In GSM your co-channel rejection is 9dB or better
in the type approval spec. Your requirement is that you can re-use the frequency when the neighbouring basestation is guaranteed to be 9dB
weaker than your own. I must admit that I am not
an expert in cell planning esp. not for IS-95 but
if two IS-95 basestations are placed next to one another can they really each have 46 connections
if the handsets hear the two basestations equally
well?
GSM is superior to CDMA. IS-95 is hot air and
marketing. The voice quality depends on the
speech codec and not on the method of transmitting
the digital data. Data is just data. I dont
know about IS-95 but in GSM you can use many
different voice codecs. The network and the
handset negotiates what codec to use very much
like your old analogue modem. Off the top of my
head I remember full rate, half rate and enhanced
full rate. Your operator may or may not support
all of these depending on the make and age of
his infrastructure, and your handset may or may
not support all of these depending on the age of
the handset.
First of all I havent experienced that GSM
breaks up in crowded areas. I have gotten
a message of "Network Busy" in such situations
and I would assume that any digital system would
give such an indication if you reach the systems capacity limits. I have used GSM without
problems in North America as well as in
Europe and it is very seldom that I have had problems with capacity.
Secondly GSM have always had closed loop power
control. The basestation request each handset
to adjust its transmitted power so it is just
strong enough for the basestation to do the
decoding. Likewise the GSM basestation will
adjust its power level according to the feedback
from the handset so it will "keep its voice down"
when it is talking to a handset close to the
basestation. That way the frequency can be re-used by neighboring cells faster, adding to
the capacity of the network. A CDMA basestation
will have to shout loud enough to be heard by the
handset with the poorest reception.
A GSM handset receives from the basestation a
list of frequencies used by neighboring
basestations and the handset reports to the network during conversation the received signal strength of each of these frequencies. If the
local cell is heavily loaded with traffic or if
the reception in neighboring cells are seen to
be better, the handset is ordered by the basestation to switch to one of the adjacent
cells. This is off course transparent to
the user.
Hmm... up to 45 conversations on the same
frequency band. If I remember correctly IS-95
uses a little less than 1.2 MHz bandwidth for
each set of channels. If this corresponds to
a maximum of 45 simultaneous conversations and
we compare with the situation in GSM where each
set of channels uses 200 kHz and have 8 timeslots
we get 8 * 1.2MHz/200kHz = 48 simultaneous full
rate links. Where is the beef?
Slashdot Mirror
In GSM your co-channel rejection is 9dB or better in the type approval spec. Your requirement is that you can re-use the frequency when the neighbouring basestation is guaranteed to be 9dB weaker than your own. I must admit that I am not an expert in cell planning esp. not for IS-95 but if two IS-95 basestations are placed next to one another can they really each have 46 connections if the handsets hear the two basestations equally well?
GSM is superior to CDMA. IS-95 is hot air and marketing. The voice quality depends on the speech codec and not on the method of transmitting the digital data. Data is just data. I dont know about IS-95 but in GSM you can use many different voice codecs. The network and the handset negotiates what codec to use very much like your old analogue modem. Off the top of my head I remember full rate, half rate and enhanced full rate. Your operator may or may not support all of these depending on the make and age of his infrastructure, and your handset may or may not support all of these depending on the age of the handset.
First of all I havent experienced that GSM breaks up in crowded areas. I have gotten a message of "Network Busy" in such situations and I would assume that any digital system would give such an indication if you reach the systems capacity limits. I have used GSM without problems in North America as well as in Europe and it is very seldom that I have had problems with capacity.
Secondly GSM have always had closed loop power control. The basestation request each handset to adjust its transmitted power so it is just strong enough for the basestation to do the decoding. Likewise the GSM basestation will adjust its power level according to the feedback from the handset so it will "keep its voice down" when it is talking to a handset close to the basestation. That way the frequency can be re-used by neighboring cells faster, adding to the capacity of the network. A CDMA basestation will have to shout loud enough to be heard by the handset with the poorest reception.
A GSM handset receives from the basestation a list of frequencies used by neighboring basestations and the handset reports to the network during conversation the received signal strength of each of these frequencies. If the local cell is heavily loaded with traffic or if the reception in neighboring cells are seen to be better, the handset is ordered by the basestation to switch to one of the adjacent cells. This is off course transparent to the user.
Hmm... up to 45 conversations on the same frequency band. If I remember correctly IS-95 uses a little less than 1.2 MHz bandwidth for each set of channels. If this corresponds to a maximum of 45 simultaneous conversations and we compare with the situation in GSM where each set of channels uses 200 kHz and have 8 timeslots we get 8 * 1.2MHz/200kHz = 48 simultaneous full rate links. Where is the beef?