LTE-SAE architecture and performance

LTE-SAE architecture and performance Per Beming, Lars Frid, Göran Hall, Peter Malm, Thomas Noren, Magnus Olsson and Göran Rune

LTE-SAE (Long-term evolution – system architecture evolution) systems promise unprecedented performance in new and existing frequency bands for 3GPP and 3GPP2 operators. The simplified and optimized architecture uses a minimum number of nodes in the user plane. In addition, new features have been introduced to simplify operation and maintenance. Ericsson’s portfolio of base stations and core network products can be upgraded to LTE-SAE, and the company is developing a range of LTE base stations for new deployments. Furthermore, Ericsson’s LTE mobile platforms are well positioned for different types of terminals and devices: broadband modules, fixed wireless terminals, and mobile terminals. This combination enables mobile broadband services to everyone, everywhere.

Background and targets Mobile broadband is rapidly becoming a reality. By 2011, Ericsson anticipates that 1.5 billion people will have broadband (Figure 1). In addition, more than half of these people will have mobile broadband, and the majority of them will be served by HSPA/LTE networks. At present, people can • surf or send e-mail with HSPA-enabled handsets and notebooks; • replace their DSL modems with HSPA modems; and • quickly upload and download videos or music with 3G phones. LTE, which is to be introduced in 3GPP Release 8, is the next major step in mobile

radio communications. It will give a superior user experience and support even more demanding applications, such as interactive TV, user-generated videos, advanced games, and professional services. LTE uses OFDM (orthogonal frequency-division multiplexing) radio access technology together with advanced antenna technologies. In addition to LTE, 3GPP has specified a flat, IP-based network architecture as part of the system architecture evolution (SAE) effort. The aim and design of the LTE-SAE architecture and concepts are to efficiently support mass-market usage of any IP-based service. The architecture is based on, and evolved from, existing GSM/WCDMA core networks to facilitate simplified operations

and smooth, cost-effective deployment. The LTE-SAE architecture reduces operating expenses (OPEX) and capital expenditures (CAPEX). The new, flat architecture, for example, means that only two node types (base stations and gateways) must scale in capacity in order to accommodate large increases in data volumes. One other area of focus has been network operation functionality, which now targets a high degree of automatic configuration. In addition, 3GPP and 3GPP2 have agreed to optimize interworking between CDMA and LTE-SAE. CDMA operators will thus also be able to evolve their networks to LTESAE and benefit from huge economies of scale and global chipset volumes. LTE is a versatile technology that fulfills or exceeds 3GPP requirements (Box A). Some of the most notable requirements follow below: • Downlink peak rates of more than 100Mbps and roundtrip time in the radio access network (RAN) of less than 10ms. • Support for flexible carrier bandwidths from less than 5MHz up to 20MHz in many new and existing spectrum bands. • Support for FDD and TDD deployments. • Support for handover and roaming to existing mobile networks, thereby providing ubiquitous coverage to all mobile subscribers from the very outset.

Figure 1 Forecasted number of broadband subscriptions

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Ericsson Review No. 3, 2007

Operators may introduce LTE flexibly, to match current network, spectrum, and business objectives for mobile broadband and multimedia services.

Technical overview Overall architecture

The main principles of the LTE-SAE architecture include • a common anchor point and gateway (GW) node for all access technologies; • an optimized architecture for the user plane – this is a departure from four to only two node types (base stations and gateways); • IP-based protocols on all interfaces; • a RAN-CN functional split similar to that of WCDMA/HSPA; • a split in the control/user plane between the mobility management entity (MME) and the gateway; and • integration of non-3GPP access technologies using client- as well as network-based mobile IP. Figure 2 shows a simplified view of the overall LTE-SAE architecture. The gateway, which includes both packet data network (PDN) and serving gateway functionality, can be configured to serve in either or both of these roles. The PDN gateway serves as a common anchor point for all access technologies, providing a stable IP point-of-presence for all users regardless of mobility within or between access technologies. The serving gateway is the anchor point for intra-3GPP mobility. The MME functionality is kept separate from the gateways to facilitate network deployment, independent technology evolution, and fully flexible scaling of capacity. GSM and WCDMA/HSPA systems are integrated into the evolved system through standardized interfaces between the SGSN (serving GPRS support node) and the evolved core network. This includes interfaces to the MME for transferring context and establishing bearers when moving between accesses, and to the gateway for establishing IP connectivity with user equipment (UE). The gateway node thus functions as a GGSN (gateway GPRS support node) for GSM and WCDMA/HSPA terminals. The architecture also allows for a common packet core network for GSM, WCDMA/ HSPA and LTE by combining the SGSN and the MME in the same node. Ericsson Review No. 3, 2007

BOX B, OVERVIEW OF LTE-SAE TRIAL INITIATIVE In May 2007, Ericsson and other leading vendors and operators launched the LTE-SAE Trial Initiative. Objectives • Drive industrialization of 3GPP LTE-SAE • Demonstrate 3GPP LTE-SAE capabilities • Promote 3GPP LTE-SAE to operators, vendors, analysts and regulators Founders • Alcatel-Lucent • Ericsson • France Telecom • Nokia • Nokia Siemens Networks • Nortel • T-Mobile • Vodafone Member commitments • Proof-of-concept demonstrations in 2007 • Interoperability tests in 2008 • End-user trials in 2009 The LTE-SAE Trial initiative is open to any organization that is committed to actively contributing to the objectives.

The home subscriber server (HSS) connects to the packet core through an interface that has been proposed and will likely be based on Diameter, not SS7. This will give a harmonized and simplified solution for control plane IP networking, since network signaling for policy control and charging is already based on Diameter.

The LTE base stations connect to the core network via the RAN-CN interface. The MME handles control signaling – for instance, for mobility. User data is forwarded between base stations and gateway nodes over an IP-based transport infrastructure. To support high-speed handover of terminals in active mode, each LTE base station is logi-

BOX A, 3GPP REQUIREMENTS FOR LTE-SAE The most pronounced 3GPP requirements for LTE-SAE: • Peak bit rate of more than 100Mbps in the downlink and greater than 50Mbps in the uplink • Compared to HSPA Release 6 baseline: ° Greater spectrum efficiency: 3-4 times the baseline in the downlink, and 2-3 times the baseline in the uplink ° Greater average cell bit rate: 3-4 times the baseline in the downlink, and 2-3 times the baseline in the uplink ° Greater bit rates at cell edges: 2-3 times the baseline in both downlink and uplink • 10ms RTT and 100ms transition time from idle mode (LTE access setup time) • Scalable bandwidths – for example, 20MHz, 15MHz, 10MHz, 5MHz and 1.25MHz • Support for FDD and TDD with as many commonalities as possible • Cost-effective migration and reduced CAPEX and OPEX For more details regarding the requirements, see 3GPP TR 25.913.2

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cally connected to all its neighboring base stations. The efforts to integrate cdma2000 access will yield a solution that supports seamless mobility between cdma2000 and LTE. The integration will support single- and dualradio handover, allowing for flexible migration from CDMA to LTE. Figure 2 shows how cdma2000 can be integrated into the LTE-SAE architecture. Because the existing QoS concept for GSM and WCDMA systems is somewhat complex, the LTE-SAE targets a QoS concept that combines simplicity and flexible access with backward compatibility. LTE-SAE has adopted a class-based quality-of-service (QoS) concept that gives operators a simple, yet effective solution to differentiating between packet services.

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