"why will WCDMA coverage stay constant despite varying call loads?"
WCDMA will breath just as EDGE will, but WCDMA-EDGE-GSM can,
with cooperation between cells, basestations and operators,
select between a lot of channels, power levels,
time slots, like multicarrier systems can, like what is
envisioned for OFDMA.
With basic GSM+EDGE+WCDMA (hierarchies) users can be placed in the
channels and airinterface which suits them and the network
best, data-voice,etc.
TDMA cells only hurt if the cells do not cooperate,
especially when too few channels and disruptive, competing
operators. (US-TDMA vs GSM-TDMA)
"CDMA's excellent interference rejection and power control
makes cell coverage changes a non-issue with adequate site
density."
Except for shuffling over the same problem to keeping
the power control within 1dB and a lot of handsets in soft
handoff (40-60%??) and no help from that for upstreams.
(2-3 basestations would have to combine the RF, IF or
full baseband signals from that handset)
Not the best for networks based on AMPS and TDMA-DAMPS where
CDMA happens to work.
But the CDMA-lesser need for frequency planning (but
more for toher) is really useful when combined with the
hierarchical system of GSM and EDGE, otherwise one must have
at least three CDMA bands, two for voice and one for data,
not to mix them. (not needed for GSM-EDGE-WCDMA)
"GSM/TDMA at 1.9ghz has existing sites in locations that
minimize coverage overlaps as it has no adjacent cell interference rejection."
GSM at 1900/1800Mhz has sites according to the number,
density of users, while 900Mhz goes for the rural areas,
for long reach and large cells (like AMPS)
Analog AMPS or NMT need a lot of interference dBs to work,
threshold of FM at 12-15-20dB while GSM works
with much more neighbor-neighbor cell intereference,
even down to negative dBs (if the sun shines and everything
is perfect)
That is, AMPS and DAMPS (US-TDMA) needs much lower
interference than GSM(-TDMA).
EDGE will bring GSM "down" to the same as US-TDMA,
but increase the data per Hz density (a matter of
power control, etc just like CDMA)
"Chances of seamless coverage at 2.1ghz are slim. No amount
of technology will fix that outside of increasing the power
or size of antenna elements."
That is a misunderstanding based on the US AMPS-DAMPS(or
US-TDMA) system vs GSM(-TDMA)
Analog (FM) systems have never been mixed with GSM in
the "GSM-world".
US decided to build a (lousy) digital system on the same
bandwidths,etc as AMPS, GSM did not, instead built
separately from the NMT, TACS,etc analog (FM) systems
existing at that time.
That is, analog+digital systems in US (AMPS+DAMPS)
and GSM-land (99% GSM, no NMT,TACS left) are
different.
One can claim that US lowered the "digital threshold"
by using US-TDMA (DAMPS,etc), more compatible with AMPS,
compared to GSM-land which took the pain of building
a totally new network,etc for GSM compared to
analog NMT,TACS,etc.
Now US payes the delayed price.
For example, US DAMPS (US-TDMA)/AMPS users where not
supposed to be able to know if they were "digital" or
"analog", some probably never got a digital connection
as the network wasn't upgraded to digital.
(great "digital voice" on the "digital phone" which
never had made a digital connection)
In contrast there were no attempt of making
analog NMT, TACS,etc compatible in any way with GSM.
As a result there is "a lot" of confusion on "TDMA",
mixing the narrowband, AMPS-compatible DAMPS (US-TDMA)
with GSM(-TDMA), never designed (or built) to coexist with
the analog stuff on the same band nor even network.
Especially not the 1800Mhz GSM, compared to
900Mhz GSM, 900Mhz GSM with similar reach as 450Mhz NMT
(and additionally the 900Mhz NMT, while US
had to go 1900Mhz for GSM)
For example, in my neighborhood (kind of rural)
there was once one 450Mhz NMT station taking care of
a some 30km radius cell (at high power levels).
Now there are some twenty 900Mhz GSM station with
long reach, but now lower power levels, shorter
reach.
Additionally 1800Mhz GSM anywhere were more users can be expected (more channels, capacity, wider band, lower
power and lower reach).
Additionally one could go into the function of
(the catalyst) 900MHz NMT, which added capacity and
made cells smaller (same thing) but which is
not needed anymore (note, 9000Mhz NMT and 900MHz GSM
do not use the same band!!)
That is, this also goes back to the mostly US problems of
freeing up (military,etc) spectra for mobile phones.
As well as mistakenly applying US-TDMA aspects,etc to
GSM-TDMA aspects, cells sizes, bandwidths, carrier
frequencies, capacity, channels, operators, interference,
etc,etc, and especially power control.
All that hype based on the use of the word "TDMA" without
specifying if
-US-TDMA
-GSM-TDMA
or even Q-CDMA-TDMA downstreams.
Ilmarinen.
Downstream packets and TDMA go hand in hand, upstream
is more complicated, "soft handoff" actually makes
both messier. (but CDMA has a place when setting
up some 10-20 temporary base stations for that
great temporary event) |
