LTE for UMTS

Evolution to LTE-Advanced

Harri Holma, Antti Toskala

• Editore: Wiley
• Anno: 2011
• ISBN:
  9781119992936
• Edizione: 2
• Argomento: Technology & Engineering
• Categoria: Mobile & Wireless Communications

Written by experts actively involved in the 3GPP standards and product development, LTE for UMTS, Second Edition gives a complete and up-to-date overview of Long Term Evolution (LTE) in a systematic and clear manner. Building upon on the success of the first edition, LTE for UMTS, Second Edition has been revised to now contain improved coverage of the Release 8 LTE details, including field performance results, transport network, self optimized networks and also covering the enhancements done in 3GPP Release 9. This new edition also provides an outlook to Release 10, including the overview of Release 10 LTE-Advanced technology components which enable reaching data rates beyond 1 Gbps.

Key updates for the second edition of LTE for UMTS are focused on the new topics from Release 9 & 10, and include:

• LTE-Advanced;
• Self optimized networks (SON);
• Transport network dimensioning;
• Measurement results.

Chapter 1

Introduction

Harry Holma and Antti Toskala

1.1 Mobile Voice Subscriber Growth

The number of mobile subscribers increased tremendously from 2000 to 2010. The first billion landmark was passed in 2002, the second billion in 2005, the third billion 2007, the fourth billion by the end of 2008 and the fifth billion in the middle of 2010. More than a million new subscribers per day have been added globally—that is more than ten subscribers on average every second. This growth is illustrated in Figure 1.1. Worldwide mobile phone penetration is 75%1. Voice communication has become mobile in a massive way and the mobile is the preferred method of voice communication, with mobile networks covering over 90% of the world's population. This growth has been fueled by low-cost mobile phones and efficient network coverage and capacity, which is enabled by standardized solutions, and by an open ecosystem leading to economies of scale. Mobile voice is not the privilege of the rich; it has become affordable for users with a very low income.

Figure 1.1 Growth of mobile subscribers

1.2 Mobile Data Usage Growth

Second-generation mobile networks—like the Global System for Mobile Communications (GSM)—were originally designed to carry voice traffic; data capability was added later. Data use has increased but the traffic volume in second-generation networks is clearly dominated by voice traffic. The introduction of third-generation networks with High Speed Downlink Packet Access (HSDPA) boosted data use considerably.

Data traffic volume has in many cases already exceeded voice traffic volume when voice traffic is converted into terabytes by assuming a voice data rate of 12 kbps. As an example, a European country with three operators (Finland) is illustrated in Figure 1.2. The HSDPA service was launched during 2007; data volume exceeded voice volume during 2008 and the data volume was already ten times that of voice by 2009. More than 90% of the bits in the radio network are caused by HSDPA connections and less than 10% by voice calls. High Speed Downlink Packet Access data growth is driven by high-speed radio capability, flat-rate pricing schemes and simple device installation. In short, the introduction of HSDPA has turned mobile networks from voice-dominated to packet-data-dominated networks.

Figure 1.2 HSDPA data volume exceeds voice volume (voice traffic 2007 is scaled to one)

Data use is driven by a number of bandwidth-hungry laptop applications, including internet and intranet access, file sharing, streaming services to distribute video content and mobile TV, and interactive gaming. Service bundles of video, data and voice—known also as triple play—are also entering the mobile market, causing traditional fixed-line voice and broadband data services to be replaced by mobile services, both at home and in the office.

A typical voice subscriber uses 300 minutes per month, which is equal to approximately 30 megabytes of data with the voice data rate of 12.2 kbps. A broadband data user can easily consume more than 1000 megabytes (1 gigabyte) of data. The heavy broadband data use takes between ten and 100 times more capacity than voice usage, which sets high requirements for the capacity and efficiency of data networks.

It is expected that by 2015, five billion people will be connected to the internet. Broadband internet connections will be available practically anywhere in the world. Already, existing wireline installations can reach approximately one billion households and mobile networks connect more than three billion subscribers. These installations need to evolve into broadband internet access. Further extensive use of wireless access, as well as new wireline installations with enhanced capabilities, is required to offer true broadband connectivity to the five billion customers.

1.3 Evolution of Wireline Technologies

Wide-area wireless networks have experienced rapid evolution in terms of data rates but wireline networks are still able to provide the highest data rates. Figure 1.3 illustrates the evolution of peak user data rates in wireless and wireline networks. Interestingly, the shape of the evolution curve is similar in both domains with a relative difference of approximately 30 times. Moore's law predicts that the data rates should double every 18 months. Currently, copper-based wireline solutions with Very-High-Data-Rate Digital Subscriber Line (VDSL2) can offer bit rates of tens of Mbps and the passive optical-fiber-based solution provides rates in excess of 100 Mbps. Both copper and fiber based solutions will continue to evolve in the near future, increasing the data rate offerings to the Gbps range.

Figure 1.3 Evolution of wireless and wireline user data rates GPON = Gigabit Passive Optical Network. VDSL = Very High Data Rate Subscriber Line. ADSL = Asymmetric Digital Subscriber Line

Wireless networks must push data rates higher to match the user experience that wireline networks provide. Customers are used to wireline performance and they expect the wireless networks to offer comparable performance. Applications designed for wireline networks drive the evolution of the wireless data rates. Wireless solutions also have an important role in providing the transport connections for the wireless base stations.

Wireless technologies, on the other hand, have the huge advantage of being able to offer personal broadband access independent of the user's location—in other words, they provide mobility in nomadic or full mobile use cases. The wireless solution can also provide low-cost broadband coverage compared to new wireline installations if there is no existing wireline infrastructure. Wireless broadband access is therefore an attractive option, especially in new growth markets in urban areas as well as in rural areas in other markets.

1.4 Motivation and Targets for LTE

Work towards 3GPP Long Term Evolution (LTE) started in 2004 with the definition of the targets. Even though High-Speed Downlink Packet Access (HSDPA) was not yet deployed, it was evident that work for the next radio system should be started. It takes more than five years from system target settings to commercial deployment using interoperable standards, so system standardization must start early enough to be ready in time. Several factors can be identified driving LTE development: wireline capability evolution, need for more wireless capacity, need for lower cost wireless data delivery and competition from other wireless technologies. As wireline technology improves, similar evolution is required in the wireless domain to ensure that applications work fluently in that domain. There are also other wireless technologies—including IEEE 802.16—which promised high data capabilities. 3GPP technologies must match and exceed the competition. More capacity is needed to benefit maximally from the available spectrum and base station sites. The driving forces for LTE development are summarized in Figure 1.4.

Figure 1.4 Driving forces for LTE development

LTE must be able to deliver performance superior to that of existing 3GPP networks based on HSPA technology. The performance targets in 3GPP are defined relative to HSPA in Release 6. The peak user throughput should be a minimum of 100 Mbps in the downlink and 50 Mbps in the uplink, which is ten times more than HSPA Release 6. Latency must also be reduced to improve performance for the end user. Terminal power consumption must be minimized to enable more use of multimedia applications without recharging the battery. The main performance targets are listed below and are shown in Figure 1.5:

• spectral efficiency two to four times more than with HSPA Release 6;
• peak rates exceed 100 Mbps in the downlink and 50 Mbps in the uplink;
• enables a round trip time of <10 ms;
• packet switched optimized;
• high level of mobility and security;
• optimized terminal power efficiency;
• frequency flexibility with allocations from below 1.5 MHz up to 20 MHz.

Figure 1.5 Main LTE performance targets compared to HSPA Release 6

1.5 Overview of LTE

The multiple-access scheme in the LTE downlink uses Orthogonal Frequency Division Multiple Access (OFDMA). The uplink uses Single Carrier Frequency Division Multiple Access (SC-FDMA). Those multiple-access solutions provide orthogonality between the users, reducing interference and improving network capacity. Resource allocation in the frequency domain takes place with the resolution of 180 kHz resource blocks both in uplink and in downlink. The frequency dimension in the packet scheduling is one reason for the high LTE capacity. The uplink user specific allocation is continuous to enable single-carrier transmission, whereas the downlink can use resource blocks freely from different parts of the spectrum. The uplink single-carrier solution is also designed to allow efficient terminal power amplifier design, which is relevant for terminal battery life. The LTE solution enables spectrum flexibility. The transmission bandwidth can be selected between 1.4 MHz and 20 MHz depending on the available sp...