The First Digital Cellular Systems – TDMA, GSM and iDEN (2G)

This section talks about the first digital cellular phone systems, including both “Digital AMPS” (D-AMPS) and GSM.  There was later a third technology that was primarily used by Nextel in the US called iDEN . All three of these technologies were based upon Time Division Multiple Access (TDMA) multiplexing technologies. These technologies are retroactively known now as “2G”


IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the North American 1G mobile system Advanced Mobile Phone System (AMPS). It was once prevalent throughout the Americas, particularly in the United States and Canada since the first commercial network was deployed in 1993. D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies.

This system is most often referred to as TDMA. That name is based on the abbreviation for time division multiple access, a common multiple access technique which is used in most 2G standards, including GSM, as well as in IS-54 and IS-136. D-AMPS competed against GSM and systems based on code division multiple access (CDMA).

D-AMPS uses existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots (hence time division) and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure in the beginning, as analogue scanners could not access digital signals. Calls were encrypted, using CMEA, which was later found to be weak.

IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol. SMS and CSD were both available as part of the GSM protocol, and IS-136 implemented them in a nearly identical fashion.

Former large IS-136 networks, including AT&T in the United States, and Rogers Wireless in Canada, have upgraded their existing IS-136 networks to GSM/GPRS. Rogers Wireless removed all 1900 MHz IS-136 in 2003, and has done the same with its 800 MHz spectrum as the equipment failed. Rogers deactivated its IS-136 network (along with AMPS) on May 31, 2007. AT&T soon followed in February 2008, shutting down both TDMA and AMPS.

Alltel (now Verizon), who primarily uses CDMA2000 technology but acquired a TDMA network from Western Wireless, shut down its TDMA and AMPS networks in September 2008. US Cellular, which now also primarily uses CDMA2000 technology, shut down its TDMA network in February 2009.

IS-54 is the first mobile communication system which had provision for security, and the first to employ TDMA technology.


The evolution of mobile communication began in three different geographic regions: North America, Europe and Japan. The standards used in these regions were quite independent of each other.

The earliest mobile or wireless technologies implemented were wholly analogue, and are collectively known as 1st Generation (1G) technologies. In Japan, the 1G standards were: Nippon Telegraph and Telephone (NTT) and the high capacity version of it (Hicap). The early systems used throughout Europe were not compatible to each other, meaning the later idea of a common ‘European Union’ viewpoint/technological standard was absent at this time.

The various 1G standards in use in Europe included C-Netz (in Germany and Austria), Comviq (in Sweden), Nordic Mobile Telephones/450 (NMT450) and NMT900 (both in Nordic countries), NMT-F (French version of NMT900), Radiocom 2000 (RC2000) (in France), and TACS (Total Access Communication System) (in the United Kingdom, Italy and Ireland). North American standards were Advanced Mobile Phone System (AMPS) and Narrow-band AMPS (N-AMPS).

Out of the 1G standards, the most successful was the AMPS system. Despite the Nordic countries’ cooperation, European engineering efforts were divided among the various standards, and the Japanese standards did not get much attention. Developed by Bell Labs in the 1970s and first used commercially in the United States in 1983, AMPS operates in the 800 MHz band in the United States and is the most widely distributed analog cellular standard. (The 1900 MHz PCS band, established in 1994, is for digital operation only.) The success of AMPS kick-started the mobile age in the North America.

The market showed an increasing demand because it had higher capacity and mobility than the then-existing mobile communication standards were capable of handling. For example, the Bell Labs system in the 1970s could carry only 12 calls at a time throughout all of New York City. AMPS used Frequency Division Multiple Access (FDMA) which enabled each cell site to transmit on different frequencies, allowing many cell sites to be built near each other.

AMPS also had many disadvantages, as well. Primarily, it did not have the ability to support the ever-increasing demand for mobile communication usage. Each cell site did not have much capacity for carrying higher numbers of calls. AMPS also had a poor security system which allowed people to steal a phone’s serial code to use for making illegal calls. All of these triggered the search for a more capable system.

The quest resulted in IS-54, the first American 2G standard. In March 1990, the North American cellular network incorporated the IS-54B standard, the first North American dual mode digital cellular standard. This standard won over Motorola’s Narrowband AMPS or N-AMPS, an analog scheme which increased capacity, by cutting down voice channels from 30 kHz to 10 kHz. IS-54, on the other hand, increased capacity by digital means using TDMA protocols. This method separates calls by time, placing parts of individual conversations on the same frequency, one after the next. TDMA tripled call capacity.

Using IS-54, a cellular carrier could convert any of its system’s analog voice channels to digital. A dual mode phone uses digital channels where available, and defaults to regular AMPS where they are not. IS-54 was backward compatible with analogue cellular and indeed co-existed on the same radio channels as AMPS. No analogue customers were left behind; they simply could not access IS-54’s new features. IS-54 also supported authentication, a help in preventing fraud.
Technology specifications

IS-54 employs the same 30 kHz channel spacing and frequency bands (824-849 and 869-894 MHz) as AMPS. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals.

The IS-54 standard specifies 84 control channels, 42 of which are shared with AMPS. To maintain compatibility with the existing AMPS cellular telephone system, the primary forward and reverse control channels in IS-54 cellular systems use the same signaling techniques and modulation scheme (binary FSK) as AMPS. An AMPS/IS-54 infrastructure can support use of either analog AMPS phones or D-AMPS phones.

The access method used for IS-54 is Time Division Multiple Access (TDMA), which was the first U.S. digital standard to be developed. It was adopted by the TIA in 1992. TDMA subdivides each of the 30 kHz AMPS channels into three full-rate TDMA channels, each of which is capable of supporting a single voice call. Later, each of these full-rate channels was further sub-divided into two half-rate channels, each of which, with the necessary coding and compression, could also support a voice call. Thus, TDMA could provide three to six times the capacity of AMPS traffic channels. TDMA was initially defined by the IS-54 standard and is now specified in the IS-13x series of specifications of the EIA/TIA.

The channel transmission bit rate for digitally modulating the carrier is 48.6 kbit/s. Each frame has six time slots of 6.67-ms duration. Each time slot carries 324 bits of information, of which 260 bits are for the 13-kbit/s full-rate traffic data. The other 64 bits are overhead; 28 of these are for synchronization, and they contain a specific bit sequence known by all receivers to establish frame alignment. Also, as with GSM, the known sequence acts as a training pattern to initialize an adaptive equalizer.

The IS-54 system has different synchronization sequences for each of the six time slots making up the frame, thereby allowing each receiver to synchronize to its own preassigned time slots. An additional 12 bits in every time slot are for the SACCH (i.e. system control information). The digital verification color code (DVCC) is the equivalent of the supervisory audio tone used in the AMPS system. There are 256 different 8-bit color codes, which are protected by a (12, 8, 3) Hamming code. Each base station has its own preassigned color code, so any incoming interfering signals from distant cells can be ignored.

The modulation scheme for IS-54 is 7C/4 differential quaternary phase shift keying (DQPSK), otherwise known as differential 7t/4 4-PSK or π/4 DQPSK. This technique allows a bit rate of 48.6 kbit/s with 30 kHz channel spacing, to give a bandwidth efficiency of 1.62 bit/s/Hz. This value is 20% better than GSM. The major disadvantage with this type of linear modulation method is the power inefficiency, which translates into a heavier hand-held portable and, even more inconvenient, a shorter time between battery recharges.
Call processing

A conversation’s data bits makes up the DATA field. Six slots make up a complete IS-54 frame. DATA in slots 1 and 4, 2 and 5, and 3 and 6 make up a voice circuit. DVCC stands for digital verification color code, arcane terminology for a unique 8-bit code value assigned to each cell. G means guard time, the period between each time slot. RSVD stands for reserved. SYNC represents synchronization, a critical TDMA data field. Each slot in every frame must be synchronized against all others and a master clock for everything to work.

Time slots for the mobile-to-base direction are constructed differently from the base-to-mobile direction. They essentially carry the same information but are arranged differently. Notice that the mobile-to-base direction has a 6-bit ramp time to enable its transmitter time to get up to full power, and a 6-bit guard band during which nothing is transmitted. These 12 extra bits in the base-to-mobile direction are reserved for future use.

Once a call comes in the mobile switches to a different pair of frequencies; a voice radio channel which the system carrier has made analog or digital. This pair carries the call. If an IS-54 signal is detected it gets assigned a digital traffic channel if one is available. The fast associated channel or FACCH performs handoffs during the call, with no need for the mobile to go back to the control channel. In case of high noise FACCH, embedded within the digital traffic channel overrides the voice payload, degrading speech quality to convey control information. The purpose is to maintain connectivity. The slow associated control channel or SACCH does not perform handoffs but conveys things like signal strength information to the base station.

The IS-54 speech coder uses the technique called vector sum excited linear prediction (VSELP) coding. This is a special type of speech coder within a large class known as code-excited linear prediction (CELP) coders. The speech coding rate of 7.95 kbit/s achieves a reconstructed speech quality similar to that of the analog AMPS system using frequency modulation. The 7.95-kbit/s signal is then passed through a channel coder that loads the bit rate up to 13 kbit/s. The new half-rate coding standard reduces the overall bit rate for each call to 6.5 kbit/s, and should provide comparable quality to the 13-kbit/s rate. This half-rate gives a channel capacity six times that of analog AMPS.

System example

The discussion of a communication system will not be complete without the explanation of a system example. A dual-mode cellular phone as specified by the IS-54 standard is explained. A dual-mode phone is capable of operating in an analog-only cell or a dual-mode cell. Both the transmitter and the receiver support both analog FM and digital time division multiple access (TDMA) schemes. Digital transmission is preferred, so when a cellular system has digital capability, the mobile unit is assigned a digital channel first. If no digital channels are available, the cellular system will assign an analog channel. The transmitter converts the audio signal to a radio frequency (RF), and the receiver converts an RF signal to an audio signal. The antenna focuses and converts RF energy for reception and transmission into free space. The control panel serves as an input/output mechanism for the end user; it supports a keypad, a display, a microphone, and a speaker. The coordinator synchronizes the transmission and receives functions of the mobile unit. A dual-mode cellular phone consists of the following:

Antenna assembly
Control panel

Successor technologies

By 1993 American cellular was again running out of capacity, despite a wide movement to IS-54. The American cellular business continued booming. Subscribers grew from one and a half million customers in 1988 to more than thirteen million subscribers in 1993. Room existed for other technologies to cater to the growing market. The technologies that followed IS-54 stuck to the digital backbone laid down by it.

A pragmatic effort was launched to improve IS-54 that eventually added an extra channel to the IS-54 hybrid design. Unlike IS-54, IS-136 utilizes time division multiplexing for both voice and control channel transmissions. Digital control channel allows residential and in-building coverage, dramatically increased battery standby time, several messaging applications, over the air activation and expanded data applications. IS-136 systems needed to support millions of AMPS phones, most of which were designed and manufactured before IS-54 and IS-136 were considered. IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol. IS-136 TDMA traffic channels use π/4-DQPSK modulation at a 24.3-kilobaud channel rate and gives an effective 48.6 kbit/s data rate across the six time slots comprising one frame in the 30 kHz channel.

Sunset for D-AMPS in the US and Canada

AT&T Mobility, the largest US carrier to support D-AMPS (which it refers to as “TDMA”), had turned down its existing network in order to release the spectrum to its GSM and UMTS platforms in 19 wireless markets, which started on May 30, 2007, with other areas that followed in June and July. The TDMA network in these markets operated on the 1900 MHz frequency and did not coexist with an AMPS network. Service on the remaining 850 MHz TDMA markets was discontinued along with AMPS service on February 18, 2008, except for in areas where service was provided by Dobson Communications. The Dobson TDMA and AMPS network was shut down March 1, 2008.

On May 31, 2007 Rogers Wireless decommissioned its D-AMPS and AMPS networks and moved the remaining customers on these older networks onto its GSM network.

Alltel (now Verizon) completed their shutdown of their D-AMPS and AMPS networks in September 2008. The last carrier in the United States to operate a D-AMPS network was U.S. Cellular, who shut down its D-AMPS network in February 2009.


The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile devices such as mobile phones and tablets. It was first deployed in Finland in December 1991. By the mid-2010s, it became a global standard for mobile communications achieving over 90% market share, and operating in over 193 countries and territories.

2G networks developed as a replacement for first generation (1G) analog cellular networks. The GSM standard originally described a digital, circuit-switched network optimized for full duplex voice telephony. This expanded over time to include data communications, first by circuit-switched transport, then by packet data transport via General Packet Radio Service (GPRS), and Enhanced Data Rates for GSM Evolution (EDGE).

Subsequently, the 3GPP developed third-generation (3G) UMTS standards, followed by fourth-generation (4G) LTE Advanced standards, which do not form part of the ETSI GSM standard.

“GSM” is a trade mark owned by the GSM Association. It may also refer to the (initially) most common voice codec used, Full Rate.


Initial development

In 1983, work began to develop a European standard for digital cellular voice telecommunications when the European Conference of Postal and Telecommunications Administrations (CEPT) set up the Groupe Spécial Mobile (GSM) committee and later provided a permanent technical-support group based in Paris. Five years later, in 1987, 15 representatives from 13 European countries signed a memorandum of understanding in Copenhagen to develop and deploy a common cellular telephone system across Europe, and EU rules were passed to make GSM a mandatory standard. The decision to develop a continental standard eventually resulted in a unified, open, standard-based network which was larger than that in the United States.

In February 1987 Europe produced the first agreed GSM Technical Specification. Ministers from the four big EU countries cemented their political support for GSM with the Bonn Declaration on Global Information Networks in May and the GSM MoU was tabled for signature in September. The MoU drew in mobile operators from across Europe to pledge to invest in new GSM networks to an ambitious common date.

In this short 38-week period the whole of Europe (countries and industries) had been brought behind GSM in a rare unity and speed guided by four public officials: Armin Silberhorn (Germany), Stephen Temple (UK), Philippe Dupuis (France), and Renzo Failli (Italy). In 1989 the Groupe Spécial Mobile committee was transferred from CEPT to the European Telecommunications Standards Institute (ETSI).
First networks

In parallel France and Germany signed a joint development agreement in 1984 and were joined by Italy and the UK in 1986. In 1986, the European Commission proposed reserving the 900 MHz spectrum band for GSM. The former Finnish prime minister Harri Holkeri made the world’s first GSM call on 1 July 1991, calling Kaarina Suonio (deputy mayor of the city of Tampere) using a network built by Nokia and Siemens and operated by Radiolinja. The following year saw the sending of the first short messaging service (SMS or “text message”) message, and Vodafone UK and Telecom Finland signed the first international roaming agreement.


Work began in 1991 to expand the GSM standard to the 1800 MHz frequency band and the first 1800 MHz network became operational in the UK by 1993, called and DCS 1800. Also that year, Telecom Australia became the first network operator to deploy a GSM network outside Europe and the first practical hand-held GSM mobile phone became available.

In 1995 fax, data and SMS messaging services were launched commercially, the first 1900 MHz GSM network became operational in the United States and GSM subscribers worldwide exceeded 10 million. In the same year, the GSM Association formed. Pre-paid GSM SIM cards were launched in 1996 and worldwide GSM subscribers passed 100 million in 1998.

In 2000 the first commercial GPRS services were launched and the first GPRS-compatible handsets became available for sale. In 2001, the first UMTS (W-CDMA) network was launched, a 3G technology that is not part of GSM. Worldwide GSM subscribers exceeded 500 million. In 2002, the first Multimedia Messaging Service (MMS) was introduced and the first GSM network in the 800 MHz frequency band became operational. EDGE services first became operational in a network in 2003, and the number of worldwide GSM subscribers exceeded 1 billion in 2004.

By 2005 GSM networks accounted for more than 75% of the worldwide cellular network market, serving 1.5 billion subscribers. In 2005, the first HSDPA-capable network also became operational. The first HSUPA network launched in 2007. (High-Speed Packet Access (HSPA) and its uplink and downlink versions are 3G technologies, not part of GSM.) Worldwide GSM subscribers exceeded three billion in 2008.


The GSM Association estimated in 2011 that technologies defined in the GSM standard served 80% of the mobile market, encompassing more than 5 billion people across more than 212 countries and territories, making GSM the most ubiquitous of the many standards for cellular networks.

GSM is a second-generation (2G) standard employing time-division multiple-Access (TDMA) spectrum-sharing, issued by the European Telecommunications Standards Institute (ETSI). The GSM standard does not include the 3G Universal Mobile Telecommunications System (UMTS) code division multiple access (CDMA) technology nor the 4G LTE orthogonal frequency-division multiple access (OFDMA) technology standards issued by the 3GPP.

GSM, for the first time, set a common standard for Europe for wireless networks. It was also adopted by many countries outside Europe. This allowed subscribers to use other GSM networks that have roaming agreements with each other. The common standard reduced research and development costs, since hardware and software could be sold with only minor adaptations for the local market.

GSM Phaseout

Telstra in Australia shut down its 2G GSM network on 1 December 2016, the first mobile network operator to decommission a GSM network. The second mobile provider to shut down its GSM network (on 1 January 2017) was AT&T Mobility from the United States. Optus in Australia completed the shut down its 2G GSM network on 1 August 2017, part of the Optus GSM network covering Western Australia and the Northern Territory had earlier in the year been shut down in April 2017. Singapore shut down 2G services entirely in April 2017.

Technical details

The network is structured into several discrete sections:

Base station subsystem – the base stations and their controllers
Network and Switching Subsystem – the part of the network most similar to a fixed network, sometimes just called the “core network”
GPRS Core Network – the optional part which allows packet-based Internet connections
Operations support system (OSS) – network maintenance

Base-station subsystem

The coverage area of each cell varies according to the implementation environment. Macro cells can be regarded as cells where the base-station antenna is installed on a mast or a building above average rooftop level. Micro cells are cells whose antenna height is under average rooftop level; they are typically deployed in urban areas. Picocells are small cells whose coverage diameter is a few dozen meters; they are mainly used indoors. Femtocells are cells designed for use in residential or small-business environments and connect to a telecommunications service provider’s network via a broadband-internet connection. Umbrella cells are used to cover shadowed regions of smaller cells and to fill in gaps in coverage between those cells.

Cell horizontal radius varies – depending on antenna height, antenna gain, and propagation conditions – from a couple of hundred meters to several tens of kilometers. The longest distance the GSM specification supports in practical use is 35 kilometres (22 mi). There are also several implementations of the concept of an extended cell, where the cell radius could be double or even more, depending on the antenna system, the type of terrain, and the timing advance.

GSM supports indoor coverage – achievable by using an indoor picocell base station, or an indoor repeater with distributed indoor antennas fed through power splitters – to deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna system. Picocells are typically deployed when significant call capacity is needed indoors, as in shopping centers or airports. However, this is not a prerequisite, since indoor coverage is also provided by in-building penetration of radio signals from any nearby cell.

GSM carrier frequencies

GSM networks operate in a number of different carrier frequency ranges (separated into GSM frequency ranges for 2G and UMTS frequency bands for 3G), with most 2G GSM networks operating in the 900 MHz or 1800 MHz bands. Where these bands were already allocated, the 850 MHz and 1900 MHz bands were used instead (for example in Canada and the United States). In rare cases the 400 and 450 MHz frequency bands are assigned in some countries because they were previously used for first-generation systems.

Regardless of the frequency selected by an operator, it is divided into timeslots for individual phones. This allows eight full-rate or sixteen half-rate speech channels per radio frequency. These eight radio timeslots (or burst periods) are grouped into a TDMA frame. Half-rate channels use alternate frames in the same timeslot. The channel data rate for all 8 channels is 270.833 kbit/s, and the frame duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM 850/900 and 1 watt in GSM 1800/1900.

Voice codecs

GSM has used a variety of voice codecs to squeeze 3.1 kHz audio into between 7 and 13 kbit/s. Originally, two codecs, named after the types of data channel they were allocated, were used, called Half Rate (6.5 kbit/s) and Full Rate (13 kbit/s). These used a system based on linear predictive coding (LPC). In addition to being efficient with bitrates, these codecs also made it easier to identify more important parts of the audio, allowing the air interface layer to prioritize and better protect these parts of the signal. GSM was further enhanced in 1997 with the enhanced full rate (EFR) codec, a 12.2 kbit/s codec that uses a full-rate channel. Finally, with the development of UMTS, EFR was refactored into a variable-rate codec called AMR-Narrowband, which is high quality and robust against interference when used on full-rate channels, or less robust but still relatively high quality when used in good radio conditions on half-rate channel.

Subscriber Identity Module (SIM)

One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM card. The SIM is a detachable smart card containing the user’s subscription information and phone book. This allows the user to retain his or her information after switching handsets. Alternatively, the user can change operators while retaining the handset simply by changing the SIM.

Phone locking

Sometimes mobile network operators restrict handsets that they sell for exclusive use in their own network. This is called SIM locking and is implemented by a software feature of the phone. A subscriber may usually contact the provider to remove the lock for a fee, utilize private services to remove the lock, or use software and websites to unlock the handset themselves. It is possible to hack past a phone locked by a network operator.

In some countries and regions (e.g., Bangladesh, Belgium, Brazil, Canada, Chile, Germany, Hong Kong, India, Iran, Lebanon, Malaysia, Nepal, Norway, Pakistan, Poland, Singapore, South Africa, Sri Lanka, Thailand) all phones are sold unlocked due to the abundance of dual SIM handsets and operators.


Integrated Digital Enhanced Network (iDEN) is a mobile telecommunications technology, developed by Motorola, which provides its users the benefits of a trunked radio and a cellular telephone. It was called the first mobile social network by many technology industry analysts. iDEN places more users in a given spectral space, compared to analog cellular and two-way radio systems, by using speech compression and time division multiple access (TDMA).


The iDEN project originally began as MIRS (Motorola Integrated Radio System) in early 1991. The project was a software lab experiment focused on the utilization of discontiguous spectrum for GSM wireless. GSM systems typically require 24 contiguous voice channels, but the original MIRS software platform dynamically selected fragmented channels in the radio frequency (RF) spectrum in such a way that a GSM telecom switch could commence a phone call the same as it would in the contiguous channel scenario.
Operating frequencies

iDEN is designed and licensed to operate on individual frequencies that may not be contiguous. iDEN operates on 25 kHz channels, but only occupies 20 kHz in order to provide interference protection via guard bands. By comparison, TDMA Cellular (Digital AMPS) is licensed in blocks of 30 kHz channels, but each emission occupies 40 kHz, and is capable of serving the same number of subscribers per channel as iDEN. iDEN uses frequency-division duplexing to transmit and receive signals separately, with transmit and receive bands separated by 39 MHz, 45 MHz, or 48 MHz depending on the frequency band being used.

iDEN supports either three or six interconnect users (phone users) per channel, and six dispatch users (push-to-talk users) per channel, using time division multiple access. The transmit and receive time slots assigned to each user are deliberately offset in time so that a single user never needs to transmit and receive at the same time. This eliminates the need for a duplexer at the mobile end, since time-division duplexing of RF section usage can be performed.


The first commercial iDEN handset was Motorola’s L3000, which was released in 1994. Lingo, which stands for Link People on the Go, was used as a logo for its earlier handsets. Most modern iDEN handsets use SIM cards, similar to, but incompatible with GSM handsets’ SIM cards. Early iDEN models such as the i1000plus stored all subscriber information inside the handset itself, requiring the data to be downloaded and transferred should the subscriber want to switch handsets. Newer handsets using SIM technology make upgrading or changing handsets as easy as swapping the SIM card. Four different sized SIM cards exist, “Endeavor” SIMs are used only with the i2000 without data, “Condor” SIMs are used with the two-digit models (i95cl, for example) using a SIM with less memory than the three-digit models (i730, i860), “Falcon” SIMs are used in the three-digit phones, (i530, i710) and will read the smaller SIM for backward compatibility, but some advanced features such as extra contact information is not supported by the older SIM cards. There is also the “Falcon 128” SIM, which is the same as the original “Falcon”, but doubled in memory size, which is used on new 3 digit phones (i560, i930).

The interconnect-side of the iDEN network uses GSM signalling for call set-up and mobility management, with the Abis protocol stack modified to support iDEN’s additional features. Motorola has named this modified stack ‘Mobis’.

Each base site requires precise timing and location information to synchronize data across the network. To obtain and maintain this information each base site uses GPS satellites to receive a precise timing reference.


Wideband Integrated Digital Enhanced Network, or WiDEN, is a software upgrade developed by Motorola and partners for its iDEN enhanced specialized mobile radio (or ESMR) wireless telephony protocol. WiDEN allows compatible subscriber units to communicate across four 25 kHz channels combined, for up to 100 kbit/s of bandwidth. The protocol is generally considered a 2.5G wireless cellular technology.


iDEN, the platform which WiDEN upgrades, and the protocol on which it is based, was originally introduced by Motorola in 1993, and launched as a commercial network by Nextel in the United States in September 1996.

WiDEN was originally anticipated to be a major stepping stone for United States wireless telephone provider Nextel Communications and its affiliate, Nextel Partners. However, beginning with the December 2004 announcement of the Sprint Nextel merger, Nextel’s iDEN network was abandoned in favor of Sprint’s CDMA network. WiDEN was deactivated on the NEXTEL National Network in October 2005 when rebanding efforts in the 800 MHz band began in an effort to utilize those data channels as a way to handle more cellular phone call traffic on the NEXTEL iDEN network. The original Nextel iDEN network was finally decommissioned by Sprint on June 30, 2013 and the spectrum refarmed for use in the Sprint LTE network.

Subscriber Units

The first WiDEN-compatible device to be released was the Motorola iM240 PC card which allows raw data speeds up to 60 kbit/s. The first WiDEN-compatible telephones are the Motorola i850 and i760, which were released mid-summer 2005. The recent i850/i760 Software Upgrade enables WiDEN on both of these phones. The commercial launch of WiDEN came with the release of the Motorola i870 on 31 October 2005, however, most people never got to experience the WiDEN capability in their handsets. WiDEN is also offered in the i930/i920 Smartphone, however, Sprint shipped these units with WiDEN service disabled. Many in the cellular forum communities have found ways using Motorola’s own RSS software to activate it. WiDEN was available in most places on Nextel’s National Network. As stated above, it no longer is enabled on the Sprint-controlled towers. Since the Sprint Nextel merger the company determined that because Sprint’s CDMA network was already 3G and going to EVDO (broadband speeds), and then EVDO Rev A, it would be redundant to keep upgrading the iDEN data network. WiDEN is considered a 2.5G technology.


Countries which have operating iDEN networks include United States of America, Canada, Colombia, Israel, Singapore, Saudi Arabia, El Salvador, and Guatemala.

Sprint Nextel provided iDEN service across the United States until its iDEN network was decommissioned for additional LTE network capacity on 30 June 2013.
SouthernLINC Wireless provided iDEN service across the United States until its iDEN network was decommissioned for additional LTE network capacity on 1 April 2019.
Telus provided iDEN service across most of Canada until its iDEN network was decommissioned on 29 January 2016.
Nextel Brazil provided iDEN service in Brazil until its iDEN network was decommissioned on 31 March 2018.

Why did iDEN fail as a technology?

iDEN failed as a technology primarily of what Nextel tried to do with the technology. Nextel tried to mix their system with public safety radio spectrum, which created all sorts of interference. In the end, Sprint (who had purchased Nextel) tried to move them into other bands. But in the end of the day, iDEN’s days were numbered anyhow. Sprint eventually moved everyone to CDMA (3G) technologies, which in turn has been replaced with 4G and now 5G OFDM technologies.

Radio interference

Due to many underlying maintenance and life cycle issues within the legacy Public safety systems of the United States, co-channel interference was a common occurrence within 800 MHz band. To resolve the problems, Nextel and the Federal Communications Commission developed a plan, approved by the FCC in August 2004, to relocate Nextel systems elsewhere in the 800 MHz band in order to reduce the potential for interference.

Before rebanding, Public Safety, Business/Industrial, SMR and ESMR’s both operate in the 851-861 MHz range. ESMR has exclusive use of the 861-866 MHz range and Public Safety has exclusive use of the 866-869 MHz range.

During rebanding, the following will occur:

– All licensees with channels between 866-869 MHz (NPSPAC) must relocate to equivalent channels between 851-854.

– All licensees other than ESMRs with channels between 851-854 MHz must relocate to equivalent channels between 854-862.

– Nextel and other ESMR operators must relinquish all channels below 862 MHz. The FCC has required Nextel to vacate all its channels in the band from 854-854.5 nationwide as soon as possible to provide additional spectrum for Public Safety needs.

– Public Safety has exclusive access to all vacated Nextel channels for 3 years, after which they are open to all eligible users.

After rebanding, Public Safety and Critical Infrastructure will have exclusive use of 851-854 MHz. ESMR systems (primarily Nextel) will have exclusive use of 862-869 MHz range, and public safety, business/industrial users, and low-power SMR’s will share the 854-862 MHz spectrum. 860-861 MHz is designated as an “Expansion Band”, and 861-862 MHz is designated as a “Guard Band”. No licensees other than ESMR are required to relocate to channels above 860 MHz.

The use of contiguous spectrum allows for simple filters to be installed to protect public safety radio systems from interference, which is currently impossible under the existing mixed allocations in the 800 MHz band.

Nextel (Sprint) paid for much of the cost of this reconfiguration, but in compensation for lost 800 MHz spectrum, the company received spectrum in the 2 GHz band at 1910–1915/1990–1995 MHz. This spectrum is near the existing Sprint PCS allocations and can be used to expand the number of channels available for that service, without needing to bid for additional capacity in a spectrum auction.

Pre-Cellular (MTS & IMTS) (0G)

Mobile phones before cellular phones

Analog Cellular (AMPS) (1G)

We had to start somewhere. A hybrid analog/digital cellular phone system

The First Digital Cellular Systems – TDMA, GSM and iDEN (2G)

Moving away from analog to first generation digital phone systems

Modern Wireless Systems (3G – 4G – 5G)

The modern era of wireless phones, where data is king