Subject to change – C.Gessner 03.2007 – 1MA111_0E
Rohde & Schwarz Products: FSQ, FSQ-K100, FSQ-K101, SMU200A, SMU-K55, SMU-K255,
SMATE200A, SMATE-K55, SMATE-K255, SMJ100A, SMJ-K55, SMJ-K255,
WinIQSIM2, AFQ100A, AFQ-K255, AMU200A, AMU-K55, AMU-K255
UMTS Long Term Evolution (LTE)
Technology Introduction
Application Note 1MA111
Even with the introduction of HSDPA and HSUPA, evolution of UMTS has not reached its end. To ensure
the competitiveness of UMTS for the next 10 years and beyond, UMTS Long Term Evolution (LTE) is being
specified in 3GPP release 8. LTE, which is also known as Evolved UTRA and Evolved UTRAN, provides
new physical layer concepts and protocol architecture for UMTS. This application note introduces LTE
technology and testing aspects.
LTE/E-UTRA
1MA111_0E 2 Rohde & Schwarz
Contents
1 Introduction.............................................................................................. 3
2 Requirements for UMTS Long Term Evolution ....................................... 4
3 LTE Downlink Transmission Scheme...................................................... 5
OFDMA .............................................................................................. 5
OFDMA parametrization..................................................................... 6
Downlink Data Transmission.............................................................. 8
Downlink Reference Signal Structure and Cell Search...................... 8
Downlink Physical Layer Procedures............................................... 10
4 LTE Uplink Transmission Scheme ........................................................ 11
SC-FDMA......................................................................................... 11
SC-FDMA Parametrization............................................................... 12
Uplink Reference Signal Structure ................................................... 13
Uplink Physical Layer Procedures ................................................... 13
5 LTE MIMO Concepts............................................................................. 15
Downlink MIMO................................................................................ 15
Uplink MIMO .................................................................................... 17
6 LTE Protocol Architecture...................................................................... 17
System Architecture Evolution (SAE)............................................... 17
E-UTRAN ......................................................................................... 18
Layer 2 structure .............................................................................. 20
Transport channels .......................................................................... 21
Logical channels .............................................................................. 21
7 LTE MBMS Concepts ............................................................................ 22
8LTE Testing............................................................................................ 23
LTE RF testing ................................................................................. 23
LTE Layer 1 and Protocol Test ......................................................... 27
9 Abbreviations......................................................................................... 27
10 Additional Information ........................................................................... 30
11 References............................................................................................ 30
12 Ordering Information ............................................................................. 30
The following abbreviations are used in this application note for R&S test
equipment:
- The Vector Signal Generator R&S® SMU200A is referred to as the
SMU200A.
- The Vector Signal Generator R&S® SMATE200A is referred to as the
SMATE200A.
- The Vector Signal Generator R&S® SMJ100A is referred to as the
SMJ100A.
- SMU200A, SMATE200A, and SMJ100A in general is referred to as the
SMx.
- The IQ Modulation Generation R&S® AFQ100A is referred to as the
AFQ100A.
- The Baseband Signal Generator and Fading Simulator R&S®
AMU200A is referred to as the AMU200A.
- The Signal Analyzer R&S® FSQ is referred to as FSQ.
LTE/E-UTRA
1MA111_0E 3 Rohde & Schwarz
1 Introduction
Currently, UMTS networks worldwide are being upgraded to High Speed
Downlink Packet Access (HSDPA) in order to increase data rate and
capacity for downlink packet data. In the next step, High Speed Uplink
Packet Access (HSUPA) will boost uplink performance in UMTS networks.
While HSDPA was introduced as a 3GPP release 5 feature, HSUPA is an
important feature of 3GPP release 6. The combination of HSDPA and
HSUPA is often referred to as HSPA.
However, even with the introduction of HSPA, evolution of UMTS has not
reached its end. HSPA+ will bring significant enhancements in 3GPP
release 7. Objective is to enhance performance of HSPA based radio
networks in terms of spectrum efficiency, peak data rate and latency, and
exploit the full potential of WCDMA based 5 MHz operation. Important
features of HSPA+ are downlink MIMO (Multiple Input Multiple Output),
higher order modulation for uplink and downlink, improvements of layer 2
protocols, and continuous packet connectivity.
In order to ensure the competitiveness of UMTS for the next 10 years and
beyond, concepts for UMTS Long Term Evolution (LTE) have been
investigated. Objective is a high-data-rate, low-latency and packet-
optimized radio access technology. Therefore, a study item was launched in
3GPP release 7 on E-UTRA (Evolved UMTS Terrestrial Radio Access) and
E-UTRAN (Evolved UMTS Terrestrial Radio Access Network). LTE/E-
UTRA will then form part of 3GPP release 8 core specifications.
This application note focuses on LTE/E-UTRA technology. In the following,
the terms LTE or E-UTRA are used interchangeably.
In the context of the LTE study item, 3GPP work first focused on the
definition of requirements, e.g. targets for data rate, capacity, spectrum
efficiency, and latency. Also commercial aspects like costs for installing and
operating the network were considered. Based on these requirements,
technical concepts for the air interface transmission schemes and protocols
were studied. Notably, LTE uses new multiple access schemes on the air
interface: OFDMA (Orthogonal Frequency Division Multiple Access) in
downlink and SC-FDMA (Single Carrier Frequency Division Multiple
Access) in uplink. Furthermore, MIMO antenna schemes form an essential
part of LTE. In an attempt to simplify protocol architecture, LTE brings some
major changes to the existing UMTS protocol concepts. Impact on the
overall network architecture including the core network is being investigated
in the context of 3GPP System Architecture Evolution (SAE).
This application note gives an introduction to LTE technology.
Chapter 2 outlines requirements for LTE.
Chapter 3 describes the downlink transmission scheme for LTE.
Chapter 4 describes the uplink transmission scheme for LTE.
Chapter 5 outlines LTE MIMO concepts.
Chapter 6 focuses on LTE protocol architecture.
Chapter 7 introduces LTE MBMS (Multimedia Broadcast Multicast Service)
concepts.
Chapter 8 explains test requirements for LTE.
Chapters 9-12 provide additional information including literature
references.
LTE/E-UTRA
1MA111_0E 4 Rohde & Schwarz
2 Requirements for UMTS Long Term Evolution
LTE is focusing on optimum support of Packet Switched (PS) Services.
Main requirements for the design of an LTE system have been captured in
3GPP TR 25.913 [1] and can be summarized as follows:
- Data Rate: Peak data rates target 100 Mbps (downlink) and 50 Mbps
(uplink) for 20 MHz spectrum allocation, assuming 2 receive antennas
and 1 transmit antenna at the terminal.
- Throughput: Target for downlink average user throughput per MHz is
3-4 times better than release 6. Target for uplink average user
throughput per MHz is 2-3 times better than release 6.
- Spectrum Efficiency: Downlink target is 3-4 times better than release
6. Uplink target is 2-3 times better than release 6.
- Latency: The one-way transit time between a packet being available at
the IP layer in either the UE or radio access network and the availability
of this packet at IP layer in the radio access network/UE shall be less
than 5 ms. Also C-plane latency shall be reduced, e.g. to allow fast
transition times of less than 100 ms from camped state to active state.
- Bandwidth: Scaleable bandwidths of 5, 10, 15, 20 MHz shall be
supported. Also bandwidths smaller than 5 MHz shall be supported for
more flexibility.
- Interworking: Interworking with existing UTRAN/GERAN systems and
non-3GPP systems shall be ensured. Multimode terminals shall support
handover to and from UTRAN and GERAN as well as inter-RAT
measurements. Interruption time for handover between E-UTRAN and
UTRAN/GERAN shall be less than 300 ms for real time services and
less than 500 ms for non real time services.
- Multimedia Broadcast Multicast Services (MBMS): MBMS shall be
further enhanced and is then referred to as E-MBMS.
- Costs: Reduced CAPEX and OPEX including backhaul shall be
achieved. Cost effective migration from release 6 UTRA radio interface
and architecture shall be possible. Reasonable system and terminal
complexity, cost and power consumption shall be ensured. All the
interfaces specified shall be open for multi-vendor equipment
interoperability.
- Mobility: The system should be optimized for low mobile speed (0-15
km/h), but higher mobile speeds shall be supported as well including
high speed train environment as special case.
- Spectrum allocation: Operation in paired (Frequency Division Duplex /
FDD mode) and unpaired spectrum (Time Division Duplex / TDD
mode) is possible.
- Co-existence: Co-existence in the same geographical area and co-
location with GERAN/UTRAN shall be ensured. Also, co-existence
between operators in adjacent bands as well as cross-border co-
existence is a requirement.
- Quality of Service: End-to-end Quality of Service (QoS) shall be
supported. VoIP should be supported with at least as good radio and
LTE/E-UTRA
1MA111_0E 5 Rohde & Schwarz
backhaul efficiency and latency as voice traffic over the UMTS circuit
switched networks
- Network synchronization: Time synchronization of different network
sites shall not be mandated.
3 LTE Downlink Transmission Scheme
OFDMA
The downlink transmission scheme for E-UTRA FDD and TDD modes is
based on conventional OFDM. In an OFDM system, the available spectrum
is divided into multiple carriers, called sub-carriers, which are orthogonal to
each other. Each of these sub-carriers is independently modulated by a low
rate data stream.
OFDM is used as well in WLAN, WiMAX and broadcast technologies like
DVB. OFDM has several benefits including its robustness against multipath
fading and its efficient receiver architecture.
Figure 1 shows a representation of an OFDM signal taken from [2]. In this
figure, a signal with 5 MHz bandwidth is shown, but the principle is of
course the same for the other E-UTRA bandwidths. Data symbols are
independently modulated and transmitted over a high number of closely
spaced orthogonal sub-carriers. In E-UTRA, downlink modulation schemes
QPSK, 16QAM, and 64QAM are available.
In the time domain, a guard interval may be added to each symbol to
combat inter-OFDM-symbol-interference due to channel delay spread. In E-
UTRA, the guard interval is a cyclic prefix which is inserted prior to each
OFDM symbol.
…
Sub-carriers
FFT
Time
Symbols
5 MHz Bandwidth
Guard Intervals
…
Frequency
Figure 1 Frequency-Time Representation of an OFDM Signal
In practice, the OFDM signal can be generated using IFFT (Inverse Fast
Fourier Transform) digital signal processing. The IFFT converts a number N
of complex data symbols used as frequency domain bins into the time
domain signal. Such an N-point IFFT is illustrated in Figure 2, where
a(mN+n) refers to the n
th
sub-channel modulated data symbol, during the
time period mT
u
<t
≤
(m+1)T
u
.