LTE: an introduction LTE offers a superior user experience and simplified technology
Executive summary Mobile broadband is a reality today and is growing fast, as members of the internet generation grow accustomed to having broadband access wherever they go, and not just at home or in the office. By 2016 there are expected to be close to 5 billion mobile broadband subscriptions worldwide. The majority of these will be served by HSPA and LTE networks. LTE is continuously being developed to make sure that future requirements and scenarios are being met and prepared for in the best way. Operators can flexibly introduce LTE to match their existing network and spectrum, to meet business objectives for mobile broadband. People can already browse the internet or send e-mails using HSPA/LTE-enabled notebooks, replace their fixed DSL modems with HSPA/LTE modems or USB dongles, and send and receive video or music using smartphones. With the introduction of LTE, the user experience is enhanced further for more demanding applications like interactive TV, mobile video blogging, advanced games or professional services. LTE offers several important benefits for users and operators: > > Performance and capacity One of the requirements of LTE is that it should provide downlink peak rates of at least 100Mbps. In the first stage, the technology allows for speeds of over 300Mbps, and Ericsson has already demonstrated LTE peak rates over 1Gbps. Furthermore, radio access network (RAN) round-trip times are expected to be less than 10ms. > > Simplicity LTE supports flexible carrier bandwidths, from 1.4MHz up to 20MHz. LTE also supports both frequency division duplex (FDD) and time division duplex (TDD). So far, a large number of bands have been identified by 3GPP for LTE, and there are more bands to come. This means that an operator may introduce LTE in new bands where it is easiest to deploy 10MHz or 20MHz carriers. Features like selfconfiguration and self-optimization will simplify and reduce the cost of network rollout and management. > > Wide range of terminals in addition to mobile feature phones, smartphones and MiFi s, many computers and consumer electronic devices, such as laptops, notebooks and tablets, incorporate LTE embedded modules. In the near future, other devices such as gaming devices and cameras will also incorporate LTE embedded modules. Since LTE supports handover and roaming to existing mobile networks, all these devices can have ubiquitous mobile broadband coverage from day one. In summary, operators can introduce LTE flexibly to match their existing network, spectrum and business objectives for mobile broadband and multimedia services.
Satisfying consumer requirements Mobile broadband subscriptions are expected to reach close to 5 billion by 2016, and around 90 percent of these subscriptions will involve the use of handheld devices. We have seen strong supporting evidence for the take-off of mobile broadband over the past few years, as can be seen from the graph below. Consumers understand and appreciate the benefits of mobile broadband. Most people already use mobile phones, and many also connect their notebooks over wireless LANs. The step toward full mobile broadband is intuitive and simple, especially with LTE that offers ubiquitous coverage and roaming with existing 2G and 3G networks. Experience gained from the HSPA arena shows that when operators provide good coverage, service offerings and terminals, mobile broadband takes off rapidly. Packet-data traffic surpassed voice traffic during May 2007 based on a world average WCDMA network load. This is mainly due to the introduction of HSPA in the networks. HSPA USB dongles and data cards were first, and smartphones are getting more and more popular. Several operators have seen a four-fold increase in data traffic in three months after they launched HSPA. The expected added volume of mobile broadband traffic generated in 2011 by 400 million new smartphone users, and 40 million new mobile broadband PC users is larger than the overall voice traffic created by more than 5 billion users. This traffic growth is payed by mobile broadband customers. In many cases, mobile broadband can compete with fixed broadband on price, performance, security and, of course, convenience. A number of broadband applications are significantly enhanced with mobility. With the introduction of smartphones, we have seen an explosion of community sites, search engines, gaming, presence applications and content-sharing like YouTube, to name just a few examples. With mobility, all these applications become significantly more valuable to users. User-generated content is particularly interesting, because it changes traffic patterns to make the uplink much more important. The high peak rates and short latency of LTE enable realtime applications such as gaming and video meetings. Subscriptions/lines (million) 9 000 8 000 7 000 6 000 5 000 4 000 3 000 2 000 1 000 Mobile subscriptions Mobile broadband subscriptions 0 2008 2009 2010 2011 2012 2013 2014 2015 2016 Year End Figure 1. Mobile broadband subscription growth from 2008-2016 excluding M2M. (Source: internal Ericsson)
Satisfying operator requirements Operators are doing business in an increasingly competitive environment. They are competing not only with other operators, but also with new players and new business models. However, having new business models also means new opportunities, and mobile operators have the advantage of being able to offer competitive delivery of mobile broadband services migrating from existing investments in 2G and 3G networks. The continuous development of LTE performance, to create increased bandwidth, higher capacity and better spectrum utilization, will bring about new potential revenue opportunities for the operator by providing new services, as well as economies of scale, enabling mobile broadband in new areas where it was not economically feasible before. In addition to high end users in urban areas, LTE can also be used for rural coverage of broadband, one example of that is Australia. This is why operators are so active in formulating strategies and driving requirements for mobile broadband through standardization bodies. Some of the world s leading operators, vendors and research institutes are members in the Next Generation Mobile Networks (NGMN) alliance. (See www.ngmn.org for a list of members.) NGMN works alongside existing standards bodies, and has established clear performance targets, fundamental recommendations and deployment scenarios for a future wide-area mobile broadband network.
Standardization of LTE LTE is the next major step in mobile radio communications, and was introduced in 3GPP Release 8. LTE uses orthogonal frequency division multiplexing (OFDM) as its radio access technology, together with advanced antenna technologies. 3GPP is a collaboration agreement, established in December 1998, that brings together a number of telecommunications standards bodies, known as organizational partners. The current organizational partners are ARIB, CCSA, ETSI, ATIS, TTA and TTC. Researchers and development engineers from all over the world representing more than 60 operators, vendors and research institutes are participating in the joint LTE radio access standardization effort. In addition to LTE, 3GPP is also defining IP-based, flat core network architecture. This architecture is defined as part of the System Architecture Evolution (SAE) effort specifying the EPC network. The LTE-SAE architecture and concepts have been designed for efficient support of mass-market usage of any IP-based service. The architecture is based on an evolution of the existing GSM/WCDMA core network, with simplified operations and smooth, cost-efficient deployment. Moreover, work has also been done by 3GPP in cooperation with 3GPP2 (the CDMA standardization body) to optimize interworking between CDMA and LTE-SAE. This means that CDMA operators are evolving their networks to LTE-SAE and enjoy the economies of scale and global chipset volumes that have been such strong benefits for GSM and WCDMA. The starting point for LTE standardization was the 3GPP RAN Evolution Workshop, held in November 2004 in Toronto, Canada. A study item was started in December 2004, with the objective of developing a framework for the evolution of the 3GPP radio access technology toward: > > Reduced cost per bit > > Increased service provisioning more services at a lower cost with better user experience > > Flexible use of existing and new frequency bands > > Simplified architecture and open interfaces > > Reasonable terminal power consumption. The study item was needed to certify that the LTE concept could fulfill a number of requirements specified in 3GPP TR 25.913 Feasibility Study of Evolved UTRA and UTRAN [1] (see the Facts box: Summary of the 3GPP Release 8 original LTE requirements ). LTE performance has been evaluated in terms of so-called checkpoints, and the results were agreed on in 3GPP plenary sessions during May and June 2007 in South Korea. These results show that LTE meets, and in some cases exceeds, the targets for peak data rates, cell-edge user throughput and spectrum efficiency, as well as VoIP and Multimedia Broadcast Multicast Service (MBMS) performance. The specification work on LTE was completed in March 2009 as the SAE specifications were included. Implementation based on the March 2009 version will guarantee backwards compatibility. To further extend the performance and capabilities of the LTE radio access technology, 3GPP initiated work on LTE Release 10 in April 2008. Bandwidth extension and spectrum aggregation, extended multi-antenna transmission and relaying are some of the functionalities that are were in Release 10 that will enable operators to manage more traffic and provide higher data rates [2]. facts Summary of the 3GPP Release 8 original LTE requirements > > Increased peak data rates: 100Mbps downlink and 50Mbps uplink > > Reduction of Radio Access Network (RAN) latency to 10ms > > Improved spectrum efficiency (two to four times compared with HSPA Release 6) > > Cost-effective migration from Release 6 Universal Terrestrial Radio Access (UTRA) radio interface and architecture > > Improved broadcasting > > IP-optimized (focus on services in the packetswitched domain) > > Scalable bandwidth of 20MHz, 15MHz, 10MHz, 5MHz, 3MHz and 1.4MHz > > Support for both paired and unpaired spectrum > > Support for interworking with existing 3G systems and non-3gpp specified systems.
Technical merits Architecture In parallel with the LTE radio access, the packet core network is also evolving to a new flat IP-based multi-access core network. This new EPC network is designed to optimize network performance, improve cost-efficiency and facilitate the uptake of mass-market multimedia services. There are only two nodes in the EPS architecture user plane: the LTE base station (enodeb) and the Packet Gateway, as shown in Figure 2. The LTE base stations are connected to the Packet Gateway using the Core Network-RAN interface, S1. Existing 3GPP (GSM and WCDMA/HSPA) and 3GPP2 (CDMA2000 1xRTT, EV-DO) systems are integrated to the EPC network through standardized interfaces providing optimized mobility with LTE. For 3GPP systems this means a signaling interface between the existing Serving GPRS Support Node (SGSN) to the Mobility Management Entity (MME) in the EPC network; for 3GPP2 a control signaling interface between the CDMA RAN and the MME. This integration will support both dual and single radio handover, allowing for flexible migration to LTE. The Home Subscriber Server (HSS) connects to the Packet Core through an IP-based interface using Diameter, and not SS7, which was used in previous GSM and WCDMA networks. Network signaling for policy control and charging is already based on Diameter. This means that all interfaces in the new architecture are IP-based. LTE-EPC has adopted an effective class-based QoS concept. This provides a foundation for operators to offer service differentiation, depending on the type of subscription or application. OFDM radio technology LTE uses OFDM for the downlink that is, from the base station to the terminal. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. It is a well-established technology: for example, in standards such as IEEE 802.11a/b/g, 802.16, HIPERLAN-2, DVB and DAB. OFDM uses a large number of narrow sub-carriers for multi-carrier transmission. The basic LTE downlink physical resource can be seen as a time-frequency grid, as illustrated in Figure 3. In the frequency domain, the spacing between the sub-carriers, Δf, is 15kHz. In addition, the OFDM symbol duration time is Figure 2. A flat EPC network supporting multi-access technologies. 1/Δf + cyclic prefix. The cyclic prefix is used to maintain orthogonally between the sub-carriers even for a time-dispersive radio channel. One resource element carries QPSK, 16QAM or 64QAM. With 64QAM, each resource element carries six bits. The OFDM symbols are grouped into resource blocks. The resource blocks have a total size of 180kHz in the frequency domain and 0.5ms in the time domain. Each user is allocated a number of so-called resource blocks in the time-frequency grid. The more resource blocks a user gets, and the higher the modulation used in the resource elements, the higher the bit rate. Which resource blocks the user gets at a given point in time, and how many, depends on advanced scheduling mechanisms in the frequency and time dimensions. Scheduling of resources can be taken every 1ms: that means two resource blocks, 180kHz wide and in total 1ms in length (called a Scheduling Block). The scheduling mechanisms in LTE are similar to those used in HSPA, and enable optimal performance for different services in different radio environments. In the uplink, LTE uses a pre-coded version of OFDM called Single Carrier Frequency Division Multiple Access (SC-FDMA). This is to compensate for a drawback with normal OFDM, which has a very high
Peak to Average Power Ratio (PAPR). High PAPR requires expensive and inefficient power amplifiers with high linearity requirements, which increases the cost of the terminal and drains the battery faster. Table 1 presents the different frequency bands stated for both FDD and TDD that are defined in 3GPP release 10, April 2011. SC-FDMA solves this problem by grouping together the resource blocks in such a way that it reduces the need for linearity, and so power consumption, in the power amplifier. A low PAPR also improves coverage and cell-edge performance. A comprehensive introduction to LTE can be found in 3G Evolution: HSPA and LTE for mobile broadband [3] and 4G: LTE/LTE-Advanced for mobile broadband [4]. Advanced antennas Advanced antenna solutions that have been introduced in HSPA Evolution are also used by LTE. Solutions incorporating multiple antennas meet next-generation mobile broadband network requirements for high peak data rates, extended coverage and extensive capacity. Advanced multi-antenna solutions are key in achieving these targets. There is no single antenna solution that addresses every scenario. Consequently, a family of antenna solutions is available for specific deployment scenarios. For instance, high peak data rates can be achieved with multi-layer antenna solutions such as 2x2 or 4x4 multiple-input, multiple-output (MIMO), whereas extended coverage can be achieved with beam-forming. In LTE Release 10 the LTE downlink multi-antenna transmission capabilities are expanded to support spatial multiplexing with up to eight transmit antennas and eight corresponding transmission layers. Frequency bands for FDD and TDD LTE can be used in both paired (FDD) and unpaired (TDD) spectrum. The first commercial LTE networks that have been launched since 2009 are FDD-based. The first TDD-based LTE network is expected to be commercially launched during 2011. The main difference between the TDD and FDD modes lies in how they use wireless spectrum. In LTE-FDD networks, two separate carriers are used, one for the downlink and one for the uplink. In TDD the uplink (UL) and downlink (DL) share a single carrier, separated in the time domain. Figure 3. The LTE downlink physical resource based on OFDM. LTE-TDD and FDD are essentially the same technology: the same chipsets can be used to access both modes which makes life easy for handset manufacturers. By using the same EPC, base station and user equipment platforms for both FDD and TDD deployments, LTE delivers a truly global solution for mobile broadband. TDD operators will for the first time be able to enjoy the economies of scale that come with broadly supported FDD products. The first LTE network infrastructure and terminal products support multiple frequency bands from day one. LTE will therefore be able to offer great economies of scale and global coverage quickly. LTE is defined to support flexible carrier bandwidths from 1.4MHz up to 20MHz, in many spectrum bands and for both FDD and TDD deployments. This means that an operator can introduce LTE in both new and existing bands. The first commercial LTE network in the world was launched by TeliaSonera in Sweden at the end of 2009, operating on the 2.6GHz band (Band 7). Since then, commercial operations have begun on Bands 1, 2, 4, 13 and 20. In contrast to earlier cellular systems, LTE will rapidly be deployed on multiple bands. Operators planning to deploy a TDD system are advised to coordinate and synchronize the UL/DL configuration with other operators in the same band or neighboring bands to reduce interference.
Table 1. FDD and TDD defined in 3GPP (April 2011).[5] E UTRA Operating Band Uplink (UL) Operating Band Downlink (DL) Operating Band Duplex Mode 1 1920 MHz 1980 MHz 2110 MHz 2170 MHz FDD 2 1850 MHz 1910 MHz 1930 MHz 1990 MHz FDD 3 1710 MHz 1785 MHz 1805 MHz 1880 MHz FDD 4 1710 MHz 1755 MHz 2110 MHz 2155 MHz FDD 5 824 MHz 849 MHz 869 MHz 894MHz FDD 6 1 830 MHz 840 MHz 875 MHz 885 MHz FDD 7 2500 MHz 2570 MHz 2620 MHz 2690 MHz FDD 8 880 MHz 915 MHz 925 MHz 960 MHz FDD 9 1749.9 MHz 1784.9 MHz 1844.9 MHz 1879.9 MHz FDD 10 1710 MHz 1770 MHz 2110 MHz 2170 MHz FDD 11 1427.9 MHz 1447.9 MHz 1475.9 MHz 1495.9 MHz FDD 12 699 MHz 716 MHz 729 MHz 746 MHz FDD 13 777 MHz 787 MHz 746 MHz 756 MHz FDD 14 788 MHz 798 MHz 758 MHz 768 MHz FDD 15 Reserved Reserved 16 Reserved Reserved 17 704 MHz 716 MHz 734 MHz 746 MHz FDD 18 815 MHz 830 MHz 860 MHz 875 MHz FDD 19 830 MHz 845 MHz 875 MHz 890 MHz FDD 20 832 MHz 862 MHz 791 MHz 821 MHz FDD 21 1447.9 MHz 1462.9 MHz 1495.9 MHz 1510.9 MHz FDD... 24 1626.5 MHz 1660.5 MHz 1525 MHz 1559 MHz FDD... 33 1900 MHz 1920 MHz 1900 MHz 1920 MHz TDD 34 2010 MHz 2025 MHz 2010 MHz 2025 MHz TDD 35 1850 MHz 1910 MHz 1850 MHz 1910 MHz TDD 36 1930 MHz 1990 MHz 1930 MHz 1990 MHz TDD 37 1910 MHz 1930 MHz 1910 MHz 1930 MHz TDD 38 2570 MHz 2620 MHz 2570 MHz 2620 MHz TDD 39 1880 MHz 1920 MHz 1880 MHz 1920 MHz TDD 40 2300 MHz 2400 MHz 2300 MHz 2400 MHz TDD 41 2496 MHz 2690 MHz 2496 MHz 2690 MHz TDD 42 3400 MHz 3600 MHz 3400 MHz 3600 MHz TDD 43 3600 MHz 3800 MHz 3600 MHz 3800 MHz TDD Note 1: Band 6 is not applicable.
End-user devices Our growing desire for 24/7 internet access is relevant to all aspects of daily life whether it enables us to remain in control of family logistics, seize exciting opportunities as they arise, feel connected to our social groups, or enjoy the freedom that mobile working offers, we re increasingly reliant on mobile broadband. Mobile broadband devices are mass-market products, and LTE-enabled devices are growing fast. The Global Mobile Suppliers Association (GSA) confirmed in July 2011 that the creation of 161 LTE-enabled user devices has already been announced by 45 suppliers. The first LTE-capable devices were USB dongles, as was the case with HSPA. Since then, however, we have seen a faster introduction of other devices taking place in a shorter time frame, such as laptops with embedded LTE, MiFi, routers, smartphones and tablets. Figure 4. Examples of devices that use LTE.
Cost-efficiency There is strong and widespread support from the mobile industry for LTE, and many vendors, operators and research institutes are participating in its standardization. Strong support for LTE from the very start has been crucial for the the creation of a healthy ecosystem. One of the key success factors for any technology is economy of scale. The volume advantage is beneficial for both handsets and infrastructure equipment. It drives down the manufacturing costs and enables operators to provide cost-efficient services to their customers. This is also one of the main reasons greenfield operators will benefit from LTE. Deployment of LTE varies from country to country, according to regulatory requirements. The first devices are multimode-based, meaning that widearea coverage, mobility and service continuity can be provided from day one. Existing legacy mobile networks can be used to fall back on in areas where LTE is not yet deployed. It is important that the deployment of LTE infrastructure is as simple and cost-efficient as possible. For example, it should be possible to upgrade existing radio base stations to LTE using plug-in units, so that they become both dual-mode and dual-band. Stand-alone base stations for LTE will also be simpler to deploy than today s products. Network rollout as well as operation and management can be simplified with plug-and-play and self-optimizing features reducing both capex and opex for the operator.
Conclusion LTE is well positioned today, and is already meeting the requirements of next-generation mobile networks both for existing 3GPP/3GPP2 operators and greenfielders. It enables operators to offer high-performance, mass-market mobile broadband services, through a combination of high bit-rates and system throughput in both the uplink and downlink with low latency. LTE infrastructure is designed to be as simple as possible to deploy and operate, through flexible technology that can be deployed in a wide variety of frequency bands. LTE offers scalable bandwidths, from 1.4MHz up to 20MHz, together with support for both FDD paired and TDD unpaired spectrum. The LTE-SAE architecture reduces the number of nodes, supports flexible network configurations and provides a high level of service availability. Furthermore, LTE-SAE interoperates with GSM, WCDMA/HSPA, TD-SCDMA, MiFi and CDMA. Today LTE is already available in USB dongles, laptop/netbooks, smartphones, routers and tablets, and will soon be available through other devices that benefit from mobile broadband.
glossary 3GPP 3rd Generation Partnership Project 3GPP2 3rd Generation Partnership Project 2 ARIB Association of Radio Industries and Businesses ATIS Alliance for Telecommunication Industry Solutions BS base station capex capital expenditure CCSA China Communications Standards Association CDMA code division multiple access CDMA2000 code division multiple access 2000 DAB Digital Audio Broadcast DL downlink DSL digital subscriber line DVB Digital Video Broadcast EPC Evolved Packet Core EPS 3GPP Evolved Packet System ETSI European Telecommunications Standards Institute E-UTRA Evolved Universal Terrestrial Radio Access EV-DO Evolution Data Optimized FDD frequency division duplex GSA Global Mobile Suppliers Association GSM Global System for Mobile communication HSPA High-Speed Packet Access HSS Home Subscriber Server IEEE Institute of Electrical and Electronics Engineers IP Internet Protocol LTE Long Term Evolution M2M machine-to-machine MBMS Multimedia Broadcast Multicast Service MIMO multiple-input,, multiple-output MME Mobility Management Entity NGMN Next Generation Mobile Networks OFDM orthogonal frequency division multiplexing opex operational expenditure PAPR Peak to Average Power Ratio PCRF policing and charging rules function QoS quality of service QPSK quadrature phase shift keying RAN radio access network SAE System Architecture Evolution SC-FDMA Single Carrier Frequency Division Multiple Access SGSN Serving GPRS Support Node TDD time division duplex TD-SCDMA Time Division Synchronous Code Division Multiple Access TTA Telecommunications Technology Association TTC Telecommunication Technology Committee TTI transmission time interval UE user equipment UL uplink UM User Management USB Universal Serial Bus UTRA Universal Terrestrial Radio Access UTRAN Universal Terrestrial Radio Access Network VoIP voice over IP WCDMA Wideband Code Division Multiple Access WLAN Wireless Local Area Network
References 1. 3GPP TR 25.913 Feasibility Study of Evolved UTRA and UTRAN 2. Ericsson White paper, 4G: LTE a 4G Solution 3. Dahlman, Parkvall, Sköld and Beming, 3G Evolution: HSPA and LTE for Mobile Broadband, Academic Press, Oxford, UK, Second edition 2008 4. Dahlman, Parkvall, Sköld, 4G: LTE/LTE-Advanced for Mobile Broadband, Academic Press, Oxford, UK, First edition 2011 5. 3GPP TS 36.104 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Base Station (BS) radio transmission and reception (Release 10)
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