MicroCell in a "daylight" basement - limited GPS lock

We work out of a basement office and have had bad service for years. Finally installing a MicroCell for use in the basement, but can't get it to keep GPS lock. Is this just not a solution for us?

Microcell is brand new - model DPH-154 - made initial GPS lock sitting by the window that faces east (110°E). We have slightly obstructed view of the sky, but mostly by trees that are about 10-20' away from the house.

If we move the microcell to the top floor and place it on a west facing window (290° W) we tend to make better GPS lock. The only problem there is the signal from the microcell doesn't make it back down two floors to where the phones are sitting. We usually get 1 "bar"/dot in the iPhone indicator and still have some calls go straight to voice mail. 

The house is in a very populated area and I expect the closest tower is less than 2 miles (as the crow flies). We just happen to hit line of sight bad when inside. If we walk about 10-20' away from the house the phones can pick up LTE fairly good (although we are about -100 signal strength).

Do we have any options to keep the microcell in the basement to give us the benefit of the boosted signal where it's most needed? The new model doesn't have an antenna input option so we can't do like some that used the old model. 

Particulars:

ISP: Comcast (plenty of speed)

wall -> modem -> router -> microcell

location: basement window facing east 

Lights: Power/Green, Network/Green, GPS/green (sometimes), 3G/blinking red

Any help/suggestion is appreciated! And I know...trying to troubleshoot something that sometimes works and sometimes doesn't is difficult, but if the device can make GPS lock it should be able to keep it, or else not rely on that lock so much to work simply to boost a signal that's actually going through internet. 

Hopefully AT&T will offer wi-fi calling sooner rather than later...and it be available to iPhone 5 users!