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4G refers to the fourth generation of cellular wireless standards. It is a successor to 3G and 2G standards. The nomenclature of the generations generally refers to a change in the fundamental nature of the service. The first was the move from analogue to digital (2G), which was followed by multi-media support (3G) and now 4G, which refers to all IP packet switched networks and increases in data speeds.
A 4G system is expected to provide a comprehensive and secure all-IP based solution where facilities such as IP telephony, ultra-broadband Internet access, gaming services and streamed multimedia may be provided to users.
The Mobile WiMAX (IEEE 802.16e-2005) mobile wireless broadband access (MWBA) standard is sometimes branded 4G, and offers peak data rates of 128 Mbit/s downlink and 56 Mbit/s uplink over 20 MHz wide channels. The IEEE 802.16m evolution of 802.16e is under development, with the objective to fulfill the IMT-Advanced criteria of 1000 Mbit/s for stationary reception and 100 Mbit/s for mobile reception.
4G is being developed to accommodate the QoS and rate requirements set by further development of existing 3G applications like wireless broadband access, Multimedia Messaging Service (MMS), video chat, mobile TV, but also new services like HDTV content, minimal services like voice and data, and other services that utilize bandwidth. It may be allowed roaming with wireless local area networks, and be combined with digital video broadcasting systems.
The 4G working group[clarification needed] has defined the following as objectives of the 4G wireless communication standard:
* Flexible channel bandwidth, between 5 and 20 MHz, optionally up to 40 MHz.
* A nominal data rate of 100 Mbit/s while the client physically moves at high
speeds relative to the station, and 1 Gbit/s while client and station are in relatively fixed positions as defined by the ITU-R,
* A data rate of at least 100 Mbit/s between any two points in the world,
* Peak link spectral efficiency of 15 bit/s/Hz in the downlink, and 6.75 bit/s/Hz in the uplink (meaning that 1000 Mbit/s in the downlink should be possible over less than 67 MHz bandwidth)
* System spectral efficiency of up to 3 bit/s/Hz/cell in the downlink and 2.25 bit/s/Hz/cell for indoor usage.
* Smooth handoff across heterogeneous networks,
* Seamless connectivity and global roaming across multiple networks,
* High quality of service for next generation multimedia support (real time audio, high speed data, HDTV video content, mobile TV, etc)
* Interoperability with existing wireless standards, and
* An all IP, packet switched network.
WiMax is using OFDMA in the downlink and in the uplink. For the next generation UMTS, OFDMA is used for the downlink. By contrast, IFDMA is being considered for the uplink since OFDMA contributes more to the PAPR related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus avoids amplifier issues. Similarly, MC-CDMA is in the proposal for the IEEE 802.20 standard. These access schemes offer the same efficiencies as older technologies like CDMA. Apart from this, scalability and higher data rates can be achieved.
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