Wireless FAQ (Revision A.5) Revised March, 2005 This FAQ is posted once per month around the 1st of the month to the following Usenet Newsgroups: alt.cellular alt.cellular-phone-tech alt.cellular.tech sdnet.wireless.pcs alt.cellular.sprintpcs alt.cellular.verizon alt.cellular.gsm.carriers.voicestream This FAQ is also available at: http://www.dvv.ru/stuff/WirelessFAQ.txt http://www.wirelessadvisor.com/wireless_faq.cfm http://www.Lanpaq.com Changes in this revision: Removed the offer to email this faq when it has changed. I will continue to do that for those that have already signed up, but I will no longer add new people to the email list. Added two phone manufacturer's URLs to A. 5.3 (Sanyo and Palm) Thank you Bob Smith for the information. Send all corrections/additions/suggestions to jdcooley@cox.net. This FAQ will concentrate on the wireless systems used in the United States, especially digital systems. I do not read all the newsgroups that this FAQ may be posted to, so please send e-mail to me rather than post suggestions to the newsgroups. Some of the answers were given in different newsgroups or taken from different Web pages and not necessarily confirmed by me. Please don't blame me for any errors, just send me the correct information! PLEASE NOTE: I will not knowingly include any "secret codes", hacking information, nor any URLs pointing to any of those. I GENERAL QUESTIONS Q 1.1 What is AMPS? A 1.1 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. Q1.2 What is GSM? A1.2 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 Spécial Mobile, but now the most accepted name is Global System for Mobile Communications. GSM uses a combination of FDMA and TDMA. FDMA: The 25Mhz-wide 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 1.3 What is TDMA? A 1.3 Time Division Multiple Access is an air interface that allows mobile stations to use the same frequency, but are separated by time slots. Q 1.4 What is CDMA? A 1.4 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. The channels are approximately 1.25Mhz wide. Q 1.4a What is the difference between TDMA and CDMA? A 1.4a (Credit: Steve Punter) 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. As you have already guessed, the main difference between TDMA and CDMA is how they share the spectrum. TDMA does so 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 1.25Mhz-wide 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 to 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 1.5 What is PCS? A 1.5 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 1.6 What is an ESN? A 1.6 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. GSM equivalent would be the IMEI. Q 1.7 What is meant by dual-mode? A 1.7 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 1.8 What is a dual-band phone? A 1.8 A dual-band phone operates on the cellular band (800Mhz) and the PCS band (1900Mhz). [Questions 1.9, 1.10, and 1.11 deleted] Q 1.12 What is GSM1900? A 1.12 It is the GSM system used in the United States on the PCS band. Q 1.13 What is a SIM card? A 1.13 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 1.14 What are the potential health hazards to using a portable wireless phone? A 1.14 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 1.15 What is IRIDIUM? What is GlobalStar? A 1.15 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. 1.16 What is EVRC? A. 1.16 [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. Q 1.17 What is 3G (3GP)? A 1.17 The short answer is: 3G is a generic term covering a range of future wireless network technologies, including cdma2000, UMTS, GPRS, WCDMA, and EDGE. 3G combines high-speed mobile access with Internet Protocol (IP) based services. This doesn't just mean fast mobile connection to the World Wide Web - by liberating us from slow connections, cumbersome equipment and immovable access points, 3G will enable new ways to communicate, access information, conduct business and learn. II TECHNICAL QUESTIONS Q 2.1 In CDMA what is meant by "slot cycle index"? A 2.1 [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 2.2 What are the frequencies of the 800MHz and 1900MHZ channels? A 2.2 The receive (RX) and transmit (TX) frequencies for the mobile units are: CELLULAR CHANNEL RX TX 1 870.030 825.030 2 870.060 825.060 3 870.090 825.090 . . 799 893.970 848.970 800-990 no voice channels 991 869.040 824.040 992 869.070 824.070 . . 1023 870.000 825.000 PCS CHANNEL RX TX 1 1930.050 1850.050 2 1930.100 1850.100 3 1930.150 1850.150 . . 1200 1990.000 1910.000 III MANUFACTURER SPECIFIC QUESTIONS Q 3.8 Which digital phone should I buy? A 3.8 (Credit: Michael Geary) 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. IV WIRELESS CARRIER SPECIFIC QUESTIONS Q 4.1 Which wireless carrier should I sign up with? A 4.1 See A 3.8. V HELPFUL URLs Q 5.1 Where can I get more information about CDMA? A 5.1 Qualcomm, Inc.: http://www.qualcomm.com CDMA Development Group: http://www.cdg.org Wireless Technical Forum: http://www.Lanpaq.com Q 5.3 What are the URLs for the major wireless phone manufacturers? A 5.3 Qualcomm: http://www.qualcomm.com Motorola: http://direct.motorola.com/hellomoto/index.html Nokia: http://www.nokiausa.com Sony Ericsson: http://www.sonyericsson.com/us/ Samsung: http://www.samsungusa.com Kyocera Wireless Corp.: http://www.kyocera-wireless.com Audiovox: http://www.audiovox.com LG: http://www.lgmobilephones.com/ Sanyo: http://www.sanyo.com/wireless/ Palm: http://www.palmone.com/us/ Q 5.4 Where can I get more information about GSM? A 5.4 http://kbs.cs.tu-berlin.de/~jutta/gsm/js-intro.html http://www.gsmworld.com A 5.4a (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/ 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 North America: http://www.communicreate.com/gsmnew.htm GSMag International: http://www.gsmag.com/ Q 5.6 What other helpful URLs are available? A 5.6 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.wirelessdimension.com (new name: point.com but URL still works) http://www.myrateplan.com Cellular Phone Information For Beginners http://web.idirect.com/~aaa/p0000003.htm Cellular, PCS and Wireless Phone Service Information http://www.wirelessadvisor.com/ Another FAQ (mostly concerning CDMA): http://denbeste.nu/cdmafaq/ A 5.6a More URLs (Credit: Bob Smith) Web Links on wireless information & FAQ's http://www.berkana.com/tower.php3 - Locator of towers near you. http://www.arcx.com/sites/ - Canadian info, but good FAQ's http://www.point.com/ - Source to compare services, phones & coverage areas. http://www.letstalk.com - Same http://www.mybestplan.com/ - Same http://www.mcw.edu/gcrc/cop/cell-phone-health-FAQ/toc.html http://www.sierrawireless.com/ Sprint PCS Phone Links http://www.sprintpcs.com/learn/help_sitemap.html http://www.sprintpcs.com/wireless/capable_phones.html Wireless Internet URL's http://www.datalink.net/home.htm http://mobile.msn.com/ http://sprintpcs.my.yahoo.com/ http://www.hz.com/ http://www.messaging.sprintpcs.com/sms/ http://www.squeezenet.com http://www.mailandnews.com/ http://www.HerMobile.com -- provides email aliases for wireless phones