Comparison of mobile phone standards

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A comparison of mobile phone standards can be done in many ways.

Issues[edit]

Global System for Mobile Communications (GSM, around 80–85% market share) and IS-95 (around 10–15% market share) were the two most prevalent 2G mobile communication technologies in 2007.[1] In 3G, the most prevalent technology was UMTS with CDMA-2000 in close contention.

All radio access technologies have to solve the same problems: to divide the finite RF spectrum among multiple users as efficiently as possible. GSM uses TDMA and FDMA for user and cell separation. UMTS, IS-95 and CDMA-2000 use CDMA. WiMAX and LTE use OFDM.

  • Time-division multiple access (TDMA) provides multiuser access 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.
  • Code-division multiple access (CDMA) This uses a digital modulation called spread spectrum which spreads the voice data over a very wide channel in pseudorandom fashion using a user or cell specific pseudorandom code. The receiver undoes the randomization to collect the bits together and produce the original data. As the codes are pseudorandom and selected in such a way as to cause minimal interference to one another, multiple users can talk at the same time and multiple cells can share the same frequency. This causes an added signal noise forcing all users to use more power, which in exchange decreases cell range and battery life.
  • Orthogonal Frequency Division Multiple Access (OFDMA) uses bundling of multiple small frequency bands that are orthogonal to one another to provide for separation of users. The users are multiplexed in the frequency domain by allocating specific sub-bands to individual users. This is often enhanced by also performing TDMA and changing the allocation periodically so that different users get different sub-bands at different times.

In theory, CDMA, TDMA and FDMA have exactly the same spectral efficiency but practically, each has its own challenges – power control in the case of CDMA, timing in the case of TDMA, and frequency generation/filtering in the case of FDMA.

For a classic example for understanding the fundamental difference of TDMA and CDMA imagine a cocktail party, where couples are talking to each other in a single room. The room represents the available bandwidth:

TDMA: A speaker takes turns talking to a listener. The speaker talks for a short time and then stops to let another couple talk. There is never more than one speaker talking in the room, no one has to worry about two conversations mixing. The drawback is that it limits the practical number of discussions in the room (bandwidth wise).
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. The drawback is that at some point, one cannot talk any louder. After this if the noise still rises (more people join the party/cell) the listener cannot make out what the talker is talking about without coming closer to the talker. In effect, CDMA cell coverage decreases as the number of active users increases. This is called cell breathing.

Comparison table[edit]

Feature NMT GSM UMTS (3GSM) IS-95 (CDMA one) IS-2000 (CDMA 2000) LTE
Technology FDMA TDMA and FDMA W-CDMA CDMA CDMA OFDMA
Generation 1G 2G 3G 2G 3G 4G
Encoding Analog Digital Digital Digital Digital Digital
Year of First Use 1981 1991 2001 1995 2000 / 2002 2009
Roaming Nordics and several other European countries Worldwide, all countries except Japan and South Korea Worldwide Limited Limited Limited
Handset interoperability None SIM card SIM card None RUIM (rarely used) SIM card
Common Interference None Some electronics, e.g. amplifiers None 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 (4 calls with VAMOS) through interleaving. 5 MHz = 2 Mbit/s. 42Mbit/s for HSPA+. Each call uses 1.8-12 kbit/s depending on chosen quality and audio complexity. Lower than CDMA-2000? 1.228  MHz = 3Mbit/s
Handoff Hard Hard Soft Soft Soft Hard
Voice and Data at the same time No Yes GPRS Class A Yes[2] No No EVDO / Yes SVDO[3] No (data only)
Voice possible though VoLTE or fallback to 2G/3G

Strengths and Weaknesses of IS-95 and GSM[4][edit]

Advantages of GSM[edit]

Disadvantages of GSM[edit]

  • Interferes with some electronics, especially certain audio amplifiers.
  • Intellectual property is concentrated among a few industry participants, creating barriers to entry for new entrants and limiting competition among phone manufacturers. Situation is however worse in CDMA-based systems like IS-95, where Qualcomm is the major IP holder.[citation needed]
  • GSM has a fixed maximum cell site range of 120 km,[5] which is imposed by technical limitations.[6] This is expanded from the old limit of 35 km.

Advantages of IS-95[edit]

  • 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.[7]
  • 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.

Disadvantages of IS-95[edit]

  • 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.
  • USSD, PTT, concatenated/E-sms are not supported by IS-95/CDMA
  • 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.

Development of the Market Share of Mobile Standards[edit]

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

Comparison of wireless Internet standards[edit]

As a reference, a comparison of mobile and non-mobile wireless Internet standards follows.

Comparison of mobile Internet access methods
Common
Name
Family Primary Use Radio Tech Downstream
(Mbit/s)
Upstream
(Mbit/s)
Notes
HSPA+ 3GPP 3G Data CDMA/FDD
MIMO
21
42
84
672
5.8
11.5
22
168
HSPA+ is widely deployed. Revision 11 of the 3GPP states that HSPA+ is expected to have a throughput capacity of 672 Mbit/s.
LTE 3GPP General 4G OFDMA/MIMO/SC-FDMA 100 Cat3
150 Cat4
300 Cat5
(in 20 MHz FDD) [8]
50 Cat3/4
75 Cat5
(in 20 MHz FDD)[8]
LTE-Advanced update expected to offer peak rates up to 1 Gbit/s fixed speeds and 100 Mb/s to mobile users.
WiMax rel 1 802.16 WirelessMAN MIMO-SOFDMA 37 (10 MHz TDD) 17 (10 MHz TDD) With 2x2 MIMO.[9]
WiMax rel 1.5 802.16-2009 WirelessMAN MIMO-SOFDMA 83 (20 MHz TDD)
141 (2x20 MHz FDD)
46 (20 MHz TDD)
138 (2x20 MHz FDD)
With 2x2 MIMO.Enhanced with 20 MHz channels in 802.16-2009[9]
WiMAX rel 2 802.16m WirelessMAN MIMO-SOFDMA 2x2 MIMO
110 (20 MHz TDD)
183 (2x20 MHz FDD)
4x4 MIMO
219 (20 MHz TDD)
365 (2x20 MHz FDD)
2x2 MIMO
70 (20 MHz TDD)
188 (2x20 MHz FDD)
4x4 MIMO
140 (20 MHz TDD)
376 (2x20 MHz FDD)
Also, low mobility users can aggregate multiple channels to get a download throughput of up to 1 Gbit/s[9]
Flash-OFDM Flash-OFDM Mobile Internet
mobility up to 200 mph (350 km/h)
Flash-OFDM 5.3
10.6
15.9
1.8
3.6
5.4
Mobile range 30 km (18 miles)
extended range 55 km (34 miles)
HIPERMAN HIPERMAN Mobile Internet OFDM 56.9
Wi-Fi 802.11
(11n)
Mobile Internet OFDM/MIMO 288.8 (using 4x4 configuration in 20 MHz bandwidth) or 600 (using 4x4 configuration in 40 MHz bandwidth)

Antenna, RF front end enhancements and minor protocol timer tweaks have helped deploy long range P2P networks compromising on radial coverage, throughput and/or spectra efficiency (310 km & 382 km)

iBurst 802.20 Mobile Internet HC-SDMA/TDD/MIMO 95 36 Cell Radius: 3–12 km
Speed: 250 km/h
Spectral Efficiency: 13 bits/s/Hz/cell
Spectrum Reuse Factor: "1"
EDGE Evolution GSM Mobile Internet TDMA/FDD 1.6 0.5 3GPP Release 7
UMTS W-CDMA
HSPA (HSDPA+HSUPA)
UMTS/3GSM General 3G CDMA/FDD

CDMA/FDD/MIMO
0.384
14.4
0.384
5.76
HSDPA is widely deployed. Typical downlink rates today 2 Mbit/s, ~200 kbit/s uplink; HSPA+ downlink up to 56 Mbit/s.
UMTS-TDD UMTS/3GSM Mobile Internet CDMA/TDD 16 Reported speeds according to IPWireless using 16QAM modulation similar to HSDPA+HSUPA
EV-DO Rel. 0
EV-DO Rev.A
EV-DO Rev.B
CDMA2000 Mobile Internet CDMA/FDD 2.45
3.1
4.9xN
0.15
1.8
1.8xN
Rev B note: N is the number of 1.25 MHz carriers used. EV-DO is not designed for voice, and requires a fallback to 1xRTT when a voice call is placed or received.

Notes: All speeds are theoretical maximums and will vary by a number of factors, including the use of external antennas, distance from the tower and the ground speed (e.g. communications on a train may be poorer than when standing still). Usually the bandwidth is shared between several terminals. The performance of each technology is determined by a number of constraints, including the spectral efficiency of the technology, the cell sizes used, and the amount of spectrum available. For more information, see Comparison of wireless data standards.

For more comparison tables, see bit rate progress trends, comparison of mobile phone standards, spectral efficiency comparison table and OFDM system comparison table.

See also[edit]

References[edit]

  1. ^ "Subscriber statistics end Q1 2007". Archived from the original on 2007-09-27. Retrieved 2007-09-22. 
  2. ^ UMTS/HSPA (3G) Mobile Broadband - Wireless from AT&T
  3. ^ CDMA Development Group Announces 'SVDO': Handle Calls and Data at same time
  4. ^ "IS-95 (CDMA) and GSM(TDMA)". Retrieved 2011-02-03. 
  5. ^ http://www.allbusiness.com/electronics/computer-electronics-manufacturing/6838169-1.html
  6. ^ http://www.arcx.com/sites/faq.htm
  7. ^ Frequently Asked PCS Questions
  8. ^ a b "LTE". 3GPP web site. 2009. Retrieved August 20, 2011. 
  9. ^ a b c "WiMAX and the IEEE 802.16m Air Interface Standard". WiMax Forum. 4 April 2010. Retrieved 2012-02-07.