3GPP LTE (Long Term Evolution) is the Third Generation Mobile Wireless Broadband Partnership Project that helps Operators to provide Wireless Broadband Services at affordable prices with enhanced performance and capacity. It improves the existing UMTS mobile phone standard to manage future requirements. It is the natural evolution of 3GPP GSM, WCDMA, and 3GPP2 CDMA networks. The final outcome of this project is the new version 8 of the UMTS standard that includes new extensions and modifications of the UMTS system. This Release is intended for use over any IP network that includes WiMAX, WiFi, and wired networks.
3GPP LTE aims to provide a set of specifications for improved efficiency and services, lowered costs, better spectrum usage and integration with other open standards. The envisioned product availability is around 2009 – 2010. The key performance and capability targets for the long-term evolution are given below.
- To provide significantly higher data rates with target peak data rates of more than 100Mbps over the downlink and 50Mbps over the uplink for every 20 MHz of spectrum
- To improve wide-area coverage with at least 200 active users in every 5 MHz cell
- To reduce latency to sub-5 ms for small IP packets so that performance can be boosted
- To increase spectrum flexibility with spectrum slices as small as 1.25 MHz and as large as 20 MHz
System Architecture Evolution (SAE)
The LTE effort to meet the technical and performance requirements requires a reduction in the number of network nodes involved in data processing and transport. This has resulted in new System Architecture Evolution (SAE) which becomes the core network architecture of 3GPP’s future LTE wireless communication standard.
The main component is the Evolved Packet Core (EPC), or SAE Core and it serves as GGSN for GPRS networks and GGSN for the new LTE networks and as a generic controller for non-3GPP network. Other components of EPC include:
- Serving GPRS Support Node (SGSN) – to provide connections for GERAN and UTRAN Networks
- Serving Gateway – to terminate the interface toward the 3GPP radio-access networks
- PDN Gateway – to control IP data services like routing, addressing, policy enforcing and providing access to non-3GPP access networks
- Mobility Management Entity (MME) – to manage control plane context, authentication and authorization
- User Plane Entity (UPE) – to manage user contexts, ciphering, packet routing and forwarding, and mobility
- 3GPP anchor – to manage mobility for 2G/3G and LTE systems
- SAE anchor – to manage mobility for non 3GPP RATs
- Policy Control and Charging Rules Function (PCRF) – to manage Quality of Service (QoS) aspects
The UMTS back-end can be accessible through a variety of means like GERAN, UTRAN, E-UTRAN, WiFi, UMB, WiMAX etc. Non-UMTS radio network users are given an entry-point into the IP network, with different levels of security. GSM/UMTS network users will have an integrated system with all authentication at every level of the system is covered. The users accessing the UMTS network through WiMAX will use the WiMAX connection one way and the UMTS link-up another way.
The air interface, Evolved-UTRA (E-UTRA) is used by UMTS operators in deploying their own wireless networks. The E-UTRA system uses OFDMA for the downlink and Single Carrier FDMA for the uplink. It uses MIMO with a maximum of four antennas per station. Quadratic Permutation Polynomial (QPP) turbo code is used as the channel coding scheme for transport blocks.
The Orthogonal Frequency Division Multiplex (OFDM) in E-UTRA offers very robust modulation and more flexibility than the older CDMA based systems by splitting the information on multiple narrowband sub carriers, with each carrier holding a portion of the information at a lower bit rate. The Link spectral efficiency is also greater than that of CDMA. The Multiple Input Multiple Output (MIMO) technology creates several spatial paths on the air interface to carry the same or different streams of information between the network and the subscriber. It increases either the coverage or the user data throughput. With the combined modulation formats of 64QAM and techniques of MIMO, E-UTRA is expected to be highly efficient than W-CDMA with HSDPA and HSUPA.
Downlink Vs Uplink
The OFDM downlink has Subcarrier spacing of 15 KHz with a maximum Number of available sub carriers of 2048. Although the mobile devices require the capacity of receiving all 2048 subcarriers, a base station supports transmission of only 72 subcarriers. The modulation formats allowed include QPSK, 16QAM and 64QAM.
The OFDM uplink allows the modulation formats of SC-FDMA multiplexing, and QPSK or 16QAM (64QAM optional) modulation. Low Peak-to-Average Power Ratio (PAPR) of SC-FDMA plays a very important role in modulation. The virtual MIMO / Spatial division multiple access (SDMA) increases the data rate in the uplink direction based on the number of antennas in the base station. This technology allows the resources to be reused.
IPv6 Networks and LTE
The main characteristic of 4G networks is based on IPv6 and all future higher level services like voice, video, messaging etc., are carried on the top of IPv6. So the focus of LTE is to enhance the packet-switched (PS) domain and the future of UMTS is on All IP Network (AIPN). With IPv6 networking, the service delivery has the maximum flexibility, decouples the user and improves scalability allowing the wealth of existing IETF standards to be leveraged. The major requirements include traffic optimal routing, simplification of network, IP-based transport, and seamless mobility.
The major concern in adopting LTE and IPv6 based SAE in enterprises is privacy. This security challenge with IP networks slows down the further adoption of these network technologies. Even if the operators and enterprises are clearly aware of the productivity improvements and cost saving benefits of using convergent communication technologies on a single infrastructure, enabling universal connectivity for users, they are reluctant to adopt the same as the technologies may compromise their privacy, put their business at risk and potentially cause significant financial loss. So an end-to-end system approach to security is necessary in next-generation wireless networks. Some of the mandatory security requirements/measures include the following.
- User authentication, authorization, and auditing
- Secure infrastructure, protocols, communication, and data storage
- Software integrity
- End to end compliance
- Secure network control, signaling and management
- Protection from unsolicited traffic