Smooth (not) equally-spaced signal strength data
Between these I only have experience with Kalman filters. They don't need equally spaced measurements but you can make it a lot easier with it. Missing measurements are really easy to cope with.

If you want a simple solution and you think that the most likely outcome of your next measurement is the same as the last one (there are no 'dynamics') you could also interpolate your missing values and use a linear filter.