Base Station Transmits

RF Cable Measurements Help Ensure 5G Networks Meet KPIs

August 2, 2022

Many operators are currently supporting 5G in existing sub 2.5 GHz bands using dynamic spectrum sharing (DSS). DSS technology allocates spectrum resources between LTE and 5G technologies in an LTE frame structure, and is often implemented with a software update to existing LTE radios and antennas. These network deployments usually implement traditional base station and antenna architectures with RF cable feeds between the two components. For this reason, tower crews must implement comprehensive RF cable testing during 5G network deployment and installation and maintenance (I&M).

Many mobile operators continue to deploy multi-band, multibeam massive MIMO hybrid antennas. These antennas are fed by RF cables from the radio. Some networks use a single hybrid antenna with at least 16 RF connectors and cables feeding it. To achieve published network KPIs, the cables must be low loss and all connectors, bends and clamping brackets formed and installed correctly.

When installing new LTE or 5G base stations that include RF cable feeds to the antenna installation tower crews need to be certain that the overall system is performing to specification. Four measurements are typically to used to verify base station operation. In this post, we will go into detail on each.

Modulation Quality

Modulation quality of LTE base stations is most commonly performed from an RF test port on the radio. Field technicians can use an instrument, such as the Anritsu Field Master Pro™ MS2090A (figure 1), with built-in measurements for occupied bandwidth (OBW), channel power, error vector magnitude (EVM), RSRP, and other modulation quality metrics. It is recommended that these measurements be made before the base station is connected to the antenna system.

Figure 1: he Field Master Pro MS2090A has built-in measurements to test RF cables.

Many 5G base stations do not have an RF test port. For this reason, over-the-air (OTA) measurements must be made. Certain field spectrum analyzers offer a comprehensive suite of modulation quality measurements. It is important for field technicians to connect the base station to the antenna via a long RF cable to the tower or via short jumper cables from a rooftop mounted base station to the antenna when testing OTA.

Cable and Antenna Measurements

Many 5G base stations are being deployed at existing LTE sites. Each tower has a loading factor that defines the maximum weight of the radios and antennas that can be  mounted. Due to legacy hardware on the tower, the radio may be required to be installed at ground level and only the antenna is tower mounted.

As the RF signal travels through the cable some energy will be dissipated in the cable and connectors. A cable insertion loss measurement must be made during installation to confirm that the loss is within specification. Low loss cables must be used to minimize the base station power and maximize  efficiency. Cables with larger diameters have less insertion loss and better power handling capabilities than smaller diameter cables but are more expensive and much heavier.

It is also important to measure the magnitude of any RF reflections in the cable and antenna system. Loss of efficiency can be caused by distortion from cable and antenna feed reflections due to the power being reflected back towards the base station. Common causes of reflections are:

• Poorly installed connectors that are loose or not correctly torqued
• Connectors that have degraded over time due to weather damage
• RF cable damage (i.e. over-tightening cable clamps and bend radius causing kinks)
• Damaged and/or incorrect antennas

Cable loss and return loss are measured as swept frequency traces across the full operating band of the antenna. Connectors that have not been torqued to the correct value can result in narrow band “suck outs” with very high insertion loss. It is important to sweep the full operating band to find such failures and recognize that cable loss has an effect on measured return loss.

Figure 2 highlights how cable loss alters the measured antenna performance. The antenna has a return loss of 15 dB but the 5 dB insertion loss improves the perceived system return loss by 10 dB. Even though this is something system engineers consider when establishing site specifications, it is important to be aware of the effects the insertion loss and cable return loss can have on the overall system return loss.

Figure 2: An example of how cable loss can affect antenna performance measurements.

A very good system return loss is not always a guarantee of a correctly installed antenna. A faulty cable with too much insertion loss or an antenna out of specification can be the cause. The result is a larger than expected signal drop. A great portion of the signal is reflected once it reaches the antenna since the match is worse than expected. The transmitted signal is lower and the coverage from the base station is reduced.

Return loss/VSWR measurement characterizes the performance of the overall system. If either is failing, field technicians need to conduct a distance-to-fault (DTF) measurement to troubleshoot the system and locate the fault’s exact location. It is important to understand that the DTF measurement is strictly a troubleshooting tool, as well as to compare relative data and monitor changes over time to identify faults and measure cable length. A DTF measurement sweeps the cable in the frequency domain and applies an Inverse Fast Fourier Transform (IFFT) to convert results from the frequency domain to the time domain.

The Field Master Pro MS2090A integrated with the Site Master S331P cable and antenna analyzer accessory is ideal for performing line sweep measurements in the field. Return loss, cable loss, and DTF can all be made with the single instrument.

Cell Site Coverage

A coverage map for the surrounding area is required to validate that base station coverage meets the planners modeling when it is brought online. The MS2090A supports downloading of digital maps directly from the Internet to display on the instrument screen. Plotting a channel power measurement onto the digital map using color to represent relative strength provides a graphical and easy to interpret overview of the cell site coverage.

EMF Measurements

Operators of cellular networks often need to reassure the local community that the total radiated power from a new cell site base station installation is not harmful. Regulators and standards bodies such as the Federal Communications Commission (FCC) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) define limits for RF field strength guaranteeing that they are safe for the general public, and for technicians working in the industry. EMF measurements need to be made to ensure the sites are compliant with the regulatory bodies’ requirements.

To learn more you can read the Testing RF Cables in Cellular Networks Combining LTE and 5G Technologies application note.

Testing Processes to Ensure Radar Altimeters Not Impacted by C-band

February 8, 2022

Even before the January 19^th launch of 5G in the United States, the latest generation of wireless technology was getting a lot of press. Not all of it was positive, though, as the Federal Aviation Administration (FAA) voiced concerns that the C-band spectrum used to rollout 5G may cause interference with avionics equipment, specifically radar altimeters. While federal regulators and billion-dollar companies debated the issue, there was one thing without dispute – network testing is a necessity.

Fortunately, the two sides – mobile operators and the aviation community – have been trying to find a solution. It began in late 2021 when carriers agreed to lower the power on their 5G towers for six months. It continued in mid-January with an agreement not to turn on 5G antennas within two miles of airport runways.  

Given the $80+ billion investment by mobile operators, the rollout of 5G was inevitable. Another certainty is that sound testing processes need to be in place to ensure interference does not occur.

Importance of Radar Altimeters

At the crux of the situation is that 5G near airports may interfere with the signals transmitted by radar altimeters. The Federal Communications Commission (FCC) conducted testing previously and concluded the 400 MHz guard band between the 3.8 GHz C-band and 4.2 GHz signal used by altimeters sufficiently addressed the issue. The FAA still has concerns, however.  

The reason for the trepidation is the importance of the altimeter. Data acquired from radio altimeters informs other safety equipment on aircraft, including navigation instruments, terrain awareness, and collision-avoidance systems. Altimeters do this by transmitting an RF signal from the aircraft down to the terrain and receive the reflected signal back. The time delay of the received signal is used to determine Above Ground Level (AGL) altitude.

Radar altimeters are either pulsed or frequency-modulated continuous wave (FMCW). Commercial aviation predominantly uses FMCW. The RF front-end in FMCW altimeters typically uses homodyne architecture, with the received signal mixed with the transmitted signal to measure the frequency difference. With linear FM chirps, this frequency difference is directly proportional to the propagation time delay, and thus altitude.

Total Test Approach  

Inherently wideband systems, radar altimeters have no requirements for front-end rejection currently. So, they may be susceptible to blocking. That is the reason for the interference concern – and why testing procedures need to be continuous.

Effective testing of base stations around airports will require an ongoing process. Proper deployment and installation will ensure that the 5G antennas do not cause interference with airline altimeters as they approach airports for landings. Continual and regular testing to ensure that base station transmissions continue to fall within the specifications and not impact an altimeter’s ability to provide accurate data to the safety systems of a plane must also be done.

All this testing requires a comprehensive toolbox for regulators, mobile operators, members of the aviation community, and/or any other professionals responsible to ensure the 5G transmissions on the C-band do not create interference. For deployment and installation, a real time spectrum analyzer (RTSA) and interference hunting solution are required. When it comes to ongoing maintenance and monitoring, interference hunting tools and remote spectrum monitoring systems are necessary. Fortunately, Anritsu provides a comprehensive portfolio to address all the requirements.

Real Time Spectrum Analysis

Anritsu’s Field Master™ Pro MS2090A (figure 1) RTSA delivers performance never previously available in a compact, handheld instrument. With continuous frequency coverage from 9 kHz to 54 GHz, The Field Master Pro, with a displayed average noise level (DANL) of -164 dBm and Third Order Intercept (TOI) of +20 dBm (typical), makes measurements such as spectrum clearing, harmonics, and distortion more accurate than previously possible.

Figure 1: Field Master Pro MS2090 Real Time Spectrum Analyzer.

A 110 MHz modulation bandwidth coupled with best-in-class phase noise performance maximizes measurement precision. Typical  amplitude accuracy of ±0.5 dB provides confidence when testing transmitter power and spurious – key measurements to prevent interference with altimeters.

Ongoing Spectrum Monitoring

A remote spectrum monitoring system (figure 2) will facilitate the identification of interference from 5G base stations. Patterns of unwanted signal activity can also be examined, providing an efficient way to characterize and locate the source of the interference problem.

Figure 2: Remote spectrum monitoring solutions can help ensure C-band transmissions do not interfere with radar altimeters.

Spectrum monitoring can serve to enforce compliance with the parameters agreed to by aviators, operators, and regulators. Also, remote spectrum monitoring allows manpower to be effectively multiplied over a wider area and when engineers are not scheduled to be on duty. Air traffic patterns and runway activity will be able to be maintained without interference from the 5G antennas efficiently with such a solution.

Anritsu remote spectrum monitors can be used with Vision off-the-shelf software application. Vision continuously monitors selected spectrum bands to locate any spurious and/or interfering signals. Historic records of the spectral activity over time are saved to a database that can be configured to sound alarms when out-of-band signals are detected. The spectrum records are searchable for detailed analysis over an extended period of time.

To learn more, you can visit a technologies page dedicated to interference, causes, and test solutions. 

C-Band ROI Requires Proper Test Tools and Procedures

November 11, 2021

The C-band spectrum auction held by the Federal Communications Commission (FCC) was surrounded with so much fanfare it seemed impossible it would meet the hype. Well, more than $80 billion later, it’s safe to say that all the “noise” seems warranted. The question now becomes, how do mobile operators get the best possible return on investment (ROI)?

Verizon (estimated 3,500 total licenses) led the way, followed by AT&T (1,621 licenses), with T-Mobile (142 licenses) rounding out the top three. Considering the investment in the midband spectrum, which is well positioned to optimize certain 5G use cases, mobile operators must have a tactical approach with deployment. A key part of that strategy must emphasize network quality to maintain customer satisfaction, meet key performance indicators (KPIs), and limit customer churn. A sound test approach from antenna installation to operation helps achieve this goal.  

Understanding C-band and its Impact

Before outlining test procedures, it’s important to consider how C-band (figure 1) fits into the 5G infrastructure. C-band has such appeal because it addresses coverage and bandwidth issues. It is part of Frequency Range 1 (FR1), which operates from 450 MHz to 6 GHz. 3GPP Release 15 stipulates the n77, n78, and n79 bands for 5G operation in the C-band. The potential service bandwidth is up to 100 MHz, making it ideal for 5G enhanced mobile broadband (eMBB) use cases.

Figure 1: C-band spectrum, including Fixed Satellite Service (FSS).

C-band utilizes Time Division Duplexing (TDD), which has spectral efficiency benefits. TDD requires only unpaired spectrum, making the technology advantageous in environments with limited frequency resources.

On the other hand, timing and synchronization challenges are common with TDD. Because downlink (DL) and uplink (UL) share the same spectrum in a TDD system, strict timing restrictions are enforced to limit interference. If synchronization is in error, TDD framing will drift outside the guard period and into adjacent time slots. The result is network performance lags due to interference.

Spectrum Clearing A Necessity

A key consideration is that much of C-band needs to be cleared before mobile operators can use the spectrum. That’s because the frequencies were (and is some cases still are) used for government, public and private broadcast and satellite services. For this reason, extra attention with respect to deploying, installing, and maintaining C-band base stations must be given.

Contractors retained by mobile operators must conduct spectrum clearing as an initial step. Typically, a handheld spectrum analyzer with an omni-directional antenna (figure 2) may be used to determine if the spectrum is clear and ready for 5G usage.

Figure 2: Handheld spectrum analyzer with omni-directional antenna is used in spectrum clearing applications.

In a similar vein, on-going interference monitoring should be conducted. The same spectrum analyzer with a directional antenna configuration can be used when a performance issue is identified to conduct an interference hunt once the network is live.

Conversely, mobile operators will be required to ensure their 5G base stations do not impact satellite transmissions that have migrated to the upper portion of the C-band. This is particularly important, as massive MIMO and beam steering used in 5G can interfere with low noise block (LNB) downconverters of satellite antenna systems. Such an unattractive scenario is possible if the antenna is too close to the satellite earth station.

eCPRI Considerations

eCPRI is a key element of a C-band base station. It enables efficient and flexible radio data transmission over a packet-based fronthaul transport network. Using Ethernet for transport has a few advantages. For one, it is backward compatible with commodity equipment, enabling greater convergence of access networks. It also makes statistical multiplexing possible, which will help lower the aggregate bit-rate requirement.

There are hurdles with eCPRI, though. Unlike CPRI, eCPRI is not a synchronous technology. GPS, precision time protocol (PTP), and synchronous Ethernet are technologies used to address synchronization. Therefore, technicians need to conduct eCPRI tests to measure throughput, delay, and packet jitter when deploying and maintaining C-band.

OTA Factors

Another key aspect of C-band verification is to ensure that Over-the-Air (OTA) network performance and coverage meet the network design specifications published by the operators. Coverage mapping tools can help satisfy this requirement.

Anritsu spectrum analyzers can accurately measure RF power measurements over a wide frequency range, which, when attached with an antenna, become Received Signal Strength (RSSI). With coverage mapping, RSSI and Adjacent Channel Power Ratio (ACPR) measurements are combined with on-screen map displays to create a versatile solution for mapping coverage.

With a touch of a button, coverage mapping can be started, so technicians at any experience level can conduct measurements. The user has full control over the threshold values and measurement settings. Each measurement point is assigned a color correlating to the threshold values, and this fully customizable function allows for quick results.

Improved Finances

For contractors, payment for services requires submission and subsequent approval of close-out reports. Smart Aligner App (figure 3), a unified reporting solution for antenna alignment and line sweep measurements helps expediate payment. With the app, close out reports can be prepared, saved as pdf files, and sent to operators from the site location, saving time and money while providing operators with confidence that new base stations have been installed according to specification.

Figure 3: Smart Aligner allows simplifies the close out report process for more efficient payment.

Reports can be submitted directly as an email attachment sent over the cellular network. Confirmation of acceptance can be given before the crew departs from the site, eliminating the additional costs and time associated with return visits. Anritsu’s handheld field base station test solutions, including Site Master™ cable and antenna analyzers support the close out app.

To learn more about Anritsu’s interference measurement tools, visit a dedicated technologies page.

On-site Close Out Report Creation Makes for More Efficient Base Station Installation Process

March 23, 2021

As cellular and public safety networks continue to further crowd the available spectrum, network planning and optimization takes on greater significance. Whether mobile operators use their own teams or hire prime contractors – aka Turf Vendors – to install base stations, close out reports are necessary before the site goes live. Using app-based processes can save time and money when conducting this necessary and important step that helps ensure new base stations are installed within compliance of the Method of Procedure (MoP).

Many new base stations utilize fiber optics from the tower base to the remote radio head (RRH) atop the tower. Short RF cables connect the RRH to the antennas. Installation teams arrive on site and conduct line sweeps on the RF cable feeds and properly align the antennas based upon MoP specifications. This is done to ensure key performance indicators (KPIs) will be met. In today’s post, we will focus on conducting line sweeps and including them in a close out report.  

Importance of Close Out Reports

Before we delve into conducting and documenting line sweeps, let’s detail the importance of close out reports. Base station installation crews must create and submit documentation before the site goes live, so improper reporting will delay the site becoming operational. A Turf Vendor contracted to do the installation is not compensated until the reports are submitted and approved.

Why are they so important? Because they verify that the base station has been installed correctly and is operating according to specification. Measurement results for the RF cables and antennas, as well as correct alignment of the antenna are contained in the report.

Creating close out reports has typically been wrought with frustration and issues. For one, they are time-consuming. Secondly, they are traditionally generated only after the crew has left the site.

App-based Reporting On-site

Fortunately, a new application that runs on Android devices provides a highly automated report generator. With the app, technicians send results data and traces directly to the network operator for approval while at the site. Measurement errors can be quickly identified by the operator, so the technician can repeat the measurement(s) and resend the report for approval. Truck rolls and other associated expenses of site installation and maintenance are reduced, as a result.

The application interfaces with a wide range of Anritsu Site Master™ cable and antenna analyzers and the Multiwave antenna alignment tools (figure 1). A single consolidated report for both sets of measurements is created, shortening the time to produce the report and expediting the site approval.

Figure 1

RF Cable and Antenna Line Sweep Basics

One critical element of the close out report is line sweep measurements. Towers typically have at least six, and perhaps 30 or more antenna systems. Each needs to be checked for RF faults. A MoP outlines the verification process and often requires six or seven sweeps per cable. That means each tower can have 36 to 180+ line sweep measurements. Simplifying report generation can save tremendous time for this reason alone.

Technicians need to sweep antenna systems during installation to verify performance of the RF cable and antenna system, and to locate any potential faults within the signal path. Line feed and antenna system faults have a variety of causes. Damaged or pinched cables, corroded connectors, or antennas are common issues. Acts of nature, such as lightning strikes and water penetration into cables, can also impact performance. Bullet holes and other acts of vandalism can damage cable systems. In all these cases, the result is poor overall system coverage and eventually dropped calls.

Another reason to conduct line sweeps is to ensure the proper components are used. For all these reasons, sweeping the cables and antennas and preparing the line sweep reports are essential parts of the overall installation process. Most technicians rely on the Site Master series for these measurements, as they are the de facto industry standard.  

Antenna System Measurements

The handheld field analyzers support the measurements technicians typically are required to conduct at the base station site. Each antenna system mounted during construction is verified via the following measurements:

• Antenna Return Loss – This will easily identify an incorrect or defective antenna. It is typically measured before installing on the tower, as well as after installation.
• Cable Insertion Loss – This can identify incorrect cable(s) and/or excessive loss usually caused by water absorption or loose/bad connectors.
• Cable Distance-to-Fault (DTF) with a 50 Ohm load on the far end – A troubleshooting measurement, it locates faults within the coaxial transmission line and various connectors/components.
• Cable DTF with a “Short” on the far end – A test to ensure proper cable length.
• Antenna and Cable System Return Loss – Typically a Pass/Fail test with the limit specified by mobile operator.
• Antenna and Cable system DTF – Often considered the “birth certificate” of the site, it is used as a reference when troubleshooting faults once the site is live.

If the antenna points in the wrong direction, the network will degrade. The three parameters of antenna alignment are:

• Azimuth is a geographic direction defined from 0° to 360° with respect to true North
• Tilt is an angular measurement of the antenna in the up and down direction, sometimes referred as uptilt or downtilt 
• Roll is an angular measurement of the antenna in the side-to-side direction, sometimes referred to as plumb 

Close Out Report Creation

All line sweep and antenna alignment measurements are transferred into the smart phone memory. With the app, all the results can be consolidated into a single report by easily transferring the data files (.dat, .vna, .pim) to the app, where they are saved to the site directory. Technicians simply choose those files to include and create a report. Figure 2 shows a sample report page based on a VSWR measurement.

Figure 2

All selected files can be previewed and consolidated into a single PDF and emailed directly from the mobile device. The report generated is suitable for submission to site management and can be easily emailed from the site to the head office.

For field technicians who need to create close out reports quickly and reliably after installing new antenna systems in the field, the Smart Aligner smartphone application offers a fast and reliable solution from the market leaders. To learn more, download this free app note.

Methods to Enhance IQ Capture for Improved Analysis of Digital Signals

November 17, 2020

IQ capture is a technique used to effectively measure digital RF signal strength. When conducting this analysis, it is important to understand the relationship between noise, sampling rates, and bit depth. By doing so, the receiver – typically a spectrum analyzer – capturing IQ data can be optimized, making it easier and faster for engineers to identify signals in post processing. 

Digital signals are “quantized,” meaning the analog signal is rounded to the nearest bit, creating error dubbed “quantization noise.” When the least significant bits are chaotically changing due to thermal noise or a wideband signal, quantization noise is “white,” or uniformly spread across all frequencies. When quantization noise has this property, it may be treated the same as any other noise source. Generally, it is preferred that the quantization noise be smaller than the analog noise.

Lowering the resolution bandwidth (RBW) on the receiver during analysis will reduce quantization noise. There are occasions, however, where quantization noise is not at all “noise-like.” If there is very little analog noise in a system and if the signal power is small compared to 1 bit, it is possible to have a situation where no bits are being toggled. In this case, the quantization noise is not noise-like; rather it is highly correlated to the signal with opposite sign.

Reducing Quantization Noise

When the quantization noise is uncorrelated to the signal, it – along with thermal noise – degrades the signal. If the quantization noise can be made much smaller than the thermal noise, then the quantization noise becomes irrelevant. It is often a design goal to make the quantization noise 10 dB less than the other noise sources. Otherwise, it will impair the signal. It is sometimes difficult, however, to make the quantization noise lower than analog noise. In this scenario, the system performance is limited by the digital performance.

While a higher sample rate reduces the quantization noise energy density, more bits are usually a more efficient approach. One additional bit reduces the quantization noise energy density by 6 dB. Compare this to doubling the sample rate, which reduces the quantization noise energy density by 3 dB. A 10-bit capture at 200 MSPS, therefore, has the same quantization noise energy density as a 12-bit capture at 25 MSPS. Engineers need to choose the minimum sample rate necessary to capture a signal that needs to be analyzed, then select a bit depth whereby digital quantization noise is lower than analog noise.

Selecting the Right Spectrum Analyzer

A spectrum analyzer has analog amplifiers and attenuators to optimize the level of the signal. To make the best use of a limited number of bits, it can be useful to fine tune receiver gain. If the input signal is too high, the signal will overflow the fixed bits. To prevent this undesirable scenario, more attenuation should be used. If the input signal is low, then the quantization noise is higher compared to the signal.

Broadband signals generally have more energy hitting the receiver’s analog-to-digital converter (ADC) than energy inside the instrument’s RBW filter. To manage this, an instrument does not overrange many dB above the reference level. In general, the best choice of bits can be made by reducing attenuation or adding amplification until the instrument overranges. Once that has been determined, users need to add 5 dB attenuation to prevent it from overranging during the signal capture.

Visual Results

Figure 1 is a plot of a signal captured by the Anritsu Field Master Pro™ MS2090A at a specified sample rate and bit depth. This figure shows how the choice of bit depth changes the noise floor. Near the carrier, 8 bits is sufficient, as the combined phase noise of the signal and receiver exceed the 8 bit quantization noise. By 10 MHz offset from the carrier, the 8 bit quantization noise is clearly higher than the analog noise floor and is degrading the measurement.

Figure 1

The 200 MSPS capture uses an analog filter with a 110 MHz wide passband. At 70 MHz offset, the receiver is no longer receiving much of the analog signal due to the analog filter. The result is the quantization noise of the lower bit depths becomes visible. The lower noise floor near the edges does not matter for actual measurements, as the signal has been filtered out at these frequencies. At this sample rate, 10 bits is usually sufficient for measurements.

Receiver Optimization

With an understanding of these interdependencies, engineers can optimize the configuration of a receiver, such as the Field Master Pro, when capturing IQ data to minimize the memory size of the resulting data file. Smaller files are typically easier to analyze in post processing tools, making the identification of all signals faster and easier.

The Field Master Pro MS2090A allows captures of up to 2 GB to be stored. Choosing a lower sample rate or bandwidth will allow a longer time record to be captured. Table 1 shows how many seconds it takes to fill 2 GB. The Field Master Pro MS2090A can also stream data through a user selected Ethernet/USB3/high-speed data port. This data may be captured to a file and post processed by a PC application for detailed analysis, such as the Bird Spectro-X.

Table 1

Table 2 shows recommended bit depths at various sample rates. Cells labeled “Too Much” indicate that the extra bits are highly unlikely to improve the measurement. The “Too Little” cells designate that the quantized bit depth is likely to degrade the measurement, although the measurements may still be quite usable. “Almost” cells show that the quantization noise is unlikely to significantly impact the measurement, but it might for certain signals.

Table 2

To learn more about how to effectively conduct IQ capture on digital signals, you can download a white paper entitled Choosing the Best Bit Depth for IQ Captures or Streams.

Effects of Various ‘Sight Screen’ Materials on 5G FR2 Transmission

April 17, 2020

As the first generation of 5G networks are being rolled out, an issue that can’t be overlooked by mobile carriers and installers is the effect of “sight screens” on transmission quality. For years, building landlords in urban areas have required operators to conceal antennas and transmission equipment used in rooftop installations so they are not seen at street level. While these screens caused minimal signal loss in LTE networks, they will have a more profound effect on 5G signals.

Another factor highlighting the importance of selecting the proper screens is that 5G radio deployments will be on more than rooftops. Street lampposts and dedicated poles will be installed in cities and other congested areas. This means the materials used for the sight screens must be properly selected or the 5G radios will transmit less efficiently at a higher power or there will be reduced coverage from each radio. 

Propagation loss due to sight screens will occur in the sub-6 GHz Frequency Range 1 (FR1) band  operating at 3.5 GHz. It is an even greater consideration with Frequency Range (FR2) transmissions since they operate at 28 GHz and 39 GHz. Because FR2 signals travel in the millimeter wave (mmWave) bands, the distance between base stations or small cells needs to be very short to provide reliable wide area coverage. For that reason, 5G FR2 radios in some American urban centers are being deployed every 100 meters. Higher frequencies are also more susceptible to outside factors such as screens.

Figure 1 shows a typical 5G FR2 radio rooftop installation. The radio is barely visible through the cut out in the sight screen being erected to hide the radios from street level. Careful selection of the materials used for this type of environment is essential to ensure optimum network performance. Materials should be accurately characterized for their RF attenuation properties to ensure networks meet key performance indicators (KPIs).

Figure 1: Sight screen installation.

Conducting Materials Measurements

One test tool to conduct these necessary measurements is the Anritsu Microwave Site Master S820E handheld cable and antenna analyzer configured with a waveguide horn antenna. Field engineers and technicians can use this field solution to conduct quantitative insertion loss measurements on a wide range of materials. Based on these results, network planners can model 5G network coverage and select materials that provide the best compromise between durability and aesthetics without sacrificing network coverage and user experience.

The S820E was used to measure the impact common office building materials will have on 5G signals. Results of the tests taken on these materials – drywall, wood paneling, regular and low-E thermopane windows, fiberglass, and office cubicle partition – can be seen in table 1.

Material Tested	Drywall	Wood Panel (3/4")	Regular Thermopane	Low E Thermopane	Fiberglass Insulation (8")	Office Cubicle Partition
Average Loss (dB)	~3	~4	~3	~43	<0.5	>60

Table 1: Propagation loss of 5G signals based upon common building material.

Let’s look at each measurement in a bit more detail:

Drywall and Wood Panel

Measurement taken with the Site Master antenna analyzer revealed that drywall and wood panels should pose no significant issues with respect to signal loss. Based on the measurement results, FR2 signals are able to propagate well through these materials.

Thermopane Glass

FR2 signals are able to propagate through a standard thermopane window (Figure 2) with little loss. The same can’t be said for the low-E (low-emissivity) thermopane window (Figure 3), which acts as a barrier for the FR2 signals. Low-E glass has a special microscopically thin reflective coating that minimizes the amount of infrared and ultraviolet light – and 5G signals – that enter a building. FR2 signals are not able to propagate through these types of windows.

Figure 2: Standard thermopane window.

Figure 3: Low-E thermopane window.

This will present some significant challenges, since many newer buildings utilize low-E thermopane windows due to their excellent overall energy efficiency. With considerably lower penetration of FR2 signal levels inside the building from 5G gNB external base stations, users may experience dropped calls, an inability to connect to a network, and very slow data speeds. In other words, all of the desired benefits provided by the wide bandwidth available in the FR2 bands will be negated by the high losses caused by the low-E type windows. 

There is also the issue of rain. Measurements indicated that a regular thermopane window created signal loss of ~3 dB. That same window’s loss increased significantly to ~17 dB with water sheeting. This could easily occur when a strong rainstorm with high winds forces the rain to fall angularly onto the glass.

Fiberglass and Office Cubical Partition

Test results indicated that commonly used fiberglass insulation poses no threat to FR2 signals. In contrast, office wall cubicle material is absolutely catastrophic to the FR2 signals, as shown in figure 4. This particular office cubical material would pose significant problems for indoor FR2 signal coverage.

Figure 4: Office cubical partition.

Manufacturers of office cubicle materials will need to investigate using different materials to obtain the desired structural strength of the cubicle partitions while minimizing FR2 propagation loss. Alternative materials will need to be considered with a focus on ensuring negligible propagation losses at FR2 frequency bands.

Canvas Fabric

Dry canvas measurement results were <0.5 dB, making it appear as though canvas fabric is a good choice for concealing antennas and/or 5G base stations. It is easy to work with, durable, and very flexible. Not everything is as it appears, however. If not properly treated to prevent moisture absorption, the canvas material becomes one of the worst possible choices! Its loss increases dramatically once it has absorbed moisture. One layer of wet canvas had ~10 dB of loss (Figures 5a and 5b).

Figure 5a: Layer of dry canvas.

Figure 5b: Layer of wet canvas.

Consider this. If an antenna system is concealed using very thick and rugged canvas that is equivalent to 4 layers of the sample tested, the insertion loss will be <0.5 dB when dry. After the canvas absorbs moisture, the insertion loss increases to ~40 dB, which makes it likely that a connection can be lost. Dry vs. wet open cell foam exhibited similar characteristics compared with the dry vs. wet canvas. You can watch a video of this effect (and others) that was taken by the testing crew.

An application note, Measuring Path Loss of 5G FR2 Transmissions Through Common Materials Found in the Signal Path, has been published and can be downloaded from the Anritsu website. It provides more insight into selecting proper sight screen materials.

Importance of EIRP Measurements When Installing and Maintaining 5G Base Stations

February 4, 2020

The importance of active antenna systems in 5G networks has significantly changed the installation and maintenance of base stations. Gone are the days of simply measuring transmitter power with an absorption power meter or by using a direct connection via a “sniffer” port in the antenna feed. Due to the vastly more complex transmitter and antenna systems necessary to achieve the efficiency and speeds of 5G, a different set of tests must be performed. Subsequently, a new generation of field solutions must be employed to conduct these measurements.

Engineers installing and maintaining 5G base stations must gather measurements that were different or not required with 4G LTE. Among the parameters that help operators determine the performance and likely coverage achievable with their 5G networks are: 

• Reference Signal Receive Power (RSRP) and Signal-to-Interference-plus-Noise Ratio (SINR) – provide a ratio between the wanted signal and any unwanted signal and noise in the channel bandwidth used.
• Reference Signal Received Quality (RSRQ) – provides a measure of the received signal quality and is derived from detected error rates.
• Error Vector Magnitude (EVM) – a quality measurement that analyzes the accuracy of the modulation transmitted relative to an idealized waveform.
• Effective Isotropic Radiated Power (EIRP) – the product of transmitter power and the antenna gain in a given direction relative to an isotropic antenna of a radio transmitter.

These measurements are necessary to provide mobile operators with an indication of how strong a connection should be to user equipment (UE) in the field.

Active Antenna Systems Impact

EIRP is vital to determine transmitter power and beam verification of a 5G base station. The reason is that active antenna systems operate much differently than the isotropic antennas used for many years in traditional cellular applications.

Isotropic antennas are typically designed to radiate in an arc of 60⁰ to 120⁰, depending on the number of sectors a base station might support. Some electro/mechanical adjustment might be included, so carriers could optimize coverage but, essentially, they were fixed. By knowing the antenna gain and input power, operators could predict signal strengths in the field and estimate performance.

5G uses directional antennas that can generate beams in multiple directions simultaneously and be steered dynamically. To achieve this, it is necessary to use a matrix or array of antennas, each being fed with different signals. At a minimum distance from the antenna, known as the far field, these signals combine together in or out of phase to create a beam-like pattern known as a phased array (figure 1).

Figure 1: 5G Phased Array.

For 5G, these active antennas typically have an individual transceiver associated with each antenna element. Each element will also have two cross-polarized radiators to improve diversity. In total, a 5G antenna may have 128 to 256 individual transceivers. All of them may be integrated with their own radiating elements, making the traditional method of measuring antenna input power impractical.

Why EIRP is Important

Based upon this antenna design change, the most useful measurement of power is EIRP. It provides the mobile operator with a reliable indicator of signal strength anywhere in a cell once path loss is taken into consideration.

Conducting EIRP measurements in the field, however, is not as straightforward as it might seem. Even sub–6 GHz 5G transmitters have the potential to use bandwidths of up to 100 MHz, therefore any measuring receiver has to be “flat” across the channel bandwidth while adequately rejecting other signals on adjacent channels. At any reasonable distance from the base station, the signal level is going to be quite small.

If measurements on a live base station are required, the field engineer or technician needs to extract the “beamed” transmission in the direction to be evaluated, as well as know the intended EIRP. This means the test instrument must be able to track the on/off periods of the signal and use that information to control the measurement timing.

The last aspect of making an EIRP measurement is to understand the various path loss elements and remove them from the equation. Free-space path loss is significant and can only be determined if the distance between the measuring antenna and the base station is known. This can be calculated using various techniques, including GPS, laser/optical rangefinders, and accurate large scale maps. Other factors include the gain of the measuring antenna and the insertion loss of any connecting cables.

Figure 2: Field Master Pro MS2090A Handheld Spectrum Analyzer.

Instruments for Accurate EIRP

A handheld spectrum analyzer with sufficient bandwidth to accurately measure signals occupying 100 MHz or more, as well as enough sensitivity and low noise floor to record EIRP at realistic distances from an active base station, is necessary to test 5G networks. The Anritsu Field Master Pro MS2090A (figure 2) is one such instrument. It also has the ability to lock onto the primary and secondary synchronization signals, so EIRP can be measured in up to eight broadcast beams that 5G base stations step sweep across a sector. This allows mobile devices to acquire synchronization to report their presence and location (figure 3).

It is also possible for fault finding and commissioning teams to place the base station in a test mode where it transmits a known “test model” signal in a given direction and strength. This allows radiation patterns to be established and field strength in complex environments to be measured. It also provides a means of using conformance test methods in the field.

Figure 3: Synchronization to Report Mobile Device Presence and Location.

Conclusion - Impact of Beamforming

It is clear that the arrival of beamforming in 5G has made traditional methods of measuring the total radiated power of a base station ineffective to optimize network coverage. Using EIRP measurements in various directions allows mobile operators to determine beam shapes, location/angles of the nulls, and safety of field strengths close to the base station. The result is minimal interference.

To learn more about how to conduct EIRP measurements and their importance when installing and maintaining 5G base stations, download this application note.

Importance of OTA Measurements in Ensuring 5G Networks Meet KPIs

November 18, 2019

The advent of 5G is finally here. In countries all over the world, spectrum allocations have been made, with 5G services generally sitting in and around 3.5 GHz or in the 28 GHz and 39 GHz millimeter-wave (mmWave) bands. There are significant architectural difference between 4G and 5G, which require network operators and device makers to make considerable investments of time, money, and manpower to enable 5G. For example, while 4G networks use omni-directional antennas to transmit ubiquitous signals, 5G networks utilize active antenna systems (AAS) with beamforming and massive MIMO to help focus strong signals toward each device in the coverage area.

Figure 1: Conducting OTA measurements will help ensure 5G networks meet KPIs

To make transmissions, 5G networks will be more densely packed with the new antenna systems that leverage beamforming technology. With this technology, power is focused into a narrow, directional beam rather than transmitting it in all directions, like with LTE. The beam is aimed and energy transmitted directly toward the mobile user or other device connected to the base station. Because these beams are transmitted with concentrated power, there are inherent radiated power characteristic that need to be monitored and their potential effects minimized to avoid interference issues. With this higher level of complexity, there needs to be a new generation of test solutions that conduct analysis differently and perform over-the-air (OTA) measurements.

5G OTA Testing

Because of its new and unique architecture, deploying and verifying 5G networks must be carried out differently than any of its predecessors. Traditional 4G/LTE test methods typically involve transmitting the expected power level while a network technician conducts measurements using equipment physically connected to the base station via a coaxial cable to an RF test connector. This type of hard connection allows calibrated measurements for channel power and modulation quality, as well as decoding some basic cell site information to be conducted. The design of an LTE macro site is usually comprised of a radio base station in an equipment room at ground level, with long RF cables feeding the antenna atop a tower. These cables are generally 10 meters or more in length. The losses and reflections in this feed to the antenna has been a common source of performance issues that require testing.

For 5G, this approach will not work, as the base station has changed in the traditional sense. There is no remote radio head (RRH) with a single test port monitoring the RF output to a common antenna. Now there is an antenna array with typically 64 elements – and there is no single test port that can monitor all of those. Testing needs to be performed on a fully formed beam OTA. For a 3.5 GHz radio, this would be at least 10 meters away. If this AAS is mounted to a rooftop or somewhere difficult to gain access to, then testing must be done at an even greater distance. OTA testing allows technicians to position themselves in the far field distance from a base station, wirelessly connecting to conduct new tests.

OTA Performance: Validation and Test

There are several critical tests to ensure 5G networks are transmitting properly, including:

Equivalent Isotropic Radiated Power (EIRP) – EIRP indicates the amount of power that would be required to be fed into an omni-directional antenna to give the same signal strength as that measured at a distance and direction from the antenna. It shows the effectiveness of beamforming technology. Essentially, knowing the EIRP measurement helps network operators validate that their transmitters are performing as promised.

Interference – The wider-band signals associated with 5G means signals are more prone to overlap, making interference an even greater concern than in 4G (as impossible as that sounds considering the worry associated with interference in existing LTE networks). Field technicians need to verify signal boundaries and determine how much a signal may be bleeding into neighboring bands.

Harmonic and Spurious – Beamformed signals can generate side lobes that can be radiated in any direction from a base station during transmission. OTA test solutions can effectively measure these signals to ensure that when high-powered signals are transmitted other signal attributes being generated are below a strength level threshold where they would cause interference. Figure 2 is a display of such a measurement taken with the Field Master Pro™ MS2090A.

Figure 2: Power measurement taken with the Anritsu MS2090A.

Other Considerations

OTA 5G measurements are typically made on the primary synchronization signals in the 5G sync signal block (SSB). The beams in the SSB are continuously transmitted and can be used to perform basic RF measurements in the field. Measurements on data channels will always be more challenging, as beams are only formed after a UE has established a data channel with the base station, and the beams are directed to the UE. So, test solutions must have signaling or UE capability to create and align with these beams to conduct necessary measurements.

Using OTA tests for all these needs will help network operators and their partners prove that new 5G networks meet key performance indicators (KPIs). That means greater consumer experience and the ability to effectively roll out 5G while also opening the door to new applications and user experiences. To learn more, download this Proving 5G: How OTA Testing Helps Enable a New Mobile Era application note.

 

How PIM Over CPRI Makes Field Testing More Efficient

December 7, 2018

The introduction of RF passive intermodulation (PIM) testing using live traffic over the Common Public Radio Interface (CPRI) link – commonly referred to as PIM over CPRI – has made verifying network performance more efficient. Operators save capital expense (CapEx) and operating expense (OpEx) while field technicians do not have to unnecessarily scale an antenna tower.

PIM over CPRI utilizes multiple unique techniques to measure PIM more efficiently. The method allows tests to be made from the ground to reduce the need to deploy tower climbing crews and eliminate the need to take the site down. In this post, we will review some additional benefits, as well as explain procedures to more accurately measure PIM.

PIM over CPRI Advantages

One key benefit is that PIM measurements made over a CPRI link are frequency-independent because the CPRI IQ data is baseband. That means a single measurement solution can conduct measurements on any LTE frequency band.

The biggest advantage of PIM over CPRI, however, is that it uses live traffic to conduct the measurement, allowing the site to stay on while tests are being done. Conventional methods send two continuous wave (CW) tones to try and locate PIM. By using live traffic, PIM over CPRI establishes a real-world PIM scenario, helping to discover PIM that is lost using the conventional method.

Conducting PIM Over CPRI

To perform the measurement, turn to max power on all unused resource blocks (RBs), which forces the radio to maximum Tx power. (Note: network performance is maintained via this approach, as RBs for live traffic are not used.) A worst-case PIM scenario is created so more interference sources will be seen. This approach will work for macro and DAS systems alike.

Figure 1 shows conceptually how PIM over CPRI can locate PIM. The righthand side shows a 2x2 MIMO in the downlink (DL) in which the subcarriers are mixing. This creates potential intermodulation products on the uplink (UL) shown on the left.

Figure 1

The PIM over CPRI algorithm looks at all the DLs and the UL simultaneously to conduct a more accurate measurement. A key element is that the measurement must be made in real time to align the UL and DLs. By doing so, the correlated PIM (shown in figure 2) can be discovered.

Figure 2

PIM Desensitization and Correlated PIM Value

Accurate PIM measurements are accomplished by using a different method then traditional RF PIM tests that measure dBc/dBm using two CW tones. PIM over CPRI uses two unique features:

• PIM Desensitization – This capability replaces dBc by establishing a relative value using dB. It uses LTE carrier RBs to quantify how much PIM degrades the UL noise floor. There is a general industry consensus that 10 dB desensitization affects data throughput by 50%, making this analysis critical to networks achieving KPIs.
  
  Figure 3 shows how to establish the PIM desensitization advanced settings, which can be done on one screen of the BTS Master MT8220T, when the PIM over CPRI option is installed. Users simply input the site configuration – either SISO, 2x2 MIMO or 2x4 – and the PIM desensitization Pass/Fail setting. Fields for the DL/UL configuration and UL under test settings must also be filled for the measurement to be conducted.

Figure 3

• Correlated PIM – This is determined in dBFS/dBm. Base station OEMs use dBFS (dB Full Scale) as a digital level that shows dB relative to the maximum value that can be represented on the CPRI link. To convert dBFS to dBm, the user needs to know the specific radio thermal noise floor specification and noise figure values. Both can be provided by the respective equipment OEM.

Figure 4 shows the effectiveness of PIM over CPRI. A nearby water tower reflected PIM back to the antenna, causing interference on the 4^th UL. PIM desensitization value was 3.34 dB, which affected the UL service quality. There was also a correlated PIM value of -63.7 dBFS, which was higher than the thermal noise floor of the radio. The result was a 3.3 dB rise in the noise floor, degrading signal transmission.

Figure 4

Conversely, figure 5 is an example of how a display may look ominous but network performance is not affected. The purple trace shows the typical shark fin that generally causes issues but, in this case, the correlated PIM value is -122 dBm. The total UL power is only -102 dBm, which is too small to impact radio performance. PIM desensitization value is only 0.04 dB, so it has virtually no impact on the UL noise floor.

Figure 5

You can learn much more about how to use live traffic over a CPRI link to identify and locate PIM by watching the PIM over CPRI webinar.   

Understanding Smart Grid Network Elements and How to Test Them

June 19, 2018

Utilities nationwide are relying on wireless networks to connect elements of the smart grid to reduce peak loads for improved operation. The smart grid also provides a means for consumers to reduce their energy costs.

This intelligent utility network features sensors throughout the transmission and distribution grid to collect data, provide real-time two-way communications to move data and electricity between utilities and consumers, and create the computing intelligence to make improvements in reliability and efficiency.

Figure 1

The smart grid integrates multiple networks, including Home Area Networks (HANs), Field Area Networks (FANs), and Wide Area Networks (WANs). A variety is necessary because the multiple smart grid applications have different network requirements in terms of data payloads, sampling rates, latency and reliability. Given the mission-critical nature of the smart grid, it is important to ensure robust signal coverage and avoid potential sources of interference for each of these wireless segments. In this post, we will delve into each network element and the test tools to ensure optimal performance.

Home Area Network (HAN)

A HAN infrastructure is typically open and must be interconnected with the Advanced Metering Infrastructure (AMI) and the Internet via a home gateway to enable high-end services. Smart grid metering and control applications require fast and secured two-way communication. In a HAN, home appliances designed with RF antennas communicate with smart meters, typically using the IEEE 802.15.4-based ZigBee 2.4 GHz communication protocol.

Field-area networks (FANs)

Filling the communication void between the core IP network and devices, and utility personnel in the field is a FAN. Cellular, narrowband and broadband point-to-multipoint (PTMP), and broadband wireless mesh networks are commonly used in a FAN. To support the varied smart grid applications, FANs must be:

• Reliable – FANs must operate even when events disable the electric grid, as communication is most critical during an outage.

• Scalable – In some cases, a FAN must cover a utility's entire service territory, so it must be able to scale according to meet the geography. It must also scale to support up to millions of connected devices.

• High performance – There are some critical applications, such as protection and safety, that are part of a FAN. Therefore, low latency is essential.

Wide Area Network (WAN) – A utility’s WAN will need to cover the entire distribution footprint, including all substations. It will have to interface with distributed power generation, storage facilities, and other distribution assets. The WAN will also be used for substation communication, distribution automation (DA), and power quality monitoring while also supporting aggregation and backhaul. 

Because a WAN is the core of the smart grid, as well as the fact it supports mission critical applications and is used for cyber security, its performance is essential. A typical utility WAN is a blend of wireless technologies, as well as high bandwidth fiber optics-based communications technologies such as SONET/SDH, and WDM/DWDM.

Tools to Test the Smart Grid

Because wireless technologies are so integral to the smart grid, there is a great need to verify signal coverage and locate interference sources that will impede successful transmissions. Utilities need to be able to analyze communication problems quickly and insure that their wireless network continues to run under a variety of conditions. To do so, a series of analysis tools should be part of any utility tool box.

Cable and Antenna Analysis - The cable and antenna system serves an important role in the overall performance of the smart grid. Slight variations in the antenna system can affect the signal and coverage area, and eventually cause dropped transmissions. Using portable cable and antenna analyzers, such as the Site Master™, to characterize communication systems can simplify maintenance and overall performance significantly. Return loss/VSWR measurements are used to characterize the system, while distance-to-fault (DTF) measurement can be used to troubleshoot problems, locate faults, and monitor changes over time.

Interference Analysis – Smart grid systems coexist in extremely complicated signal environments. This is particularly true at industrial, scientific and medical (ISM) frequencies, such as the 2.4 GHz band used by WLAN, Zigbee, and Bluetooth. Household appliances, particularly microwave ovens, are also potential sources of interference. Various cellphone frequencies, WiFi and other technologies are also common in today’s home, making signal integrity quite the challenge. To locate causes of interference so they can be corrected, a handheld spectrum analyzer such as the one shown in figure 2 should be used.

Figure 2

Indoor Coverage Mapping - To plan and optimize wireless networks, utilities must identify the coverage their transmissions provide in a given geographical area. For indoor signal analysis, coverage mapping makes it easy to identify coverage quality throughout any facility. With this tool, taking signal strength measurements is as simple as walking through the facility with the appropriate handheld analyzer. Real-time updates of signal quality can be provided, so network planners can identify areas where additional transmitters or repeaters may be needed to insure high signal quality.

Outdoor Coverage Mapping - Outdoor coverage mapping enables the utility to optimize the network by identifying signal coverage in an outdoor environment. Assisted with GPS, areas of relative signal strength can be automatically measured and precisely correlated with location. The analyzer can be set up to take automated measurements either as a function of distance or time, so it can be used by technicians with any level of experience. Data can be displayed later in a variety of formats, including third-party vendors such as GoogleEarth™.

The smart grid has transformed how utilities deliver electricity to consumers, as well as how customers can have greater control of costs. It has also created a variety of considerations for utility managers, the least of which is maintaining high signal quality. Using the proper test tools can help achieve the necessary KPIs for success. To learn which test tools are right for you, visit this dedicated smart grid page.