USB compact; Softing has the PROFIusb; ABB has the NDA121; Just about every company that does PROFIBUS master cards has come out with a USB to PROFIBUS solution.