Huawei B525 Router - T-Mobile Unlimited Internet, Weak Signal in Basement, Antenna or New Router?

Hi. I have unlimited t-mobile internet and a Huawei b525 router that I got without antennas. I live in Warsaw but the problem is that I live in the basement and the router shows 1 to 3 signal lines. In good hours the speed is 6-8 Mb / s in worse 1-2. When I go outside, I take 30-40 Mb / s from my phone. So I would like to ask you what to do in such a situation? Buy an antenna? How so, which one? Or maybe another router?

And what street is it in Warsaw? Show screen from the Network cell Info application (DATA tab) on the phone outside and speedtest. The B525 management application is based on the Android application http://www.mediafire.com/file/79obbe81eufdt7t/Huawei_Manager_1.2_PL.apk/file. It can force LTE bands and aggregation of 2 LTE bands on B525, shows BTS signal and CID parameters which you use on B525 in T-Mobile. Download, connect to WiFi with B525 on your phone, log in to HManager on B525 (192.168.8.1) and show the screen when the router in the basement. Of course, you must have an external antenna and its selection after tests.

Hi. This is Jagielska street.
Screen from Network cell info https://iv.pl/images/45294448960312202449.jpg
Screen from HM 1.2 https://iv.pl/images/83225837200862715836.jpg

There is a 3G connection on the phone, no BTS data. Test outside? On the router, a connection with BTS Networks at Puławska 557 on LTE800, very poor signal parameters. LTE2600 T-Mobile and LTE1800NW are still working on BTS and aggregation of these 3 bands. Force LTE2600 and then LTE1800 in Hmanager, try to put B525 out the window. The LTE800 is poor SINR and hence low speeds. Other nearby NetWorks BTSs with these bands are Puławska 538 and Bażancia 34.

In 2600 it doesn't connect at all and in 1800 there is a connection but 0 dashes

At home, you will not connect to LTE2600, even LTE1800 hence the request to issue B525 for the window. And no strokes, only ss from Hmanager.