Spectrum Analysis
User Guide
September 2020
Version 1.5
About This Document
This document discusses three 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, 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
8-Sep-2020
V1.5
Description
• Update for new NA address
• Update for RTS 3.6.6
2-Mar-2020
V1.4
New logo
Chris Culver
Sharon Redfoot
30-Aug-2019
V1.3
Updated PRB RSSI interference
Jesse Raasch, Zhang Dandan,
Sharon Redfoot
screen shot
CaoJianhua, Xie Sun
26-Aug-2019
V1.2
SME comments
16-Jly-2019
V1.1
Draft English version
SMEs/Contributors
Author/Editor
Yang Yanan, Nitisha Potti
Jocelyn Watson
CaoJianhua, Jesse Raasch,
Sharon Redfoot
Nitisha Potti
19-May-2019
V1.0
China version
CaoJianhua (Shawn)
ii
Sharon Redfoot
Support Resources
•
Documentation - Baicells product data sheets, this document, and other technical manuals may be
found at Baicells > Resources > Documentation.
•
Support - How to open a support ticket, 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
5700 Tennyson Pkwy., #300, Plano, TX 75024,
USA
Phone
+86-10-62607100
+1-888-502-5585
contact@Baicells.com
sales_na@Baicells.com or
support_na@Baicells.com
www.Baicells.com
https://na.Baicells.com
Email
Website
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Table of Contents
1.
INTRODUCTION ................................................................................................................................ 1
2.
UL PRB RSSI REPORT ......................................................................................................................... 1
3.
SPECTRUM SCANNING MODE ........................................................................................................... 3
4.
3.1
DESCRIPTION .......................................................................................................................................................3
3.2
CONFIGURATION ..................................................................................................................................................3
3.3
INTERPRETING THE RESULTS ....................................................................................................................................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 customer premise equipment (CPE) 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 three 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 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.
1
Figure 2: No Interference
Figure 3: With Interference
2
3. Spectrum Scanning Mode
3.1
Description
For cell planning, troubleshooting, and RF optimization, the eNB Spectrum Scanning Mode feature is 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, CPEs 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 Analyzer to set spectrum scanning parameters (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. Perform a warm reboot of 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 two uplink frequency domain results and two 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.
4
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.
5
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 CPEs that are passing traffic against the DL path loss, if there
is a significant difference (in dB) across multiple CPEs 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 CPEs 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.
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