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Netmanias Interview with HFR - Fronthaul Solutions for LTE/LTE-A C-RAN (Cloud RAN)
May 27, 2014 | By Dr. Harrison J. Son (tech@netmanias.com)
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HFR is probably most known as a vendor of wired/wireless network equipment like Mobile fronthaul, Carrier Ethernet, FTTx, etc. Today, we are going to hear from Dr. J.H. Lee (jongheonlee@hfrnet.com), CTO of HFR about one of its most popular solutions, flexiHaulTM, a mobile optical access solution.



1. Welcome! Thank you for being with us. Can you tell us a little bit about HFR first?


HFRHFR was founded in 2000. And we have been providing wired/wireless operators and enterprises with various equipment such as WDM including Mobile Fronthaul, Carrier Ethernet, FTTx, Wi-Fi, Repeaters, etc.


2. What are the concept and position of your flexiHaul?


HFR: Our flexiHaul product line is a family of fronthaul units that connects BBUs and RRHs in the emerging next generation architecture, C-RAN.


Our flexiHaul series are WDM solutions. What they do is to aggregate (fronthauling) macro/micro/small RRH (CPRI) traffic, and aggregate (backhauling) legacy base station, compact base station (pico), and Wi-Fi traffic to a single aggregation network.



3. These C-RAN and fronthaul may sound new to some of us. Can you tell us more about them?


HFRSure. To handle soaring data traffic, operators have been making macro cells smaller, and this has apparently left the operators with more cells to build and operate. To save costs in building and operating cell sites, a new architecture called C-RAN was introduced. It is also known as “Centralized RAN” or “Cloud RAN”.


With this C-RAN, operators can simply leave all RRHs in their cell sites, but move only BBUs to a centralized location at central offices or master cell sites. C-RAN has drastically lowered the cell site cost (Capex/Opex), and has maximized the effects of CoMP and eICIC of LTE-A.


This helps to improve not only service quality, but also network performance. Because of these benefits, many operators around the world have been conducting trial tests for C-RAN deployment. And two of the most advanced LTE operators in South Korea, and also in the world, SK Telecom and KT, already succeeded in commercializing it back in 2012.


Now that RRHs and BBUs are remotely separated in C-RAN, a new network was required in order to deliver a huge volume of baseband I/Q streams between the two across CPRI or OBSAI link. Previously, both RRHs and BBUs were located in eNBs, and the transport network between eNBs and EPC was called backhaul. Now in C-RAN, these new CPRI and OBSAI networks are called fronthaul.


4. I see. Then, fronthaul is a newly defined segment in a mobile operator’s access network. What are the technical requirements for the fronthaul then?


HFRThe fronthaul network should be able to satisfy requirements under LTE layer protocol operation and under the CPRI specification. First of all, ultra-high transmission capacity (as high as 2.5 Gbps~10 Gbps) for delivering baseband I/Q data is required, and latency caused within equipment in the fronthaul network should be minimized to a few msecs to maximize the distance between BBUs and RRHs. 


In-C-RAN, since RRH has no GPS antenna, it extracts clock from I/Q bit stream received from BBU. And then it removes jitter and generates the clocks (CPRI/sampling/carrier frequency, etc.) to be used in the RRH system. So, the RRH system performance varies depending on the quality of the recovered clock. That’s why jitter has to be minimized in the fronthaul network, and the CPRI specification defines the maximum frequency accuracy budget as ±0.002 ppm. Also, to guarantee the time/phase synchronization required in LTE-A (eICIC, CoMP), the CPRI time/phase synchronization should be strictly ensured in the fronthaul as well. So, we can say ensuring low latency and synchronization between BBU and RRH are the most important and demanding jobs for the fronthaul.


5. You mean, transport capacity, low-latency and highly accurate synchronization are key factors, right?


HFR: That’s right.


6. I see. Then, what possible ways have been suggested to satisfy such demanding technical requirements?


HFR: There have been several ways. First, in terms of technology, the best option would be using dark fiber. But the problem with this option is that it would only work for those who already have plenty of fiber, and others including most operators would have to lease it. And obviously this can cost a lot. For example, a network with LTE Carrier BW of 20MHz, 2x2 antenna, 3-sector, 2 bands would require 6 RRHs in each cell site, which means 6 leased fibers in each cell site.


The second option would be OTN, which I would say has room for improvement. The problem with this option is that, latency and jitter are caused during OTN mapping/demapping/multiplexing. And this leads to longer latency in the fronthaul network, and degraded RRH system performance, respectively. So, the OTN standards and equipment development need to be improved in a way that can optimize CPRI transmission.


The third option is WDM. With WDM, just a single or two fibers can cover tens of CPRI channels. So, fiber costs can be lowered, and high-volume transmission is possible. There are two types of WDM, passive and active. The best part of passive WDM is that it is inexpensive, and requires no power supply. Besides, little latency or jitter is caused, and so the distance between BBU and RRH can be maximized, without affecting LTE/LTE-A performance much. Active WDM is bidirectional (single fiber). So, dark fiber costs can be lowered. And by using Muxponder, the number of l required can be minimized, which can further lower the fiber costs. What’s even better, operators can even monitor the quality of the fronthaul network by running a self loopback test on active WDM units. But, one thing to note is that active WDM may cause latency and jitter, which should be kept under certain levels.


7. I see. What kinds of technologies have been used in building the fronthaul network with the current commercial C-RAN?


HFR: C-RAN was commercialized by Korean mobile operators for the first time in the world. They have adopted both passive and active WDM, and we also support both of them. But, today I will only talk about flexiHaul solution, which is an active WDM solution.


8. Now, let’s talk about your fronthaul solution, flexiHaul.


HFR: Our flexiHaul solution consists of the HSN series (HSN 8500/8300/8100/8110). HSN 8500 models are installed in BBU pool sites, and support 40 λs and 72 CPRI ports. These models support the three CPRI service cards, i) transponder card that supports three option 3/4/5/6 CPRI ports, ii) Muxponder card that supports four option 3/4 CPRI ports, and iii) Muxponder card that supports two option 3/4/5/6 CPRI ports. And all three CPRI cards have been deployed in SK Telecom’s commercial network.


Muxponder cards use one λ per card. So, fewer λ are required. And that allows HSN 8500 to aggregate RRHs at the maximum level. HSN8300/8100/8110 models are RTs installed at cell sites. If you want to see their specifications, you can see the table in the booklet that I gave you earlier.



9. How many RRHs can one HSN 8500 unit cover?


HFR: One HSN 8500 unit has up to 72 option 3/4 CPRI ports. So, each can aggregate up to 72 RRHs. By default, it can have two rings, and each ring has up to 36 CPRI ports. This means, operators can aggregate CPRI traffic from 36 RRHs with just a single fiber, and boost the transmission capacity of each ring up to 90 Gbps. Of course, they can create custom configuration that would fit best into their networks.



10. Then, tens of RRHs are connected to centralized BBUs through the fronthaul rings. What if there is a fiber cut? Will that leave tens of devices disconnected?


HFR: That’s right. But, fortunately, our flexiHaul solution offers instant protection switching within 50 msec in case of a fiber cut. So, CPRI traffic is detoured without delay, preventing any service interruption.  


11. Does the flexiHaul solution meet the fronthaul requirements you mentioned earlier?


HFR: The flexiHaul solution is a fronthaul solution using WDM, so has no capacity issue. One HSN 8500 can deliver CPRI traffic up to 180 Gbps. It has many excellent technical features we have developed to minimize latency and jitter which can affect LTE/LTE-A. So, for example, in a ring with COT and RTs, a fronthaul end-to-end latency excluding fiber latency can be kept under 1μsec, and jitter can be kept under a few nsecs.


More than 3,500 flexiHaulTM units are currently running in SK Telecom's commercial LTE/LTE-A network. And I guess that proves our solution has met all the strict technical requirements of fronthaul.


12. I saw CPRI/OBSAI, and also GE and GPON cards plugged in a flexiHaul unit. What are those cards for? 


HFR: When a legacy operator builds an LTE network, there are already legacy 3G base stations in its cell sites. Our flexiHaul RT units (HSN 8300/8100) accommodate 3G BSs through the GE interface, and connect LTE RRHs through the CPRI interface. That way, they can accommodate the two access networks in a single network.


GE and GPON cards connect small cells (pico) or Wi-Fi APs. If no fiber is available in a small cell area, operators can connect small cells by accessing microwave devices through the GE interface.


13. In case of wholesale, a fronthaul provider must monitor the quality of fronthaul and report to mobile operators. Then, the two demarcation points would be the one between RRH and RT (HSN 8300/8100), and the other one between BBU and COT (HSN 8500). What key performance indicators are provided?  


HFR: Our solution checks the transmission quality of each CPRI signal as well as optical fiber, through real-time monitoring of BER of optical and CPRI signals transmitted/received at CPRI ports. At each CPRI port transmission interval, a loopback test can be run for troubleshooting.


14. What are the benefits that your flexiHaul solution can bring to operators?


HFR: First of all, our solution can save them a lot in costs of building and operating networks. Because the flexiHaul solution features WDM, dark fiber costs will go down. If they use Muxponder cards that can connect four CPRI ports to one l, the cost will go down even further.


And because the flexiHaul solution keeps a one-way latency less than 1 msec, the fiber distance in the fronthaul network can be increased up to 25 km. If the distance between BBU and RRH increases, the fewer BBU COs are required. This allows operators to centralize more BBUs, and lower down costs in maintaining sites. 


15. So, the No. 1 benefit is saving costs. I guess that would be the biggest benefit to operators especially when higher traffic doesn’t mean higher profits like these days. Any other benefits?


HFR: HFR’s fronthaul solution offers extremely low latency and jitter. So, it can maximize the performance of LTE-Advanced features such as CoMP and eICIC, eventually improving the LTE-A service quality and network performance. These days operators are in fierce competition to attract customers. With our solution, operators can prevent customer churn and attract new subscribers by providing better service quality than other competitors.


Our ring protection within 50 msecs feature ensures any link failure is recovered instantly to minimize LTE/LTE-A service interruption. Not only that, operators can monitor the quality of the fronthaul link through BER and CV (Code Violation) of CPRI data that is being monitored in real time.


16. C-RAN was initially proposed by China’s CM. But, it was Korean operators (e.g., SK Telecom) who actually commercialized it. And a fronthaul network, which made C-RAN work, was also commercialized by Korean operators for the first time in the world. Then there came your flexiHaul series. You have done a pretty impressive job of developing and introducing new solutions that the market has wanted right in time. But, now many vendors, stimulated by huge popularity of C-RAN, are working hard to develop new fronthaul products. What makes the flexiHaul solutions better and more competitive than that of your competitors?


HFR: We have been stabilizing and optimizing systems in real commercial networks, and have accumulated technical know-how for many years. And those experiences and know-how are our biggest assets that can make us ready to work any time. Our solutions are not in the proof of concept (POC) step, but are fully proven, ready to use. That’s what really put us ahead of everyone else. We are the ONLY one who can achieve the best time-to-market with the least trial and error in building a fronthaul network. 


17. Operators may have different requirements depending on what they are trying to do. Some may want to build a new LTE network, and others may want to migrate their current networks into LTE networks. And what they have in their current network and the infrastructure they can further attain vary from operator to operator. One may build macro/micro cells using C-RAN (Macro/Micro RRH) or D-RAN (Macro base station), and also build small cells using C-RAN (Small RRH) or D-RAN (Compact base station). What are the possible network architectures that your solution can configure?


HFR: You are right. Every operator has their own RAN architectures/scenarios they want, depending on their needs and resources, like available infrastructure, future roadmap, and so on. That’s what our flexiHaul solution is for. Because it supports many different RAN architectures. You name it, we have it.



18. What are the examples of the large-scaled deployment of the flexiHaul solution?


HFR: We have deployed the flexiHaul solution in SK Telecom’s network since 2012, helping the company to build its nation-wide fronthaul network, in 84 major cities. 80% of the fronthaul networks were built with active WDM, and 50% of the units deployed were our flexiHaul. Also, we went global. Since 2013, we have conducted many trial tests with operators in Europe and Asia.



19. Did you run an IOT with a particular vendor? Because, if not, it would take long for an operator to complete integration, right?  


HFR: In SK Telecom’s commercial network, our solutions are interworking with BBUs and RRHs from Samsung and Ericsson. We also completed an IOT with NSN and other RAN vendors.


20. Small cells give operators more pressure on fiber than macro cells. Can operators still go for C-RAN? Is there any solution to it?


HFR: We are actually discussing it with CPRI over Microwave vendors.


21. This would be my last question. What does your roadmap look like?


HFR: We are working on fronthaul and backhaul solutions for small cells as they are expected to grow drastically.


22. C-RAN sounds like a pretty good option for operators to manage cost and performance issues. It looks like fronthaul is the key that can make the option work. And I have to admit that I got an impression that you guys know exactly what to do when it comes to fronthaul. Well, I guess that’s it for today. Thank you so much for your time!


HFR: Thank you for having me!




About Netmanias (www.netmanias.com)

NMC Consulting Group (Netmanias) is an advanced and professional network consulting company, specializing in IP network areas (e.g., FTTH, Metro Ethernet and IP/MPLS), service areas (e.g., IPTV, IMS and CDN), and wireless network areas (e.g., Mobile WiMAX, LTE and Wi-Fi) since 2002.


About HFR (www.hfrnet.com)

HFR has been actively responding to the Cloud RAN market under LTE environment. We expect that our front-haul solution will become representative product in global equipment market. Also, HFR has been leading the high-speed internet equipment with the development for Giga Internet service area. Based on its competitive solutions in the wire and wireless communications fields, HFR is determined to become Korea’s leading network equipment company.


For more information, please visit www.hfrnet.com





BBU      Baseband Unit

CO       Central Office

CoMP    Coordinated Multi-Point

COT     Central Office Terminal

CPRI     Common Public Radio Interface

C-RAN   Centralized/Cloud RAN

CWDM   Coarse WDM

D-RAN   Distributed RAN

DWDM   Dense WDM

eICIC    enhanced Inter-Cell Interference Coordination

IOT       Inter-Operability Test

LTE       Long Term Evolution

MTSO    Mobile Telephone Switching Office

OBSAI    Open Base Station Architecture Initiative

RAN       Radio Access Network

RRH       Remote Radio Head

RT         Remote Terminal

WDM     Wavelength Division Multiplexing

sunil chinnadurai 2015-07-14 17:00:30

Good to know these info!! Thanks:)


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