R&S®FSQ-K10x (LTE Downlink)
LTE Downlink Measurement
Application
User Manual
(;×6DZ)
1173.0620.42 ─ 06
User Manual
Test & Measurement
This manual describes the following firmware applications:
● R&S®FSQ-K100 EUTRA / LTE FDD Downlink Measurement Application (1308.9006.02)
● R&S®FSQ-K102 EUTRA / LTE MIMO Downlink Measurement Application (1309.9000.02)
● R&S®FSQ-K104 EUTRA / LTE TDD Downlink Measurement Application (1309.9422.02)
This manual is applicable for the following R&S analyzer models with firmware 4.7x SP4 and higher:
● R&S®FSQ3 (1307.9002K03)
● R&S®FSQ8 (1307.9002K07)
● R&S®FSQ26 (1307.9002K13)
● R&S®FSQ40 (1307.9002K30)
● R&S®FSG8 (1309.0002.08)
● R&S®FSG13 (1309.0002.13)
© 2012 Rohde & Schwarz GmbH & Co. KG
Muehldorfstr. 15, 81671 Munich, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
E-mail: info@rohde-schwarz.com
Internet: http://www.rohde-schwarz.com
Printed in Germany – Subject to change – Data without tolerance limits is not binding.
R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG.
Trade names are trademarks of the owners.
The following abbreviations are used throughout this manual: R&S®FSQ is abbreviated as R&S FSQ.
Customer Support
Technical support – where and when you need it
For quick, expert help with any Rohde & Schwarz equipment, contact one of our Customer Support
Centers. A team of highly qualified engineers provides telephone support and will work with you to find a
solution to your query on any aspect of the operation, programming or applications of Rohde & Schwarz
equipment.
Up-to-date information and upgrades
To keep your instrument up-to-date and to be informed about new application notes related to your
instrument, please send an e-mail to the Customer Support Center stating your instrument and your wish.
We will take care that you will get the right information.
Europe, Africa, Middle East
North America
Latin America
Asia/Pacific
China
Phone +49 89 4129 12345
customersupport@rohde-schwarz.com
Phone 1-888-TEST-RSA (1-888-837-8772)
customer.support@rsa.rohde-schwarz.com
Phone +1-410-910-7988
customersupport.la@rohde-schwarz.com
Phone +65 65 13 04 88
customersupport.asia@rohde-schwarz.com
Phone +86-800-810-8228 /
+86-400-650-5896
customersupport.china@rohde-schwarz.com
1171.0200.22-06.00
R&S®FSQ-K10x (LTE Downlink)
Contents
1 Preface....................................................................................................7
1.1 Documentation Overview.............................................................................................7
1.2 Typographical Conventions.........................................................................................8
2 Introduction............................................................................................9
2.1 Requirements for UMTS Long-Term Evolution..........................................................9
2.2 Long-Term Evolution Downlink Transmission Scheme..........................................11
2.2.1 OFDMA.........................................................................................................................11
2.2.2 OFDMA Parameterization.............................................................................................12
2.2.3 Downlink Data Transmission.........................................................................................14
2.2.4 Downlink Reference Signal Structure and Cell Search.................................................14
Contents
2.2.5 Downlink Physical Layer Procedures............................................................................16
2.3 References...................................................................................................................16
3 Welcome...............................................................................................18
3.1 Installing the Software................................................................................................18
3.2 Application Overview..................................................................................................18
3.3 Support........................................................................................................................20
4 Measurement Basics...........................................................................21
4.1 Symbols and Variables...............................................................................................21
4.2 Overview......................................................................................................................22
4.3 The LTE Downlink Analysis Measurement Application..........................................22
4.3.1 Synchronization.............................................................................................................22
4.3.2 Channel Estimation and Equalizitaion...........................................................................24
4.3.3 Analysis.........................................................................................................................24
4.4 Performing Time Alignment Measurements.............................................................25
4.5 Performing Transmit On/Off Power Measurements.................................................27
5 Measurements and Result Displays...................................................30
5.1 Numerical Results.......................................................................................................30
5.2 Measuring the Power Over Time...............................................................................33
5.3 Measuring the Error Vector Magnitude (EVM)..........................................................35
5.4 Measuring the Spectrum............................................................................................38
3User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
5.4.1 Frequency Sweep Measurements................................................................................39
5.4.2 I/Q Measurements.........................................................................................................42
5.5 Measuring the Symbol Constellation........................................................................45
5.6 Measuring Statistics...................................................................................................46
6 Configuring and Performing the Measurement.................................49
6.1 Performing Measurements.........................................................................................49
6.2 General Settings..........................................................................................................50
6.2.1 Defining Signal Characteristics.....................................................................................50
6.2.2 Configuring the Input Level...........................................................................................52
6.2.3 Configuring the Data Capture.......................................................................................54
6.2.4 Configuring On/Off Power Measurements....................................................................55
6.2.5 Triggering Measurements.............................................................................................56
Contents
6.3 Configuring MIMO Setups..........................................................................................57
6.4 Configuring Spectrum Measurements......................................................................57
6.4.1 Configuring SEM Measurements..................................................................................58
6.4.2 Configuring ACLR Measurements................................................................................58
6.4.3 Configuring Gated Measurements................................................................................59
6.5 Advanced General Settings.......................................................................................59
6.5.1 Controlling I/Q Data.......................................................................................................59
6.5.2 Controlling the Input......................................................................................................60
6.5.3 Configuring the Baseband Input....................................................................................61
6.5.4 Configuring the Digital I/Q Input....................................................................................63
6.6 Configuring Downlink Signal Demodulation............................................................63
6.6.1 Configuring the Data Analysis.......................................................................................63
6.6.2 Compensating Measurement Errors.............................................................................66
6.6.3 Configuring MIMO Setups.............................................................................................67
6.7 Configuring Downlink Frames...................................................................................67
6.7.1 Configuring TDD Signals...............................................................................................67
6.7.2 Configuring the Physical Layer Cell Identity..................................................................69
6.7.3 Configuring PDSCH Subframes....................................................................................70
6.8 Defining Advanced Signal Characteristics...............................................................72
6.8.1 Defining the PDSCH Resource Block Symbol Offset....................................................73
6.8.2 Configuring the Reference Signal.................................................................................73
4User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
6.8.3 Configuring the Synchronization Signal........................................................................74
6.8.4 Configuring the Control Channels.................................................................................74
7 Analyzing Measurement Results........................................................78
7.1 Selecting a Particular Signal Aspect.........................................................................78
7.2 Defining Measurement Units......................................................................................79
7.3 Defining Various Measurement Parameters.............................................................79
7.4 Selecting the Contents of a Constellation Diagram.................................................80
7.5 Scaling the Y-Axis.......................................................................................................81
7.6 Using the Marker.........................................................................................................82
8 File Management..................................................................................84
8.1 File Manager................................................................................................................84
8.2 SAVE/RECALL Key.....................................................................................................85
Contents
9 Remote Commands.............................................................................86
9.1 Overview of Remote Command Suffixes..................................................................86
9.2 Introduction.................................................................................................................86
9.2.1 Long and Short Form....................................................................................................87
9.2.2 Numeric Suffixes...........................................................................................................87
9.2.3 Optional Keywords........................................................................................................88
9.2.4 Alternative Keywords....................................................................................................88
9.2.5 SCPI Parameters..........................................................................................................88
9.3 Selecting and Configuring Measurements...............................................................91
9.3.1 Selecting Measurements...............................................................................................91
9.3.2 Configuring Frequency Sweep Measurements.............................................................92
9.4 Remote Commands to Perform Measurements.......................................................93
9.5 Remote Commands to Read Numeric Results.........................................................95
9.6 Remote Commands to Read Trace Data.................................................................102
9.6.1 Using the TRACe[:DATA] Command..........................................................................102
9.6.2 Remote Commands to Read Measurement Results...................................................112
9.7 Remote Commands to Configure the Application.................................................115
9.7.1 Remote Commands for General Settings...................................................................115
9.7.2 Configuring MIMO Setups...........................................................................................123
9.7.3 Advanced General Settings........................................................................................124
5User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
9.7.4 Configuring Downlink Signal Demodulation................................................................127
9.7.5 Configuring Downlink Frames.....................................................................................131
9.7.6 Defining Advanced Signal Characteristics..................................................................135
9.8 Analyzing Measurement Results.............................................................................140
9.8.1 General Commands for Result Analysis.....................................................................140
9.8.2 Using Markers.............................................................................................................142
9.8.3 Scaling the Vertical Diagram Axis...............................................................................143
9.9 Configuring the Software.........................................................................................145
List of Commands..............................................................................147
Index....................................................................................................151
Contents
6User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
1 Preface
Preface
Documentation Overview
1.1 Documentation Overview
The user documentation for the R&S FSQ consists of the following parts:
"Getting Started" printed manual
●
Documentation CD-ROM with:
●
– Getting Started
– User Manuals for base unit and options
– Service Manual
– Release Notes
– Data sheet and product brochures
Getting Started
This manual is delivered with the instrument in printed form and in PDF format on the
CD. It provides the information needed to set up and start working with the instrument.
Basic operations and handling are described. Safety information is also included.
User Manuals
User manuals are provided for the base unit and each additional (software) option.
The user manuals are available in PDF format - in printable form - on the Documentation
CD-ROM delivered with the instrument. In the user manuals, all instrument functions are
described in detail. Furthermore, they provide a complete description of the remote control commands with programming examples.
The user manual for the base unit provides basic information on operating the R&S FSQ
in general, and the Spectrum mode in particular. Furthermore, the software options that
enhance the basic functionality for various measurement modes are described here. An
introduction to remote control is provided, as well as information on maintenance, instrument interfaces and troubleshooting.
In the individual option manuals, the specific instrument functions of the option are
described in detail. For additional information on default settings and parameters, refer
to the data sheets. Basic information on operating the R&S FSQ is not included in the
option manuals.
Service Manual
This manual is available in PDF format on the CD delivered with the instrument. It
describes how to check compliance with rated specifications, instrument function, repair,
troubleshooting and fault elimination. It contains all information required for repairing the
R&S FSQ by replacing modules.
7User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Release Notes
The release notes describe the installation of the firmware, new and modified functions,
eliminated problems, and last minute changes to the documentation. The corresponding
firmware version is indicated on the title page of the release notes. The most recent
release notes are provided in the Internet.
Preface
Typographical Conventions
1.2 Typographical Conventions
The following text markers are used throughout this documentation:
Convention Description
"Graphical user interface elements"
KEYS Key names are written in capital letters.
File names, commands,
program code
Input Input to be entered by the user is displayed in italics.
Links
"References" References to other parts of the documentation are enclosed by quotation
All names of graphical user interface elements on the screen, such as dialog boxes, menus, options, buttons, and softkeys are enclosed by quotation marks.
File names, commands, coding samples and screen output are distinguished by their font.
Links that you can click are displayed in blue font.
marks.
8User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
2 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, the evolution of UMTS has not reached its
end. HSPA+ will bring significant enhancements in 3GPP Release 7. The objective is to
enhance the performance of HSPA-based radio networks in terms of spectrum efficiency,
peak data rate and latency, and to exploit the full potential of WCDMAbased 5 MHz
operation. Important features of HSPA+ are downlink multiple input multiple output
(MIMO), 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. The 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 evolved UMTS terrestrial radio access
(EUTRA) and evolved UMTS terrestrial radio access network (EUTRAN). LTE/EUTRA
will then form part of 3GPP Release 8 core specifications.
Introduction
Requirements for UMTS Long-Term Evolution
This introduction focuses on LTE/EUTRA technology. In the following, the terms LTE or
EUTRA 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 such as 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: orthogonal frequency division multiple access (OFDMA) in downlink
and single carrier frequency division multiple access (SC-FDMA) 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).
● Requirements for UMTS Long-Term Evolution.........................................................9
● Long-Term Evolution Downlink Transmission Scheme...........................................11
● References..............................................................................................................16
2.1 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 are documented in 3GPP TR 25.913 [1] and can be
summarized as follows:
9User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Data Rate: Peak data rates target 100 Mbps (downlink) and 50 Mbps (uplink) for 20
●
MHz spectrum allocation, assuming two receive antennas and one transmit antenna
are at the terminal.
Throughput: The target for downlink average user throughput per MHz is three to four
●
times better than Release 6. The target for uplink average user throughput per MHz
is two to three times better than Release 6.
Spectrum efficiency: The downlink target is three to four times better than Release
●
6. The uplink target is two to three 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 MHz, 10 MHz, 15 MHz, and 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 EUTRAN and UTRAN/GERAN shall be less than 300 ms for realtime
services and less than 500 ms for non-realtime 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. Costef-
●
fective 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 multivendor equipment
interoperability.
Mobility: The system should be optimized for low mobile speed (0 to 15 km/h), but
●
higher mobile speeds shall be supported as well, including high speed train environment as a 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 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.
Introduction
Requirements for UMTS Long-Term Evolution
10User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Introduction
Long-Term Evolution Downlink Transmission Scheme
2.2 Long-Term Evolution Downlink Transmission Scheme
2.2.1 OFDMA
The downlink transmission scheme for EUTRA FDD and TDD modes is based on conventional OFDM.
In an OFDM system, the available spectrum is divided into multiple carriers, called subcarriers, which are orthogonal to each other. Each of these subcarriers 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 2-1 shows a representation of an OFDM signal taken from 3GPP TR 25.892 [2].
In this figure, a signal with 5 MHz bandwidth is shown, but the principle is of course the
same for the other EUTRA bandwidths. Data symbols are independently modulated and
transmitted over a high number of closely spaced orthogonal subcarriers. In EUTRA,
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-OFDMsymbol-interference due to channel delay spread. In EUTRA, the guard interval is a cyclic
prefix which is inserted prior to each OFDM symbol.
Fig. 2-1: Frequency-Time Representation of an OFDM Signal
In practice, the OFDM signal can be generated using the inverse fast Fourier transform
(IFFT) 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 2-2, where a(mN+n) refers to the nth subchannel modulated data
symbol, during the time period mTu < t ≤ (m+1)Tu.
11User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Fig. 2-2: OFDM useful symbol generation using an IFFT
The vector sm is defined as the useful OFDM symbol. It is the time superposition of the
N narrowband modulated subcarriers. Therefore, from a parallel stream of N sources of
data, each one independently modulated, a waveform composed of N orthogonal subcarriers is obtained, with each subcarrier having the shape of a frequency sinc function
(see figure 2-1).
Introduction
Long-Term Evolution Downlink Transmission Scheme
figure 2-3 illustrates the mapping from a serial stream of QAM symbols to N parallel
streams, used as frequency domain bins for the IFFT. The N-point time domain blocks
obtained from the IFFT are then serialized to create a time domain signal. Not shown in
figure 2-3 is the process of cyclic prefix insertion.
Fig. 2-3: OFDM Signal Generation Chain
In contrast to an OFDM transmission scheme, OFDMA allows the access of multiple
users on the available bandwidth. Each user is assigned a specific time-frequency
resource. As a fundamental principle of EUTRA, the data channels are shared channels,
i.e. for each transmission time interval of 1 ms, a new scheduling decision is taken
regarding which users are assigned to which time/frequency resources during this transmission time interval.
2.2.2 OFDMA Parameterization
A generic frame structure is defined for both EUTRA FDD and TDD modes. Additionally,
an alternative frame structure is defined for the TDD mode only. The EUTRA frame
structures are defined in 3GPP TS 36.211. For the generic frame structure, the 10 ms
radio frame is divided into 20 equally sized slots of 0.5 ms. A subframe consists of two
consecutive slots, so one radio frame contains 10 subframes. This is illustrated in fig-
ure 2-4 (Ts expresses the basic time unit corresponding to 30.72 MHz).
12User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Fig. 2-4: Generic Frame Structure in EUTRA Downlink
figure 2-5shows the structure of the downlink resource grid for the duration of one down-
link slot. The available downlink bandwidth consists of subcarriers with a spacing of
Δf = 15 kHz. In the case of multi-cell MBMS transmission, a subcarrier spacing of Δf =
7.5 kHz is also possible. can vary in order to allow for scalable bandwidth operation
up to 20 MHz. Initially, the bandwidths for LTE were explicitly defined within layer 1 specifications. Later on a bandwidth agnostic layer 1 was introduced, with for the different
bandwidths to be specified by 3GPP RAN4 to meet performance requirements, e.g. for
out-of-band emission requirements and regulatory emission limits.
Introduction
Long-Term Evolution Downlink Transmission Scheme
Fig. 2-5: Downlink Resource Grid
One downlink slot consists of OFDM symbols. To each symbol, a cyclic prefix (CP)
is appended as guard time, compare figure 2-1. depends on the cyclic prefix length.
The generic frame structure with normal cyclic prefix length contains
= 7 symbols.
This translates into a cyclic prefix length of TCP≈5.2μs for the first symbol and TCP≈4.7μs
for the remaining 6 symbols. Additionally, an extended cyclic prefix is defined in order to
cover large cell scenarios with higher delay spread and MBMS transmission. The generic
frame structure with extended cyclic prefix of T
≈16.7μs contains = 6 OFDM sym-
CP-E
bols (subcarrier spacing 15 kHz). The generic frame structure with extended cyclic prefix
13User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Introduction
Long-Term Evolution Downlink Transmission Scheme
of T
≈33.3μs contains = 3 symbols (subcarrier spacing 7.5 kHz). table 2-1 gives
CP-E
an overview of the different parameters for the generic frame structure.
Table 2-1: Parameters for Downlink Generic Frame Structure
Configuration Number of Symbols Cyclic Prefix
Normal cyclic prefix Δf=15 kHz
Extended cyclic prefix Δf=15 kHz
Extended cyclic prefix Δf=7.5 kHz
2.2.3 Downlink Data Transmission
7 160 for first symbol
6 512 16.7 µs
3 1024 33.3 µs
Data is allocated to the UEs in terms of resource blocks. A physical resource block consists of 12 (24) consecutive subcarriers in the frequency domain for the Δf=15 kHz
(Δf=7.5 kHz) case. In the time domain, a physical resource block consists of DL N
consecutive OFDM symbols, see figure 2-5. is equal to the number of OFDM symbols
in a slot. The resource block size is the same for all bandwidths, therefore the number of
available physical resource blocks depends on the bandwidth. Depending on the required
data rate, each UE can be assigned one or more resource blocks in each transmission
time interval of 1 ms. The scheduling decision is done in the base station (eNodeB). The
user data is carried on the physical downlink shared channel (PDSCH). Downlink control
signaling on the physical downlink control channel (PDCCH) is used to convey the
scheduling decisions to individual UEs. The PDCCH is located in the first OFDM symbols
of a slot.
Length in Samples
144 for other symbols
Cyclic Prefix
Length in µs
5.2 µs for first symbol
4.7 µs for other symbols
symb
2.2.4 Downlink Reference Signal Structure and Cell Search
The downlink reference signal structure is important for cell search, channel estimation
and neighbor cell monitoring. figure 2-6 shows the principle of the downlink reference
signal structure for one-antenna, two-antenna, and four-antenna transmission. Specific
predefined resource elements in the time-frequency domain carry the reference signal
sequence. Besides first reference symbols, there may be a need for second reference
symbols. The different colors in figure 2-6 represent the sequences transmitted from up
to four transmit antennas.
14User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Introduction
Long-Term Evolution Downlink Transmission Scheme
Fig. 2-6: Downlink Reference Signal Structure (Normal Cyclic Prefix)
The reference signal sequence carries the cell identity. Each reference signal sequence
is generated as a symbol-by-symbol product of an orthogonal sequence rOS (three of
them existing) and a pseudo-random sequence r
PRS
(170 of them existing). Each cell
identity corresponds to a unique combination of one orthogonal sequence rOS and one
pseudo-random sequence r
PRS
, allowing 510 different cell identities.
Frequency hopping can be applied to the downlink reference signals. The frequency
hopping pattern has a period of one frame (10 ms).
During cell search, different types of information need to be identified by the handset:
symbol and radio frame timing, frequency, cell identification, overall transmission bandwidth, antenna configuration, and cyclic prefix length.
Besides the reference symbols, synchronization signals are therefore needed during cell
search. EUTRA uses a hierarchical cell search scheme similar to WCDMA. This means
that the synchronization acquisition and the cell group identifier are obtained from different synchronization signals. Thus, a primary synchronization signal (P-SYNC) and a
secondary synchronization signal (S-SYNC) are assigned a predefined structure. They
are transmitted on the 72 center subcarriers (around the DC subcarrier) within the same
predefined slots (twice per 10 ms) on different resource elements, see figure 2-7.
15User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Fig. 2-7: P-SYNC and S-SYNC Structure
As additional help during cell search, a common control physical channel (CCPCH) is
available which carries BCH type of information, e.g. system bandwidth. It is transmitted
at predefined time instants on the 72 subcarriers centered around the DC subcarrier.
In order to enable the UE to support this cell search concept, it was agreed to have a
minimum UE bandwidth reception capability of 20 MHz.
Introduction
References
2.2.5 Downlink Physical Layer Procedures
For EUTRA, the following downlink physical layer procedures are especially important:
Cell search and synchronization
●
See above.
Scheduling
●
Scheduling is done in the base station (eNodeB). The downlink control channel
PDCCH informs the users about their allocated time/frequency resources and the
transmission formats to use. The scheduler evaluates different types of information,
e.g. quality of service parameters, measurements from the UE, UE capabilities, and
buffer status.
Link adaptation
●
Link adaptation is already known from HSDPA as adaptive modulation and coding.
Also in EUTRA, modulation and coding for the shared data channel is not fixed, but
rather is adapted according to radio link quality. For this purpose, the UE regularly
reports channel quality indications (CQI) to the eNodeB.
Hybrid automatic repeat request (ARQ)
●
Downlink hybrid ARQ is also known from HSDPA. It is a retransmission protocol. The
UE can request retransmissions of incorrectly received data packets.
2.3 References
[1] 3GPP TS 25.913: Requirements for E-UTRA and E-UTRAN (Release 7)
[2] 3GPP TR 25.892: Feasibility Study for Orthogonal Frequency Division Multiplexing
(OFDM) for UTRAN enhancement (Release 6)
[3] 3GPP TS 36.211 v8.3.0: Physical Channels and Modulation (Release 8)
[4] 3GPP TS 36.300: E-UTRA and E-UTRAN; Overall Description; Stage 2 (Release 8)
16User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
[5] 3GPP TS 22.978: All-IP Network (AIPN) feasibility study (Release 7)
[6] 3GPP TS 25.213: Spreading and modulation (FDD)
[7] Speth, M., Fechtel, S., Fock, G., and Meyr, H.: Optimum Receiver Design for Wireless
Broad-Band Systems Using OFDM – Part I. IEEE Trans. on Commun. Vol. 47 (1999) No.
11, pp. 1668-1677.
[8] Speth, M., Fechtel, S., Fock, G., and Meyr, H.: Optimum Receiver Design for OFDMBased Broadband Transmission – Part II: A Case Study. IEEE Trans. on Commun. Vol.
49 (2001) No. 4, pp. 571-578.
Introduction
References
17User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
3 Welcome
The EUTRA/LTE software application makes use of the I/Q capture functionality of the
following spectrum and signal analyzers to enable EUTRA/LTE TX measurements conforming to the EUTRA specification.
R&S FSQ
●
R&S FSG
●
This manual contains all information necessary to configure, perform and analyze such
measurements.
● Installing the Software.............................................................................................18
● Application Overview...............................................................................................18
● Support....................................................................................................................20
Welcome
Installing the Software
3.1 Installing the Software
For information on the installation procedure see the release notes of the R&S FSQ.
3.2 Application Overview
Starting the application
Access the application via the "Mode" menu.
► Press the MODE key and select "LTE".
Note that you may have to browse through the "Mode" menu with the "Next" key to
find the LTE entry.
Presetting the software
When you first start the software, all settings are in their default state. After you have
changed any parameter, you can restore the default state with the PRESET key.
CONFigure:PRESet on page 145
Elements and layout of the user interface
The user interface of the LTE measurement application is made up of several elements.
18User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Welcome
Application Overview
1 = Title Bar: shows the currently active measurement application
2 = Table Header: shows basic measurement information, e.g. the frequency
3 = Result Display Header: shows information about the display trace
4 = Result Display Screen A: shows the measurement results
5 = Result Display Screen B: shows the measurement results
6 = Status Bar: shows the measurement progress, software messages and errors
7 = Softkeys: open settings dialogs and select result displays
8 = Hotkeys: control the measurement process (e.g. running a measurement)
The status and title bar
The title bar at the very top of the screen shows the name of the application currently
running.
The status bar is located at the bottom of the display. It shows the current measurement
status and its progress in a running measurement. The status bar also shows warning
and error messages. Error messages are generally highlighted.
Display of measurement settings
The header table above the result displays shows information on hardware and measurement settings.
19User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
The header table includes the following information
Freq
●
The analyzer RF frequency.
Mode
●
Link direction, duplexing, cyclic prefix and maximum number of physical resource
blocks (PRBs) / signal bandwidth.
Meas Setup
●
Shows number of transmitting and receiving antennas.
Sync State
●
The following synchronization states may occur:
– OK The synchronization was successful.
– FAIL (C) The cyclic prefix correlation failed.
– FAIL (P) The P-SYNC correlation failed.
– FAIL (S) The S-SYNC correlation failed.
Any combination of C, P and S may occur.
SCPI Command:
[SENSe]:SYNC[:STATe]? on page 95
Ext. Att
●
Shows the external attenuation in dB.
Capture Time
●
Shows the capture length in ms.
Welcome
Support
3.3 Support
If you encounter any problems when using the application, you can contact the
Rohde & Schwarz support to get help for the problem.
To make the solution easier, use the "R&S Support" softkey to export useful information
for troubleshooting. The R&S FSQ stores the information in a number of files that are
located in the R&S FSQ directory C:\R_S\Instr\user\LTE\Support. If you contact
Rohde & Schwarz to get help on a certain problem, send these files to the support in
order to identify and solve the problem faster.
20User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
4 Measurement Basics
This chapter provides background information on the measurements and result displays
available with the LTE Analysis Software.
● Symbols and Variables...........................................................................................21
● Overview.................................................................................................................22
● The LTE Downlink Analysis Measurement Application...........................................22
● Performing Time Alignment Measurements............................................................25
● Performing Transmit On/Off Power Measurements................................................27
Measurement Basics
Symbols and Variables
4.1 Symbols and Variables
The following chapters use various symbols and variables in the equations that the
measurements are based on. The table below explains these symbols for a better understanding of the measurement principles.
a
l,kâl,k
b
l,k
Δf, Δ
coarse
Δf
res
ζ
H
l,k, l,k
i time index
î
, î
coarse
fine
k subcarrier index
l OFDM symbol index
N
FFT
data symbol (actual, decided)
boosting factor
carrier frequency offset between transmitter and
receiver (actual, coarse estimate)
residual carrier frequency offset
relative sampling frequency offset
channel transfer function (actual, estimate)
timing estimate (coarse, fine)
length of FFT
N
g
N
s
N
RE
number of samples in cyclic prefix (guard interval)
number of Nyquist samples
number of resource elements
n subchannel index, subframe index
n
l,k
Φ
l
noise sample
common phase error
r(i) received sample in the time domain
r
, r'
, r''
l,k
l,k
l,k
received sample (uncompensated, partially compensated, equalized) in the frequency domain
21User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
T useful symbol time
Measurement Basics
Overview
T
g
T
s
4.2 Overview
guard time
symbol time
The digital signal processing (DSP) involves several stages until the software can present
results like the EVM.
The contents of this chapter are structered like the DSP.
4.3 The LTE Downlink Analysis Measurement Application
The block diagram in figure 4-1 shows the EUTRA/LTE downlink measurement application from the capture buffer containing the I/Q data to the actual analysis block. The
outcome of the fully compensated reference path (green) are the estimates â
transmitted data symbols a
samples r''
of the measurement path (yellow) still contain the transmitted signal impair-
l,k
. Depending on the user-defined compensation, the received
l,k
of the
l,k
ments of interest. The analysis block reveals these impairments by comparing the reference and the measurement path. Prior to the analysis, diverse synchronization and
channel estimation tasks have to be accomplished.
4.3.1 Synchronization
The first of the synchronization tasks is to estimate the OFDM symbol timing, which
coarsely estimates both timing and carrier frequency offset. The frame synchronization
block determines the position of the P-/S-Sync symbols in time and frequency by using
the coarse fractional frequency offset compensated capture buffer and the timing estimate î
to position the window of the FFT. If no P-/S-Sync is available in the signal,
coarse
the reference signal is used for synchronization. The fine timing block prior to the FFT
allows a timing improvement and makes sure that the EVM window is centered on the
measured cyclic prefix of the considered OFDM symbol. For the 3GPP EVM calculation
according to 3GPP TS 36.211 (v8.9.0), the block “window” produces three signals taken
at the timing offsets
timing offset is used.
, and . For the reference path, only the signal taken at the
22User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
kl
lTfNNjlkNNjj
klklkl
NeeeHAR
CFOres
resFFTS
SFO
FFTS
CPE
l
,
22
,,,
.
Measurement Basics
The LTE Downlink Analysis Measurement Application
Fig. 4-1: Block diagram for the LTE DL measurement application
After the time to frequency transformation by an FFT of length N
, the phase synchro-
FFT
nization block is used to estimate the following:
● the relative sampling frequency offset ζ (SFO)
● the residual carrier frequency offset Δf
(CFO)
res
● the common phase error Φl (CPE)
According to 3GPP TS 25.913 and 3GPP TR 25.892, the uncompensated samples can
be expressed as
(4 - 1)
where
the data symbol is a
●
the channel transfer function is h
●
the number of Nyquist samples is Ns within the symbol time T
●
the useful symbol time T=Ts-T
●
the independent and Gaussian distributed noise sample is n
●
, on subcarrier k at OFDM symbol l
l,k
l,k
g
s
l,k
Within one OFDM symbol, both the CPE and the residual CFO cause the same phase
rotation for each subcarrier, while the rotation due to the SFO depends linearly on the
subcarrier index. A linear phase increase in symbol direction can be observed for the
residual CFO as well as for the SFO.
The results of the tracking estimation block are used to compensate the samples r
l,k
23User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
2
,
,
,
,
''
,
,
ˆ
kl
kl
kl
klkl
kl
b
a
Eb
ar
EVM
kl
kl
kl
ln
b
ar
EVM
,
,
''
,
,
ˆ
Whereas a full compensation is performed in the reference path, the signal impairments
that are of interest to the user are left uncompensated in the measurement path.
After having decided the data symbols in the reference path, an additional phase tracking
can be utilized to refine the CPE estimation.
Measurement Basics
The LTE Downlink Analysis Measurement Application
4.3.2 Channel Estimation and Equalizitaion
As shown in figure 4-1, there is one coarse and one fine channel estimation block. The
reference signal-based coarse estimation is tapped behind the CFO compensation block
(SFO compensation can optionally be enabled) of the reference path. The coarse estimation block uses the reference signal symbols to determine estimates of the channel
transfer function by interpolation in both time and frequency direction. A special channel
estimation (
) as defined in 3GPP TS 36.211 is additionally generated. The coarse
estimation results are used to equalize the samples of the reference path prior to symbol
decision. Based on the decided data symbols, a fine channel estimation is optimally performed and then used to equalize the partially compensated samples of the measurement
path.
4.3.3 Analysis
The analysis block of the EUTRA/LTE downlink measurement application allows to compute a variety of measurement variables.
EVM
The error vector magnitude (EVM) measurement results 'EVM PDSCH QPSK/16-QAM/
64-QAM' are calculated according to the specification in 3GPP TS 36.211.
All other EVM measurement results are calculated according to
(4 - 2)
on subcarrier k at OFDM symbol l, where b
is the boosting factor. Since the average
l,k
power of all possible constellations is 1 when no boosting is applied, the equation can be
rewritten as
(4 - 3)
The average EVM of all data subcarriers is then
24User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
l k
kl
REdata
data
data
data
EVM
N
EVM
2
,
1
tsjQtsItr
|1|balancegain modulator Q
}1arg{mismatch quadrature Q
Measurement Basics
Performing Time Alignment Measurements
(4 - 4)
The number of resource elements taken into account is denoted by N
RE data
.
I/Q imbalance
The I/Q imbalance can be written as
(4 - 5)
where s(t) is the transmit signal, r(t) is the received signal, and I and Q are the weighting
factors. We define that I:=1 and Q:=1+ΔQ.
The I/Q imbalance estimation makes it possible to evaluate the
(4 - 6)
and the
(4 - 7)
based on the complex-valued estimate
.
Other measurement variables
Without going into detail, the EUTRA/LTE downlink measurement application additionally
provides the following results.
Total power
●
Constellation diagram
●
Group delay
●
I/Q offset
●
Crest factor
●
Spectral flatness
●
4.4 Performing Time Alignment Measurements
The MIMO measurement application provides the possibility to perform time alignment
measurements between the different antennas for 2 or 4 TX antenna MIMO configurations. The time alignment error values represent the time offset between the considered
antenna and antenna 1 and will be displayed in the result summary. A schematic description of the results is provided in figure 4-3.
25User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
A test setup for time alignment measurements is shown in figure 4-2. The dashed connections are only required for 4 TX antenna MIMO configuration. For best measurement
result accuracy it is recommended to use cables of the same length and identical combiners as adders.
Fig. 4-2: Time alignment measurement hardware setup
Measurement Basics
Performing Time Alignment Measurements
For a successful time alignment measurement, make sure to set up the measurement
correctly.
the subframe selection in the general settings menu must be set to "All"
●
enable "Compensate Crosstalk" in the demodulation settings, see screenshot below
●
Note that the time alignment measurement only uses the reference signal and therefore
ignores any PDSCH settings (e.g. it does not have an influence on this measurement if
the PDSCH MIMO scheme is set to transmit diversity or spatial multiplexing).
The EVM will usually be very high for this measurement. This does not effect the accuracy
of the time alignment error measurement result.
26User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
Measurement Basics
Performing Transmit On/Off Power Measurements
Fig. 4-3: Schematic description of the time alignment results
4.5 Performing Transmit On/Off Power Measurements
The technical specification in 3GPP TS 36.141 prescribes the measurement of the transmitter OFF power and the transmitter transient period of an EUTRA/LTE TDD base
transceiver station (BTS) operating at its specified maximum output power. A special
hardware setup is required for this measurement since the actual measurement is done
27User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
at very low power during the transmitter OFF periods requiring low attenuation at the
analyzer input. The signal power during the transmitter ON periods in this test scenario
is usually higher than the specified maximum input power of the R&S FSx signal analyzer
and will cause severe damage to the analyzer if the measurement is not set up appropriately.
Test setup
Measurement Basics
Performing Transmit On/Off Power Measurements
To protect the analyzer input from damage, an RF limiter has to be applied at the analyzer
input connector, as can be seen in figure 2-16. Table 1.1 shows the specifications the
used limiter has to fulfill.
Min. acceptable CW input power BTS output power minus 10 dB
Min. acceptable peak input power BTS peak output power minus 10 dB
Max. output leakage 20 dBm
Max. response time 1 µs
Max. recovery time 1 µs
An additional 10 dB attenuation should be placed in front of the RF limiter to absorb
eventual reflected waves because of the high VSWR of the limiter. The allowed maximum
CW input power of the attenuator must be lower than the maximum output power of the
BTS.
Performing the measurement
If an external trigger is used, before the actual measurement can be started, the timing
must be adjusted by pressing the 'Adjust Timing' hotkey. The status display in the header
of the graph changes from 'Timing not adjusted' to 'Timing adjusted' and the run hotkeys
are released. Relevant setting changes again lead to a 'Timing not adjusted' status display.
If the adjustment fails, an error message is shown and the adjustment state is still "not
adjusted". To find out what causes the synchronization failure, you should perform a
regular EVM measurement (i.e. leave the ON/OFF Power measurement). Then you can
use all the measurement results like EVM vs. Carrier to get more detailed information
28User Manual 1173.0620.42 ─ 06
R&S®FSQ-K10x (LTE Downlink)
about the failure. The timing adjustment will succeed if the Sync State in the header is
OK.
Using a R&S FSQ or R&S FSG it is recommended to use the external trigger mode since
for high power signals a successful synchronization is not guaranteed under certain circumstances.
Pressing the 'Run Single' hotkey starts the averaging of the traces of the number of
frames given in the 'General Settings' dialog. After performing all sweeps, the table in the
upper half of the screen shows if the measurements pass or fail.
Measurement Basics
Performing Transmit On/Off Power Measurements
29User Manual 1173.0620.42 ─ 06
Loading...