5G has been a major topic for the past few years and is filled with new opportunities to interconnect with devices and services at greater speeds. For many of these industries who are seeking the next-generation mobile technology, progress for this innovation has accelerated and will become a reality very soon. The thirst for data on mobile devices has exploded and estimates suggest that the number of connected devices is expected to exceed 50 billion by 20201. Because of this huge global demand for data, manufacturers are currently finalizing the hardware/software for 5G based on the global 3GPP specifications to ensure the networks can implement and support the new technology.
Within the US, operators such as Verizon and AT&T have been deploying 5G in test cities around the country from rural and urban areas to certify that the network can fully live up to the 5G standards and eliminate any issues with deployment, operation and maintenance2&3. If things go as expected, a nationwide rollout should happen by 2020. What makes 5G so revolutionary is the bandwidth and latency it can deliver to our latest devices and how this will impact the future of our global economy and society which will enable millions of users to thrive in an everchanging, smarter and connected world.
As the Industrial Revolution of the 1760-1840’s transformed the global economy and standard of living through the introduction of new manufacturing processes from hand to machine, 5G looks to revolutionize the digital era by ushering in the platform on which A.I., IoT and other M2M devices can communicate at the bandwidths and latencies needed to unlock their full potential. Currently, 4G LTE supports theoretical downlink transmission speeds of up to 150Mbps. Based on data gathered from ‘real world’ 4G speed tests, the fastest was recorded in Singapore at up to 46.6Mbps4. The US ranked much lower at 16.31Mbps according to the report. In fact, Verizon states their 4G LTE network ranges from 5 and 12Mbps with peak download speeds up to 50Mbps5.
5G promises to catapult 4G by 10x or up to 1,000+ Mbps coupled with extremely low latency. Early demonstrations by Nokia have shown that 5G can drop latencies down from 90-100ms to 1-3ms when moving from 4G to 5G technology6. The immediate use cases that can benefit from 5G are data-hungry applications that rely on real-time connections such as autonomous cars or machine learning. However, the impact of 5G’s technology will be felt much broader in scope by transforming our lives by delivering services much faster and more efficiently then we could ever imagine. Who will benefit the most from 5G? Smart Cities look to benefit the most from 5G. Initiatives have already started to build these smart cities that implement sensors throughout to monitor and manage transportation, public safety, public works, etc. Large metropolitan communities will benefit the most because of their large economies of scale.
Comba Telecom has been hard at work developing the technology that will deliver 5G to the masses from base station antennas, indoor DAS networks and smart cities. Apart from massive MIMO antenna, the Pre-5G DAS is also our latest 5G innovation. It provides high-performance indoor coverage for IoT and M2M communications. The pre-5G DAS supports advanced LTE as well as Massive MIMO technology thereby enabling convenient and smooth network upgrades in the future. Also, it provides coverage to both distribution points and hot spots and hence supports the IoT and locating features.
Smart Pole is one of our highlighted solutions to address the smart cities requirements along with 5G evolution. Comba’s Smart Pole helps accelerate the 5G rollout by integrating Wifi, mobile network connection, IoT sensors, ScanViS solution for CCTV surveillance, USB charging terminal, energy saving, and Smart cloud central management and control system into a single central location all the while concealing the infrastructure from the public. It is designed to make lighting infrastructure a much more aesthetic and smarter product for citizens, helping cities and municipalities that want to offer a multi-purpose street solution.
Comba is showcasing its 5G technology at this year’s Mobile World Congress Americas in Los Angeles, California, USA from September 12-14, 2018 in booth Hall West Stand W.1128.
1 “Cisco: Enterprises Are Leading The Internet of Things Innovation”, Huffpost, Vala Afshar, 2017, Aug 28, https://www.huffingtonpost.com/entry/cisco-enterprises-are-leading-the-internet-of-things_us_59a41fcee4b0a62d0987b0c6
2 “Verizon to test 5G in 11 cities”, CNN tech, Selena Larson, 2017, Feb 22, https://money.cnn.com/2017/02/22/technology/verizon-5g-testing/index.html
3 “AT&T Adds Three More U.S. Cities to 5G Plans as It Races Verizon”, Bloomberg, Scott Moritz, 2018, Jul 20, https://www.bloomberg.com/news/articles/2018-07-20/at-t-adds-three-more-u-s-cities-to-5g-plans-as-it-races-verizon
4 “The State of LTE”, Open Signal, 2018 Feb, https://opensignal.com/reports/2018/02/state-of-lte
5 “4G LTE speeds vs. your home network”, Verizon Wireless, 2013, May 9, https://www.verizonwireless.com/articles/4g-lte-speeds-vs-your-home-network/
6 “Nokia 5G Demonstration Video – 5G: driving the automation of everything”, Nokia uniteChannel, 2016, Sep, 22, https://youtu.be/ndkzlyjAn7g
Can’t have one without the other. Well, maybe you can, but you may fall out of grace with your AHJ. Both NFPA & IFC fire codes require system gain to be set 20dB lower than system isolation. Why is isolation so important? Ever look at the output of a BDA that begins to oscillate? It’s not pretty.
Have a look:
Let’s start by explaining what we mean by isolation. Practically all Public Safety in-building coverage enhancement systems require a Bi-Directional Amplifier (BDA), also defined by the FCC as a Signal Booster device. These devices amplify weak signals received from the repeater site and reradiate them indoors. The challenging part is that they reradiate the same frequencies as they receive. To give an analogy, have you ever sat in an auditorium and the person giving the speech walks too close to the monitor with the mic causing an awful squeal that gets louder and louder until he moves farther away, or the sound guy reduces gain on that mic channel? That kind of feedback can happen in a BDA system as well and is known as oscillation. If an in-building system lacks isolation, it will begin to oscillate, or feedback into itself. As it oscillates, the BDA will get “louder” and “louder” until it either protects itself by reducing gain, shutting down, or burns up. What I mean by louder here is that the amplitude of the RF signal being re-radiated continues to increase until the BDA amplifier is driven into saturation. An amplifier operating in this non-linear region will produce ugly intermodulation products and unwanted noise that can seriously degrade the Public Safety repeater site performance and even interfere with adjacent cellular systems.
Where did the value 20dB come from?
Previous Code only required 15dB greater isolation than Gain. Changes to the 2016 NFPA 1221 code increased that value to 20dB. So why the change? Depending on the manufacturer and technology used, some BDAs can exhibit stable operation with only 10 or 15 dB less gain than isolation. It’s what we can’t control that may have lead code writers to revisit this value. For example, let’s say an office environment uses aluminum blinds that just happened to be closed during the AHJ walk-around testing and the system passes. Now the building becomes occupied and the new tenants open the blinds and in this 4-story L-shaped building we now have line-of-sight between in-building antenna and Donor antenna on building rooftop.
Let’s assume that we have lost 10dB isolation with the blinds open and the BDA automatically reduces its’ gain to avoid oscillation. If gain gets reduced, then it’s likely that your system will no longer comply with code. This reduction in coverage may go undetected until the next scheduled system test, or worse, during an actual life-threatening incident. Increasing the isolation requirement adds more margin to help absorb some of the changing RF environment factors that are difficult to emulate during AHJ testing. This is just one basic example of how isolation can be affected by something so seemingly trivial. Other scenarios affecting isolation could be: shipping dock doors opened, using donor antennas that lack sufficient directionality, poorly assembled/connectorized cables near the BDA or donor antenna, the use of multiple BDAs looping back on each other, reflective surfaces, ducting from vents, and possibly the most common is lack of RF attenuation between the donor antenna on the roof and indoor antennas one floor below.
Since many modern BDAs incorporate circuitry that helps prevent the ugly by-products resulting from oscillation, why worry about isolation at all? Unfortunately, It’s nearly impossible to predict how much isolation a system will achieve until it is installed. During the design phase we tend to design using a BDA’s maximum gain and maximum power values. However, a word of caution, with many BDAs on the market spec’d at 90 or 95 dB of gain, especially in the 700/800 MHz bands, achieving isolation of 110 to 115dB may prove challenging.
Let’s highlight the importance of isolation using actual numbers. Consider the case where a field tech measured the 800 MHz control channel at the rooftop during a site survey and determined that the RSSI into the BDA will be -65dBm. You, as the system designer, determine that a 20-channel simulcast system results in a 20dBm output power per channel level, this assumes the use of a 2W BDA (10*log(20 Ch’ls) – 33dBm = 20dBm). Therefore, the actual gain needed in order to reach the per-channel power is 85dB (20dBm-(-65dBm)=85dB). You submitted your design based on 20dBm per channel and you learn that you’ve been awarded the project. A short time later installation is completed and now it’s your turn to shine. You arrive at the site to optimize the system. You proceed to commission the system using Comba’s cool built-in system isolation measurement feature and the software displays 90dB of isolation. According to code, the gain must be set to 20dB less than isolation. In this case, your max gain can only be set to 70dB. If we add 70dB of gain to our -65dBm input signal, our output is only +5dBm, or 15dB less than our original design parameter. So now you’re in panic mode knowing you’ll never achieve necessary coverage at this level. What gives? Is there something wrong with the BDA? Or is it simply isolation issue? You can easily confirm isolation by shutting off the BDA, disconnecting the donor and DAS cables from BDA and perform your own test by injecting signal from Signal generator into either the donor or passive DAS systems and monitoring the other side with spectrum analyzer. Sure enough, you’ve confirmed the accuracy of Comba’s built-in signal generator feature to be spot-on and next step is to resolve isolation issue.
Start by using the same signal generator & analyzer configuration and methodically disconnect each floor until isolation improves. Once you’ve determined which floor(s) are causing the problem, you may be able to narrow down to a specific antenna. Adding an attenuator pad to an antenna or entire branch circuit may get isolation back to where it needs to be.
Bear in mind that while adding attenuation may fix isolation issues, degraded coverage might become collateral damage. Furthermore, if a Class A BDA is being used, Time Delay Interference (TDI) issues may surface when indoor signals no longer dominate donor signals.
If you suspect your application may have isolation issues, you might try the following:
1. Use a high isolation donor antenna. Even though your donor site may be close and antenna gain is not needed, the use of a highly directional antenna, and thus high gain, offers the benefit of narrow beamwidth. Narrow beamwidth means more signal is directed away from the building rather than leaked into the building. The improvement in beamwidth alone may afford us 10-20dB more isolation and hence 10-20dB more gain.
Another bonus is the antenna gain. Inherently, high isolation antennas have more gain due in part to the more focused beam. In the example above, our RSSI was measured to be -65dBm. At this input level we determined that 85dB of gain is needed to reach max power-per-channel of 20dBm However, we could only achieve 70dB gain due to insufficient isolation. Using this same example, if we swap the donor antenna with a high isolation antenna having 10 dB more gain, the new RSSI into BDA becomes -55dBm. With -55dBm input, we now only require 75dB of gain to hit target output of 20dBm/channel. Reducing BDA gain means less isolation is required. Our new isolation requirement of 95dB (75dB gain + 20dB margin= 95dB target isolation) is 5dB over the previously measured value of 90dB. But wait. Once you’ve swapped the donor antenna for the high isolation antenna, re-run the isolation test and you’ll likely find that your isolation increased by 10-20dB. The resulting increased isolation combined with the need for lower gain may completely erase the isolation issue. There are true benefits to using high isolation antennas, however one tradeoff is cost. These high isolation antennas can be 5 to 10 times the cost of the more common 7-10dBi yagi antenna.
2. If coverage is required throughout the top floors near the donor antenna location, then try designing using more antennas at lower power. More antennas mean more passive loss which ultimately improves isolation.
3. As a last resort, try relocating the Donor Antenna to create more physical separation between the offending indoor antenna and Donor Antenna. If a maintenance or mechanical room exists on the rooftop, try mounting the Donor Antenna to facility walls in a manner that would increase isolation.
In summary, if you can’t meet the gain reflected in your link budget, suspect lack of isolation as the culprit. Better yet, if you suspect up front that your application may be a good candidate for isolation problems, bite the bullet and design in that high isolation antenna and add a few more antennas to those top floors. A few extra dollars spent on the front end may save you even more on the tail end.
…and if you’re in a pinch, call Comba. Public Safety in-building system solutions is what we do.
Downloads: Gain vs. Isolation
Well, for starters, many municipalities have--or are in the process of adopting--code requiring reliable in-building Public Safety communications, which oftentimes calls for the use of a Bi-directional Amplifier (BDA). A BDA is designed to boost/amplify weak off-air signals and re-radiate them in-doors. While these devices work well at enhancing in-building coverage, they also amplify noise. Some regions of the US are experiencing explosive growth in BDA implementations, and consequently AHJ’s are forced to engage and protect their countywide systems from degradation resulting from BDA generated noise.
In this article we focus specifically on the Uplink path. The downlink path generally has sufficient Signal-to-Noise ratio to ensure quality communications between Public Safety Base and Portables. There are, however, some cases where downlink noise may have a similar desensing effect in applications where both commercial and Public Safety DAS coexist. A discussion of this issue and how to mitigate can be found in the “The Mechanics of Colocation Filters” tech brief article published April 2018 on the Comba Website.
Here’s why AHJs are becoming hyperaware of the impact BDA’s have on their donor noise floor. Let’s start by defining how site noise floor fits into the bigger picture. Site noise can vary depending on the ambient RF environment. For example, in a rural setting where the only antenna on the tower is the Public Safety base station antenna, it’s possible that the receive sensitivity of the site could approach the thermal noise floor (kTB) plus some Noise Figure (NF) value applicable to the receiver equipment used. Let’s consider the kTB noise power of a 12.5 KHz channel to be -133dBm, which is the absolute theoretical best noise floor that can exist for that bandwidth signal. And then apply a NF of 6dB that represents noise added by the receiver equipment. Now we have a new noise floor of -127dBm (-133dBm + 6dB = -127dBm). A minimum signal strength from a distance portable or mobile should be at least 17dB above this noise floor, also known as the Signal-to-Noise Ratio (SNR). A SNR of 17dB generally results in a Delivered Audio Quality (DAQ) of 3.0; a minimum design parameter used in national codes and many local codes as it relates to Emergency Responder Radio Coverage Systems (ERRCS).
Consider the hypothetical example where a mobile radio 20 miles from the Donor Site was communicating just fine with a signal level of -110dBm (17dB SNR) into the donor site, or at least until a new BDA installation approximately 2 miles from the donor site raised the noise floor by 6dB. This 6dB rise in noise will deteriorate the mobile’s SNR down to 11dB, and consequently, clear intelligible communications between the mobile and donor site no longer exists. The mobile must reduce its path loss by 6dB to recover from the degradation induced by the BDA. If you’ve ever calculated a link budget then you know that free-space power loss is inversely proportional to the square of the distance, meaning that the mobile radio must move to a distance within 10 miles of the donor site to reestablish a SNR of 17dB and DAQ of 3.0. In short, all those First Responders operating in the radius zone between 10 miles out to 20 miles will have their communications either mildly, or in some cases severely, affected by a single BDA that was improperly installed.
Noise in the Real World
In the example above, we used a rural setting with an ideal noise floor which rarely exists. Now it’s time to get real.
Most Public Safety in-building code requires a minimum signal level of -95dBm into the donor site’s receiver frontend and an SNR of 17dBm minimum. A 17dB SNR would suggest a site noise floor of -112dBm. This -112dBm noise floor value does in fact align closely with “real world” site noise levels prevalent in RF congested urban environments.
Matching Site Noise
Let’s examine a case where a Class B (broadband) BDA is commissioned to match the Donor site noise floor of -112dBm. Did you know that tweaking the BDA gain to match the site noise floor will actually raise the site noise by 3dB? In the following graphic we show BDA#1 noise has been adjusted to match the -112dBm site noise floor and consequently we see a noise rise of 3dB at the site. A portable trying to communicate over a voice channel some distance away will experience a 3dB hit to its SNR, reducing a once acceptable 17dB SNR down to 14dBm. Now let’s look at the impact that 16 Class B BDAs have on site noise if all were optimized to match initial noise floor value of -112dBm. Every time we double the number of BDAs, we also double the noise contribution. Consequently, in this example, 16 BDAs will have a seriously detrimental effect on site performance. As more and more BDA’s are installed within the vicinity of the Donor site, it becomes very clear why AHJs are getting involved and holding system integrators to a higher standard.
Going 15dB Better
The following is an actual scenario where the AHJ must review and approve your link budget before turning up BDA. In this region of the US, code requires that noise generated by the BDA must be attenuated to 15dB below site noise floor of -115dBm. To comply, the commissioning engineer will work with the AHJ to ensure no degradation occurs at the donor site once the BDA is turned on. Since it is not possible to measure noise levels below site noise floor, the AHJ will expect BDA gain and power settings to closely match theoretical values submitted with link budget.
Why is it so important that BDA noise is 15dB below site noise? Simple. In-band Noise is additive as shown in the graphic above. If 16 BDAs (Class B) where installed at various distances from a Donor Site and all sites were perfectly optimized such that their noise levels arriving at the Donor Site were adjusted down to -130dBm, then the composite noise contribution from all 16 BDAs is actually -118dBm (10*log(16 BDAs)+(-130dBm)=-118dBm). This still seems acceptable right? After all, we are still 3 dB below the donor site noise floor. Now consider the case where we have 30, or 40, or 80 BDA’s? Is it conceivable that a Donor Site will serve 80 BDAs? The answer is yes. It’s happening now, and the number of BDA implementations will continue to rise because of code mandates.
Let’s use an actual scenario from a large metro area system and run the math for 80 BDAs: 10*LOG(80 BDAs) = 19dB. If we add the 19dB of composite noise contribution from 80 BDAs to the -130dBm noise floor that each individual BDAs was setup for, then we get -130dBm +19dB = -111dBm, which will certainly get the AHJ’s attention as their site Noise Floor has now increased by 4dB. As previously stated, any impact to the donor site noise floor will adversely affect its greater coverage area.
Class A or Class B?
Which Class of BDA has the least impact on the Donor Site noise floor? The answer is a resounding “Class A” and here’s why. Most Class A BDAs on the market today utilize digital technology with sharp filters designed to pass only desired frequencies. One benefit Class A offers in addition to sharp filter characteristics is that they generally have a squelch threshold where the channel remains quiet until a sufficiently strong signal is detected. Conversely, in a broadband device, such as Class B BDA, all frequencies within a set passband are transmitted continuously. What this means is that the Class B BDA is amplifying and transmitting noise continuously.
Let’s run through a simplified link budget to compare and understand this point.
· Distance from Donor Site to Serving Site = 2 miles.
· Total path loss between sites including antenna gains and cable losses = 90dB
· Donor Site Noise Floor as stipulated by local AHJ code: -115dBm/12.5KHz
· Serving Site Noise Floor as stipulated by local AHJ code: -115dBm/12.5KHz
Class B – Uplink Link budget
-115dBm Serving Site noise floor @ 12.5KHz bandwidth (taken from code)
+90dBm BDA set at full gain
+ 5dB BDA Noise Figure
-90dBm Total Path loss
-110dBm Noise Floor arriving at input of Donor site receive equipment
-(-130dBm) Noise Floor required by Code (15dB lower than Donor Site noise floor)
20dB Amount of additional noise suppression needed to comply with code
Class A – Uplink Link budget
-115dBm Serving Site noise floor @ 12.5KHz bandwidth
+60dBm* BDA set to 90dB gain and no traffic. Channel is squelched.
+ 5dB BDA Noise Figure
-90dBm Total Path loss
-133dBm Noise Floor arriving at input of Donor site receive equipment: -115+60+5-90= -140dBm, however this level is below the theoretical best and therefore we default to -133dBm value for 12.5KHz
-(-130dBm) Noise Floor required by Code (15dB lower than Donor Site noise floor)
0dB Amount of additional noise suppression needed to comply with code.
*Even though a channel might be squelched, some noise is created by the DSP process and amplified by the uplink wideband Power Amplifier of BDA. A Class A device produces 20-40dB less in-band noise than a Class B device. In this example we use 30dB as the noise improvement over Class B
One caveat regarding the above calculation is that FCC allows up to 75KHz window filters for Class A devices. Depending on the bandwidth of the channel filter and how sharp it’s roll-off, some noise rise may occur at adjacent channels.
Resounding Just Got Better
While there is no argument that Class A devices are the better choice for throttling back in-band noise, is it enough? In the example above, we demonstrated how the Class A device generates approximately 30dB less noise than the Class B device. Wouldn’t it be ideal if during that 99% of the time when a BDA sits idle waiting to serve our First Responders, that it generate no noise whatsoever, ZERO NOISE?
In true innovative character, Comba has recently added several improvements to our CriticalPoint™ Public Safety product line, to include this ideal ZERO NOISE quieting feature. Contact your local Sales Manager or Comba USA in Milpitas CA for more details on this feature and many others.
Downloads: Whats the Fuss About Uplink Noise
Our article on CBRS was recently featured on Connected Real Estates latest fourth edition of their magazine. For those of you that missed the chance to read this from our partner, we have added this below.
Perhaps the biggest news in the wireless industry going as it pertains to commercial real estate is CBRS. C.B.R.S.—if you’re in the wireless industry in any capacity, you have probably heard those four initials mentioned one time or another. But, you might not know exactly what is, how it works, why it’s important, or all of the above. This overview is to answer those questions and more about this service that will soon transform the wireless game for property owners.
WHAT EXACTLY IS CBRS?
CBRS stands for Citizens Broadband Radio Service. The Federal Communications Commission established CBRS as a way for shared wireless broadband use of the 3550- 3700 MHz band, which is more commonly known as the 3.5 GHz band.
HOW WILL CBRS WORK?
CBRS is a Time Division Duplex (TDD) band that only LTE is allowed to use. The radio interface mimics the one that’s used when LTE is deployed at other frequencies. The CBRS frequency allocation will span LTE Band 42 and LTE Band 43.
WHAT MAKES A CBRS ROLLOUT SO SIGNIFICANT?
Access to CBRS will allow commercial property managers to deploy their own private LTE networks with a combination of unlicensed, shared and licensed spectrum. With CBRS, a building owner can give their tenants or customers, depending on the venue, LTE coverage for their devices without paying traditional carriers to do so. More simply put, when the 3.5 GHz band is opened, more devices will be able to come online with better coverage and capacity. This will work wonders for venue owners who have either struggled to meet the coverage or capacity demands within their building, but also for those who have a desire to implement Internet of Things (IoT) devices. As the number of mobile devices increases, it is imperative venue owners can keep up with the times, and adding a CBRS network is a giant step in the right direction.
HOW WILL CBRS BE STRUCTURED?
Part of CBRS’ infrastructure is built through the Spectrum Access System (SAS). This system makes the three-tiered spectrum-sharing framework the FCC adopted for CBRS a possibility.
The three tiers of CBRS spectrum use are:
• Incumbent—for existing users like Department of Defense personnel and US Naval Radar, incumbents get permanent priority and site-specific protection for registered sites.
• Priority Access License (PAL)—for organizations that pay a fee for use. Organizations can request up to four PAL’s for three years in a limited geographic area. Only the lower 100 MHz of the band is for sale.
• General Authorized Access—the remainder of the spectrum, open for general use.
SAS is a coordinator within the CBRS 3.5 GHz band and works to shield the higher-tier users from lower tier users and optimizes efficient use of the available spectrum in the band for all users. The system also has a record of all CBRS radio base stations with information such as the stations’ tier status, location and whatever other details needed to coordinate frequency, transmit power assignments and keep an eye and protect the band from interference. Currently at least 80 MHz of the 150 MHz spectrum must be available for GAA use, according to FCC rules. Exceptions can be made if no Incumbents are present. Sometimes all of the 150 MHz could be available if neither Incumbents nor Priority Access Users are in the area.
WHAT WILL CBRS DO FOR BUSINESSES?
CBRS will be beneficial for several different business models. Currently, if a building owner wants to have LTE in their venue, they are beholden to a wireless carrier. Any data that their network picks up goes to the carrier, with a private LTE network however, that sensitive data stays in-house and retain it for a much lower cost than paying a carrier. With CBRS, businesses, building owners even cities would have more flexibility with the technology they could use. A lot of Internet of Things (IoT) devices work better through LTE than they do on Wi-Fi, but Wi-Fi is a less expensive option, so users either go with less than stellar coverage or without IoT devices in their venue. As CBRS becomes available however, those same building owners, city officials and business owners could have security cameras around their premises or on their streets that operate on their private networks. When it comes to who could benefit from CBRS access, the possibilities are endless.
HOW DOES CBRS COMPARE TO WI-FI?
CBRS is expected to be an improvement on Wi-Fi on a couple of different fronts. First, CBRS will be a private LTE network, where Wi-Fi is an unlicensed system. Almost everyone uses Wi-Fi, which means the spectrum is usually congested and numerous devices are competing with interfering with each other. Wi-Fi also isn’t always the most secure service, which can be a concern for any business where it’s crucial to keep customers’ information and data private. Meanwhile, CBRS will give enterprises and venue owners to buy their own protected spectrum for significantly less money than it would have cost before. CBRS will not only be a cost saving tool for building owners, but it’s expected to improve connectivity to the point it could replace Wi-Fi. From a speed perspective, LTE services could reach 1Gbps inside and approximately be 5 to 10 times faster than that outdoors. Lastly, CBRS will allot building owners more opportunities to use Internet of Things (IoT) devices that they might not have been able to, at least not as effectively, with Wi-Fi. Security cameras and central door locking systems are a couple of things building owners might find worker better over an LTE network as opposed to Wi-Fi, and it won’t be as expensive to have. Not only will devices like this be more effective on an LTE network, but also more secure. Wi-Fi networks are unencrypted, which would make it easier for a cyber thief to get into any of your systems that you’re running through it. CBRS however uses TD-LTE modulation with a sophisticated encryption for data transmission. Think about the IoT devices you use in your building. Now think about the data transmitted from them over Wi-Fi; wouldn’t it be reassuring knowing that information being moved on an encrypted network? That’s what will give CBRS an edge over Wi-Fi.
HOW MUCH WILL CBRS COST?
There are several aspects of CBRS that will make it appealing to building owners, but perhaps the most appealing is the installation costs. Any enterprise or building owner who uses a Wi-Fi network now, can expect a similar cost if they deployed CBRS. The difference being they’ll have a private LTE network and be able to use IoT devices more effectively. There’s also savings in the fact that CBRS is a shared licensed band so the owner does not have pay a license fee to a mobile network operator. Instead, they’ll register with Spectrum Allocation Servers (SAS) and pay it a fee. Meanwhile while, Wi-Fi is free, it’s unlicensed, less secure, and it still costs money to deploy the system.
IS ANYONE WORKING WITH CBRS NOW?
Since the FCC has not made a decision about CBRS yet, no one is using the service in an official capacity yet. However, some companies are working with “pre-CBRS” equipment; technology that could be deployed and ready to use once CBRS is officially out in the market. Although CBRS has been a hot topic more so among the wireless telecommunications industry, cable providers have expressed a lot of interest recently, too. Comcast for example planned to run fixed and mobile wireless trials in Philadelphia earlier this year using spectrum in the 3650-3700 MHz band. Wave Wireless also requested an experimental Special Temporary Authorization (STA) from the FCC to conduct tests in the CBRS band for six months in a technology office space and a hotel in Washington, DC. Meanwhile, another cable operator interested in bringing wireless opted to try CBRS rather than dig and put in fiber because they figured fixed wireless, especially on the CBRS band would be able to help in terms of connectivity. Plus original equipment manufacturers like Comba Telecom are interested this spectrum and are actively looking out for how they can provide solutions for their customers. In other words, if companies all over the telecommunications industry are getting equipment ready for CBRS or are requesting trials despite no ruling from the FCC yet, you can bet that it’s likely to happen and businesses trust it’s going to work.
OK, SO WHAT DOES THIS ALL MEAN?
For starters, it means that CBRS is most likely going to be at our doorsteps very soon. When it does arrive, it’s best to be prepared because there is so much to be gained from having access to a private LTE network from cost savings, better coverage, technological advancements and options for increasing revenue streams. For the first time in a long time, building and business owners won’t have to as reliant on mobile operators for data and wireless services.
Downloads: Understanding CBRS
With Explosive Growth in Wireless Devices, Quality of In-Building Connectivity is Critical for Retention and Desirability
In the ultra-competitive realm of Commercial Real Estate (CRE) building owners and managers must offer the latest technology to keep their existing tenants happy and lure new ones. With an estimated 50 billion wireless devices coming online by 2020, CRE brokers will have to ensure that the in-building wireless connectivity they offer for their properties provides the highest quality of service to keep their clients happy and maintain the highest possible rate of retention.
However, there are two technology choices that offer in-building connectivity, Wi-Fi and distributed antenna systems (DAS) and CRE brokers need to know how each one potentially serves in-building connectivity before they make a decision on how to best fulfill their clients’ in-building coverage needs. For example, if Wi-Fi is chosen at the expense of DAS, tenants may not be happy with the limited services they receive on their device and decide not to renew their lease.
Wi-Fi has been around since the early 2000’s, i.e. 802.11g (2003), and has easily become the most recognized solution for wireless connectivity. This is why Wi-Fi is often the solution CRE professionals go to as the solution to offer. However, often times Wi-Fi bandwidth can become constrained when too many users connect to a network resulting in a negative customer experience. While Wi-Fi offers a cost-effective way to connect tenants and customers to the internet, it does have its drawbacks.
Adding a Distributed Antenna Systems (DAS) can offer a solution to augment Wi-Fi traffic and increase capacity. This will help alleviate coverage problems and keep tenants and customers happy. Although Wi-Fi calling is an emerging capability in high demand, it is also important to note that not every client has access to this feature. For example, certain operators only allow Wi-Fi calling on devices that are purchased from them – BYOD subscribers won’t get Wi-Fi calling and in some case, they won’t able to utilize a competitive capability known as Voice over LTE (VoLTE).
DAS is a network of small antennas installed in a building, and powered by an amplification system, utilizing either a Bi-directional Amplifier (BDA) and/or Active Fiber system that relays cellular signals from either a rooftop donor antenna or from a base station that is installed by the operator on the premises. The operator then retransmits the signals throughout the building to provide optimal wireless coverage. DAS has been around for many years, but has only become more prevalent recently because of technology exposure as hardware and installation costs have dropped substantially.
How can a DAS solution help to provide both capacity and coverage to an existing Wi-Fi and what advantages does it have over Wi-Fi?
Today virtually everyone uses a smartphone – all smartphones are Wi-Fi capable (and so are tablets.) A user’s device can access the internet, through the Wi-Fi system, which is ultimately connected to the internet through the building’s internet service. However, Wi-Fi Access Points (APs) each have their own “radios”, and have a capability known as “channel hopping” to find the highest data throughput. These two attributes can often create interference and loss of connection issues that occur within the Wi-Fi network. These issues occur specifically within the interior of the building and don’t involve the building internet connection.
So how can DAS provide assistance? Today, the wireless operator networks provide very high data throughput speeds; the advent of “4G” and now LTE has improved operator networks such that the data speeds can oftentimes be even better than the speeds obtained over Wi-Fi/broadband internet connections. And since the small DAS antennas are “passive” devices, there is little to no chance of any type of interference between those antennas. In addition, the wireless operators spend a great amount of time and money to ensure that all subscribers can have access to the internet (capacity) through their network, and that a high level of service quality (data throughput) is delivered.
As one can see, then – a DAS to support cellular can provide very robust, sometimes even better, high speed internet connectivity.
(And another fact to know: due to the architecture of a DAS system, a DAS antenna has significantly greater coverage area than Wi-Fi APs – typically, there are only 1/3 to 1/2 as many DAS antennas as Wi-Fi APs required for the same size coverage area).
As was mentioned earlier, some subscribers can utilize Wi-Fi calling – if they can. And some can utilize VoLTE – if they can. If neither of these are options – then the only assurance to quality voice calls is over the wireless network. And this may not be possible without a DAS.
Another important note – if a subscriber made a 911 or other urgent/emergency call and they have noWi-Fi or VoLTE capability (or the Wi-Fi network is not working) – their emergency call then must be made over the cellular network. And, if there is no cellular coverage in the building (meaning no DAS) – then their emergency call will not go through.
Security is a high priority for everyone. Wi-Fi has some potential security vulnerabilities. A recent report found that “All Wi-Fi networks' are vulnerable to hacking, security expert discovers.”1 Security is at the heart of all businesses and it’s in the best interest of the CRE professional to ensure any system they offer has a robust security protocol. Although a DAS doesn’t provide security itself, the network operator that the DAS is connected to will deploy data encryption and a dedicated pipeline, rather than a shared resource where data can be compromised.
Operators are always looking to keep their network Quality of Service (QoS) at optimal levels. Interference can cause a big problems with keeping calls and internet traffic flowing. Operator network engineers are always keeping an eye on their territories to ensure their QoS meets their company’s strict standards. If any interference is detected they are quick to identify and mitigate the interference. This extends to the DAS signals as well, ensuring high-quality signals within the building. Wi-Fi on the other hand has been notoriously vulnerable to interference, especially in multi-tenant buildings.
Wi-Fi will continue to be a staple of CRE offerings, but DAS is quickly becoming attractive, as it’s been recently referred to as the 4th utility to keep tenants connected and happy. The cost of owning and installing a DAS system has come down in recent years with total cost of ownership, running as low as $0.50/sq ft. For these reasons, DAS installations should become more prevalent in commercial buildings to offer customers a better wireless online experience than Wi-Fi alone.
There are several reasons why combining Public Safety and Commercial (Cellular) active DAS may not be the best choice, as discussed in my Jan 2018 Tech Brief on “Why Public Safety Convergence is History”. However, in certain applications, a common passive DAS might be a practical and cost-effective choice. Colocations filters are a must for combined passive DAS solutions, but before you venture down that road be sure to check with your Authority Having Jurisdiction (AHJ) for confirmation on whether code will allow shared passive DAS.
Before jumping into the mechanics of how to use colocation filters, let’s first discuss why we need them. As the name implies, these filters are used when a Public Safety and Commercial in-building DAS systems are to be collocated within the same building. Whether on separate DAS or combined, some level of additional filtering is usually required to avoid interference between the two. An exception might be in cases where approximately 60dB or more isolation can be maintained between the DAS’. This may prove challenging to find sufficient real estate where placement of indoor antennas from separate DAS are not line-of-sight of each other. Depending on the gain of the antennas and openness of the environment, this may mean spacing antennas >100 ft.
The two bands of concern are Verizon’s 700 MHz upper C-block (uplink band 776-787 MHz) and 850 MHz cellular band (uplink 817-849 MHz). In both cases, uplink communications into the cellular remote units can be desensed by the Public Safety in-building system when sharing a common passive DAS, or in separated DAS that lack sufficient isolation.
Two types of colocation filters are required: a wideband noise reject filter, and a strong carrier signal reject filter. The “wideband noise” filter attenuates out-of-band noise, which is inherent with all amplifications devices. Wideband noise must be attenuated at the output of the Public Safety device, whether it be a BDA or a Public Safety fiber remote unit. Refer to “Filter A” in Figure 1. for placement of wideband noise reject filter. Once the noise reaches the commercial DAS, it is considered in-band and can no longer be attenuated without also attenuating desired cellular channels.
The “strong carrier” filter is placed in-line with each commercial fiber remote and is designed to reject the out-of-band strong carriers generated by the downlink of the Public Safety BDA or Public Safety fiber remote. Refer to “Filter B” in Figure 1. for placement of the strong carrier reject filter.
Now that we’ve touched on why we need these filters, let’s discuss the impact they will have on your DAS design. Each filter introduces loss into the system and loss effects coverage. Typical losses are around 1-2dB at the upper bands >1GHz, and 4-5dB at the lower bands. The good news is that most commercial DAS designs are modeled around coverage at the PCS and AWS bands where cable losses and propagation characteristics are more limiting than the lower bands. Consequently, the lower bands generally have plenty of margin to absorb 4-5dB of attenuation introduced by these filters, assuming equal output power at all bands.
Word of Caution: Some suppliers of cellular DAS product recognized the advantage of this coverage disparity between upper and lower bands and have addressed this by packaging lower power amplifiers for lower bands and higher power amplifiers for upper bands into their fiber remotes. It’s safe to state that in a shared DAS, 700MHz and 850MHz amplifiers with output powers up to 6dB lower than the upper PCS/AWS bands will still produce favorable results. This statement may not apply in all scenarios, so I encourage scrutinizing link budgets closely before designing a shared DAS using fiber remotes with unequal output powers.
The following example assumes all cellular fiber remotes have equal output power per band.
Figure 1 below is a system block diagram showing the placement of colocation filters for a shared passive DAS system. The diagram depicts the actual configuration used in the iBwave design, which was used to generate the heatmaps which are also included.
The following design parameters were used to model the system and visualize the coverage impact resulting from the addition of colocation filters.
· 12 Story building
· Each floor 30K square feet
· Total square footage 360K
· High Density RF environment
· 24 Channels @ 800 MHz Public Safety band
· 2 Channels @ 700 MHz LTE band
· 3 Channels @ 2100 MHz LTE band
· 5 Watt cellular remote units
· Each cellular remote serves 4 floors for a total of 120K square feet of coverage per remote
· 1 each, 2 Watt 800 MHz Public Safety BDA serving entire building.
All floorplans in the example building are considered to have same layout and propagation characteristics. For this reason, the following heatmaps apply to the same floor.
Let’s start by showing the AWS, 2100 MHz LTE heatmaps, which as mentioned above, is one of the upper bands that limits coverage and typically dictates the overall design layout. The first AWS heatmap shows LTE coverage using 6 antennas with no colocation filter and no Public Safety services added:
Notice in the legend that at least 96.5% of floor meets the -95dBm RSRP design criterion. Design requirements may vary between operators and regions.
Now let’s add colocation Filter B into the link budget.
Adding 1dB plus jumper losses reduces coverage to 89.7%. Not bad, but some reconfiguration of design may be required for operator approval.
Now let’s add the 10dB directional coupler to the link budget which is necessary to complete the shared DAS design. Refer to the “10dB DC” red component in Figure 1, placed directly after Filter B. A 10dB coupler was selected to minimize the impact on the commercial DAS while meeting coverage requirement for Public Safety system as dictated by AHJ. System Designers often select 3dB hybrid devices for combining Public Safety and Cellular DAS. While this is an acceptable design approach, the results might leave you with an over-designed Public Safety system and call for more cellular remotes than otherwise necessary. In this example, the use of a 10dB Directional Coupler offers the best balance.
The additional losses from the filter + 10dB directional coupler + RF jumper cables results in coverage degradation to 75%. At this level of degradation, a forth fiber remote unit will be required to meet the 95% coverage at -95dBm RSRP.
YOU CAN STOP READING NOW: We have reach the focal point of this article: A shared DAS will require colocation filters; filters do add loss, loss adversely affects coverage. A shared passive DAS will add cost, but that additional cost may still be lower and esthetically more desirable than implementing a separate passive DAS.
AHJ’s arounds the country are adopting and enforcing local and National building codes which require proof of coverage for our First Responders in new construction, and in some cases existing buildings. Cellular inbuilding coverage is viewed as a forth utility, consequently collocation of Public Safety and Commercial DAS is on the rise. Don’t forget the colocation filters.
STILL A SKEPTIC? READ ON: If you’re curious about the impact on 700 LTE commercial service and Public Safety due to the high insertion losses from the colocation filters, the following heatmaps should provide the confirmation you’re looking for.
Using the same progression of heatmaps shown for the AWS band above, let’s see what happens to the 700 MHz coverage as we add the filter, RF jumpers and Public Safety injection point. The first heatmap below shows normal 700 MHz coverage, i.e., no filter, RF jumper, or 10dB directional coupler losses. The system is considered a “hot” system, as is expected when designing for AWS coverage and amplifier output powers are similar. In fact, we still have 99.1% coverage even at -80dBm. This would suggest that we have at least a 15dB margin to work with when adding filters losses.
In this next heatmap, we add the filter and one extra RF jumper. Recall that in the lower bands the colocation filter loss increases to 4dB. Notice the 99.1% coverage at -80dBm went down to 91.9%. So, while we see some impact from the filter, we still have considerable margin before our reference signal dips down to -95dBm.
We mentioned previously that the 10dB directional coupler was the best ratio to balance impact on the commercial services system, yet low enough loss to ensure that the Public Safety system still met AHJ’s coverage requirements. The next heatmap adds 0.8dB loss introduced by the directional coupler and loss from one more RF jumper cable. The -80dBm coverage threshold goes down to 57.1%, however, we are still around 99.5% coverage at -85dBm, which is well above our minimum design threshold of -95dBm RSRP.
Now for the real test. What about the 800 MHz Public Safety system that is subjected to the 10dB coupling loss? As mentioned previously, the 10dB directional coupler was the best ratio to minimize impact on commercial services, yet low enough loss to ensure that the Public Safety system still met AHJ’s coverage requirements. The next heatmap includes the 10dB loss introduced by the directional coupler, plus the Public Safety “wideband noise” Filter A, plus the RF jumpers.
AHJ’s have widely adopted threshold -95dBm over 95% of the coverage area as acceptable for Public Safety in-building systems. The following heatmap show 98.3% coverage at 95dBm, which passes most NFPA/IFC code as well as local ordinances and AHJ mandates.
Here’s the take-away: A 2W Public Safety BDA subjected to 4dB of wideband filter attenuation, and 10dB of directional coupler attenuation, and 5dB of splitter loss, can still provide comparable coverage to a commercial services DAS configured with three 5W fiber remotes.
One caveat: Not all applications are cookie-cutter, 12-story buildings like what is represented in this example. Results can vary drastically depending on propagation characteristics of the building and physical layout.
· • Don’t shy away from sharing the passive portion of a commercial DAS with a Public Safety coverage system if local codes allow for it.
· • Colocation filters will be increasingly important going forward. Know when and where to use them effectively.
· • 10dB Directional Couplers for use as Public Safety injection point are generally better that 3dB Hybrid devices.
· • If contemplating the use of commercial fiber remotes with un-equal output powers confirm lower bands can tolerate the extra losses induced by colocation filter and attenuation.
· • 2W power rating for Public Safety BDA’s and fiber remotes is a wise choice when colocations filters are to be used. Colocation filters can add $1500-$2000 per locations. Lower power alternatives will require more filters.
· • The benefit of combining commercial and public safety passive DAS system can be a practical and cost-effective choice to separate systems.
Comba offers Public Safety Fiber DAS product for larger applications where the BDA can no longer provide reliable communications. If you have questions regarding whether a shared passive DAS is right for your application, Comba’s engineering team would love to hear from you. Let’s talk.
Downloads: The Mechanics of Colocations Filters