Rohde&Schwarz R&S®FSV-K10x LTE DL - for R&S®FSVR User Manual
R&S®FSV-K10x (LTE Downlink)
LTE Downlink Measurement
Application
User Manual
(;ÚÚË2)
1176.7661.02 ─ 04.1
User Manual
Test & Measurement
This manual describes the following firmware applications:
●
R&S®FSV-K100 EUTRA / LTE FDD Downlink Measurement Application (1308.9051.02)
●
R&S®FSV-K102 EUTRA / LTE MIMO Downlink Measurement Application (1310.9151.02)
●
R&S®FSV-K104 EUTRA / LTE TDD Downlink Measurement Application (1309.9774.02)
The contents of this manual correspond to the following R&S®FSVR models with firmware version 2.23 or
higher:
●
R&S®FSVR7 (1311.0006K7)
●
R&S®FSVR13 (1311.0006K13)
●
R&S®FSVR30 (1311.0006K30)
●
R&S®FSVR40 (1311.0006K40)
The software contained in this product makes use of several valuable open source software packages. For information, see the
"Open Source Acknowledgement" on the user documentation CD-ROM (included in delivery).
Rohde & Schwarz would like to thank the open source community for their valuable contribution to embedded computing.
© 2015 Rohde & Schwarz GmbH & Co. KG
Mühldorfstr. 15, 81671 München, Germany
Phone: +49 89 41 29 - 0
Fax: +49 89 41 29 12 164
Email: info@rohde-schwarz.com
Internet: www.rohde-schwarz.com
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®FSV is abbreviated as R&S FSV. R&S®FSVR is abbreviated as
R&S FSVR.
R&S®FSV-K10x (LTE Downlink)
Contents
1 Introduction............................................................................................ 7
1.1 Requirements for UMTS Long-Term Evolution.......................................................... 7
1.2 Long-Term Evolution Downlink Transmission Scheme............................................9
1.2.1 OFDMA........................................................................................................................... 9
1.2.2 OFDMA Parameterization............................................................................................. 10
1.2.3 Downlink Data Transmission.........................................................................................12
1.2.4 Downlink Reference Signal Structure and Cell Search.................................................12
1.2.5 Downlink Physical Layer Procedures............................................................................14
1.3 References...................................................................................................................14
2 Welcome............................................................................................... 16
Contents
2.1 Installing the Software................................................................................................16
2.2 Application Overview..................................................................................................16
2.3 Support........................................................................................................................ 18
3 Measurement Basics........................................................................... 19
3.1 Symbols and Variables...............................................................................................19
3.2 Overview...................................................................................................................... 20
3.3 The LTE Downlink Analysis Measurement Application.......................................... 20
3.3.1 Synchronization.............................................................................................................20
3.3.2 Channel Estimation and Equalizitaion...........................................................................22
3.3.3 Analysis.........................................................................................................................22
3.4 Performing Time Alignment Measurements.............................................................23
3.5 Performing Transmit On/Off Power Measurements.................................................25
4 Measurements and Result Displays...................................................27
4.1 Numerical Results.......................................................................................................27
4.2 Measuring the Power Over Time............................................................................... 30
4.3 Measuring the Error Vector Magnitude (EVM)..........................................................34
4.4 Measuring the Spectrum............................................................................................ 37
4.4.1 Frequency Sweep Measurements................................................................................ 38
4.4.2 I/Q Measurements.........................................................................................................41
4.5 Measuring the Symbol Constellation........................................................................ 45
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4.6 Measuring Statistics................................................................................................... 45
4.7 3GPP Test Scenarios.................................................................................................. 48
5 Configuring and Performing the Measurement.................................50
5.1 Performing Measurements.........................................................................................50
5.2 Defining General Measurement Characteristics...................................................... 51
5.2.1 Defining Signal Characteristics..................................................................................... 52
5.2.2 Configuring the Input Level........................................................................................... 53
5.2.3 Configuring the Data Capture....................................................................................... 55
5.2.4 Configuring On/Off Power Measurements.................................................................... 56
5.2.5 Triggering Measurements............................................................................................. 57
5.3 Configuring MIMO Setups.......................................................................................... 58
5.4 Configuring Spectrum Measurements...................................................................... 59
Contents
5.4.1 General ACLR and SEM Configuration.........................................................................59
5.4.2 Configuring SEM Measurements.................................................................................. 60
5.4.3 Configuring ACLR Measurements................................................................................ 61
5.5 Defining Advanced Measurement Characteristics.................................................. 62
5.5.1 Controlling I/Q Data.......................................................................................................62
5.5.2 Controlling the Input...................................................................................................... 63
5.5.3 Configuring the Digital I/Q Input.................................................................................... 64
5.6 Configuring the Signal Demodulation.......................................................................64
5.6.1 Configuring the Data Analysis.......................................................................................64
5.6.2 Compensating Measurement Errors............................................................................. 67
5.6.3 Configuring MIMO Setups.............................................................................................68
5.7 Configuring Downlink Frames................................................................................... 69
5.7.1 Configuring TDD Signals...............................................................................................69
5.7.2 Configuring the Physical Layer Cell Identity..................................................................70
5.7.3 Configuring PDSCH Subframes....................................................................................72
5.8 Defining Advanced Signal Characteristics...............................................................74
5.8.1 Defining the PDSCH Resource Block Symbol Offset....................................................75
5.8.2 Configuring the Reference Signal................................................................................. 75
5.8.3 Configuring the Synchronization Signal........................................................................ 76
5.8.4 Configuring the Control Channels................................................................................. 77
5.8.5 Configuring the Shared Channel...................................................................................81
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6 Analyzing Measurement Results........................................................ 82
6.1 Selecting a Particular Signal Aspect.........................................................................82
6.2 Defining Measurement Units......................................................................................83
6.3 Defining Various Measurement Parameters.............................................................83
6.4 Selecting the Contents of a Constellation Diagram.................................................84
6.5 Scaling the Y-Axis.......................................................................................................85
6.6 Using Markers............................................................................................................. 86
7 File Management..................................................................................88
7.1 File Manager................................................................................................................ 88
7.2 SAVE/RECALL Key..................................................................................................... 89
7.3 Test Models................................................................................................................. 89
8 Remote Commands............................................................................. 91
Contents
8.1 Overview of Remote Command Suffixes.................................................................. 91
8.2 Introduction................................................................................................................. 92
8.2.1 Conventions used in Descriptions.................................................................................92
8.2.2 Long and Short Form.................................................................................................... 93
8.2.3 Numeric Suffixes........................................................................................................... 93
8.2.4 Optional Keywords........................................................................................................ 93
8.2.5 Alternative Keywords.................................................................................................... 94
8.2.6 SCPI Parameters.......................................................................................................... 94
8.3 Measurement Selection.............................................................................................. 96
8.4 Measurement Execution.............................................................................................98
8.5 Numeric Result Query.............................................................................................. 100
8.6 Measurement Result Query......................................................................................108
8.6.1 Using the TRACe[:DATA] Command.......................................................................... 108
8.6.2 Reading Results..........................................................................................................118
8.7 General Settings........................................................................................................121
8.7.1 Defining Signal Characteristics................................................................................... 121
8.7.2 Configuring the Input Level......................................................................................... 123
8.7.3 Configuring the Data Capture..................................................................................... 126
8.7.4 Configuring On/Off Power Measurements.................................................................. 127
8.8 MIMO Setups............................................................................................................. 128
8.9 Advanced Settings....................................................................................................129
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8.9.1 Controlling I/Q Data.....................................................................................................129
8.9.2 Controlling the Input.................................................................................................... 129
8.9.3 Configuring the Digital I/Q Input.................................................................................. 130
8.10 Trigger Configuration............................................................................................... 131
8.11 Spectrum Measurements......................................................................................... 132
8.12 Signal Demodulation................................................................................................ 136
8.12.1 Configuring the Data Analysis.....................................................................................136
8.12.2 Compensating Measurement Errors........................................................................... 138
8.12.3 Configuring MIMO Setups...........................................................................................139
8.13 Frame Configuration.................................................................................................140
8.13.1 Configuring TDD Signals.............................................................................................140
8.13.2 Configuring the Physical Layer Cell Identity................................................................141
8.13.3 Configuring PDSCH Subframes..................................................................................142
Contents
8.14 Advanced Signal Characteristics............................................................................ 145
8.14.1 Defining the PDSCH Resource Block Symbol Offset..................................................145
8.14.2 Configuring the Reference Signal............................................................................... 145
8.14.3 Configuring the Synchronization Signal...................................................................... 146
8.14.4 Configuring the Control Channel.................................................................................147
8.14.5 Configuring the Shared Channel.................................................................................150
8.15 Measurement Result Analysis................................................................................. 151
8.15.1 Selecting Displayed Data............................................................................................ 151
8.15.2 Selecting Units............................................................................................................ 154
8.15.3 Using Markers............................................................................................................. 154
8.15.4 Using Delta Markers....................................................................................................157
8.15.5 Scaling the Vertical Diagram Axis............................................................................... 159
8.16 Software Configuration............................................................................................ 160
List of Commands..............................................................................163
Index....................................................................................................167
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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, 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.........................................................7
● Long-Term Evolution Downlink Transmission Scheme.............................................9
● References..............................................................................................................14
1.1 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:
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●
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. Costeffective 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
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Introduction
Long-Term Evolution Downlink Transmission Scheme
1.2 Long-Term Evolution Downlink Transmission Scheme
1.2.1 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 1-1 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 interOFDM-symbol-interference due to channel delay spread. In EUTRA, the guard interval
is a cyclic prefix which is inserted prior to each OFDM symbol.
Fig. 1-1: 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 1-2, where a(mN+n) refers to the nth subchannel modulated data
symbol, during the time period mTu < t ≤ (m+1)Tu.
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Fig. 1-2: 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 1-1).
Introduction
Long-Term Evolution Downlink Transmission Scheme
figure 1-3 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 1-3 is the process of cyclic prefix insertion.
Fig. 1-3: 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.
1.2.2 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 figure 1-4 (Ts expresses the basic time unit corresponding to 30.72 MHz).
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Fig. 1-4: Generic Frame Structure in EUTRA Downlink
figure 1-5shows the structure of the downlink resource grid for the duration of one
downlink 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
performance requirements, e.g. for out-of-band emission requirements and regulatory
emission limits.
Introduction
Long-Term Evolution Downlink Transmission Scheme
for the different bandwidths to be specified by 3GPP RAN4 to meet
Fig. 1-5: Downlink Resource Grid
One downlink slot consists of OFDM symbols. To each symbol, a cyclic prefix
(CP) is appended as guard time, compare figure 1-1. 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
CP-E
≈16.7μs
contains = 6 OFDM symbols (subcarrier spacing 15 kHz). The generic frame
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Introduction
Long-Term Evolution Downlink Transmission Scheme
structure with extended cyclic prefix of T
carrier spacing 7.5 kHz). table 1-1 gives an overview of the different parameters for the
generic frame structure.
Table 1-1: Parameters for Downlink Generic Frame Structure
Configuration Number of Symbols Cyclic Prefix
Normal cyclic prefix Δf=15 kHz 7 160 for first symbol
Extended cyclic prefix Δf=15 kHz 6 512 16.7 µs
Extended cyclic prefix Δf=7.5 kHz 3 1024 33.3 µs
1.2.3 Downlink Data Transmission
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 1-5.
bols 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.
≈33.3μs contains = 3 symbols (sub-
CP-E
Cyclic Prefix
Length in Samples
144 for other symbols
Length in µs
5.2 µs for first sym-
bol
4.7 µs for other
symbols
is equal to the number of OFDM sym-
symb
1.2.4 Downlink Reference Signal Structure and Cell Search
The downlink reference signal structure is important for cell search, channel estimation
and neighbor cell monitoring. figure 1-6 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 1-6 represent the sequences transmitted from up
to four transmit antennas.
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Introduction
Long-Term Evolution Downlink Transmission Scheme
Fig. 1-6: 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 r
(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 r
and one pseudo-random sequence r
PRS
, allowing 510 different cell identities.
OS
OS
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 (PSYNC) 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 1-7.
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Fig. 1-7: 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
1.2.5 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.
1.3 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)
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[4] 3GPP TS 36.300: E-UTRA and E-UTRAN; Overall Description; Stage 2 (Release 8)
[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
OFDM-Based Broadband Transmission – Part II: A Case Study. IEEE Trans. on Commun. Vol. 49 (2001) No. 4, pp. 571-578.
Introduction
References
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2 Welcome
The EUTRA/LTE measurement 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 FSVR
This manual contains all information necessary to configure, perform and analyze such
measurements.
● Installing the Software.............................................................................................16
● Application Overview...............................................................................................16
● Support....................................................................................................................18
Welcome
Installing the Software
2.1 Installing the Software
For information on the installation procedure see the release notes of the R&S FSVR.
2.2 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 "More" softkey to find the LTE entry.
Second LTE channel
The application provides a second LTE channel that you can access via the Mode
menu with the softkey labeled "LTE2".
This second channel has the same functionality as the LTE channel. You can use it to
perform measurements on two LTE channels with a different configuration, for example
to test carrier aggregation.
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 160
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Elements and layout of the user interface
The user interface of the LTE measurement application is made up of several elements.
Welcome
Application Overview
1 = Channel Bar: contains all currently active measurement applications
2 = Table Header: shows basic measurement information, e.g. the frequency
3 = Result Display Header: shows information about the 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
The status bar
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.
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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 99
●
Ext. Att
Shows the external attenuation in dB.
●
Capture Time
Shows the capture length in ms.
Welcome
Support
2.3 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 FSVR stores the information in a number of files that
are located in the R&S FSVR 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.
18User Manual 1176.7661.02 ─ 04.1
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3 Measurement Basics
● Symbols and Variables........................................................................................... 19
● Overview................................................................................................................. 20
● The LTE Downlink Analysis Measurement Application...........................................20
● Performing Time Alignment Measurements............................................................23
● Performing Transmit On/Off Power Measurements................................................25
Measurement Basics
Symbols and Variables
3.1 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
T useful symbol time
19User Manual 1176.7661.02 ─ 04.1
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Measurement Basics
Overview
T
g
T
s
3.2 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.
3.3 The LTE Downlink Analysis Measurement Application
The block diagram in figure 3-1 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
received samples r''
of the measurement path (yellow) still contain the transmitted
l,k
. Depending on the user-defined compensation, the
l,k
of the
l,k
signal impairments 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.
3.3.1 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
at the timing offset is used.
, and . For the reference path, only the signal taken
20User Manual 1176.7661.02 ─ 04.1
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kl
lTfNNjlkNNjj
klklkl
NeeeHAR
CFOres
resFFTS
SFO
FFTS
CPE
l
,
22
,,,
.
Measurement Basics
The LTE Downlink Analysis Measurement Application
Fig. 3-1: Block diagram for the LTE DL measurement application
After the time to frequency transformation by an FFT of length N
, the phase syn-
FFT
chronization block is used to estimate the following:
●
the relative sampling frequency offset ζ (SFO)
●
the residual carrier frequency offset Δf
●
the common phase error Φl (CPE)
(CFO)
res
According to 3GPP TS 25.913 and 3GPP TR 25.892, the uncompensated samples can
be expressed as
(3 - 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
21User Manual 1176.7661.02 ─ 04.1
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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
3.3.2 Channel Estimation and Equalizitaion
As shown in figure 3-1, 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.
3.3.3 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/16QAM/64-QAM' are calculated according to the specification in 3GPP TS 36.211.
All other EVM measurement results are calculated according to
(3 - 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
(3 - 3)
The average EVM of all data subcarriers is then
22User Manual 1176.7661.02 ─ 04.1
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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
(3 - 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
(3 - 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
(3 - 6)
and the
(3 - 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
3.4 Performing Time Alignment Measurements
The measurement application allows you to perform Time Alignment measurements
between different antennas.
You can perform this measurement in 2 or 4 Tx antenna MIMO setups.
The result of the measurement is the Time Alignment Error. The Time Alignment Error
is the time offset between a reference antenna (for example antenna 1) and another
antenna.
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The Time Alignment Error results are summarized in the Result Summary.
A schematic description of the results is provided in figure 3-2.
Measurement Basics
Performing Time Alignment Measurements
Fig. 3-2: Time Alignment Error (4 Tx antennas)
Test setup
Successful Time Alignment measurements require a correct test setup.
A typical hardware test setup is shown in figure 3-3. Note that the dashed connection
are only required for MIMO measurements on 4 Tx antennas.
Fig. 3-3: Hardware setup
For best measurement result accuracy it is recommended to use cables of the same
length and identical combiners as adders.
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In the application, make sure to correctly apply the following settings.
●
select a reference antenna in the MIMO Configuration dialog box (not "All")
●
set the Subframe Selection to "All"
●
turn on Compensate Crosstalk in the "Demodulation Settings"
●
Note that the Time Alignment meaurement only evaluates the reference signal and
therefore ignores any PDSCH settings - for example, it does not have an influence
on this measurement if the PDSCH MIMO scheme is set to transmit diversity or
spatial multiplexing.
Measurement Basics
Performing Transmit On/Off Power Measurements
3.5 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 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
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
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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
For the transmit ON/OFF power measurements according to 36.141, 6.4, the test
model E-TM1.1 has to be used. For more information on loading the test model settings see chapter 7, "File Management", on page 88.
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.
Measurement Basics
Performing Transmit On/Off Power Measurements
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 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.
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4 Measurements and Result Displays
The LTE measurement application features several measurements to examine and
analyze different aspects of an LTE signal.
The source of the data that is processed is either a live signal or a previously recorded
signal whose characteristics have been saved to a file. For more information see
"Selecting the Input Source" on page 63.
For more information on the functionality to actually perform the measurement see
chapter 5.1, "Performing Measurements", on page 50.
● Numerical Results...................................................................................................27
● Measuring the Power Over Time............................................................................ 30
● Measuring the Error Vector Magnitude (EVM)........................................................34
● Measuring the Spectrum.........................................................................................37
● Measuring the Symbol Constellation.......................................................................45
● Measuring Statistics................................................................................................45
● 3GPP Test Scenarios..............................................................................................48
Measurements and Result Displays
Numerical Results
4.1 Numerical Results
Result Summary............................................................................................................27
Result Summary
The Result Summary shows all relevant measurement results in numerical form, combined in one table.
▶ Press the "Display (List Graph)" softkey so that the "List" element turns blue to view
the Result Summary.
Remote command:
DISPlay[:WINDow<n>]:TABLe on page 98
Contents of the result summary
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Measurements and Result Displays
Numerical Results
The table is split in two parts. The first part shows results that refer to the complete
frame. For each result, the minimum, mean and maximum values are displayed. It also
indicates limit check results where available. The font of 'Pass' results is green and that
of 'Fail' results is red.
In addition to the red font, the application also puts a red star ( ) in front of
failed results.
EVM PDSCH QPSK Shows the EVM for all QPSK-modulated resource elements of the PDSCH
channel in the analyzed frame.
FETCh:SUMMary:EVM:DSQP[:AVERage]? on page 102
EVM PDSCH 16QAM Shows the EVM for all 16QAM-modulated resource elements of the PDSCH
channel in the analyzed frame.
FETCh:SUMMary:EVM:DSST[:AVERage]? on page 103
EVM PDSCH 64QAM Shows the EVM for all 64QAM-modulated resource elements of the PDSCH
channel in the analyzed frame.
FETCh:SUMMary:EVM:DSSF[:AVERage]? on page 103
Time Alignment Error 2,1 /
3,1 / 4,1
Shows the timing difference in MIMO setups between antenna 1 and another
antenna (2, 3 or 4).
FETCh:SUMMary:TAE<antid>? on page 107
By default, all EVM results are in %. To view the EVM results in dB, change the EVM
Unit.
The second part of the table shows results that refer to a specifc selection of the frame.
The statistic is always evaluated over the subframes.
The header row of the table contains information about the selection you have made
(like the subframe).
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EVM All Shows the EVM for all resource elements in the analyzed frame.
EVM Phys Channel Shows the EVM for all physical channel resource elements in the analyzed
EVM Phys Signal Shows the EVM for all physical signal resource elements in the analyzed
Frequency Error Shows the difference in the measured center frequency and the reference
Sampling Error Shows the difference in measured symbol clock and reference symbol clock
Measurements and Result Displays
Numerical Results
FETCh:SUMMary:EVM[:ALL][:AVERage]? on page 102
frame.
A physical channel corresponds to a set of resource elements carrying information from higher layers. PDSCH, PBCH or PDCCH, for example, are physical channels. For more information see 3GPP 36.211.
FETCh:SUMMary:EVM:PCHannel[:AVERage]? on page 103
frame.
The reference signal, for example, is a physical signal. For more information
see 3GPP 36.211.
FETCh:SUMMary:EVM:PSIGnal[:AVERage]? on page 104
center frequency.
FETCh:SUMMary:FERRor[:AVERage]? on page 104
relative to the system sampling rate.
FETCh:SUMMary:SERRor[:AVERage]? on page 107
I/Q Offset Shows the power at spectral line 0 normalized to the total transmitted power.
FETCh:SUMMary:IQOFfset[:AVERage]? on page 105
I/Q Gain Imbalance Shows the logarithm of the gain ratio of the Q-channel to the I-channel.
FETCh:SUMMary:GIMBalance[:AVERage]? on page 105
I/Q Quadrature Error Shows the measure of the phase angle between Q-channel and I-channel
deviating from the ideal 90 degrees.
FETCh:SUMMary:QUADerror[:AVERage]? on page 106
RSTP Shows the reference signal transmit power as defined in 3GPP TS 36.141. It
is required for the "DL RS Power" test.
It is an average power and accumulates the powers of the reference symbols
within a subframe divided by the number of reference symbols within a subframe.
FETCh:SUMMary:RSTP[:AVERage]? on page 106
OSTP Shows the OFDM symbol transmit power as defined in 3GPP TS 36.141.
It accumulates all subcarrier powers of the 4th OFDM symbol. The 4th (out of
14 OFDM symbols within a subframe (in case of frame type 1, normal CP
length)) contains exclusively PDSCH.
FETCh:SUMMary:OSTP[:AVERage]? on page 105
Power Shows the average time domain power of the analyzed signal.
FETCh:SUMMary:POWer[:AVERage]? on page 106
Crest Factor Shows the peak-to-average power ratio of captured signal.
FETCh:SUMMary:CRESt[:AVERage]? on page 102
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Measurements and Result Displays
Measuring the Power Over Time
4.2 Measuring the Power Over Time
This chapter contains information on all measurements that show the power of a signal
over time.
Capture Buffer...............................................................................................................30
On / Off Power.............................................................................................................. 31
Capture Buffer
The Capture Buffer result display shows the complete range of captured data for the
last data capture. The x-axis represents time. The maximum value of the x-axis is
equal to the Capture Time. The y-axis represents the amplitude of the captured I/Q
data in dBm (for RF input).
Fig. 4-1: Capture buffer without zoom
The header of the diagram shows the reference level, the mechanical and electrical
attenuation and the trace mode.
The green bar at the bottom of the diagram represents the frame that is currently analyzed.
A blue vertical line at the beginning of the green bar in the Capture Buffer display represents the subframe start. Additionally, the diagram contains the "Start Offset" value.
This value is the time difference between the subframe start and capture buffer start.
When you zoom into the diagram, you will see that the bar may be interrupted at certain positions. Each small bar indicates the useful parts of the OFDM symbol.
30User Manual 1176.7661.02 ─ 04.1
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