Evolution of Cellular Systems 21
1.6.3 LTE
The drastic growth of use of the Internet was the motivation for mobile broadband. As
the mobile devices were continuously integrating various applications dealing with
information, communication and medium of entertainments, it was the demand of time
to enable the on‐demand access to multimedia content from anywhere. Statics showed
that by the end of March 2009, the number of mobile broadband subscribers reached 225
million. To meet this huge number of services with higher performance, LTE design
integrates some important radio and core network technologies. Amongst those technologies, the key features of LTE are discussed in three subsections below [10,24]:
1.6.3.1 Orthogonal Frequency Division Multiplexing (OFDM)
Orthogonal Frequency Division Multiplexing (OFDM) was the key difference between
the existing 3G systems and the LTE. The traditional 3G systems were based on UMTS
and CDMA 2000, where CDM techniques were used. OFDMA provides high data rates
along with many more advantages. Due to high data rates, there are more probabilities
of intersymbol interference because of multipath. OFDMA was the solution for the
problem, by using multicarrier modulation, where high bit rate data streams are divided
into several parallel lower bit rates. OFDMA also reduced the computational complexity, because of the implementation of Fast Fourier Transform (FFT). There were other
advantages such as coding and interleaving diversity, efficient multicarrier scheme,
efficient support of broadcast services, etc.
1.6.3.2 SC‐FDE and SC‐FDMA
To achieve better battery life, the Single Carrier Frequency Equalization (SC‐FDE)
transmission method used to transmit the data symbols are sent as a sequence of QAM
symbols with an added cyclic prefix. For the uplink of LTE implements, SC‐FDMA
(multiple version of SC‐FDE) allows multiple users to use parts of the frequency spectrum. The complexity of the transmitter and receiver is increased for using these
systems.
1.6.3.3 Multi‐antenna Technique
The multi‐antenna technique provides the solutions of system capacity, link robustness
and spectral efficiency. It is possible to combat multipath fading and obtain transmit
diversity by using multi‐antenna. Beamforming is possible by using multi‐antenna so that
the transmitted signals can be directed towards the most efficient direction of the receiver.
It reduces the signal‐to‐interference ratio. Another important feature is multiuser MIMO,
which allows multiple users in the uplink.
1.6.4 LTE Network Architecture
There are a few differences between the architecture of UMTS and the LTE systems
architecture, which is depicted in Figure 1.10. Unlike the UMTS architecture, there is no
RNC, SGSN and GGSN blocks in the LTE. In LTE, the Node B is known as eNode B,
which is connected to Serving Gateway (S‐GW) to terminate interface towards the
3GPP radio access network and Packet Data Network Gateway (P‐GW) to control
IP data services, including routing, allocating of IP address, enforcing policy, and
1.6.3 LTE
The drastic growth of use of the Internet was the motivation for mobile broadband. As
the mobile devices were continuously integrating various applications dealing with
information, communication and medium of entertainments, it was the demand of time
to enable the on‐demand access to multimedia content from anywhere. Statics showed
that by the end of March 2009, the number of mobile broadband subscribers reached 225
million. To meet this huge number of services with higher performance, LTE design
integrates some important radio and core network technologies. Amongst those technologies, the key features of LTE are discussed in three subsections below [10,24]:
1.6.3.1 Orthogonal Frequency Division Multiplexing (OFDM)
Orthogonal Frequency Division Multiplexing (OFDM) was the key difference between
the existing 3G systems and the LTE. The traditional 3G systems were based on UMTS
and CDMA 2000, where CDM techniques were used. OFDMA provides high data rates
along with many more advantages. Due to high data rates, there are more probabilities
of intersymbol interference because of multipath. OFDMA was the solution for the
problem, by using multicarrier modulation, where high bit rate data streams are divided
into several parallel lower bit rates. OFDMA also reduced the computational complexity, because of the implementation of Fast Fourier Transform (FFT). There were other
advantages such as coding and interleaving diversity, efficient multicarrier scheme,
efficient support of broadcast services, etc.
1.6.3.2 SC‐FDE and SC‐FDMA
To achieve better battery life, the Single Carrier Frequency Equalization (SC‐FDE)
transmission method used to transmit the data symbols are sent as a sequence of QAM
symbols with an added cyclic prefix. For the uplink of LTE implements, SC‐FDMA
(multiple version of SC‐FDE) allows multiple users to use parts of the frequency spectrum. The complexity of the transmitter and receiver is increased for using these
systems.
1.6.3.3 Multi‐antenna Technique
The multi‐antenna technique provides the solutions of system capacity, link robustness
and spectral efficiency. It is possible to combat multipath fading and obtain transmit
diversity by using multi‐antenna. Beamforming is possible by using multi‐antenna so that
the transmitted signals can be directed towards the most efficient direction of the receiver.
It reduces the signal‐to‐interference ratio. Another important feature is multiuser MIMO,
which allows multiple users in the uplink.
1.6.4 LTE Network Architecture
There are a few differences between the architecture of UMTS and the LTE systems
architecture, which is depicted in Figure 1.10. Unlike the UMTS architecture, there is no
RNC, SGSN and GGSN blocks in the LTE. In LTE, the Node B is known as eNode B,
which is connected to Serving Gateway (S‐GW) to terminate interface towards the
3GPP radio access network and Packet Data Network Gateway (P‐GW) to control
IP data services, including routing, allocating of IP address, enforcing policy, and