First be sure you aren't confusing cellular signal vs Wi-Fi signal. Then carefully consider your use.
Since you mentioned download speeds it makes me think you are more concerned about moving and using large amounts of data and at speeds, such as streaming video, YouTube videos, etc.
If that is the case, then there is a great chance it's your Wi-Fi signal you should optimize, not your cellular. While some cellular devices and providers can provide the bandwidth and speed to do the above, it generally comes at a major expense as you will need a large data plan from your cellular provider. And the majority of those type plans, even if unlimited will "clamp down" on your available speed when you reach a certain monthly amount of data usage such as 10 gigs. Up to 10 it rocks, but if you use 10 gigs of a 10 GB plan 15 days into the month, then the next 2 weeks will be aggravatingly slow.
Wifi on the other hand doesn't care how much data you move...it cares about how fast you want it to be capable of based on your networking needs. For example, if you want to stream HD or 4K HD without buffering (when your video stops and you see that circling thingy), you'll need a certain minimum speed to do that.
If your wireless or ISP provider plan you pay for is capable of that speed you can stream to your heart's content without buffering, as much as you want.
Try that on cellular and you may be able to do that up to a point each month, but you are using up your total data "bucket" allowed at that speed for that month. Think of it as a well that holds a certain amount of water
A water truck comes by once a month to make sure your well is full
Your well also has a low level float in it that when engaged turns on a hose that dribbles in enough water to let you stay hydrated, but just barely and it never increases the water in the well.
Until you hit that float you can drink as much water and as fast as you want from that well, but only until you drain the well. Then you're stuck with the hose only until the water truck comes back for it's monthly replenish of your well.
Wifi, on the other hand is a hose that can stay on and blast at whatever speed you want and are willing to pay for monthly through your provider. There's no well...just a steady supply that can provide just as much water at any time as your cellular "well" did at it's fullest. Again, you decide how fast you want to drink then choose the Wi-Fi speed necessary. The faster the more expensive, so choose your speed based on your needs.
Advantages of cellular are that your data plan travels with you wherever you go. Wifi is local to your home. But Wi-Fi is also available at Wi-Fi "hotspots". That's why so many businesses allow you access to their Wi-Fi, where you are limited to their speed, but are able to stay connected. They do this as a service to customers.
With Wi-Fi, most smart phones allow you to access your network and also allow you to make calls via Wi-Fi. When you use the Wi-Fi on your phone you are not using your cellular "well water", so it doesn't count as water you drank from the well.
Cellular tends to be far more expensive if you need large amounts of data at Wi-Fi equivalent speeds each month. But it also allows you to access it wherever your phone can reach a cellular tower and can seamlessly provide signal from tower to tower. But if you hit a "dead area" you lose your data access the same as you do when you can't make a phone call, or experience a call where you or the other person can't hear part or all of what you are saying.
So, if you are looking to optimize speed and amount of data with no "throttling down" after a set monthly amount and you need it for your set location, then Wi-Fi is what you are after.
If you don't have Wi-Fi at your home or really need the mobility then cellular is your only real option...but probably an expensive one, unless your monthly data use and speed needs are small.
Keep in mind, cellular signal boosters/extenders are very different animals from Wi-Fi boosters/extenders. Getting one won't help the other.
That said, 5g is changing a lot of things including the above dynamic. Of course you would then need 5g capable smart phones with a cellular provider offering adequate 5g in your area.
Long read, but I hope it helps. If you decide it's Wi-Fi you need to boost rather than cellular I could tell you more about what you need based on what you want. For instance extenders vs mesh networking. A lot of people go the wrong way on that.
