Spectrum Analysis User Guide

August 2019

Version 1.3

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About This Document

This document discusses 3 Baicells eNodeB (eNB) features developed to help operators detect and

troubleshoot RF interference issues: UL PRB RSSI Report, Spectrum Scanning Mode, and Interference Detection.

These features are available for Baicells Nova-227, Nova-233, and Nova-243 eNBs as of software version

BaiBS_RTS_3.3.x. Per the Baicells Configuration & Network Administration Guide and the Baicells Operations,

Maintenance, & Troubleshooting Guide, we recommend that users already be familiar with general

configuration and operation of these eNB products.

Copyright Notice

Baicells Technologies, Inc., copyrights the information in this document. No part of this document may be

reproduced in any form or means without the prior written consent of Baicells Technologies, Inc. The Baicells

logo is a proprietary trademark of Baicells Technologies, Inc. Other trademarks mentioned in this document

belong to their owners.

Disclaimer

All products, services, and features bought from Baicells Technologies, Inc., are subject to the constraints of

the company's business contract and terms. All or part of the products, services, or features described in this

document might not be your specific Baicells network. Unless stated in the contract, Baicells Technologies, Inc.,

does not make any explicit or default statement or guarantee about the contents of this document.

Unless stated otherwise, this document serves only as a user guide, and all descriptions / information /

suggestions mean no guarantee, neither explicit nor implicit. The information in this document is subject to

change at any time without notice. For more information, please consult with a Baicells technical engineer or

the support team. Refer to the “Contact Us” section.

Revision Record

Date Version Description SMEs/Contributors Author/Editor

30-Aug-2019

26-Aug-2019

V1.3

V1.2

Updated PRB RSSI interference

screen shot

SME comments

Jesse Raasch, Zhang Dandan,

CaoJianhua, Xie Sun

Sharon Redfoot

16-Jly-2019 V1.1 Draft English version CaoJianhua, Jesse Raasch, Nitisha

Potti

Sharon Redfoot

19-May-2019 V1.0 China version CaoJianhua (Shawn) Sharon Redfoot

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Support Resources

• Documentation - Baicells product data sheets, this document, and other technical manuals may be

found at Baicells > Resources > Documentation.

• BaiTips - The BaiTips, under Baicells > Resources > BaiTips are where periodic suggestions about how

to improve equipment performance are posted.

• FAQs - Take advantage of our most frequently asked questions by searching the database under

Baicells > Resources > FAQs.

• Support - How to open a support ticket or process an RMA, and the Support Forum are at Baicells >

Support.

Contact Us

Baicells Technologies Co., Ltd. Baicells Technologies North America, Inc.

China North America

Address 3F, Bldg. A, No. 1 Kai Tuo Rd, Haidian Dist,

Beijing, China 555 Republic Dr., #200, Plano, TX 75074, USA

Phone +86-10-62607100 +1-888-502-5585

Email contact@Baicells.com

sales_na@Baicells.com or

support_na@Baicells.com

Website www.Baicells.com https://na.Baicells.com

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Table of Contents

1. INTRODUCTION ................................................................................................................................ 1

2. UL PRB RSSI REPORT ......................................................................................................................... 1

3. SPECTRUM SCANNING MODE ........................................................................................................... 3

3.1 DESCRIPTION ........................................................................................................................................................... 3

3.2 CONFIGURATION ...................................................................................................................................................... 3

3.3 INTERPRETING THE RESULTS ........................................................................................................................................ 4

4. INTERFERENCE DETECTION ................................................................................................................ 9

List of Figures

FIGURE 1: LTE > UL PRB RSSI REPORT ......................................................................................................................................... 1

FIGURE 2: NO INTERFERENCE ....................................................................................................................................................... 2

FIGURE 3: WITH INTERFERENCE .................................................................................................................................................... 2

FIGURE 4: SPECTRUM SCANNING MODE ........................................................................................................................................ 3

FIGURE 5: FIRST UPLINK SUBFRAME FREQUENCY DOMAIN DATA ......................................................................................................... 5

FIGURE 6: SECOND UPLINK SUBFRAME FREQUENCY DOMAIN DATA ..................................................................................................... 5

FIGURE 7: FIRST UPLINK SUBFRAME TIME SAMPLES ......................................................................................................................... 6

FIGURE 8: SECOND UPLINK SUBFRAME TIME SAMPLES ..................................................................................................................... 6

FIGURE 9: FIRST UPLINK SUBFRAME FREQUENCY DOMAIN DATA ......................................................................................................... 7

FIGURE 10: SECOND UPLINK SUBFRAME FREQUENCY DOMAIN DATA ................................................................................................... 7

FIGURE 11: FIRST UPLINK SUBFRAME TIME DOMAIN DATA ................................................................................................................ 8

FIGURE 12: SECOND UPLINK SUBFRAME TIME DOMAIN DATA ............................................................................................................ 8

FIGURE 13: INTERFERENCE DETECTION .......................................................................................................................................... 9

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1. Introduction

RF interference is one of the biggest challenges for operators to overcome in providing reliable wireless

broadband quality of service. Unwanted signals that interfere with communications between an LTE eNodeB

(eNB) and user equipment (UE) can lead to attachment failures, frequently dropped connections,

retransmissions, and an overall negative impact on network performance.

Baicells provides multiple, GUI-based RF measurements and visual Key Performance Indicators (KPI) to help

operators monitor and troubleshoot individual components as well as their overall Baicells network. In

BaiBS_RTS_3.3.x, Baicells introduced 3 built-in eNB features to give operators additional methods for cell

planning, detecting and troubleshooting interference, and optimizing RF performance: UL PRB RSSI Report,

Spectrum Scanning Mode, and Interference Detection.

2. UL PRB RSSI Report

The UpLink (UL) Physical Resource Block (PRB) Received Signal Strength Indicator (RSSI) Report feature is

probably the first thing you should check when you suspect you may have an interference issue. RSSI measures

the total received wideband power, including noise. When you run this report, the eNB looks for UE subframes

not being used (no PRBs assigned, no traffic) to take the RSSI measurement.

By default this feature is disabled. In the eNB GUI, go to the LTE menu > UL PRB RSSI Report to enable it (Figure

1). Next, set the report period. This time period determines how often the report will run, and may be set from

1 to 255 seconds. The feature will remain enabled and continue to run until you reset it to Disable; it will not

automatically shut off.

Figure 1: LTE > UL PRB RSSI Report

The report will display a graph in real-time at the bottom of the window, showing the total UL RSSI (in dBm)

along the y-axis for each PRB along the x-axis. Since there are multiple antenna elements, the Baicells eNB

reports each RF chain - ANT1 and ANT2. Only 20 MHz of bandwidth (or working mode) can be detected at one

time.

Figure 2 provides an example of a report in a clean (no interference) environment. Figure 3 shows a report in

an environment with interference.

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Figure 2: No Interference

Figure 3: With Interference

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3. Spectrum Scanning Mode

3.1 Description

For cell planning, troubleshooting, and RF optimization, the eNB Spectrum Scanning Mode feature may be

used to analyze signal amplitude (strength) as it varies by signal frequency on the uplink. Simply put, a scan

graph represents what is happening in the RF spectrum. This helps in determining the best frequency to use

and where there may be interference.

Frequency scanning encompasses In-phase and Quadrature (I/Q) data in the physical layer, using time and

frequency information from the baseband. The scan looks at the uplink data within a configured frequency

range for up to 20 MHz at a time.

IMPORTANT: When an eNB is operating in spectrum scanning mode, UEs will not be able to attach to the eNB.

3.2 Configuration

In order to get the most channel information over-the-air, while the eNB is operating in spectrum scanning

mode the TDD subframe assignment is set to "1" and the special subframe pattern is set to "7". These settings

are restored to their previous values when the eNB is set back to Normal mode.

To initiate spectrum scanning, follow the steps below.

1. In the eNB GUI, go to LTE > Spectrum scanning mode (Figure 4).

2. Set the Mode field to Spectrum Scan Mode, and select the country code, band, and frequency range

you wish to analyze. The start and end frequencies must be within the same band, and there must be

a 20 MHz gap between StartFrequency and EndFrequency.

3. Save the settings.

Figure 4: Spectrum Scanning Mode

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4. Reboot the eNB.

5. Once the eNB finishes rebooting, in the GUI go back to LTE > Spectrum scanning mode and select

Sweep to start the scan. It usually takes about one minute.

6. To see the scan results, click on Get Result. The results will appear at the bottom of the window.

Examples of results are shown below in section 3.3.

7. When you are finished, remember to set the Mode field back to Normal and reboot the eNB to exit

the spectrum scanning mode and return to normal operating mode.

When initiating a scan, possible error messages you may see include:

• Frequency Lock error - Start and end frequencies entered in the GUI are out of range or not supported

• Gain error - Indicates an offset error in converting the baseband signal to RF signal strength

• Sync error - Indicates an issue with the I/Q data where the uplink subframe starting point cannot be

identified. Rebooting the eNB may clear this error.

• PCI error - The Physical Cell Identifier (PCI) cannot be read from the GUI setting or is out of range

NOTE: The Reset button in the GUI window is intended to reset the configuration; however, at this time there is a known issue with this function.

3.3 Interpreting the Results

There are two types of scan results: frequency domain and time domain. For 20 MHz* spectrum, when you

run the scan you will get 2 uplink frequency domain results and 2 time domain results, where:

• First UL subframe = Combined UL subframes from the first half-frame (subframes 2 or 7)

• Second UL subframe = Combined UL subframes from the second half-frame (subframes 3 or 8)

*NOTE: The actual usable bandwidth is 18 MHz (20 MHz minus 2 MHz), because 1 MHz for the start frequency

and 1 MHz for the end frequency are omitted.

Following are two scenarios, one where there is no interference and one where there is interference.

1. Frequency Domain

For this general example, look at the scan of 20 MHz in Figure 5 and Figure 6. The x-axis shows the frequency,

and the y-axis is equivalent to the power of the subcarrier in dBm. Each vertical data point represents one

Orthogonal Frequency Division Multiplexing (OFDM) symbol. One subframe will have 14 overlapping vertical

data points from 14 OFDM symbols.

The spike shown in the middle of this frequency chart is subcarrier 0, which is used for synchronization and

cannot be used to transmit data. In both scans the power is about -115 dBm, which means the channel is clean

in these subframes.

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Figure 5: First Uplink Subframe Frequency Domain Data

Figure 6: Second Uplink Subframe Frequency Domain Data

2. Time Domain

Now let's look at the time domain charts. Notice the two colors, orange and blue, in the examples in Figure 7

and Figure 8. One color is the real data, and one is the imaginary* part of the baseband signal. The primary

frequency scan analyzes the baseband I/Q data. The I/Q data is obtained from the eNB, focusing on 1 chain of

uplink I/Q data from antenna 0**.

The input data is from the uplink RF signal, and the output is the baseband signal. Therefore, the power in the

frequency domain is the calculated RF power (dBm), and the power in the time domain is the baseband

sampling point (amplitude). The x-axis shows the sampling point count, where 30720 sampling points is

equivalent to 1 millisecond. Only the symbols with traffic are calculated; the results do not include the UL/DL

transmission switch symbol, which uses a high power level and would skew the data.

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The sampling pattern in the time domain graphs can also be used to help identify the source of any scanned

RF, such as OFDM, CDMA, GSM, GPS, etc. A relatively flat graph means no noise.

*Related to Fast Fourier Transform algorithms

**It is possible to use 2 chains of UL I/Q data.

Figure 7: First Uplink Subframe Time Samples

Figure 8: Second Uplink Subframe Time Samples

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1. Frequency Domain

In this scenario the eNB is scanning frequency range 3666-3686 MHz. There is a neighbor cell using center

channel 3686 MHz, 20 MHz bandwidth, and subframe 2:7. Figure 9 and Figure 10 show the first and second UL

subframe frequency domain data. Interpretations are written in red text on the figures.

Figure 9: First Uplink Subframe Frequency Domain Data

Figure 10: Second Uplink Subframe Frequency Domain Data

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2. Time Domain

Figure 11 provides a sample of the first UL subframe time domain data, which shows the strength of the

interfering signal(s) from a time domain aspect. Figure 12 is the second sample, which shows close to the

same results.

Figure 11: First Uplink Subframe Time Domain Data

Figure 12: Second Uplink Subframe Time Domain Data

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4. Interference Detection

The Interference Detection feature may be used to trigger an alarm notification based on UL and DL path loss.

When the eNB compares the UL path loss from all UEs that are passing traffic against the DL path loss, if there

is a significant difference (in dB) across multiple UEs for a specified period of time, there is likely UL interference

occurring. The calculation of path loss considers measurements such as RS power, RSRP, SNR, PRB utilization,

and noise floor. When the configured thresholds are met, the eNB sends an alarm (ID 11224) to the OMC.

To configure the feature, in the eNB GUI go to LTE > Advanced > Interference Detection (Figure 13). In the

dialogue box that opens, select Enable and configure the Detect Threshold (in dB), Alarm Threshold (%), and

Alarm Period (minutes). Table 1 describes each field.

Figure 13: Interference Detection

Table 1: Interference Detection

Parameter Description

Interference Detection Enable or disable the interference detection function.

Detect Threshold Interference detection threshold, based on the amount of difference, in dB,

between UL and DL path loss. Range is 1-20 dB. Default is 5 dB.

Alarm Threshold Alarm trigger threshold, based on the percentage of all UEs passing traffic that are

meeting the detection threshold for the amount of time specified in the Alarm

Period field. Range is 1-100%. Default is 60%.

Alarm Period Set the minimum period of time that the interference detection threshold is

sustained before the alarm is triggered. Range is 1-60 minutes. Default is 5 minutes.