Editing 4G (section)

== Principal technologies in all candidate systems ==
{{more citations needed section|date=August 2015}}

=== Key features ===
The following key features can be observed in all suggested 4G technologies:
* Physical layer transmission techniques are as follows:<ref name="WWRF WG5">{{cite web |last1=Fettweis |first1=G. |last2=Zimmermann |first2=E. |last3=Bonneville |first3=H. |last4=Schott |first4=W. |last5=Gosse |first5=K. |last6=de Courville |first6=M. |year=2004 |title=High Throughput WLAN/WPAN |url=http://www.wireless-world-research.org/fileadmin/sites/default/files/about_the_forum/WG/WG5/Briefings/WG5-br2-High_Throughput_WLAN_WPAN-V2004.pdf |archive-url=https://web.archive.org/web/20080216083847/http://www.wireless-world-research.org/fileadmin/sites/default/files/about_the_forum/WG/WG5/Briefings/WG5-br2-High_Throughput_WLAN_WPAN-V2004.pdf |archive-date=2008-02-16 |website=WWRF}}</ref>
** [[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]]) in the downlink or ''single-carrier frequency-domain-equalization'' (SC-FDE) in the uplink: 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.<ref>{{Cite web |last=Dahmen-Lhuissier |first=Sabine |title=4th Generation (LTE) |url=https://www.etsi.org/technologies/mobile/4G?jjj=1719328472364 |access-date=2024-06-25 |website=ETSI |language=en-gb}}</ref>
** [[turbo code|Turbo principle]] [[error-correcting code]]s: To minimize the required [[Signal-to-noise ratio|SNR]] at the reception side
* [[Channel-dependent scheduling]]: To use the time-varying channel
* [[Link adaptation]]: [[Adaptive modulation]] and error-correcting codes
* [[Mobile IP]] utilized for mobility
* IP-based [[femtocell]]s (home nodes connected to fixed Internet broadband infrastructure)

As opposed to earlier generations, 4G systems do not support circuit switched telephony. IEEE 802.20, UMB and OFDM standards<ref>{{cite web |title=4G standards that lack cooperative relaying |url=http://tikonaplans.blogspot.in/2012/07/4g-standards-that-lack-cooperative.html|date=July 5, 2012}}</ref> lack [[soft-handover]] support, also known as [[Cooperative wireless communications|cooperative relaying]].

=== Multiplexing and access schemes ===
{{Importance section|date=May 2010}}
Recently, new access schemes like [[OFDMA|Orthogonal FDMA]] (OFDMA), [[SC-FDMA|Single Carrier FDMA]] (SC-FDMA), Interleaved FDMA, and [[Multi-carrier code-division multiple access|Multi-carrier CDMA]] (MC-CDMA) are gaining more importance for the next generation systems. These are based on efficient [[Fast Fourier transform|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 adaptive traffic scheduling.

[[WiMax]] is using OFDMA in the downlink and in the uplink. For the [[LTE (telecommunication)]], OFDMA is used for the downlink; by contrast, [[Single-carrier FDMA]] is used for the uplink since OFDMA contributes more to the [[Crest factor|PAPR]] related issues and results in nonlinear operation of amplifiers. IFDMA provides less power fluctuation and thus requires energy-inefficient linear amplifiers. Similarly, MC-CDMA is in the proposal for the [[802.20|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 require 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 64[[QAM]] 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, 4G is based on packet switching ''only''. This requires [[Network latency|low-latency]] data transmission.

As IPv4 addresses are (nearly) [[IPv4 address exhaustion|exhausted]],<ref group=Note>The exact exhaustion status is difficult to determine, as it is unknown how many unused addresses exist at ISPs, and how many of the addresses that are permanently unused by their owners can still be freed and transferred to others.</ref> [[IPv6]] is essential to support the large number of wireless-enabled devices that communicate using IP. By increasing the number of [[IP address]]es available, IPv6 removes the need for [[network address translation]] (NAT), a method of sharing a limited number of addresses among a larger group of devices, which has [[network address translation#Issues and limitations|a number of problems and limitations]]. When using IPv6, some kind of NAT is still required for communication with legacy IPv4 devices that are not also IPv6-connected.

{{As of|2009|06}}, [[Verizon Communications|Verizon]] has posted specifications that require any 4G devices on its network to support IPv6.<ref>
{{cite web
    | url = http://lteuniversity.com/get_trained/expert_opinion1/b/hoomanrazani/archive/2009/06/15/lte-device-requirements-for-verizon-wireless.aspx
    | title = LTE Device Requirements for Verizon Wireless
    | date = June 16, 2009
    | access-date = April 23, 2024
    | archive-url = https://web.archive.org/web/20180306142655/http://lteuniversity.com/get_trained/expert_opinion1/b/hoomanrazani/archive/2009/06/15/lte-device-requirements-for-verizon-wireless.aspx
    | archive-date = March 6, 2018
}}
</ref><ref>
{{cite web
    | last = Morr
    | first = Derek
    | title = Verizon mandates IPv6 support for next-gen cell phones
    | date =June 9, 2009
    | url = http://www.personal.psu.edu/dvm105/blogs/ipv6/2009/06/verizon-mandates-ipv6-support.html
    | access-date = June 10, 2009
}}
</ref>

=== Advanced antenna systems ===
{{Main|MIMO|Multi-user MIMO}}

The performance of radio communications depends on an antenna system, termed [[smart antenna|smart]] or [[intelligent antenna]]. Recently, [[Multiple antenna research|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 for 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.

=== Open-wireless Architecture and Software-defined radio (SDR) ===
One of the key technologies for 4G and beyond is called Open Wireless Architecture (OWA), supporting multiple wireless air interfaces in an [[open architecture]] platform.

[[Software-defined radio|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.