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A high gain directional antenna on a CDMA phone would extend battery life since the transmitter would not have to run at as high a power level as with an omnidirectional antenna. Good for fixed operation.

Yes, that has been my experience, too.

Before that, I could hit a tower 40 miles away with an analog bag phone and a directional antenna, and did so often, working on oil rigs.

Digital was a pain because it was designed to work where there are sidewalks (close in), and I had to get a booster for the CDMA phone, adapters and hook that to the antenna. Without it the battery would die in no time, looking for signal.

The results were seldom as good as with the analog phone--more dropped calls or 'no service' moments, even if connections had less static.

Now AT&T has bought out my carrier and I have to change phones (GSM, now) and equipment yet again--and have it work the first time.

CDMA works by having the tower send control information to the phone to ensure that each handset produces the same RF field strength at the receiving antenna. If you're a long distance from the tower or inside a building that attenuates the signal, the phone transmitter has to be run at a higher power level to achieve the expected strength at the tower. The rough value is set using the GPS location of the tower and the calculated GPS location of the handset. That coarse setting is then fine tuned based on the observed RF level arriving. A high gain antenna helps by directing the RF to the tower and reducing the amount of power required to achieve the required RF field strength.

TDMA/GSM doesn't have that same equal field strength constraint. It isn't trying to pick out a signal by correlation of a pseudo-random number stream unique to the handset. It does have other impairments. The stream is time sensitive and subject to Rayleigh fading when reflected multi-path signals mixed 180 degrees out of phase and cause signal dropout. Multipath actually helps CDMA by comparison.The multiple correlators expect out of phase arrival and leverage it as the PN streams are correlated and summed. I haven't looked at how LTE is implemented, but the move to 700 MHz should significantly improve penetration of signals into buildings.