4G

4G refers to the fourth generation of cellular wireless standards. It is a successor to 3G and 2G families of standards. The nomenclature of the generations generally refers to a change in the fundamental nature of the service, non-backwards compatible transmission technology and new frequency bands. The first was the move from 1981 analog (1G) to digital (2G) transmission in 1992. This was followed, in 2002, by 3G multi-media support, spread spectrum transmission and at least 200 kbit/s, soon expected to be followed by 4G, which refers to all-IP packet-switched networks, mobile ultra-broadband (gigabit speed) access and multi-carrier transmission. Pre-4G technologies such as mobile WiMAX and first-release 3G Long term evolution (LTE) have been available on the market since 2006^[1] and 2009^[2][3][4] respectively.

Overview

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.^[5][6]

In all suggestions for 4G, the CDMA spread spectrum radio technology used in 3G systems and IS-95 is abandoned and replaced by frequency-domain equalization 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.

Predecessors of 4G

LTE

Samsung LTE modem

The pre-4G technology 3GPP Long Term Evolution (LTE) is often branded "4G", but the first LTE release does not fully comply with the IMT-Advanced requirements. LTE has a theoretical net bit rate capacity of up to 100 Mbit/s in the downlink and 50 Mbit/s in the uplink if a 20 MHz channel is used - and more if Multiple-input multiple-output (MIMO), i.e. antenna arrays, are used.

The world's first publicly available LTE-service was opened in the two Scandinavian capitals Stockholm (Ericsson system) and Oslo (a Huawei system) on the 14 December 2009, and branded 4G. The user terminals were manufactured by Samsung ^[2] Most major mobile carriers in the United States and several worldwide carriers have announced plans to convert their networks to LTE beginning in 2011.

The physical radio interface was at an early stage named High Speed OFDM Packet Access (HSOPA), now named Evolved UMTS Terrestrial Radio Access (E-UTRA).

LTE Advanced (Long-term-evolution Advanced) is a candidate for IMT-Advanced standard, formally submitted by the 3GPP organization to ITU-T in the fall 2009, and expected to be released in 2012. The target of 3GPP LTE Advanced is to reach and surpass the ITU requirements. LTE Advanced should be compatible with first release LTE equipment, and should share frequency bands with first release LTE.^[7]

WiMAX

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 1 Gbit/s for stationary reception and 100 Mbit/s for mobile reception.^[8] The world's first commercial mobile WiMAX service was opened by KT in Seoul, South Korea on 30 June 2006.^[1]

Sprint Nextel has announced that it will be using WiMAX, branded as a "4G" network.^[9]

UMB (formerly EV-DO Rev. C)

UMB (Ultra Mobile Broadband) was the brand name for a discontinued 4G project within the 3GPP2 standardization group to improve the CDMA2000 mobile phone standard for next generation applications and requirements. In November 2008, Qualcomm, UMB's lead sponsor, announced it was ending development of the technology, favouring LTE instead.^[10] The objective was to achieve data speeds over 275 Mbit/s downstream and over 75 Mbit/s upstream.

Flash-OFDM

At an early stage the Flash-OFDM system was expected to be further developed into a 4G standard.

Objective and approach

Objectives

4G is being developed to accommodate the quality of service (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.^[6]
• 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,^[11]
• A data rate of at least 100 Mbit/s between any two points in the world,^[11]
• Peak link spectral efficiency of 15 bit/s/Hz in the downlink, and 6.75 bit/s/Hz in the uplink (meaning that 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.^[6]
• Smooth handoff across heterogeneous networks,^[12]
• Seamless connectivity and global roaming across multiple networks,^[13]
• High quality of service for next generation multimedia support (real time audio, high speed data, HDTV video content, mobile TV, etc.)^[13]
• Interoperability with existing wireless standards,^[14] and
• An all IP, packet switched network.^[13]
• Femtocells (home nodes connected to fixed Internet broadband infrastructure)

Approaches

Consideration points

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

Principal technologies

• Physical layer transmission techniques^[15]
  • 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 (see iBurst).

Components

Access schemes

As the wireless standards evolved, the access techniques used also exhibited increase in efficiency, capacity and scalability. The first generation wireless standards used plain TDMA and FDMA. In the wireless channels, TDMA proved to be less efficient in handling the high data rate channels as it requires large guard periods to alleviate the multipath impact. Similarly, FDMA consumed more bandwidth for guard to avoid inter carrier interference. So in second generation systems, one set of standard used the combination of FDMA and TDMA and the other set introduced an access scheme called CDMA. Usage of CDMA increased the system capacity, but as a theoretical drawback placed a soft limit on it rather than the hard limit (i.e. a CDMA network setup does not inherently reject new clients when it approaches its limits, resulting in a denial of service to all clients when the network overloads; though this outcome is avoided in practical implementations by admission control of circuit switched or fixed bitrate communication services). Data rate is also increased as this access scheme (providing the network is not reaching its capacity) is efficient enough to handle the multipath channel. This enabled the third generation systems, such as IS-2000, UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA, to use CDMA as the access scheme. However, the issue with CDMA is that it suffers from poor spectral flexibility and computationally intensive time-domain equalization (high number of multiplications per second) for wideband channels.

Recently, new access schemes like Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved FDMA and Multi-carrier CDMA (MC-CDMA) are gaining more importance for the next generation systems. These are based on efficient FFT algorithms and frequency domain equalization, resulting in a lower number of multiplications per second. They also make it possible to control the bandwidth and form the spectrum in a flexible way. However, they require advanced dynamic channel allocation and traffic adaptive scheduling.

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.

The other important advantage of the above mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMO environments since the spatial multiplexing transmission of MIMO systems inherently requires high complexity equalization at the receiver.

In addition to improvements in these multiplexing systems, improved modulation techniques are being used. Whereas earlier standards largely used Phase-shift keying, more efficient systems such as 64QAM are being proposed for use with the 3GPP Long Term Evolution standards.

IPv6 support

Unlike 3G, which is based on two parallel infrastructures consisting of circuit switched and packet switched network nodes respectively, 4G will be based on packet switching only. This will require low-latency data transmission.

By the time that 4G is deployed, the process of IPv4 address exhaustion is expected to be in its final stages. Therefore, in the context of 4G, IPv6 support is essential in order to support a large number of wireless-enabled devices. By increasing the number of IP addresses, IPv6 removes the need for Network Address Translation (NAT), a method of sharing a limited number of addresses among a larger group of devices, although NAT will still be required to communicate with devices that are on existing IPv4 networks.

As of June 2009, Verizon has posted specifications that require any 4G devices on its network to support IPv6.^[16]

Advanced Antenna Systems

The performance of radio communications depends on an antenna system, termed smart or intelligent antenna. Recently, multiple antenna technologies are emerging to achieve the goal of 4G systems such as high rate, high reliability, and long range communications. In the early 1990s, to cater the growing data rate needs of data communication, many transmission schemes were proposed. One technology, spatial multiplexing, gained importance for its bandwidth conservation and power efficiency. Spatial multiplexing involves deploying multiple antennas at the transmitter and at the receiver. Independent streams can then be transmitted simultaneously from all the antennas. This technology, called MIMO (as a branch of intelligent antenna), multiplies the base data rate by (the smaller of) the number of transmit antennas or the number of receive antennas. Apart from this, the reliability in transmitting high speed data in the fading channel can be improved by using more antennas at the transmitter or at the receiver. This is called transmit or receive diversity. Both transmit/receive diversity and transmit spatial multiplexing are categorized into the space-time coding techniques, which does not necessarily require the channel knowledge at the transmitter. The other category is closed-loop multiple antenna technologies, which require channel knowledge at the transmitter.

Software-Defined Radio (SDR)

SDR is one form of open wireless architecture (OWA). Since 4G is a collection of wireless standards, the final form of a 4G device will constitute various standards. This can be efficiently realized using SDR technology, which is categorized to the area of the radio convergence.

History of 4G and pre-4G technologies

• In 2002, the strategic vision for 4G — which ITU designated as IMT-Advanced — was laid out.
• In 2005, OFDMA transmission technology is chosen as candidate for the HSOPA downlink, later renamed 3GPP Long Term Evolution (LTE) air interface E-UTRA.
• In November 2005, KT demonstrated mobile WiMAX service in Busan, South Korea. ^[17]
• In June 2006, KT started the world's first commercial mobile WiMAX service in Seoul, South Korea.^[1]
• In mid-2006, Sprint Nextel announced that it would invest about US$5 billion in a WiMAX technology buildout over the next few years^[18] ($5.45 billion in real terms^[19]). Since that time Sprint has faced many setbacks, that have resulted in steep quarterly losses. On May 7, 2008, Sprint, Imagine, Google, Intel, Comcast, Bright House, and Time Warner announced a pooling of an average of 120 MHz of spectrum; Sprint merged its Xohm WiMAX division with Clearwire to form a company which will take the name Clear.
• In February 2007, the Japanese company NTT DoCoMo tested a 4G communication system prototype with 4x4 MIMO called VSF-OFCDM at 100 Mbit/s while moving, and 1 Gbit/s while stationary. NTT DoCoMo completed a trial in which they reached a maximum packet transmission rate of approximately 5 Gbit/s in the downlink with 12x12 MIMO using a 100 MHz frequency bandwidth while moving at 10 km/h,^[20] and is planning on releasing the first commercial network in 2010.
• In September 2007, NTT Docomo demonstrated e-UTRA data rates of 200 Mbit/s with power consumption below 100 mW during the test.^[21]
• In January 2008, a U.S. Federal Communications Commission (FCC) spectrum auction for the 700 MHz former analog TV frequencies began. As a result, the biggest share of the spectrum went to Verizon Wireless and the next biggest to AT&T.^[22] Both of these companies have stated their intention of supporting LTE.
• In January 2008, EU commissioner Viviane Reding suggested re-allocation of 500–800 MHz spectrum for wireless communication, including WiMAX.^[23]
• February 15, 2008 - Skyworks Solutions released a front-end module for e-UTRAN.^[24][25][26]
• In April 2008, LG and Nortel demonstrated e-UTRA data rates of 50 Mbit/s while travelling at 110 km/h.^[27]
• In 2008, ITU-R established the detailed performance requirements of IMT-Advanced, by issuing a Circular Letter calling for candidate Radio Access Technologies (RATs) for IMT-Advanced.^[28]
• April 2008, just after receiving the circular letter, the 3GPP organized a workshop on IMT-Advanced where it was decided that LTE-Advanced, an evolution of current LTE standard, will meet or even exceed IMT-Advanced requirements following the ITU-R agenda.
• On 3 March 2009, Lithuanian's LRTC announcing the first operational "4G" mobile WiMAX network in Baltic states.^[29]
• In December 2009, Sprint began advertising "4G" service in selected cities in the United States, despite average download speeds of only 3-6Mbps with peak speeds of 10Mbps (not available in all markets).^[30]
• On December 14, 2009, the first commercial LTE deployment was in the Scandinavian capitals Stockholm and Oslo by the Swedish-Finnish network operator TeliaSonera and its Norwegian brandname NetCom (Norway). TeliaSonera branded the network "4G". The modem devices on offer were manufactured by Samsung (dongle GT-B3710), and the network infrastructure created by Huawei (in Oslo) and Ericsson (in Stockholm). TeliaSonera plans to roll out nationwide LTE across Sweden, Norway and Finland^[3][31]. TeliaSonera used spectral bandwidth of 10 MHz, and single-in-single-out, which should provide physical layer net bitrates of up to 50 Mbit/s downlink and 25 Mbit/s in the uplink. Introductory tests showed a TCP throughput of 42.8 Mbit/s downlink and 5.3 Mbit/s uplink in Stockholm.^[4]
• On 25 February 2010, Estonia's EMT opened LTE "4G" network working in test regime.^[32]
• On 5 June 2010, Sprint Nextel released the first 4G Smartphone, the HTC Evo 4G.
• On July 2010, Uzbekistan's MTS deployed LTE in Tashkent.^[33]

Deployment plans

In May 2005, Digiweb, an Irish fixed and wireless broadband company, announced that they have received a mobile communications license from the Irish Telecoms regulator, ComReg. This service will be issued the mobile code 088 in Ireland and will be used for the provision of 4G Mobile communications.^[34][35] Digiweb launched a mobile broadband network using FLASH-OFDM technology at 872 MHz.

On September 20, 2007, Verizon Wireless announced that it plans a joint effort with the Vodafone Group to transition its networks to the 4G standard LTE. On December 9, 2008, Verizon Wireless announced that they intend to build and begin to roll out an LTE network by the end of 2009. Since then, Verizon Wireless has said that they will start their rollout by the end of 2010.

On July 7, 2008, South Korea announced plans to spend 60 billion won, or US$58,000,000, on developing 4G and even 5G technologies, with the goal of having the highest mobile phone market share by 2012, and the hope of an international standard.^[36]

Telus and Bell Canada, the major Canadian cdmaOne and EV-DO carriers, have announced that they will be cooperating towards building a fourth generation (4G) LTE wireless broadband network in Canada. As a transitional measure, they are implementing 3G UMTS that went live in November 2009.^[37]

Sprint offers a 3G/4G connection plan, currently available in select cities in the United States.^[38] It delivers rates up to 10 Mbit/s.

In the United Kingdom, O2 is to use Slough as a guinea pig in testing the 4G network and has called upon Huawei to install LTE technology in six masts across the town to allow people to talk to each other via HD video conferencing and play PlayStation games while on the move.^[39].

Verizon Wireless has announced that it plans to augment its CDMA2000-based EV-DO 3G network in the United States with LTE. AT&T, along with Verizon Wireless has chosen to migrate toward LTE from 2G/GSM and 3G/HSPA by 2011.^[40]

The U.S. FCC is exploring the possibility of deployment and operation of a nationwide 4G public safety network which would allow first responders to seamlessly communicate between agencies and across geographies, regardless of devices. In June 2010 the FCC released a comprehensive white paper which indicates that the 10 MHz of dedicated spectrum currently allocated from the 700 MHz spectrum for public safety will provide adequate capacity and performance necessary for normal communications as well as serious emergency situations.^[41]

Beyond 4G research

A major issue in 4G systems is to make the high bit rates available in a larger portion of the cell, especially to users in an exposed position in between several basestations. In current research, this issue is addressed by macro-diversity techniques, also known as group cooperative relay, and also by beam-division multiple access.^[42]

Pervasive networks are an amorphous and at present entirely hypothetical concept where the user can be simultaneously connected to several wireless access technologies and can seamlessly move between them (See vertical handoff, IEEE 802.21). These access technologies can be Wi-Fi, UMTS, EDGE, or any other future access technology. Included in this concept is also smart-radio (also known as cognitive radio technology) to efficiently manage spectrum use and transmission power as well as the use of mesh routing protocols to create a pervasive network.

4G wireless standards

In September 2009 the technology proposals have been submitted to ITU-R as 4G candidates.^[43] Basically all proposals are based on two technologies:

• LTE Advanced standardized by the 3GPP
• 802.16m standardized by the IEEE

First set of 3GPP requirements on LTE Advanced has been approved in June 2008.^[44] LTE Advanced will be standardized in 2010 as part of the Release 10 of the 3GPP specification. LTE Advanced will be fully built on the existing LTE specification Release 10 and not be defined as a new specification series. A summary of the technologies that have been studied as the basis for LTE Advanced is summarized in a technical report.^[45]

References

Additional resources

• Alcatel-Lucent chair on Flexible Radio, working on the concept of small cells
• Nomor Research: White Paper on LTE Advance the new 4G standard
• Brian Woerner (June 20–22, 2001). "Research Directions for Fourth Generation Wireless" (PDF). Proceedings of the 10th International Workshops on Enabling Technologies: Infrastructure for Collaborative Enterprises (WET ICE ’01). Massachusetts Institute of Technology, Cambridge, MA, USA. http://csdl2.computer.org/comp/proceedings/wetice/2001/1269/00/12690060.pdf.  (118kb)
• Sajal Kumar Das, John Wiley & Sons (April 2010): "Mobile Handset Design", ISBN 978-0470824672
• Suk Yu Hui; Kai Hau Yeung (December 2003). "Challenges in the migration to 4G mobile systems". Communications Magazine, IEEE (City Univ. of Hong Kong, China) 41: 54. doi:10.1109/MCOM.2003.1252799. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1252799&isnumber=28028. 
• "4G Mobile". Alcatel-Lucent. 2005-06-13. http://www.alcatel.com/publications/abstract.jhtml?repositoryItem=tcm%3A172-262211635. 
• Will Knight (2005-09-02). "4G prototype testing". New Scientist. http://www.newscientist.com/article.ns?id=dn7943. 
• "Caribbean telecoms to invest in 4G wireless networks". Caribbean Net News. 2006-06-27. http://www.caribbeannetnews.com/cgi-script/csArticles/articles/000021/002142.htm. 
• "High speed mobile network to launch in Jersey". BBC News. 2010-03-19. http://news.bbc.co.uk/local/jersey/hi/people_and_places/arts_and_culture/newsid_8574000/8574436.stm. 
• "Future use of 4G Femtocells". 2010-03-10 ]. http://www.ict-befemto.eu/.