4G

4G (also known as beyond 3G), an acronym for Fourth-Generation Communications System, is a term used to describe the next step in wireless communications. A 4G system will be able to provide a comprehensive IP solution where voice, data and streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and at higher data rates than previous generations. There is no formal definition for what 4G is; however, there are certain objectives that are projected for 4G.

These objectives include: that 4G will be a fully IP-based integrated system. This will be achieved after wired and wireless technologies converge and will be capable of providing 100 Mbit/s and 1 Gbit/s speeds both indoors and outdoors, with premium quality and high security. 4G will offer all types of services at an affordable cost.


Objective and Approach
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Objectives
4G is being developed to accommodate the quality of service (QoS) and rate requirements set by forthcoming applications like wireless broadband access, Multimedia Messaging Service, video chat, mobile TV, High definition TV content, DVB, minimal service like voice and data, and other streaming services for "anytime-anywhere". The 4G working group has defined the following as objectives of the 4G wireless communication standard:

-A spectrally efficient system (in bits/s/Hz and bit/s/Hz/site),
-High network capacity: more simultaneous users per cell,
-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,
-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.
In summary, the 4G system should dynamically share and utilise network resources to meet the minimal requirements of all the 4G enabled users.

Approaches
As described in 4G consortia including WINNER, WINNER - Towards Ubiquitous Wireless Access, and WWRF, a key technology based approach is summarized as follows, where Wireless-World-Initiative-New-Radio (WINNER) is a consortium to enhance mobile communication systems.

Consideration points
-Coverage, radio environment, spectrum, services, business models and deployment types, users

Principal technologies
-Baseband techniques
--OFDM: To explot the frequency selective channel property
--MIMO: To attain ultra high spectral efficiency
--Turbo principle: To minimize the required SNR at the reception side
-Adaptive radio interface
-Modulation, MIMO spatial processing including multi-antenna and multi-user MIMO, relaying including fixed relay networks (FRNs) and the cooperative relaying concept, multi-mode protocol
It introduces a single new ubiquitous radio access system concept, which is flexible to a variety levels of beyond 3G wireless systems.

Wireless System Evolution
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First generation: Almost all of the systems from this generation were analog systems where voice was considered to be the main traffic. These systems could often be listened to by third parties. some of the standards are NMT, AMPS, Hicap, CDPD, Mobitex, DataTac

Second generation: All the standards belonging to this generation are commercial centric and they are digital in form. Around 60% of the current market is dominated by European standards. The second generation standards are GSM, iDEN, D-AMPS, IS-95, PDC, CSD, PHS, GPRS, HSCSD, and WiDEN.

Third generation: To meet the growing demands in the number of subscribers (increase in network capacity), rates required for high speed data transfer and multimedia applications, 3G standards started evolving. The systems in this standard are basically a linear enhancement of 2G systems. They are based on two parallel backbone infrastructures, one consisting of circuit switched nodes, and one of packet oriented nodes. The ITU defines a specific set of air interface technologies as third generation, as part of the IMT-2000 initiative. Currently, transition is happening from 2G to 3G systems. As a part of this transition, lot of technologies are being standardized. From 2G to 3G: 2.75G - EDGE and EGPRS, 3G - CDMA 2000,W-CDMA or UMTS (3GSM), FOMA, 1xEV-DO/IS-856, TD-SCDMA, GAN/UMA. Similarly from 3G to 4G: 3.5G - HSDPA, HSUPA, Super3G - HSOPA/LTE

Fourth generation: According to the 4G working groups, the infrastructure and the terminals of 4G will have almost all the standards from 2G to 4G implemented. Even though the legacy systems are in place to be adopted in 4G for the existing legacy users, going forward the infrastructure will however only be packet based, all-IP. Also, some proposals suggest having an open platform where the new innovations and evolutions can fit. The technologies which are being considered as pre-4G are used in the following standard version: WiMax, WiBro, 3GPPLong Term Evolution and 3GPP2 Ultra Mobile Broadband.

Components
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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 a new access scheme called CDMA. Usage of CDMA increased the system capacity and also placed a soft limit on it rather than the hard limit. Data rate is also increased as this access scheme is efficient enough to handle the multipath channel. This enabled the third generation systems to used CDMA as the access scheme IS-2000, UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA. The only issue with the CDMA is that it suffers from poor spectrum flexibility and scalability.

Recently, new access schemes like Orthoganal FDMA, Single Carrier FDMA, Interleaved FDMA and Multi-carrier code division multiple access are gaining more importance for the next generation systems. WiMax is using OFDMA in the downlink and in the uplink. For the next generation UMTS, OFDMA is being considered 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
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.

It is generally believed that 4th generation wireless networks will support a greater number of wireless devices that are directly addressable and routable. Therefore, in the context of 4G, IPv6 is an important network layer technology and standard that can 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.

In the context of 4G, IPv6 also enables a number of applications with better multicast, security, and route optimization capabilities. With the available address space and number of addressing bits in IPv6, many innovative coding schemes can be developed for 4G devices and applications that could aid deployment of 4G networks and services.

Advanced Antenna Systems
The performance of radio communications obviously depends on the advances of an antenna system, refer to 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 90s, 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 increases the data rate into multiple folds with the number equal to minimum of the number of transmit and receive antennas. This is called MIMO (as a branch of intelligent antenna). 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 necessary require the channel knowledge at the transmit. The other category is closed-loop multiple antenna technologies which use the 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.

Developments
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The Japanese company NTT DoCoMo has been testing 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 recently reached 5 Gbit/s with 12x12 MIMO while moving at 10 km/h, and is planning on releasing the first commercial network in 2010.

Digiweb, an Irish fixed and wireless broadband company, has 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.

Pervasive networks are an amorphous and presently entirely hypothetical concept where the user can be simultaneously connected to several wireless access technologies and can seamlessly move between them (See handover, 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.

Sprint plans to launch 4G services in trial markets by the end of 2007 with plans to deploy a network that reaches as many as 100 million people in 2008.... and has announced WiMax service called Xohm. Tested in Chicago, this speed was clocked at 100 Mbit/s.

Verizon Wireless announced on September 20, 2007 that it plans a joint effort with the Vodafone Group to transition its networks to the 4G standard LTE. The time of this transition has yet to be announced.

The German WiMAX operator Deutsche Breitband Dienste (DBD) has launched WiMAX services (DSLonair) in Magdeburg and Dessau. The subscribers are offered a tariff plan costing 9.95 euros per month offering 2 Mbit/s download / 300 kbit/s upload connection speeds and 1.5 GB monthly traffic. The subscribers are also charged a 16.99 euro one-time fee and 69.90 euro for the equipment and installation.DBD received additional national licenses for WiMAX in December 2006 and have already launched the services in Berlin, Leipzig and Dresden.

American WiMAX services provider Clearwire made its debut on Nasdaq in New York on March 8, 2007. The IPO was underwritten by Merrill Lynch, Morgan Stanley and JP Morgan. Clearwire sold 24 million shares at a price of $25 per share. This adds $600 million in cash to Clearwire, and gives the company a market valuation of just over $3.9 billion.

Applications
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The killer application of 4G is not clear, though the improved bandwidths and data throughput offered by 4G networks should provide opportunities for previously impossible products and services to be released. Perhaps the "killer application" is simply to have mobile always on Internet, no walled garden and reasonable flat rate per month charge. Existing 2.5G/3G/3.5G phone operator based services are often expensive, and limited in application.

Already at rates of 15-30 Mbit/s, 4G should be able to provide users with streaming high-definition television. At rates of 100 Mbit/s, the content of a DVD, for example a movie, can be downloaded within about 5 minutes for offline access.

Pre-4G Wireless Standards
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According to a Visant Strategies study there will be multiple competitors in this space:

-WiMAX - 7.2 million units by 2010 (May include fixed and mobile)
-Flash-OFDM - 13 million subscribers in 2010 (only Mobile)
-3GPP Long Term Evolution of UMTS in 3GPP - valued at US$2 billion in 2010 (~30% of the world population)
-UMB in 3GPP2
-IEEE 802.20
Fixed WiMax and Mobile WiMax are different systems, as of July 2007, all the deployed WiMax is "Fixed Wireless" and is thus not yet 4G (IMT-advanced) although it can be seen as one of the 4G standards being considered.

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