If there is no GPS signal or the signal is poor, these are the things you can try:

1. Try adjusting the GPS antenna
The antenna should be always mounted outside, unobstructed with a clear view of the sky (never behind a wall or a plate).

If the GPS is used on a vehicle, the best option is to put it on the roof. 

2. On GPS devices where it is possible to set external or internal antenna check if external antenna is set (on older device it is possible internal antenna should be set). 

3. Set receiver mode to standalone and reset the GPS receiver. Power cycling the device can also help. 

4. If DS-IMU is used, it is recommended to be mounted close to the antenna and correct offsets from the antenna to the IMU need to be entered.