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Nextivity Cel-Fi QUATRA 4000 Fiber HUB Introduction

Oct 02, 2020

A new accessory now available for use with Cel-Fi QUATRA 4000 and 4000i systems is called Cel-Fi QUATRA 4000 Fiber HUB.

Review features and configuration options for Cel-Fi QUATRA 4000 with the Fiber HUB.

Addition of Fiber HUB to Nextivity QUATRA 4000 & 4000i:

Addition of Cel-Fi QUATRA 4000 Fiber HUB

Set-up of Fiber HUB with Nextivity QUATRA 4000 & 4000i:

Set-up Diagram of Fiber HUB with Nextivity QUATRA 4000 & 4000i

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Evolution of Nextivity's Cel-Fi to fiber connectivity.

Nextivity is a global company that make a number of solutions that provide coverage, specifically in-building coverage, but they are also focused on aspects like mobile coverage in vehicles as well. The headquarters are located in San Diego with offices in a number of places around the world.

Today, they do business in about 100 different countries with about 200 different operators across the world. They develop everything at their headquarters in San Diego, and all of the products are based on a custom chip that is developed at Nextivity.

That details all of their technology and all the signal processing that really sets them apart from most of their competitors. They also write all the software, develop the radios, do the product design, and at the end of the day, they tie all of this together with a number of cloud products and apps to make sure that the use of their product is as easy as possible.

Nextivity Product Range.

Cel-Fi has introduced the number of products over the last few years including Cel-Fi GO series. They have won a number of awards, especially for Cel-Fi QUATRA products. has experienced the difference that a QUATRA system can make to an in-building installation.

With Cel-Fi QUATRA 4000 Fiber Hub, it is only going to be better and more flexible to provide in-building coverage in buildings with no cell signal. Fiber Hub is an additional element in the QUATRA 4000 portfolio, and as the name says, it introduces ability to add fiber connectivity within a Cel-Fi QUATRA system.

What does the Fiber Hub do?

The Fiber Hub expands the network unit's capacity from 6 to 12 units on average. It is connected to the network unit using optical fiber. This means that the hub can  be installed up to two kilometers or about one and a quarter miles away from the Network Unit (NU). This allows it to have a lot of flexibility to cover larger spaces, to bring signals into areas where previously it wasn't even possible.

The QUATRA Evolution.

With the QUATRA 4000 evolution and the QUATRA 1000 evolution as well, Cel-Fi started off with a system that used Cat-5 cable to connect the Network Unit (NU) and the Coverage Unit (CU). You could go 100 meters between the NU and the CU.

Then Cel-Fi added QUATRA range extender which allowed us to go 200 meters between the NU and the CU. Recently, Cel-Fi has brought out an app note that showed that if you use higher quality cable like Cat-6 or Cat-7 cable, you can go 150 meters between an NU and a CU. Then if you add the QUATRA range extender to that, you can actually reach 300 meters between the NU and the CU.

That starts to give us quite a large footprint for these systems, but there are often cases where you want to go even farther between the NU and the CU - That is where the "Fiber Hub" comes in. Right now, you can extend that distance up to one and a quarter miles, plus the number of CUs that you can support has increased from 6 to 12.

How does the Fiber Hub actually work?

You can have the NU as you would normally have it with its donor sources either as off-air donor antennas, or it could be small cells as well that are driving the QUATRA 4000. Then from this QUATRA 4000 NU, you can still have your six local CUs, just like you would always have it. Each CU can either be connected to an antenna directly or drive a small passive DAS network to give you multiple antennas in every CU. This part of the picture really has remained unchanged from what it is with a standard QUATRA 4000.

Now with the Fiber Hub, though, we have got this extra option to string a fiber to a remote hub. Then this remote hub can also drive six CUs. Each one of these 6 CUs are stock standards CUs, just like you have them with the QUATRA 4000. Every CU can be connected to an antenna directly that can drive a small passive DAS system which is the basic architecture.

However, when you think about the QUATRA Fiber Hub, it basically looks just like an NU instead of getting the donor signals directly from a source like off air or from a small cell, all of those donor signals are combined over this fiber and sent to the hub. Then the hub uses those donor signals to drive the CUs.

Where can the QUATRA Fiber Hub be used?

The Cel-Fi QUATRA Fibre HUB can be used with any of existing QUATRA 4000 or 4000i devices. It is the same for both. The CUs that are used with the system are also the standard QUATRA 4000 CUs, so no change or anything needed for that. It is just a new element, single mode fiber, that gets introduced so that you can connect through the fiber.

Typical use cases - multi-building site.

There're a few concepts that we have that we think this hub would make a big difference. The first one is a multi-building site. Typically, in a site like this, it is really difficult to reach all of the buildings from a single point. This typically means that we would have to install network units in some of these remote buildings and, of course, if we installed a network unit, we either need to have roof access for a donor antenna, or we would need to bring a small cell to that building.

With the use of the Fiber Hub, that is no longer needed. We can locate our end use in the building where we have roof access for our donor antenna for example, and then we can locate the Fiber Hub in a remote building. Of course, now we don't need any roof access for our donor antennas anymore for that remote building.

There's a case study of a multi-site building like this where we used a number of Fiber Hubs to give coverage in all of the buildings.

Typical use cases - high-rise buildings.

The second concept that we have is for high-rise buildings. We have had QUATRA 4000 installed in a number of high-rise buildings. What sometimes happens is that from the location where we can have the NUs, for example, at the top of the building to the bottom of the building - That run exceeds the run length that we can get with a standard category cable.

However, with the use of the Fiber Hub, we can locate Fiber Hubs on lower floors in such an example that is beyond the normal category cable reach. Then from that location, we can then branch out with our CUs to where we need the coverage.

Typical use cases - remote locations.

The last application is remote location. So there're few examples of areas where we have a really remote location that needs to have coverage. However, the coverage and the distance from where the donor signal is available is just farther than what we can achieve over std. category cable. One example of such a remote location would be in mining applications.

We have a number of mines in USA where sulphide products are used to provide coverage down the shaft. In this case, it gives you the ability to reach farther. We have done some installs as well for data center applications, where the location where we can actually grab the signal is quite remote from where the actual coverage is needed deep inside the data center, which sometimes is underground or inside a mountain, etc.

Again, this is a great example of where we can really move that donor signal over a long distance using the Fiber Hub. Therefore, we put the NU in the location where we have coverage, and then we would put the CU or the hubs where we need the coverage. Then from there, we can distribute to a number of CUs.

Fiber Hub Specs.

Let us look at the details of the Fiber Hub. The model number Q40-1234FNU is the product that is available for order now and is shipping already. As we mentioned, the use of the Fiber Hub will double the number of CUs that we can have for NU.

Typically, what we could use is a single mode fiber to connect the NU and the hub, but we provide the option for us to install our own SAP+ module. That is not something that Nextivity sells; it is a standard off-the-shelf part, and depending on what SFP+ module we use, we can obviously go different distances.

Therefore, typically, we would use a single mode fiber, but if for some reason, we need to use multimode, we could do that as well in conjunction with Fiber HUB.

Product Overview.

The product basically looks just like a QUATRA 4000 or 4000i NU. One of the big differences of course, is that there's no donor ports on it because as we mentioned, the donor signal comes in through the fiber. But for the rest, it looks and feels just like a QUATRA 4000 NU. Of course, we need power to be brought to the hub location.

All of the CUs that are connected to the hub still get their power using POE, just like we would have in a normal QUATRA 4000 NU, but the hub itself needs to be powered. On the NUs, there's a port there for a SFP+ module. That is the place where we actually insert the SFP+ module, both on the NU side and the Hub side that will allow us to connect the fiber between the two. The LAN port that is on the device is unused in the case of the Fiber Hub.

The hub is integrated into Nextivity's wave portal system.

When we deploy a system and we have a NU, a HUB, and CUs, then we will actually see all of those elements on the wave portal. All of the communication, all 12 CUs that we would have in the system, are visible on the wave portal. That level of visibility includes the collection of all of the data that occurs inside of the HUB.

The HUB will send all of that information over the fiber link to the main NU. The main NU is then connected to the cloud, using either a LAN port or the built-in LTE modem. Therefore, the HUB itself doesn't have any connectivity other than the fiber link that we have to the main NU. That is why there's also no LTE antenna on the top of the system.

SFP+ transceivers.

The small form-factor pluggable (SFP+) is a compact, hot-pluggable network interface module used for both telecommunication and data communications applications. As we mentioned earlier, SFP+ transceivers are standard common off-the-shelf parts, and there's nothing special about them. We can really use any SFP+ module that we deem suitable.

Typically, we use a single mode fiber because the reach is so much longer than for a multi-mode fiber. But there's no specific limitation that we cannot use multi-mode if we wanted to use multi-mode fiber. Again, Nextivity does not supply these, they're available off the shelf, and we can either buy them ourselves or work with the distributors to source the modules as well as the fiber optic cable.

It is easy to install the SFP+ module. To push it in, the cable needs to be terminated correctly. We can buy pre-terminated cables that are off-the-shelf items that come from Nextivity, but we can source it from any supplier or manufacturer. It is simple just like we would plug in a Cat-5 cable or Cat-6 cable for the CUs, we just plug the SFP+ module in, plug in the cable, and we're ready to go.

Two examples of SFP+ modules that Nextivity has used in their lab and that they have tested: 6G CPRI Wireless, 15km SFP+ Optical Transceiver and 10gb/s 10km 1310 nm Single Mode Datacom SFP+ Optical Transceiver. These are by no means the only ones that we can use. The only requirement that we have on the SFP+ module is it has to support a minimum of six gigabit per second operation. The 6G CPRI Wireless, 15km SFP+ Optical Transceiver is a six gigahertz, six gigabit per second module, and you can see that you can reach 15 kilometers with this. The 10gb/s 10km 1310 nm Single Mode Datacom SFP+ Optical Transceiver is a 10 gigabit that can reach 10 kilometers.


Earlier we said that the range that we can go is two kilometers. Even though we can buy an SFP+ module that has a theoretical range that is much larger than the two km., the Nextivity system limits the distance to 2 kms. This has to do with overall delay that can be introduced in the system to maintain our compatibility with all of the network signalling that happens between a phone and base station.

Therefore, we can't introduce an arbitrary long delay into that part, or else we will start to run into various issues. That is why the limitation of the system is two kilometers, whereas the limitation of the module itself maybe 15 kilometers or 10 kilometers.

Case Study.

There's a K8-12 school that had a number of different buildings on the campus. The total size of the of the buildings was 128,000 square foot, but distributed over three different buildings.

These buildings were not really interconnected, and there wasn't a way to get Cat-6 cabling from one building to the other. There was already conduit run between the buildings that already had fiber inside, and we wanted to reuse this fiber connectivity between the buildings as the easiest way for us to get the donor signals into the remote buildings.

The walk test results prior to installing the system showed coverage was really poor, going on to non-existent - especially in one building. The way in which the system was installed was that in the main building, we had three QUATRA 4000 NUs. Essentially, one of the NUs drove coverage for the main building where these NUs were located, and then the other two NUs were used to connect to Fiber Hubs that were in remote buildings.

Therefore, there were two hubs in two different buildings, and these HUBs basically were connected to CUs. The CUs were co-located with the Fiber HUB, and these CUs drove a passive DAS network into the building to give the coverage that they needed inside of each one of the remote buildings. We had one NU giving coverage locally and one drove a number of CUs that were distributed in the main building.

Then we had the two additional QUATRA 4000 NUs that each one drove as a HUB, and then the HUBs drove additional CUs. With this installation, the post results are obviously a lot better than what it was before. The data rates were great. One of the reasons why the performance is great, of course, is that that link with the fiber link between the NU and the fiber HUB is a lossless link.

Just like we have a lossless connection between our NUs and CUs, using obviously digital transport across the medium, that same lossless architecture is carried forward on the fiber side.

Launch Plans.

Existing NUs do require a software upgrade to support the Fiber HUB. The software upgrade will either automatically boost it if our systems are connected, or we can upgrade using the Cel-Fi compass. We always use the latest software for our systems in any case.

More fiber development for other QUATRA products.

This is the first product that Cel-Fi has that uses fiber or that introduces fiber for their product portfolio, but it definitely will not be the last one. They do have a plan to expand their footprint for QUATRA 4000 as well as for other products to make not just the physical footprint of the devices, but also the number of use cases where we can actually use a QUATRA system to increase that as much as we can. We believe fiber will be a key part of that effort. Watch out for some future announcements for additional products to come that will use fiber.

Questions and answers.

1. Can you go through whether you can cast this or daisy chain these, or is it one for one NU to Fiber Hub?

It is one for one. 1 NU can drive 1 HUB. If you need 5 HUBs, you need 5 NUs. Pricewise, fiber HUB is in the same realm roughly as what an NU would be; it is not the same price, but it is in the same ballpark. Then, of course, there's additional cost of the fiber modules and the actual optical fiber. Given that, when should you think about using the fiber HUB? If you have a site that is large, where you have probably 3, 4 plus NUs, you can definitely consider adding a hub into that design. It is not always the best way to do it, but the way you can think about it is that if we have got CUs number 1 to 6, I connect to the NU and CU, number 7, I connect to the hub. Now if I have a strong enough donor signal, of course, I can split that out between two NUs, and I don't need a hub. But when we get to the point where we have to think about whether we really need to have another donor antenna to make sure that the donor signal is strong enough, at that point, it is probably a great idea to think about using the HUB instead of punching through more holes onto the roof for additional donor antennas.

2. There are two donor source options: antennas and small cells. Does every carrier have approved small cells and do you work with all the carriers in United States for small cells?

All three of the major carriers have small cells. We can work with all of the small cells. It is sometimes absolutely the best option for us to use small cells, especially if the building is large. By large, we mean large in terms of the number of users. If we have a one and a half million square foot factory facility, and there're not that many people inside, off air is really the way to go. But if you have a one and a half million square foot multi-use facility with tons of people in it, and your donor signal quality is not great, then you really should look at using a small cell as your source. Therefore, we can work with small cells as well as off air antenna (OTA). The majority of installs that we do are off air, but there're different cases where it makes sense to use a small cell. The performances you get out of the system when you connect the small cell is awesome. One of the main reasons why we like the fiber HUB concept is in fact the reason that we don't need to have as many donor antennas when the number of NUs become large. So, if the number of NUs that we need to cover the space gets to the three, four, five range, then we definitely think about using the hub to spare us having to add additional antennas onto the roof and having to punch through and bring coax to the NUs.

3. What are the implications on using 911 if you're using a Fiber Hub?

There are two parts that we would like to address. The first one is the practical aspects, and the second one is what does the FCC say? From a practical aspect, the location of a subscriber for 911 purposes is determined by one of two methods. The first method and what is most commonly used today is still GPS coordinates. In that case, the donor signal, where it came from, etc. has no impact on the accuracy of your 911 location. The second method is network based, for example, using time difference of arrival schemes, and so forth. In that case, the presence of a booster, any booster, does cause an error in the reported location of a handset. This issue was dealt with, and that error is caused by the delay that is introduced by the system. So the delay generally introduced by the booster is longer than the delay that you have from the fiber. The FCC has already dealt with this issue and ruled, and said that ability to make a phone call so that you actually can talk to 911 is the most important thing. Therefore, more so than potentially an error in where you are located, it is more important to be able to make the emergency call itself which booster would help enable the caller to do. Therefore, there should be no fear here that using the fiber and having a long fiber in the mix creates a new set of problems that hasn't already been looked at and addressed. The FCC has already looked at this, addressed it and approved the QUATRA systems for enterprise use with this knowledge.

4. Is this manageable in a portal, and what is the way to do that?

The system is fully manageable within the wave portal. In the wave portal, we can have access to all of the systems that are deployed. When we do your install, then we have full access to the system. The most important part of access of the wave portal is it gives you so much rich data in terms of what is going on in the system, the quality of the donor signals. With the recent releases of the wave portal, we can see things like the distance between a CU and a NU, so we know whether your cables are too long. In addition to information about the environment in which it is operating, it also provides operational status of the devices. Many management systems tell you about the status of the device, and Wave obviously does that as well, but it is that extra information that you get about the environment that makes the difference in terms of debugging a system, to help us find out what is wrong.

5. We have some kind of varying levels of knowledge so please elaborate about whether signalling is between the systems itself, if it is the same as far as six or seven or five, and is this RF over ethernet?

For a typical QUATRA system, you need to bring a donor signal to the network unit. That typically is done using off-air antennas with a coax cable run to the network unit. Then from the network unit, there are two ethernet cables that connect each CU to a NU. Therefore two to each and in total, because we have six CUs, there are 12 ethernet cables that we can use. Each one of these CUs is powered using POE from the network unit, so we don't have to worry about any power inside of the building. We just plug the CU in, and it gets all its power over these two cables. The link between the CU and NU is a digital link, but it uses ethernet signalling, but you are not allowed to put a switch or a hub or anything like that in the middle. Therefore, it is a point-to-point link between the CU, so we must string cable between each NU and CU. That link is a lossless link, so basically, we have an analog signal running over the wire. It is a digital, lossless link, so after we have cleaned up the donor signal and done a bunch of signal processing on it and improved the quality of the donor signal as much as possible, that good quality donor signal is basically what gets carried over the ethernet cable to the CU. Then the CU turns that digital signal into an RF signal and gets transmitted either from the antenna, or distributed over the passive DAS network. In the same way, the Fiber HUB doesn't use typical RF over fiber. Thus, we modulate the laser with the RF signal; it is a pure digital transmission between the NU and CU, which is why we can use standard off the shelf SAP+ modules. In end when it reaches the HUB, the signal that arrives at this hub is a digital signal that gets turned into the analog radio signals through each one of the CUs again.

6. Will the DEX files be available for design?

Yes. The HUB looks just like an NU, so it is not a big change in terms of the design principles.

7. More on the SFP+ module: Does the portal expose any of the management plane data from the module?

Not from the module.

8. Will this product work with other QUATRA 1000 and 2000? If not, will there be a range extender like that in the future?

This only works with QUATRA 4000 and 4000i, but Cel-Fi absolutely plans to extend the fiber portfolio well beyond the QUATRA 4000. They see value in this for all of our enterprise products, the whole QUATRA range of products, so over the next few months, you will definitely see some more announcements.

9. Is there a back call option if the macro signal isn't strong enough to pick up the antenna?

If at the site there wasn't a strong enough off-air signal, yes you can definitely do that. The use case where we see this more is the ones that we mentioned earlier, a mine, the data center, etc., but there may be other applications as well. If there's a signal at the site that you know is really weak, or the quality is poor, then you should also consider using a small cell there as a donor option. Having a single small cell that we distribute throughout the whole building is by far the most efficient way to get the small cell signal into the building.

10. What are the impacts on capacity using the Fiber Hub?

Network capacity is the goal here, so because the HUB has got a lossless connection to the network unit, there's no signal degradation or anything like that. Therefore, the base station capacity is not specifically impacted by the Fiber HUB. The base station capacity that is determined by mainly the off air quality of the signal that you can get, which is obviously why our network unit has separate donor antennas for the different operators. In uplink direction, it is lossless transmission, so there's no specific impact. As general guidance, if we have a good SNR as a donor signal, then typically, we find that cell side capacity is not really an issue. For most buildings, up to a million square foot, it is generally good and even larger than that, as we mentioned. If it is something like a factory or a warehouse, if we have a really large building multi-use, thousands of people in it, that is where we definitely think about the capacity issue and talk to operators in the region and just coordinate with them.

11. Does this support MIMO?

The QUATRA 4000 doesn't support MIMO, and the QUATRA 4000 app also doesn't support MIMO. There's nothing inherent about the Fiber HUB that doesn't support MIMO, so as we think about you know future products on the fiber side of things, typically the fiber product would support whatever the NU supports. Therefore, if we have an NU that supports MIMO, the HUB will support MIMO.

12. Legacy implementation questions. If you have a 1000 or 2000 implementation out there, is there anything that can be leveraged by that design if you're kind of upgrading to 4000, or is it really just an upgrade of equipment?

That is a difficult question. If you want to upgrade, for example, a site with 2000s to give you the coverage of the four operators, you know you can just rip out the NUs and CUs and replace them with QUATRA 4000 NUs and CUs, and you will be great, your system would work perfectly well. Additional advantages that you get with the QUATRA 4000, though, is that has got better ability to drive passive DAS segments. Therefore, if you do a rip and replace two QUATRA 2000s, for example, and you have a few holes, then consider some small passive DAS networks off a few of your CUs. Drive three, four, five antennas off the CU, and that is going to allow you to get a much more even coverage footprint inside the building. Opportunities like that would enhance the coverage in specific areas. That is one issue to consider. The second issue that we would look at is actually optimizing the donor signal quality. With the separate antennas for each operator on a QUATRA 4000, we think it is a good time if you replace a QUATRA 1000 or 2000 to just repoint the antenna sighting that you have. Plug the Cel-Fi COMPASS to help. For a QUATRA 1000 and 2000, you could do antenna pointing using the web. For 4000 and for all the other products, including 1000 and 2000, the Cel-Fi COMPASS is a really great tool to get us optimum antenna pointing for all of the different operators that will maximize both the S-N-R of the donor signal, as well as the coverage footprint that we're going to get from our QUATRA system. Thus, if we're going to revisit the site with 1000 and 2000, those would be the two things we would consider. We will make sure the donor antennas are optimized, and secondly, we would think about doing some filling coverage with antennas that we can run off a CU.

13. What about time delay? Was the time delay added to the system regarding the hub?

That is one of the things that Cel-Fi worked really hard on, and that was to make sure that extra delay that gets added into the system is as slow as possible. This, over and above the delay through the fiber, in which there's nothing that you can do, there's only about a microsecond or so worth of additional delay. Therefore, the system continues to operate in the same typical delay budget that you would have for a QUATRA 4000. With addition of the fiber, it does introduce a little bit of extra delay but not significantly, and all of the algorithms that we have within the system, like our echo cancellation algorithms and things like that can all accommodate the additional delay that the fiber brings, but it is not a significant delay.

14. How can you calculate the uplink noise increase in the donor site?

Uplink noise increase should not be noticeable, and the reason why that is the case is that the way in which the signals from the CUs are combined, there's a sort of specific dynamic scaling that is used. Thus adding a serious number seven, eight, nine, ten, eleven, twelve, actually doesn't double the amount of noise that goes to the base station because the noise level is scaled, and, just like all of our QUATRA systems, the CU doesn't contribute to any uplink noise if there's no uplink signal present. Thus there's a gate on the uplink that basically you can think of it sitting here, so there's no handset here, the CU is not contributing to any noise level, and then once the CU starts to transmit on the uplink, there's a scaling of how the signals get added together that actually limit the total noise level that the base station would see. Thus, it is not a linear edition, so you shouldn't see any significant change in the noise level at the base station compared to what you would have today.

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  • Wow. Some of the articles here are short and others are long. This article is like the “War and Peace” of articles. I didn’t pick up too much reading this but I did get a basic grasp on how Fiber HUB can help with multi-building sites and high rises.

    Willard S. on
  • Introduction to Nextivity Cell Hub. Thought I was stepping into an Introduction to Brain Surgery class but this was amazingly easy to follow, despite my lack of technical knowledge. I know why people use fiber hubs now and also why this model is helpful for certain locations where cell phone service is spotty.

    Neal Freeman on
  • The only thing different about Cel-Fi HUB is that it enables pushing signals up to 2 miles away from one building to another. That other building will not need donor signal – with this Fiber HUB, it can directly broadcast to interior antennas.

    Mike Fulcher on
  • I’ve read about cell phone boosters for homes, offices, and factories and I’ve read about distributed antenna systems. I’m not sure where Cel-Fi fits into things. Could you describe what is different (or similar) about this?

    Isiah Crawford on
  • Cell phone boosters seem like helpful devices, but I didn’t know there are situations where a traditional booster doesn’t work. After reading this and other blogs, it appears there are boosters to help with any situation whether you need to run fiber or just put in a regular signal booster.

    Ian Francis on
  • A lot of the information here was jargon I just don’t understand, but something struck me as important when it comes to using cell phones for 911 calls. There’s the problem of cell phones not always providing the exact location of the call (as opposed to the old landlines) but this article brought up the important point that it’s better to be able to call 911 than not to be able to. If this Nextivity Cel-Fi allows the school to have cell access in places it couldn’t, then it’s a good thing and worth having (at least I think so).

    Alan Patterson on

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