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LTE (telecommunication)

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Long Term Evolution (LTE) describes the latest standardization work by 3rd Generation Partnership Project (3GPP) in the mobile network technology tree previously realized the GSM/EDGE and UMTS/HSxPA network technologies that now account for over 85% of all mobile subscribers.[1] In this latest standardization work which started in late 2004, the 3GPP (set out in December, 1998) defines a set of high level requirements (new high-speed Radio Access method) for mobile communications systems to compete with other latest cellular broadband technologies, particularly WiMAX.

In preparation for further increasing user demands and tougher competition from new radio access technologies, LTE is enhanced with a new radio access technique called Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).[1] Via this technology LTE is expected to improve end-user throughput, increase sector capacity, reduce user plane latency, and consequently offer superior user experience with full mobility.

Unlike other latest deployed technologies such as HSPA, LTE is accommodated within a new Packet Core architecture called Enhanced Packet Core (EPC) network architecture. Technically, 3GPP specifies the EPC to support the E-UTRAN. EPC is designed to deploy TCP/IP protocols thus enabling LTE to support all IP-based services including voice, video, rich media and messaging with end-to-end Quality of Service (QoS). The EPC network architecture also enables improved connections and hand-over to other fixed-line and wireless access technologies while giving an operator the ability to deliver a seamless mobility experience.[2]

To achieve all the targets mentioned herein, LTE Physical Layer (PHY) employs advanced technologies that are new to cellular applications. These include Orthogonal Frequency Division Multiple Access (OFDMA) and multiple-input and multiple-output (MIMO) data transmission. Smart Antennas are also deployed to accomplish those targets. Furthermore, the LTE PHY deploys the OFDMA for the Downlink (DU) - that is from the Base Station (BS) to the User Equipment (UE) and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the Uplink (UL). These technologies will further minimize the LTE system and UE complexities while allowing flexible spectrum deployment in existing or new frequency spectrum.[2]

LTE enjoys the support from a collaborative group of international standards organizations and mobile-technology companies that form the 3GPP. However, a strong support comes from Ericsson and Qualcomm who decided not to support WiMAX, the competitor of LTE [3]. Alcatel-Lucent is also a key contributor to LTE standards, having held the rapporteur position on the MIMO working group since 2002. Motorola which also supports WiMAX claims to be the leading contributor in LTE standards such as Radio Access Network (RAN) 1 & 2 and a top three contributor to EPC 1 & 2 standards.[1] The standardization work on LTE is continuing, and Motorola claims to introduce LTE in ‘Q4 2009 [4]. However, LTE is assumed to dominate world’s mobile infrastructure markets after 2011.[5]

Standardization Path

The standardization of LTE started in November 2004, when the RAN Evolution Workshop in Toronto, Canada, accepted contributions from more than 40 operators, vendors and research institutes that included 3GPP members and nonmembers organizations. Contributions were merely a range of views and proposals on the UTRAN. Following those contributions, 3GPP started a feasibility study, in December 2004, so as to develop a new framework for evolution of the 3GPP Radio Access technology towards:

  • Increased data rates
  • Reduced cost per bit
  • Increased service provisioning - that is more services with better user experience
  • Flexibility in usage of both new and existing frequency bands
  • High-data-rate
  • Low-latency
  • Simple architecture, open interface and packet-optimized RAN technology

Put simply, the study maps out specifications for RAN that are capable to support the wireless broadband internet scenario which is already enjoyed in today’s cable networks – adding full mobility to enable exciting new service possibilities.[5]

Currently LTE specifications are described in 3GPP Release 8. The 3GPP Release 8 is the latest set of standards that describes the technical evolution of 3GPP mobile network systems. It is the successor of 3GPP Release 7 that includes a set of specifications for HSPA+, the ‘missing bridge’ between HSPA and LTE. Actually HSPA+ is described in both, the 3GPP Release 7 and 8, allowing the designing of simpler ‘flat’, all-IP based network architecture and bypassing many of the legacy equipments required for UMTS/HSPA.[5]

The specifications of the 3GPP Release 8 standard are assumed to complete at the end of 2008. Obviously the finalization of the 3GPP Release 8 will further progress the market interest in commercial deployment of LTE. The 3GPP Release 8 will compile the completion of 3GPP Release 7 HSPA+ features, Voice over HSPA and EPC specification and Common IP Multimedia Subsystem (IMS) [6].

LTE Key Features

As it has been discussed earlier, technically speaking, a fundamental objective of the 3GPP LTE project is to offer higher data speeds for both DL and UL transmissions. In addition to that, it is obviously LTE to be characterized by reduced packet latency while promising a superior experience in online gaming, Voice over IP (VoIP) videoconferencing and other real-time professional services. Now that based on the feasibility study under 3GPP, the following are the important features of LTE:

OFDMA on the DL and SC-FDMA on the UL

3GPP Release 8 specifies an all-new RAN that combines OFDMA-based modulation and multiple access schemes for the downlink, as well as SC-FDMA for uplink. These new technologies (OFDM schemes) are deliberately deployed to split available spectrum into thousands of extremely narrowband carriers, such that each carrier is capable of carrying a part of signal. This is what is known as multiple carrier transmission.[2]

To enhance the OFDM schemes, LTE also employs other higher order modulation schemes such as 64QAM and sophisticated Forward Error Correction (FEC) schemes such as tail biting, convolutional coding and turbo coding. Furthermore, complementary radio techniques such as MIMO and Beam Forming with up to four antennas per station are also deliberately deployed for further enhancement of innate spectral efficiency of OFDM schemes.[5]

The results of these radio interface features are obvious, enabling LTE to have improved radio performance. As such they yield the spectral efficiency up to 3 to 4 times that of HSDPA Release 6 in the LTE DL and up to 2 to 3 times that of HSUPA Release 6 in UL.[2][7] Consequently, theoretically, the DL peak data rates extend up to 300Mbit/s per 20MHz of spectrum. Similarly, theoretical UL peak data rates can reach 75Mbit/s per 20MHz of spectrum as well as supporting at least 200 active users per cell in 5MHz.[5]

All-IP Packet Optimized Network Architecture

LTE has a ‘flat’, all-IP based core network with a simplified architecture, open interface and fewer system nodes. Indeed, the all-IP based network architecture together with the new RAN reduces network latency, improved system performance and provide interoperability with existing 3GPP and non-3GPP technologies. Within 3GPP, all-IP based core network architecture is now known as Evolved Packet Core (EPC). EPC is the result of standardization work within 3GPP which targeted to convert the existing System Architecture Evolution (SAE) to an all-IP system.[5]

Advanced Antenna Techniques

LTE is enhanced with MIMO, Spatial-Division Multiple Access (SDMA) and Beam Forming.[8] These are advanced radio antenna techniques which are complementary to each other. These techniques are deployed for better air interface via enhancing the innate spectral efficiency of OFDM schemes. Furthermore, these techniques can be used to trade-off between higher sector capacity, higher user data rates, or higher cell-edge rates, and thus enable mobile operators to have finer control over the end-user experience [9].

 

System Architecture

Evolved Radio Access Network (RAN)

The evolved RAN consists of the LTE base station (eNode B) that interfaces with the UE. The eNode B contains the PHY, Media Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers. Therefore the eNode B performs some tasks such as resource management, admission control, scheduling and enforcement of negotiated UL QoS.

Serving Gateway (SGW)

The SGW guides and forwards user data packets. Furthermore, during inter-eNode B handover SGW acts as the mobility anchor for the user plane. It can also act as an anchor for mobility between LTE technology and other 3GPP technologies. When the UE is in idle state, the SGW terminates the DL data path of the UE and triggers paging when DL data arrives for the UE.

Mobility Management Entity (MME)

MME handles Control Signaling for mobility. When the UE is in idle mode, the MME is responsible for UE tracking and paging procedure that includes retransmissions. MME is also involved in the bearer activation/deactivation process. In addition MME can choose the SGW for a UE at the initial attach and at time of intra-LTE handover involving core Network (CN) node relocation. MME can interact with the Home Subscriber Server (HSS) so as to authenticate the user.

Packet Data Network Gateway (PDN GW)

PDN GW is a point of exit and entry of traffic for the UE. PDN GW performs packet filtering and acts as the anchor for mobility between 3GPP and non-3GPP technologies such as WiMAX and 3GPP2.[1]


Networks Upgrading to LTE

LTE is deemed to become a next generation mobile communications standard or 4G mobile communications standard that started with today’s 2G and 3G networks. Technically, the design of LTE is based on today’s 3GPP family of cellular networks that dominated by Global System for Mobile communication (GSM), General Packet Radio Service (GPRS) and Enhanced Data rate for GSM Evolution (EDGE) as well as Wideband Code Division Multiple Access (WCDMA) and High Speed Packet Access (HSPA). Therefore LTE ensures a smooth evolutionary path to higher speeds and reduced latency to these existing networks.

Contrary to today’s networks that deploy hybrid packet/circuit switched networks, LTE uses the advanced new radio interface. As such to harness the full potential of LTE it requires an evolution from the existing network architecture to a simplified, all-IP environment architecture. This evolution has advantages to operator’s point of view. These advantages include reduced costs for variety of services, blended applications combining voice, video and data services plus interworking with other fixed and wireless networks.

Furthermore since the design of LTE is based on today’s UMTS/HSPA family of standards, it will obvious enhance the capabilities of the existing cellular network technologies to delivery broadband services which were accustomed to fixed broadband networks. In other words, LTE will unify the voice-oriented environment of today’s mobile networks with the data-centric service possibilities of the fixed Internet. To the operator’s point of view, the smooth upgrading of the existing networks to LTE will allow the introduction of LTE’s all-IP concept progressively. As such operator will be able to retain the value of its existing voice-based service platforms at the same get the benefit of high performance in data services delivered by LTE network

Carrier adoption

  • Most carriers supporting GSM or HSPA networks can be expected to upgrade their networks to LTE at some stage:
  • However, several networks that don't use these standards are also upgrading to LTE:
    • Alltel, Verizon Wireless, 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. [11] They have chosen to take the natural GSM evolution path as opposed to the 3GPP2 CDMA2000 evolution path Ultra Mobile Broadband (UMB). Verizon Wireless plans to begin LTE trials in 2008.[12]
    • Telus Mobility and Bell Mobility have announced that they will adopt LTE as their 4G wireless standard.[13]

LTE Vs WiMAX

WiMAX and 3GPP LTE are the two wireless technologies that will eventually be used to deliver data at a very high speed (up to 100 Mbit/s for WiMAX and up to 300 Mbit/s for LTE) beyond the 3G technologies. This high speed offered by the two technologies is fast enough to potentially replace cable broadband connections with wireless and enable some existing services currently deemed to be too bandwidth-hungry to be delivered using existing mobile technologies.

Contrary to LTE which is still under standardization, WiMAX is already in the market with the first national fixed-WiMAX rollout in the 3.5GHz range was carried out by Wateen Telecom in Pakistan. However, the world's first large scale mobile WiMAX deployment is due in the US. This is the joint venture between Sprint Nextel Corp. and Clearwire Corp. and it is expected to reach 120 million to 140 million people in the U.S by the end of 2010. On the other hand, LTE is assumed to dominate world’s mobile infrastructure markets after 2011. As such, some wireless operators such as AT&T Inc. and Verizon have already stated plans to adopt LTE, with major rollouts planned for 2011 or 2012.

As it has been discussed herein, LTE is the natural upgrade path for GSM/EDGE and UMTS/HSxPA network technologies that now account for over 85% of all mobile subscribers in the world. On upgrading to LTE, the existing GSM/EDGE and UMTS/HSxPA operators can use their current infrastructure (BT towers) integrating with new equipments making the whole process to be cost effective. When compared to WiMAX, an operator has to start from ground zero to setup a WiMAX network. Therefore LTE will have a significant global advantage over WiMAX in the long term.[14]

Operators & Vendors

Based on core network architectures of WiMAX and LTE, obviously, the two technologies will both be adopted, with LTE be the best upgrading option for GSM/EDGE and UMTS/HSxPA and WiMAX mostly appealing to cable operators. This can be seen in the US where by Sprint and Clearwire are aligned behind WiMAX, while Verizon Wireless and AT&T are behind LTE.

WiMAX is under the WiMAX forum, comprises of more than 500 vendors and mobile operators such as Vodafone. The forum was established to promote solutions based on the IEEE 802.16 standards. As for equipment manufacturers, Intel has invested billions of dollars in WiMAX research and chip sets and showed off conceptual mobile Internet devices at the Consumer Electronics. Vodafone as a mobile operator and Motorola Corp they both support WiMAX and LTE. However LTE enjoys a strong support from Qualcomm and Ericsson who decided not to support WiMAX.

From Technical Point of View

Both LTE and WiMAX use OFDMA in downlink and deploy MIMO technology, to improve reception in a single cell site. However a WiMAX network process all the information in a wider channel so as to optimize channel usage to the maximum. LTE, on the other hand, organizes the available spectrum into smaller chunks.[8]

Since WiMAX sticks with OFDMA in the downlink as well as in uplink, LTE uses SC-OFDMA in uplink. A major drawback of OFDMA-based system is its high Peak to Average Power Ratio (PAPR). As such a high PAPR requires expensive and inefficient power amplifiers which eventually increase the cost of the user equipment and drains the battery faster . Therefore SC-FDMA is theoretically designed to work more efficiently with lower-power end-user devices than OFDM is by grouping together the resource blocks and hence reduce the need for power amplifiers.

Technology Demos

  • In February 2007, Ericsson demonstrated for the first time in the world LTE with bit rates up to 144 Mbit/s[15]
  • 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.[16]
  • 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 100 mW during the test.[17]
Motorola 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 and LTE chipset. [5]
Ericsson demonstrated the world’s first end-to-end LTE call on handheld and LTE FDD and TDD mode on the same base station platform.[18]
Freescale Semiconductor demonstrated streaming HD video with peak data rates of 96 Mbit/s downlink and 86 Mbit/s uplink.[19]
NXP Semiconductors demonstrated a multi-mode LTE modem as the basis for a software-defined radio system for use in cellphones.[20]
picoChip and mimoOn demonstrated an LTE base station reference design. This runs on a common hardware platform (multi-mode / software defined radio) together with their WiMAX architecture.[21]
Alcatel-Lucent demonstrated live high-speed video connection over LTE supporting dozens of DVD-quality and high-definition video streams simultaneously, using Alcatel-Lucent infrastructure and LGE devices.[22]
  • In March 2008, NTT DoCoMo demonstrated LTE data rates of 250 Mbit/s in an outdoor test.[23]
  • In April 2008, Motorola demonstrated the first EV-DO to LTE hand-off - handing over a streaming video from LTE to a commercial EV-DO network and back to LTE. [6]
  • In April 2008, LG and Nortel demonstrated LTE data rates of 50 Mbit/s while travelling at 110 km/h. [24]
  • On September 18, 2008, Mobile operator T-Mobile and Nortel Networks achieved data rates of up to 170 Mbit/s for downloads and up to 50 Mbit/s for uploads. T-Mobile, the wireless business of Deutsche Telekom achieved these speeds in a car in range of three cell sites on a highway in Bonn, Germany at an average speed of 67 km/h.[25]

Conformance testing

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.[26]

See also

References

  1. ^ a b c d "Long Term Evolution (LTE)" (PDF). Motorola. Retrieved 2008-10-30. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  2. ^ a b c d "Long Term Evolution (LTE): A Technical Overview by Motorola" (PDF). Motorola. Retrieved 2008-10-31. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  3. ^ [1] WiMAX Guide: In association with Motorola, October 2007
  4. ^ [2]Motorola LTE Update: Interview with Darren McQueen
  5. ^ a b c d e f "Standardising the future of mobile communications with LTE". UMTS Forum. Retrieved 2008-10-29. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  6. ^ [3] Updates to 3GPP Release 7 and Release 8 White Paper
  7. ^ Jim Zyren. Dr. Wes McCoy (ed.). "Overview of 3GPP LTE Physical Layer" (PDF). Freescale Semiconductor. Retrieved 2008-11-02. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  8. ^ a b Jurjen Veldhuizen. "The difference between WiMAX and LTE from technical specifications". Retrieved 2008-11-01.
  9. ^ [4]3GPP Long Term Evolution: Qualcomm Incorporated, January 2008
  10. ^ "AT&T develops wireless broadband plans". Retrieved 2008-08-25.
  11. ^ "Alltel Jumps on LTE Bandwagon". Retrieved 2008-08-25.
  12. ^ Nuttall, Chris (2007-11-29). "Verizon set to begin trials of 4G network". The Financial Times. Retrieved 2007-12-01. {{cite news}}: Check date values in: |date= (help); Italic or bold markup not allowed in: |publisher= (help)
  13. ^ reportonbusiness.com: Wireless sales propel Telus results
  14. ^ Matt Hamblen. "WiMax vs. Long Term Evolution: Let the battle begin". Computerworld. Retrieved 2008-11-02. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  15. ^ Ericsson demonstrates live LTE at 144mbps
  16. ^ Nomor Research: World's first LTE demonstration
  17. ^ NTT DoCoMo develops low power chip for 3G LTE handsets
  18. ^ Petzke, Kai "LTE: Der UMTS-Nachfolger steht in den Startlöchern", teltarif.de, March 1 2008.
  19. ^ Gardner, W. David. "Freescale Semiconductor To Demo LTE In Mobile Handsets". InformationWeek. Retrieved 2008-11-01. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  20. ^ Walko, John. "NXP powers ahead with programmable LTE modem". EE Times. Retrieved 2008-11-02. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  21. ^ Walko, John. "PicoChip, mimoOn team for LTE ref design". EE Times. Retrieved 2008-11-02. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  22. ^ "Alcatel-Lucent highlights its wireless broadband leadership, IP transformation and network integration capabilities at Mobile World Congress 2008". Alcatel-Lucent. Retrieved 2008-10-31. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  23. ^ NTT DoCoMo Achieves 250Mbps Downlink in Super 3G Field Experiment
  24. ^ Nortel and LG Electronics Demo LTE at CTIA and with High Vehicle Speeds :: Wireless-Watch Community
  25. ^ a b Researchers demo 100 Mbit/s MIMO with SDMA / virtual MIMO technology
  26. ^ "MCC task force 160 Description". European Telecommunications Standards Institute. Retrieved 2008-10-29. {{cite web}}: Italic or bold markup not allowed in: |publisher= (help)
  • H. Ekström, A. Furuskär, J. Karlsson, M. Meyer, S. Parkvall, J. Torsner, and M. Wahlqvist, "Technical Solutions for the 3G Long-Term Evolution," IEEE Commun. Mag., vol. 44, no. 3, March 2006, pp. 38–45
  • 3rd Generation Partnership Project (3GPP); Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)
  • 3rd Generation Partnership Project (3GPP); Technical Specification Group Radio Access Network; Physical Layer Aspects for Evolved UTRA
  • E. Dahlman, H. Ekström, A. Furuskär, Y. Jading, J. Karlsson, M. Lundevall, and S. Parkvall, "The 3G Long-Term Evolution - Radio Interface Concepts and Performance Evaluation," IEEE Vehicular Technology Conference (VTC) 2006 Spring, Melbourne, Australia, May 2006
  • C. Mathas, "LTE: From Zero to 32 Million in Three Years, says ABI Research," Mobile Handset Design Line, June 12, 2008.[7]
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