RRU-BBU connections - questions

[mobileopticsguy]

I'm trying to get a handle on the specifics of RRU-BBU connections. Ultimately I care about the number of SFP/SFP+ transceivers an RRU is equipped with.

 

I know the RRU-BBU can be connected via either two-fiber with TX and Rx on different fibers, or single-fiber if bi-directional, so let's use the term 'links' instead of 'number of fibers' to keep things simple.

 

1. How many 'links' does an RRU need back to the BBU?  What determines how many are required?

 

2. How many transceivers can an RRU handle? I know they aren't all identical, so what is typical, what is the max, etc.?

 

I think based on my research that the answer is very nearly always '1 link per RRH to the BBU'. (One exception I know of is the NSN FlexiRadio RRU which has three optical ports.) A colleague believes the answer is '1 per attached RF transceiver', which means multiple fiber links from one RRU.  Who's right?

 

Another question - in a Ground Mount Option build, with the RRU located at the bottom of the tower, is the connection up to the panel copper or fiber?  I read here that 'existing cables can be reused' which seems to imply copper in at least some instances.

 

 

Thanks.

[lilotimz]

 

 

Another question - in a Ground Mount Option build, with the RRU located at the bottom of the tower, is the connection up to the panel copper or fiber?  I read here that 'existing cables can be reused' which seems to imply copper in at least some instances.

 

 

Thanks.

 

All final connections to antennas are coax jumpers. 

 

GMO builds utilize existing copper coax jumpers which can be dozens to hundred+ feet long. Full build modern sites utilize hybrid cable with fiber and power up to the tower top radio unit and then the final connection from radio unit to antenna are copper coax.

[mobileopticsguy]

With the GMO, are the RRUs are still connected to the BBU via a fiber optic connection, just a shorter one? 

[MrZorbatron]

With the GMO, are the RRUs are still connected to the BBU via a fiber optic connection, just a shorter one? 

Connections to the radios are always optical.  This is one of the benefits of the remote radio, the elimination of the signal loss in the long coaxial cable going up the tower.  Since optical has zero loss, the change from generally 200+ ft of antenna feed line to 6, can make a huge difference in cell site performance.  You can use that difference to either save power by decreasing radio power where additional capability is not required in densely deployed areas, or to extend signal range and improve in building coverage in sparsely deployed areas.  Additionally, with the reduction of interference, better radio performance should be possible.

[joshnys8913]

Also the shorter the coax the better.