LTE-Advanced Air Interface Technology

Xincheng Zhang, Xiaojin Zhou

• Publisher: CRC Press
• Year: 2012
• eBook ISBN: 9781466578814
• Topic: Computer Science
• Subtopic: Information Technology
• Index: Computer Science

Opportunities are at hand for professionals eager to learn and apply the latest theories and practices in air interface technologies. Written by experienced researchers and professionals, LTE-Advanced Air Interface Technology thoroughly covers the performance targets and technology components studied by 3GPP for LTE-Advanced. Besides being an expla

Chapter 1

From LTE to LTE-A

Exponential growth in traffic volume calls for high data rates with mobility to meet the ever-increasing user demands. Multimedia traffic is increasing far more rapidly than speech traffic and will increasingly dominate traffic flows. Enhanced peak data rates are definitely necessary to support advanced services and applications. According to Nielsen’s Law, network connection speeds for high-end home users will increase by 50% per year, or double every 21 months (as shown in Figure 1.1). This growth rate is slightly slower than Moore’s Law of processor power growth (double in 18 months).

From 1980, with the bulky first-generation analog handsets, the wireless cellular communications industry traveled a long evolutionary path (as shown in Figure 1.2) and now enjoys a major presence in the world. When Global System for Mobile Communication (GSM) multiple access technology was selected 1987, Code Division Multiple Access (CDMA) was already proposed. When Wideband Code Division Multiple Access (WCDMA) multiple access technology was selected 1998, orthogonal frequency-division multiple access (OFDMA) was already proposed. The Long Term Evolution (LTE) study item was initiated in the Third-Generation Partnership Project (3GPP) back in 2004 to develop a framework for the evolution of the 3GPP radio access technology toward a high-data-rate, low-latency, and packet-optimized radio access technology. An LTE market opportunity has emerged during the past two years, and consequently most vendors now have relatively well-defined solutions that are scheduled to be ready for initial rollout. We believe that LTE will become the dominant mobile network technology and that most network operators will upgrade to it. But are there any other real options? Has the industry reached the ultimate multiple access?

Figure 1.1 Nielsen’s Law of Internet Speed.

Figure 1.2 Mobile communication system evolution.

1.1 Review of LTE

1.1.1 Wireless Technologies

Wireless technology is playing a profound role in networking and communications because it provides two fundamental capabilities: mobility and access. Today’s wireless market winners (shown in Figure 1.3) are medium-capacity mobile broadband networks, including Enhanced Data Rates for GSM Evolution (EDGE), WCDMA, High Speed Packet Access (HSPA), and the LTE of the International Telecommunications Union (ITU) family, wireless local-area networks (WLAN), and Worldwide Interoperability for Microwave Access (WiMAX) of the Institute of Electrical and Electronics Engineers (IEEE) family. Currently, IEEE 802.16-2004/802.16e (Portable and Mobile WiMAX) and 3GPP LTE are two major mobile broadband radio technologies.

In the ITU family, the Universal Mobile Telecommunications System (UMTS) employs the wideband CDMA radio-access technology to establish third-generation (3G) wireless networks. The primary benefits of UMTS include high spectral efficiency for voice and data, and simultaneous voice and data capability for users. Initial UMTS network deployments were based on 3GPP Release 99 specifications, in which the maximum theoretical downlink rate is just over 2 Mbps. Since then, Rel-5 defined High-Speed Downlink Packet Access (HSDPA), which delivers downlink (DL) peak theoretical rates of 14 Mbps, and Rel-6 defined High-Speed Uplink Packet Access (HSUPA). With HSPA-capable devices, the network uses HSPA (HSDPA/HSUPA) for data transmission. Now, HSPA+ with 42-Mbps capability on the downlink by higher-order modulation and multiple-input, multiple-output (MIMO) and 11.5 Mbps on the uplink (UL) have been widely deployed.

Figure 1.3 Popular wireless technologies. The dashed lines indicate the two evolution paths and directions of IEEE and 3GPP.

LTE is a standard for wireless data communications technology and an evolution of the GSM/UMTS standards. The LTE specification provides downlink peak rates of 300 Mbps (4x4 MIMO), uplink peak rates of 75 Mbps, and quality of service (QoS) provisions permitting round-trip times of less than 10 ms. LTE has the ability to manage fast-moving mobiles and provides support for multicast and broadcast streams. LTE supports scalable carrier bandwidths, from 1.4 MHz to 20 MHz, and supports both frequency-division duplexing (FDD) and time-division duplexing (TDD) system. The architecture of the network is simplified to a flat IP-based network architecture called the Evolved Packet Core (EPC), designed to replace the general packet radio service (GPRS) core network and support seamless handovers for both voice and data to cell towers with older network technology such as GSM, UMTS and CDMA2000. The possible peak data rates along the LTE evolution path are summarized in Figure 1.4.

Figure 1.4 Evolution of the mobile network.

LTE Advanced (LTE-A) is expected to provide higher data rates while maintaining coverage proportional to LTE Release 8 (Rel-8). It aims to provide peak data rates of 1 Gbps in downlink and 500 Mbps in uplink, bandwidth scalability up to 100 MHz, increased spectral efficiency up to 15 bps/Hz in uplink (UL) and 30 bps/Hz in DL, improved cell-edge capacity, as well as decreased user and control plane latencies relative to LTE Rel-8.

1.1.2 LTE Performance

LTE Rel-8 is one of the primary broadband technologies based on Orthogonal Frequency-Division Multiplexing (OFDM), which is currently being commercialized. During 2005, LTE and System Architecture Evolution (SAE) study items were set up in 3GPP. Both operators and manufacturers were keen to push these study items because they were facing competition from other technologies such as WiMAX. Operators are looking for significant improvements compared to current UMTS releases that provide an architecture that is better suited to the shift from circuit-switched communications toward packet data and a radio technology that enables spectrum refarming. LTE Rel-8 provides high peak data rates of 150 Mbps (2x2 MIMO) on the downlink and 75 Mbps on the uplink for a 20-MHz bandwidth and allows flexible bandwidth operation of from 1.4 MHz up to 20 MHz. LTE Rel-8, which is mainly deployed in a macro/micro cell layout, provides improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multiantenna support, flexible bandwidth operation, and seamless integration with existing systems. Not only is OFDMA good for single cell, but also a better solution may be optimized for full intercell interference coordination. A comparison of the requirements and performance results of LTE is shown in Table 1.1.

The LTE network architecture is designed with the goal of supporting packet-switched traffic with seamless mobility, QoS, and minimal latency. LTE Rel-8 supports a cell average spectral efficiency gain of 2–3 times HSPA Rel-6, with radio network user plane latency below 10 ms (round-trip time, or RTT). The packet-switched approach in LTE allows support for all services including voice through packet only connections. Therefore, a highly simplified flatter architecture is adopted by LTE with only two node types: evolved Node-B (eNB) and mobility management entity/gateway (MME/GW). Compared to 3G systems, LTE reduced the number of different types of radio access network (RAN) nodes and their complexity, reduced capital expenditure (CAPEX) and operating expenses (OPEX), and reduced the complexity of terminals. The LTE network would coexist with both the UMTS/HSPA terrestrial radio access network (UTRAN) and the GSM/EDGE radio access network (GERAN).

Table 1.1 LTE Requirements versus LTE Performance

1.1.3 Challenges to the Next-Generation Network

Although LTE has much better performance than its predecessors, ongoing improved service requirements always put challenges ahead of wireless network development. The next-generation network requires lower radio latency, higher spectral efficiency, and more flexible and faster mobility, as well as some kind of cognitive radio that enables optimized spectrum usage over multiple operators. All these requirements need evolution at the air interface and new network topology development, as illustrated in Figure 1.5.

Furthermore, the IP-optimized mobile network in the future will provide various types of communications services through high bandwidth, low latency, and new packet-optimized broadband radio technologies. Based on the modern flat network structure, the next-generation network (as illustrated in Figure 1.6) will deploy many state-of-the-art technologies, including cooperative multipoint communication, cognitive radio, multilayer communication, heterogeneous networks and advanced MIMO, to implement a brand new mobile communication architecture. The flat network architecture will provide support to distributed antennas, multiple radio access, and hybrid networking, while aiming to achieve “green” communication. With the existence of smart terminals and the popularity of mobile Internet, a more powerful mobile network should be developed to provide a better user experience.

Figure 1.5 Challenges to mobile networks.

Figure 1.6 Next-generation mobile networks.

1.2 Performance Targets of LTE-A

In order to exceed the performance requirements for International Mobile Telecommunications-Advanced (IMT-A),...

Table of contents

• Cover
• Title Page
• Copyright
• Contents
• Preface
• About the Authors
• 1 From LTE to LTE-A
• 2 Carrier Aggregation
• 3 Collaborative Multipoint
• 4 MIMO
• 5 Relaying
• 6 Self-Organizing Network
• 7 Heterogeneous Networks
• 8 Interference Suppression and eICIC Technology
• Glossary of Acronyms
• Bibliography
• Index