Broadband over a mobile network is an abomination. The signal strength is too volatile, causing horrible attenuation and the end user sees that frequent disconnections, peaky connection rates and especially terrible performance in poor weather. High-speed internet is too sensitive a technology to be implemented effectively over mobile networks.

Having said that, you can maybe improve performance by moving your computer (or the receiver) to the part of your house which gets the best mobile phone coverage. And if that fails there might be a high-gain aerial you can attach, but that may cost a bit of money.