Long-Term Evolution (LTE) (3GPP TS 36.300) is a cellular network technology for mobile phone systems, which has a history of almost thirty years. The cellular network capacity can be defined as the average throughput (or data bit rate) per user which is the key issue in providing high quality services for users. It is well known that cellular network suffers from the limited network capacity, especially with the increase in the number of users in the network. This drives the cellular networks towards Broadband Wireless Access (BWA) such as LTE for providing high-speed wireless access over a wide area while satisfying the Quality of Service (QoS) requirement for a variety of services.
Figure 1 illustrates the milestones of cellular technologies from the second generation (2G) to the fourth generation (4G) and shows the increase of the network capacity. Before 2G, the first generation (1G) of cellular network is analog FDMA system, developed in the early of 1980. The use of digital modulation such as TDMA (Time Division Multiple Access) is the significant progress of the 2 generation (2G), as compared to 1G. GSM (Global System for Mobile Communications) is the most popular 2G system, representing the huge success of 2G. Most GSM networks (in Europe) operate in the 900 MHz or 1800 MHz bands. However, the 850 MHz and 1900 MHz bands were used in Canada and the United States. In the 2G mobile system, roaming and security are enhanced with the support of user handoff from a base station (BS) to a neighboring BS.
LTE evolution path
The 2G cellular system with the addition of General Packet Radio Service (GPRS) and Enhanced Data Rates for GSM Evolution (EDGE) is mostly referred as the 2.5G. The original GSM is limited by its network capacity and the per user data rate is scaled by several kbits/s. Upon the original GSM system, the packet data capability is added for packet-oriented mobile data service by means of GPRS in 1997. GPRS provides data rates of 56 kbit/s or more. In 1999, EDGE further improved the speed data transmission. EDGE is also known as Enhanced GPRS (EGPRS) and is first deployed on the GSM system in 2003. The Evolved EDGE typically offers bit-rates of 400kbit/s.
UMTS is one of the third generation (3G) of mobile communication and is the first version is release in 1999 (release99 (R99)). Most of the UMTS systems use Wideband Code Division Multiple Access (WCDMA), which achieves a higher speed and supports more users compared to TDMA. It supports the maximum theoretical data rate of 21 Mbit/s and the user can expect a rate up to 384 kbit/s for R99 handsets and 7.2 Mbit/s for HSDPA handsets in the downlink connection. CDMA2000 EV DO is another 3G technology that is operated on the IP-based backbone. Its downlink achieves up to 2.4 Mbit/s with Rev. 0 and up to 3.1 Mbit/s with Rev. A. The uplink rate for Rev. 0 can operate up to 153 kbit/s while Rev. A can operate at up to 1.8 Mbit/s. The CDMA2000 EV-DO Rev. A and EV-DO Rev. B are considered as the 3.5G technology, offering high data rates for users. High-Speed Downlink Packet Access (HSDPA) is alternative 3.5G network developed based on the UMTS for higher data transfer speeds and capacity. The HSDPA downlink speeds achieve 1.8, 3.6, 7.2 and 14.0 Mbit/s and HSPA+ achieves higher data rate with speeds of up to 42 Mbit/s downlink and 84 Mbit/s with Release 9 of the 3GPP standards.