Mobile Phone System:
Cellular, personal communication service (PCS), and third generation 3G mobile radio systems are all cellular wireless communication networks that provide for voice and data communication throughout a wide geographic area. Cellular systems divide ‘large geographic areas’ area into small radio areas (cells) that are interconnected with each other. Each cell coverage area has one or several transmitters and receivers that communicate with mobile telephones within its area.
The cellular system connects mobile radios (called mobile stations) via radio channels to base stations. Some of the radio channels (or portions of a digital radio channel) are used for control purposes (setup and disconnection of calls) and some are used to transfer voice or customer data signals. Each base station contains transmitters and receivers that convert the radio signals to electrical signals that can be sent to and from the mobile switching center (MSC). The MSC contains communication controllers that adapt signals from base stations into a form that can be connected (switched) between other base stations or to lines that connect to the public telephone network. The switching system is connected to databases that contain active customers (customers active in its system). The switching system in the MSC is coordinated by call processing software that receives requests for service and processes the steps to setup and maintain connections through the MSC to destination communication devices such as to other mobile telephones or to telephones that are connected to the public telephone network.
When linked together to cover an entire metro area, the radio coverage areas (called cells) form a cellular structure resembling that of a honeycomb. Cellular systems are designed to overlap each cell border with adjacent cell borders to enable a “hand-off” from one cell to the next. As a customer (called a subscriber) moves through a cellular system, the mobile switching center (MSC) coordinates and transfers calls from one cell to another and maintains call continuity. Key drivers for the mobile telephone market growth include new wireless technology (3G) service availability and the replacement market for mobile phones with new capabilities such as camera phones, color displays, and increased accessory capabilities.
More at:
http://en.wikipedia.org/wiki/History_of_mobile_phones
Technologies:
The key technologies used in cellular mobile radio include cellular frequency reuse, analog cellular (1st generation), digital mobile radio (2nd generation), packet based digital radio (2 ½ generation), and wideband radio (3rd generation).
Cellular Frequency Reuse:
To conserve the limited amount of radio spectrum (maximum number of available radio channels), the cellular system concept was developed. Cellular systems allow reuse of the same channel frequencies many times within a geographic coverage area. The technique, called frequency reuse, makes it possible for a system to provide service to more customers (called system capacity) by reusing the channels that are available in a geographic area.
1st – Generation:
Analog Mobile Radio:
To allow for the conversion from analog systems to digital systems, some cellular technologies allow for the use of dual mode or multi-mode mobile telephones. These handsets are capable of operating on an analog or digital radio channel, depending on whichever is available. Most dual mode phones prefer to use digital radio channels, in the event both are available. This allows them to take advantage of the additional capacity and new features such as short messaging and digital voice quality, as well as offering greater capacity.
Regardless of the size and type of radio channels, all cellular and PCS systems allow for full duplex operation. Full duplex operation is the ability to have simultaneous communications between the caller and the called person. This means a mobile telephone must be capable of simultaneously transmitting and receiving to the radio tower. The radio channel from the mobile telephone to the radio tower is called the uplink and the radio transmission channel from the base station to the mobile telephone is called the downlink. The uplink and downlink radio channels are normally separated by 45 MHz to 80 MHz.
One of the key characteristics of cellular systems is their ability to handoff (also called handover) calls from one radio tower to another while a call is in process. Handoff is an automatic process that is a result of system monitoring and short control messages that are sent between the mobile phone and the system while the call is in progress. The control messages are so short that the customer usually cannot perceive that the handoff has occurred.
Analog cellular systems are regularly characterized by their use of analog modulation (commonly FM modulation) to transfer voice information. Ironically, almost all analog cellular systems use separate radio channels for sending system control messages. These are digital radio channels.
In early mobile radio systems, a mobile telephone scanned the limited number of available channels until it found an unused one, which allowed it to initiate a call. Because the analog cellular systems in use today have hundreds of radio channels, a mobile telephone cannot scan them all in a reasonable amount of time. To quickly direct a mobile telephone to an available channel, some of the available radio channels are dedicated as control channels. Most cellular systems use two types of radio channels, control channels and voice channels. Control channels carry only digital messages and signals, which allow the mobile telephone to retrieve system control information and compete for access.
The basic operation of an analog cellular system involves initiation of the phone when it is powered on, listening for paging messages (idle), attempting access when required and conversation (or data) mode.
When a mobile telephone is first powered on, it initializes itself by searching (scanning) a predetermined set of control channels and then tuning to the strongest one. During the initialization mode, it listens to messages on the control channel to retrieve system identification and setup information.
After initialization, the mobile telephone enters the idle mode and waits to be paged for an incoming call and senses if the user has initiated (dialed) a call (access). When a call begins to be received or initiated, the mobile telephone enters system access mode to try to access the system via a control channel. When it gains access, the control channel sends an initial voice channel designation message indicating an open voice channel. The mobile telephone then tunes to the designated voice channel and enters the conversation mode. As the mobile telephone operates on a voice channel, the system uses Frequency Modulation (FM) similar to commercial broadcast FM radio. To send control messages on the voice channel, the voice information is either replaced by a short burst (blank and burst) message or in some systems, control messages can be sent along with the audio signal.
A mobile telephone’s attempt to obtain service from a cellular system is referred to as “access”. Mobile telephones compete on the control channel to obtain access from a cellular system. Access is attempted when a command is received by the mobile telephone indicating the system needs to service that mobile telephone (such as a paging message indicating a call to be received) or as a result of a request from the user to place a call. The mobile telephone gains access by monitoring the busy/idle status of the control channel both before and during transmission of the access attempt message. If the channel is available, the mobile station begins to transmit and the base station simultaneously monitors the channel’s busy status. Transmissions must begin within a prescribed time limit after the mobile station finds that the control channel access is free, or the access attempt is stopped on the assumption that another mobile telephone has possibly gained the attention of the base station control channel receiver.
If the access attempt succeeds, the system sends out a channel assignment message commanding the mobile telephone to tune to a cellular voice channel. When a subscriber dials the mobile telephone to initiate a call, it is called “origination”. A call origination access attempt message is sent to the cellular system that contains the dialed digits, identity information along with other information. If the system allows service, the system will assign a voice channel by sending a voice channel designator message, if a voice channel is available. If the access attempt fails, the mobile telephone waits a random amount of time before trying again. The mobile station uses a random number generating algorithm internally to determine the random time to wait. The design of the system minimizes the chance of repeated collisions between different mobile stations which are both trying to access the control channel, since each one waits a different random time interval before trying again if they have already collided on their first, simultaneous attempt.
To receive calls, a mobile telephone is notified of an incoming call by a process called paging. A page is a control channel message that contains the telephone’s Mobile Identification Number (MIN) or telephone number of the desired mobile phone. When the telephone determines it has been paged, it responds automatically with a system access message that indicates its access attempt is the result of a page message and the mobile telephone begins to ring to alert the customer of an incoming telephone call. When the customer answers the call (user presses “SEND” or “TALK”), the mobile telephone transmits a service request to the system to answer the call. It does this by sending the telephone number and an electronic serial number to provide the users identity.
After a mobile telephone has been commanded to tune to a radio voice channel, it sends mostly voice or other customer information. Periodically, control messages may be sent between the base station and the mobile telephone. Control messages may command the mobile telephone to adjust its power level, change frequencies, or request a special service (such as three way calling).
To conserve battery life, a mobile phone may be permitted by the base station to only transmit when it senses the mobile telephone’s user is talking. When there is silence, the mobile telephone may stop transmitting for brief periods of time (several seconds). When the mobile telephone user begins to talk again, the transmitter is turned on again. This is called discontinuous transmission.
Analog Cellular Systems:
There are many types of analog and digital cellular systems in use throughout the world. Analog systems include AMPS, TACS, JTACS, NMT, MCS and CNET.
Advanced Mobile Phone Service (AMPS):
Advanced Mobile Phone Service (AMPS) was the original analog cellular system in the United States. It is still in widespread use and by 1997; AMPS systems were operating in over 72 countries. The AMPS system continues to evolve to allow advanced features such as increased standby time, narrowband radio channels, and anti-fraud authentication procedures.
Total Access Communication System (TACS):
The Total Access Communication System (TACS) is very similar to the US EIA-553 AMPS system. Its primary differences include changes to the radio channel frequencies, radio channel bandwidths, and data signaling rates. The TACS was introduced to the U.K. in 1985. After its introduction in the UK in 1985, over 25 countries offered TACS service. The introduction of the TACS system was very successful and the system was expanded to add more channels through what is called Extended TACS (ETACS).
The TACS system was deployed in 25 kHz radio channels, compared to the 30 kHz channels used in AMPS. This narrower radio bandwidth reduced the data speed of the signaling channel.
Nordic Mobile Telephone (NMT):
There are two Nordic Mobile Telephone (NMT) systems; NMT 450 that is a low capacity system and NMT 900 that is a high capacity system. The Nordic mobile telephone (NMT) system was developed by the telecommunications administrations of Sweden, Norway, Finland, and Denmark to create a compatible mobile telephone system in the Nordic countries. The first commercial NMT 450 cellular system was available at the end of 1981. Due to the rapid success of the initial NMT 450 system and limited capacity of the original system design, the NMT 900 system version was introduced in 1986. There are now over 40 countries that have NMT service available. Some of these countries use different frequency bands or reduced number of channels.
The NMT 450 system uses a lower frequency (450 MHz) and higher maximum transmitter power level which allows a larger cell site coverage areas while the NMT 900 system uses a higher frequency (approximately the same 900 MHz band used for TACS and GSM) and a lower maximum transmitter power which increases system capacity. NMT 450 and NMT 900 systems can co-exist which permits them to use the same switching center. This allows some NMT service providers to start offering service with an NMT 450 system and progress up to a NMT 900 system when the need arises.
Narrowband AMPS (NAMPS):
Narrowband Advanced Mobile Phone Service (NAMPS) is an analog cellular system that was commercially introduced by Motorola in late 1991 and was deployed worldwide. Like the existing AMPS technology, NAMPS uses analog FM radio for voice transmissions. The distinguishing feature of NAMPS is its use of a “narrow” 10 kHz bandwidth for radio channels, a third of the size of AMPS channels. Because more of these narrower radio channels can be installed in each cell site, NAMPS systems can serve more subscribers than AMPS systems without adding new cell sites. NAMPS also shifts some control commands to the sub-audible frequency range to facilitate simultaneous voice and data transmissions.
Japanese Mobile Cellular System (MCS):
Japan launched the world’s first commercial cellular system in 1979. Because this system had achieved great success, several different types of cellular systems have evolved in Japan. These include the MCS-L1, MCSL2, JTACS and NTACS systems. The MCS-L1 was the first cellular system in Japan, which was developed and operated by NTT. The system operates in the 800 MHz band. The channel bandwidth is 25 kHz and the signaling is at 300 bps. The control channels are simulcast from all base stations in the local area. This limits the maximum capacity of the MCS-L1 system.
Because the MCS-L1 system could only serve a limited number of customers, the MCS-L2 system was developed. It uses the same frequency bands as the MCS-L1 system. The radio channel bandwidth was reduced from 25 kHz to 12.5 kHz with 6.25 kHz interleaving. This gives the MCS-L2 system 2,400 channels. The control channels transfer information at 2,400 bps and the voice channels can use either in-band (blank and burst) signaling at 2,400 bps or sub-band digital audio signaling at 150 bps. MCS-L2 mobile telephones have diversity reception (similar to diversity receive used in base stations). While this increases the cost and size of the mobile telephones, it also increases the performance and range of the cellular system.
CNET:
CNET is an analog cellular system that is used in Germany, Portugal, and South Africa. The first CNET system started operation in Germany in 1985. The primary objective of the CNET system was to bridge the gap of cellular systems in Germany until the digital European system could be introduced
MATS-E:
The MATS-E system is used in France and Kuwait. The MATS-E system combines many of the features used in different cellular systems. MATS-E uses the standard European mobile telephone frequency bands.
More at:
http://tinyurl.com/6e4hzp
http://en.wikipedia.org/wiki/Advanced_Mobile_Phone_System
2nd - Generation:
Digital Mobile Radio:
There are two basic types of systems; analog and digital. Analog systems commonly use FM modulation to transfer voice information and digital systems use some form of phase modulation to transfer digital voice and data information. Although analog systems are capable of providing many of the services that digital systems offer, digital systems offer added flexibility as many of the features can be created by software changes.
Digital cellular systems use two key types of communication channels, control channels and voice channels. A control channel on a digital system is usually one of the sub-channels on the radio channel. This allows digital systems to combine a control channel and one or more voice channels on a single radio channel. The portions of the radio channel that is dedicated as a control channel carries only digital messages and signals that allow the mobile telephone to retrieve system control information and compete for access. The other sub-channels on the radio channel carry voice or data information.
The basic operation of a digital cellular system involves initiation of the phone when it is powered on, listening for paging messages (idle), attempting access when required and conversation (or data) mode.
When a digital mobile telephone is first powered on, it initializes itself by searching (scanning) a predetermined set of control channels and then tuning to the strongest one. During the initialization mode, it listens to messages on the control channel to retrieve system identification and setup information. Compared to analog systems, digital systems have more communication and control channels. This can result in the mobile phone taking more time to search for control channels. To quickly direct a mobile telephone to an available control channel, digital systems use several processes to help a mobile telephone to find an available control channel. These include having the phone memorize its last successful control channel location, a table of likely control channel locations and a mechanism for pointing to the location of a control channel on any of the operating channels.
After a digital mobile telephone has initialized, it enters an idle mode where it waits to be paged for an incoming call or for the user to initiate a call. When a call begins to be received or initiated, the mobile telephone enters system access mode to try to access the system via a control channel. When it gains access, the control channel sends a digital traffic channel designation message indicating an open communications channel. This channel may be on a different time slot on the same frequency or to a time slot on a different frequency. The digital mobile telephone then tunes to the designated communications channel and enters the conversation mode. As the mobile telephone operates on a digital voice channel, the digital system commonly uses some form of phase modulation (PM) to send and receive digital information.
A mobile telephone’s attempt to obtain service from a cellular system is referred to as “access”. Digital mobile telephones compete on the control channel to obtain access from a cellular system. Access is attempted when a command is received by the mobile telephone indicating the system needs to service that mobile telephone (such as a paging message indicating a call to be received) or as a result of a request from the user to place a call. Digital mobile telephones usually have the ability to validate their identities more securely during access than analog mobile telephones. This is made possible by a process called authentication. Authentication processes share secret data between the digital mobile phone and the cellular system.
If the authentication is successful, the system sends out a channel assignment message commanding the mobile telephone to change to a new communication channel and conversation can begin.
After a mobile telephone has been commanded to tune to a radio voice channel, it sends digitized voice or other customer data. Periodically, control messages may be sent between the base station and the mobile telephone. Control messages may command the mobile telephone to adjust its power level, change frequencies, or request a special service (such as three way calling). To send control messages while the digital mobile phone is transferring digital voice, the voice information is either replaced by a short burst (called blank and burst or fast signaling), or else control messages can be sent along with the digitized voice signals (called slow signaling).
Most digital telephones automatically conserve battery life as they transmit only for short periods of time (bursts). In addition to savings through digital burst transmission, digital phones ordinarily have the capability of discontinuous transmission that allows the inhibiting of the transmitter during periods of user silence. When the mobile telephone user begins to talk again, the transmitter is turned on again. The combination of the power savings allows some digital mobile telephones to have 2 to 5 times the battery life in the transmit mode.
Digital technology increases system efficiency by voice digitization, speech compression (coding), channel coding, and the use of spectrally efficient radio signal modulation.
Standard voice digitization in the Public Switched Telephone Network (PSTN) produces a data rate of 64 kilobits per second (kbps). Because transmitting a digital signal via radio requires about 1 Hz of radio bandwidth for each bps, an uncompressed digital voice signal would require more than 64 kHz of radio bandwidth. Without compression, this bandwidth would make digital transmission less efficient than analog FM cellular, which uses only 25-30 kHz for a single voice channel. Therefore, digital systems compress speech information using a voice coder or Vocoder. Speech coding removes redundancy in the digital signal and attempts to ignore data patterns that are not characteristic of the human voice. The result is a digital signal that represents the voice audio frequency spectrum content, not a waveform.
A Vocoder characterizes the input signal. It looks up codes in a code book table that represents various digital patterns to choose the pattern that comes closest to the input digitized signal. The amount of digitized speech compression used in digital cellular systems varies. For the IS-136 TDMA system, the compression is 8:1. For CDMA, the compression varies from 8:1 to 64:1 depending on speech activity. GSM systems compress the voice by 5:1.
Digital Cellular Systems:
The types of 2nd generation digital cellular systems include GSM, IS-136 TDMA and CDMA.
Global System for Mobile Communication (GSM):
The Global System for Mobile Communications (GSM) system is a global digital radio system that uses Time Division Multiple Access (TDMA) technology. GSM is a digital cellular technology that was initially created to provide a single-standard pan-European cellular system. GSM began development in 1982, and the first commercial GSM digital cellular system was activated in 1991. GSM technology has evolved to be used in a variety of systems and frequencies (900 MHz, 1800 MHz and 1900 MHz) including Personal Communications Services (PCS) in North America and Personal Communications Network (PCN) systems throughout the world. By the middle of 2003, 510 networks in 200 countries offered GSM service.
The GSM system is a digital-only system and was not designed to be backward-compatible with the established analog systems. The GSM radio band is shared temporarily with analog cellular systems in some European nations.
When communicating in a GSM system, users can operate on the same radio channel simultaneously by sharing time slots. The GSM cellular system allows 8 mobile telephones to share a single 200 kHz bandwidth radio carrier waveform for voice or data communications. To allow duplex operation, GSM voice communication is conducted on two 200 kHz wide carrier frequency waveforms.
The GSM system has several types of control channels that carry system and paging information, and coordinates access like the control channels on analog systems. The GSM digital control channels have many more capabilities than analog control channels such as broadcast message paging, extended sleep mode, and others. Because the GSM control channels use only a portion (one or more slots), they typically co-exist on a single radio channel with other time slots that are used for voice communication.
A GSM carrier transmits at a bit rate of 270 kbps, but a single GSM digital radio channel or time slot is capable of transferring only 1/8th of that, about 33 kbps of information (actually less than that, due to the use of some bit time for non-information purposes such as synchronization bits).
North American TDMA (IS-136 TDMA):
The North American TDMA system (IS-136) is a digital system that uses TDMA access technology. It evolved from the IS-54 specification that was developed in North America in the late 1980’s to allow the gradual evolution of the AMPS system to digital service. The IS-136 system is sometimes referred to as Digital AMPS (DAMPS) or North American digital cellular (NADC).
In 1988, the Cellular Telecommunications Industry Association created a development guideline for the next generation of cellular technology for North America. This guideline was called the User Performance Requirements (UPR) and the Telecommunications Industry Association (TIA) used this guideline to create a TDMA digital standard, called IS-54. This digital specification evolved from the original EIA-553 AMPS specification. The first revision of the IS-54 specification (Rev 0) identified the basic parameters (e.g. time slot structure, type of radio channel modulation, and message formats) needed to begin designing TDMA cellular equipment. There have been several enhancements to IS-54 since its introduction and in 1995; IS-54 was incorporated as part of the IS-136 specification.
A primary feature of the IS-136 systems is their ease of adaptation to the existing AMPS system. Much of this adaptability is due to the fact that IS- 136 radio channels retain the same 30 kHz bandwidth as AMPS system channels. Most base stations can therefore replace TDMA radio units in locations previously occupied by AMPS radio units. Another factor in favor of adaptability is that new dual mode mobile telephones were developed to operate on either IS-136 digital traffic (voice and data) channels or the existing AMPS radio channels as requested in the CTIA UPR document. This allows a single mobile telephone to operate on any AMPS system and use the IS-136 system whenever it is available.
The IS-136 specification concentrates on features that were not present in the earlier IS-54 TDMA system. These include longer standby time, short message service functions, and support for small private or residential systems that can coexist with the public systems. In addition, IS-136 defines a digital control channel to accompany the Digital Traffic Channel (DTC). The digital control channel allows a mobile telephone to operate in a single digital-only mode. Revision A of the IS-136 specification now supports operation in the 800 MHz range for the existing AMPS and DAMPS systems as well as the newly allocated 1900MHz bands for PCS systems. This permits dual band, dual mode phones (800 MHz and 1900 MHz for AMPS and DAMPS). The primary difference between the two bands is that mobile telephones cannot transmit using analog signals at 1900MHz. The IS-136 cellular system allows for mobile telephones to use either 30 kHz analog (AMPS) or 30 kHz digital (TDMA) radio channels. The IS-136 TDMA radio channel allows multiple mobile telephones to share the same radio frequency channel by time-sharing. All IS-136 TDMA digital radio channels are divided into frames with 6 time slots. The time slots used for the correspondingly numbered forward and reverse channels are time-related so that the mobile telephone does not simultaneously transmit and receive.
The RF power levels for the mobile phones are almost exactly the same as for the AMPS telephones. The primary difference in the power levels is a reduction in minimum power level that mobile telephones can be instructed to reduce to. This allows for very small cell coverage areas, typically the size of cells that would be used for wireless office or home cordless systems.
Extended TDMA (E-TDMA):
Extended TDMA was developed by Hughes Network Systems in 1990 as an extension to the existing IS-136 TDMA industry standard. ETDMA uses the existing TDMA radio channel bandwidth and channel structure and its receivers are tri-mode as they can operate in AMPS, TDMA, or ETDMA modes. While a TDMA system assigns a mobile telephone fixed time slot numbers for each call, ETDMA dynamically assigned time slots on an as needed basis. The ETDMA system contains a half-rate speech coder (4 kb/s) that reduces the number of information bits that must be transmitted and received each second. This makes use of voice silence periods to inhibit slot transmission so other users may share the transmit slot. The overall benefit is that more users can share the same radio channel equipment and improved radio communications performance. The combination of a low bit rate speech coder, voice activity detection, and interference averaging increases the radio channel efficiency to beyond 10 times the existing AMPS capacity.
ETDMA radio channels are structured into the same frames and slots structures as the standard IS-54 radio channels. Some or all of the time slots on all of the radio channels are shared for ETDMA communication, which is similar to IS-54 and IS-136 radio channels, or else slots can be shared on different frequencies. When a Mobile telephone is operating in extended mode, the ETDMA system must continually coordinate time slot and frequency channel assignments. The ETDMA system performs this by using a time slot control system. On an ETDMA capable radio channel some of the time slots are dedicated as control slots on an as needed basis. ETDMA systems can assign an AMPS channel, a TDMA full-rate or half-rate channel, or an ETDMA channel. The existing 30 kHz AMPS control channels are used to assign analog voice and digital traffic channels.
Integrated Dispatch Enhanced Network (iDEN):
Integrated Dispatch Enhanced Network (iDEN) a digital radio system that provides for voice, dispatch and data services. iDEN was formerly called Motorola Integrated Radio System (MIRS). iDEN was deployed in 1996 for enhanced specialized mobile radio (E-SMR) service. The iDEN system radio channel bandwidth is 25 kHz and it is divided into frames that have 6 times slots per frame. The iDEN system allows 6 mobile radios to simultaneously share a single radio channel for dispatch voice quality and up to 3 mobile radios can simultaneously share a radio channel for cellular like voice quality.
Code Division Multiple Access (IS-95 CDMA):
Code Division Multiple Access (CDMA) system (IS 95) is a digital cellular system that uses CDMA access technology. IS-95 technology was initially developed by Qualcomm in the late 1980’s. CDMA cellular service began testing in the United States in San Diego, California during 1991. In 1995, IS-95 CDMA commercial service began in Hong Kong and now many CDMA systems are operating throughout the world, including a 1.9 GHz all-digital system in the USA that has been operating since November 1996.
Spread spectrum radio technology has been used for many years in military applications. CDMA is a particular form of spread spectrum radio technology. In 1989, CDMA spread spectrum technology was presented to the industry standards committee but it did not meet with immediate approval. The standards committee had just resolved a two-year debate between TDMA and FDMA and was not eager to consider another access technology.
The IS-95 CDMA system allows for voice or data communications on either a 30 kHz AMPS radio channel (when used on the 800 MHz cellular band) or a new 1.25 MHz CDMA radio channel. The IS-95 CDMA radio channel allows multiple mobile telephones to communicate on the same frequency at the same time by special coding of their radio signals.
The CDMA system is compatible with the established access technology, and it allows analog (EIA-553) and dual mode (IS-95) subscribers to use the same analog control channels. Some of the voice channels are replaced by CDMA digital transmissions, allowing several users to be multiplexed (shared) on a single RF channel. As with other digital technologies, CDMA produces capacity expansion by allowing multiple users to share a single digital RF channel.
CDMA systems use a maximum of 64 coded (logical) traffic channels, but they cannot always use all of these. To obtain a maximum of 64 communication channels for each CDMA radio channel, the average data rate for each user should approximate 3 kbps. If the average data rate is higher, less than 64 traffic channels can be used. CDMA systems can vary the data rate for each user dependent on voice activity (variable rate speech coding), thereby decreasing the average number of bits per user to about 3.8 kbps. Varying the data rate according to user requirement allows more users to share the radio channel, but with slightly reduced voice quality. This is called soft capacity limit.
Japanese Personal Digital Cellular (PDC):
The PDC system is a TDMA technology with a radio interface that is very similar to IS-136, in that it has six timeslots and an almost identical data rate, and a core network architecture that is very similar to GSM. PDC operates in both the 900 MHz and 1,400 MHz regions of the radio spectrum.
More at:
http://en.wikipedia.org/wiki/2G
http://www.arcelect.com/2g-3g_cellular_wireless.htm
http://en.wikipedia.org/wiki/GSM
http://en.wikipedia.org/wiki/CDMA
Generation 2.5:
Packet Based Digital Cellular:
Packet Based Cellular (commonly called - generation 2.5, or 2.5G) are 2nd Generation cellular technologies that have been enhanced to provide for advanced communication applications. Packet based digital cellular systems help the industry transition from one capability to a much more advanced capability. In cellular telecommunications, 2.5G systems used improved digital radio technology to increase their data transmission rates and new packet based technology to increase the system efficiency for data users.
Upgraded Digital Cellular System:
The types of upgraded 2nd generation digital cellular systems (generation 2.5) include GPRS, EDGE, and CDMA2000, 1xRTT. General Packet Radio Service (GPRS): General Packet Radio Service (GPRS) is a portion of the GSM specification that allows packet radio service on the GSM system. The GPRS system adds (defines) new packet channels and switching nodes within the GSM system. The GPRS system provides for theoretical data transmission rates up to 172 kbps.
Enhanced Data Rates for Global Evolution (EDGE):
Some also refer it to as generation 2.75 technology. Enhanced Data Rates for global Evolution (EDGE) is an evolved version of the global system for mobile (GSM) radio channel that uses new phase modulation and packet transmission to provide for advanced high-speed data services. The EDGE system uses 8 levels Phase Shift Keying (8PSK) to allow one symbol change to represent 3 bits of information. This is 3 times the amount of information that is transferred by a standard 2 level Gaussian Minimum Shift Keying (GMSK) signal used by the first generation of GSM system. This results in a radio channel data transmission rate of 604.8 kbps and a net maximum delivered theoretical data transmission rate of 384 kbps. The advanced packet transmission control system allows for constantly varying data transmission rates in either direction between mobile radios.
CDMA2000, 1xRTT:
CDMA2000 is a 3G standard that allows operators to evolve from their existing IS-95 networks to offer 3G services. The original CDMA2000 proposal contained two distinct evolutionary phases, the first known as 1xRTT used the same 1.25 MHz channels as IS-95 but delivered increased capacity and data rates compared to IS-95. The second phase was known as 3xRTT that uses three times the spectrum of IS-95, that is 3.75 MHz. The 3xRTT concept would deliver data rates up to 2 Mbps, a requirement for any 3G technologies. However recent evolutions of 1xRTT are offering data rates in excess of this and therefore it is unlikely that 3xRTT is required. By the middle of 2003 there were a total of 60 commercial 1xRTT networks offering service.
Evolution Data Only (1xEVDO):
The evolution of existing systems for data only (1xEVDO) is an evolved version of the CDMA2000 1xRTT system. The 1xEVDO system uses the same 1.25 MHz radio channel bandwidth as the existing IS-95 system that provides for multiple voice channels and medium rate data services. The 1xEVDO version changes the modulation technology to allow for data transmission rates up to 2.5 Mbps. The 1xEVDO system has an upgraded packet data transmission control system that allows for bursty data transmission rather than for more continuous voice data transmission.
Evolution Data and Voice (1xEVDV):
The evolution of existing systems for data and voice (1xEVDV) is an evolved version of the CDMA2000 1xRTT system that can be used for data and voice service. The 1xEVDV system provides for both voice and high-speed data transmission services in the same 1.25 MHz radio channel bandwidth as the existing IS-95 system. The 1xEVDV Vision allows for a maximum data transmission rate of approximately 2.7 Mbps.
More at:
http://en.wikipedia.org/wiki/GPRS
http://en.wikipedia.org/wiki/GPRS_Core_Network
http://en.wikipedia.org/wiki/2.5G
3rd Generation:
Wideband Digital Cellular:
Wideband Digital Cellular (commonly called 3rd generation) is cellular technology that uses wideband digital radio technology as compared to 2nd generation narrowband digital radio. A wideband digital cellular system that permits very high- speed data transmission rates through the use of relatively wide radio channels. In this system, the radio channels are much wider many tens of times wider than 2nd generation radio channels. This allows wideband digital cellular systems to send high-speed data to communication devices. This system also uses communication servers to help to manage multimedia communication sessions. Aside from the use of wideband radio channels and enhanced packet data communication, the 3rd generation systems typically use the same voice network switching systems (such as the MSC) as 2nd generation mobile communications systems.
Wideband Digital Cellular Systems:
The 3rd generation wireless requirements are defined in the International Mobile Telecommunications “IMT-2000” project developed by the International Telecommunication Union (ITU). The IMT-2000 project that defined requirements for high-speed data transmission, Internet Protocol (IP)-based services, global roaming, and multimedia communications. After many communication proposals were reviewed, two global systems are emerging; wideband code division multiple access (WCDMA) and CDMA2000.
More at:
http://www.itu.int/osg/imt-project/
http://www.itu.int/osg/imt-project/docs/What_is_IMT2000-2.pdf
Wideband Code Division Multiple Access (WCDMA):
WCDMA is a 3rd generation digital cellular system that uses radio channels that have a wider bandwidth than 2nd generation digital cellular systems such as GSM or IS-95 CDMA. WCDMA is normally deployed in a 5 MHz channel plan.
The Third Generation Partnership Project (3GPP) oversees the creation of industry standards for the 3rd generation of mobile wireless communication systems (WCDMA). The key members of the 3GPP include standards agencies from Japan, Europe, Korea, China and the United States. The 3GPP technology, also known as the Universal Mobile Telecommunications System (UMTS), is based on an evolved GSM core network that contains 2.5G elements, namely GPRS switching nodes. This concept allows a GSM network operator to migrate to WCDMA by adding the necessary 3G radio elements to their existing network, thus creating ‘islands’ of 3G coverage when the networks first launch.
A large number of GSM operators have secured spectrum for WCDMA and many network launches are imminent, with live networks presently in Japan, the United Kingdom and Italy.
Code Division Multiple Access 2000 (CDMA2000):
CDMA2000 is a family of standards that represent an evolution from the IS- 95 code division multiple access (CDMA) system that offer enhanced packet transmission protocols to provide for advanced high-speed data services. The CDMA2000 technologies operate in the same 1.25 MHz radio channels as used by IS-95 and offer backward compatibility with IS-95. The CDMA2000 system is overseen by the Third Generation Partnership Project 2 (3GPP2). The 3GPP2 is a standards setting project that is focused on developing global specifications for 3rd generation systems that use ANSI/TIA/EIA-41 Cellular Radio Intersystem Signaling.
Time Division Synchronous CDMA (TD-SCDMA):
On a global basis it likely that WCDMA and CDMA2000TM will dominate the 3G market, however in China there is growing support for a homegrown standard known as Time Division Synchronous CDMA (TD-SCDMA). TDSCDMA offers voice services and data services, both circuit-switched and packet-switched, at rates up to 2 Mbps. It uses a Time Division Duplex (TDD) technique in which transmit and receive signals are sent on the same frequency but at different times. The timeslots on the radio carrier can either be allocated symmetrically for services such as speech or asymmetrically for data services where the bit rates in the two directions of transmission may differ significantly.
More at:
http://en.wikipedia.org/wiki/W-CDMA
http://www.ericsson.com/technology/tech_articles/WCDMA.shtml
http://en.wikipedia.org/wiki/CDMA2000
http://www.cdg.org/technology/3g.asp
http://tinyurl.com/6mqygd
Future Enhancements:
There are likely to be many future enhancements to mobile radio. Some of the key innovations include software defined radios, spatial division multiple access (SDMA), and 4th generation mobile telephones.
Software Defined Radios:
Software defined radios are transceiver devices that use digital signal processing to create and decode radio messages. Because they use digital signal processing for almost all functions, it is possible to change access technologies and radio transmission characteristics through software changes. Thus it may be possible in the future for a handset or other terminal to download the necessary parameters of a network as the mobile moves from one technology to another.
Spatial Division Multiple Access (SDMA):
Spatial Division Multiple Access (SDMA) is a technology that increases the quality and capacity of wireless communications systems. Using advanced algorithms and adaptive digital signal processing; Base Stations equipped with multiple antennas can more actively reject interference and use spectral resources more efficiently. This would allow for larger cells with less radiated energy, greater sensitivity for portable cellular phones, and greater network capacity.
Fourth Generation (4G) Networks:
Even before 3G networks are fully launched and utilized, various study groups are considering the shape of the next generation of cellular technology, so called 4G. There is no single global vision for 4G as yet but the next generation of network is likely to be all IP-based, offer data rates up to 100 Mbps and support true global mobility. One route towards this vision is the convergence of technologies such as 3G cellular and Wireless LANs (WLANs).
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