Comparison of mobile phone standards

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Global System for Mobile Communications (AKA GSM, around 80–85 % market share) and IS-95 (AKA cdmaOne, around 10–15 % market share[1]) 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.

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.

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.

For 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.


[edit] Comparison table

Feature NMT GSM UMTS (3GSM) IS-95 (CDMA one) CDMA 2000
Generation 1G 2G 3G 2G 3G
Digital No Yes Yes Yes Yes
Year of First Use 1981 1991 2001 1995 2000 / 2002
Worldwide market share[2] 0% 72% 12% 0.6% 12%
Roaming Scandinavia Worldwide, 200+ countries Worldwide Limited Limited
Handset interoperability None SIM card SIM card None RUIM (not commonly implemented)
Operator locking Monopoly Unlockable Unlockable ESN ESN
Common Interference None Interferes with some electronics, such as amplifiers None None None
Signal quality/coverage area Good coverage due to low frequencies Good coverage indoors on 850/900 MHz. Repeaters possible. 35 km hard limit. Smaller cells and lower indoors coverage on 2100 MHz; equivalent coverage indoors and superior range to GSM on 850/900 MHz. Unlimited cell size, low transmitter power permits large cells Unlimited cell size, low transmitter power permits large cells
Frequency utilization/Call density Very low density 0.2 MHz = 8 timeslots. Each timeslot can hold up to 2 calls through interleaving. 5 MHz = 2 Mbit/s. Each call uses 1.8-12 kbit/s depending on chosen quality and audio complexity.  ? Comparable to UMTS  ? Comparable to UMTS
Battery life Low, due to high transmitter power (1 watt) Very good due to simple protocol, good coverage and mature, power-efficient chipsets. Lower due to high demands of WCDMA power control and young chipsets. Lower due to high demands of CDMA power control. Lower due to high demands of CDMA power control and young chipsets.
Handoff Hard Hard Soft Soft Soft
Breathing No No Yes Yes Yes
Intellectual property Scandinavian telecom operators Concentrated among a few manufacturers Concentrated among a few manufacturers Qualcomm Qualcomm

[edit] Advantages of 2G GSM

[edit] 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.[citation needed]
  • GSM has a fixed maximum cell site range of 35 km, which is imposed by technical limitations. [3]

[edit] Advantages of IS-95

  • Capacity is IS-95's biggest asset; it can accommodate more users per MHz of bandwidth than any other technology.
  • Has no built-in limit to the number of concurrent users.
  • Uses precise clocks that do not limit the distance a tower can cover.[4]
  • Consumes less power and covers large areas so cell size in IS-95 is larger.
  • Able to produce a reasonable call with lower signal (cell phone reception) levels.
  • 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.

[edit] 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 each other, they are normally installed on much shorter towers. Because of this, IS-95 may not perform well in hilly terrain.
  • IS-95 covers a smaller portion of the world, and IS-95 phones are generally unable to roam internationally.
  • Manufacturers are often hesitant to release IS-95 devices due to the smaller market, so features are sometimes late in coming to IS-95 devices.
  • Even barring subsidy locks, CDMA phones are linked by ESN to a specific network, thus phones are typically not portable across providers.

[edit] Development of the Market Share of Mobile Standards

This graphic compares the market shares of the different mobile standards.

Cellphone subscribers by technology (left Y axis) and total number of subscribers globally (right Y axis)

In a fast growing market, GSM/3GSM (red) grows faster than the market and is gaining market share, the CDMA family (blue) grows at about the same rate as the market, while other technologies (grey) are being phased out.

[edit] See also

[edit] References

  1. ^ "Subscriber statistics end Q1 2007". Retrieved on 2007-09-22. 
  2. ^
  3. ^
  4. ^ Frequently Asked PCS Questions
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