LONG TERM EVOLUTION (LTE) TECHNOLOGY

Abstract

To be able to offer users a mobile broadband service over a truly fourth generation or 4G network a provider will have to completely upgrade their entire network infrastructure the 3rd Generation Partnership Project (3GPP) has standardized a further development of UMTS. The successor to UMTS is referred to as long term evolution (LTE) and will permit more powerful and more spectral-efficient mobile radio transmission. LTE uses both frequency division duplex (FDD) and time division duplex (TDD) as duplex modes. This paper describes the LTE technology in detail and highlights any differences between LTE TDD and LTE FDD technology. Special characteristics and specific challenges to be faced during network planning are also described.

Full text

International Journal of Latest Technology in Engineering Management & Applied Science (IJLTEMAS)
69
ISSN 2278 – 2540 VOLUME 1, ISSUE 3, JUNE 2012
LONG TERM EVOLUTION (LTE) TECHNOLOGY
Gyan vardhan artist1 (gyanvardhan19@gmail.com) SITE,Nathwdara(Raj)
Mahendra kumar bairwa2 (mahendrabairwa84@gmail.com) SITE,Nathwdara
Priyanka Parihar(er.priyankap@gmail.com)LMCT,Indore(MP)
Mohit Arora(er.m.arora@gmail.com),Sec Sikar (Raj)
Abstract— To be able to offer users a mobile
broadband service over a truly fourth generation or
4G network a provider will have to completely
upgrade their entire network infrastructure the 3rd
Generation Partnership Project (3GPP) has
standardized a further development of UMTS. The
successor to UMTS is referred to as long term
evolution (LTE) and will permit more powerful and
more spectral-efficient mobile radio transmission. LTE
uses both frequency division duplex (FDD) and time
division duplex (TDD) as duplex modes. This paper
describes the LTE technology in detail and highlights
any differences between LTE TDD and LTE FDD
technology. Special characteristics and specific
challenges to be faced during network planning are
also described.
Keywords— 3GPP , UMTS, LTE
I
NTRODUCTION
LTE is the next step in the evolution of the UMTS
technology. As the successor to UMTS, LTE should
make transmissions possible at data rates of over 100
Megabit/s in the downlink and over 50 Megabit/s in
the uplink as well as reduce latency for packet
transmissions. LTE support bandwidths of up to 20
MHz. Scalable bandwidths help ensure that LTE is
compatible with existing mobile radio systems.
Orthogonal frequency division multiple access
(OFDMA) is the multiple access method used in the
LTE downlink. The LTE uplink is based on the
single-carrier frequency division multiple access (SD-
FDMA) mode. This mode is similar to OFDMA, but
has the advantage SC-FDMA that signals exhibit a
lower peak-to-average power ratio (PAPR).
LTE has two different duplex modes for separating
the transmission directions from the user is the base
station and back: frequency division duplex (FDD)
and time division duplex (TDD).In the case of FDD,
the downlink and uplink are transmitted using
different frequencies. In TDD , the downlink and the
uplink are on the same frequency and the separation
occurs in the time domain, so that each direction in a
call is assigned to specific timeslots. This paper
describes the details of the LTE TDD (TD-LTE)
technology and highlights any differences from the
LTE FDD technology. Special characteristics and
specific challenges to be faced during network
planning are also described.
Frequency bands
The TDD duplex mode is used for transmissions
in unpaired frequency bands. This means that the
TDD bands already defined for UMTS can also
be used for LTE TDD. The TDD bands defined
by 3GPP are presented in Table 1, although it is
possible that more bands will be added
Table 1: LTE TDD frequency bands
LTE TDD Physical layer
Frame structure

International Journal of Latest Technology in Engineering Management & Applied Science (IJLTEMAS)
70
ISSN 2278 – 2540 VOLUME 1, ISSUE 3, JUNE 2012
Both the uplink and downlink for LTE are
divided into radio ames, each 10 ms in length
Figure 1 shows the frame structure for LTE TDD
Figure 1: TDD frame structure
The frame consists of two "half-frames" of equal
length, with each half-frame consisting of either 10
slots or 8 slots plus the three special fields downlink
pilot time slot (DwPTS), guard period (GP) and
uplink pilot time slot (UpPTS) in a special sub frame.
Each slot is 0.5 ms in length and two consecutive slots
form exactly one sub frame, just like with FDD. The
lengths of the individual special fields depend on the
uplink/downlink configuration selected by the
network, but the total length of the three fields
remains constant at 1 ms.
Resource structure
The resource structure is exactly the same for both
LTE TDD and LTE FDD. The smallest resource unit
in the time domain is an OFDM symbol in the
downlink and an SC-FDMA symbol in the uplink.
The number of OFDM/SC-FDMA symbols in a slot
depends on the length of the prefix being used as a
guard period between the symbols. The smallest
dimensional unit for assigning resources in the
frequency domain is a "resource block" (RB) with a
bandwidth of 180 kHz, which corresponds to Nsc=12
subcarriers, each at 15 kHz offset from carrier. The
uplink and downlink parameters are listed in Table 2,
Figure 2 shows the resource structure for LTE.
Figure 2: Slot structure
Table 2: Uplink/downlink parameterization of LTE
In contrast to UMTS WCDMA/HSPA, various
different bandwidths are supported for LTE, making it
compatible with existing mobile radio networks. The
channel bandwidth is defined by the number of
available resource blocks NRB and is scalable. This
scalability allows radio resources to b e used
efficiently. Table 3 lists the bandwidths supported by
LTE and the associated number of resource blocks
NRB. These parameters are defined the same for LTE
TDD and LTE FDD.
Table 3: LTE bandwidths

International Journal of Latest Technology in Engineering Management & Applied Science (IJLTEMAS)
71
ISSN 2278 – 2540 VOLUME 1, ISSUE 3, JUNE 2012
Uplink/downlink configurations
LTE TDD uses the same frequency bands for the
uplink and the downlink. The transmission
directions are separated by carrying the UL and
DL data in different sub frames. The distribution
of sub frames between the transmission
directions can be adapted to the data traffic and is
done either symmetrically (equal number of DL
and UL sub frames) or asymmetrically Table4
shown the UL/DL configurations that are defined
for LTE TDD. In this table, "D" means that DL
data is transmitted in this sub frame. Similarly,
"U" indicates uplink data transmission and "S"
specifies that the special fields DwPTS, GP and
UpPTS are transmitted in this sub frame.
Table 4: Uplink/downlink configurations
LTE TDD Protocol layer
In order to meet the demands for high data rates and
short latency, the protocol architecture for LTE has
also been modified. Figure 3 shows the network
architecture developed for LTE and the functionality
of the individual nodes.
The base station (eNB) handles functions such as
uplink and downlink scheduling, mobility control,
radio bearer and admission control. It is connected to
the evolved packet core ( EPC) via the S1 interface.
The EPC consists of a serving gateway ( S-GW), a
mobility management entity (MME) and a packet data
network gateway (P-GW).
Figure 3: 3GPP SAE network architect
CONCLUSION
In this paper, The the LTE technology is described
using network and protocol architecture above applies
to both LTE FDD and LTE TDD. The control
information for the radio resource control (RRC)
protocol will differ as a result of the described
differences in the physical layer between LTE FDD
and LTE TDD.
REFERENCES
[1] Peter W .C. Chan, Ernest S. Lo, Ray R.Wang:
"The Evolution Path of 4G Networks, IEEE,
December 2010
[2] 3GPP TS 36.104; Base Station (BS) radio
transmission and reception (Release 11)
[3] 3GPP TS 36.211; Physical channels and
modulation (Release 11)
[4] 3GPP TS 36.212; Multiplexing and channel
coding (Release 11)
[5] 3GPP TS 36.213; Physical layer procedures
(Release 11)
[6] Harri Holma, Sanna Heikkinen, Otto-Aleksanteri
Lehtinen: "Interference Consideration for UMTS
Terrestrial Radio Access.