Q
What is AMPS? UP
A. The Advanced
Mobile Phone System (AMPS) is the analog system used
in the United States for cellular telephones. It uses Frequency
Modulation
(FM). AMPS uses the FDMA air interface. The channels are
30Khz wide. The
frequency band for AMPS is 824Mhz to 849Mhz and 869Mhz to 894Mhz.
Q What
is GSM?
A. GSM was
established in 1982 as a European standard for digital wireless
communications. The first system was on line in 1991. GSM is now used
in many
countries around the world. The original name was Groupe Sp?ial
Mobile, but
now the most accepted name is Global System for Mobile Communications.
GSM uses a combination of FDMA and TDMA. FDMA: The 25Mhz
band is
divided into 124 frequencies of 200Khz each. One or more of
those frequencies
are assigned to each base station. TDMA: Each of those
frequencies uses 8
time slots.
Q
What is TDMA?
A . Time Division
Multiple Access is an air interface that allows mobile
stations to use the same frequency, but are separated by time slots.
Q
What is CDMA?
A . Code Division
Multiple Access is an air interface that allows mobile
stations to use the same frequency, but are separated by unique
digital codes.
CDMA uses spread spectrum techniques. The standard (IS-95) was
published
by the Telecommunications Industry Association (TIA) in July, 1993 and
revised to IS-95A in May, 1995. IS-95B is being developed now. The
channels
are approximately 1.25Mhz wide.
Q
What is the difference between TDMA and CDMA?
UP
A
The first thing you have to learn is that "TDMA" is used
frequently as a
direct reference to IS-136. This is an ambiguous reference,
since there
are actually three technologies that presently use a form of Time
Division
Multiple Access. Be careful when talking with people who use TDMA in
this way.
Of the four competing
technologies, IS-136 (Cantel), GSM (Fido), and iDEN
(Mike) use their own versions of TDMA. IS-95 (Bell Mobility &
Clearnet PCS)
is an implementation of CDMA.
US Carriers:
IS-136: AT&T, BellSouth, Southwestern Bell
GSM: Omnipoint, Pacific Bell Mobile
Service, others
IS-95: Airtouch, GTE, Bell Atlantic,
Sprint PCS, Primeco, others]
As you have already
guessed, the main difference between TDMA and CDMA is
how they share the spectrum. TDMA does so using by assigning each user
on a
channel a different "slot" in time. IS-136 and iDEN have 3
slots per
channel, while GSM has 8 slots per channel. Note that a GSM channel is
much
wider than an IS-136 or iDEN channel. Each user "takes
turns" transmitting
and receiving in their designated time slot.
CDMA on the other hand
has everyone on the channel transmitting and
receiving AT THE SAME TIME. Conventional wisdom would lead you to
believe
this is impossible, but it works because of a modulation technique
known as
Spread Spectrum. A CDMA channel is very wide (1.25 Mhz actually). Each
user
is only transmitting a small amount of data, which would normally fit
well
into a much smaller (narrow) channel. What the transmitter does is to
take
this small number of bits and spread it out over the entire 1.25 Mhz
channel. It does so using an encoding technique that makes each user's
bits
interfere very little with everyone else's. The receiver's job is to
"unspread" the bits and extract only the data from the
desired user.
Because this wide
channel can accommodate many different people using it at
the same time, the channel is said have "soft capacity",
since the upper
limit on the number of users is determined strictly by how much
interference
a subscriber is willing to endure. Up to a certain point, the level of
inter-user interference is well within the capability of the voice
coding
algorithm to correct. In a TDMA system, the capacity is "hard
coded" by the
number of slots allocated to a channel.
CDMA also offers a
unique feature known as "soft handoff". TDMA systems use
what is known as a "hard handoff", since the connection with
one site must
be broken and then a new connection created. CDMA systems keep your
call
connected through 3 (the spec allows up to 6, but that isn't used)
different
sites. Your phone can pick and choose between these 3 sites at any
time, and
can in fact combine the signals from two or more sites at the same
time.
It would take volumes to
go into the necessary detail required to explain
the true differences. I therefore recommend you buy a book called
"Wireless
Personal Communications Systems" by David J. Goodman. It's an
Addison-Wesley
publication, and its ISBN number is 0-201-63470-8. This book is a
marvelous
source of information about the various technologies (excluding iDEN)
used
in North America.
Q
What is PCS?
UP
A. The Federal
Communications Commission (FCC) opened a new frequency
band for digital phones and named the new service Personal
Communication
Services (PCS). The band is generally referred to as the 1900Mhz
(1.9Ghz)
band. The band is from 1850Mhz to 1990Mhz.
Q
What is an ESN?
A. The Electronic
Serial Number is a 32-bit number that is stored in the
phone. It is used, along with other numbers, to identify your phone.
Q
What is meant by dual-mode?
A. A dual-mode
phone operates on two modes. Usually this refers to
phones that use digital and analog, however it also pertains to phones
that
operate on AMPS and N-AMPS.
Q
What is a dual-band phone?
A. A dual-band
phone operates on the cellular band (800Mhz) and the
PCS band (1900Mhz).
Q
What is D-AMPS?
A. The Digital
Advanced Mobile Phone System is similar to GSM.
D-AMPS uses the TDMA air interface. The main difference between
GSM
and D-AMPS is that GSM uses 8 time slots rotated at 214 times per
second
and D-AMPS uses 3 time slots rotated at 50 times per second. The
standard
for D-AMPS is IS-136.
Q
What is N-AMPS?
A . Narrow-band
Advanced Mobile Phone Service was developed by
Motorola. The 30Khz channels used in AMPS were divided into
three
10Khz channels to add more capacity to the cellular system.
Q
Are D-AMPS and N-AMPS compatible with AMPS?
UP
A. Yes. All
D-AMPS and N-AMPS phones must be fully compatible with
AMPS systems. In addition, any system that is using D-AMPS or
N-AMPS must
also provide AMPS. You can use either of those phones all over
the United
States.
Q
What is GSM1900?
A. It is the GSM
system used in the United States on the PCS band.
Q
What is a SIM card?
A. The SIM
(Subscriber Identity Module) card is a "smart card" used by
a subscriber to GSM. The card contains information about the
user and can be
plugged into another GSM phone. This allows the user to use
another GSM
phone as if it was his/her own phone.
Q
What are the potential health hazards to using a portable
wireless phone?
A. The 'short'
answer is that there is no known health hazards associated with
the proper use of portable wireless phones. For more technical
information on this
subject go to http://www.fcc.gov/oet/. The Office of Engineering
and Technology
(OET) has a number of bulletins on the subject. The two that you
want to start
with are OET56 and OET65C. OET56 gives a lot of other
references.
Q
What is IRIDIUM? What is GlobalStar?
A. The IRIDIUM and
GlobalStar systems will use low earth orbit satellites
for wireless communication. A special handset will allow the user to
communicate
via ground based cellular or by satellite. For the latest information
see:
http://www.iridium.com
http://www.globalstar.com
Q
What is EVRC?
A.. [Credit: Bill
Walker]
EVRC is the Enhanced Variable Rate Coder. It is an 8 kbps
vocoder
that's supposed to sound about as good as the current 13 kbps vocoder.
Thus, you can have the same voice quality while improving the capacity
of the system (which can handle more 8 kbps calls than 13 kbps calls.
As far as I know, the only place it's currently commercially deployed
is Korea.
Q
In CDMA what is meant by "slot cycle index"?
UP
A. [Credit: Bill
Walker]
On the CDMA Paging Channel (this is the shared channel that all phones
listen to for incoming calls and other control info), time is divided
into
"slots". To conserve power, phones that are currently
idle only "wake up"
and listen for messages on the Paging Channel during their assigned
slots. The slot cycle index determines how often the phone's
slot comes
around. If the slot cycle index is 0, the phone wakes up every
1.28
seconds. If it's one, it wakes up every 2.56 seconds. If
it's two, it's
every 5.12 seconds, and so on. The larger the setting, the more
power is
conserved, but the longer it takes to page the phone for an incoming
call. You can imagine that if it were set to 10.24 seconds, few
callers
would hang on the line long enough for you to answer your phone.
There are two settings
that govern this. One is the "preferred slot cycle
index" in the phone, and can be set via service programming.
The other is
the "maximum slot cycle index" set in the base station and
broadcast in
overhead messages on the Paging Channel. The phone has to use
whichever
number is smaller.
Q
Which digital phones are made by Motorola for use in the U. S.?
[For updates, see A 5.3 for Motorola's URL]
A. M75 800Mhz/AMPS/TDMA
M70
800Mhz/AMPS/TDMA
GSM
1.9 StarTAC(tm) 8500g/8000g 1900Mhz/GSM(TDMA)
MicroTAC
Select(tm) 6000e 1900Mhz/GSM(TDMA)
"
"
3000e
"
"
"
"
"
2000e
"
"
"
MicroTAC(tm)
SC-725 This is a CDMA phone.
Q
Which digital phones are made by Nokia for use in the U. S.?
UP
[NOTE: I no longer
update the following list. See A 5.3 for Nokia's URL]
A. Nokia 2120 800Mhz/TDMA/AMPS (IS-54B)
Nokia
2160 "
"
"
(same as 2120 but added IS-136 support)
Nokia
2168 "
"
"
(IS-136)
Nokia
2180 800Mhz/CDMA/AMPS (IS-95)
Nokia
2190 1900Mhz/GSM(TDMA)
Nokia
6120 800Mhz/TDMA/AMPS
Nokia
6160 1900Mhz/TDMA and 800Mhz/TDMA/AMPS chosen in
that
order. (Credit: Norman F. Smith)
Nokia
6190 see A 3.2a
A .a
Nokia 6190 is a GSM1900 handset. It comes with a detachable
analog module,
which (when inserted between the phone and battery) allows it to be
used on
AMPS network. AMPS is the old analog system which operates at
800 MHz. So,
Nokia 6190 truly is a dual mode (GSM/AMPS) and dual band (1900/800)
unit.
A .b
GSM Datacards and AMPS/DAMPS modems
The Nokia 2190 with a
data card works like this. Since GSM networks
are all digital to start with no modem is necessary to convert to an
analog signal. The data card acts as an interface between where
the
computing device expects a modem to be and the phone. Newer
products
"Soft Modem" to eliminate any need for a hardware interface.
For GSM, basically you can say that there is no modem since nothing is
being MOdulated and DEModulated at your location. As your transmission
is sent over the phone lines it hits a modem only when it
reaches a stretch of
analog line.
If using the Nokia 2160
or 2180, the analog modems for the AMPS/DAMPS
system do basically the same thing in digital mode with the addition
of
analog support. In analog support mode, you are basically just making
a
regular call as if you would dialing out though a regular land line.
The
average speeds in analog mode are 2400 to 4800 Bps.
You must of course dial
into a special number in order to use the
digital mode for both systems. The average speeds in digital mode are
9600 to 14400 Bps.
Q
Where can I get more information about the Nokia 6190?
UP
A. Steve Punter
has a Web page dedicated to the Nokia 6190.
http://www.globalserve.net/~punter/Nokia6190.htm
Q
Which digital phones are made by Ericsson for use in the U. S.?
[NOTE: I no longer
update the following list. See A 5.3 for Ericsson's URL]
A. PD 328 & PD 398 Dual-band, Dual-mode. AMPS
& TDMA on 800 Mhz,
TDMA
only on 1900 Mhz. Both phones are only
available
through Southwestern Bell.
LX
77 & LX 100 Same specs as above, but only available through
AT&T
Wireless Services.
DH
318, DH 368, DH 388 Listed as "Dual-mode". Assume
this means
800Mhz/TDMA/AMPS
CH
388 & CF 388 1900Mhz/TDMA (GSM-1900 phones)
Q
Which digital phones are made by Qualcomm for use in the U. S.?
[NOTE: I no longer
update the following list. See A 5.3 for Qualcomm's URL]
A. QCP-820 800Mhz/CDMA/AMPS
QCP-1920
1900Mhz/CDMA
QCP-2700
800Mhz/AMPS 1900Mhz/CDMA
Q
Phone 1900Mhz/CDMA
Q800
800Mhz/CDMA/AMPS
Q
Which digital phones are made by Sony for use in the U. S.?
[NOTE: I no longer
update the following list. See A 5.3 for Sony's URL]
A. CM-M1300 800Mhz/CDMA/AMPS
CM-S1101
1900Mhz/CDMA
CM-B3200
800Mhz/AMPS 1900Mhz/CDMA
CM-Z100
1900Mhz/CDMA (very small..3.6" x 2.4" x 1",
5.3 oz.)
I have also seen posts giving CM-2100 as the model number for the
CM-S1101. The
numbers listed above are taken directly from the shipping boxes on
3/23/98.
Q
Which digital phones are made by Samsung for use in the U. S.?
UP
[NOTE: I no longer
update the following list. See A 5.3 for Samsung's URL]
A. Samsung makes a model SCH-1000 and a model SCH-1900. Both
are 1900mhz,
CDMA only.
Q
Which digital phone should I buy?
A.
Which phone is "better" will depend more on the service
provided by a
given carrier than the actual piece of equipment you hold in your
hand.
So backing up a bit,
here is the way to answer your question:
First, investigate the
various wireless carriers in your area. Look up
their price plans, get feedback from customers about their coverage
and reliability, and then finally see what kind of phones they offer.
Then, and only then, it
starts to make sense to think about which
model of phone. You may well find the decision has already been made
for you--most digital carriers sell only certain phones that work with
their service.
Q
Which wireless carrier should I sign up with?
A. See A 3.7.
V HELPFUL URLs
Q
Where can I get more information about CDMA?
A. Qualcomm, Inc.:
http://www.qualcomm.com
CDMA
Development Group: http://www.cdg.org
Q
Where can I get a comparison of the Sony Z100 phone to the
Qualcomm Q phone?
A. http://www.geocities.com/yosemite/6686/sprintpcs.htm
Q30
What are the URLs for the major wireless phone manufacturers?
UP
A . Qualcomm:
http://www.qualcomm.com
Motorola:
http://www.mot.com
Nokia:
http://www.nokia.com
Ericsson:
http://www.ericsson.com
Samsung:
http://www.samsung.com
Sony:
http://www.sel.sony.com/SEL/consumer/
Q
Where can I get more information about GSM?
A. http://kbs.cs.tu-berlin.de/~jutta/gsm/js-intro.html
http://www.gsmworld.com
A .a (Special
Thanks to: George Czajkowski)
GSM Memorandum of Understanding Association
(official GSM page, includes history of GSM):
http://www.gsmworld.com
Overview of the Global
System for Mobile Communications (GSM):
http://ccnga.uwaterloo.ca/~jscouria/GSM/
An Introduction to GSM:
http://www.bellsouthdcs.com/balston.html
Global Systems for
Mobile Communications (GSM): Services and Architecture:
http://www.dg-tech.com/gsm.htm
GSM Security and
Encryption (technical paper):
http://www.semionoff.com/cellular/hacking/phreaking/gsm-secur.html
GSM Information:
http://www.bit.net.au/~nogi/gsm/
Robert's GSM Information
Page:
http://huizen.dds.nl/~elsinga/gsm/
Cellular GSM Phones:
http://www.geocities.com/CapeCanaveral/2042/nokia.html
GSM all over the world
(links to GSM related sites):
http://www.webring.org/cgi-bin/webring?ring=gsm;list
GSM Mobile Page in
English:
http://hem.passagen.se/borjeg/index-en.htm
GSM North America:
http://www.communicreate.com/gsmnew.htm
GSMag International:
http://www.gsmag.com/
Q
Where can I get more information about Short Messaging Service?
A.
GPA Technology Pty. Ltd.
http://www.winpos.com/SMS/sms.htm
Q
What other helpful URLs are available?
UP
A .
Steve Punter's page. Contains lots of interesting info. Check
it out!
http://www.arcx.com/sites
Comparisons of phones
and services - national
http://www.wirelessoutpost.com
http://www.wirelessdimension.com
Comparisons of phones
and services - Boston
http://www.picante.com/~gtaylor/cellphones.html
Description of CDMA
technology
http://www.cdg.org/a_ross/
Wireless Today industry
links
http://www.wirelesstoday.com/links.htm
Cellular Phone
Information For Beginners
http://web.idirect.com/~aaa/p0000003.htm
