Access to and extract NMEA messages in vb.net

Hello friends,

I have a Montana 680 gps device and I want to extract NMEA sentences from the device by Visual Basic.Net. My gps radio has the option “NMEA IN/OUT” among other settings. My ASUS laptop has no COM port. It has only USB ports. I use Serial Port object in my vb code to read the NMEA sentences. But the code gives the error COM port, say , COM3, does not exist, because there is no COM port on my laptop. Do I need to make some special setting on my GPS radio? How do I code in vb.net to access and get NMEA sentences? I use Visual Basic.Net programming language. Do I need to convert my USB port to a virtual COM port by a software? If yes, how do I do it?

Thank you for your any assistance.