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.
Comparison table
| Feature | NMT | GSM | UMTS | IS-95 | CDMA2000 |
|---|---|---|---|---|---|
| Technology | FDMA | TDMA | W-CDMA | CDMA | CDMA |
| Generation | 1G | 2G | 3G | 2G | 3G |
| Digital | No | Yes | Yes | Yes | Yes |
| Year of First Use | 1981 | 1991 | 2001 | 1995 | 2000 |
| Worldwide market share[2] | 0% | 80% | 4% | 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 | ? | 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 due to 2100 MHz frequency | 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 | ? | Concentrated among a few industry participants | Concentrated among a few industry participants | Qualcomm | Qualcomm |
