Introduction
LTE (Long Term Evolution) is the preferred development path of GSM/W-CDMA/HSPA networks currently deployed, and an option for evolution of CDMA networks. This essential evolution 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.
Why LTE
lthough 3G/3.5G technologies such as HSPA/EV-DO deliver significantly higher bit rates than 2G technologies, they do not fully satisfy the “wireless broadband” requirements of instant-on, always-on and multi-megabit throughput. With LTE delivering even higher peak throughput and much lower latency, mobile operators (either 3GPP or 3GPP2 based) have a unique opportunity to evolve their existing infrastructure to next- generation wireless networks. These networks will deliver their subscriber’s Quality of Experience (QoE) expectations in terms of real-time services such as Voice Over IP, Multi-User Gaming Over IP, High Definition Video On Demand and Live TV. This will also continue to improve the quality of delivery for all legacy applications (e-mail, internet browsing, MMS, etc.)
The improved speed and low latency provided by LTE will offer a much improved end-user experience for all corporate services:
• For applications where data throughput is important - faster e- mail and file uploads, enhanced VPN connection, high-speed internet, etc. and;
• For interactive applications where latency is crucial - IMS based VoIP, mail and file synchronization with an on-line server, peer-to-peer applications such as “NetMeeting”, SIP multimedia services including video and voice conference over IP, application sharing, etc.
In addition to typical corporate applications, we expect an increased interest from the vertical markets where information accuracy, reliability and immediacy are key: medical applications where latency and high resolution imaging are highly important; machine-to-machine communication where security and immediacy are crucial; live network based navigation; etc. The mass market will benefit from improvements delivered by LTE for all person-to-person and internet community applications: Push-to-See, improved quality for VoIP, photo and video downloading / uploading for personal blogs, online gaming, mobile social networks (such as YouTube, myspace), and “Second
life” type applications etc. On top of those improvements, LTE will enable the introduction of new services, such as High Definition Video (or HD TV) and multi-user interactive gaming:
• HD TV requires between 10 to 20 Mbits/s bandwidth (18 Mbits/s for example with Blue Ray standard), which is higher than current HSPA capabilities.
• Interactive multi-user gaming is extremely sensitive to latency: the very low latency offered by LTE (less than 10ms versus 60ms with HSPA) is key for fighting games, car races, or any action games involving a large number of simultaneous users. In addition, the higher throughput offered will enable high-resolution video games. Lastly LTE will play a key role in the development of N-uple services at home (IP TV, Internet, telephone, mobile…services bundle). We are observing an increasing need for broadband access at home and the same will apply to mobile services for two main reasons. Firstly, as subscribers become used to higher speeds at home, they will require the same quality of service when they are mobile so as to benefit from a seamless experience. The second reason is the possibility of offering higher bandwidth in remote areas where ADSL throughput is no longer sufficient and fibre
may not be economically viable compared with LTE. In those areas the same LTE infrastructure will deliver mobile services as well as broadband access at home, bringing economies of scale.
With the recent introduction of HSDPA and EV-DO Rev A, we have observed a significant increase in mobile data traffic, with some operators quadrupling their Packet Switched traffic in one
year. At this growth rate, and with the proliferation of new applications on the network, cells in hot spots will be quickly saturated and the network will require densification in these overloaded areas. This can be delivered by using a higher capacity solution such as LTE.
LTE and Multimedia Broadcast Multicast Service The Multimedia Broadcast Multicast Service (MBMS) enables multiple users to receive data over the same radio resource. This creates a more efficient approach for delivering content, such as video programming, to which multiple users have subscriptions. However, with HSPA, MBMS does not match the capabilities of broadcasting and/or broadband wireless technologies (such as DVB-H or WiMAX). With an OFDM/SC-FDMA (Orthogonal Frequency Division Multiplex /Single-Carrier Frequency Division Multiple Access) system, LTE provides the possibility of operating MBMS in a single frequency network mode where significant performance gains (up to five times existing capacity) can be achieved without additional receiver complexity. LTE will consequently dramatically enhance MBMS, and match DVB-H and WiMAX, capabilities.
Reducing the Total Cost of Ownership Another key driver behind LTE is the reduction of the cost per
byte, which is expected to decrease by a factor of six compared with HSPA today. This cost reduction is derived from network simplification, with flat IP architecture and the enhanced capacity delivered by the new radio technologies implemented by LTE.
What Is LTE Technology?
In order to prepare for wireless operator’s future needs and to ensure the competitiveness of their mobile systems over the next ten years, a progression of network architecture, as well as an evolution of the radio interface is required. This is being evaluated in the 3GPP System Architecture Evolution (SAE), Long Term Evolution (LTE) and HSPA Evolution (HSPA+) Study Items. From a network deployment perspective it is likely that HSPA enhancements will be introduced first followed by the progression to a radio interface (LTE). LTE will allow operators to achieve even greater peak throughputs in higher spectrum bandwidth, and to benefit from greater capacity at a reduced cost. Initial deployments are targeted for 2009.
LTE characteristics include:
• Peak LTE throughputs (high spectral efficiency)
− DL: 100 Mb/s SISO (Single Input Single Output);
− 173 Mb/s 2x2 MIMO (Multiple Input Multiple Output);
− 326 Mb/s 4x4 MIMO; for 20 MHz
− UL: 58 Mb/s 16 QAM
− 86 Mb/s 64 QAM (based on 1 Tx UE)
• Increased Spectrum efficiency over Release 6 HSPA
− DL: 3-4 times HSDPA for MIMO (2,2)
− UL: 2-3 times E-DCH for MIMO(1,2)
• Ultra low Latency
− less than 10 msec for round-trip delay (RTD) from UE to
server
− Reduced call setup times (50-100ms)
− =>wired user experience
• Capacity per cell
− 200 users for 5 MHz, 400 users in larger spectrum
allocations
• Flexible spectrum use maximizes flexibility
− 1.4, 3/3.2, 5, 10, 15, 20 MHz
− All frequencies of IMT-2000: 450 MHz to 2.6 GHz
LTE is being developed by the 3GPP (3rd generation Partnership Project) standards body that is also responsible for GSM and W-CDMA. LTE standards are currently being developed and are expected to be finalized in early 2008. In order to reach this performance, LTE will make the best use of the latest technologies on the market. For radio, a new modulation scheme is being used based on OFDM, and the latest antenna technologies, such as MIMO will be deployed. For the core network, an IP based network topology will also be introduced to considerably reduce network complexity. LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) on the downlink, which is better suited than W-CDMA for achieving high peak data rates in high spectrum bandwidth. On the uplink LTE uses SC-FDMA (Single Carrier Frequency Division Multiple Access), a technology that provides advantages in power efficiency and resulting terminal battery life versus a pure OFDM approach.
MIMO refers to a technique that employs multiple transmit and receive antennas, often in combination with multiple radios and parallel data streams. This results in numerous data paths effectively operating in parallel and, through appropriate decoding, a multiplicative gain in throughput. For example, with a 2X2 MIMO system, a gain of a factor of 2 is expected on the peak
throughput. LTE also requires new network architecture, with the main functional entities being: the e-node B on the access side, and the Serving (S) and Packet Data Network (PDN) gateways and the
Mobile Management Entity (MME) in the core network, as depicted in the figure below.
LTE is a pure packet system, with no support for legacy circuit- switched voice/data. This shift allows a significant simplification of the network, reducing the number of nodes and improving operational efficiencies. This network simplification also removes any bottlenecks from the system, ensuring the network permanently runs at peak efficiency. The next figure shows the impacts of this simplification comparing traditional UMTS elements and LTE nodes, and provides a macroscopic mapping of User Plane and Control Plane between nodes.
In contrast to UMTS architecture, no Radio Network Controller (RNC) is required: the RNC’s functions are collapsed into the eNodeB. On the Core network side, the Mobility Management Entity (MME) assumes the role of the SGSN for the control plane, and the serving and PDN gateways ensure the role of user plane, routing user data traffic to the network edge, replacing the GGSN.
