GSM and IS-95 are the two most prevalent mobile communication technologies. Both technologies have to solve the same problem: to divide the finite RF spectrum among multiple users. Rough plot of Earths atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves. ...

TDMA (Time Division Multiple Access - underlying technology used in GSM's 2G) does it by chopping up the channel into sequential time slices. Each user of the channel takes turns to transmit and receive signals. In reality, only one person is actually using the channel at a specific moment. This is analogous to time-sharing on a large computer server. Time Division Multiple Access (TDMA) is a technology for shared medium (usually radio) networks. ... 2G (or 2-G) is short for second-generation wireless telephone technology. ... Alternate uses: see Timesharing Time-sharing is an approach to interactive computing in which a single computer is used to provide apparently simultaneous interactive general-purpose computing to multiple users by sharing processor time. ...

CDMA (Code Division Multiple Access - underlying technology used in GSM's 3G and IS-95's 2G) on the other hand, uses a special type of digital modulation called spread spectrum which spreads the voice data over a very wide channel in pseudorandom fashion. The receiver undoes the randomization to collect the bits together and produce the sound. General Information Generically (as a multiplexing scheme), code division multiple access (CDMA) is any use of any form of spread spectrum by multiple transmitters to send to the same receiver on the same frequency channel at the same time without harmful interference. ... 3G (or 3-G) is short for third-generation technology. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Digital modulation (also referred to as shift keying) is a modulation in which the modified parameter of the carrier signal can take only discrete values. ... Spread-spectrum telecommunications is a technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. ... A pseudo-random number is a number belonging to a sequence which appears to be random, but can in fact be generated by a finite computation. ...

As a trivial comparison imagine a cocktail party, where couples are talking to each other in a single room. The room represents the available bandwidth. In GSM, a speaker takes turns talking to a listener. The speaker talks for a short time and then stops to let another pair talk. There is never more than one speaker talking in the room, no one has to worry about two conversations mixing. In CDMA, any speaker can talk at any time; however each uses a different language. Each listener can only understand the language of their partner. As more and more couples talk, the background noise (representing the noise floor) gets louder, but because of the difference in languages, conversations do not mix.

Advantages of 2G GSM

• GSM is mature; this maturity means a more stable network with robust features.
• Less signal deterioration inside buildings.
• Ability to use repeaters.
• Talktime is generally higher in GSM phones due to the pulse nature of transmission.
• The availability of Subscriber Identity Modules allows users to switch networks and handsets at will.
• GSM covers virtually all parts of the world so international roaming is not a problem.

A Radio Repeater is a combination of a radio receiver and a radio transmitter that receives a weak or low-level signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Roaming is a general term in wireless telecommunications that refers to the extending of connectivity service in a location that is different from the home location where the service was registered. ...

Disadvantages of 2G GSM

• Pulse nature of TDMA transmission used in 2G interferes with some electronics, especially certain audio amplifiers. 3G uses W-CDMA now.
• Intellectual property is concentrated among a few industry participants, creating barriers to entry for new entrants and limiting competition among phone manufacturers.
• GSM has a fixed maximum cell site range of 35 km, which is imposed by technical limitations. [1]

W-CDMA (Wideband Code Division Multiple Access) is a type of 3G cellular network. ...

Advantages of IS-95

• Capacity is IS-95's biggest asset. It can accommodate more users per MHz of bandwidth than any other technology.
• IS-95 has no built-in limit to the number of concurrent users.
• IS-95 uses precise clocks that do not limit the distance a tower can cover. [2]
• IS-95 consumes less power and covers large areas so cell size in IS-95 is larger.
• IS-95 is able to produce a reasonable call with lower signal (cell phone reception) levels.
• IS-95 uses soft handoff, reducing the likelihood of dropped calls.
• IS-95's variable rate voice coders reduce the rate being transmitted when speaker is not talking, which allows the channel to be packed more efficiently.
• Has a well-defined path to higher data rates.

A megahertz (MHz) is one million (106) hertz, a measure of frequency. ... This article or section does not cite its references or sources. ... Soft handoff refers to a feature used by CDMA, where a cell phone can transition between cells to seemlessly keep a connection, while moving between the overlapped coverage zones. ...

Disadvantages of IS-95

• Most technologies are patented and must be licensed from Qualcomm.
• Breathing of base stations, where coverage area shrinks under load. As the number of subscribers using a particular site goes up, the range of that site goes down.
• Because IS-95 towers interfere with themselves, they are normally installed on much shorter towers. Because of this, IS-95 may not perform well in hilly terrain.
• IS-95 only covers a very small portion of the world, so that IS-95 subscribers need so called "global phones"[3] (which have additional GSM capabilities built into them) when they travel to other countries.
• Because of the broader availability of GSM, it is more appealing for companies to develop new innovations for the GSM standard than for IS-95, so they are able to penetrate a bigger market. For example, a comparing product for the iPhone is not available for IS-95.