The RRH: High or Low?

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I don’t know how many of you are aware how the RRH, remote radio head, is mounted at the tower. First, what is a radio head? It is the RF unit that connects to the antenna. It receives the data from the BBU, base band unit, and converts that data to the RF and then send it to the antenna, see below.

BBU RRH Antenna

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So, why am I showing you this? Because there is a buzz in the industry that is forcing the carriers make a decision. Should they get high or should they stay low? High or low, tower or ground, tough decisions! Let’s look at the options and the pros and cons.

Go high! If you decide to mount on the tower, what are the pros? The RF properties are great because you have very short RF jumpers between the RRH and the antenna. This means that you have very low loss and less chance of problems from the RF cable.  You run fiber up the tower which has low loss. RF cables are very expensive compared to fiber and they are harder to run, so the short jumpers are cost-effective.

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Go high has some cons. Fiber is not a natural tower climber skill, so the fiber terminations need to be done in the air. You will need to run power up the tower to power each RRH. The weight on the tower increases so the loading will increase so the costs go up with improving the structural integrity of the tower. The break out box is now up in the air where only a tower climber can access it. This dog-tags_clearbackgrondmeans that every problem you may have with fiber, RF jumpers, or the RRH all need to get a tower climber to repair it. This adds cost to the maintenance and it add delays to the repair. So if you have a sector down due to a faulty fiber, you need to schedule the tower crew to repair it and you need to hope the weather permits the climb. Then you need to pay for it. These are all big problems!

Go low! If you decide to mount on the ground then you need to build the structure to mount the RRHs. This may add cost but it may be cheaper than having the tower crew pull everything up in the air and mounting it on the tower so this may be a wash. The pros would be that the RRH is where you can work on it. The fiber is where you can clean and repair it easily. You have access to one side of the RF cables for you to look at and troubleshoot. If there are problems then your site tech can troubleshoot all the way to the RF connector. This saves cost on the climber and saves time on the schedule. The loading on the tower will be lower so you may not have to beef up the tower to handle all of the additional weight.

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The cons of the low mount are this. To run the RF cable up the tower is very expensive, so is the cable. You also have to ground and properly route all the cables. Speaking of cables, you will have higher RF loss, you will have a Cover V7 LTEgreater chance of interference, so sweep each cable and mount each cable properly. This may be a problem and will add costs up front. One last thing, if the RRHs are mounted on the ground then security could be an issue because they will be exposed.

So what do you do? It depends what is important to you. If you are concerned about maintenance and repair, then low is the best option. If you are not concerned about the tower loading and the costs up front, then high is the best option. I know that the biggest complaint about high is the repair costs and time. It seems like making changes is a problem. Upgrades may be a problem.

Some things to consider either way.

  • MIMO will add many RF lines between the RRH and the antenna. 4T4R would be 8 cables between the RRH and the antenna. 8T8R would be 16 cables.
  • Each RRH may weigh between 30lbs to 100lbs depending upon what is in it.
  • There could be 3 to 12 sectors on each tower. This could be a factor.
  • RF cables over 10 feet will be much larger and more expensive cable.
  • Each tower climb post installation will cost money and require scheduling of days to weeks.
  • If there is a mass outage the climbers will all be booked.
  • Longer cables will need to be swept after the installation whereas the short jumpers could be assembled and swept before the installation.
  • Tower improvements could be needed to hold the extra weight of the radio heads.
  • Troubleshooting may be quicker if the site tech can get to the RRH.
  • The larger the coax the more it costs.
  • Climbers may need to terminate the larger coax cables on the tower if they run long RF cables.
  • Climbers will need to have fiber skills if the RRH is mounted in the air.

There you go, now you have a new way to look at the RRH and the installation issues that you may face. I hope it helps!

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