E-UTRA

e-UTRAN or eUTRAN is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. It is the abbreviation for evolved UMTS Terrestrial Radio Access Network, also referred to as the 3GPP work item on the Long Term Evolution (LTE) also known as the Evolved Universal Terrestrial Radio Access (E-UTRA) in early drafts of the 3GPP LTE specification.

It is a radio access network standard meant to be a replacement of the UMTS, HSDPA and HSUPA technologies specified in 3GPP releases 5 and beyond. Unlike HSPA, LTE's E-UTRA is an entirely new air interface system, unrelated to and incompatible with W-CDMA. It provides higher data rates, lower latency and is optimized for packet data. It uses OFDMA radio-access for the downlink and SC-FDMA on the uplink. Trials started in 2008.

EUTRAN architecture as part of a LTE and SAE network

Features

EUTRAN has the following features:

• Peak download rates of 292 Mbit/s for 4x4 antennas, 143 Mbit/s for 2x2 antennas with 20 MHz of spectrum.
• Peak upload rates of 71 Mbit/s for every 20 MHz of spectrum.
• Low data transfer latencies (sub-5ms latency for small IP packets in optimal conditions), lower latencies for handover and connection setup time.
• Support for terminals moving at up to 350 Km/h or 500 km/h depending on the frequency band.
• Support for both FDD and TDD duplexes as well as half-duplex FDD with the same radio access technology
• Support for all frequency bands currently used by IMT systems by ITU-R.
• Flexible bandwidth: 1.4 MHz, 3 MHz, 5 MHz 15 MHz and 20 MHz are standardized. By comparison, W-CDMA uses fixed size 5 MHz chunks of spectrum.
• Increased spectral efficiency at 2-5 times more than in 3GPP (HSPA) release 6
• Support of cell sizes from tens of meters of radius (femto and picocells) up to over 100 km radius macrocells
• Simplified architecture: The network side of EUTRAN is composed only by the enodeBs
• Support for inter-operation with other systems (e.g. GSM/EDGE, UMTS, CDMA2000, WiMAX...)
• Packet switched radio interface.

Rationale for E-UTRA

Although UMTS, with HSDPA and HSUPA and their evolution, deliver high data transfer rates, wireless data usage is expected to continue increasing significantly over the next years due to the increase offering and demand of services and content on the move and the continued reduction of costs for the final user. This increase is expected to require not only faster networks and radio interfaces but also more cost efficient than what is possible by the evolution of the current standards. Thus the 3GPP consortium set the requirements for a new radio interface (EUTRAN) and core network evolution (System Architecture Evolution SAE) that would fulfill this need.

This improvements in performance allow wireless operators to offer quadruple play services - voice, high-speed interactive applications including large data transfer and feature-rich IPTV with full mobility.

Starting with the 3GPP Release 8, e-UTRA is designed to provide a single evolution path for the GSM/EDGE, UMTS/HSPA, CDMA2000/EV-DO and TD-SCDMA radio interfaces, providing increases in data speeds, and spectral efficiency, and allowing the provision of more functionality.

Architecture

EUTRAN consists only of enodeBs on the network side. The enodeB performs tasks similar to those performed by the nodeBs and RNC (radio network controller) together in UTRAN. The aim of this simplification is to reduce the latency of all radio interface operations. eNodeBs are connected to each other via the X2 interface, and they connect to the packet switched (PS) core network via the S1 interface.

EUTRAN protocol stack

EUTRAN protocol stack

The EUTRAN protocol stack consist of :

• Physical layer : Carries all information from the MAC transport channels over the air interface. Takes care of the link adaptation (AMC), power control, cell search (for initial synchronization and handover purposes) and other measurements (inside the LTE system and between systems) for the RRC layer.
• MAC : The MAC sublayer offers a set of logical channels to the RLC sublayer that it multiplexes into the physical layer transport channels. It also manages the HARQ error correction, handles the prioritization of the logical channels for the same UE and the dynamic scheduling between UEs, etc..
• RLC : It transports the PDCP's PDUs. It can work in 3 different modes depending on the reliability provided. Depending on this mode it can provide: ARQ error correction, segmentation/concatenation of PDUs, reordering for in-sequence delivery, duplicate detection, etc...
• PDCP: For the RRC layer it provides transport of its data with ciphering and integrity protection. And for the IP layer transport of the IP packets, with ROHC header compression, ciphering, and depending on the RLC mode in-sequence delivery, duplicate detection and retransmission of its own SDUs during handover.
• RRC: Between others it takes care of: the broadcasted system information related to the access stratum and transport of the non-access stratum (NAS) messages, paging, establishment and release of the RRC connection, security key management, handover, UE measurements related to inter-system (inter-RAT) mobibility, QoS, etc..

Interfacing layers to the EUTRAN protocol stack:

• NAS: Protocol between the UE and the MME on the network side (outside of EUTRAN). Between others performs authentication of the UE, security control and generates part of the paging messages.
• IP

Physical layer (L1) design

E-UTRA uses orthogonal frequency-division multiplexing (OFDM), multiple-input multiple-output (MIMO) antenna technology depending on the terminal category and can use as well beamforming for the downlink to support more users, higher data rates and lower processing power required on each handset. For the UL it uses both OFDM and Single Carrier FDMA (SC-FDMA) depending on the physical channel.

In the uplink LTE uses both OFDMA and a precoded version of OFDM called Single Carrier Frequency Division Multiple Access (SC-FDMA) depending on the channel. This is to compensate for a drawback with normal OFDM, which has a very high peak-to-average power ratio (PAPR). High PAPR requires more expensive and inefficient power amplifiers with high requirements on linearity, which increases the cost of the terminal and drains the battery faster. For the uplink, in release 8 and 9 multi user MIMO / Spatial division multiple access (SDMA) is supported; release 10 introduces also SU-MIMO.

In both OFDM and SCFDMA transmission modes a cyclic prefix is appended to the transmitted symbols. Two different lengths of the cyclic prefix are available to support different channel spreads due to the cell size and propagation environment. These are a normal cyclic prefix of 4.7µs, and a extended cyclic prefix of 16.6µs.

LTE supports both (FDD) and (TDD) modes. While FDD makes use of paired spectra for UL and DL transmission separated by a duplex frequency gap, TDD uses the same frequency carrier to, alternatively in time, transmit data from the base station to the terminal and viceversa. Both modes have its own frame structure within LTE and these are aligned with each other meaning that similar hardware can be used in the base stations and terminals to allow for economy of scale. The TDD mode in LTE is aligned with TD-SCDMA as well allowing for coexistence.

The LTE transmission is structured in the time domain in radio frames. Each of these radio frames is 10 ms long and consists of 10 sub frames of 1 ms each. For non-MBMS subframes the OFDM subcarrier spacing in the frequency domain is 15 kHz. Twelve of these subcarriers together are called a resource block. A LTE terminal can be allocated in the downlink or uplink a minimum of 1 resource block during 1 subframe.

All L1 transport data is encoded using turbo coding and a contention-free quadratic permutation polynomial (QPP) turbo code internal interleaver. L1 HARQ with 8 (FDD) or up to 15 (TDD) processes is used for the downlink and up to 8 processes for the UL

EUTRAN physical channels and signals

Downlink (DL)

In the downlink there are several physical channels:

• The Physical Control Channel (PDCCH) carries between others the downlink allocation information, uplink allocation grants for the terminal.
• The Physical Control Format Indicator Channel (PCFICH) used to signal the length of the PDCCH.
• The Physical Hybrid ARQ Indicator Channel (PHICH) used to carry the acknowledges from the uplink transmissions.
• The Physical Downlink Shared Channel (PDSCH) is used for L1 transport data transmission. Supported modulation formats on the PDSCH are QPSK, 16QAM and 64QAM.
• The Physical Multicast Channel (PMCH) is used for broadcast transmission using a Single Frequency Network
• The Physical Broadcast Channel (PBCH) is used to broadcast the basic system information within the cell

And the following signals:

• The synchronization (PSS and SSS) are meant for the UE to discover the LTE cell and do the initial synchronization.
• The reference signals (cell specific, MBSFN, and UE specific) are used by the UE to estimate the channel for the different channels.
• Positioning reference signals (PRS), added in release 9, meant to be used by the UE for OTDOA positioning (a type of multilateration)

Uplink (UL)

In the uplink there are three physical channels:

• Physical Random Access Channel (PRACH) is used for initial access and when the UE losses its uplink synchronization,
• Physical Uplink Shared Channel (PUSCH) carries the L1 UL transport data together with control information. Supported modulation formats on the PDSCH are QPSK, 16QAM and depending on the user equipment category 64QAM. PUSCH is the only channel, which because of its greater BW, uses SC-FDMA
• Physical Uplink Control Channel (PUCCH) carries control information. Note that the Uplink control information consists only on DL acknowledges as well as CQI related reports as all the UL coding and allocation parameters are known by the network side and signaled to the UE in the PDCCH.

And the following signals:

• Reference signals (RS) used by the enodeB to estimate the uplink channel to decode the terminal uplink transmission.
• Sounding reference signals (SRS) used by the enodeB to estimate the uplink channel conditions for each user to decide the best uplink scheduling.

User Equipment (UE) categories

For release 8 and 9, 5 LTE UE categories are defined depending on the maximum peak data rate and MIMO capabilities support.

User Equipment Category	Maximum L1 datarate Downlink	Maximum number of DL MIMO layers	Maximum L1 datarate Uplink
Category 1	9.8 Mbits/s	1	4.9 Mbit/s
Category 2	48 Mbits/s	2	24 Mbit/s
Category 3	97 Mbits/s	2	48 Mbit/s
Category 4	143 Mbits/s	2	48 Mbit/s
Category 5	292 Mbits/s	4	71 Mbit/s

Note: These are L1 transport data data rates not including the different protocol layers overhead.

EUTRAN releases

As the rest of the 3GPP standard parts E-UTRA is structured in releases.

• Release 8, frozen in 2008, specified the first LTE standard
• Release 9, frozen in 2009, included some additions to the physical layer like dual layer (MIMO) beamforming transmission or positioning support
• Release 10, frozen in 2011, introduces to the standard several LTE Advanced features like carrier aggregation, uplink SU-MIMO or relays, aiming to a considerable L1 peak data rate increase.

All LTE releases have been designed so far keeping backward compatibility in mind. That is, a release 8 compliant terminal will work in a release 10 network, while release 10 terminals would be able to use its extra functionality.

Frequency bands and channel bandwidths

From Tables 5.5-1 "E-UTRA Operating Bands" and 5.6.1-1 "E-UTRA Channel Bandwidth" of 3GPP TS 36.101, the following table lists the specified frequency bands of LTE and the channel bandwidths each listed band supports:

EUTRAN Operating Band	Uplink (UL) Operating Band BS Receive UE Transmit	Downlink (DL) Operating Band BS Transmit UE Receive	Duplex Mode	Channel Bandwidths (MHz)	Alias	Region(s)
001 I (1)	017 1920 MHz to 1980 MHz	017 2110 MHz to 2170 MHz	FDD	5, 10, 15, 20	UMTS IMT, "2100"	Japan, Europe, Asia
002 II (2)	012 1850 MHz to 1910 MHz	012 1930 MHz to 1990 MHz	FDD	1.4, 3, 5, 10, 15, 20	PCS, "1900"	Canada, US, Latin America
003 III (3)	010 1710 MHz to 1785 MHz	010 1805 MHz to 1880 MHz	FDD	1.4, 3, 5, 10, 15, 20	DCS 1800, "1800"	Finland, Hong Kong, Germany
004 IV (4)	009 1710 MHz to 1755 MHz	013 2110 MHz to 2155 MHz	FDD	1.4, 3, 5, 10, 15, 20	AWS, "1.7/2.1 GHz"	Canada, US, Latin America
005 V (5)	006 824 MHz to 849 MHz	006 869 MHz to 894 MHz	FDD	1.4, 3, 5, 10	Cellular 850, UMTS850	Canada, US, Australia, Chile
006 VI (6)	007 830 MHz to 840 MHz	007 875 MHz to 885 MHz	FDD	5, 10	UMTS800	Japan
007 VII (7)	021 2500 MHz to 2570 MHz	021 2620 MHz to 2690 MHz	FDD	5, 10, 15, 20	IMT-E, "2.6 GHz"	EU
008 VIII (8)	008880 MHz to 915 MHz	008925 MHz to 960 MHz	FDD	1.4, 3, 5, 10	GSM, UMTS900, EGSM900	EU, Latin America
009 IX (9)	012 1749.9 MHz to 1784.9 MHz	011 1844.9 MHz to 1879.9 MHz	FDD	5, 10, 15, 20	UMTS1700	Canada, US, Japan
010 X (10)	011 1710 MHz to 1770 MHz	013 2110 MHz to 2170 MHz	FDD	5, 10, 15, 20	UMTS, IMT 2000	Brazil, Uruguay, Ecuador, Peru
011 XI (11)	009 1427.9 MHz to 1447.9 MHz	009 1475.9 MHz to 1495.9 MHz	FDD	5, 10	PDC	Japan (Softbank, KDDI, DoCoMo)
012 XII (12)	001 698 MHz to 716 MHz	001 728 MHz to 746 MHz	FDD	1.4, 3, 5, 10	lower SMH blocks A/B/C	US
013 XIII (13)	003 777 MHz to 787 MHz	003 746 MHz to 756 MHz	FDD	5, 10	upper SMH block C	US
014 XIV (14)	004 788 MHz to 798 MHz	004 758 MHz to 768 MHz	FDD	5, 10	upper SMH block D	US
017 XVII (17)	002 704 MHz to 716 MHz	002 734 MHz to 746 MHz	FDD	5, 10
018 XVIII (18)	002 815 MHz to 830 MHz	002 860 MHz to 875 MHz	FDD	5, 10, 15
019 XIX (19)	002 830 MHz to 845 MHz	002 875 MHz to 890 MHz	FDD	5, 10, 15
020 XX (20)	005 832 MHz to 862 MHz	005 791 MHz to 821 MHz	FDD	5, 10, 15, 20	EU's Digital Dividend 800 MHz	EU
021 XXI (21)	005 1447.9 MHz to 1462.9 MHz	005 1495.9 MHz to 1510.9 MHz	FDD	5, 10, 15
024 XXIV (24)	005 1626.5 MHz to 1660.5 MHz	005 1525 MHz to 1559 MHz	FDD	5, 10
033 XXXIII (33)	016 1900 MHz to 1920 MHz		TDD	5, 10, 15, 20
034 XXXIV (34)	020 2010 MHz to 2025 MHz		TDD	5, 10, 15
035 XXXV (35)	014 1850 MHz to 1910 MHz		TDD	1.4, 3, 5, 10, 15, 20
036 XXXVI (36)	019 1930 MHz to 1990 MHz		TDD	1.4, 3, 5, 10, 15, 20
037 XXXVII (37)	017 1910 MHz to 1930 MHz		TDD	5, 10, 15, 20
038 XXXVIII (38)	023 2570 MHz to 2620 MHz		TDD	5, 10, 15, 20		EU
039 XXXIX (39)	015 1880 MHz to 1920 MHz		TDD	5, 10, 15, 20
040 XL (40)	021 2300 MHz to 2400 MHz		TDD	5, 10, 15, 20	IMT-2000	China, India
041 XLI (41)	021 2496 MHz to 2690 MHz		TDD	5, 10, 15, 20
042 XLII (42)	021 3400 MHz to 3600 MHz		TDD	5, 10, 15, 20
043 XLIII (43)	021 3600 MHz to 3800 MHz		TDD	5, 10, 15, 20

Technology demos

• In September 2007, NTT Docomo demonstrated e-UTRA data rates of 200 Mbit/s with power consumption below 100 mW during the test.

• In April 2008, LG and Nortel demonstrated e-UTRA data rates of 50 Mbit/s while travelling at 110 km/h.

• February 15, 2008 - Skyworks Solutions has released a front-end module for e-UTRAN.

See also

• 3GPP Long Term Evolution (LTE)
• System Architecture Evolution (SAE)
• Fourth Generation Networks (IMT-Advanced)
• LTE Advanced (4G version of LTE)
• UMTS, UMTS-TDD, WiMAX
• List of device bandwidths

External links

• 3GPP Long Term Evolution page
• LTE 3GPP Encyclopedia
• 3G Americas - UMTS/HSPA Speeds Up the Wireless Technology Roadmap. 3G Americas Publishes White Paper on 3GPP Release 7 to Release 8. Bellevue, WA, July 10, 2007