Hya Lee
Basically a trade-off was decided between
available spectrum vs technology cost 20 years ago,
plus the cross-over point between antenna size and
losses like building wall materials, wet leaves
on trees etc.
Also 10-20 years ago the band-width
per channel needed only to support a single 2-way
voice call, so little spectrum was needed per call.
UHF offered a good compromise between the conflicting
factors. Antenna size can be small, losses through
building materials is only around 10 dB or so, and
pipework within buildings ensured re-radiation was
possible within a building in UHF. Adequate transmitter
power and low receiver noise factors could be achieved
at low cost and high repeatability in MMICs at UHF.
All this implied a good economic cell radius per
base station, so UHF represented the cross-over
spectrum where all the conflicting factors for mobile
telephones met.
Today there is inevitably a
shift towards higher frequencies (L and C band)
as technology costs fall, MMICs improve and band-width
demand rises.
