nb-iot measurements with r&s®tsmx scanner … · higher than for legacy lte. to improve the...

NB-IoT measurements with R&S®TSMx scanner Application Note

Products:

ı R&S®TSMW

ı R&S®TSME

ı R&S®TSMA

ı R&S®ROMES4

ı R&S®ROMES4NPA

ı R&S®ROMES4N34

ı R&S®TSMx-K34

This document describes the highlights of NB-IoT scanning use cases and functionality of R&S®TSMx

products together with R&S®ROMES4 and R&S®ROMES4NPA.

Note:

Please find the most up-to-date document on our homepage

App

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Man

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3.20

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V1.

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Table of Contents

V1.0 Rohde & Schwarz R&S®TSMx scanner

2

Table of Contents

1 Introduction ......................................................................................... 3

1.1 NB-IoT / Cat NB1 technical aspects - a brief introduction ....................................... 3

1.1.1 What is NB-IoT? ............................................................................................................. 3

1.1.2 NB-IoT spectrum implementation .................................................................................. 4

1.2 Measurement use cases for NB-IoT ........................................................................... 5

2 Coverage and quality measurements ............................................... 7

2.1 Synchronization signal measurements ..................................................................... 7

2.2 Reference signal measurements................................................................................ 7

2.3 Other parameters ......................................................................................................... 9

3 Layer 3 Broadcast channel demodulation ...................................... 10

3.1 MIB (Master Information Block) ................................................................................11

3.2 SIB1 (System Information Block 1) ..........................................................................11

4 Multi-technology measurements ..................................................... 13

4.1 LTE + NB-IoT measurements ....................................................................................13

4.2 GSM + NB-IoT measurements ..................................................................................15

4.3 Spectrum (RF power scan) measurements .............................................................16

5 Post processing of R&S®ROMES4 measurement results with NPA

............................................................................................................ 18

6 Literature ........................................................................................... 21

7 Ordering Information ........................................................................ 22

Introduction


3

1 Introduction

1.1 NB-IoT / Cat NB1 technical aspects - a brief introduction

NB-IoT ("Narrowband IoT" also known as Cat NB1) is a new 3GPP technology for IoT

(Internet of things). IoT is a tern describing "connecting things to the internet", which

means collecting and post processing their data, mostly cloud-based. One of the most

popular example is the intelligent parking area, which regularly updates a database of

free parking sites, which is available for the driver on its smartphone or infotainment

system.

IoT means reducing costs and creating the base to increase the efficiency of

processes. A smart power meter for example can send the measured energy

consumption value to the energy provider, without requiring an action from the

consumer or energy provider.

1.1.1 What is NB-IoT?

The standardization targets arise from the IoT use cases. While traditional mobile

broadband technologies target higher data rates reached by a higher complexity (for

example for video streaming), the IoT technology goes the other way round. To

maintain the efficiency of intelligent parking areas or smart meters, the battery life

should be as long as possible, which leads the one of the major targets like low power

consumption and therefore reduced complexity. Most of the smart meters are located

in the basement, which requires sufficient RF conditions even in deep-indoor

environments. For example, modulation and coding schemes for poor RF conditions

and corresponding link budgets are used as well as simplified receiver architectures.

NB-IoT as a standardized technology is also called Cat NB1. In the diagram below,

also Cat NB2 is mentioned which is an enhanced version of Cat NB1.

Cat M1 is also an IoT radio access technology standard, but it requires more complex

receiver structures. It is based on a 1.4 MHz carrier, supporting additional services (like

voice) and higher data rates.

Introduction


4

Figure 1: 3GPP standardization targets, mobile broadband vs. internet of things (IoT)

1.1.2 NB-IoT spectrum implementation

NB-IoT is a very flexible technology in terms of spectrum implementation. It only

requires a narrowband carrier (180 kHz only), preferably implemented 700 / 800 / 900

MHz spectrum to ensure sufficient indoor penetration.

Figure 2: Bandwidth and spectrum occupation of a NB-IoT carrier

Introduction


5

In most cases, the spectrum is heavily occupied by mobile broadband services (for

example LTE-A with carrier aggregation). To overcome this problem, NB-IoT supports

three different operation modes, which provides the possibility for spectrum refarming

and "seamless implementation" in available LTE carriers.

In-band operation uses one physical resource block in an existing LTE carrier,

requiring no dedicated NB-IoT spectrum outside of the LTE carrier. Another alternative

is placing the NB-IoT carrier in the guard-band of an existing LTE carrier.

One example for spectrum refarming is exchanging GSM carriers with NB-IoT carriers

using the same bandwidth. Like GSM carriers, the NB-IoT carriers are implemented as

stand-alone carriers in the spectrum (stand-alone mode).

Figure 3: Comparison of NB-IoT operation modes

1.2 Measurement use cases for NB-IoT

Each rollout of a new technology starts with reference coverage measurements to

compare real-field measurements with coverage prediction models, which might have

to be tuned. Coverage is essential for every technology, especially when indoor

availability is part of major use cases. This is in particular valid for the NB-IoT

technology where the required Maximum Coupling Loss (MCL) is more than 20 dB

higher than for legacy LTE.

To improve the link budget for indoor applications, it is common to power-boost NB-IoT

carriers. Typical power-boost values are 6 … 9 dB (compared to traditional LTE in in-

band operation). Increasing the power means also creating a completely different

CINR (signal to interference and noise ratio) situation all over the network resulting in

optimization need.

LTE network deployments are typically optimized for handling increasing data traffic.

To overcome capacity bottlenecks, operators densified their networks during the past

years. A densified network has typically more active sites than needed for coverage

only. This necessarily leads to a mixed situation. Sites, predominantly used for network

densification in LTE, might not require transmitting a (power-boosted) NB-IoT carrier in

order to provide sufficient NB-IoT coverage. This situation directly leads to an

interference situation between LTE and NB-IoT networks, requiring to measure the

impact of NB-IoT on LTE and vice versa. But it's not only an interaction with LTE - the

same problem can occur, if traditional GSM or WCDMA900 spectrum is refarmed to

use it for NB-IoT.

Introduction


6

Once the first devices / user equipments are active in the network, troubleshooting is

required to solve problem reports. Sufficient RF conditions are basic requirements for a

satisfying quality of service. Heavily occupied spectrum and power-boosting can lead

to a critical interference situation with the impossibility to transfer any data in the

network at all. Multi-technology scanner measurements provide deep insights in RF

conditions and help to locate and solve interference problems.

Note: For all examples below, R&S®ROMES4 is used. R&S®ROMES4 is a powerful drivetest tool, including scanner and UE based

measurements covering all major 3GPP mobile network radio access technologies.

To keep track of the spectrum situation, R&S®TSMx network scanners additionally

provide the possibility for simultaneous spectrum measurements (RF power scan). The

waterfall / time sweep diagram shows the spectrum constellation over time.

Figure 4: Spectrum measurement (traditional GSM carriers and power-boosted NB-IoT in-band

operation in a 5 MHz LTE carrier - blue box)

Scanner measurements are passive, not requiring an active network subscription.

Passive measurements are not limited to a certain band or network, creating a perfect

possibility to benchmark networks.

Coverage and quality measurements


7

2 Coverage and quality measurements

2.1 Synchronization signal measurements

Coverage measurements typically include measurements based on synchronization

signals. Synchronization signals are used by the user equipment to synchronize on

NB-IoT carriers in a certain frequency band. The NB-IoT carrier includes primary and

secondary synchronization signals. For NB-IoT scanner based measurements, the

secondary synchronization signal (NSSS) is used. The secondary synchronization

signal is located in radio frame #9.

NPBCH NPSS NSSS

Subframe 0 1 2 3 4 5 6 7 8 9

Figure 5: NB-IoT radio frame showing positions of NPBCH, NPSS and NSSS.

The following parameters are measured based on the secondary synchronization

signal:

NSSS Power: Represents the actual power of each NB-IoT signal (12 subcarriers) for

which the scanner identifies a physical cell ID (NPCI). The value is based on the NSSS

(secondary synchronization signal).

NSSS CINR: Carrier to interference and noise ratio (based on NSSS)

2.2 Reference signal measurements

Reference signal measurements typically represent the RF conditions for user and

control data-carrying signals. Reference signals are represented by the signals in blue

color in Figure 6.



8

Figure 6: Resource grid with primary and secondary synchronization signals and NB-IoT reference

signals belonging to antenna port Tx0

ENodeB antennas are typically cross-polarized antennas, providing two ports. In

traditional LTE, this is used for MIMO 2x2 (transmitting two data streams between

multiple antennas on Tx and Rx side; spatial multiplexed layers). NB-IoT itself does not

support MIMO 2x2 (spatial multiplexing) but it is possible to transmit the NB-IoT signal

from only one or both eNodeB antenna ports to increase the probability to achieve

sufficient RF conditions at the user equipment location. The scanner is able to

distinguish between the reference signals from both antenna ports (Tx0, Tx1 with

different locations in the resource grid) and provides reference signal measurements

for each port separately. This is from particular interest when NB-IoT networks are for

example running on indoor coverage systems with two SISO / one port antennas,

creating a different coverage for both antenna ports.

Figure 7: Reference signals of antenna ports Tx0 and Tx1

The following parameters are measured based on the reference signals:

NRSRP: Measurement of the linear average power of the resource elements, that

carry NB-IoT reference signals. The power level represents the averaged power of one

single reference signal (one RE).

NRSRQ: The NRSRQ (reference signal receive quality) is calculated as the ratio of

RSRP and RS-RSSI and reported in dB (log operation).



9

)(log10 10RSRSSI

RSRPRSRQ

NRS CINR: The NRS CINR (reference signal carrier to interference and noise ratio)

measurement is based on the resource elements where reference signals are

guaranteed to be there (3GPP specification; assuring compatibility with different

eNodeB configurations).

NRS RSSI: The NRS RSSI averages the received power of those OFDM symbols that

carry reference signals. The power is measured across the entire NB-IoT bandwidth

(12 resource elements). RSSI measurements include inference, noise and the desired

signal.

2.3 Other parameters

NRSSI: The received signal strength indicator represents the total power received by

the scanner inside the 180 kHz bandwidth of a NB-IoT channel. This power includes all

possible NB-IoT signals transmitting in the channel as well as noise and interference

from other cells.

Synchronization and reference signal measurements can be found in the NB-IoT Top

N View in ROMES4.

Figure 8: NB-IoT scanner Top N view displaying synchronization and reference signal measurement

parameters.

N N

N

Layer 3 Broadcast channel demodulation


10

3 Layer 3 Broadcast channel demodulation

Next to power, quality and CINR measurements, the scanner is able to demodulate the

MIB and SIB messages. MIB (Master Information Block) and SIB (System Information

Block) are broadcast messages, which carry network configuration related data. The

most popular data are mobile network code (MNC), mobile country code (MCC), cell

ID, reselection instructions for the user equipment and many more. Especially for NB-

IoT cells the deployment mode (in-band, guard-band or stand-alone) as well as same

or different PCI, compared to the legacy LTE cell, is listed in the MIB message.

The Layer 3 BCH demodulation can be enabled in the scanner configuration page

(from ROMES4 18.0 and onwards). In ROMES4 18.0 release, MIB and SIB1 is

supported. Other SIBs will follow in subsequent releases.

Figure 9: NB-IoT scanner configuration page with MIB and SIB1 demodulation enabled

MIB and SIB data is demodulated for each cell, exceeding the minimum threshold (RF

conditions) for demodulating the Layer 3 BCH data. This threshold is different for MIB

and SIB1, because they are coded in different ways. As a result, it is possible to

discover more cells in the NB-IoT Top N view (by using synchronization and reference

signals) than demodulating and displaying in the NB-IoT scanner BCH view.

The MIB / SIB data is broadcasted periodically, which might lead to a short latency

after discovering the NB-IoT cell in the Top N View (using synchronization and

reference signals).

The MIB and SIB demodulation results are shown in the NB-IoT scanner BCH view in

a tree structure. It is sorted by providers, channels (frequencies) and corresponding

PCIs.



11

Figure 10: NB-IoT scanner tree-structure for selecting Layer 3 messages during the demodulation

process of MIB and SIB1.

The NB-IoT demodulator supports dynamic PDUs, which means that different versions

of discovered MIB and SIB1s are decoded and displayed with a timestamp in the PDU

variant list (Figure 11).

3.1 MIB (Master Information Block)

The following information is included in MIB:

ı Access baring information with reference to other SIBs

ı CRS offset info for the NB-IoT carrier

ı Operation mode info (e. g. In-band Same PCI)

ı Raster offset from traditional LTE channel raster

ı Scheduling info for SIB1 and reference to other SIBs

ı Most significant bits of the system frame number

3.2 SIB1 (System Information Block 1)

The following information is included in SIB1:

ı Cell baring information

ı Cell identity, tracking area code

ı Downlink bitmap for downlink transmission

ı Frequency band indicator

ı Intra Frequency selection

ı Multi Band Info List (reference to other frequency bands)

ı CRS power offset (NRS power offset compared to LTE CRS)

ı PLMN identity list

ı Allowed Pmax for the user equipment



12

ı Minimum quality and power receive level values for accessing the NB-IoT cell

ı Scheduling Info List (reference to other SIBs) and SI location

Figure 11: NB-IoT scanner BCH view during MIB demodulation

Multi-technology measurements


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4 Multi-technology measurements

4.1 LTE + NB-IoT measurements

Simultaneous LTE and NB-IoT measurements allow deep RF insights for NB-IoT in-

band deployments. NB-IoT In-band deployments use a certain LTE physical resource

block (PRB) within standard LTE PRBs. Especially in networks with a mixed

deployment situation of LTE and NB-IoT it is important to consider the impact of NB-

IoT on LTE and vice versa. LTE subband measurements allow measurements on the

reference signals of each subcarrier.

Figure 12: Multiple scanner drivers loaded in R&S®ROMES4

NB-IoT uses different reference signals, which are detected by the LTE scanner as

noise during SINR and RSRQ measurements on the LTE reference signals. This effect

is increased by having NB-IoT in-band operation and not all eNodeBs have NB-IoT

active ( "mixed deployment situation", details can be found below).

Figure 13: Measurement and visualization of the NB-IoT carrier in the LTE subband view showing the

LTE RS-SINR

Depending on the eNodeB configuration, it is possible to restrict using the neighbored

LTE PRBs around the NB-IoT in-band carrier from carrying LTE data traffic. LTE traffic



14

is represented by the lower SINR / RSRQ over the LTE subbands visualized in the LTE

subband view.

Figure 14: Visualization of the LTE carrier including the NB-IoT carrier without scheduling LTE data

traffic on the physical resource blocks around the NB-IoT PRB (blue marker).

It's not only the data traffic, which is increasing the interference. Interference is also

caused by neighbor cells, especially if there is a mixed deployment situation of LTE-

only and LTE sites including in-band NB-IoT. In the case, where surrounding LTE-only

sites schedule traffic on the PRB used for NB-IoT in the LTE + NB-IoT cluster, the

CINR of NB-IoT worsens with increasing LTE data traffic scheduled on LTE only

neighbor cells. The traffic is visualized as a reduced RS CINR (red colors) in the LTE

subband view.

For better indoor penetration, the NB-IoT carrier is typically power-boosted (+6…+12

dB). This power-boost can be verified by comparing the LTE scanner RSRP

measurements with the NRSRP measurements from the NB-IoT scanner (same

physical cell and NB-IoT in-band operation is required). For RSRP calculation in both,

LTE and NB-IoT scanner results, the same averaging over the received reference

signal power is used, which leads to comparable values.



15

Figure 15: Simultaneous LTE and NB-IoT scanner operation can be used to verify the power-boost

for indoor and outdoor scenarios (comparing for example the RSRP; blue marker).

4.2 GSM + NB-IoT measurements

Figure 16: Multiple scanner drivers loaded in R&S®ROMES4

Interference detected by RF power scan measurements, can be evaluated with the

NB-IoT scanner as well. Interference typically leads to reduced CINR values for

synchronization and reference signal measurements.

NB-IoT and GSM carriers occupy the same bandwidth, which simplifies refarming

(exchanging one GSM carrier by a NB-IoT stand-alone carrier). Therefore, power

measurements over the whole carriers are comparable. The parameter NRSSI refers

to the power in the whole spectrum occupied by the NB-IoT carrier. Both is taken into

account, signal plus interference and noise. In the interference case, the NRSSI also

contains power from interfering GSM carriers. The corresponding parameter to NRSSI

in GSM measurements is Ptotal.

Interference always leads to reduced signal to noise plus interference and carrier to

interference ratios. Both values can be measured and compared during a multi-

technology measurement (GSM and NB-IoT). Typical scenarios leading to interference

are the overlap area between two clusters, one with refarming (GSM NB-IoT) the

other one without refarming only using traditional GSM carriers. Especially on higher

levels in high-rise buildings, interference from other GSM and NB-IoT is very likely due

to the propagation characteristics of GSM900 frequencies. The result is a low C/I value

measured by the GSM scanner.



16

Figure 17: Relevant GSM scanner measurements (displayed in the ROMES4 GSM scanner Top N

View) to detect NB-IoT interference

4.3 Spectrum (RF power scan) measurements

It is possible to detect the NB-IoT carrier with 180 kHz bandwidth using the RF power

scan. For better indoor penetration, the NB-IoT carrier is typically power-boosted

(+6…+12 dB) and is therefore visualized as a peak in the spectrum.

Figure 18: Visualization of a NB-IoT in-band carrier in the RF power scan / spectrum view (blue

marker).

Another use case for RF power scan is to detect the overall noise floor in a heavily

occupied spectrum. While adjacent subbands of traditional LTE typically affect in-band

carriers, guard-band and stand-alone NB-IoT carriers are affected by noise floor and

other GSM or WCDMA900 carriers. Traditional GSM typically uses high power levels

to provide basic coverage, which leads to significant ranges of coverage and therefore

to interference. Figure 19 shows a RF power scan waterfall diagram with a significant

noise floor coming from multiple GSM900 carriers received in that particular location. In

this case, NB-IoT was deployed in stand-alone mode around 960 MHz and affected by

interference from WCDMA900 and a neighbored GSM carrier.



17

Figure 19: RF power scan including GSM, UMTS/WCDMA900 and NB-IoT carrier (blue marker).

Post processing of R&S®ROMES4 measurement results with NPA


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5 Post processing of R&S®ROMES4

measurement results with NPA

The network problem analyzer (R&S®ROMES4NPA) tool is a powerful post-

processing tool for R&S®ROMES4 files. The R&S®ROMES4NPA is able to scan and

analyze R&S®ROMES4 files in an efficient way to display cell statistics and network

problem spots, simplifying the post-processing and problem analysis after drive testing.

For each scanner parameter (based on sync and reference signals) available in the

ROMES4 Top N Pool, the occurrence share during the drive test is evaluated.

Thresholds and different colors are user-configurable.

Figure 20: Parameters and user configurable colors including their occurrence share during the drive

test.

The R&S®ROMES4NPA also provides NB-IoT Cell Statistics. Maximums and

averages of synchronization and reference signals RF parameters are evaluated for

each PCI discovered during the drive test.

Furthermore, the user gets statistics about the occurrence and rating (Top N) of the

cell during the drive test.

Next to cell statistics, the detection and visualization of problem spots in the network

(already known from LTE) is also supported for NB-IoT scanner data. In the following

screenshot, a NB-IoT scanner drive test .rscmd file is analyzed to detect network



19

problem spots. For NB-IoT scanner results it the following problem spot categories are

available:

Figure 21: Network Problem Analyzer NB-IoT problem spot categories and their occurrence during

the drive test

For all network problem categories, user-configurable thresholds ("Coverage Analysis

Data Processor") for the corresponding RF parameters can be defined. The

ROMES4NPA comes up with default values.

Figure 22: User-configurable Thresholds for networks problem spots



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After running the data processor, drive test data and the detected problem spots

(based on the threshold) are shown on a map.

Figure 23: Map screenshot of detected problem spots along the drive test

Each problem spot is available in a list as well including a description of the problem.

Literature


21

6 Literature

Only internal information sources and data from own field tests were used.

Ordering Information


22

7 Ordering Information

Designation Type Order No.

TSMW-Scanner Option: NB-IoT: Sync and reference signal

measurement, MIB / SIB decoding is planned for ROMES4

18.0 / 18.1

TSMW-K34 1515.7436.02

TSME-Scanner Option: NB-IoT: Sync and reference signal


18.0 / 18.1

TSME-K34 1522.6731.02

TSMA-Scanner Option: NB-IoT: Sync and reference signal


18.0 / 18.1

TSMA-K34 1524.6468.02

ROMES4 Driver: TSMW

supports TSMW GSM/WCDMA, CDMA20001x/EVDO,

WiMAX, LTE, Cat NB1 / NB-IoT, TETRA, RF Power Scan.

Single User License.

ROMES4T1W 1117.6885.02

ROMES4 Driver: TSME

supports TSME GSM/WCDMA, CDMA2000/1xEV-DO,

WiMAX, LTE, Cat NB1 / NB-IoT, TETRA, RF Power Scan.

Single User License.

ROMES4T1E 1117.6885.82

ROMES4 NPA Plugin: NB-IoT Analysis based on Sync and

reference signal measurements (scanner based)

ROMES4N34 4900.5206.02

TSMW-Scanner Option: NB-IoT: Sync and reference signal

measurement

MIB / SIB decoding planned for ROMES4 18.0 / 18.1

TSMW-K34 1515.7436.02

TSME-Scanner Option: NB-IoT: Sync and reference signal

measurement

MIB / SIB decoding planned for ROMES4 18.0 / 18.1

TSME-K34 1522.6731.02

Glossary


23

Glossary

CINR vs. SINR:

CINR is used for NB-IoT scanner measurements

SINR is used for LTE scanner measurementss

Rohde & Schwarz

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leaders in its established business fields. The

company is headquartered in Munich, Germany. It

also has regional headquarters in Singapore and

Columbia, Maryland, USA, to manage its operations

in these regions.

Regional contact

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This application note and the supplied programs

may only be used subject to the conditions of use

set forth in the download area of the Rohde &

Schwarz website.

Version V1.0 | R&S®R&S®TSMx scanner

R&S® is a registered trademark of Rohde & Schwarz GmbH & Co.

KG; Trade names are trademarks of the owners.

Rohde & Schwarz GmbH & Co. KG

Mühldorfstraße 15 | 81671 Munich, Germany

Phone + 49 89 4129 - 0 | Fax + 49 89 4129 – 13777

www.rohde-schwarz.com

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