The problem is the GPS standard protocol is NMEA which was designed for RS-232 serial ports where the port is connected to one device. There is no transmission/interface standard for USB GPS devices, in fact GPS devices are not even included in the USB standard. Some manufacturers include an additional driver that makes their USB GPS device appear to other software as if it is connected to an RS-232 serial port. This enables ArcGIS to function with the device, assuming it is using the NMEA protocol. Contact the GPS manufacturer to determine if the GPS unit being used has a driver that does this. Do a general search on the Internet for 'USB Serial port emulator'. There are a number of manufacturers of emulators that work. Another option is to purchase a USB serial cable. Make sure it includes a driver that makes the USB emulate RS-232. If the GPS device itself supports only the USB and not the RS-232 serial, the GPS device manufacturer usually provides a driver that does the same thing as a USB-to-serial adapter.
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