Base Station Transmits

Field Trials Help Bring 5G Closer to Market

December 5, 2017

The race to 5G has shifted to the fast lane, with the 3GPP accelerating the release of the 5G New Radio (NR) standard, with a full out 5G deployment by 2019. This has placed added pressure on chipset, mobile device and network element manufacturers, as well as mobile operators to finish the last mile as quickly as possible. Grabbing market share in the next-generation wireless technology will require more than being first to market, however. Proof of performance and cost will be two other contributing factors to achieve 5G success.

5G networks are already being deployed by multiple carriers but on a limited basis. Of course, testing on those base station rollouts are necessary to ensure network operation but that is only half the equation. The second part is how will user equipment (UE) operate in the 5G world? The answer began to be answered in Morgan Hill, CA, where Anritsu has a facility. It was on the roads of this Silicon Valley city that a leading network equipment manufacturer (NEM) conducted a series of tests on its 28 GHz 5G radios.

5G Testing Ground

Field trials were conducted to determine how radios for 5G fixed wireless access will compete with fiber to the home. Because there were no 5G towers readily available, the NEM required the use of the Anritsu Spectrum Master™ MS2720T spectrum analyzer (figure 1) to test the performance of these next-generation 28 GHz 5G radios in a coverage mapping exercise. The spectrum analyzer was used to measure key parameters of the NEM prototype radio in a variety of real-world environments.

Figure 1

The 5G radio was mounted in multiple locations at varying heights in different urban and rural settings. Because of the significant free space attenuation at 28 GHz, a horn antenna was used in conjunction with the Spectrum Master MS2720T to provide additional receiver gain. Moreover, the directional nature of the horn antenna required the use of four MS2720T antenna pairs to provide complete 360-degree receive capability. In addition, each MS2720T handheld spectrum analyzer was configured with a GPS location receiver.

As the engineers drove the truck (figure 2) through the streets of Morgan Hill, the handheld spectrum analyzers were able to plot received signal strength with location. To acquire comprehensive data on the NEM’s radio performance, the route taken for the Over-the-Air (OTA) measurements passed through various environmental conditions, including attenuation from tree foliage, and multi-path from houses and office buildings.  

Figure 2

Measurement and Analysis

Each Spectrum Master MS2720T was connected to a respective horn antenna via an RF cable. This configuration allowed all received power acquired by the handheld spectrum analyzers to be displayed simultaneously on a PC in real-time for immediate analysis. The engineers conducted coverage mapping and power of arrival due to multi-path effects (figures 3 and 4), among other measurements.

Figure 3

Figure 4

The outdoor coverage mapping capability of the MS2720T handheld spectrum analyzers provided several benefits during the day-long series of tests throughout the region:

• Only one frequency carrier was required to monitor RSSI or ACPR and to set up the instrument, i.e. reference level and pre-amplification
• Color-coded thresholds (levels) on the map led to quicker analysis
• Maps were configured by GPS distance or time increment
• Measurements could be exported as a .kml for use with Google Earth

The Spectrum Master MS2720T handheld spectrum analyzers also featured Anritsu’s easyMap Tools. For the tests conducted on the 5G radios, real-time maps that included the location where each measurement was created were displayed and stored on a PC in real-time. Additionally, easyMap Tools enables downloading of maps for on-instrument mapping.

This exercise confirmed the suitability of the Spectrum Master MS2720T for field trials of the first-generation 5G fixed wireless access radios. The testing also helped the NEM evaluate its design in real-world environments, which will aid in bringing it to market early.

A full case history on this story can be found here.

How 5G New Radio Specification Decision Affects Base Station Design

September 19, 2017

The recent decision by the 3GPP during its meeting in Croatia to move the schedule for 5G standardization up six months was welcome news to carriers, chipset makers, device manufacturers and others in the wireless industry. It not only keeps 5G on schedule for 2020, it may have even escalated the rollout to sometime in 2019. Furthering the notion of a closer 5G horizon is that 36 operators worldwide have begun pre-standardized trials, all with the goal of launching the next generation of wireless technology sooner rather than later.

The first 3GPP 5G New Radio (NR) specification will be part of Release 15, scheduled for release before year’s end, and will focus on Non-Standalone (NSA) 5G. NSA will leverage existing LTE networks but will also rely on high-frequency millimeter waves (mmWave) between 28 GHz – 38 GHz. The integration of these bands will place various pressure points on base stations and how they are going to be used. Because of this, field engineers and technicians need to understand how the first phase of 5G will be deployed and how to properly test it to achieve established key performance indicators (KPIs).

NSA Architecture

NSA will utilize existing LTE radio and the evolved packet core network as an anchor for mobility management and coverage. It will also add a new radio access carrier to enable certain use cases, primarily fixed-wireless broadband. Core mobile device actions, such as scheduling and handovers, will be conducted using the LTE channel to leverage its broader coverage.

Data capacity – along with lower latency and longer battery life – is a key selling feature of 5G. These promised high-bandwidth services at faster speeds will require a broader pipe than the 20 MHz bandwidth LTE can provide. That is where mmWave technologies come into play. With aggregated channel bandwidths of 1 GHz and higher, mmWave frequencies will deliver on the promise of 5G.

Macro Cells and Small Cells Importance

Because 5G is meant to augment 4G, both macro cells and small cells will play key roles in the pre-standardized period – as well as the 5G NR initial phase. Existing macro cells will be used for the LTE elements. Many existing base stations have been upgraded to incorporate technologies such as C-RAN and CPRI to make for a smooth transition to 5G.

Small cells, which are low-powered radio access nodes that can be installed in short increments due to their compact size, have become a critical part of wireless networks. They have proven to be an excellent method to provide capacity in areas where it’s difficult to build macro cell sites, particularly urban geographies. While small cells have been initially used for LTE networks, they will gain new prominence in 5G, as they will be an effective means to compensate for the short range of mmWave signals.  

Testing Procedures

5G trials and ultimately the official deployment of the next generation technology will require test procedures similar to today’s processes. As is the case currently, limiting interference will be vital in 5G, as the high-bandwidth services will have much more stringent requirements because the slightest effect on a signal can have demonstrative results. Key measurements will remain channel power, occupied bandwidth, return loss, passive intermodulation (PIM), and adjacent channel power ratio (ACPR). The integration of fiber into these networks also mean traditional optical measurements, such as OTDR tests, must be conducted on both the fronthaul and back haul.

A big difference as it relates to testing is going to be in measurement accuracy. Interference hunting requires the ability to spot, find and fix a known interferer as quickly as possible so 5G networks meet KPIs. Accurate measurements can help locate a problem faster, saving valuable time and money. To achieve this, operators and those responsible for network performance and maintenance will need a full portfolio of interference tools.

Remote spectrum monitors are a cost-efficient method to observe network performance 24/7/365 and send alerts when performance dips below pre-determined thresholds. When those instances occur, solutions such as the Mobile Interference Hunting System can quickly and reliably locate interfering signals from a moving vehicle, even when there are multiple sources.

Handheld test instruments, such as the BTS Master™ MT8220T, that combine the measurement capability of 30 instruments can be used for an interference hunt, as well. Often, it is used with the Handheld Interference Hunter MA2700A that features a GPS receiver and antenna, electronic compass, and user-selectable preamplifier to help expedite locating and correcting interference issues. Utilization of all these tools will help keep 5G networks operational, just as they are accomplishing the task today.

To learn more about interference and test solutions to quickly and efficiently locate their sources, visit this educational interference hunting webpage.

Reduce Base Station OpEX with BBU Emulation

June 30, 2017

Today’s base stations integrate multiple technologies. From traditional RF cables and fiber optic lines to small cells and macro cells, field engineers and technicians must test and verify more elements than ever before.

This integration is part of a decade-long evolution that has also seen radios travel from the base station on the ground to atop the tower, with a baseband unit (BBU) installed in the equipment room. While this configuration has helped reduce operating expenses (OpEX) by shrinking the size of the building and lowering the equipment room air conditioning cost, it has created new testing challenges.

To meet these challenges, test solutions have evolved, as well. Fiber tests have become a necessity, which may appear foreign to field technicians who have spent their careers in the RF space. Solutions that integrate RF and fiber testing with built-in measurements are now available to address this aspect. Another issue – a costly one at that – is that by moving radios to the top of the tower the installation process can be more time consuming and expensive. New techniques are available on this front, as well, to help reduce costs while ensuring operation.

Test Considerations

CPRI was integrated into base stations to connect the Remote Radio Heads (RRHs) atop the tower with the (BBU) in the base station. Some of the new test considerations faced by the incorporation of CPRI are listed in figure 1. A few things to note with this list is that absolute measurements can be made in dBm on RF signals, while CPRI has relative measurements in dB. Another big difference is that a center frequency can be specified when conducting spectrum-based measurements in the RF domain. Because everything is baseband with CPRI, tests are frequency agnostic. Also, a full span can be covered with an RF test whereas with CPRI only so much IQ data is transmitted, so there is a limit to the maximum span seen on the analyzer.

Figure 1

Logically, CPRI integration in base stations has expanded the tests that are necessary to ensure network operation. Common CPRI-based tests are shown in figure 2.

Figure 2

Faster Turn Up Time; Lower OpEx

The integration of RRHs on top of the tower has led to a change in the deployment of base stations. During the initial stage, the RRH is installed with the fiber optic cable, antennas and other elements. Once that is completed, the BBUs are commissioned. This multi-step process adds time and costs to the project. A new test technique – BBU emulation – has been developed to solve this problem.

There are two main advantages of BBU emulation:

1. Faster turn up time, resulting in carriers collecting revenue earlier from a new site and greater profits for contractors
2. Lower OpEx

The latter benefit can be realized in both new construction and existing sites. We have talked to people in the field and 3-6 truck rolls are typically necessary to fully commission a new site. One crew is deployed to install the RRH and associated elements. A second crew is then sent to commission the BBU. Upon completion of the BBU install, testing is commenced. If there is an issue with the RRH, fiber, antennas, etc., it will be revealed at this time, requiring the original crew to return to fix any issues. The BBU crew will then return a second time to verify the base station.  

BBU emulation streamlines the entire process by allowing technicians to test the RRH infrastructure without a commissioned BBU. The result is that tests are made with the construction equipment still at the site, so if any repairs need to be made the crew is already at the location.

BBU emulation can also be used to monitor and test existing base stations. Currently, the general practice is to replace the BBU when a problem is detected. If the issue persists, the RRH is swapped out. This approach can create “No Trouble Found” (NTF) costs from the manufacturer, all of which are eliminated when using BBU emulations.

All necessary installation tests can be made with BBU emulation, including line sweep of jumper cables and antennas, and cleaning and viewing of all fiber connectors. Verifying SFP port location and suitability can also be conducted with BBU emulation. By SFP port suitability, we mean to ensure that the port is compatible with the CPRI line rates used at the base station. (One note: the most common are Line Rate 3, Line Rate 5 and Line Rate 7.)

Conducting BBU Emulation Tests

The benefits of BBU emulation can be realized using an appropriately configured handheld analyzer, such as the BTS Master MT8220T (figure 3). When conducting tests, the user must ensure there is power to the RRH and the SFP supports the required line rate. Both ends of the fiber must be cleaned with the proper tools. The duplex fiber pair between the RRH SFP and tester SFP must then be connected. Once that is completed, the analyzer should be configured in BBU emulation mode, allowing the instrument to provide the system clock and serve as the master.

When it is in BBU emulation mode, the analyzer immediately starts an auto negotiation of line rate. Communications with the RRH are established over CPRI Link via Ethernet link, HDLC (High level Data Link Control), or a proprietary method developed by the vendor. The field technician can select the RRH to be tested from the list (IP address), and OEM Command and Management messages can be exchanged over the Ethernet connection between the BTS Master and RRH.  

After the BBUs have been commissioned, overall system performance needs to be validated by checking uplink spectrum for interferers. One method is to install an optical TAP in the system, which facilitates performance testing from ground level in the equipment room without taking the tower down. When conducting this test, field technicians must remember that the analyzer needs to be in normal CPRI mode to monitor the CPRI link and that it is no longer supplying the system clock.

Summary Carriers and contractors can save valuable time and money by using BBU emulation to test new and existing base stations. It can verify that RRH system components are installed correctly, as well as RRH system functionality, while also testing for interference issues. It allows for quicker commercialization of new construction sites and is useful for troubleshooting existing installations.

To learn more about BBU emulation, watch this informative webinar.

With New 5G CPRI Specification on Horizon, Test Tools Continue Evolution

March 29, 2017

The latest CPRI specification remains on schedule to be releaed in August of this year, according to a news release published by the CPRI Industry Initiave. The new specification, known as eCPRI, will place emphasis on 5G fronthaul support and is expected to include increased efficiency to meet the anticipated high-speed, high-bandwidth needs of 5G networks. The goal of the eCPRI specification is to offer numerous benefits to engineers designing base stations. Among the expected advantages are:

1. A new physical layer split point to enable a ten-fold reduction of the required bandwidth
2. Required bandwidth that can scale flexibly based on the user’s plane traffic
3. Use of mainstream transport technologies such as Ethernet to possibly carry eCPRI and other traffic simultaneously in the same switched network
4. Use of sophisticated coordination algorithms for optimal radio performance
5. Easy-to-upgrade foundation so future introductions can be done via software updates in the radio network.

In addition to the new eCPRI specification, work continues to further develop the existing CPRI specifications to keep it as a competitive option for all deployments with dedicated fiber connections in fronthaul, not only 5G.

This comes as no surprise to anyone involved in the design and deployment of base stations. After all, the integration of CPRI into the traditional RF space of an eNodeB was done to address the faster speeds and higher bandwidths associated with LTE networks. Plus, many of the existing CPRI specifications have 5G elements within them.

For engineers and field technicians, though, while one eye may be on 2020 when 5G is expected to launch, the other is clearly focused on current base stations, which continue to evolve in their own right. To verify performance of today’s base stations, test solutions must have new features that not only meet the technology challenges but also the demands for more time- and cost-effective testing procedures.

Base Station Performance Updates

CPRI Line Rate 8, which operates at 10.1376 Gbps, is becoming more common in base stations. While its faster transmission speeds are better suited for streaming and similar applications, it also means test instrumentation must keep pace. Fortunately, handheld analyzers are now available that support CPRI Line Rate 8.

Another example is that newer Base Band Units (BBUs) are supporting and implementing 20 MHz compression technology. Handheld test solutions that are durable enough to withstand the terrain associated with bases stations will now also have to provide 20 MHz compression support. Figure 1 shows an example of the Anritsu BTS Master, which now has a compression capability that allows for resampling of 20 MHz bandwidth IQ data signals from 30.72 Msps to 23.04 Msps to meet this market condition.

Figure 1

Uplink Interference

One of the biggest issues facing operators right now is interference on the uplink, which can drastically affect KPIs. To address this concern, handheld test tools have the capability to tap into the CPRI fiber link and monitor the uplink spectrum. Coupled with an ultra-fast sweep speed when conducting CPRI RF measurements, these solutions make it much easier for field technicians to capture and analyze transient and bursty signals typical of many interference types. Another recent feature is the ability to tune to anywhere within the spectrum and zoom in for more detailed analysis, to better and more efficiently locate issues that may hinder network performance.

Multi AxC Traces

Making base station testing more efficient is another key goal for most operators. Again, test solutions are advancing to make verifying and troubleshooting networks faster and easier. For example, there is now the ability to view from one to four AxC Group traces in a single spectrum view (figure 2). A Dual Display capability that allows two different AxC traces, such as spectrum and Spectrogram, to be viewed simultaneously is also now available.

Figure 2

The combination of Multi Trace AxC and Dual Display gives users plenty of flexibility in looking for interferers by being able to look at the different MIMO signals simultaneously. It also allows RF engineers to look at RF loading and balance, also known as diversity testing, between MIMO radios on a live signal.

Staying up-to-date with base station technologies is no easy task. That’s one reason why Anritsu published a dedicated Base Station Technologies page that offers insight on all aspects of base stations and ensuring their deployment, installation, and operation. You can also download a white paper entitled Improving Wireless Network Flexibility Using CPRI Technology.

Procedures to Eliminate Common Fiber Connection Failures in LTE Base Stations

February 2, 2017

Base stations have undergone quite the evolution as wireless networks advanced from 3G to 4G. To accommodate the fast speeds and high bandwidth associated with LTE networks, Common Public Radio Interface (CPRI) technology is now commonplace, used to connect a Baseband Unit (BBU) and one or more Remote Radio Heads (RRH) sitting atop the tower. As part of this progression, fiber optic cable, which has extremely low transmitted signal loss to accommodate LTE networks, is prevalent in base station design.

Technicians spent decades handling copper. Now they are installing and maintaining fiber, which has many different characteristics than coax. There are several causes of failure in fiber connections, but here are the most common – and ways to prevent them.

1. Dirty Fiber – Simply touching a connector end with a bare finger can leave oil on the fiber, which will affect performance. That is one reason why 60%-75% of the alarms, failures and poor throughput issues found in modern cellular systems are due to dirty fiber. As you can see in figures 1 and 2, a dirty fiber connector can result in failed International Electrotechnical Commission (IEC) tests. These can include the IEC 61300-3-35 pass/fail test profile, which is an industry-accepted procedure that ensures that a fiber is clean and damage free. 

Figure 1. A dirty fiber connector end fails IEC 61300-3-35 standard based test.

Figure 2. After a cleaning, the same fiber connector end easily passes IEC 61300-3-35 standard test.

2. Mismatched Small Form-Factor Pluggable (SFP) Modules – Using improper line rate, optical wavelength or fiber type will lower network performance. Single mode (SM) fiber’s most frequent wavelengths are 1550 nm and 1310 nm, while the most common wavelengths used with multimode (MM) fiber are 850 nm and 1300 nm. For best results, matched pairs of modules between BBU and RRH should be used. 

3. Incorrect Fiber Type – It is crucial to use the correct fiber type that is matched to the SFP or SFP+ type in a particular system. If MM fiber is used in a SM system, or vice-versa, the system may work over very short distances, but there will be propagation issues if used for long distances. The center conductor of the MM and SM fibers have different diameters. MM typically uses 850 nm lasers; the propagation of its signal would be affected if passed through a SM fiber and vice versa.

4. Distance Between BBU and RRH – Problems may occur when there is too much distance between the BBU and RRH for the required line rate associated with the SFP and fiber. MM fiber is typically not capable of high-speed data transmission of greater than 1 Gb/s over long distances. SM fiber should always be used in this case. Costs of SM fiber and modules have decreased significantly, and with data rates constantly increasing, SM equipment is being used in the majority of systems being deployed.

5. Damaged Fiber – As any technician knows, fiber is more sensitive than coax. Surface damage, such as scratches or chips, as well as pinching from excessive bending can cause a significant loss in optical transmit power. Something as simple as over tightening a cable tie can cause sharp bends that damage the fiber. Prevent these issues by properly protecting, housing and installing optical fiber.

6. Incorrect Tx/Rx Connections – Many of today’s systems use hybrid cable assemblies that bundle power, fiber and sometimes CAT 5e cables. The fiber ends may be terminated with single LC connectors, therefore it is important to make sure that the Tx and RX are connected to the correct ports on the SFP. Other examples of incorrectly connected Tx or Rx can be found in systems with redundancy protection.

7. Connectors Not Fully Seated in SFP Modules – Both duplex and simplex LC connectors are quite small and rather delicate. Small plastic tabs lock the LC connectors in place once they are inserted far enough into the SFP modules. Similar to Cat53 or Cat 6, the tabs must be pressed downward to unlock before being carefully pulled out. It is incredibly vital for the connectors to be fully locked in order for the system to function correctly. Even the smallest gap between the fiber end and the receiver or transmitter will result in significant signal loss. 

8. Wrong Sectors Connected – It is possible to improperly connect the fiber pair to the wrong sector RRH in a typical multi-sector RRH system being fed from a single BBU. As systems become more complex there will be many fiber pairs, and if they are not all properly identified and connected to the right locations, the system will not function at its optimal performance.

9. Improper SFP Connections - Many RRHs have additional SFP ports to support daisy chain topologies. Plugging the SFP module into the wrong SFP port on the RRH will make the system inoperable. The BBU generates the master clock, and the RRH has a master clock output on its second SFP port. If the connection between the BBU and RRH is using these two connectors, they each try to set the master clock, and the CPRI link will not configure.  

Test Tools

Technicians can prevent these fiber issues through specific pass/fail tests and inspections. Fortunately, there are several handheld products, such as the Anritsu Site Master™ S331L and the Microwave Site Master™ S820E, that offer Visual Inspection Probe (VIP) capability. VIP mode captures connector images digitally and shows them on the analyzer’s large display so technicians can perform visual inspections on fiber optic connectors and automatically conduct pass/fail testing per the IEC 61300-3-35 standard. These instruments can help facilitate these tests and be part of an inspection process that is absolutely crucial to ensure functioning systems.

A new technology page focusing in the today’s base stations has just been published by Anritsu. There, you can access a new application note that details the importance of inspecting and cleaning fiber in an optical BBU/RRH link.

Eight Steps to Verify RRH Performance More Economically and Efficiently

December 16, 2016

As we explained in our last post, baseband unit (BBU) emulation is a highly effective method of managing and reducing time-driven costs during site build, commissioning, and troubleshooting of 4G networks. It allows wireless field engineers and technicians to test remote radio head (RRH) performance from the ground to validate and sign off on the installation before the BBU is installed, thereby reducing repeat site visits by crews.

Selecting the proper test solutions, such as the Anritsu BTS Master™ handheld base station tester, is only part of the equation that equals these benefits. Understanding how to conduct these measurements is also important. Here are eight steps to take when conducting tests using BBU emulation.

Step One: Set up the BBU

The first step is somewhat obvious. You need to make sure the RRH is powered up and that the Small Form Factor Pluggable (SFP) optical transceivers being installed support the required line rates of the test. Because you will be dealing with fiber optic cables it’s important to clean both ends of the fibers and connectors with proper cleaning gear.

Once the antenna has been installed, you will connect the duplex fiber pair between the RRH SFP and the tester SFP. You can then set the test solution into BBU emulation mode so it becomes the master.

As opposed to normal RF tests in which everything occurs almost instantaneously, BBU tests often involve delays of 20-40 seconds because commands and responses are sent and received. All the lights on the analyzer interface will turn green when a valid CPRI link between the test unit and the RRH has been established (Figure 1).

  Figure 1

Step 2: Establish Communication

Over CPRI Link Once a link has been established between the RRH SFP and the tester SFP, communication with the RRH can begin. After sending commands, you will receive a response with the IP address of the RRH. Commands, which are determined by the RRH equipment manufacturers, can be sent to the instrument in multiple ways, including Ethernet link, High Level Data Link Control (HDLC) and proprietary methods.

All active RRHs in the daisy chain will request their own IP addresses, which will be allocated by the test instrument. A list of RRH IP addresses on the CPRI connection is displayed in the order in which they are communicated to the BBU.

Step 3: Identifying IP Addresses

When you click on the IP address displayed in the BTS Master interface (or similar instrument), you will be presented with a set of commands that ask for the manufacturer, model number, running firmware, frequency range, power levels and other specifications. This information helps validate that the correct equipment is installed in the proper location. It also helps prevent a common error – connecting the SFP in the wrong port. Figure 2 shows how it should be connected. When all IPs are identified, it becomes easier to determine which specific piece isn’t working properly in the event of a system error.

Figure 2: correct SFP connection

At this point, SFP tests can be conducted. You can query the SFP, which will report back data such as its wavelength and supported bit rate. Again, by having the vendor name and serial number displayed, it is easier to keep track of what is and is not working.

Step 4: LTE Waveform Test Models

Many of the functionality tests on an RRH require loading a waveform file into the RRH and then transmitting it. These waveforms come in different pattern lengths and different 3GPP test models:

• E-Tm 1.1 – RF-based test

o Test unwanted emissions, occupied bandwidth, ACLR, transmitter intermodulation and RS absolute accuracy

• E-Tm 1.2 – RF-based test

o Unwanted emissions and ACLR are measured

• E-TM 2 – Tests at Minimum Power

o Measures total power dynamic range, EVM of single 56QAM PRB allocation and frequency error

• E-TM 3.1 – Tests at Maximum Power

o Tests output tower dynamics, total power dynamic range, transmitted signal quality and EVM for 64QAM modulation

• E-TM 3.2

o Frequency error, transmitted signal quality and EVM for 16QAM modulation are measured

• E-TM 3.3

o Tests transmitted signal quality, frequency error and EVM for QPSK modulation

Note: 3.1, 3.2 and 3.3 send out three typical modulations that are used in LTE networks.

When the LTE wave file has been loaded into the unit an acknowledgement will be sent. You then can pick the proper center frequency for transmission; keep in mind that the BBU software running on the test unit dictates the proper frequency range and output power. After selecting the waveform test model, measurements can be made.

Step 5: Validate the Antenna

Using a spectrum analyzer, over the air (OTA) measurements should be conducted to confirm that the sector is transmitting a strong signal. To acquire specific data, the signal can also be demodulated. This latter step isn’t always necessary, but it is useful for troubleshooting existing antenna units.

Step 6: Measure the RRH Antenna Port VSWR

Return loss (VSWR) measurements should be made at this point in the process. When the radio is transmitting, you are basically using it to make the measurement. You can even set Pass/Fail limits for the results and determine if the values are within the necessary ranges.

Step 7: View PIM on the RRH Uplink

When the system is installed, tests for possible PIM can be conducted. Use E-TM 2 to establish a baseline, and then use E-TM 3.1 to transmit maximum power to see if the uplink is affected. Minimum hold trace and normal trace can also be used to validate if PIM is present (Figure 3). If the minimum trace stays flat, it is probably the result of a separate interference issue that is not PIM (Figure 4).

Figure 3: a noise floor that is not flat

Figure 4: a flat noise floor

Step 8: Check Fully Commissioned Installation

Even after the BBUs have been fully installed and commissioned, you should still return and test the system to make sure everything is working properly. If a site needs to be troubleshooted, crews will typically use an optical TAP. Some carriers are installing TAPs in their sites, but in other cases, crews will have to use their own. It can be installed between the BBU and the RRH to monitor the existing live network. It is important to make sure that the test instrument is in normal CPRI mode rather than BBU mode when troubleshooting. In this case, you can make the uplink RF measurements to check for any interference or possible PIM issues.

You can also measure the downlink to verify that the BBU is transmitting its LTE signal according to specification. It is important to validate that there is no interference that will drastically affect your KPIs.

To learn more on this important topic that can save you time and money, watch a BBU Emulation webinar.

BBU Emulation Saves Time and Money During RRH Installation and Testing

December 5, 2016

As the wireless industry moves towards Remote Radio Head (RRH) hardware to address the significant increase in mobile data traffic, the need to emulate the Baseband Unit (BBU) becomes a key tool for managing and reducing time-driven costs during site build, commissioning, and troubleshooting. Utilizing the proper emulation tools can help maximize network profits while also saving valuable time by reducing repeat site visits by crews to commission new sites.

In a Common Public Radio Interface (CPRI) site design, the BBU is connected to the tower-mounted or pole-mounted RRH via a fiber optic line. In a typical build project, the RRH is mounted and the BBU is installed later. If problems arise with the RRH, they’re not discovered until after the BBU is installed and commissioned. Resolution involves creating and tracking a trouble ticket, then scheduling and performing subsequent site visits – all of which incurs unanticipated operational expenses (OpEx) and reduces profit margin.

RRH installations can be plagued by various hardware complications. There may be issues with the RRH itself, problems with the Small Form Factor Pluggable (SFP) optical transceivers, RF glitches with coax cables or antennas, and complications with the fiber optic lines or connectors. Additionally, there can be problems with the on-site RF environment, including Passive Intermodulation (PIM) from nearby metal-junction issues or poor RF connectors, and interference from nearby RF sources. RRH antennas need to be adjusted for tilt and azimuth to manage PIM, reduce environmental RF noise, and to optimize downlink performance.

Troubleshooting or managing these potential issues requires the RRH to be connected to a working BBU. In most new build scenarios, however, the BBU may be installed but has not been commissioned and is not available to verify the operation of the RRH. It is in these scenarios where the value of a BBU emulator will be realized.

Testing RRH

Initial testing of an RRH (either in-place, or in a depot prior to going on-site) may be done by attaching a BBU emulator via a section of fiber optic line. This confirms that the RRH is configured correctly, responding properly to CPRI signals, and that the RRH will be able to attach successfully to the actual BBU. Testing of the SFPs may also be necessary, and is easily accomplished with a BBU emulator. Testing from the base of the tower provides confirmation that the fiber optic line is intact, the SFP is installed in the correct port and that the fiber is clean and seated properly.

Determining if PIM is an issue is done by analyzing the uplink receiver and looking for characteristic patterns in the noise floor, while the RRH is transmitting a LTE signal. Environmental RF noise will also appear during this test. It may be possible to reduce or eliminate PIM and any environmental noise by adjusting the RRH antennas for tilt or azimuth. Likewise, adjusting RRH antennas for optimized downlink performance is best done with the RRH activated by a BBU emulator, and measuring signal performance at the anticipated user locations using an LTE analyzer.

A key value of the BBU emulator is the time and cost savings realized from testing and resolving these problems before the BBU is commissioned, thus reducing truck rolls. This approach helps ensure that projects will be completed on-time and within budget constraints. Anritsu’s BBU Emulation, available on the BTS Master™ MT8220T handheld base station analyzer, replicates the functions of a standard BBU. Field engineers and technicians can use a solution such as this to fully test and exercise the RRH with both feet on the ground to validate and sign off on the installation before the BBU is installed (figure 1).

  Figure 1

Anritsu has developed an informative webinar on the topic to help streamline RRH installations. You can access the presentation entitled Validating the Performance of Cellular Networks with CPRI Fiber Interfaces Between Ground Level Baseband Units and Tower Mounted Radios here.

The Effect of Return Loss on Mobile Networks and How to Improve It

September 22, 2016

When designing and building 4G infrastructure, one goal of engineers is to maximize the RF signal level throughout the coverage area. Assuming the noise level remains constant, higher signal levels result in faster data rates and fewer dropped calls, ultimately resulting in happier customers and greater revenue for operators.

Operators often specify that the worst case reflections – a.k.a. return loss – over the operating frequency range of the system must be 18 dB to maintain the desired signal levels. Another way of looking at this is that the reflected signal must be less than 1/64th the magnitude of the signal transmitted into the system. As feed systems become shorter and antenna systems are required to operate over broader frequency ranges, however, achieving an 18 dB return loss may not be practical for today’s wireless networks.

Return Loss Impact on Power

One thing to remember is that additional dBs of improvement in return loss have less impact on power lost, thereby debunking the belief that “a change of 3 dB means the power is doubled or cut in half.” It is a common mistake to misapply this rule and falsely believe that improving return loss from 15 dB to 18 dB, for example, will double the coverage area of a site. What actually occurs is that the power lost is reduced by half (relative to its starting value) when the return loss changes by 3 dB.

To help understand the coverage impact associated with changes in return loss, we will assume a typical site configuration and use the propagation loss equation shown below to solve for the distance “d” associated with a desired signal level.

Propagation loss (LP)= –27.56 + 20*Log10(f) +n*10*Log10(d) Where:

f = Frequency (MHz)

d = Distance (m)

n = 3.0 for urban morphology

In this example, we will assume the following site configuration:

Power transmitted by the radio (PT) = 20W = 43 dBm Frequencies of interest = 700 MHz, 850 MHz, 1900 MHz, 2100 MHz Feed system loss due to absorption (LA) = 2.5 dB

Feed system loss due to reflections (LR) = Equation 6

Antenna gain (G) = 17 dBi

Desired power level arriving at the mobile (PR) =  –75 dBm

Looking at specific examples, the change in coverage distance can be evaluated for a return loss improvement from 15 dB to 18 dB and from 17 dB to 18 dB as shown in Table 1 and Table 2.

Table 1

Table 2

As can be seen in figure 1, the coverage distance is improved, but only slightly.

Figure 1  

Good Methods

If the operator determines that the non-compliant return loss specification is unacceptable and instructs the crew to perform repairs to achieve the desired value, it is important to use the proper methods. Here are two “good” changes that improve return loss without negatively impacting another variable that might degrade overall site performance.

1. Disconnect and reverse an existing jumper cable – By doing so, you can change the phase relationship of reflections in the system. Sometimes, this change can cause a “failing” system to pass.
2. Distance-to-Fault (DTF) measurement – This proven test can determine the RF connection with the highest individual return loss contribution. Opening this connection and improving workmanship may cause a “failing” system to now pass.

Bad Techniques

Conversely, here are a few approaches that are not recommended when trying to improve return loss.

1. Loosening a RF connector – Adjusting the phase relationship of reflections in the system by loosening the connector and then taping over it is not acceptable. Loose connectors degrade the mechanical reliability of the feed system, as well as generate passive intermodulation (PIM).
2. Increasing jumper cable lengths – If the antenna is the highest source of reflection in a system (which is often the case), adding 0.5 dB of cable loss will result in 1.0 dB improvement in return loss measured at the system input. While this might seem like a good idea, the added insertion loss has a negative impact on site coverage. Improving the system return loss from 17 dB to 18 dB by adding 0.5 dB of cable loss will result in a significant reduction in site coverage. Adding loss is never a good way to improve site performance!

Anritsu offers a complete line of cable and antenna analysis solutions and automation tools to help wireless professionals measure return loss and manage cell sites. To learn more about this subject and the solutions, download a white paper entitled The Impact of Return Loss on Base Station Coverage in Mobile Networks.

Proper Test Tools Simplify Sports Venue DAS Install

July 12, 2016

Distributed Antenna Systems (DAS) pose many challenges, including the fact they are usually installed in havens for interference. However, as the case study below shows, using the proper test solutions, such as handheld cable and antenna analyzers, passive intermodulation analyzers and a cloud-based software solution, can help successfully deploy DAS networks – in this case ensuring operation while reducing test time by 70%.

Project Situation

A large state university on the east coast was upgrading the wireless network in its basketball arena to provide spectators with improved venue coverage/capacity, particularly for high-bandwidth services. Communication Technology Services (CTS), the contractor hired by Crown Castle for the project, needed test tools that could simplify the complex challenge of collecting thousands of traces to verify the DAS installations in a very tight time window.

The 8,000-seat indoor multi-purpose arena posed a set of obstacles that ranged from building architecture to environmental conditions. CTS Project Manager Legion Marks and his team had only a few weeks to install the DAS network throughout the basketball facility. To verify the network, more than 2,000 traces had to be done on the various passive branches that stretched across the complex. Some venues have 10,000 to 15,000 traces required. All of the traces had to be reviewed and approved before the project could be closed out. In the past, there was a time lag in compiling and presenting results to the Crown Castle RF Engineering team, which could result in project delays. They needed a more automated testing solution to compile and upload data for quicker reviews in order to track the cycle time and ensure data integrity.

“With the emergence of LTE technology, DAS complexity and density has greatly increased along with demand for line sweep detail. It is a daunting task to manage the large amount of traces during a project. The DAS industry as a whole needs a powerful trace management tool. Thankfully, we had SkyBridge Tools,” explained Marks.

Test Solutions Save Time Marks, experienced in engineer, furnish, and install (EF&I) management, selected a suite of Anritsu field solutions. His team used Site Master™ “E” and “L” series cable and antenna analyzers, as well as the PIM Master™ MW82119B. SkyBridge Tools™ Test Manager cloud-based trace management tool was used with all the instruments to simplify the testing processes associated with the DAS installation. It provided a number of benefits, including:

Automated Test Scripts – The easyTest™ feature of SkyBridge Tools makes it simple to create a set of instrument control scripts based on Crown Castle’s MOP (Method of Procedure). This allowed the CTS team to conduct measurements by pressing a single button per test.

Reporting – Skybridge Tools offers a one-click solution for reporting.

Marks could track the progress of the project by simply logging into his account, eliminating the tedious, time-consuming and error-prone practice of manually compiling data and sending a periodic report. Marks explained, “Skybridge Tools eliminated many of the headaches with manipulating large amounts of trace data, including pass/fail review, naming convention mistakes, and batch processing. It even allowed me to export the data into a tabulated form, which reduces manual data entry for closeout documentation.”

All of this made for a seamless process. Team members would upload completed traces to SkyBridge Tools. Once Marks approved them, each batch was made available to Crown Castle RF engineers through Skybridge Tools for their review. The result was a very efficient method to verify the installation of the entire DAS network, allowing Crown Castle to ensure that all the test criteria has been met with all the corrections in place, before approving the project.

The Anritsu staff went above and beyond when it came to support, according to Marks. Hands-on training was provided to CTS and it was completed in only three hours so the team could begin gathering traces the same day.

Results

CTS was able to meet the project timeline in large part because SkyBridge Tools created a highly efficient method for storing traces that shaved at least 70% off the job timeline, according to Marks. Crown Castle was able to review and approve the project more quickly, ultimately allowing the project to be closed out faster and for payment to be expedited.

“Skybridge Tools takes trace management to the next level. I see a huge value in it for my company, both on cost savings and customer service. After implementing this process, I don’t see any other way to collect large amounts of trace data,” said Marks.

SkyBridge Tools helped CTS close out the sports venue project more efficiently, get paid faster and move on to the next project. To learn more about SkyBridge Tools can to help your DAS installations, visit a comprehensive page on the cloud-based solution.

Cloud-based Test Tools Simplify and Expedite DAS Installation Process

June 28, 2016

Every mobile communications report published has a recurring theme – mobile date usage is skyrocketing to new heights. People rely on their mobile devices (smartphones, tablets, etc.) more than desktop and laptop computers in everything they do and wherever they are. In fact, approximately 80% of mobile usage happens indoors and not just from the comfort of a living room couch via Wi-Fi. Consumers use their smartphones while shopping in brick and mortar stores (84% of them according to Google) and another study found that three quarters of workers would consider leaving their current mobile operator to get better coverage in their office.

All of this makes it imperative for providers (and landlords) to ensure coverage in malls, office buildings and other venues. Not only will it ensure mobile data usage for potentially increased revenue, it will help reduce churn because consumers have high service quality expectations when using their mobile devices indoors.

There is just one problem – indoor coverage is not simple. “Outside-in” signal loss can be up to 7 dB due to windows, and reach 10 dB for brick or 12 dB for concrete walls. Metal wall framing may cause a loss of up to 10 dB, while concrete floors can result in losses approaching 30 dB, according to one analyst group. That is why there has been tremendous growth in the deployment of In-building Wireless (IBW) systems, specifically Distributed Antenna Systems (DAS).

Despite the challenges associated with DAS, the aforementioned market conditions provide compelling business reasons for operators to deploy indoor networks to accommodate their customers. Providers in North America and Asia-Pacific have particularly taken an interest, evident by the statistics in figure 1.

Figure 1

Understanding DAS

Hybrid and/or passive DAS has become a popular architecture for multi-operator, multi-NEM, multi-technology applications because it is able to accept RF inputs from a variety of signal sources, making the DAS network equipment manufacturer as well as technology (2G, 3G, 4G) neutral. When possible, DAS antennas should be placed in locations with a clear view of the environment they are serving rather than near metal objects such as light fixtures, ceiling tile frames and metal HVAC ductwork. Placement close to these objects can generate high levels of passive intermodulation (PIM), even with transmit power levels as low as 20 dBm (100 mW).

Studies conducted by Anritsu indicate that external PIM sources close to IBW antennas are more likely to impact performance at low frequencies, such as 700 MHz, 850 MHz, and 900 MHz. Best practice when deploying low-frequency band systems is to perform a low power PIM test at each candidate antenna location prior to final installation. Internally generated PIM is worst at the higher frequencies, so in this case a PIM test at one of the higher bands, such as 2100 MHz or 2600 MHz, is best practice. Eliminating PIM in DAS is discussed on our PIM Source blog.

A DAS may require 1,000 to 15,000 traces, photos, and other deliverables to show that the installation meets performance standards. This can be as much as 100x more than what is required when installing a typical tower-based antenna system. When you consider each of these deliverables needs to be inspected, renamed, and perhaps have the markers and limit lines set and judged, the task can become quite lengthy and costly if the traditional manual inspection process is used.

Given the complexity and myriad technologies used in DAS, as well as the technical aptitude of some technicians, there is a definite need for simplified testing processes to the DAS installation workflow. Fortunately, there are now cloud-based tools to ensure time savings for operators and allow contractors to more quickly close out jobs, get paid and move on to the next project. One such solution is SkyBridge Tools™ from Anritsu, which enables reliable and quick creation of test plans, fast and accurate testing, and assists in report creation.

Test Plan

A sound test plan is the best first step in simplifying the test process. Data can be imported from iBwave designer, Excel, and operator-supplied test criteria with the assistance of a wizard to create detailed Test Plans such as the one shown in figure 2. This documentation enables test sequencing, job progress tracking, trace judgement, and report generation.

Figure 2

Test Sequencing

After the test plan is created, pressing one button will create instrument control scripts for that specific plan. Necessary tests, proper instrument setups, limit lines, and accurate file names for traces are included. These scripts can then be run on certain Anritsu field instruments, including Site Master™, BTS Master™, and PIM Master™ handheld analyzers, greatly reducing technician workload. Failures are often visible while the cable is still connected to the instrument. Missing or duplicated tests, misconfigured setups, and misnamed traces are eliminated through this tool.

Reporting

A key element to the DAS testing process is the reporting mechanism to verify the tests were conducted properly and the results sound. Traditional PDF or zipped reports are standard formats but having a CSV file with one row per test is also sometimes necessary and advantageous. Automated reports in a variety of formats forever eliminates the tedious and inconsistent processes used in the past.

There is much more to learn about IBW systems and the various system architectures, such as DAS, Distributed Radio Systems (DRS) and Distributed Small Cells (DSC), as well as how to test each. You can download an Understanding IBW white paper to gain more information.