2.4 GHz WiFI limits your downloads to 300 Mbits/sec.
An AC750-class (for example, the TP-Link Travel Router) extender has a limit of 433 Mb/sec transfer speed on 5 GHz, so it is only marginally faster than using 2.4 GHz.
For higher speeds, you need faster routers e.g., the AC1200,- and AC1500- class routers. Many of them will run off 12V supply.
Be mindful that the Raspberry Pi 4 (ASIAIR Pro) Ethernet port is itself limited to about 950 Mb/sec (barely qualifying as Gigabit), so while an AC1200-class (about 900 Mbps on 5 GHz) will help, you probably won't see much further improvement with AC1500 and higher classes. On top of that, depending on ZWO's implementation, you may not achieve the 950 Mbps LAN performance.
For ultimate speeds, you can convert your house network to something like an eero (now owned by Amazon) Mesh network, and placing one of the eero full-sized routers next to the ASIAIR Pro. The eero uses 9V USB Power Delivery as power supply, and there are converters available from 12V, albeit a router like that will deplete a battery rapidly. The full sized eero routers uses both 5.2 and 5.8 GHz WiFi bands as its backbone network.
But as I mentioned above, the weakest link may still be the Raspberry Pi 4's LAN port.
ZWO may have already scaled the image before downloading it to your tablet. If not, that is what they should do. I.e., write full sized images to the local memory stick that is attached to the Raspberry Pi 4, but transmitting a binned image to the ASIAIR app, binned and cropped appropriately to the zoom level the user has chosen in the tablet.
Chen
