【資料名稱】：LTE-Rel-8

【資料作者】：xxx

【資料日期】：2012-01-25

【資料語言】：英文

【資料格式】：PDF

【資料目錄和簡介】：

0163-6804/09/$25.00 © 2009 IEEE IEEE Communications Magazine • April 2009
INTRODUCTION
The long-term evolution (LTE) as defined by the
3rd Generation Partnership Project (3GPP) is a
highly flexible radio interface [1, 2]; its initial
deployment is expected by the end of 2009. The
first release of LTE provides peak rates of 300
Mb/s, a radio-network delay of less than 5 ms, a
significant increase in spectrum efficiency compared
to previous cellular systems, and a new flat
radio-network architecture designed to simplify
operation and to reduce cost. LTE supports both
frequency-division duplex (FDD) and time-division
duplex (TDD), as well as a wide range of
system bandwidths in order to operate in a large
number of different spectrum allocations. Furthermore,
LTE also aims for a smooth evolution
from earlier 3GPP systems such as time divisionsynchronous
code division multiple access (TDSCDMA)
and wide-band code division multiple
access/high-speed packet access
(WCDMA/HSPA), as well as 3GPP2 systems
such as code division multiple access (cdma)2000.
Finally, LTE also constitutes a major step toward
international mobile telephony (IMT)-Advanced.
In fact, the first release of LTE already includes
many of the features originally considered for
future fourth-generation systems [3].
For an in-depth description of LTE, the reader
is referred to [1]. A companion article [4] in
this issue discusses the link-layer design. In this
article, we provide an overview of the first
release of LTE, release-8. The basic transmission
schemes in uplink and downlink are described,
and various aspects of LTE, such as spectrum
flexibility, multiple-antenna transmission, and
inter-cell interference coordination are discussed.
This is followed by a set of simulation
results, exemplifying the performance of LTE.
Finally, we offer a short overview of the current,
ongoing work on the evolution of LTE toward
LTE-Advanced and the full IMT-Advanced
capability.
LTE: AN OVERVIEW
BASIC TRANSMISSION SCHEME
Orthogonal frequency-division multiplexing
(OFDM), with data transmitted on a large number
of parallel, narrow-band subcarriers, is the
core of the LTE downlink radio transmission.
Due to the use of relatively narrowband subcarriers
in combination with a cyclic prefix, OFDM
transmission is inherently robust to time dispersion
on the radio channel without a requirement
to resort to advanced and potentially complex
receiver-side channel equalization. For the downlink,
this is an attractive property because it simplifies
the receiver baseband processing with
reduced terminal cost and power consumption as
consequences. This is especially important considering
the wide transmission bandwidths of LTE,
and even more so in combination with advanced
multi-antenna transmission, such as spatial multiplexing
(discussed below in this section).
For the uplink, where the available transmission
power is significantly lower than for the
downlink, the situation is somewhat different.
Rather than the amount of processing power at
the receiver, one of the most important factors in
the uplink design is to enable highly power-efficient
transmission. This improves coverage and reduces
terminal cost and power consumption at the transmitter.
For this reason, single-carrier transmission,
based on discrete Fourier transform (DFT)-precoded
OFDM, sometimes also referred to as singlecarrier
frequency-division multiple access
(SC-FDMA), is used for the LTE uplink. DFTprecoded
OFDM has a smaller peak-to-average
power ratio than regular OFDM, thus enabling
less complex and/or higher-power terminals.
The basic protocol structure of LTE is illustrated
in Fig. 1. The radio link control (RLC)
and medium access control (MAC) layers, among
other tasks, are responsible for retransmission
handling and multiplexing of data flows. In the
physical layer, the data that is to be transmitted
is turbo coded and modulated using one of the
following: quadrature-phase shift keying (QPSK),
16-QAM, or 64-QAM, followed by OFDM modulation.
The subcarrier spacing is 15 kHz and two
cyclic-prefix lengths are supported in both uplink
and downlink, a normal cyclic prefix of 4.7 μs,
suitable for most deployments and an extended
ABSTRACT
This article provides an overview of the LTE
radio interface, recently approved by the 3GPP,
together with a more in-depth description of its
features such as spectrum flexibility, multi-antenna
transmission, and inter-cell interference control.
The performance of LTE and some of its
key features is illustrated with simulation results.
The article is concluded with an outlook into the
future evolution of LTE.