4G is the short name for fourth-generation wireless, the stage of broadband mobile communications that will supersede the third generation (3G). Although carriers and governing standards bodies have not agreed upon exactly what 4G will be, it is expected to use available radio spectrum more efficiently and as a result, provide end users with cable-modem transmission speeds which will support high-quality streaming video.

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.

This article uses 4G to refer to IMT-Advanced (International Mobile Telecommunications Advanced), as defined by ITU-R, an IMT-Advanced cellular system must have target peak data rates of up to approximately 100 Mbit/s for high mobility such as mobile access and up to approximately 1 Gbit/s for low mobility such as nomadic/local wireless access, according to the ITU requirements. Scalable bandwidths up to at least 40 MHz should be provided. In all suggestions for 4G, the CDMA spread spectrum radio technology used in 3G systems and IS-95 is abandoned and replaced by frequency schemes, for example multi-carrier transmission such as OFDMA. This is combined with MIMO (i.e., multiple antennas (Multiple in Multiple Out)), dynamic channel allocation and channel-dependent scheduling.

4G is being developed to accommodate the QoS and rate requirements set by further development of existing 3G applications like mobile broadband access, Multimedia Messaging Service (MMS), video chat, mobile TV, but also new services like HDTV. 4G may allow roaming with wireless local area networks, and may interact with digital video broadcasting systems.

The 4G working group 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 1 Gbit/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

§ femcells (home nodes connected to fixed Internet broadband infrastructure)

Consideration points

§ Coverage, radio environment, spectrum, services, business models and deployment types, users.

Principal technologies

§ Physical layer transmission techniques

§ MIMO: To attain ultra high spectral efficiency by means of spatial processing including multi-antenna and multi-user MIMO

§ Frequency-domain-equalization, for example Multi-carrier modulation (OFDM) or single-carrier frequency-domain-equalization (SC-FDE) in the downlink: To exploit the frequency selective channel property without complex equalization.

§ Frequency-domain statistical multiplexing, for example (OFDMA) or (Single-carrier FDMA) (SC-FDMA, a.k.a. Linearly precoded OFDMA, LP-OFDMA) in the uplink: Variable bit rate by assigning different sub-channels to different users based on the channel conditions

§ Turbo principle error-correcting codes: To minimize the required SNR at the reception side

§ Channel-dependent scheduling: To utilize the time-varying channel.

§ Link adaptation: Adaptive modulation and error-correcting codes

§ Relaying, including fixed relay networks (FRNs), and the cooperative relaying concept, known as multi-mode protocol

4G features

According to the members of the 4G working group, the infrastructure and the terminals of 4G will have almost all the standards from 2G to 4G implemented. Although legacy systems are in place to adopt existing users, the infrastructure for 4G will be only packet-based (all-IP). Some proposals suggest having an open Internet platform. Technologies considered to be early 4G include: Flash-OFDM, the 802.16e mobile version of WiMax (also known as WiBro in South Korea), and HC-SDMA).