X300B

LTE-4G ref ​here

Step 1: Install USB packages

kmod-usb-net-cdc-ether 
kmod-usb-net-qmi-wwan 
kmod-usb-net-rndis 
kmod-usb-serial 
kmod-usb-serial-option
kmod-usb-serial-wwan 
kmod-usb-wdm 
usb-modeswitch

Install LTE-4G packages

luci-proto-qmi
uqmi 

Step 2: Create the QMI interface Go to Network => Interfaces => click "Add new interface" You can input any name you like. In this example, I named my interface "4G". In the protocol field choose "QMI". If you don't see QMI on the list, you have not installed the right packages or haven't rebooted the router.

Step 3: Please note that two interfaces showed up. One called "4G" and another one "Virtual dynamic interface (DHCP client)" called "4G_4". The "_4" means that the interface has an IPv4 IP address. This is based on the "PDP Type" selected in the previous step. If your carrier supports IPv6, you can use that as well (not recommended).
Get signal info status

root@OpenWrt:~# uqmi -d /dev/cdc-wdm0 --get-signal-info
{
        "type": "lte",
        "rssi": -68,
        "rsrq": -14,
        "rsrp": -100,
        "snr": 2.000000
}
root@OpenWrt:~# uqmi -d /dev/cdc-wdm0 --get-data-status
"connected"
root@OpenWrt:~# uqmi -d /dev/cdc-wdm0 --get-current-settings
{
        "pdp-type": "ipv4",
        "ip-family": "ipv4",
        "mtu": 1500,
        "ipv4": {
                "ip": "172.30.0.9",
                "gateway": "172.30.0.10",
                "subnet": "255.255.255.252"
        },
        "ipv6": {

        },
        "domain-names": {

        }
}
root@OpenWrt:~# 

GPS

On /dev/ttyUSB2

AT+QGPS=1                       Starts GPS service + NMEA Feed on /dev/modemGPS
AT+QGPSEND                      Stops GPS Service + NMEA Feed on /dev/modemGPS
AT+QGPSCFG="gpsnmeatype",xxx    Configure which NMEA output sentences are generated (See SIMCOM GPS Page)
AT+QGPSLOC?                     Run on AT command port to give a one-shot reading
AT+QGPSGNMEA="GGA"              Run on AT command port to give a one-shot reading of GPS Fix Data, Time, Position and related fix data

Ex.

AT+QGPSLOC?
+QGPSLOC: 232222.0,1343.4258N,10039.1887E,0.8,2.1,2,0.00,0.0,0.0,231122,09

Read Lat,Lon ref ​here
13+(43.4258/60) = 13.723763
100+(39.1887/60) = 100.653145

On /dev/ttyUSB1 the data will continue update GPS location

root@OpenWrt:~# picocom -b 115200 /dev/ttyUSB1
$GPGGA,233253.00,1343.426109,N,10039.188521,E,1,08,0.8,2.5,M,-25.0,M,,*46

We use ser2net to stream out the lat,lon

root@GL-X300B:/etc# tail -2 ser2net.conf
8888:raw:400:/dev/ttyUSB1:115200 8DATABITS NONE 1STOPBIT

Then on other terminal run

root@GL-X300B:~# curl -v --http0.9 192.168.8.1:8888 
> GET / HTTP/1.1
> Host: 192.168.8.1:8888
> User-Agent: curl/7.66.0
> Accept: */*
> 
$GPGGA,235831.00,1343.426963,N,10039.186482,E,1,08,0.8,1.9,M,-25.0,M,,*43
$GPRMC,235831.00,A,1343.426963,N,10039.186482,E,0.0,201.3,231122,1.1,W,A,V*51