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Why do we need antenna-integrated RRH (Remote Radio Antenna, RRA)?
March 02, 2015 | By In-Ho Kim, Head of AAS group, KMW (inghoo@kmw.co.kr)
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For the rest of the Q2 2015 issue of Korea Communication Review magazine please click here

 

 

Contents

1. Background of Antenna-Integrated RRH

2. Features of Antenna-Integrated RRH

3. Outlook for the Antenna-Integrated RRH Market

4. Installation Issues in the Small Cell Market

 

* RRA is a brand name of antenna-integrated RRH by the author's company

 

1. Background of Antenna-Integrated RRH

 

Mobile data traffic has been soaring ever since smartphones were first introduced and spread throughout the world. The traffic increase gave rise to faster introduction of 4G - well maybe too fast because now operators are having a hard time lowering costs of building and operating networks. In response, mobile base stations are being transformed accordingly. RRHs are more commonly used because they can minimize radio transmission loss by allowing radio parts, which used to be installed indoor, to be placed closer to antennas.

 

Most RRHs and antennas today are placed pretty close to each other on a building's rooftop, tower, etc., but they still need a 2~3-meter-long connection cable between them to exchange signals with each other. As RRHs are moved out of a building and onto a rooftop, where only antennas used to be placed, operators are facing new challenges -  securing space for a variety of products from different manufacturers that are run by different operators for different frequency bands, and achieving reliability of the frame structures where those products are mounted.

 

Figure 1. Evolution of base station and RRH tower

 

Particularly installing RRHs and antennas on building rooftops or small towers in big cities can be not only undesirable from an aesthetic point of view, but also an obstacle in building a network from operators' point of view.

 

To solve these issues in distributed cell sites, antenna-integrated RRH solution was introduced.

 

2. Features of Antenna-Integrated RRH

 

In 2012, Ericsson introduced Antenna-Integrated Radio (AIR), the first of this type, soon followed by our Remote Radio Antenna (RRA1), Huawei's Active Antenna Unit (AAU), etc. These types of antenna-integrated RRHs have the following four characteristics:

 

Figure 2. Antenna-Integrated RRH solutions: Ericsson (AIR), Huawei (AAU) and KMW (RRA)

 

  1) Less signal transmission loss between antenna and RRH

 

In a conventional cell cite, an antenna and RRH are connected usually with a 2~3-meter-long connection cable, and this contributes to transmission loss of about 0.6~0.7 dB. An antenna-integrated RRH solution however can eliminate this loss, resulting in more energy savings. Antenna-integrated RRH solutions from other developers may minimize the length of connection cables, but still need a connection cable, short or long, to work. However, our Multi Semi Blind Mating (MSBC) solution can literally eliminate the necessity of a connection cable, consequently minimizing the transmission loss. Also it is the only solution that allows only the defective RRH to be replaced on the site.

 

This RRH-replaceable solution is particularly helpful to RRHs that are intended to support multi-band frequencies (e.g. dual band, tri-band). For instance, let's say there is an all-in-one dual band RRH that supports both 1.8 GHz and 700 MHz. If 1.8 GHz RRH fails, then not only the failed RRH, but also the other working 700 MHz RRH has to be replaced. For this reason, some operators in Japan or Europe prefer onsite-replaceable solutions.

 

We are currently developing a solution that will allow for onsite replacement of only the failed RRH. With this solution, any failed RRH can be easily replaced on the site without using any tool in just 3 steps. The key factors of this solution are:

 

-    Development of compact and light RRH (2T4R, 12L, 12kg)

-    Multi Semi Blind Connection (MSBC) solution

-    Special latch design

 

Figure 3. RRA (antenna-integrated RRH solution by KMW)

 
  2) Less CAPEX/OPEX burden on operators

 

In conventional structures, antennas and RRHs have to be installed separately, which means higher installation costs and more space to lease. On the other hand, an antenna-integrated RRH gives operators advantage of lower costs of installation and space lease because it only takes one installation of an antenna. So it is a very cost-efficient option when we think about the money that can be saved throughout the entire leasing period. Also, it is a smart space-saving solution to overcome limited lease space issues.

 

Figure 4. Challenges for operators

 
  3) Reduction of physical load on frame structures

 

Frame structures on towers or rooftops of a building are affected not only by weight of the installed products, but also by wind loads. Because our new solution RRA allows RRHs to be attached right to the back of an antenna, wind loads on the face of RRHs can be eliminated. This can help to install more RRHs in limited space on towers or rooftops of buildings.

 

Figure 5. RRA tower (less wind load in the back of antenna)

 
  4) Development of eco-friendly structure and improvement of Passive Inter-modulation Distortion (PIMD) quality

 

One of the most common cell site structures that we find on rooftops or small towers of buildings in cities consists of antennas, RRHs and cables that connect the two. I personally believe these eco-friendly structures should be modified to be, at least, without any connection cable.  What has satisfied this need the most so far would be Ericsson's AIR (see Figure 2). Probably because Ericsson cooperated with a professional design consulting firm from the initial stage of the development, the company could end up with AIR - with a nicer and simpler design. Not much impressive reliability or price competitiveness, though.

 

Connecting an antenna with RRHs in a tower is a pretty demanding and dangerous job that can be done by only those with experiences. Improper connection by a less-experienced person can cause poor PIMD and waterproofing issues. When more than two frequencies are combined, a new unwanted frequency can be generated as a result of the synthesis of fundamental and harmonic waves of the two original frequencies. This distortion is called PIMD. Distorted signals detected within the receiving frequency band can affect the receiving performance of system. This is why PIMD is considered as an important factor in RF products. So, if we can just skip this whole troublesome connecting process, there will be no problem to take care of at all.

 

Figure 6. Connecting antennas and RRHs (not an easy job!)

 

As discussed so far, the antenna-integrated RRH solution certainly offers features that can take care of the issues the distributed cell sites have. However, the concept of the integrated solution – moving RRHs next to an antenna, where replacement of failed RRH(s) can be tricky - has been a concern, particularly to operators who tend to be conservative unavoidably. Operators have once had a similar concern. During the transition from the conventional cell site to the distributed cell site structure (see Figure 1), they were worried about moving radio parts (filter + amplifier) up to towers, again where replacement can be tricky.

 

Today, RRHs are commonly used in LTE networks, and the Mean Time Between Failure (MTBF) issue has also been improved as more advanced production technologies and parts have become available.

 

3. Outlook for the Antenna-Integrated RRH Market

 

Table 1 shows the EJL Wireless Research’s forecast of the antenna-integrated RRH market. The market is expected to continue to grow after 2015. KMW is also planning to supply our products in the US market starting 2015.

 

Table 1. Antenna-integrated RRH (Semi-Active Antenna) market forecast

Table 59. Global BTS Semi-Active/Integrated Active Panel Forecast, 2012-2017 (Units)

 Antenna Type 2012  2013E  2014E            2015E  2016E  2017E 
 Passive to BTS via feeder run 677,649  537,551  433,305  376,892  353,703  249,837 
 Passive to RRH 2,565,447  2,350,202  2,239,578  2,087,498  2,078,323 

2,053,354 

 Semi-Active Antenna 60,759  60,404  67,815  71,572  86,891  164,102 
 Integrated Active Antenna 130  100  130  1,000  4,000  13,000 
 Total 3,303,985  2,948,257  2,740,828  2,536,962  2,522,917  2,480,293 

Source: EJL Wireless Research LLC Estimates (September 2013)

 

4. Installation Issues in the Small Cell Market

 

Discussion on installation of small cell base stations (except DAS), as well as macro cell stations, has also begun. While macro base stations can be installed in towers or on rooftops, small cell base stations are usually installed in places that can be easily spotted, like on street lights, bus stops, 2nd or 3rd floor of buildings, etc. And the number of small cell base stations to be installed is likely to be greater than that of macro cell base stations.

 

To address this, lots of converged/integrated solutions are being introduced. The two most noteworthy solutions are KMW's Green Cell and Ericsson's Zero Site, both of which features a small cell base station that can be installed on a pole with energy-saving LED street lights. The biggest benefit of these solutions is that they can improve street landscape by minimizing the appearance of all these IT equipment and eliminating all the messy cables (CCTV option available in Green Cell).

 

Figure 7. Street light-integrated small cell solutions

 

There are some challenges facing these solutions as well. Installing new street lights with small cells is a quite expensive procedure. Besides, the solutions and their installations have to satisfy all the conditions under the relevant laws and regulations. Given that, it would take some time until they can be finally implemented. Nevertheless, if we can somehow make them run on renewable energy, which happens to be one of my research areas, independently from the central energy source, they can actually be a feasible and useful idea in future urban planning.

 

A number of feasible ideas on small cell solutions have been shared. I personally believe that the No. 1 priority in small cell solutions should be design or convergence. That's because people do not like to see untidy and messy cables hanging off street lights or buildings, and thus operators are likely to face more challenges and restrictions when installing small cell base stations than when installing macro cell base stations.

 

Anyway, the most practical approach for now would be an all-in-one solution similar to macro cell, which would not be easy due to limited installation spaces for the foregoing reasons. A Japanese operator has requested for a solution to this issue.

 

Figure 8. Small cell solutions

 

Another possible approach would be installing RRHs somewhere that cannot be easily spotted, like behind signs or frame structures. However judging from my own experiences of conducting eco-friendly researches, it is less likely that operators would love the idea because of high costs required for product lineup, installation and management.

 

For me, the keywords are naturalness and convergence. With a simpler design and softer light, we can make the small cell hardware platform not look like a typical communication device. Furthermore, we can add more features like street light, CCTV, beamvertising, etc., transforming it from a conventional mono-function platform into a useful multi-function platform. More interesting ideas can be brought up to help operator to build up a positive brand image.

 

Figure 9. Radio Bank (KMW Small Cell Hardware Platform)

 

 

About author

 

 

In-Ho Kim (inghoo@kmw.co.kr, +82-31-307-8573)

Head of AAS group, KMW 

  • A Head of Active Antenna System (AAS) Group at KMW's RF Research Center for R&D of antenna and RF radio
  • Research/development fields: Active Antenna System, RF Radio (Antenna, RRH)
  • Research interests: Beam forming Calibration, Small-cell, Massive MIMO, Thermal and Light Weight material architecture

 

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