3GPP LTE (Long Term Evolution) is the name given to a project within the Third Generation Partnership Project to improve the UMTS
mobile phone standard to cope with future technology evolutions. Goals
include improving spectral efficiency, lowering costs, improving
services, making use of new spectrum and refarmed spectrum
opportunities, and better integration with other open standards. The
LTE air interface will be added to the specification in Release 8 and
can be found in the 36-series  of the 3GPP
specifications. Although an evolution of UMTS, the LTE air interface is
a completely new systems based on OFDMA in the downlink and SC-FDMA
(DFTS-FDMA) in the uplink that efficiently supports multi-antenna
techologies (MIMO). The architecture that will result from this work is called EPS (Evolved Packet System) and comprises E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved Packet Core) on the core side.
While 3GPP Release 8 has yet to be ratified as a standard, much of
the standard will be oriented around upgrading UMTS to a so-called fourth generation mobile communications technology, essentially a wireless broadband Internet system with voice and other services built on top.
The standard includes:
Peak download rates of 326.4 Mbit/s for 4x4 antennas, 172.8 Mbit/s for 2x2 antennas for every 20 MHz of spectrum. 
Peak upload rates of 86.4 Mbit/s for every 20 MHz of spectrum.
5 different terminal classes have been defined from a voice centric
class up to a high end terminal that supports the peak data rates. All
terminal will be able to process 20 MHz bandwidth.
At least 200 active users in every 5 MHz cell. (i.e., 200 active data clients)
Sub-5ms latency for small IP packets
Increased spectrum flexibility, with spectrum slices as small as 1.5 MHz (and as large as 20 MHz) supported (W-CDMA
requires 5 MHz slices, leading to some problems with roll-outs of the
technology in countries where 5 MHz is a commonly allocated amount of
spectrum, and is frequently already in use with legacy standards such
as 2G GSM and cdmaOne.) Limiting sizes to 5 MHz also limited the amount of bandwidth per handset
Optimal cell size of 5 km, 30 km sizes with reasonable performance,
and up to 100 km cell sizes supported with acceptable performance
Co-existence with legacy standards (users can transparently start a
call or transfer of data in an area using an LTE standard, and, should
coverage be unavailable, continue the operation without any action on
their part using GSM/GPRS or W-CDMA-based UMTS or even 3GPP2 networks such as CDMA or EV-DO)
Supports MBSFN (Multicast Broadcast Single Frequency Network). This
feature can deliver services such as Mobile TV using the LTE
infrastructure, and is a competitor for DVB-H-based TV broadcast.
A large amount of the work is aimed at simplifying the architecture
of the system, as it transits from the existing UMTS circuit + packet
switching combined network, to an all-IP flat architecture system.
Preliminary requirements have been released for LTE Advanced, expected to be part of 3GPP Release 10.
If possible LTE Advanced will be a software upgrade for LTE networks
and enable peak download rates over 1Gbit/s that fully supports the 4G
requirements as defined by the ITU-R. It also targets faster switching
between power states and improved performance at the cell edge. A first
set of requirements has been approved in June 2008. 
The LTE standard reached the functional freeze milestone in March
2008. Stage 2 Freeze is scheduled for mid 2008 and official
ratification in December 2008. The standard has been complete enough
that hardware designers have been designing chipsets, test equipment
and base stations for some time. LTE test equipment has been shipping
from several vendors since early 2008 & Motorola demonstrated a LTE RAN standard compliant eNodeB and LTE chipset at Mobile World Congress 2008.
An "All IP Network" (AIPN)
A characteristic of so-called "4G" networks such as LTE is that they are fundamentally based upon TCP/IP,
the core protocol of the Internet, with higher level services such as
voice, video, and messaging, built on top of this. In 2004, the 3GPP
proposed this as the future of UMTS and began feasibility studies into
the so-called All IP Network (AIPN.) These proposals, which included recommendations in 2005 for 3GPP Release 7 (though some aspects were in releases as early as 4),
form the basis of the effort to build the higher level protocols of
evolved UMTS. The LTE part of this effort is called the 3GPP System Architecture Evolution.
At a glance, the UMTS back-end becomes accessible via a variety of means, such as GSM's/UMTS's own radio network (GERAN, UTRAN, and E-UTRAN), WiFi, and even competing legacy systems such as CDMA2000 and WiMAX.
Users of non-UMTS radio networks would be provided with an entry-point
into the IP network, with different levels of security depending on the
trustworthiness of the network being used to make the connection. Users
networks would use an integrated system where all authentication at
every level of the system is covered by a single system, while users
accessing the UMTS network via WiMAX and other similar technologies
would handle the WiMAX connection one way (for example, authenticating
themselves via a MAC or ESN address) and the UMTS link-up another way.
E-UTRA Air Interface
Release 8's air interface, E-UTRA (Evolved UTRA, the E- prefix being common to the evolved equivalents of older UMTS
components) would be used by UMTS operators deploying their own
wireless networks. It's important to note that Release 8 is intended
for use over any IP network, including WiMAX and WiFi, and even wired networks.
The proposed E-UTRA system uses OFDMA for the downlink (tower to handset) and Single Carrier FDMA (SC-FDMA) for the uplink and employs MIMO with up to four antennas per station. The channel coding scheme for transport blocks is turbo coding and a contention-free quadratic permutation polynomial (QPP) turbo code internal interleaver.
The use of OFDM, a system where the available spectrum is divided
into thousands of very thin carriers, each on a different frequency,
each carrying a part of the signal, enables E-UTRA to be much more
flexible in its use of spectrum than the older CDMA based systems that dominated 3G.
CDMA networks require large blocks of spectrum to be allocated to each
carrier, to maintain high chip rates, and thus maximize efficiency.
Building radios capable of coping with different chip rates (and
spectrum bandwidths) is more complex than creating radios that only
send and receive one size of carrier, so generally CDMA based systems
standardize both. Standardizing on a fixed spectrum slice has
consequences for the operators deploying the system: too narrow a
spectrum slice would mean the efficiency and maximum bandwidth per
handset suffers; too wide a spectrum slice, and there are deployment
issues for operators short on spectrum. This became a major issue with
the US roll-out of UMTS over W-CDMA, where W-CDMA's 5 MHz requirement often left no room in some markets for operators to co-deploy it with existing GSM standards.
OFDM has a Link spectral efficiency greater than CDMA, and when combined with modulation formats such as 64QAM, and techniques as MIMO, E-UTRA has proven to be considerably more efficient than W-CDMA with HSDPA and HSUPA.
The subcarrier spacing in the OFDM
downlink is 15 kHz and there is a maximum of 1200 subcarriers
available. Number of subcarriers is dependent on the used bandwidth
(1.4MHz and up to 20Mhz),subcarriers don't occupy 100% of the used
bandwidth as Cyclic Prefixes (Guards) occupies a part of it.The Mobile
devices must be capable of receiving all subcarriers but a base station
need only support transmitting 72 subcarriers. The transmission is
divided in time into time slots of duration 0.5 ms and subframes of
duration 1.0 ms. A radio frame is 10 ms long.
Supported modulation formats on the downlink data channels are QPSK, 16QAM and 64QAM.
For MIMO operation, a distinction is made between single user MIMO, for enhancing one users data throughput, and multi user MIMO for enhancing the cell throughput.
The currently proposed uplink uses SC-FDMA multiplexing, and QPSK or 16QAM (64QAM optional) modulation. SC-FDMA is used because it has a low Peak-to-Average Power Ratio
(PAPR). Each mobile device has at least one transmitter. If virtual
MIMO / Spatial division multiple access (SDMA) is introduced the data
rate in the uplink direction can be increased depending on the number
of antennas at the base station. With this technology more than one
mobile can reuse the same resources.
In September 2006, Siemens Networks (today Nokia Siemens Networks)
showed in collaboration with Nomor Research the first live emulation of
a LTE network to the media and investors. As live applications two
users streaming an HD-TV video in the downlink and playing an
interactive game in the uplink have been demonstrated.
The first presentation of an LTE demonstrator with HDTV streaming (>30 Mbit/s), video supervision and Mobile IP-based handover between the LTE radio demonstrator and the commercially available HSDPA radio system was shown during the ITU trade fair in Hong Kong in December 2006 by Siemens Communication Department.
In September 2007, NTT Docomo demonstrated LTE data rates of 200 Mbit/s with power consumption below 100mW during the test.
demonstrated how LTE can accelerate the delivery of personal media
experience with HD video demo streaming, HD video blogging, Online
gaming and VoIP over LTE running a RAN standard compliant LTE network
& LTE chipset. 
Ericsson demonstrated a portable LTE terminal showing streaming video. 
However, several networks that don't use these standards are also upgrading to LTE:
Verizon Wireless, Bell Mobility, the newly formed China Telecom/Unicom and Japan's KDDI
have announced they have chosen LTE as their 4G network technology.
This is significant, because these are CDMA carriers and are switching
networking technologies to match what will likely be the 4G standard
worldwide. They have chosen to take the natural GSM evolution path as opposed to the 3GPP2CDMA2000 evolution path Ultra Mobile Broadband (UMB). Verizon Wireless plans to begin LTE trials in 2008. Bell Mobility plans to start LTE deployment in 2009-2010.
Telus Mobility has announced that it will adopt LTE as its 4G wireless standard.
It has been suggested that TTCN-3
test specification language will be used for the purposes of LTE
conformance testing. As of March 2008, TTCN-3 test suite development
has been underway at ETSI.