3GPP LTE Long Term Evolution
LTE (Long Term Evolution) is the preferred development path of GSM/WCDMA/HSPA networks currently deployed, and an option for evolution of CDMA networks. This will enable networks to offer the higher data throughput to mobile terminals needed in order to deliver new and advanced mobile broadband services.
The primary objectives of this network evolution are to provide these services with a quality at least equivalent to what an end-user can enjoy today using their fixed broadband access at home, and to reduce operational expenses by means of introducing flat IP architecture.
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 resulting 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.
This is a 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 resulting 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 4×4 antennas, 172.8 Mbit/s for 2×2 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. Sub-5ms latency for small IP packets Increased spectrum flexibility, with spectrum slices as small as 1.5 MHz (& 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 cdmaOne
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.
PU2RC as an practical solution for MU-MIMO has been adopted to use in 3GPP LTE standard. The detailed procedure for the general MU-MIMO operation is handed to the next release, 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 Freezed 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 shipedfrom several vendors since early 2008 & Motorola demonstrated a LTE RAN standard compliant eNodeB and LTE chipset
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 of GSM/UMTS 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),
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).