
This is a comparison of standards of wireless networking technologies for devices such as
mobile phone
A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This rad ...
s. A new
generation
A generation is all of the people born and living at about the same time, regarded collectively. It also is "the average period, generally considered to be about 20–30 years, during which children are born and grow up, become adults, and b ...
of cellular standards has appeared approximately every tenth year since
1G systems were introduced in 1979 and the early to mid-1980s.
Issues
Global System for Mobile Communications
The Global System for Mobile Communications (GSM) is a family of standards to describe the protocols for second-generation ( 2G) digital cellular networks, as used by mobile devices such as mobile phones and mobile broadband modems. GSM is also ...
(GSM, around 80–85% market share) and
IS-95
cdmaOne, most often simply referred to as CDMA, is a 2G digital cellular technology. It was the commercial name for Interim Standard 95 (IS-95), a technology that was developed by Qualcomm and later adopted as a standard by the Telecommunica ...
(around 10–15% market share) were the two most prevalent 2G mobile communication technologies in 2007. In 3G, the most prevalent technology was
UMTS
The Universal Mobile Telecommunications System (UMTS) is a 3G mobile cellular system for networks based on the GSM standard. UMTS uses Wideband Code Division Multiple Access, wideband code-division multiple access (W-CDMA) radio access technolog ...
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
Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...
.
WiMAX
Worldwide Interoperability for Microwave Access (WiMAX) is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide physical layer (PHY) and media access control (MAC) options.
The WiMA ...
and
LTE
LTE may refer to:
Science and technology
* LTE (telecommunication) (Long-Term Evolution), a mobile telephony standard
** LTE Advanced, an enhancement
** LTE Advanced Pro, a further enhancement
* Compaq LTE, a line of laptop computers
* Leukotrie ...
use
OFDM
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. OFDM has developed into a popular scheme for ...
.
*
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
In computing, time-sharing is the Concurrency (computer science), concurrent sharing of a computing resource among many tasks or users by giving each Process (computing), task or User (computing), user a small slice of CPU time, processing time. ...
on a large computer server.
*
Frequency-division multiple access (FDMA) provides multiuser access by separating the used frequencies. This is used in GSM to separate cells, which then use TDMA to separate users within the cell.
*
Code-division multiple access (CDMA) This uses a
digital modulation
Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information.
The process encodes information in form of the modulation or message ...
called
spread spectrum
In telecommunications, especially radio communication, spread spectrum are techniques by which a signal (electrical engineering), signal (e.g., an electrical, electromagnetic, or acoustic) generated with a particular Bandwidth (signal processi ...
which spreads the voice data over a very wide channel in
pseudorandom
A pseudorandom sequence of numbers is one that appears to be statistically random, despite having been produced by a completely deterministic and repeatable process. Pseudorandom number generators are often used in computer programming, as tradi ...
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
Orthogonal frequency-division multiple access (OFDMA) is a multi-user version of the popular orthogonal frequency-division multiplexing (OFDM) digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers ...
(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
Strengths and weaknesses of IS-95 and GSM
Source:
Advantages of GSM
* Less signal deterioration inside buildings.
* Ability to use
repeater
In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some ...
s.
* Talktime is generally higher in GSM phones due to the pulse nature of transmission.
* The availability of
Subscriber Identity Module
A typical SIM card (mini-SIM with micro-SIM cutout)A SIM card or SIM (subscriber identity module) is an integrated circuit (IC) intended to securely store an international mobile subscriber identity (IMSI) number and its related key, which are u ...
s allows users to switch networks and handsets at will, aside from a
subsidy lock.
* GSM
covers virtually all parts of the world so international
roaming
Roaming is a wireless
Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or oth ...
is not a problem.
* The much bigger number of
subscribers globally creates a better
network effect
In economics, a network effect (also called network externality or demand-side economies of scale) is the phenomenon by which the Value (economics), value or utility a user derives from a Goods, good or Service (economics), service depends on th ...
for GSM handset makers, carriers and end users.
Disadvantages of GSM
* 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.
* GSM has a fixed maximum cell site range of 120 km, which is imposed by
technical limitations. This is expanded from the old limit of 35 km.
Advantages of IS-95
* Capacity is IS-95's biggest asset; it can accommodate more users per
MHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...
of
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
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.
* 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
* Most technologies are patented and must be licensed from
Qualcomm
Qualcomm Incorporated () is an American multinational corporation headquartered in San Diego, California, and Delaware General Corporation Law, incorporated in Delaware. It creates semiconductors, software and services related to wireless techn ...
.
* ''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
This graphic compares the market shares of the different mobile standards.
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
As a reference, a comparison of mobile and non-mobile wireless Internet standards follows.
See also
*
Advanced Mobile Phone System
Advanced Mobile Phone System (AMPS) was an analog mobile phone system standard originally developed by Bell Labs and later modified in a cooperative effort between Bell Labs and Motorola. It was officially introduced in the Americas on October ...
*
Car phone
A car phone is a mobile radio telephone specifically designed for and fitted into an automobile.
This service originated with the Bell System and was first used in St. Louis, Missouri, on June 17, 1946.
Overview United States
The original equ ...
*
Comparison of wireless data standards
*
Spectral efficiency comparison table
Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given bandwidth in a specific communication system. It is a measure of how efficiently a limited frequency spectrum i ...
*
SMS
Short Message Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile phones exchange short text messages, t ...
– contain the content of its standardization
References
{{DEFAULTSORT:Comparison Of mobile phone standards
Mobile telecommunications standards
Lists of standards
Computing comparisons